De Brandbrief

februari 2015Technologiestichting STW

Nr 21 Schone en Zuinige Verbranding

Brandbrief2015Clean Combustion Concepts

Colofon

Brandbrief

De brandbrief, met een oplage van 450 exemplaren, is een uitgave van het Platform van het STW- technologieprogramma Schone en Zuinige Verbranding (SZV). De Brandbrief bericht over lopende zaken in het programma, vorderingen van onderzoek en ander nieuws van participerende bedrijven en universi-teiten De uitvoering is in handen van Technologiestichting STW.

Redactie

Prof.dr.ir. Th.H. van der Meer

Universiteit TwenteDr .L.J. Korstanje

Technologiestichting STWA.M. van der Stroom

Technologiestichting STW

Voor een exemplaar van de Brandbrief kunt u zich aanmelden bij het programmabureau. Dit is de laatste uitgave van De Brandbrief.

Programmabureau Schone

en Zuinige Verbranding

Postadres

Technologiestichting STWLinda de GrootSchone en Zuinige VerbrandingPostbus 30213502 GA UTRECHT

Internet

www.stw.nl/nl/programma039s/ clean-combustion-concepts

Concept en uitgave

Technologiestichting STW, UtrechtOntwerp

Room for ID’s, NieuwegeinRealisatie

Argante Argante AmsterdamFotografie

Betrokken instellingenDruk

Repro-afdeling FOM/STW-bureau

Niets uit deze uitgave mag worden overgenomen of vermenigvuldigd zonder uitdrukkelijke toestemming van de redactie.

STW-nummer

2015/00765/STWISBN

978-90-73461-88-8

Samenstelling Platform

Schone en Zuinige Verbranding

Prof.dr.ir. Th.H. van der Meer, voorzitter

Universiteit TwenteProf.dr.ir. R.S.G. Baert

TNO AutomotiveDr.ir. M.F.G. Cremers

DNV GL EnergyProf.dr. L.P.H. de Goey

Technische Universiteit EindhovenIr. B. Hakstege

DAF Trucks NVDr.ir. J.H.A. Kiel

ECNDr.ir. W. de Jong

Technische Universiteit DelftProf.dr. H.B. Levinsky

DNV GL EnergyDr.ir. L. Post

Shell Global Solutions InternationalDr.ir. P. Pronk

Tata SteelDr.ir. C.J.A. Pulles

KIWA TechnologyProf.dr. D.J.E.M. Roekaerts

Technische Universiteit DelftIr. J.N.A. Koomen

Stork ThermeqDr. L.J. Korstanje, secretaris

Technologiestichting STW

2 Brandbrief STW 2015

Brandbrief 2015Nr 21 Schone en Zuinige Verbrandingfebruari 2015Technologiestichting STW

3Schone en zuinige verbranding

Inhoud

06 Voorwoord

07 1 / Projects08 MILDNOX: Fuel flexibility and NO formation in dilute combustion

12 BIOxyFuel: Torrefied Biomass Combustion under Oxy-fuel Conditions in Coal Fired Power Plants

14 XCiDE: Crossing the Combustion modes in Diesel Engines

17 HiTAC: Heavy Fuel-Oil Combustion in a HiTAC Boiler

20 ULRICO: Ultra Rich Combustion of Natural Gas to Syngas

23 MoST: Multi-scale modification of swirling combustion for optimized gas turbines

26 ALTAS: Advanced Low NOx Flexible Fuel Gas Turbine Combustion, Aero and Stationary

28 flexFLOX: Flameless combustion conditions and efficiency improvement of single- and

multiburner-FLOXTM furnaces in relation to changes in fuel and oxidizer composition

31 2 / Promotions32 Dr. L. Zhou 30 September 2013

33 Dr. S. Ayyaoureddi 9 January 2014

35 Dr. P.G.M. Hoeijmakers 28 January 2014

37 Dr. M. Shahi 24 September 2014

39 Ir. N. Speelman September 2015



Voorwoord

Beste Brandbrief lezer,

Met gemengde gevoelens presenteren we hier Brandbrief no. 21. Met een tevreden en trots

gevoel presenteren we in deze Brandbrief de resultaten van de 8 projecten die intussen zijn

afgerond binnen het Perspectief programma Clean Combustion Concepts. Met de resultaten van

deze projecten zijn stappen gezet naar schonere en zuinigere verbrandingstechnologiën, waar

de betrokken industriële deelnemers mee verder kunnen.

Nu het CCC programma succesvol is afgesloten komt ook het Platform Schone en Zuinige

Verbranding tot een einde. Een platform waarbinnen gedurende de afgelopen 18 jaar de univer-

sitaire groepen met een aantal belangrijke bedrijven en instituten het verbrandingsonderzoek

in Nederland hebben afgestemd. We kunnen met een tevreden gevoel terugkijken op een zeer

vruchtbare samenwerking binnen het platform. Aan de andere kant is het natuurlijk jammer dat

aan dit platform nu een einde komt. Voor de toekomst zijn we echter bijzonder positief gestemd,

omdat de functie van het platform SZV vanaf nu wordt overgenomen door de Nederlandse

Vereniging voor Vlamonderzoek, de NVV. Ook de jaarlijkse nationale conferentie COMBURA zal

in de toekomst door de NVV worden georganiseerd. We zijn ervan overtuigd dat hiermee de

overlegstructuur van de academische groepen en de contacten met het bedrijfsleven van deze

groepen gewaarborgd zijn. Het is nog niet duidelijk wat de toekomst zal zijn van deze Brandbrief.

Zeker is dat dit de laatste aflevering is in deze vorm.

Theo van der Meer (Voorzitter Platform Schone en Zuinige Verbranding)

Philip de Goey (Voorzitter Programmacommissie Clean Combustion Concepts)


Projects

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Projectleaders: prof.dr. H.B. Levinsky, prof.dr. L.P.H. de Goey, dr. A.V. Mohkov, dr.ir. J.A. van Oijen

Combustion using highly preheated air, together with diluted air and/or fuel, is a clean combustion concept that combines high efficiency and low pollutant emissions in industrial heating processes. Having names such as flameless oxidation, high efficiency combustion and MILD combustion, these methods allow the use of recuperated heat in high-temperature processes without the penalty of increased NOx emissions, and offer the possibility of substantially homogenizing the temperature field in furnaces.

To permit the optimization of NOx control, and to provide insight into the ultimate low-NOx potential of these methods, in the proposed research we investigate the paths to NO formation in dilute, high temperature combustion. Towards this end, we have performed quantitative laser diagnostic measurements of flame structure, using Raman and LIF in the laminar coflow geometry (see Fig. 1), combined with detailed numerical simulations of the structure of the reaction zone (see Fig. 2). An important part of this research is the analysis of the preheating and dilution of the fuel and/or oxidizer on spatial structure and NO formation.

The predictive power of the detailed simulations made using the GRI-Mech 3.0 chemical mechanism is tested by comparison of the measured and calculated distributions of temperature and major species fractions. Laminar diffusion flames with different degree of preheating of the coflow and fuel were studied. The structures of a normal non-preheated diffusion flame (Case NP) and a MILD flame with preheated and diluted reactants (Case M) are compared here. Calculated temperature distributions of these flames are shown in Fig. 2. The flame temperature and major species (CO, CO2, N2, H2, H2O, CH4 and O2) were also measured using spontaneous Raman scattering and

NO species using Laser-Induced Fluorescence. The ma-thematical description of the model is governed by a set of conservation equations for mass, momentum, energy and species in the cylindrical coordinate. The GRI Mech. 3.0 chemical mechanism is used to obtain the required ther-modynamic and transport data involved. Mixture-Averaged transport is used to calculate diffusion velocities of each species. Radiation effects were also added to calculation using optically-thin approximation.

Measurements of the in-house developed diffusion burner are compared against computations and a good agreement was found for major species and temperature (see Fig 3). NO concentration obtained by Laser Induced Fluorescence is compared with computations as shown in Fig. 4. It is seen that amount of NO is predicted with a reasonable accuracy (see Fig 4). Additionally, measurements have been performed using a LJHC burner for Case M. In this burner the diluted oxidizer coflow is generated by a lean premixed ceramic burner. In essence, this geometry is a diluted laminar “jet in hot coflow”. Computations of this flame have also been performed using detailed chemistry of GRI 3.0 and Mixture-Averaged transport.

Comparison of computations and measurements of tem-perature for this flame is shown in Fig. 5 at three different heights above the fuel jet exit. The “mild” increase in temperature in the mixing layer (~200 K) is indicative of MILD combustion under these conditions. NO concentra-tions of this burner are also compared with computations (see Fig. 6). It is seen that NO fractions are below 10 ppm in which majority of the NO is formed in the coflow.

To study flame stabilization of this combustion regime, we perform numerical study of the the H2-enriched Delft Jet-in-Hot Coflow (DJHC) burner which is shown in Fig.7. This burner mimics conditions of Mild combustion in which a fuel jet is ignited due to being issued into hot burned gases of coflow. Base fuel in the experiments is Dutch Natural Gas (DNG) and very recently it has been mixed with various amounts of H2. It has been observed that addition of H2 has a significant effect on the flame structure and stabiliza-tion mechanism of the lifted turbulent non-premixed flame.

The present study also reports on the numerical investi-gation of preferential diffusion effects in autoignition of H2 containing fuels. These effects are implemented in the FGM technique for LES of Mild combustion. For this purpose, a flamelet-based combustion model has been developed based on Non-unity Lewis mixing layers for LES of the turbulent igniting CH4/H2 flames in a hot environment. Various amounts of H2 ranging from 0 to 25 percent of fuel volume have been added to the base fuel and a significant change in lift-off height and stability of

MILDNOX: Fuel flexibility and NO formation in dilute combustion


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1 Measurement of a MILD flame in the laminar jet-in-hot-coflow (LJHC) burner.

2 Temperature computa-tions of (left) Case NP and (right) Case M.

3 The measured (symbols) and calculated temperature (lines) in Case NP at three different heights as a function of the radial distance.

4 The measured (symbols) and calculated NO in Case NP at three different heights as a function of the radial distance.

5 The measured (symbols) and calculated temperature in Case M at three different heights as a function of the radial distance.

6 The measured (symbols) and calculated NO in Case M at three different heights as a function of the radial distance.


tion of the random noise generator has been successfully reproduced the experimental inflow turbulent fluctuations.The temperature field has been computed by application of the developed LES-FGM-PDF model employing non-unity Lewis numbers. Instantaneous snapshots of the tempera-ture field are shown in Fig. 10. In these snapshots the for-mation of ignition kernels can be observed. This observation corresponds to experimentally observed ignition kernels.

A comparison of Favre-averaged distributions of predicted OH mass fraction for all studied cases with unity Lewis and non-unity Lewis numbers (not shown here) indicates that the concentration of OH increase significantly by addition of hydrogen. Inclusion of preferential diffusion in the combustion model affects the stabilization and lift-off height of the predicted flames significantly, especially for DJHC-05H2 and DJHC-10H2 (5 and 10% H2 addition, respectively). By comparison with the most probable flame

the flames has been observed. The goal of this research is not to provide a comprehensive validation of all cases against experimental data (which is not available) but to illustrate effect of preferential diffusion in complex inter-actions of mixing and kinetic on the flame’s stability.The LES has been performed by taking into account variances of controlling variables that have been computed by pre-sumed beta-PDF approach. Turbulent inflow conditions are generated using a random noise generator.

Comparison of computed mean streamwise velocities against measurements is shown in Fig.8 for case DJHC-00H2 (pure DNG). It can be seen that the mean velocity field agrees very well with the measurements.

Fig. 9 shows a comparison of the computed and measured RMS values of streamwise and spanwise velocity and the resulting turbulent kinetic energy. It is clear that applica-

7 Schematic of Delft Jet-in-Hot Coflow (DJHC) burner of Oldenhof et al.

8 Comparison of computed radial profiles of mean stream-wise velocity at heights Z = 15, 60 and 90 (solid lines) against measurements (open symbols) for Case 00H2.

9 Comparison of computed centerline RMS values of streamwise and spanwise velocity and turbulent kinetic energy (solid lines) against measurements (symbols) for Case 00H2.

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different from those in the JHC burners. For instance, Reynolds numbers might be larger which can increase turbulence intensities. Furthermore, entrainment of burned gas into the fuel stream shifts most reactive mixture fraction toward the fuel stream. In this condition, turbulent structures have a larger impact on ignition events resulting in an increased role of turbulence transport with respect to molecular diffusion. In the future research, experimental and numerical investigations of these conditions are indis-pensable in order to move toward more practical situations.

luminescence line, it is indicated that hydrogen enriched cases require inclusion of preferential diffusion effects in the combustion model for an accurate prediction of lift-off height especially for cases DJHC-05H2 and DJHC-10H2.

Concluding Remarks

We have developed an efficient and reliable numerical model to predict MILD combustion of natural gas and hydrogen mixtures. With this model, new furnaces for the high-temperature process industry can be developed.In real furnaces, however, the conditions might be quite

Publications

[1] S.E. Abtahizadeh, PhD Thesis “Numerical study of Mild combustion from laminar flames to Large Eddy Simulation of turbulent flames with Flamelet Generated Manifolds”, Eindhoven University of Technology (2014). Advisers: Prof. Dr. Philip de Goey and Dr. Ir. Jeroen van Oijen

[2] Sepman, A., Abtahizadeh, E., Mokhov, A., van Oijen, J., Levinsky, H., de Goey, P. Experimental and numerical studies of the effects of hydrogen addition on the structure of a laminar methane–nitrogen jet in hot coflow under MILD conditions. Int. J. Hydrogen Energy, Vol. 38, 13802-13811 (2013).

[3] Abtahizadeh, S.E., Sepman, A.V., Hernandez-Perez, F.E., van Oijen, J., Mokhov, A.V., de Goey, P. and Levinsky, H.B. Numerical and experimental investigations on the influence of preheating and dilution on transition of laminar coflow diffusion flames to Mild combustion regime. Combust. Flame Vol. 160, 2359-2374 (2013).

[4] Abtahizadeh, S.E., Oijen, J.A. van, Goey, L.P.H. de (2012). Numerical study of Mild combustion with entrainment of burned gas into oxidizer and/or fuel streams. Combustion and Flame, 159(6), 2155-2165.

[5] Sepman, A.V., Abtahizadeh, S.E., Mokhov, A.V., Levinsky, H.B. and de Goey, P. Numerical and experimental studies of the NO formation in laminar coflow diffusion flames on their transition to MILD combustion regime. Combust. Flame. Vol. 160, 1364-1372 (2013).

[6] Mokhov, A.V., Smirnov, B.M., Dutka, M., Vainchtein, D., Levinsky, H.B. and De Hosson, J. Th.M. Formation of chain aggregates in external electric field. Chem. Phys. Lett. Vol. 570, 104-108 (2013).

[7] Sepman, A.V., Toro, V., Mokhov, A.V. and Levinsky, H.B. Determination of temperature and concentrations of main components in flames by fitting measured Raman spectra. J. Appl. Phys. B, Vol. 112, 135-147 (2013).

[8] Sepman, A.V., Mokhov, A.V., and Levinsky, H.B. Spatial structure and NO formation of a laminar methane–nitrogen jet in hot coflow under MILD conditions: A spontaneous Raman and LIF study. Fuel, 103, pp.705-710 (2013).

[9] Sepman, A.V., Mokhov, A.V. and Levinsky H.B. The effects of the hydrogen addition on the HCN profiles in fuel-rich-premixed, burner-stabilized C1-C3 alkane flames. Int. J. Hydrogen Energy, vol. 36, no. 21, pp. 13831-13837 (2011).

[10] Sepman, A.V., Mokhov, A.V. and Levinsky H.B. Extending the predictions of chemical mechanisms for hydrogen combustion: comparison of predicted and measured flame temperatures in burner-stabilized 1D flames. Int. J. Hydrogen Energy, Vol. 36, pp. 9298-9303 (2011).

[11] Sepman, A.V., Mokhov, A.V., and Levinsky, H.B. The effects of hydrogen addition on NO formation in atmospheric-pressure, fuel-rich-premixed, burner-stabilized methane, ethane and propane flames. Int. J. Hydrogen

Acknowledgement: The authors would like to thank STW for sponsoring this project

under the CCC program project number: 10414.

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10 Computed instantaneous distributions of temperature field using FGM-LES-PDF model with non-unity Lewis numbers for Case DJHC-00H2. These snapshots show the localized temperature rise corresponding to formation of ignition kernels.


1

Projectleaders: prof.dr.ir. G. Brem, dr. C.W.M. van der Geld, prof.dr.ir. B.J. Geurts, prof.dr. L.P.H. de Goey, prof.dr. J.G.M. Kuerten, prof.dr.ir. Th.H. van der Meer, dr.ir. J.A. van Oijen

The objective of the BIOxyFuel project was to increase understanding and predictive capabilities of torrefied biomass combustion at high co-firing rates under oxy-fuel conditions in coal fired power plants. The combination of biomass co-firing and oxy-fuel power plants will have a double effect on the reduction of CO2. In fact, the combi-nation of oxy-fuel combustion and biomass could be used as a sink for CO2. The research program is carried out for different types of biomass and torrefied biomass as from an economic perspective fuel flexibility is essential because of fluctuating availability and prices of the different biomass streams. Industrial partners involved in the project were NVV, KEMA, and TSA (electricity power companies).

Research method

The scientific results of the research program are the development of new and unique experimental facilities in The Netherlands, advanced mathematical models for the key processes at different scales (particle, flow, furnace), and model validation using data from full-scale plants.

Results

In the experimental phase the reactivity, burnout, and emissions of raw and torrefied biomass are measured. In this way more insight has been obtained in the dominating combustion mechanisms of coal/biomass-mixtures under both air-blown and oxyfuel conditions.

Parallel to the experimental work different models have been developed, ranging from a single particle model, to a particle-laden turbulent flow model and a furnace or full-scale model. The single particle biomass combustion model has been validated using experimental findings and integrated in the particle-laden turbulent flow simula-tions under pyrolysis conditions. These models have been integrated in a furnace model, that is validated against experimental data obtained from measurement campaigns at a full-scale power plant while co-firing biomass.

The BIOxyFuel project has contributed to the CCC programme by developing a new combustion concept, reducing unwanted emissions (CO2, NOx), giving insight in a higher fuel flexi-bility (different types of torrefied biomass/coal mixtures), improving the potential use of sustainable fuels (biomass).

BIOxyFuel: Torrefied Biomass Combustion under Oxy-fuel Conditions in Coal Fired Power Plants


Publications

[1] Haseli, Y., Oijen, J.A. van & Goey, L.P.H. de (2013). A quasisteady analysis of oxy-fuel combustion of a wood char particle. Combustion Science and Technology, 185(4), 533-547. in Web of Science

[2] Haseli, Y., Oijen, J.A. van & Goey, L.P.H. de (2013). Reduced model for combustion of a small biomass particle at high operating temperatures. Bioresource Technology, 131, 397-404; in Web of Science

[3] Haseli, Y., Oijen, J.A. van & Goey, L.P.H. de (2012). Predicting the pyrolysis of single biomass particles based on a time and space integral method. Journal of Analytical and Applied Pyrolysis, 96(July), 126-138; in Web of Science

[4] Haseli, Y., Oijen, J.A. van & Goey, L.P.H. de (2012). A simplified pyrolysis model of a biomass particle based on infinitesimally thin reaction front approximation. Energy & Fuels, 26(6), 3230-3243; in Web of Science

[5] Haseli, Y., Oijen, J.A. van & Goey, L.P.H. de (2012). Analytical solutions for prediction of the ignition time of wood particles based on a time and space integral method. Thermochimica Acta, 548, 65-75; in Web of Science

[6] Haseli, Y., Oijen, J.A. van & Goey, L.P.H. de (2011). A detailed one-dimen-sional model of combustion of a woody biomass particle. Bioresource Technology, 102(20), 9772-9782; in Web of Science

[7] Haseli, Y., Oijen, J.A. van & Goey, L.P.H. de (2011). Modeling biomass particle pyrolysis with temperature-dependent heat of reactions. Journal of Analytical and Applied Pyrolysis, 90(2), 140-154; in Web of Science

[8] Haseli, Y., Oijen, J.A. van & Goey, L.P.H. de (2011). Numerical study of the conversion time of single pyrolyzing biomass particles at high heating conditions. Chemical Engineering Journal, 169(1-3), 299-312; in Web of Science

[9] E. Russo, J.G.M. Kuerten, B.J. Geurts, Delay of biomass pyrolysis by gas-particle interaction, J. Anal. Appl. Pyrolysis, 110, 88-99 (2014)

[10] E. Russo, J.G.M. Kuerten, B.J. Geurts. C.W.M. van der Geld, Water droplet condensation and evaporation in turbulent channel flow, J. Fluid Mech., 749, 666-700 (2014)

[11] E.M.Gucho, E.A.Bramer and G.Brem,” Experimental studies of torrefied biomass co-firing with coal in drop tube furnace, June 06, 2011, 19th European Biomass Conference and Exhibition, Berlin

[12] E.M.Gucho, K.Shazhad, E.A.Bramer and G.Brem,” Parametric study on the torrefaction of beech wood and miscanthus for co-firing application.”, ToTeM 37, 22-23 September 2011, Technical University of Wroclaw, Poland

[13] E.M.Gucho, E.A.Bramer and G.Brem, ‘Áir and oxyfuel combustion of torrefied biomass in new spiral combustion reactor’, 3rd Oxyfuel Combustion Conference, 9-13 September 2013, Ponferrada, Spain

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Projectleaders: dr.ir. L.M.T. Somers, dr. N.J. Dam,prof.dr. L.P.H. de Goey

Ever increasing demands from legislation forces OEM’s of HD Diesel engines to apply EGR (Exhaust Gas Recirculation) often in combination with after treatment systems (SCR, DPF). This will induce a so-called fuel penalty and increases the cost of the powertrain. Hence the active research in intrinsically clean combustion concepts that apply a more premixed type of combustion (HCCI, PCCI). Unequivocally these concepts try to create a more or less homogeneous charge but still rely on auto-ignition. To achieve this, injection of fuel has to be separated from the ignition event allowing ample mixing time. Principally separation can be obtained by lowering the temperature and/or the reactivity of the fuel.The goal of the project is to

– Determine the load range for PCCI with conventional diesel fuels

– Similar but with alternative (high-octane) fuels– Develop a combustion model in a CFD setting that

naturally takes the fuel reactivity into account– Build a knowledge base on new combustion concepts

Research method

To adequately determine concept boundaries a special engine set-up is used. It is based on a HD diesel engine which is adapted such that one-cylinder is separated from the rest. The test-cylinder has a separate intake and exhaust allowing for flexible setting of temperature, boost pressure and EGR percentage (up to 75%). The fuel injec-tion equipment applies a modern common-rail system able to deliver pressures up to 3500 bar (mostly limited by the injector) and is freely programmable. All exhaust emission are measured. In figure 1 a photograph of the engine is depicted.

The numerical approach is based on the efficient FGM methodology. This methodology is a chemical reduction method that is based on a so-called ‘flamelet approach’ in combination with a tabulation method. In this project the method is extended for modelling engine combustion, including features like ignition for diffusive and pre-mixed combustion of large alkane (i.e. automotive) fuels.

Results

First experiments on PCCI applying regular diesel fuel revealed that the applicable load range is small and introduces a fuel penalty. The compression needs to be lowered and high levels of EGR are inevitable to reach the necessary separation between injection and ignition. This is mainly due to the low resistance of diesel fuel, as it is designed to be, against auto-ignition. A promising path to a PCCI concept is proven to be a change in fuel reactivity.Two prevailing implementations to reach that currently exist: RCCI and PPC. RCCI is a dual-fuel concept and PPC applies a single fuel (blend) with a moderate but much higher octane number than diesel (see figure 2).

In contrast to normal dual fuel applications in RCCI the low octane fuel (diesel) is injected early to ensure separation between ignition and injection. Initial experiments show the potential of the approach for a reduction of NOx by one order of magnitude compared to regular diesel at similar EGR levels (figure 3). In fact the soot and NOx emissions

XCiDE: Crossing the Combustion modes in Diesel Engines

1 The single cylinder HD diesel engine at the TU/e (Cyclops).

2 Hi-octane PCCI concepts.

RCCI

Dual-fuel

PPC

Single-fuel


After that it has been applied to a RCCI study with varying gasoline content (figure 5).

The results are promising as the method predicts the same trend as the experim-ents show. The big advantage of the numerical app-roach is that it is now possible to investigate where exactly the emissions are created. Detailed informa-tion as presented in figure 6 can pinpoint exact measures to deal with the specific problems of the new concepts.

The program has come to the conclusion that these new concepts pro-vide a way to develop clean and efficient engines. A larger follow-up of the project is currently formulated in which DAF, TNO and Shell will participate actively. Clearly the optimization of the fuel together with engine technology offers a win-win situation to reduce the carbon footprint of the transport sector considerably.

are below EUROVI limits without a DPF and after treat-ment system. The fuel economy has improved by nearly 10% which shows its potential towards CO2 reduction.

The RCCI concept also has its drawbacks mainly due to trapped fuel in crevices and ‘overleaning’. This results in relatively high CO and UHC (Unburned HydroCarbons) emis-sions compared to conventional diesel combustion (CDC).

The PPC concepts does not suffer from high UHC and CO emissions because of the fact the fuel can be targeted better towards the piston bowl. It was found that the specific composition of the fuel blend is not really important but the performance is mainly determined by the Fuel octane number. A such even Naphtha fuels and low injection pressures can be used as shown in figure 4. Consequently cheaper injection equipment can be applied and the demand for high grade fuels can be minimized. Note that this on itself can lead to CO2 reduction at the production side of the fuel as well.

As these concepts heavily rely details of the mixing process and combustion computational fluid dynamics (CFD) will be a necessary tool to optimize these concepts in relation to the fuel composition. As fuel details are important chemical kinetic schemes need to be incorporated in an efficient way. In this project the FGM methodology is extended to CDC and RCCI/PPC combustion. To validate the approach it has been extensively compared to the detailed database of the Engine Combustion Network (www.sandia.gov/ecn),

3 Specific NOx emissions (logarithmic scale!) at medium load at different timings . The diamonds are results from an RCCI experiment applying 90% gasoline/10% diesel.

4 Effect of fuel pres-sure on soot emissions. Three naphtha blends in the PPC concept compared to regular diesel in a CDC concept.

5 Prediction of 50% heat release (CA50) as a function of gasoline percentage in RCCI experiment.

6 CO mass-fraction of a PCCI case running on regular diesel depicting highest levels in the crevice region.

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Journal Publications

[1] Egüz, U., Leermakers, C.A.J., Somers, L.M.T. & Goey, L.P.H. de (2014). Mode-ling of PCCI combustion with FGM tabulated chemistry. Fuel, 118, 91-99.

[2] Egüz, U., Ayyapureddi, S., Bekdemir, C., Somers, L.M.T. & Goey, L.P.H. de (2013). Manifold resolution study of the FGM method for an igniting diesel spray. Fuel, 113, 228-238.

[3] Egüz, U., Maes, N.C.J., Leermakers, C.A.J., Somers, L.M.T. & Goey, L.P.H. de (2013). Predicting auto-ignition characteristics of RCCI combustion using a multi-zone model. International Journal of Automotive Techno-logy, 14(5), 693-699.

[4] Egüz, U., Leermakers, C.A.J., Somers, L.M.T. & Goey, L.P.H. de (2013). Premixed charge compression ignition combustion modeling with a multi-zone approach including inter-zonal mixing. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 227(9), 1313-1324.

[5] Egüz, U., Ayyapureddi, S., Bekdemir, C., Somers, L.M.T. & Goey, L.P.H. de (2012). Modeling fuel spray auto-ignition using the FGM approach: effect of tabulation method. SAE International Journal of Engines: 2012-01-0157

[6] Egüz, U., Somers, L.M.T., Leermakers, C.A.J. & Goey, L.P.H. de (2011). Multi-zone modelling of PCCI combustion. International Journal of Vehicle Design, 55(1), 76-90

[7] U. Egüz, L.M.T. Somers, C.A.J. Leermakers, L.P.H. de Goey, Multi-zone mo-delling of PCCI combustion, Int. J. of Vehicle Design, 55(1), 76-90, (2011)

[8] C.A.J. Leermakers, M.P.B. Musculus, In-cylinder soot precursor growth in a low-temperature combustion diesel engine: Laser-induced fluorescence of polycyclic aromatic hydrocarbons, Proceedings of the Combustion Institute, Available online 19 July 2014, ISSN 1540-7489, http://dx.doi.org/10.1016/j.proci.2014.06.101

[9] C.A.J. Leermakers, P.C. Bakker, B.C.W. Nijssen, L.M.T. Somers, B.H. Johans-son, Low octane fuel composition effects on the load range capability of partially premixed combustion, Fuel, Volume 135, 1 November 2014, Pages 210-222, ISSN 0016-2361, http://dx.doi.org/10.1016/j.fuel.2014.06.044

[10] Leermakers, C.A.J., Luijten, C.C.M., Somers, L.M.T., Goey, L.P.H. de & Albrecht, B.A. (2013). Experimental study on the impact of operating conditions on PCCI combustion. International Journal of Vehicle Design, 62(1), 1-20.

[11] Leermakers, C.A.J., Bakker, P.C., Somers, L.M.T., Goey, L.P.H. de & Johansson, B.H. (2013). Commercial Naphtha blends for partially premixed combustion. SAE International Journal of Fuels and Lubricants, 6(1):2013-01-1681

[12] Leermakers, C.A.J., Bakker, P.C., Somers, L.M.T., Goey, L.P.H. de & Johansson, B.H. (2013). Butanol-diesel blends for partially premixed combustion. SAE International Journal of Fuels and Lubricants, 6(1):2013-01-1683

[13] Leermakers, C.A.J., Somers, L.M.T. & Johansson, B.H. (2012). Combustion phasing controllability with dual fuel injection timings. SAE International Journal of Engines, 2012:01-1575

[14] Leermakers, C.A.J., Luijten, C.C.M., Somers, L.M.T., Kalghatgi, G.T. & Albrecht, B.A. (2011). Experimental study of fuel composition impact on PCCI combustion in a heavy-duty diesel engine. SAE International Journal of Engines, 2011-01-1351-1/20.

[15] Leermakers, C.A.J., Berge, B. van den, Luijten, C.C.M., Somers, L.M.T., Goey, L.P.H. de & Albrecht, B.A. (2011). Gasoline–diesel dual fuel : effect of injection timing and fuel balance. SAE International Journal of Engines, 4(3):2011-01-2437

[16] C.A.J. Leermakers, C.C.M. Luijten, L.M.T. Somers, G.T. Kalghatgi, B.A. Albrecht, Experimental Study of Fuel Composition Impact on PCCI Combustion in a Heavy-Duty Diesel Engine, SAE Technical Papers, -, 2011-01-1351, (2011)

[17] M.D. Boot, C.C.M. Luijten, L.M.T. Somers, U. Egüz, D.D.T.M. van Erp, B.A. Albrecht and R.S.G. Baert, ‘Uncooled EGR as a Means of Limiting Wall-Wetting under Early DI Conditions’, SAE Technical Papers, 2009, 2009-01-0665.

[18] M.D. Boot, C.C.M. Luijten, L.M.T. Somers, U. Egüz, D.D.T.M. van Erp, B.A. Albrecht, R.S.G. Baert, Uncooled EGR as a Means of Limiting Wall-Wetting under Early Direct Injection Conditions, in Homogeneous Charge Compression Ignition Engines, 2009; Editors: SAE, 10.4271/2009-01-0665, SAE International, Book Chapter ISBN 978-0-7680-2138-7 (2009)

Conference papers

[19] U. Egüz, C.A.J. Leermakers, L.M.T. Somers and L.P.H. de Goey (2011), ‘Preliminary analysis of soot and UHC emissions under PCCI conditions’, Proceedings of European Combustion Meeting (ECM2011), 28 June- 1 July 2011, Cardiff, Wales.

[20] U. Egüz, C. Bekdemir, L.M.T. Somers and L.P.H. de Goey (2011), ‘Study of PCCI modeling with the FGM approach’, Proceedings of Towards Clean Diesel Engines (TCDE), 8-9 June 2011, Chester, United Kingdom.

[21] U. Egüz and L.M.T. Somers (2011), ‘Modeling of PCCI Combustion with FGM Approach’, Oral Presentation, International Conference on Numerical Combustion (ICNC), 27-29 April, 2011, Corfu, Greece.

[22] U. Egüz, C.A.J. Leermakers, L.M.T. Somers and L.P.H. de Goey (2010) ‘Multi-zone Modelling of PCCI Combustion with CFD Coupling for Stratification’, Proceedings of Towards Sustainable Combustion (Speic2010), 16-18 June 2010, Tenerife, Spain.

Conference posters

[23] L.M.T Somers, C.A.J. Leermakers and U. Egüz (2010), ‘Crossing the Combustion Modes in Diesel Engines’, Oral Presentation, Combura 2010, 12-13 October 2010, Maastricht, the Netherlands.

[24] C.A.J. Leermakers, B.A. Albrecht, L.M.T. Somers, C.C.M. Luijten, Euro VI without fuel penalty?, in 7th International Automotive Congress.nl; Helmond, Netherlands, Conference Poster (2010)

[25] B. Berge, van den , C.A.J. Leermakers, L.M.T. Somers, C.C.M. Luijten, L.P.H. de Goey, Impact of fuels with lower reactivity on PCCI combustion in a heavy-duty engine, in Combura; Maastricht, Netherlands, Conference Poster (2010)

[26] C.A.J. Leermakers, L.M.T. Somers, C.C.M. Luijten, L.P.H. de Goey, Euro VI without fuel penalty?, in Combura; Maastricht, Netherlands, Conference Poster (2010)

[27] C.A.J. Leermakers, R.P.C. Zegers, L.M.T. Somers, C.C.M. Luijten, N.J. Dam, L.P.H. de Goey, High speed combustion imaging, in Combura; Maastricht, Netherlands, Conference Poster (2010)

Acknowledgement: The authors would like to thank STW for sponsoring this project under the CCC program project number: 10417 and DAF, Delphi, Shell and Avantium for their contributions.


1

HiTAC: Heavy fuel-oil combustion in a HiTAC boiler

Projectleaders: prof.dr.ir. Th.H. van der Meer, prof.dr. D.J.E.M. Roekaerts, dr.ir. M.J. TummersPhD’s: S.L. Zhu, H.R. Correia Rodrigues

The aim of this project was to improve the efficiency and reduce NOx and CO emissions of heavy fuel-oil combustion in industrial boilers by applying “High Temperature Air Combustion (HiTAC)”. HiTAC relies on rapid dilution of fuel and combustion air with combustion products before the combustion reactions take place. In the case of liquid fuels this leads to the question whether the entrainment rate of an evaporating fuel spray can be high enough to reach sufficiently dilute conditions of the fuel. A very detailed experimental study was performed at Delft University of Technology of spray flames of light fuel-oils (ethanol and acetone) in hot-diluted co-flow conditions. In parallel field tests were performed at Stork Thermeq in a 9 MW test boiler with spray flames of heavy fuel-oil with hot-diluted combustion air. The fuel-oil for these experiments was provided and characterized by Shell Global solutions

specifically for this project. Numerical modeling of both the Delft laboratory scale flame as well as the Stork industrial test boiler were done at the University of Twente with the aim of coupling both experiments and understanding the underlying processes. Finally Stork developed water-steam cycles optimized for the application in combination with HiTAC combustion

Research method

A laboratory test burner was developed for a spray flame in hot diluted co-flow. Figure 1 shows an ethanol flame from this burner in a co-flow with a temperature of 1300 K and an oxygen concentration of 9.3%. Several numerical methods were used for detailed in-flame measurements, such as: high speed visualization of the liquid break-up process; Phase Doppler anemometry (PDA) for simultane-ous measurements of droplet velocity and size statistics; coherent anti-Stokes Raman spectroscopy (CARS) for gas-phase temperature statistics and laser Doppler anemometry for co-flow velocity measurements.

A numerical model was developed within Ansys-Fluent with a pressure-swirl atomizer model including coalescence, secondary break-up and evaporation of the droplets, a laminar flamelet model for combustion, the discrete ordinate models for radiation and the k- model for turbulence. This model was first used to simulate a well-documented spray flame from literature, the so-called NIST flame. Then the model was used for simulations of the Delft laboratory flame and finally for the Stork test boiler. For the last simulations the Eddy Dissipation model was used as the combustion model in stead of the flamelet model.

1 Ethanol spray flame in hot diluted co-flow.


In the Stork 9 MW test facility experiments were conducted under conditions of elevated combustion air temperature, high amount of flue gas recirculation and fuel staging, aiming at more uniform temperature distributions throughout the combustion chamber. Conventional gas analysers were used to monitor NOx, CO and O2 in the flue gases.

Results

When comparing conventional ethanol spray flames with ethanol spray flames in hot-diluted co-flow the results of this project show that for the flames in hot-diluted co-flows: 1. The mean flame temperatures are more uniform with

less steep temperature gradients. With an oxygen concentration of only 6% the numerical simulations showed that the difference between peak temperature and co-flow temperature drops to about 200 K.

2. The maxima of the mean flame temperature are similar or considerably lower, depending on temperature and O2 concentration of the co-flow. Also the NOx concentrations were reduced considerably. Figure 2 shows computed results of the peak mean temperature under various co-flow conditions.

3. The turbulent temperature fluctuations are much lower. The measurements showed maximal temperature fluctuations of 700 K in the conventional ethanol flame and maximal temperature fluctuations of 200 K in the flame with a co-flow temperature of 1200 K and an oxygen concentration of 9.2%.

4. From the experiments on the lab scale burner it was concluded that small droplets are quickly vaporized and

the combustion process is mainly depending on the mixing of the fuel vapor with the entrained flow and the ignition delay time. Higher co-flow temperatures leads do a reduction of the flame lift-off height and an earlier formation of intermediate species leading to an increase of the peak temperature in lower axial position.

From these observations it is clear that the conditions in the flames in a hot-diluted co-flow are close to HiTAC conditions.

Although experimental restrictions did not make it possible to reach HiTAC conditions in the field tests with the 9 MW boiler, the results from the field test and the results from the numerical simulations on the same boiler are promising. The experiments showed that flue gas recirculation as well as fuel staging led to a decrease in NOx by 20%. The combination of flue gas recirculation and fuel staging decreased NOx by 30%.

Simulation results in the test boiler showed that an increase of the temperature of the combustion air from 373 K to 746 K leads to a higher peak temperature in the combustion chamber from 2240 K to 2390 K. A reduction of the O2 concentration of the combustion air from 23.065 wt% to 11.5325 wt% results in more uniform temperature distribution with a peak temperature of 1510 K. Further numerical investigation was done with recycling various ratios of flue gas into the primary and secondary air respectively for introducing various O2 concentration conditions for the combustion air flow. The predicted temperature difference between the average

2 Model predictions of peak temperature as a func-tion of co-flow conditions.

2


temperature and the peak temperature showed that the case with the lowest O2 concentration in the primary air has the smallest temperature difference in the boiler. It was also shown that besides thermal NOx, fuel NOx is an important contributor to NOx formation in heavy fuel-oil combustion. By introducing flue gas recirculation, thermal NOx can be reduced to a very low level, leaving the fuel NOx playing the dominant role. The interaction between soot and radiation also showed considerable influence on the predicted temperature profiles. In the case with hot

Publications

[1] S. Zhu, D.J.E.M. Roekaerts, and T.H. van der Meer, Numerical study of a methanol spray flame. 5th European Combustion Meeting, T. Griffiths (Ed.), Cardiff, UK, 2011, paper 067, 6 pages

[2] S. Zhu, D.J.E.M. Roekaerts, and T.H. van der Meer, Numerical simulation of a turbulent methanol spray flame using the Euler-Lagrange method and the steady laminar flamelet model. In Proceedings of the Mediterranean Combustion Symposium. Chia Laguna, Sardinia, Italy, 2011

[3] H. Rodrigues, M.J. Tummers, D.J.E.M. Roekaerts, Experiments on turbulent ethanol reacting sprays in HiTAC conditions, 12th International Conference on Liquid Atomization and Spray Systems, Heidelberg, September, 2-6, 2012

[4] S. Zhu, D.J.E.M. Roekaerts, A.K.Pozarlik, B. Venneker, T.H. van der Meer, Numerical investigation towards a HiTAC condition in a 9MW heavy fuel-oil boiler, 6th European Combustion Meeting, Lund, Sweden, 25-28th June, 2013.

[5] L. Ma, S. Zhu, H.R.C. Rodrigues, M.J. Tummers, T.H. van der Meer and D.J.E.M. Roekaerts, Numerical investigation of ethanol spray-in- hot-coflow flame using steady flamelet model, 8th Mediterranean Combustion Symposium, Çesme Izmir, Turkey, September 8-13, 2013, Paper EGTSC-13, 13 pages, Editors: Nevin Selcuk, Federico Beretta, Mohy S. Mansour, and Andrea d’Anna. Publisher: International Centre For Heat and Mass Transfer, METU, Ankara, Turkey

[6] H.R.C.Rodrigues, M.J. Tummers, D.J.E.M. Roekaerts, Turbulent Spray Combustion in hot-diluted co-flow, 9th Asia-Pacific Conference on Combustion, Gyeongju Hilton, Gyeongju, Korea, 19-22 May 2013, 4 pp

[7] H.R.C. Rodrigues, M.J. Tummers and D.J.E.M. Roekaerts , Turbulent Spray Combustion of ethanol and acetone flames in flameless conditions, In: European Combustion Meeting – 2013 Paper P3-80, 6 pp, June 25-28, 2013, Lund, Sweden, ISBN 978-91-637-2151-9

[8] H. Correia Rodrigues, M.J. Tummers, E.H. van Veen, D.J.E.M. Roekaerts, Effects of coflow temperature and composition on ethanol spray flames in hot-diluted coflow, Int. J. Heat Fluid Flow, 2014, http://dx.doi.org/10.1016/j.ijheatfluidflow.2014.10.006

combustion air, the peak temperature was reduced by 140 K and the NOx emission was reduced to about one fourth.

The results from this project are promising with respect to HiTAC combustion of heavy-fuel oil in boilers. The next step is to further develop this boiler concept by realizing optimal internal recirculation in the combustion chamber. For this reason Stork will use numerical simulations, which will be validated with experiments in a new test boiler, which is currently under development

[9] Hugo Correia Rodrigues, Mark J. Tummers, Eric H. van Veen, Dirk J.E.M. Roekaerts, Spray flame structure in conventional and hot-diluted combustion regime, Combustion and Flame, 2014 http://dx.doi.org/10.1016/j.combustflame.2014.07.033

[10] L. Ma, H.R. Correia Rodrigues , S. Zhu , M.J. Tummers , D.J.E.M. Roekaerts, Modelling of Delft Spray-in-Hot-Coflow flame with steady flamelet and FGM, in Book of Abstracts of the 23rd Biennial Meeting of the Belgian Section of the Combustion Institute, Brussels, 27-28 May, 2014, 2 pages

[11] Shanglong Zhu, Dirk Roekaerts, Artur Pozarlik, Theo van der Meer, Eulerian-Lagrngian RANS model simulations of the NIST turbulent methanol spray flame, submitted to Combustion Science and Technology

[12] Shanglong Zhu, Dirk Roekaerts, Artur Pozarlik, Hugo Rodriguez, Theo van der Meer, Numerical investigation towards HiTAC conditions in laboratory-scale ethanol spray combustion, in preparation

[13] Hugo Rodrigues, Spray combustion in moderate and intense low-oxygen conditions. An experimental study, PhD thesis, 2015, TU Delft.


ULRICO: Ultra Rich Combustion of Natural Gas to Syngas

Projectleaders: dr.ir. J.B.W. Kok, Prof.dr. D.J.E.M. Roekaerts

A major issue in Partial Combustion plants is to achieve an optimal syngas output composition, with low soot content and small combustor volume. These are conflicting demands and the design needs to be optimized with a view to the downstream process. To achieve high hydrogen and carbon monoxide concentrations a high combustor volume is required. But this will result in high soot content of the product gas. This will lead to fouling of downstream heat exchanger systems and hence to loss of reliability and high costs of maintenance. Gasification plant users and manufacturers will use the knowledge from this project to improve existing plants and optimize designs for new plants. With the expected increasing demand for new fuels like synthetic Diesel, syngas and hydrogen the proposed project will render crucial information and design tools on chemical reaction processes and soot formation in ultra rich conditions. Both experimental tests at elevated

pressure and CFD modeling will be employed. The work is carried out by PhD student Marc Woolderink at the University of Twente and PostDoc Michael Stoellinger at the Technical University of Delft, supervised by Prof. Dirk Roekaerts (TUD) and Dr. Jim Kok (UT). The work was supported by the industrial partners Shell Global Solutions (financial support and engineering guidance) and ANSYS Europe (CFD modeling support).

Research method

A rich combustion test rig at elevated pressure was realized at the UT. Numerical modelling of the turbulent rich combustion process of perfectly premixed natural gas and oxidizer to syngas, and of a nonpremixed system with pro-duct gas recirculation was performed at both UT and TUD.

AT the UT The gaseous chemistry is described by a reaction progress variable based combustion model with tabulated detailed chemistry. The soot formation and radiative heat loss of the gases and the soot particles is taken into account by 2 extra transport equations. All models are implemented in the commercially available CFD package ANSYS-CFX and applied on a premixed reactor design and a nonpremixed design with product gas back mixing.

At the TUD a simple semi-empirical soot model based on the soot number density and soot mass concentration is adopted in a transported PDF method for turbulent diffusion flames. The gas phase chemistry is reduced by a flamelet generated manifold (FGM) based on the mixture

1 Schematic cross section of reactor. 2 Partial oxidation reactor experimental setup.

1 2


fraction, progress variable and enthalpy loss. To account for the radiative heat transfer, the Reynolds averaged radiative transfer equation (RTE) is solved by means of a discrete transfer method. The proposed modeling approach is validated in simulations of two turbulent non-premixed methane-air flames at 1 bar and 3 bar pressure.

Results

Experiments

In this research measurements were done on the setup with a reactor with swirl stabilized flame (Figs 1,2) at several pressures and at equivalence ratios 2 to 4. A sample flow was extracted from the reactor downstream the oxidation front. This flow was quenched and diluted rapidly in order to avoid changes in chemical composition and soot particle growth and coagulation. For this application a special dilution system with dilution factor 104 was developed in the project. Upstream of the dilution step the gas composition was analysed with a gas chromatograph and downstream the dilution step, the soot concentration and size distribution (2-200 nm)was measured with a Scanning Mobility Particle Sizer.

Previous experiments with a very similar setup and under the same conditions were done by Albrecht et al. [1] but without measurement of soot particle concentration. In figure 3 the experimental concentration measurements are shown. All CO concentration measurements show a generally decreasing trend with increasing equivalence ratios from F=2.5 to F=4.0. Table 1 gives the measured species concentrations at an equivalence ratio F of 3 and their values at 50 ms in Chemkin PSR, Chemkin Premix and chemical equilibrium. It can be concluded that the dry mole fraction of CO measured in the produced syngas is approximately 0.16, which is significantly lower than the equilibrium value of 0.24. This is a clear indication that the

mixture would move more in the direction of equilibrium if the residence time in the reactor would have been longer. This also explains the decreasing CO concentration at high equivalence ratio’s, which is contradictory with equilibrium data. At high equivalence ratio the chemical reactions slow down, necessitating an increased residence time to reach equilibrium. This emphasizes the need of an accurate chemical activity prediction far from equilibrium.

Simulations

The CFI model was applied on a premixed natural gas flame, Nitrox40 as oxidizer, a preheat temperature of 573 K, equivalence ratio of 2.5 and a pressure of 4.0 bar. The axial velocity flow field shows a central recirculation area. The reaction progress variable shows a delay by chemical reaction kinetics after a steep increase in the flame front, steadily rising throughout the entire reactor until it reaches CCFI =0.88 at the outlet. The soot particle number density increases the most in the flame front, keeps increasing for a certain length before decreasing towards the outlet. In Figure 5 the axial profiles of CO, H2, C2H2 and the temperature of the CFI simulation have been plot. It can be seen that the CFI model is able to predict the endothermic reforming processes that are taking place downstream of the flame front in ultra-rich combustion. The decrease in temperature after the flame front due to reforming reactions is visible, as well as the steady increase of CO and H2 and decrease of C2H2.

3 Comparison of measured CO concentration in syngas produces on basis of natural gas/Nitrox.table Measured and predicted species concentrations [vol %] in dried produced syngas.

3


Comparison with experimental data shows a good match with predictions for the gas mass fractions of major species H2, CO and CH4. The concentration of C2H2 is overpredicted, as well as the amount of soot produced. This is probably due to the one way coupling of the gaseous chemical reaction model to the solid phase soot production model. Consumption of C2H2 by soot production is not accounted for. In addition there are large uncertainties in the soot model, that also need much better to be taken care of. The project has resulted in improved insight in the processes of oxidation and soot formation at rich conditions, and in a set of CFD design tools. In particular the modeling of soot formation and its coupling to gaseous chemistry is shown to need improvement. This work will lead to cleaner and more reliable fuel gas to syngas reactors, with application to Gas To Liquid processes and steam reformers for hydrogen production.

Publications

[1] Stoellinger, M., Roekaerts D., PDF modelling of soot formation in turbulent non-premixed flames using tabulated chemistry, European Combustion Meeting, 2013.

[2] Woolderink, M.H.F., Kok, J.B.W., Ultrarich combustion of natural gas to syngas, GT2011-46383, Proceedings ASME Turbo Expo 2011, Vancouver, Canada, 2011

[3] M.H.F. Woolderink, J.B.W. Kok, Modeling Ultra Rich Combustion Of Natural Gas Using A Reaction Progress Variable, Proc. 13th International Conf Numerical Combustion, April 27-29, 2011, Corfu, Greece.

[4] Kok J.B.W., Albrecht, B.A., Woolderink M.H.F., Non-adiabatic turbulent ultra rich combustion of natural gas, proc. 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, 16 – 18 July 2012, Malta, ISBN: 978-1-86854-986-3, 2012.

[5] M.H.F. Woolderink, J.B.W. Kok, Modeling of and experiments on ultrarich combustion and soot formation, to be submitted to Combustion and Flame 2015

[6] M.H.F. Woolderink, J.B.W. Kok, Ultra-rich distributed oxidation combustor: numerical modeling and measurements, to be submitted to Combustion Science and Technology, 2015.

Acknowledgment: The work in this paper was performed with the support of the STW-project 10420.

4 Predicted soot particle number density.

5 Predicted axial profile of temperature and H2, CO and C2H2 mass fraction.

5

4


Projectleaders: dr.ir. R.J.M. Bastiaans, prof.dr.ir. B.J. Geurts, prof.dr.ir. Th.H. van der Meer

In the project MoST, a systematic investigation on how to increase the efficiency of combustion conversion rate in premixed flams through turbulence enhancement was performed. Take for example the case of ultra-low NOx burners, e.g., the low swirl burner (LSB), which operate in the lean premixed regime. In these burners, the combus-tion rate is very much dependent on the turbulence level associated with the upstream flow mixture, such that the resulting flame is often not very ‘intense’ under lean conditions. To avoid such problem and to take the most of the benefit of clean combustion processes, one could enhance the mixing of the reactive mixture towards to the flame front by adding turbulence in the core of the flame. Based on similar procedures, this project focused on the investigation of different strategies that either generate turbulence efficiently or generate specific turbulence that might be efficient for premixed combustion.

In the search of resonant turbulence conditions, i.e., tur-bulence stimulation, in premixed combustion, the research methods of project MoST were essentially based on experimental and computational approaches. As a result, a direct collaboration between the University of Twente (UT), focusing on the experimental part, and the Eindhoven University of Technology (TU/e) focusing on the numerical part, was established.

Research method

Two different strategies to generate turbulence for a low-swirl burner (Fig.1) were experimentally assessed at UT. The first approach consist of a rotating active grid composed out of two perforated disks. The second uses fractal grids which are obtained by truncating a self-similar fractal pattern at some level of refinement. Both type of grids where successfully used before in wind-tunnel ex-periments to elevate the turbulence levels. By performing hot-wire measurements the enhancement of the turbu-lence can be quantified. The resulting flame properties were assessed using laser-induced fluorescence (LIF). By capturing instantaneous cross-sections of the flame the turbulent flame speed can be determined.

At TU/e, a suitable flow modulation strategy for turbu-lence enhancement in premixed combustion was investi-gated through numerical experiments focusing on the use of spatially modulated turbulence. To cite an example, we investigate the effects of a spatially modulated stoichio-metric methane-air turbulent Bunsen flame using direct numerical simulations (DNS) of the Navier-Stokes equati-ons coupled with a tabulated chemistry technique, namely the flamelet generated manifold (FGM). In these numerical

MoST: Multi-scale modification of swirling combustion for optimized gas turbines

1 2

1 Photograph of low-swirl flame.

2 Normalized local consump-tion speed as function of the normalized turbulent velocity for the different flames.


and combustion is observed as for a V-shaped flame. Figure 2 illustrates the enhancement of both variables. There is an increase in flame surface density and a wide-ning of the flame brush as well as much finer flame wrinkling for the cases involving a multi-scale grid. Since the range of embedded scales mainly controls the turbulence intensity and the blockage ratio the low-swirl stabilization, engineering fractal grids for low-swirl combustion can be done with relative ease. It has also been verified that the low NOx emissions, a key feature of low-swirl burners, are not affected when using fractal grids.

In terms of the numerical experiments we restrict to the case where through a parametric variation using different length-scales we study the global response of the turbulent Bunsen flame. For a qualitative view on the effect that the imposed modulations have on the flame front, in Figure 3 we show snapshots of the Bunsen flame for a reference case, i.e., without imposed modulation, and with the applied perturbation.

To quantify such effects, we consider, as an example, the effects of the modulation on the flame wrinkling. The flame wrinkling is a property which measures the distor-

experiments, the premixed flame was agitated in space and time by a hybrid forcing consisting on filtered small-scale random perturbations and a coherent large-scale spatially periodic modulation imposed at the inflow plane.

Results

The active grid measurements showed a promising energy spectrum with distinct peaks. However, there was no operating frequency identified where the turbulent kinetic energy or the dissipation rate was maximized. The variation in turbulent flame speed was of the same order as the measurement uncertainty. Therefore, it could not be concluded that the specific fluctuations introduced by the active grid are directly causing additional wrinkling of the flame front.

Concerning the fractals grids, first a rod-stabilized, V-shaped flame was used as such stabilization mechanism allows for considerable more variation in upstream fractal grid geometry. By increasing the range of embedded scales the turbulence is intensified. With respect to the reference case the turbulence intensity can be more than quadrupled while for the turbulent flame speed more than doubling is observed. When the standard grid in a low-swirl burner was replaced by fractal grids a similar increase in turbulence

3 3D snapshots view of the flame front colored with vorticity in the z-direction, (left) reference flame (right) example of a modulated flame.

4 Results of the averaged global surface wrinkling (left) and (right) the averaged flame height as a function of the modulation scales. Both results are normalized by the corresponding properties obtained for the unmodulated reference flame.

3

4


Publications

[1] A.A. Verbeek, Efficiently generated turbulence for an increased flame speed PhD thesis, University of Twente, The Netherlands.

[2] A.A. Verbeek, P.A. Willems, G.G.M. Stoffels, B.J. Geurts and T.H. van der Meer, Enhancement of turbulent flame speed of V-shaped flames in fractal-grid-generated turbulence, (2014), under review at Combustion and Flame.

[3] A.A. Verbeek, T.W.F.M. Bouten, G.G.M. Stoffels, B.J. Geurts and T.H. van der Meer, Fractal turbulence enhancing low-swirl combustion, Combustion and Flame 162 (2015) pp. 129-143.

[4] A.A. Verbeek, R.C. Pos, G.G.M. Stoffels, B.J. Geurts and T.H. van der Meer, A compact active grid for stirring pipe flow (2013), in: Experiments in Fluids, 54:10(1594).

[5] A.A. Verbeek, W. Jansen, G.G.M. Stoffels and T.H. van der Meer, Improved flame front curvature measurements for noisy OH-LIF images (2013), in: 8th World Conferences on Experimental Heat Transfer, Fluid Mecha-nics and Thermodynamics, Lisbon, Portugal.

[6] A.A. Verbeek, R.C. Pos, G.G.M. Stoffels, B.J. Geurts and T.H. van der Meer, The Generation of Resonant Turbulence for a Premixed Burner (2012), in: Engineering Turbulence Modelling and Measurements ETMM9, Thes-saloniki, Greece

[7] A.A. Verbeek, G.G.M. Stoffels, R.J.M. Bastiaans and T.H. van der Meer, Optimization of Combustion in Gas Turbines by applying Resonant Tur-bulence (2011), in: IGU Research Conference 2011, Seoul, South Korea

[8] A.A. Verbeek, R.C. Pos, G.G.M. Stoffels and T.H. van der Meer, Resonant Turbulence applied to a Low Swirl Burner (2011), in: European Combus-tion Meeting 5, Cardiff, UK.

[9] Cardoso de Souza, T., Geurts, B.J., Bastiaans, R.J.M., de Goey, L.P.H. (2014). Modulation of a turbulent bunsen flame by upstream perturbations, Proceedings of the 10th International Ercoftac Symposium on Engi-neering Turbulence Modeling and Measurements (ETMM10), Marbella, Spain.

[10] Cardoso de Souza, T, et al. Steady large-scale modulation of a modera-tely turbulent co-flow jet, Journal of Turbulence 15.5 (2014): 273-292.

[11] Cardoso de Souza, T., Bastiaans, R.J.M., de Goey, L.P.H., Geurts, B.J. (2014). Space-time modulation of turbulence in co-flow jets, submitted to Physics of Fluids (in review).

[12] Cardoso de Souza, T (2014). Modulated turbulence for premixed flames, PhD thesis, Technische Universiteit Eindhoven, The Netherlands.

[13] Cardoso de Souza, T., Bastiaans, R.J.M., Geurts, B.J., de Goey, L.P.H. (2012). DNS of a Large-Scale modulated turbulent mixing layer, Proceedings of the 9th International Ercoftac Symposium on Engineering Turbulence Modeling and Measurements (ETMM9), 6-8 June 2012, Thessaloniki, Greece.

[14] Cardoso de Souza, T., Bastiaans, R.J.M., Geurts, B.J., de Goey, L.P.H. (2011). LES and RANS of premixed combustion in a gas-turbine like combustor using the flamelet generated manifold approach, Proceedings of ASME Turbo Expo 2011, June 6-10, 2011, Vancouver, Canada, (pp. GT2011-46355-1/9).

[15] Cardoso de Souza, T., Bastiaans, R.J.M., Geurts, B.J., de Goey, L.P.H. (2011). Numerical analysis of a swirl stabilized premixed combustor with the flamelet generated manifold approach, In H. Kuerten et al. (Ed.), Proceedings of the Direct and Large-Eddy Simulation VIII (DLES8), 7-9 July 2010, Eindhoven, The Netherlands, (Ercoftac Series, pp. 321-326). Springer.

[16] Cardoso de Souza, T., Bastiaans, R.J.M., Geurts, B.J., de Goey, L.P.H. (2011). Large Eddy Simulations of Stabilized Premixed Combustion using FGM, Proceedings of European Combustion Meeting (ECM), 28 June-1 July 2011, Cardiff, Wales.

swirl flames modulated by fractal grid generated turbulence was observed.

The main outcome of the project MoST consisted on the search of combustion rate intensification in premixed flames, e.g., low swirl flames, or envelope flame types, by means of turbulence stimulation through fractal grids or spatially periodic modulation. In this research the primary focus was on methane-air mixtures, such that further research is required to establish our main conclusions to other types of fuels, e.g., hydrogen and other hydro-carbons fuels. The research developed through project MoST promotes a significant contribution to premixed combustion and turbulence control research, especially for those focused on generating heat and momentum through combustion using clean and efficient approaches.

tions on the flame front by the turbulent motions and consequently this property determine the flame surface area of conversion. In Figure 4, we show quantitatively the modulation effects on the surface wrinkling and the flame height as a function of the length-scales used to agitate the Bunsen flame. As can be observe, an optimum enhancement of the conversion rate by a factor of 2 for the surface wrinkling, relatively to a reference case, can be obtained when large-length scales are used to modulate the flame, i.e., low values of K.L, where K is the modulation wave-number and L a characteristic length-scale.

In general, although restrict to an envelope flame type, these results are in qualitative agreement with the experimental results obtained at TU where a significant enhancement of the global consumption speed of low


ALTAS: Advanced Low NOx Flexible Fuel Gas Turbine Combustion, Aero and Stationary

Projectleaders: dr.ir. R.J.M. Bastiaans, prof.dr. L.P.H. de Goey, dr.ir. J.A. van Oijen

In spite of the increasing presence of renewable energy sources, fossil fuels will remain the primary supply of the world’s energy needs for the upcoming future. Modern gas-turbine based systems represent one of the most efficient large-scale power generation technology currently available. Alongside this, gas-turbine power plants operate with very low emissions, have flexible operational characteristics and are able to utilize a broad range of fuels. It is expected that gas-turbine based plants will play an important role as an effective means of converting combustion energy in the future as well, because of the vast potential energy savings. The numerical approach to the design of complex systems such as gas-turbines has gained a continuous growth of interest in the last few decades. This because simulations are foreseen to provide a tremendous increase in the combustor efficiency, fuel-flexibility and quality over the next future.

Research Method

Several numerical models have been developed in order to reduce the costs of flame simulations for engineering applications. In the present project the Flamelet- Generated Manifold (FGM) chemistry reduction method is implemented and extended for the inclusion of all the features that are typically observed in stationary gas- turbine combustion. These include stratification effects, heat loss and turbulence. Along this process, the model validity is investigated by comparison with experimental data or detailed chemistry results. In parallel to this work, a novel method of capturing the interaction between turbulence-chemistry is developed and applied. This new method is named as Filtered Flamelet Generated Manifold (FFGM).

Results and Conclusions

The use of FGM as a combustion model shows that combustion features at gas turbine conditions can be satisfactorily reproduced with a reasonable computational effort. Furthermore, the technique shows great benefits in terms of calculation time and stability of the simulation. Overall, the application of the present FGM model in combination with standard turbulence models available in commercial CFD codes provides a phenomenal tool for the simulation of nearly any technically relevant partially premixed turbulent combustion problem. The developed combustion model retains most of the physical accuracy of a detailed simulation while drastically reducing its computational time, paving the way for new developments of alternative fuel usage in a cleaner and more efficient combustion. In addition to this, it is concluded that spatially filtered flamelets present the possibility of accurate predictions of turbulent combustion in the scenario of increasing computational power.

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1 Progress of the reaction in a slice plane of a gas-turbine model combustor.


Publications Produced Within the Project

[1] Donini, A. (2014). Advanced turbulent combustion modeling for gas turbine application. PhD Thesis. Eindhoven: Technische Universiteit Eindhoven. ((Co-)promot.: prof.dr. L.P.H. de Goey, dr.ir. R.J.M. Bastiaans & dr.ir. J.A. van Oijen).

[2] Mukhopadhyay, S. (2014). Modeling turbulent combustion using spati-ally filtered flamelets. PhD Thesis. Eindhoven: Technische Universiteit Eindhoven. ((Co-)promot.: prof.dr. L.P.H. de Goey, dr.ir. R.J.M. Bastiaans & dr.ir. J.A. van Oijen).

[3] Donini, A., Bastiaans, R.J.M., Oijen, J.A. van & Goey, L.P.H. de (2014). Dif-ferential diffusion effects inclusion with flamelet generated manifold for the modeling of stratified premixed cooled flames. Proceedings of the Combustion Institute.

[4] Donini, A., Bastiaans, R.J.M., Oijen, J.A. van & Goey, L.P.H. de (2014). Numerical Simulations of a Turbulent High-Pressure Premixed Cooled Jet Flame with the Flamelet Generated Manifolds Technique. Journal of Engineering for Gas Turbines and Power.

[5] Donini, A., Bastiaans, R.J.M., Oijen, J.A. van & Goey, L.P.H. de (2014). The application of flamelet-generated manifold in the modeling of partially premixed cooled flames. Conference Paper : Proceedings of the 15th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery (ISROMAC 15).

[6] Donini, A., Bastiaans, R.J.M., Oijen, J.A. van & Goey, L.P.H. de (2014). The application of flamelet-generated manifold in the modeling of stratified premixed cooled flames. Conference Paper: Proceedings of the ASME Turbo Expo 2014: GT2014-26210.

[7] Donini, A., Martin, S.M., Bastiaans, R.J.M., Oijen, J.A. van & Goey, L.P.H. de (2013). High pressure jet flame numerical analysis of CO emissions by means of the flamelet generated manifolds technique. Conference Paper : 11th International Conference of Numerical Analysis and Applied Mathematics 2013 (ICNAAM-2013), AIP Conference Proceeding 1558, 136-139.

[8] Donini, A., Martin, S.M., Bastiaans, R.J.M., Oijen, J.A. van & Goey, L.P.H. de (2013). Numerical simulations of a premixed turbulent confined jet flame using the flamelet generated manifold approach with heat loss inclusion. Conference Paper : Proceedings of the ASME Turbo Expo GT2013-94363.

[9] Donini, A., Martin, S.M., Bastiaans, R.J.M., Oijen, J.A. van & Goey, L.P.H. de (2013). Application of flamelet generated manifolds approach with heat loss inclusion to a turbulent high-pressure premixed confined jet flame. Proceedings Direct and Large Eddy Simulation XI, ERCOFTAC.

[10] Donini, A., Bastiaans, R.J.M., Oijen, J.A. van, Day, M.S. & Goey, L.P.H. de (2011). A priori assessment of the potential of flamelet generated manifolds to model lean turbulent premixed hydrogen combustion. Proceedings of Direct and Large-Eddy Simulation VIII, ERCOFTAC.

[11] Donini, A., Bastiaans, R.J.M., Oijen, J.A. van, Day, M.S. & Goey, L.P.H. de (2011). A priori analysis of lean turbulent premixed hydrogen combustion DNS simulation : FGM testing and sub-grid scale analysis. Proceedings of the 5th European Combustion Meeting (ECM2011), Cardiff, UK.

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2 Instantaneous source term snapshots at different levels of FFGM filtering.


1 300 kWth, max, MEEC furnace at TU Delft.

flexFLOX: Flameless combustion conditions and efficiency improvement of single- and multiburner-FLOXTM furnaces in relation to changes in fuel and oxidizer composition

Projectleaders: prof.dr. D.J.E.M. Roekaerts, dr.ir. W. de Jong, dr.ir. M.J. Tummers

Flameless combustion is a clean combustion concept leading to strongly reduced pollutant emissions compared to traditional combustion processes. To reach the flameless combustion regime the air (and/or fuel) streams are diluted with hot combustion products with a temperature sufficiently high for the combustion process to be stable and occurring in a distributed reaction zone. In furnace applications it leads to a higher efficiency because of the more extensive use of air preheat. To widen the range of applicability of the this technology, the impact of changes in fuel and oxidizer composition on the combustion process in furnaces operated using flameless combustion has been investigated. Dutch natural gas (DNG) being the base-line fuel, also the combustion of biogas (represented as mixture of DNG and CO2) and mixtures of DNG and H2 has been investigated. The industrial partners Tata Steel, Shell, WS GmbH, Numeca Int. and Celsian Glass and Solar have been actively involved in the project and have carried out part of the research.

Research method

By combining detailed measurements and modeling, in single- and multi-burner furnaces insight has been gained in the flame structure, heat transfer enhancement and emission reduction. The relevant turbulent reactive mixing processes were examined using laser diagnostic methods and computed in detail using detailed and reduced chemical models and using statistical models for turbulence and turbulence chemistry interaction.

An existing “Delft-jet-in-hot-coflow” (DJHC) burner was used to mimic conditions of flameless conditions with well-defined temperature and oxygen concentrations of the oxidizer. High speed camera observations of chemiluminescence revealed the characteristics of the flame stabilization process. Particle image velocimetry (PIV) and Coherent anti-Stokes Raman spectroscopy

(CARS) were used to measure local instantaneous properties of velocity and temperature.

In the multiburner 300 kWth,max MEEC furnace experimental studies were made of the relations between burner configuration, firing mode, throughput, heat sink thermal capacity and fuel type. Local temperature was measured using both thermocouples and spectroscopic methods (CARS) in the near burner zone. A new probe was developed and used to obtain species concentration profiles for a range of operating conditions.

Computational modeling of the DJHC experiments and the MEEC furnace was done using different levels of modeling complexity. The predictive power of the Eddy-Dissipation-Concept model in combination with relatively detailed chemical mechanisms and of transported probability density function (PDF) methods in combination with Flamelet Generated Manifolds (FGM) was explored.

1


The MEEC furnace (figure 1) turned out to be a very valuable setup to study the influence of burner configuration and operation parameters on emissions. The CFD simulation of this furnace remains a difficult task. The best results so far have been obtained with skeletal chemical mechanism in combination with EDC model, but the validation of the model is incomplete. The new results obtained with the species probe provide valuable information on in furnace concentrations. They can be used in validation of CFD models provided the CFD models incorporate the presence of the probe in the furnace.

As a result of the flexFLOX project burner manufacturer WS GmbH will be able to use the new insights from experiments and modeling in the extension of the operations of their burners towards larger fuel flexibility. Companies operating furnaces (Tata Steel and Shell) will be able to use the insights on fuel flexibility and on optimal burner arrangements in the retrofit of existing furnaces and construction of new ones. Software companies (Numeca Int.) or engineering companies with own codes (Celsian Glass and Solar) will use the new models to support their customers. At the university in a follow-up project a new single-burner-furnace (SBF) that resulted from the flexFLOX project will be studied with similar methods as used in the flexFLOX project, using a burner provided by WS GmbH.

The project contributed to the overall objectives of the CCC program by elucidating the fundamental aspects of flameless combustion in turbulent flow conditions and bringing this clean combustion technique closer to wide-spread application.

Results

The transition from flame stabilization by ignition kernels to flame stabilization flame propagation in flameless combustion conditions was fully clarified by a parametric study with varying H2 content or CO2 content in the jet fuel and varying coflow composition and temperature (figure 2).

Apart from fuel composition, also temperature and oxygen concentration determine whether or not a flameless combustion mode can be reached. The implication for furnaces is that whether or not flameless combustion is possible, not only depends on the fuel and air properties but also on process conditions such as furnace tempera-ture. Provided the temperature of the flue gas entrained into the near burner zone can be kept below a certain bound, flameless combustion will be accessible also for fuels containing substantial amounts of H2.

A new model, 4D-FGM for three stream mixing and ignition with heat loss, has been developed and applied in simulations of jet-in-hot-coflow flames in combination with the transported PDF method. A full set of model predictions has been obtained for all the cases of DNG diluted with CO2, and validated with the experimental data. Complementary to this, Large Eddy Simulation results of the DNG diluted with H2 cases have been obtained at TU/e in the frame of CCC MildNOx project.

Comparison of the results of this project for jet-in-hot-coflow flames with literature results show that the FGM tabulated chemistry combined with RANS/transported PDF provides an accurate and cost-effective model for CFD simulations of jet-in-coflow flameless combustion systems, i.e. more accurate than the EDC model and more cost-effective than LES.

2

2 Images of the jet-in-hot-coflow flame base at different H2 –levels, for a long exposure time of 1 s (left) and for a short exposure time of 0.5 ms (right). The red ellipse points out an autoignition kernel and the red crosses denote the fuel pipe exit.


Poster presentation abstracts

[1] G. Sarras, M.K. Stöllinger and D.J.E.M. Roekaerts, Simulation of the Delft-jet-in-hot-coflow burner using transported PDF methods and FGM tabulated chemistry, In: A. Dreizler, A. Kemp land R. Barlow (Eds.), Book of abstracts of TNF11 “Eleventh International Workshop on Measurement and Computation of Turbulent Flames”, July 26–28, 2012, Darmstadt, Germany, pp 14-15

[2] L.D. Arteaga Mendez, M.J. Tummers and D.J.E.M. Roekaerts, Effect of fuel and oxidizer composition on jet-in-coflow flames, In: A. Dreizler, A. Kemp land R. Barlow (Eds.), Book of abstracts of TNF11 “Eleventh International Workshop on Measurement and Computation of Turbulent Flames”, July 26–28, 2012, Darmstadt, Germany, pp 54-55

[3] Gerasimos Sarras, Michael Stoellinger and Dirk Roekaerts, Simulation of the Delft-jet-in-hot-coflow burner using transported PDF method and FGM tabulated chemistry, Abstract of Work-in-Progress poster, Thirthy-Fourth International Symposium on Combustion, Warsaw, 2012, poster W4P100

[4] Jie Lu, Eun-Seong Cho, Eric van Veen, Wiebren de Jong and Dirk Roekaerts, Coherent anti-Stokes Raman spectroscopy measurement in a regenerative multi-burner flameless oxidation furnace, Abstract of Work-in-Progress poster, Thirthy-Fourth International Symposium on Combustion, Warsaw, 2012, poster W5P035

[5] G. Sarras, L.D. Arteaga Mendez, S.Y. Mahmoudi Larimi, M.J. Tummers, D.J.E.M. Roekaerts, Flame structure and lift-off height of biogas combustion in jet-in-hot coflow flame, Abstract of Work-in-Progress Poster, Int. Conf. Dynamics of Explosive and Reactive Systems (ICDERS), Taipei, July 28, August 2, 2013, poster #269, p. 120


[1] E.-S. Cho, D. Shin, J. Lu, W. de Jong and D.J.E.M. Roekaerts, Configuration effects of natural gas fired multi-pair regenerative burners in a flamelessoxidation furnace on efficiency and emissions, Applied Energy, 107 (2013) 25-32

[2] G. Sarras, Y. Mahmoudi, L.D. Arteaga Mendez, E.H. van Veen, M.J. Tum-mers, and D.J.E.M. Roekaerts, Modeling of Turbulent Natural Gas and Biogas Flames of the Delft Jet-in-Hot-Coflow Burner: Effects of Coflow Tempera-ture, Fuel Temperature and Fuel Composition on the Flame Lift-Off Height, Flow, Turbulence and Combustion, 93 (2014) 4, 607-635

[3] L.D. Arteaga Mendez, E.H. van Veen, M.J. Tummers and D.J.E.M. Roekaerts, Effect of hydrogen addition on the structure of natural-gas jet-in-hot-coflow flames, Proceedings of the Combustion Institute, 2014, http://dx.doi.org/10.1016/j.proci.2014.06.146

Conference papers

[1] E.-S. Cho, J. Lu, W. de Jong and D. Roekaerts, Emission characteristics of a flameless oxidation furnace with various multi-burner configurations, European Combustion Meeting, Cardiff, June 29- July 1, 2011, T. Griffiths (Ed.), Cardiff, UK, paper 212, 1-6

[2] M.A. Etaati, D. Roekaerts, G. Sarras and M. Stoellinger, Modeling of the Delft jet-in-hot-coflow burner as a non-adiabatic three stream problem, European Combustion Meeting, Cardiff, June 29- July 1, 2011, T. Griffiths (Ed.), Cardiff, UK, paper 293, 1-6

[3] G. Sarras, M.K. Stoellinger and D.J.E.M. Roekaerts, Transported PDF simulations of the Delft-jet-in-hot-coflow, burner based on 3D FGM tabulated chemistry, In: Book of Extended Abstracts, Turbulence, Heat and Mass Transfer 7, K.Hanjalic, Y.Nagano, D.Borello, S.Jakirlic (Eds.), Begell House, Inc., 2012, pp 729 – 732

[4] G. Sarras, M.K. Stoellinger and D.J.E.M. Roekaerts, Transported PDF simulations of the Delft-jet-in-hot-coflow, burner based on 3D FGM tabulated chemistry, In: Proceedings Turbulence, Heat and Mass Transfer 7, K.Hanjalic, Y.Nagano, D.Borello, S.Jakirlic (Eds.), 2012, 10 pages

[5] L.D. Arteaga Mendez, M.J. Tummers, D.J.E.M. Roekaerts, Effect of Hydrogen on the Stabilization Mechanism of Natural Gas jet-in-hot- coflow Flames, European Combustion Meeting – 2013, June 25-28, 2013, Lund, Sweden, Paper P1-16, 1-4

[6] G.Sarras, M.K.Stoellinger, D.J.E.M. Roekaerts, Transported PDF simulations of the Delft Jet-in-Hot-Coflow burner based on 4D-FGM tabulated chemistry, European Combustion Meeting – 2013, June 25-28, 2013, Lund, Sweden, Paper P1-80, 1-6, ISBN 978-91-637-2151-9.

[7] Y. Mahmoudi, G. Sarras, L.D. Arteaga Mendez, M. Çelik, M.J. Tummers, and D.J.E.M. Roekaerts, Flame structure and stabilization mechanism of biogas flame in a jet-in-hot-coflow burner, 8th Mediterranean Combustion Symposium, September 8-13, 2013, Çesme, Izmir, Turkey, Paper TC-16, 1-12, Editors: Nevin Selcuk, Federico Beretta, Mohy S. Mansour, and Andrea d’Anna. Publisher: International Centre For Heat and Mass Transfer, METU, Ankara, Turkey.

,


2Promotions

Schone en zuinige verbranding

Dr. L. Zhou 30 September 2013Dr. S. Ayyaoureddi 9 January 2014Dr. P.G.M. Hoeijmakers 28 January 2014Dr. M. Shahi 24 September 2014Ir. N. Speelman September 2015 (expected)

31

Emission reduction in compression-ignition engines by fuel tuning

Lei ZhouPromotiondate: 30 September 2013

Excessive consumption of fossil fuels is leading to global environmental degradation effects, such as the green-house effect, acid rain, and ozone depletion. The main rea-son for these increased pollution levels, notwithstanding stringent emission regulations, is related for a large part to road transport [1]. Moreover, combustion of various fuels in this sector (e.g. diesel engines) leads to emission of several harmful pollutants, such as NOx, CO, HC, and soot.

These pollutants contribute to several detrimental effects on human health; especially long-term health effects are associated with particulate matter (PM), of which the main constituent is soot. Consequently, in order to adopt ap-propriate lignin based bio-fuels as alternatives for diesel to obtain lower soot emission, this project is focused on the exploration of the mechanisms of soot formation by using advanced measurement methods by combining fundamen-tal investigation and applied research.

Research method

As shown in Figure 1, the fundamental research is ac-complished by a special designed High Pressure Vessel and Burner (HPVB) with an optical accessibility for laser diagnostic techniques. It provides capabilities of burning vaporized liquid fuels in laminar diffusion flames and the research focuses on the impact of fuel molecular struc-ture on the sooting tendencies of relevant fuels and biofuels. Besides, the HPVB setup is designed to allow measurements at elevated pressures. For the prospective of applications of relevant fuels in compression ignition engines, the research is focused on the effect of molecular structure on the NOx-soot emissions trade-off and corres-ponding engine performance. This is realized by means of experiments on a modified DAF heavy-duty diesel engine.

Results

According to the results both on the flame research and engine research, it becomes clear that saturated cyclic oxy-genate fuels are better than diesel in terms of soot pro-duction or emission. Moreover, the cyclic oxygenates are in an earlier stage of the depolymerization process of lignin than the linear compounds. As a result, it is worthwhile to further investigate cyclic oxygenates, including saturated cyclic oxygenates and aromatics oxygenates. Then, further research proves that aromatics (2-phenyl ethanol) are better than saturated rings (cyclohexaneet-hanol), based on the measurements of emissions and performance on a heavy duty compression ignition engine. Given that it is worth to focus on aromatic fuels due to their less cost in the process of depolymerization from lignin, two more types of aromatic oxygenates (anisole and benzyl alcohol) as well as 2-phenyl ethanol have been investigated. The results demonstrate that benzyl alcohol outperforms all of the aromatics, with respect to engine performance and emissions

11 Lower emission by fuel tuning.


1

Sridhar Ayyapureddi Promotiondate: 9 January 2014

Flamelet generated manifold (FGM) is a tabulated chemistry approach which is one of the most efficient and accurate methods to model reactive flows. This method has been applied to model diesel engine combustion. The industry is in need of such models for their engine development work. The main focus of this thesis work is to bring enhancements in this approach to achieve a robust and complete model in-order to predict the complex diesel spray combustion processes

more accurately. The three aspects dealt with in this thesis are the all important auto-ignition delay, full engine cycle simulations and pollutant emissions. A dedicated commercial engine CFD code STAR-CD has been used to model turbulent induced sprays (two-phase flow). In this framework, FGM i.e. lookup based method is implemented with a tabulated chemistry (igniting flamelets or homogeneous reactors) to account for auto-ignition phenomena in a constant combustion volume. Many other aspects of this tabulation technique (table resolution and turbulence chemistry interaction etc) have been tested and evaluated to improve the predic-tability of the model for the ignition characteristics at a wide range of engine-like conditions. The model validation is done using wide set of experimental data available from Engine Combustion Network consortium. Some key results are shown in Figure1.

Additional dimensions for FGM are necessary to apply it in a variable geometry and non-adiabatic wall boundary conditions for engine cycle simulations. Variable Enthalpy and pressure based FGM implemented for engine cycle simulations and the improvements in the predictions corresponding to the flame structure, species concen-trations and local temperature predictions are examined. The main outcome from this study: (a) defining the local

Advances in the Application of Flamelet Generated Manifold for Diesel Engine Combustion Modeling

1 Contours of key parame-ters from CFD simulation with FGM based on Ignition flame-lets (left) and Homogeneous reactors (right).


state identifier in CFD for lookup (b) the optimum number levels. The engine data and experimental cylinder pressure (and heat release data) from DAF engines have been used for model validation as shown in Figure 2. Note that FGM is based on a detailed chemical model and no tuning parameters are needed in the approach. Eventually, the implementation of pollutant formation sub-models for engine applications within the FGM approach is performed. The relatively well understood NOx formation processes are implemented, Soot modelling poses a more significant challenge due to its complexity associated with the formation processes and the lack of complete understanding in literature. A soot model, which includes more detailed processes is developed and analysed with respect to available literature. Further, simulation of the soot fields of one of the ECN spray is performed and the results are compared with available experimental data from the network. The Figure 3 shows the main result.

Concluding the thesis work has shown the extension of FGM to engine simulations and its applicability to model all relevant processes efficiently without the often needed tuning constants involved in commonly used methods in industry. Only the soot model still needs more attention.

3 FGM model validation for soot predictions (left) against the experimental observati-ons (right).

2 Figure 2. FGM model validation with 5 pressure levels against DAF engine experimental data.

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3


Suppression of thermo-acoustic instabilities in central heating equipment by burner design optimization and active control

Dr. P.G.M. HoeijmakersPromotiondate: 28 January 2014

Boilers and central heating systems are highly susceptible to acoustic instability of combustion. In essence, the flame acts as an amplifier of acoustic waves. Such waves are reflected back towards the flame at the inlet and outlets of the system, thereby causing a resonant unstable feedback loop.

This problem is especially pronounced under premixed fuel lean operation, widely used in this kind of systems due to the lower thermal NOx emissions. New generations of heating equipment are needed to minimize these emissions and to adapt to variations in gas composition (both geographical and in time). In the design phase of new heating equipment the problem of acoustic instability is often handled by trial and error, after the first prototypes are built. This significantly increases costs and design time. The goal of this project is to develop the methods and solutions necessary to predict the problem early in the design stage, and ultimately to mitigate thermoacoustic instabilities altogether.

Approach

Due to the coupled nature of the phenomenon both the acoustics as well as the flame behaviour of a combustion system are important. The research therefore focused on ways to solve to problem on both sides of this equation.

In terms of the flame behaviour, it is crucial to understand how exactly the heat release responds to excitation of the acoustic velocity. This response can be quantified by a so called flame transfer function. The flame transfer function is strongly dependent on flow, mixture and geometrical properties of the burner. A thorough understanding of the interrelation between these properties is desirable to speed up the burner design cycle and obtain he desired response without too much trail and error. In addition, a further decrease in development time can be achieved by performing numerical simulations of the flame

transfer function. Therefore, an important part of the current project was the validation of a computational fluid dynamics approach to simulate the flame dynamics for perforated plate burner decks. Alternatively, in order to facilitate active control approaches in an actual appliance, a cheap and reliable sensor is needed to detect flame oscillations, as well as open the possibility for in-situ flame transfer function measurements.

The acoustical response of the system is equally important to the occurrence of acoustic oscillations. In many cases the oscillation frequency is strongly coupled to the passive (without flame) eigenmodes of the system. An interesting approach is therefore to increase the acoustic losses of the system up to a level that it no longer can support any eigenmodes, i.e. apply system boundaries which do not reflect any acoustic waves. Under such conditions, the feedback loop should be broken, and therefore no instabilities should occur.

Results

The flame transfer functions of laminar bunsen type flames were simulated using a FLUENT code. The simulations and measurements showed a very good agreement. This opens the possibility to perform the parameterization of the flame transfer function in terms of the burner geometrical parameters, e.g. hole size and pitch, towards the regime of realistic burner geometries.

Regarding an alternative measurement sensor for the flame heat release, an interesting new development was the use of an ionization sensor. Such sensors are already widely employed to measure the presence of the flame on the burner deck, but the current project also investigated the possibility to actually measure the heat release fluctuations. As it turned out, it is entirely possible to |measure the flame transfer function were the the ionization sensor acts as the heat release sensor. This opens the possibility of in-situ flame transfer function measurements, and ultimately cheap active control strategies in realistic appliances.

The subject of increasing the acoustic losses to suppress thermoacoustic instabilities was first extensively investigated from a theoretical viewpoint. Surprisingly, it turns out that when the flame is placed amidst anechoic boundary conditions, thermoacoustic instabilities may still occur. The reason for this is that the flame may be ‘open-loop’ unstable. This is a consequence of the fact that the flame can possess intrinsically unstable eigen-modes, which dominate the system. This behavior was entirely unexpected, and formed the motivation for an experimental quest to validate the theoretical predictions.


In order to increase the acoustic losses in an experimental setting, a large acoustic horn was designed and build, see figure 1. An acoustic horn is a very efficient way to radiate the acoustic waves present in a duct system to the environment. As a consequence the reflection coefficient is very low over a wide frequency range, e.g. 150-1000 Hz. With horns attached to both the up- and downstream sides of the flames, an extensive set of experiments were conducted, using different fuel flow rates, equivalence ratios and burner geometries. As predicted by theory, many thermoacoustic instabilities were still encountered. However, not all results were as expected, and further research is still needed to provide an unequivocal answer to the question if the predicted intrinsic instability may easily occur in practice.

In summary, the project led to significant advances in the understanding and modeling of thermoacoustic instabilities, with a number of results which could lead to innovative design solutions in the future.

1 The horn in the laboratory.


[1] Hoeijmakers, P.G.M., Lopez Arteaga, I., Kornilov, V.N. , Goey, L.P.H. de & Nijmeijer, H. (2013). Accuracy assessment of thermo-acoustic instability models using binary classication. International Journal of Spray and Combustion Dynamics, 5(3), 201-224.

[2] Hoeijmakers, P.G.M., Lopez Arteaga, I., Kornilov, V.N. , Goey, L.P.H. de & Nijmeijer, H. (2014), Intrinsic instability of flame-acoustic coupling, Combustion and Flame [In Press].

[3] Hoeijmakers, P.G.M., Lopez Arteaga, I., Kornilov, V.N. , Goey, L.P.H. de & Nijmeijer, H. (2014), Flames in context of thermo-acoustic stability bounds, Proceedings of the Combustion Institute [In Press].

[4] Peerlings L. B.W., Manohar, Kornilov V. N., de Goey L.P.H. “Flame ion generation rate as a measure of the flame thermo-acoustic response”, Combustion and Flame, 160 (2013) 2490–2496.

[5] Volkov E.N., Kornilov V.N. and de Goey L.P.H., “Experimental evaluation of DC electric field effect on the thermoacoustic behaviour of flat premixed flames”, Proc. Combust. Inst., v. 34, issue 1, (2013) 955–962

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Modeling of complex physics and combustion dynamics in a combustor with a partially premixed turbulent flame

Mina ShahiPromotiondate: 24 September 2014

Teneinde de vorming van stoichiometrische gebieden in vlammen in een gasturbineverbrandingskamer te voor-komen, en daarmee ook de vorming van stikstof oxiden, is voor gasturbines een alternatieve verbrandings-technologie geintroduceerd door middel van mengselarme voorgemengde verbranding. Hiermee kan voldaan worden aan steeds strenger wordende eisen aan de maximale stikstofoxide emissie voor industriele gasturbine motoren voor krachtopwekking. De gerealiseerde lage emissie van stikstofoxiden en koolmonoxide door toepassing van de nieuwe verbrandingstechnologie leidt echter tot een verhoogde gevoeligheid voor thermo-akoestischeinstabiliteiten. Deze worden gedreven door de terug-

koppelingslus tussen vrijkomende warmte, druk- en stromingsfluctuaties. De drukoscillaties die worden veroorzaakt door de thermo-akoestische instabiliteiten kunnen zeer hoge amplituden bereiken, waardoor ernstige schade en een sterk verkorte levensduur van de gasturbine kan ontstaan. Om deze reden is het belangrijk al in de ontwerpfase van een gasturbineverbrandingskamer te kunnen bepalen of onder gegeven omstandigheden een stabiele vlam wordt gerealiseerd. Hiervoor is de beschikbaarheid van nauwkeurige modellen voor de voor-spelling van amplitude en frequentie van drukoscillaties noodzakelijk.

Het werk gepresenteerd in de dissertatie van Mina Shahi, is verricht in het kader van het Marie Curie project “LIMOUSINE” en focusseert zich op de numerieke model-lering van de interactie tussen de gekoppelde velden van stroming, druk en warmte voor de voorspelling van het optreden van spontane druk oscillaties met hoge amplitude in gas turbine motoren.

In dit proefschrift worden twee gekoppelde methoden beschouwd voor de numerieke berekeningen. Bij de eerste methode worden de phenomenen in zowel fluidum als structureel domein in een oplossingsdomein numeriek opgelost. De gekoppelde vergelijkingen voor beide domeinen worden simultaan opgelost met behulp van de ANSYS-CFX code, met dezelfde tijdstap voor zowel fluidum als structureel domein.in deze aanpak speelt de strategie voor het bepalen van de discrete punten in het rekendomein een belangrijke rol voor de berekening van de amplitude van de druk fluctuaties. De koppeling tussen structuur en fluidum is heel sterk op het grensvlak. In deze thesis wordt aan deze aanpak gerefereerd als de Conjugated Heat Transfer (CHT) aanpak.

In de tweede methode wordt de interactie tussen fluidum en structuur gekoppeld aan de wandvibratie met behulp van een gepartioneerde aanpak met een schema voor sterke koppeling. Hier worden twee afzonderlijke oplos-singsmethoden en rekendomeinen gebruikt (ANSYS-CFX and ANSYS Multiphysics), die worden gekoppeld door middel van geschikte randvoorwaarden en interpolaties

1 2


1 The LIMOUSINE combustor: thermal load on the structure in an unstable operating condition. Red dot on structure center is the laser vibrometer beam.

2 Sketch of the fluid and solid regions as one computational domain.

op het grensvlak. De grensvlakinformatie wordt tussen beide codes uitgewisseld op iedere tijdstap. In deze thesis wordt aan deze aanpak gerefereerd als de twee-weg FSI aanpak. Beide methoden zijn gevalideerd met de experimentele data verkregen voor de LIMOUSINE verbrandingskamer in limiet oscillatie. (zie fig 1 en 2).

Voorafgaand aan de bovengenoemde onderzoeken (CHT en FSI), in het tweede en derde deel van dit werk, zijn de analyse en validatie berekeningen uitgevoerd van het ‘fluïdum-only’ domein. In deze werkwijze, de zogenaamde ‘zero-way coupling approach’ wordt de terugkoppeling van de vibrerende wanden naar het akoestische veld in de verbrandingskamer verwaarloosd. Hierbij zijn de effecten van het roostertype op de nauw-keurigheid van de voorspelde gegevens eerst onderzocht, en vervolgens de invloed van de turbulente verbranding modellering op de voorspelde vlamdynamiek geëvalueerd. Aangezien bij deze benadering de demping / amplificatie-effecten veroorzaakt door de verbrandingskamerwand (door bijvoorbeeld warmteverlies of vervorming) niet in aanmerking wordt genomen, is het belangrijk om een accurate randvoorwaarde te kiezen die de werkelijke fysische toestand zo dicht mogelijk benadert. Daarom worden verschillende thermische randvoorwaarden toegepast en de effecten op de eigenschappen van de instabiliteiten geëvalueerd.

De resultaten van de fluïdum-only simulatie toonde een voorspelling met overschatting van de frequentie en grootte van de opgetreden thermo instabiliteit. Berekeningen met de isotherme verbrandingskamerwand voorspelde het begin van de instabiliteiten correct. In dit geval week de voorspelde frequentie 9,5% af van de experimentele data. Echter, het modelleren van de thermische interactie van de verbrandingskamer wand en de reagerende stroom met behulp van de CHT aanpak kan de voorspellingen verbeteren en houden rekening met de warmte penetratiediepte in de wand. Bij deze benadering werd thermo-akoestische instabiliteit voor-speld met een afwijking kleiner dan 1% (zie fig 3). Het fluidum-structuur interactie model (FSI) voorspelde correct de frequentie van de instabiliteit, maar de amplitude van de berekende druksignalen werd hoger voorspeld dan gemeten. De belangrijkste vibratiefrequentie werd correct voorspeld. Zowel de gemeten en voorspelde resultaten laten zien dat de terugkoppeling van de vibrerende wand naar het akoestisch veld gering is.

3


3 Pressure spectrum for 40kW and l=1.4 : experiment (solid line), CHT numerical prediction (dash-dot).

1 Ethanol spray flame in hot diluted co-flow. 1


Model development for ionization phenomena in premixed laminar flames

Nico SpeelmanPromotiondate: September 2015 (expected)

Moderne hoogrendementsketels en andere verbrandings-toestellen gebruiken om veiligheidsredenen een vlam-detectie circuit. Deze circuits maken gebruik van elektrische stromen die optreden als gevolg van vlamionisatie. Eerder is aangetoond dat de elektrische stromen die optreden in deze vlammen gerelateerd kunnen worden aan de equivalentie verhouding van de vlam in kwestie en door deze correlatie is het mogelijk om het vlamdetectie circuit te gebruiken voor actieve vlamsturing. Om dit mogelijk te maken is een gedetailleerde kennis nodig over de interactie

tussen de geladen deeltjes, die de stromen faciliteren, en de elektrische velden die gebruikt worden.

In dit onderzoek is een nieuw fysisch en numeriek model ontwikkeld, dat in staat is om deze elektrische stromen in vlakke voorgemengde vlammen te voorspellen. Het model maakt gebruik van Poisson’s vergelijking om de elektrische spanningen te berekenen. Verder wordt in het model gemaakt van een multi-component diffusie model, dat tevens de elektrische krachten op de geladen deeltjes mee neemt, om het transport van de neutrale én geladen deeltjes te modelleren. Dit model is ingebouwd in de be-staande CHEM1D vlamsimulatiesoftware en dit is gebruikt om experimenten na te bootsen. De numerieke simulaties laten een goede gelijkenis zien in de stroom-spannings-karakteristiek. Fysische fenomenen, zoals saturatie en het diodisch effect, laten zich goed voorspellen en de relatie tussen de stroomsterktes en de equivalentie verhouding wordt ook goed voorspeld voor equivalentieverhoudingen tussen 0.6 en 1.2.

De simulaties laten een duidelijk verband zien tussen de saturatiestromen en het totaal aantal geladen deeltjes die ontstaan in de elementaire reacties. De elektrische spanning waar saturatie optreedt is daarentegen vooral afhankelijk van de electronenrecombinatie en de diffu-siviteit van de geladen deeltjes. Deze kennis is vervolgens

gebruikt om het chemisch mechanisme te optimaliseren ten opzichte van de experimenteel bepaalde stroom-sterktes.

Om het toepassingsgebied van het geoptimaliseerde mechanisme te bepalen zijn is een vergelijking gemaakt tussen de numeriek voorspelde waarden en een nieuwe set metingen. Deze metingen zijn uitgevoerd door Bosch Thermotechniek BV in Deventer in een opstelling die anders is dan de meetopstelling die gebruikt is voor de optimalisatie. De numerieke resultaten laten hierin een klein, maar acceptabel verschil zien ten opzichte van de experimenten.

Hierna is het model, samen met het geoptimaliseerde mechanisme gebruikt om de fysische achtergronden van interessante eigenschappen van de stroom-spannings-karakteristiek te onderzoeken. Voor sterke elektrische velden is de stroomsterkte onafhankelijk van de opgelegde spanning. Dit saturatiegedrag wordt veroorzaakt door het wegtrekken van de elektronen uit het vlamplasma en de dominantie van de elektrische krachten over Fick diffusie voor de positieve ionen. Door met de numeriek simulaties het diodisch effect te bestuderen wordt duidelijk dat dit veroorzaakt wordt door de grotere afstand die de zwaardere positieve ionen moeten afleggen om de negatieve elektrode te bereiken.

De vlamdetectie circuits zijn gebaseerd op het diodisch effect samen met een wisselspanningsveld. Om het gedrag van vlammen in wisselspanningsvelden te onderzoeken, zijn er simulaties uitgevoerd van zulke situaties en deze zijn vergeleken met experimenten. In de experimenten is gevonden, dat de vlammen in wisselspanningsvelden met een voltage hoger dan het saturatievoltage een eerste respons zien die sterker is dan de saturatiestroom. Deze overshoot kan vooral gezien worden wanneer de frequentie ongeveer 100 Hz of lager is, maar de absentie hiervan in velden met een frequentie die hoger is wordt toegeschreven aan een capacitief effect in de meetopstelling.

De overshoot wordt ook voorspeld in de numerieke simulaties en aan de hand hiervan is het mogelijk om de fysische achtergronden van deze overshoot te onder-zoeken. Hieruit is geconcludeerd dat de overshoot veroorzaakt wordt door de tijdsrespons van de geladen stoffen in het vlamplasma. De concentraties van de geladen deeltjes is lager dan wat op basis van stationaire simulaties werd verwacht. Dit betekent dat de geladen deeltjes in instationaire elektrische velden veel sneller uit de stroming worden getrokken door het elektrisch veld, waardoor de stroomsterkte hoger is, wanneer tijds-afhankelijke velden worden beschouwd.



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