Verslag Final Version Roel Peters

8/3/2019 Verslag Final Version Roel Peters

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Graduation Project

Penetration and dispersion research ofnon-reacting evaporating diesel sprays

Author:

Roel Peters

Supervisors: Exam commission:

ir. P.J.M. Frijters prof. dr. ir. R.S.G. Baert

dr. ir. L.M.T. Somers prof. dr. ir. L.P.H. de Goey

prof. dr. ir. R.S.G. Baert dr. ir. L.M.T. Somers

dr. ir. C.C.M. Luijten

dr. ir. H.P. van Kemenade

dr. R.J.H. Klein-Douwel

ir. P.J.M. Frijters

Eindhoven University of Technology

Mechanical Engineering - Combustion Technology

14th March 2007


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Acknowledgements

I would like to thank my family, especially my parents, for the support they have given me duringmy study and during this graduation project. They are the persons I always could ask advise indifficult times and gave me the space to develop. Also I thank my friends for showing interest inmy study.

For the graduation project my special thanks goes out to my mentor Peter Frijters. Together wehave solved many problems, and although several times the setbacks were very frustrating, thegood humor always prevailed. Furthermore I appreciate the advise and support from Bart Somers,Rik Baert, Carlo Luijten, Xander Seijkens and all other supporting staff.

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Summary

In the EHPC (Eindhoven High Pressure Cell) visualization experiments are conducted on thevapor spray and the liquid core. To obtain an idea of the reproducibility of the sprays producedby different nozzles or different holes from the same nozzle, the momentum flux of these sprays ismeasured. Also it is tried to determine the dimensionless parameters for several nozzles.

Momentum flux measurements are performed on the sprays from various nozzles with an ac-curacy of at least 5 %. The momentum flux measurements are concentrated on 9 mm nozzles.Obviously due to geometrical differences between the nozzles there are differences in momentumflux between the sprays of various nozzles. More important are the differences in momentum fluxfrom individual sprays from the holes from the same nozzle. There is an asymmetrical patternbetween the sprays which can mutually differ 10-15 %. This makes further comparison betweenvisualization experiments, such as Schlieren and laser light scattering recordings, with differentnozzles very difficult and unreliable. In visualization experiments there is the choice to use blocked(all except one hole are blocked) and unblocked nozzles. Therefore the momentum flux of sprayfrom both types of nozzles are measured. Furthermore mass flow measurements are conducted on7 mm nozzles to retrieve dimensionless parameters which characterize the nozzle. Unfortunatelydue to problems with a pressure sensor the mass flow measurements are not reliable and thus thedetermined dimensionless parameters are also not reliable.

With Schlieren techniques the vapor spray of a diesel injection are recorded. To retrieve a goodquality visualization only one spray can be recorded. Therefore the nozzle can be blocked or thethimble can be used (which does not block any hole). A blocked nozzle produces a spray whichpenetrates faster and has a smaller dispersion angle compared to a spray from an unblocked nozzle.This is probably caused by an altered flow through a blocked nozzle. The altered flow results ina lower level of cavitation which reduces the breakup processes that promote the dispersion of aspray. The reduced dispersion results in a faster penetration.The dispersion angle is determined at various ambient gas densities and temperatures. Due todisturbances in the surroundings of the spray the determined angle was larger than in reality.Therefore a correlation has been set up at lower ambient gas temperatures where the disturbancesare not as profound. It was found that:

tan(/2) = e5,085104Ta2,932 0,32831,157104Taa (1)

Furthermore an dependence on the ambient air density of 0,16a to 0,28a was found which coincides

with values mentioned in several literature sources.Also the penetration is determined of sprays injected into environments at different temperaturesand densities. It was compared to several models described in various literature sources and allthese models over predicted the penetration. Especially in the initial phase the models predicteda greater penetration velocity than was measured. The measured penetration has a dependenceon the ambient air density of 0,31a to

0,33a which coincides with values provided in several

literature sources.3167 The liquid core of a diesel spray was visualized with laser light scattering techniques. Thereproducibility at high ambient air temperatures was sufficient, a 2 of 0,6 mm. However, at lower

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ambient air temperatures the accuracy deteriorated. The fuel temperature was held constant atabout 60 C.A blocked nozzle produced a larger liquid core than a nozzle where the thimble was applied on

(an unblocked nozzle). A blocked nozzle produced a longer liquid core than a unblocked nozzle.The difference of 4 mm was almost constant over a wide ambient air temperature range.The main measurement results are compared to the Siebers model and the Hiroyasu model. Withthe angle correlation obtained from the Schlieren experiments, and multiplied by 0,4, the mea-surements were similar to the predictions of the Siebers model at high ambient air temperaturesand densities. At lower temperatures the Siebers model over predicted the liquid core length. Atlow densities the Siebers model showed an other trend than the measurement data. The Hiroyasumodel over predicts the liquid core length. After subtracting a constant value from the resultsof the the Hiroyasu model, it produced a similar result as the Siebers model. Deviations can becaused by different interpretation of the liquid core length, the used correlations for the models orshortcomings in the models.Also measurement data from Sandia National Laboratories are compared with the TU/e measure-

ments for different fuels (B100, FTD and DF2). There was no good comparison; especially atlower ambient air densities the Sandia measurements gave a substantially larger liquid core thanthe TU/e measurement. Possible errors can be caused by different interpretation of the liquid corelength or the corrections for the Sandia measurement due to different measurement conditions arenot sufficient.Finally it is tried to describe the droplet breakup within the spray. Therefore bag-breakup andstripping-breakup are compured to the visual results. This yielded no conclusive results.

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List of symbols

Quantity Unit Descriptionmf kg s1 Fuel mass flowma kg s

1 Air mass flow

mdrop kg Mass of a fuel dropletf kg m3 Fuel densitya kg m

3 Air density (or density of combustion gases)g kg m

3 Density of gases surrounding a droplet -

fa

Mf N Momentum fluxA m2 Nozzle orifice (flow) area

Aeff m2 Effective flow areaAp,S/2 m

2 or pixels Area of the spray at half way the spray distanceA m2 Cross section of the spray (for Siebers model only)

veff m s1 Effective fuel velocityv m s1 Fuel velocity

vd0 m s1 Initial droplet velocityvd m s1 Velocity of a fuel dropletvg m s

1 Velocity of the gases surrounding a fuel dropletvth m s1 Theoretical fuel velocity

vdown m s1 Downstream fuel velocity in the nozzle hole

vu p m s1 Upstream fuel velocity in the nozzle hole

vf m s1 Velocity of the fuel droplets (for Hiroyasu model only)f N m

1 Surface tension of fuelU m s1 Velocity of the fuel/air mixture (for Siebers model only)

dpnozzle P a Pressure drop across the nozzlePup P a Upstream pressure in the nozzle (equal to sac volume pressure)

Pdown P a Downstream pressure in the nozzle (equal to ambient air pressure)

Pa P a Pressure of the fuel/air mixture (for Siebers model only)Ps P a Pressure of the saturated fuel/air mixture (for Siebers model only)Cd - Discharge coefficient

CM - Dimensionless momentum coefficientCa - Area contraction coefficientCv - Dimensionless momentum coefficientCcd - Critical discharge coefficient

CaN - Cavitation numberCaNc - Critical cavitation number

K - Cavitation number by Nurickd0 m Nozzle orifice diameter

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Quantity Unit Description

Ddrop m Droplet diameter rad Spray angle

a P a s Dynamic viscosity of airTa K Ambient air temperature (or combustion gas temperature)Tf K Fuel temperatureTs K Temperature of saturated fuel/air mixture (for Siebers model only)

Tf,s K Temperature of fuel in saturated condition (for Hiroyasu model only)tevap s Time required for fuel vaporization (for Hiroyasu model only)

Tdown K Downstream fuel temperature in the nozzle holeTup K Upstream fuel temperature in the nozzle hole

a - Factor for Siebers angleI - Recording intensity (between 1-4096)

- Stoichiometric ratioS m Spray penetrations m The distance a droplet has traveled

S - Dimensionless spray penetrationx m Spray tip distance from the orifice (for Siebers model only)

x+ m Maximum spray penetrationx - Dimensionless distance from the orificeL m Length of the spray

L - Dimensionless spray lengtht s Time

t0 s Time of start of injectiontbreakup,k s Time at which liquid core breaks up

tb s Lifetime of a droplet in the bag breakup regimets s Lifetime of a droplet in the stripping breakup regime

L(t) m Liquid core length as function of time (for Hiroyasu model only)

(t) - Dimensionless timet+ s Maximum timeUf m s1 Initial injection/fuel velocity (for Siebers model only)ha J kg

1 Specific enthalpy of airhf J kg

1 Specific enthalpy of fuelMa kg mol1 Molar mass of air or combustion gasesMf kg mol

1 Molar mass of the fuelZa - Compressibility factor of airZf - Compressibility factor of fuel

a - Coefficient to correct the determined spray angleb - Coefficient in the Siebers model

cp,a J kg1 K1 Specific heat of aircp,f J kg

1 K1 Specific heat of airCD - Drag coefficient of droplets

SM Dk m Sauter Mean Diameter for droplets at slice kka W m

1 K1 Heat conductivity of airkf W m1 K1 Heat conductivity of fuelBT - Heat transfer numberBM - Mass transfer number

Lvap,f,s J kg1 Heat of vaporization of fuel at saturated condition

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Quantity Unit Descriptionrs m Spray radiusrd m Droplet radius

rg0 m Vapor spray radius at the orificed - Volume fraction of fuel dropletsRe - Reynolds numberW e - Weber numberZ - Ohnesorge numberC - Coefficient, 13D - Coefficient,

Qh cc m1 Hydraulic capacity of a nozzle

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Contents

1 Introduction 1

I Injector nozzle research 32 Nozzle characteristics 4

2.1 Determination dimensionless parameters Cd and CM . . . . . . . . . . . . . . . . . 62.2 Determination of the cavitation number . . . . . . . . . . . . . . . . . . . . . . . . 7

3 Measurement techniques 93.1 Momentum measurement technique . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2 Mass flow measurement techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4 Experimental results 114.1 Momentum measurement results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.1.1 Analysis of a single force measurement . . . . . . . . . . . . . . . . . . . . . 12

4.1.2 Momentum flux measurement results around fully open nozzles . . . . . . . 134.1.3 Momentum flux profile of a single spray (blocked nozzle) . . . . . . . . . . . 154.2 Mass flow measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.3 Experimentally determined nozzle characteristics . . . . . . . . . . . . . . . . . . . 17

5 Conclusion 19

II Penetration and dispersion research of non-reacting evaporatingdiesel sprays 20

6 Behavior of the evaporating spray 216.1 Dispersion angle of non-evaporating and evaporating sprays . . . . . . . . . . . . . 21

6.2 Penetration of non-evaporating and evaporating sprays . . . . . . . . . . . . . . . . 23

7 Methods for conducting experiments and analysis of Schlieren recordings 267.1 Visualization of a diesel spray with the EHPC . . . . . . . . . . . . . . . . . . . . . 26

7.1.1 Operation of the EHPC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267.1.2 Schlieren visualization techniques . . . . . . . . . . . . . . . . . . . . . . . . 28

7.2 Analysis models of Schlieren recordings . . . . . . . . . . . . . . . . . . . . . . . . 297.2.1 Spray angle determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307.2.2 Spray length determination . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

7.3 Error estimation of Schlieren recordings . . . . . . . . . . . . . . . . . . . . . . . . 357.3.1 Statistical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357.3.2 Comparison of a blocked nozzle and the use of the thimble . . . . . . . . . 38

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8 Analysis of the Schlieren recordings 408.1 Dispersion angle of the spray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408.2 Penetration of the spray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

III Liquid core research of non-reacting diesel sprays 44

9 Liquid core behavior 459.1 Siebers liquid scaling law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459.2 The Hiroyasu spray model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

10 Methods for conducting experiments and analysis of laser scattering recordings 5310.1 Liquid core visualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5310.2 Model for liquid core processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

10.2.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5510.2.2 Methods for analyzing the various features . . . . . . . . . . . . . . . . . . 55

10.3 Error estimation of the laser light scattering recordings . . . . . . . . . . . . . . . . 6010.3.1 Statistical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6010.3.2 Comparison of a blocked nozzle and the use of the thimble . . . . . . . . . 62

11 Analysis of the laser light scattering recordings 6411.1 Measurement results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6511.2 Comparison with Siebers liquid scaling equation . . . . . . . . . . . . . . . . . . . 6711.3 Comparison to results Sandia National Laboratories . . . . . . . . . . . . . . . . . 7011.4 Comparison with the Hiroyasu model . . . . . . . . . . . . . . . . . . . . . . . . . . 71

IV Conclusions and recommendations 73

12 Conclusion 7412.1 Nozzle characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7412.2 Dispersion angle and penetration of evaporating sprays . . . . . . . . . . . . . . . . 7412.3 L iquid core research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7512.4 Comparison liquid core and vapor spray . . . . . . . . . . . . . . . . . . . . . . . . 76

13 Recommendations 7713.1 Nozzle characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7713.2 Dispersion angle and penetration of evaporating sprays . . . . . . . . . . . . . . . . 7713.3 L iquid core research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

A Drawings of the thimble and nozzle 1

B Experimental setup 4

C Drawings of the momentum measurement setup 6

D Momentum measurement results around 9 mm nozzles 12

E Scheme of EHPC components 14

F Argon addition 15

G Schlieren reproducibility measurement results 16

H Results main Schlieren experiments 18

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I Siebers liquid scaling law input variables. 24

J Specifications of the filter used for laser light scattering 28

K Results Siebers main experiments 29

L Comparison of Schlieren and laser light scattering recordings 31

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List of Figures

2.1 Schematic view of a nozzle of a diesel DI injection unit. The tip of the nozzle ismagnified [WDK+04]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Photograph of a nozzle which is installed in the EHPC. On the nozzle the thimbleis applied. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.3 Photograph of a nozzle which is installed in the EHPC without the thimble appliedon it. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.4 Schematic view of cavitation in a nozzle. . . . . . . . . . . . . . . . . . . . . . . . 62.5 The discharge coefficient Cd as function of the cavitation number CaN. C

cd and

CaNc are the critical discharge coefficient and the critical cavitation number re-spectively. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.1 Schematic view of the placement of the force sensor on the nozzle for momentummeasurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.1 Needle lift profile of a single injection with a duration of 3 ms. . . . . . . . . . . . 134.2 Force profile of a single force measurement. . . . . . . . . . . . . . . . . . . . . . . 134.3 Results of the momentum measurements around nozzle A. The arrows indicate the

center position of the individual sprays. . . . . . . . . . . . . . . . . . . . . . . . . 144.4 Results of the momentum measurements around nozzle C. The arrows indicate the

center position of the individual sprays. The third arrow on the left side indicatesthe center of the spray which is used in further visualization experiments. . . . . . 14

4.5 Average momentum flux of the spray of nozzle type A (blue line) and C (red line). 154.6 The momentum flux profile of the spray of two holes of nozzle B. The middle of the

force profiles are placed on the 0 mark afterwards. . . . . . . . . . . . . . . . . . 164.7 Results of the mass flow measurements of one hole of nozzle B for the five different

injections pressures: 100, 150, 200, 300 and 400 bar. . . . . . . . . . . . . . . . . . 174.8 Results of the mass flow measurements of another hole of nozzle B for the five

different injections pressures: 100, 150, 200, 300 and 400 bar. . . . . . . . . . . . . 17

6.1 The dispersion angle versus the af

ratio for non-evaporating sprays which are pre-

sented in [NS96]. The upper blue line is the power fit for the measurements withthe nozzle with d0 = 340 m (triangle data points). The lower red line is the powerfit for the measurements with the nozzle with d0 = 257 m (cross data points) andwith d0 = 198 m (circle data points). Ta 450 K and Ta 300 K . . . . . . . . 22

6.2 The dispersion angle versus the af ratio for evaporating sprays which are presented

in [NS96]. The dashed line are the power fit curves from Fig. 6.1. The upperblue line is the power fit for the measurements with the nozzle with d0 = 340 m(triangle data points). The lower red line is the power fit for the measurementswith the nozzle with d0 = 257 m (cross data points) and with d0 = 198 m (circledata points). Ta 1000 K. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

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6.3 Comparison of evaporating spray penetration measurements (at Ta = 1000 K)with non-evaporating spray penetration measurements (at Ta = 451 K) which arepresented in [NS96]. The injection pressure is 1370 bar

15 bar and the nozzle

hole diameter d0 = 257 m. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

7.1 Photograph of the EHPC (Eindhoven High Pressure Cell) at the TU/e. . . . . . . 267.2 Pressure and temperature profile after the ignition which initiates pre-combustion.

The red dashed line indicate the injection timing. Filling conditions of the EHPC:1705 mg C2H2, 21715 mg N2, 4158 mg Ar and 4555 mg O2. . . . . . . . . . . . . 27

7.3 A schematic of the principle of the Schlieren technique. . . . . . . . . . . . . . . . 287.4 A schematic of the principle of the Schlieren technique in combination with the

EHPC setup. a. injection nozzle b. liquid core c. fuel vapor d. sapphire windowe. Xe-lamp f. plate with pinhole g. positive lens (f=1000 mm) h. positive lens(f=1000 mm) i. plate with pinhole j. ingoing parallel light beams k. outgoingparallel light beam l. metal casing. . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.5 An example of a original Schlieren recording (upper image) and a artificial coloredSchlieren recording (lower image). The pre-combustion started 780 ms before thisimage. The injection started 1,15 ms before this image. The nominal conditionsin the EHPC: Ta = 1305 K, a = 9,15 kg/m

3 and pfuel = 1105 bar. The redline and the positions p1 and p2 indicate the area that has been analyzed for angledetermination, O1 and O2 represent the origin of the lower and upper half of thespray (see section 7.2.1). The red box indicates the spray tip (see section 7.2.2). . 30

7.6 Intensity profile from a cross section of the spray indicated by the arrow in Fig. 7.5. 327.7 The derivative of the intensity profile from a cross section of the spray indicated by

the arrow in Fig. 7.5. Pixel number 8,5 is the location of the boundary or edge ofthe spray. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

7.8 Histogram of 5000 permutations of 1 missing points on the spray edge for the angledetermination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32




7.12 Determination of the spray tip [NS96].; . . . . . . . . . . . . . . . . . . . . . . . . 337.13 Visualization of the spray tip. The spray from a previous frame is shown and at the

spray tip the spray in the current frame is shown. On the left side the differencebetween the two spray is shown. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

7.14 The influence of the chosen number of points that represent the spray tip on thedetermined penetration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

7.15 The influence of the chosen threshold for determining the spray tip on the deter-mined penetration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

7.16 Spray tip penetration as function of time (solid red). A power fit between t = 0 msand t = 0,94 ms is applied (solid blue line). The dashed blue lines are the 2 errorbounds of the power fit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

7.17 Spray tip penetration as function of time (solid red). A power fit between t =0,165 ms and t = 0,94 ms is applied (solid blue line). The dashed blue lines are the2 error bounds of the power fit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

7.18 Edge recognition by the software. . . . . . . . . . . . . . . . . . . . . . . . . . . . 367.19 Histogram of the tan(/2) determination of one spray during one injection. . . . . 367.20 Spray tip penetration as function of time of all the reproducibility measurements. . 377.21 The average spray tip penetration (solid red line) with the 2 bounds (dashed blue

lines). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377.22 The correlation between spray angle and spray penetration at 0,6 ms. . . . . . . . 38

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7.23 The correlation between fuel pressure and spray penetration at 0,6 ms. . . . . . . 387.24 Difference between spray angles of a blocked nozzle and of a nozzle on which a

thimble is applied. Measured at a = 9,6

0,3 kg/m3 and pf = 831

76 bar. . 39

7.25 Difference in penetration between a spray produced with a blocked nozzle and ofa nozzle on which a thimble is applied. Measured at a = 9,6 0,3 kg/m3 andpf = 831 76 bar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

7.26 Difference in penetration between a spray produced with a blocked nozzle and of anozzle on which a thimble is applied at the initial phase of the injection. Measuredat a = 9,6 0,3 kg/m3 and pf = 831 76 bar. . . . . . . . . . . . . . . . . . . 39

8.1 Experimental results of the Schlieren recordings. The solid lines are the linear fitof the data points for each density. The dashed line indicates the correlation of Eq.6.3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

8.2 Schlieren recordings of a spray with Ta = 432 K, a = 15,93 kg/m3 (left side). Anda spray with Ta = 1287 K, a = 16,11 kg/m

3 (right side). . . . . . . . . . . . . . . 42

8.3 Experimental results of the Schlieren recordings. The solid lines are the power fitsof the data points for each ambient air temperature. The green line indicates thecorrelation of Eq. 6.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

8.4 Initial spray penetration of several measurement compared to Eq. 6.11 (dashed line). 438.5 The relation between penetration and ambient air density a. The solid lines are

power fits through the measured points . . . . . . . . . . . . . . . . . . . . . . . . 43

9.1 Schematic view of the idealized spray model used to develop the liquid length scale[Sie99, Sie98, HMS99]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

9.2 Schematic view of the Hiroyasu spray model. . . . . . . . . . . . . . . . . . . . . . 50

10.1 Schematic view of the laser light scattering setup. a. injection nozzle b. liquidcore c. fuel vapor d. sapphire window e. laser f. laser beam g. cylindrical lens h.

mirror i. cylindrical lens j. scattered laser light k. 2D lens l. broadband filter m.narrow band filter n. high speed camera o. metal casing. . . . . . . . . . . . . . . 54

10.2 Section AA of Fig. The horizontal arrows indicate the laser sheet. The spray isaimed at an angle of 37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

10.3 A frame from a recorded mie scattering movie after the preparations are con-ducted by the software. The spray is artificially colored (original recordings arein grayscale). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

10.4 A frame from a recorded laser light scattering movie from a relative big liquid corebefore and after the preparations are conducted by the software. The spray isartificially colored (original recordings are in grayscale). . . . . . . . . . . . . . . . 56

10.5 The average of the intensity profile along the centerline of all frames. The centerlinewidth is 3 pixels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

10.6 The rate of change of the average intensity profile across 10 pixels. 5810.7 An example of the liquid core end determination of a large spray (Ta = 650 K,

a = 25 kg/m3 and pfuel = 1162 bar). The length of the indicated liquid corelength is 42,0 mm. The spray is artificially colored. . . . . . . . . . . . . . . . . . 58

10.8 An example of the liquid core end determination of a small spray (Ta = 1500 K,a = 25 kg/m3 and pfuel = 1202 bar). The length of the indicated liquid corelength is 6,9 mm. The spray is artificially colored. . . . . . . . . . . . . . . . . . . 58

10.9 The intensity profile along the centerline of a single frame. . . . . . . . . . . . . . 5910.10The fluctuations in liquid core length. . . . . . . . . . . . . . . . . . . . . . . . . . 5910.11Example 1 of a discrete Fourier transformation of the liquid core length. . . . . . 6110.12Example 2 of a discrete Fourier transformation of the liquid core length. . . . . . 6110.13Example 3 of a discrete Fourier transformation of the liquid core length. . . . . . 6210.14Liquid core length with a blocked nozzle (red line) and with the use of a thimble

(blue line). The dotted lines represent the 2 borders. . . . . . . . . . . . . . . . . 63

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10.15Initial liquid speed with a blocked nozzle (red) and with the use of a thimble (blue). 63

11.1 Liquid core length (scatter plot) at 7 different ambient air densities and the power

fits for each density (solid lines). The injection pressure was 1165 63 bar. . . . 6611.2 Liquid core length solid line with the lower and upper 2 bounds (dashed line) at

7 different densities. The injection pressure was 1165 63 bar. . . . . . . . . . . 6611.3 Liquid core length (scatter plot) at 7 different ambient air densities and the Siebers

liquid scaling equation results (solid lines) wherein Eq. 8.1 is used as a correlationfor the angle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

11.4 Liquid core length (scatter plot) at 7 different ambient air densities and the Siebersliquid scaling equation results (solid lines) wherein Eq. 9.4 is used as a correlationfor the angle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

11.5 Liquid core length as function of the ambient air density. Crosses: measured data.Circles: data points according Siebers liquid scaling equation. Solid line: power fitof the experimental data. Dashed line: power fit of the Siebers data points. . . . . 69

11.6 Relative error between measured data and Siebers liquid scaling equation. 6911.7 Difference between measured data and Siebers liquid scaling equation ((measureddata)-(liquid scaling equation predictions)). . . . . . . . . . . . . . . . . . . . . . . 69

11.8 Comparison of Sandia measurements with different kind of fuels with our experi-mental results. The difference in used orifice diameter, Ca and fuel temperatureis corrected for the measurement results to the measurement conducted at SandiaNational Laboratories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

11.9 Comparison of Sandia measurements with different kind of fuels with our experi-mental results. The difference in used orifice diameter and Ca is corrected for themeasurement results to the measurement conducted at Sandia National Laborato-ries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

11.10Comparison of the experimental results with the original Hiroyasu model (solidlines) at different densities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

11.11Comparison of the experimental results with the adjusted Hiroyasu model (solidlines) at different densities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

A.1 Drawing of the top view of the thimble. The maximum angle is given to illustratethe space between the cone of the thimble and the spray. . . . . . . . . . . . . . . 1

A.2 Drawing 1/2 of a 7 mm nozzle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2A.3 Drawing 2/2 of a 7 mm nozzle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

B.1 Flowchart of the experimental setup of momentum measurements of the spray. . . 4B.2 Flowchart of the experimental setup of mass flow measurements. . . . . . . . . . . 5

C.1 Drawing of the momentum measurement setup. . . . . . . . . . . . . . . . . . . . 7C.2 Drawing of the momentum measurement setup. . . . . . . . . . . . . . . . . . . . 8

C.3 Drawing of the momentum measurement setup. . . . . . . . . . . . . . . . . . . . 9C.4 Drawing of the momentum measurement setup. . . . . . . . . . . . . . . . . . . . 10C.5 Drawing of the momentum measurement setup. . . . . . . . . . . . . . . . . . . . 11

E.1 Scheme which relates the essential components of the EHPC. . . . . . . . . . . . . 14

F.1 Values ofcp for different mixtures. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

H.1 Power fits of the measured spray penetration of the main Schlieren recordings atdifferent temperatures and densities. . . . . . . . . . . . . . . . . . . . . . . . . . 21

H.2 Power fits of the measured spray penetration of the main Schlieren recordings atdifferent temperatures and a density of 16,0 kg/m3. . . . . . . . . . . . . . . . . . 21

H.3 Power fits of the measured spray penetration of the main Schlieren recordings atdifferent temperatures and a density of 25,2 kg/m3. . . . . . . . . . . . . . . . . . 22

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H.4 Comparison of the power fits (solid lines) of the measured spray penetration of themain Schlieren recordings at different densities and the measured spray penetra-tions of evaporating sprays presented in [NS96]. The dashed lines are the adjusted

measurements according 6.12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22H.5 Comparison of the power fits (solid lines) of the measured spray penetration of the

main Schlieren recordings at different densities with the correlation of Eq. 6.12. . 23H.6 Comparison of the power fits (solid lines) of the measured spray penetration of the

main Schlieren recordings at different densities with the correlation of Eq. 6.13. . 23

I.1 The density of diesel as function of diesel temperature. . . . . . . . . . . . . . . . 24I.2 The specific heat of diesel as function of diesel temperature. . . . . . . . . . . . . 24I.3 The latent heat of vaporization of diesel as function of diesel temperature. . . . . 25I.4 The partial vapor pressure of diesel as function of diesel temperature. . . . . . . . 25I.5 The compressibility factor of diesel as function of diesel temperature. . . . . . . . 25I.6 The specific enthalpy of diesel as function of diesel temperature. . . . . . . . . . . 25

I.7 The compressibility factor of air as function of diesel temperature and air density. 26I.8 The specific enthalpy of diesel as function of air temperature. . . . . . . . . . . . 26I.9 The air viscosity as function of air temperature. . . . . . . . . . . . . . . . . . . . 27

L.1 Laser light scattering recording conditions: a = 6,52 kg/m3, Ta = 1009 K andpfuel = 1165 bar. Schlieren recording conditions: a = 6,46 kg/m

3, Ta = 1006 Kand pfuel = 1165 bar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

L.2 Laser light scattering recording conditions: a = 6,51 kg/m3, Ta = 1480 K andpfuel = 1172 bar. Schlieren recording conditions: a = 6,46 kg/m3, Ta = 1480 Kand pfuel = 1170 bar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

L.3 Laser light scattering recording conditions: a = 16,16 kg/m3, Ta = 985 K and

pfuel = 1118 bar. Schlieren recording conditions: a = 16,01 kg/m3, Ta = 984 Kand pfuel = 1135 bar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32



L.6 Detailed recordings of the tip of the liquid core where breakup phenomena occur.The width of a single image is 7,8 mm and its duration is 9,8 s. The conditionswere: Ta = 650 K, a = 25 kg/m

3 and pfuel = 1165 bar. . . . . . . . . . . . . . . . 34

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List of Tables

4.1 Scheme of the nozzles that are used for the different experiments. Qh is the hydrauliccapacity of a nozzle, expressed in cc m1. ID is the notation which is used in thisreport to identify the nozzles. The L/D ratio is unknown for these nozzles andestimated at 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.2 Measured momentum of the sprays of nozzle type A. . . . . . . . . . . . . . . . . . 144.3 Measured momentum of the sprays of nozzle type C. . . . . . . . . . . . . . . . . . 144.4 Dimensionless parameters for nozzle B for two holes. . . . . . . . . . . . . . . . . . 18

7.1 Measurements conditions for statistical analysis. . . . . . . . . . . . . . . . . . . . 35

8.1 Schlieren measurements schedule, pf = 1167 bar 79 bar. . . . . . . . . . . . . . 40

9.1 Variables for Eq. 9.11 and their source . . . . . . . . . . . . . . . . . . . . . . . . . 50

10.1 Measurements conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6010.2 Liquid core reproducibility measurement results. . . . . . . . . . . . . . . . . . . . 60

11.1 Laser light scattering measurements schedule, pf = 1165 bar (nominal). . . . . . . 6511.2 Measurements conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

C.1 Part list for the momentum measurement setup. . . . . . . . . . . . . . . . . . . . 6C.2 Kistler FSH 9203 Force sensor specifications. . . . . . . . . . . . . . . . . . . . . . 6

D.1 Momentum measurement results of the nozzle A. . . . . . . . . . . . . . . . . . . . 12D.2 Momentum measurement results of the nozzle C. . . . . . . . . . . . . . . . . . . . 13

G.1 Spray angles of the Schlieren reproducibility measurements. . . . . . . . . . . . . . 16G.2 Power fits of the Schlieren reproducibility measurements. . . . . . . . . . . . . . . . 17

H.1 Measured spray angles main Schlieren experiments. . . . . . . . . . . . . . . . . . . 18H.2 Coefficients of the power fit through the measured spray penetration. . . . . . . . . 20

K.1 Measured liquid core length in the laser light scattering experiments. . . . . . . . . 29

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Chapter 1

Introduction

In the European Union transportation by road and on water contributes about 50 % to the emis-sion of carbon oxides, from which half originates from heavy duty diesel engines. Furthermorethese engines are responsible for 20 % of the total particle emissions. Therefore more stringentlegislative regulations will be enforced to reduce these emissions. However, these regulations maynot increase the fuel consumption of these engines. To accomplish this the engine manufacturerhas, among several other options, to realize a further optimization of the engine design. This re-quires a good understanding of the combustion process and how these processes are influenced byengine design and settings. Therefore within the STW group a project is started to set up a modelwhich describes the formation of carbon oxides and carbon particles in heavy duty diesel engines[dGKvM04]. To accomplish this it is required to obtain a good understanding of the combustionprocesses. The fuel spray penetration and dispersion have great influence on these combustionprocesses (such as turbulent effects) and it is therefore essential to obtain a good characterizationof fuel sprays. In this graduation project research is conducted on the penetration, dispersion and

evaporation of fuel sprays to establish a better understanding of the behavior of such a spray.Experiments are conducted in the EHPC (Eindhoven High Pressure Cell), stationed at the Techni-cal University Eindhoven (TU/E), to research non-reacting diesel sprays. The EHPC is a constantvolume chamber, that is optically accessible, where diesel injection can be performed at conditionsapproaching realistic in-cylinder DI diesel engine conditions. It is important that measurementdata can be compared to other experiments or models to validate them. Also it is essential todetermine how much variation is present between the sprays. In this respect the nozzle of theinjection unit is a critical part; it determines to a large extent the behavior of the spray. Sincea wide variety of nozzles is available it is essential that the nozzle is characterized properly; onlythen meaningful comparisons with other experimental data or models can be made. The charac-terization is realized at a common rail setup at the TU/E developed by X.L.J. Seijkens. In Part Iresults and discussion of the characterization of the nozzles, and the difference between the sprays

are described.The spray behavior itself comprises a range of complex physical and chemical processes which aredifficult to incorporate in the engine design or computer models. Therefore empirical relationshave been developed for the spray behavior which are essential for the engine designer and thedevelopers of multi-dimensional computational models. Due to time and resource restrictions thisgraduation project is narrowed down to non-reacting diesel sprays. Two elements of the spray canbe distinguished: the diesel vapor and the liquid core of the spray. With Schlieren visualizationtechniques high speed recordings are made to determine the progression of the spray and sprayangle in the vapor phase. Software routines are developed to analyze these recordings and deter-mine the spray penetration and angle. In part II comparisons are made between the experimentalresults and the measurements conducted at Sandia National Laboratories.Furthermore the liquid core of the spray is recorded with laser light scattering techniques. Mostimportant feature hereby is the liquid core penetration. Penetration of the liquid core is needed to

promote fuel-air mixing, but can lead to greater emissions and power loss if liquid fuel impinges

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and collects on the piston or cylinder wall. Dennis L. Siebers [Sie99, Sie98] and Hiroyuki Hiruyaso[HIY96] have developed models based on two different philosophies to predict the liquid core pen-etration. Also a number of experiments have been conducted in relation to the liquid core length

at Sandia National Laboratories. These experiments and models will be compared to the resultsof the experiments conducted at the TU/E in part III.

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Part I

Injector nozzle research

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Chapter 2

Nozzle characteristics

The diesel spray produced in a DI diesel engine has great influence on the efficiency and poweroutput of the engine. The nozzle of a DI diesel injection unit contributes for a large part to theformation of the spray. Fig. 2.1 is a schematic of such a nozzle. A technical drawing is providedin Figs. A.2-A.3 in appendix A.

Fuel supply

Needle

Hole

Sac volume

Figure 2.1: Schematic view of a nozzle of a dieselDI injection unit. The tip of the nozzle is magnified[WDK+04].

Several important properties of a nozzle are: The geometry of the holes

The geometry of the nozzle sac volume and needle

The sac volume

The number of holes

The angle at which the holes are aimed

The diameter of the holes

The number of holes

A wide range of nozzle types is available of which all of the mentioned characteristics can vary.To relate further research it is essential that the results are coupled to the correct nozzle charac-

teristics. It is not possible to fully characterize a nozzle; the geometry of the nozzle and holes are

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difficult to determine but have great influence on the development of the spray. To characterizethe nozzle, including the geometry, the discharge coefficient, Cd, and the momentum coefficient,CM, are determined by measuring the momentum flux and mass flow of a spray [PGSG04]. The

methods used to determine the momentum flux are presented in chapter 3. In section 2.1 therelation between the measured momentum flux and CM and the measured mass flow and Cd arelined out. Cavitation in the nozzle hole influences the mass flow through the hole, this is explainedin section 2.2. By determining the Cd and CM of the nozzle, the nozzle is not fully characterizedbut the most essential features of the nozzle are determined.This method only determines the global characteristics of a nozzle. However, in the EHPC itis practically impossible to produce valuable recordings of multiple sprays. Therefore one sprayproduced by a nozzle is analyzed. It is possible that each hole does not produce the same spray;there can be an asymmetry present between the different sprays or a defect in one or more of theholes (change of hole geometry) [KK04]. Thus it is important to know how large the differencesbetween the unique sprays of a nozzle are and if there is an asymmetrie present. If there is asignificant difference between the sprays it is difficult to get a good comparison between visual-

ization experiments conducted with different nozzles. To obtain an estimate for these differencesthe momentum flux of sprays of a nozzle are mutually compared.Also there are two methods used to achieve a single spray. One method uses a thimble whichpasses one spray and collects the other sprays and drains them, as shown in Fig. 2.2. A technicaldrawing of the top view of the thimble is provided in Fig. A.1 in appendix A. With the othermethod all the holes, except the one from the desired spray, are blocked. The nozzle is then in-stalled as shown in Fig. 2.3. Both methods successfully isolate one spray but unfortunately bothmethods also have a potentially different influence on the nozzle characteristics. Obviously thismakes comparison with other experiments more difficult. Therefore experiments are conductedto characterize an untreated nozzle and a nozzle from which all holes except one are blocked.Unfortunately there is no good method to measure the momentum and mass flow of a nozzle onwhich a thimble is installed. So the effect of the thimble itself cannot be determined. In chapter 4all the experimental results are presented and in chapter 5 the conclusion and discussion of theseresults are presented.

Figure 2.2: Photograph of a nozzle which is in-stalled in the EHPC. On the nozzle the thim-ble is applied.

Figure 2.3: Photograph of a nozzle which isinstalled in the EHPC without the thimble ap-plied on it.

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2.1 Determination dimensionless parameters Cd and CM

The determination of Cd and CM of the nozzle can be derived by mass and momentum balances

[PGSG04]. The mass flow can be determined with the following equation:

mf =

A0

vfdA (2.1)

where v is the velocity of the fuel traveling through the hole, f the fuel density and A the controlsurface through which the fuel flows. The momentum flux of the spray can be calculated with thefollowing equation:

Mf =

A0

v2fdA (2.2)

Due to the high flow velocity in the nozzle, areas with relative low pressure occur, see Fig. 2.4. Inthese areas vapor bubbles originate, a phenomenon called cavitation. The cavitation reduces theeffective flow area, Aeff, as shown in Fig. 2.4.

Low pressure

zones

Aeff

AeffVena contracta

Low pressure

zone

needle

nozzle

Figure 2.4: Schematic view of cavitation in a nozzle.

Due to the decrease in the flow area the velocity increases to veff. In reality the flow throughthe holes will probably develop to a poiseuille flow. But in this case it is assumed that the velocityprofile of the flow is straight. The Aeff and veff can be determined by combining Eqs. 2.1 and2.2:

veff =Mfmf

(2.3)

Aeff =m2f

Mf(2.4)

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With Bernoullis law the theoretical velocity can be determined (with a flow area A0):

vth =2dpnozzle

f (2.5)

Subsequently the dimensionless coefficient Cd can be determined by:

Cd =mf

A0fvth=

mf

A0

2fdpnozzle(2.6)

In a similar way the dimensionless coefficient CM, which is the ratio of momentum, can be deter-mined by:

CM =Mf

A0fu2th=

MF2A0dpnozzle

(2.7)

The nozzle can now be characterized with the two dimensionless numbers obtained with Eqs. 2.6and 2.7. Two other dimensionless coefficients which can be used:

Cv =veffvth

(2.8)

Ca =Aeff

A0(2.9)

where veff is determined in Eq. 2.3. With Eqs. 2.8 and 2.9, Cd and CM can be determined:

Cd = Cv Ca (2.10)CM = C

2v Ca (2.11)

2.2 Determination of the cavitation numberIn section 2.1 it was lined out that cavitation influences the coefficients Cd and CM. To estimatethe influence of the cavitation, a dimensionless cavitation number can be defined. The rate ofcavitation depends on the pressure drop across the nozzle orifice [GAC00]:

CaN =(Pup Pdown)(Pdown Pv) (2.12)

where Pup is the injection pressure, Pdown is the ambient pressure in which the fuel is injected andPv is the vapor pressure. The Pv can be omitted since it is very small:

CaN =Pup Pdown

Pdown(2.13)

Nurick [Nur76] used another form of pressure difference ratio referred as cavitation parameter K:

K =(Pup Pv)

(Pup Pdown) (2.14)

An expression relating the discharge coefficient and the contraction coefficient Cc with the cavi-tation parameter can be obtained:

K =

CdCc

2(2.15)

Subsequently Cd can be expressed in terms of cavitation number CaN:

Cd = Cc K0,5 = Cc1 + 1CaN0,5

(2.16)

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Using Eq. 2.16 the mass flow of a cavitating flow can be determined.

mf = fCcdA0

2 |dpnozzle|f 1 + CaN

CaN (2.17)

In Fig. 2.5 an example is shown in which Cd is drawn as function of CaN. Earlier experimentsconducted under supervision of X.L.J. Seykens at the TU/e resulted in CaNc 0, 5. At a certainpoint Cd reaches a peak value at the critical CaN (CaN

c). At higher cavitation numbers thanCaNc the Cd is independent of CaN and solely dependent on the Reynolds number. In theexperiments to determine the momentum of the spray and in the visualization experiments in partI and II, the CaN is high resulting in a nearly constant Cd value.

Cd

Critical point

Ccd

CaN CaNc

Figure 2.5: The discharge coefficient Cd as function of thecavitation number CaN. Ccd and CaN

c are the criticaldischarge coefficient and the critical cavitation number re-spectively.

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Chapter 3

Measurement techniques

To determine Cd and CM it follows from Eqs. 2.6 and 2.7 that the mass flow and momentum fluxof the spray coming out of the nozzle have to be determined. Both aspects are measured withdifferent experimental setups.

3.1 Momentum measurement technique

An injector is installed on a common rail system with data acquisition devices. A scheme of thetotal setup is shown in Fig. B.1 in appendix B. For a more complete description of the experimentalsetup see [SSB00] and its accompanying literature. To measure the momentum exerted by thespray a force sensor is aimed at the spray as shown in Fig. 3.1. In Figs. C.1-C.5 in appendix Cthe technical drawings of this setup are provided . In these drawings the sensor tip diameter is 4mm, however the measurements are conducted with a spray tip which has a diameter of 2 mm.

The specification of the Kistler FSH 9203 force sensor is provided in table C.2 in appendix C.This force is equal to the momentum flux. The spray hits the sensor tip which completely catchesthe spray receiving the full momentum of the spray. The sensor holder can be aimed to every holein the nozzle.

Sensor

holder

Holes

Sensor tip

Force

sensor

Nozzle

Figure 3.1: Schematic view ofthe placement of the force sen-sor on the nozzle for momentummeasurements.

Shortcoming of the momentum measurements It is geometrically impossible to place thesensor tip directly in front of the nozzle hole; the spray has to travel about 1 mm to reach the sen-sor tip. Nevertheless at this distance the interaction with the air surrounding the spray is minimalresulting in minimal diffusion of the spray; almost no momentum loss in other directions is present.Obviously the spray will encounter air resistance but it is expected this effect is negligible withrespect to the momentum of the spray. Measurements with nozzle A and dpnozzle = 1000 5 bar

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(see table 4.1) at different distances from the nozzle hole show that around 1 mm distance themeasured momentum flux is at its maximum. As the spray hits the sensor tip a part of the spraybounces back due to elastic collisions of droplets, which increases the measured force by the force

sensor. It is difficult to estimate these additional measured forces. When the spray impinges thesensor tip a large part of its kinetic energy is lost due to viscous dissipation [GA00]. Also most ofthe spray is deflected at an tangential or almost tangential angle. These two contribution lead tosmall additional forces due to elastic collisions of the droplets.The line up of the sensor holder to the injector holes also causes difficulties. There is no goodmethod to get a good alignment of these two components. Therefore measurements are conductedaround a hole. When properly aligned the highest force will be measured due to minimal momen-tum loss in other directions (ie. force components).In part II results are presented regarding spray angles. In these results 30 degrees is the maximumangle. With this angle the sensor tip area is sufficient to capture the full spray.

3.2 Mass flow measurement techniquesThe mass flow measurement can only take place when all, except one, nozzle holes is blocked dueto limitations of the high pressure pump. The injector nozzle is installed in a Zeuch vessel [SSB00].The outlet of this vessel is restricted causing a back pressure in the Zeuch vessel. By adjustingthis restriction the back pressure can be altered and thus also the CaN (see Eq. 2.13). After thisrestriction a mass flow meter is installed. In Fig. B.2 in appendix B a scheme is presented whichdescribes the experimental setup of the mass flow measurement.

Shortcoming of the mass flow measurements The fuel pressure is measured before theinjector which means the pressure drop across the injector and nozzle is unknown. It is estimatedthe mentioned pressure drop is around 20 to 30 bar. AMESim simulation confirmed this estimation.The fuel heats up right after the restriction as the kinetic energy of the fuel is converted into heat.

This obviously causes problems in determining the fuel density. The only solution to this problemis to wait till the temperature of (all) the fuel has stabilized.

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Chapter 4

Experimental results

A selection of experimental results will be presented which characterize the type of nozzle anddefines possible asymmetry of the nozzle. A momentum measurement is conducted on the nozzlewhich is used for spray visualization studies. The holes of this nozzle cannot be blocked as thisadjustment is a permanent one and could damage the nozzle. Therefore other nozzles of similarhole geometry are used from which holes are blocked. In the experiments 7 and 9 mm nozzles areused, but only experimental data of the 9 mm is used for further analysis. The following featuresof the nozzles are analyzed:

The force profile of one measurement is analyzed for possible filtering requirements and foran indication of the reproducibility of the measurements.

A momentum measurement is conducted around two fully open 9 mm nozzles. The differ-ences between these measurements are analyzed.

The asymmetry in the momentum measurements of each nozzle is analyzed and compared.

The momentum flux of a fully open nozzle is compared to one which has all, except one,nozzle holes blocked.

The mass flow through two holes of the same nozzle is measured and the Cd of these holesis determined.

A range of nozzles have been used in the experiments. In table 4.1 a summary is presented ofwhat type of nozzle are used for the experiments. All momentum flux measurements are conductedwith an injection pressure dpnozzle = 1000 5 bar.Welding the nozzle holes is at this point the only reliable way to block the holes of a nozzle.Unfortunately this method is permanent. However, before this method was used, nozzle B wasblocked with epoxy. This method is very unreliable, it cannot withstand high pressures for along time. But this method is not permanent which makes it possible to repeat measurements on

different holes of the same nozzle. This only worked with nozzle B for two neighboring holes.

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Table 4.1: Scheme of the nozzles that are used for the different experiments. Qh is the hydrauliccapacity of a nozzle, expressed in cc m1. ID is the notation which is used in this report to identifythe nozzles. The L/D ratio is unknown for these nozzles and estimated at 4.

ID Nozzle type Q Experiments in which Nozzle Nr. of [ccm1] it is used diameter [m] holes

A DLLZ160PV3770 599 Momentum measurements 199 3 6684 569 06 with all holes open

B DLLZ160PV3770 594 Momentum measurements 206 3 6684 569 04 with blocked nozzle

Mass flow measurementswith blocked nozzle

C DLLZ160PV3770 447 Momentum measurements 177 3 6683 569 03 with all holes open

Main Schlieren experimentsMain liquid core measurements

D DLLZ160PV3770 346 Schlieren recordings 126 3 8685 569 05 with varying fuel temp.

Liquid core recordingwith varying fuel temp.

E DLLZ160PV3770 362 Reproducibility test for 120 8685 569 10 Schlieren recordings

F DLLZ 160PV3770 762 Reproducibility test for 193 3 8013 10 laser light scattering

4.1 Momentum measurement results4.1.1 Analysis of a single force measurement

In Fig. 4.1 the needle lift as function of time of a single injection is shown. The excitation durationof the coil was 3 ms. In Fig. 4.2 the force profile of a single momentum measurement is shown.When the injection starts, the force sensor has a disturbance possibly caused by the vibrationcoming from the magnetic coil which initiates the needle lift. In first instance needle relaxationtakes place due to the elastic deformation of the needle. After the needle relaxation the needlebegins to lift and a spray begins to form with ever increasing momentum. By comparing needle liftdata and spray recordings it was determined that the injection starts at 13,5 % of the total needlelift due to the elastic deformation of the needle. After about 0,6 ms the needle has lifted from13,5 % to the fully lifted position and the spray exerts a maximum force on the force sensor. This

maximum force is exerted for about 2,5 ms. After this period the needle falls back on the seat inabout 0,5 ms (to the 13,5 % position). Thus the total injection time is 3,6 ms. To determine themomentum of the spray, the average force is determined between in two red lines which are shownin Fig. 4.2.Considerable high frequency fluctuations are present in the measured force signal. There are twomain causes for these fluctuations. The most important one is during the injection and originatesfrom pressure variations in the high pressure fuel line to the injector. These are caused by thefuel pump and pressure wave interactions in the common rail. These variation have a frequencyof about 3 to 5 kH z. Also in Amesim simulations a pressure wave with a frequency of 5 kH z ispresent between the atomizer chamber and the sac volume (thus along the injector needle). Thereis also a fluctuating signal noticeable after the injection has completed. Sinusoidal vibrations occur,with a low frequency compared to the previous mentioned noise. These variations are caused by

the mechanical vibrations in the experimental setup itself. Especially when the needle starts to

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lift a vibration is initiated which fades out quickly. These disturbances are filtered out with smallband notch filters, but there is no noticeable difference in the results of filtered and the unfilteredsignals. This problem can be solved by mechanically separating the different components from the

force sensor.

0 1 2 3 4 5 6 7320

340

360

380

400

420

440

460

time [ms]

needlelift[]

Figure 4.1: Needle lift profile of a single injec-tion with a duration of 3 ms.

0 1 2 3 4 5 6 71

0

1

2

3

4

5

time [ms]

force[N]

Figure 4.2: Force profile of a single force mea-surement.

4.1.2 Momentum flux measurement results around fully open nozzles

From two unblocked nozzles the momentum is determined at 10 intervals around the nozzle. Thetwo nozzle types A and C are used in these experiments. The latter type is used in the mainEHPC experiments. The complete measurement results are in tables D.1 and D.2 in appendix D.The 2 error is 1-2 %. The measurement data is summarized in Figs. 4.3 and 4.4. Both nozzleshave 6 injection holes. In Fig. 4.3 the sprays are noticeable from the force measurements; theholes, and thus the middle of the sprays, are at approximately 20, 70, 130, 200, 260 and320. Around these positions the complete spray hits the sensor tip. As the sensor holer is rotatedfurther a part of the spray misses the sensor tip causing a fast drop in the measured momentumflux. In the range of the angle of the sensor holder in which the complete spray hits the sensor theexerted momentum flux depends on the force components (ie. force directions) which results in asinusoidal momentum flux profile within this range. After approximately 10-15 from the centerof the spray the measured force drops of; the spray misses the front of the sensor tip completelybut still reaches the sensor tip and therefore it registers a force of about 1 ,5 N. Exactly betweenthe holes, at 100, 170 and 350, a relative high force is measured. Most obvious cause is that twoneighboring sprays hit the force sensor instead of one. Momentum measurement around nozzleswith more holes contain these peaks between every neighboring holes, supporting the statementof multiple sprays hitting the force sensor. Nevertheless the force should be around 2 1,5 Ninstead of the measured 4,7 4,8 N. At this point there is no good and reliable explanation forthis phenomenon. Possibly the neighboring spray influence each other in such a way that moredroplets bounce back with more velocity, or a greater mass of droplets bounces back, which causesthe force sensor registering a larger force. In Fig. 4.4 the results for the nozzle that is used in themain experiments with the EHPC are shown. Its profile is not as distinct as nozzle A. Obviouslyit is not always clear what the middle of the spray is in Fig. 4.4, only at an angle of 300 and240 the middle of the spray can be identified. The middle of the remaining sprays are located at

60

intervals removed from the two identified sprays. In Fig. 4.4 no high measured forces between

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0 50 100 150 200 250 300 3500

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

angle [degrees]

averageforce[N]

Figure 4.3: Results of the momentum mea-surements around nozzle A. The arrows in-dicate the center position of the individualsprays.

0 50 100 150 200 250 300 3500

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

angle [degrees]

averageforce[N]

Figure 4.4: Results of the momentum mea-surements around nozzle C. The arrows in-dicate the center position of the individualsprays. The third arrow on the left side in-dicates the center of the spray which is usedin further visualization experiments.

neighboring sprays are present.

For both measurements the average momentum for each spray is determined. The angle at whichthe measured force is at its maximum is the center of a spray. The measuring point whichrepresents the center position of a spray, and its two neighboring positions, are averaged to obtainthe average spray momentum. In tables 4.2 and 4.3 the results are summarized.

Table 4.2: Measured momentum of the sprays of nozzle type A.

Hole nr. 1 2 3 4 5 6Average momentum flux [N] 3,69 4,04 3,74 3,61 3,58 3,52 [N] 0,18 0,12 0,08 0,1 0,16 0,14Relative error [%] 4,9 3,0 2,1 2,8 4,5 4,0

Table 4.3: Measured momentum of the sprays of nozzle type C.

Hole nr. 1 2 3 4 5 6Average momentum flux [N] 2,92 2,85 2,95 2,9 2,96 3,272 [N] 0,04 0,05 0,05 0,08 0,06 0,07Relative error [%] 1,4 1,8 1,7 2,8 2,0 2,1

In Fig. 4.5 the data from tables 4.2 and 4.3 are graphically processed.Both nozzles show an increase in momentum flux of the sprays around one hole; hole 2 of nozzleA and hole 6 of nozzle C. For nozzle A this increase in momentum flux is about 8-15 % compared

to the rest of the holes. For nozzle C this value is 10-15 %. Most probable cause is an asymmetricgeometry of the needle, needle tip or more likely the geometry of the needle tip housing. The

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distance between the needle and the hole differs for each hole, blocking the flow to the holes ina different degree causing an asymmetrical momentum flux distribution of the sprays. In [KK04]similar experimental results have been obtained; differences between spray momentum flux of a

single nozzle ranged from 14 % to 22 %. In [KK04] this asymmetrical phenomenon was also noticedin mass flow through the holes, ranging from 13 % to 14 %.

1 2 3 4 5 62.5

3

3.5

4

4.5

Nozzle number

Av

erageforce[N]

Figure 4.5: Average momentum flux of the spray of nozzletype A (blue line) and C (red line).

Nozzle A has a average spray momentum flux of 3,69 N and nozzle C has a average spraymomentum flux of 2,97 N, which means nozzle A has 19,5 % larger momentum compared tonozzle C. Due to the larger Qh of nozzle A a larger fuel mass is injected during one injection. Themomentum flux is related to the mass flow by Mm2:

M = m veff = m mfAeff

(4.1)

Nozzle A has a 19,7 % larger Qh than nozzle C which theoretically would result in a 43,4 % largermomentum flux for nozzle A. The difference between the measured and predicted momentum fluxcan be caused by geometrical differences between the two nozzles. Also the sprays from nozzle Acan have a larger dispersion angle which decreases the momentum flux in axial direction. Thiscould explain the high measured forces between the sprays as shown in Fig. 4.3, which are absent

in Fig. 4.4. Unfortunately no further quantitative conclusions can be drawn on this matter.The spray coming out of hole number 3 of nozzle C will be used in further visualization experimentsdescribed in part II and III. This hole produces a spray with an average momentum compared tothe other sprays produced by this nozzle.

4.1.3 Momentum flux profile of a single spray (blocked nozzle)

From Figs. 4.3 and 4.4 in section 4.1.2 it already became apparent that the momentum flux profileof a single hole is not exactly symmetrical. Therefore momentum flux measurements are conductedto obtain a momentum flux profile of a single spray. Nozzle B is used for these experiments.All holes, except one, are blocked of this nozzle and the force that the single spray exerts ismeasured. Measurements are conducted with small intervals in rotation of the force sensor toobtain a complete momentum flux profile of the spray. This is conducted for two neighboringsprays of the nozzle. The results are shown in Fig. 4.6. The maximum momentum flux of both

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sprays are 4,05 0,04 N and 4,02 0,03 N, only deviating 0,7 % from each other. The angleover which the momentum flux is measured is larger for one hole. But this is not the actual sprayangle, which is smaller. This is caused by the geometrical setup of the sensor tip and the nozzle.

Most important result is that the geometry of the holes cause nearly symmetrical momentum fluxprofiles.The maximum momentum flux of the spray, around 4,0 N, is considerably higher than the averagemomentum flux of 3,7 N of nozzle A, which is a relative difference of 8 %. We cannot determinewhether this can be attributed to an extreme asymmetry between the individual nozzle holes likefound for hole 2 from nozzle A in Fig. 4.5 or due to blocking of the other holes with nozzle B.In a fully open nozzle the pressure in the sac volume drops when the needle opens. Because inthis case only one hole is available the pressure drop in the sac volume is less and thus a higherpressure difference across the nozzle hole is maintained. According to Bernoullis law (Eq. 2.5)this increased pressure difference results in an increased flow velocity through the nozzle hole.Also the mass flow will increase due to the increased velocity. X.L.J. Seykens has used AMESimsoftware to simulate the difference between a normal nozzle and a nozzle from which only one hole

is open. It resulted in a 5,8 % increase in mass flow and 5,1 % increase in velocity.

40 30 20 10 0 10 20 30 400

0.5

1

1.5

2

2.5

3

3.5

4

4.5

angle [degrees]

averageforce[N]

Figure 4.6: The momentum flux profile of the spray of twoholes of nozzle B. The middle of the force profiles are placedon the 0 mark afterwards.

The increased mass flow and increase in velocity combined result in a 11,2 % increase in

momentum flux. The real value should be slightly lower because the increase in the velocityincreases the effect of cavitation which reduces the mass flow and thus also the momentum. Themeasured difference of 8 % is of the same magnitude as s11 ,2 % making the blocking of the nozzlea probable cause for the increase in momentum.

4.2 Mass flow measurements

Due to restriction of the high pressure pump mass flow measurements are only possible withnozzles from which only one hole is open. The measurements are conducted with nozzle B. Thesame holes are used as in the determination of the momentum profile of a single spray. Theinjection pressure is held constant and the back pressure in the Zeuch vessel is changed to get arange of prailpzeuch

pzeuch, which is the CaN. This is done for five different injection pressures. In Fig.

4.7 and 4.8 the results are shown for the measurement of the two holes respectively. Normally the

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lines in both figures should lie on top of each other. This is obviously not the case, especially inFig. 4.7 (these measurements were conducted after the measurements from which the results areshown in Fig. 4.8). The probable cause of this deviation is a drift in the injection pressure sensor

(i.e. common rail pressure sensor); after the high pressure pump was switched off the measuredpressure remained at 10-20 bar while it should be 0 bar. This can also be noticed in the Figs.4.7-4.8: the largest deviation is present at relative low injection pressures where the error causedby the drift results in the largest relative error. Unfortunately this problem became apparent afterthe epoxy blocking on nozzle B had failed and made nozzle B unsuitable for further measurements.Most important result is the Cd value at high CaN. Due to the drift in the pressure sensor it isdifficult to determine a reliable Cd value. By averaging these values the Cd is 0,77 pm 0,02 for thefirst hole, and 0,78 0,01 for the second hole.The CaNc in Fig. 4.7 is 2 2,5. In Fig. 4.8 the CaNc is 1,5 2. It was expected, on the basisof earlier experiments, that CaNc is around 0,5. The deviation could be caused by the drift inthe pressure sensor. The measurements began with a low injection pressure and subsequently theinjection pressure was increased.

0 30 60 90 120 150.7

0.75

0.8

0.85

0.9

CaN

Cd

100 bar

150 bar

200 bar

300 bar

400 bar

Figure 4.7: Results of the mass flow measure-ments of one hole of nozzle B for the five dif-ferent injections pressures: 100, 150, 200, 300and 400 bar.

0 30 60 90 120 1500.7

0.75

0.8

0.85

0.9

CaN

Cd

100 bar

150 bar

200 bar

300 bar

400 bar

Figure 4.8: Results of the mass flow measure-ments of another hole of nozzle B for the fivedifferent injections pressures: 100, 150, 200,300 and 400 bar.

4.3 Experimentally determined nozzle characteristics

Only from nozzle B all dimensionless parameters can be determined for two of its holes. Theseparameters are summarized in table 4.4. Nozzle B and A are similar as they are from the same type.Nozzle A is compared to C in section 4.1.2 (nozzle C is used in the main experiments in the EHPC).It was shown in that section that the sprays from nozzle C produced spray with substantionallylower momentum fluxes. Thus it must be noticed that the dimensionless parameters in table 4.4are not exactly similar to the dimensionless parameters of nozzle C.

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Table 4.4: Dimensionless parameters for nozzle B for two holes.

Hole nr. 1 2

Mf [N] 4, 05 0, 04 4, 02 0, 03mf [g/s] 8,5 0,1 Not measuredCd 0,77 0,02 0,78 0,01Cm 0,61 0,03 0,61 0,03Cv 0,96 0,02 0,96 0,02Ca 0,66 0,04 0,66 0,04

Results for nozzle C In section 4.1.2 it is shown that the momentum flux is asymmetricallydivided over the sprays. Visualization experiments are conducted on sprays of hole 3 which hasan average momentum flux for this nozzle. In section 4.1.3 it was shown that a detailed singlemomentum flux profile is typically symmetrical. Although this is tested with another nozzle it is

assumed the same holds for hole number 3 of nozzle C.

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Chapter 5

Conclusion

The measured force profile of the injections, for example as shown in Fig. 4.2, have a repro-ducibility uncertainty ranging from 1,4 to 4,5 %. For nozzle C, which is used in the visualizationexperiments, the reproducibility uncertainty is lower: 1,4 to 2,8 %. This uncertainty is consider-able lower than other uncertainties in the visualization experimented presented in Part II and III.Therefore it is assumed that variations in the needle lift and other effects which take place beforethe fluid exits the nozzle orifice, have a negligible influence on the visualization results.Measurements of nozzle A and C showed that the individual holes of each nozzle do not producesprays with equal momentum flux. This asymmetry is caused by asymmetry of the needle or thesac volume geometry. Difference between the measured momentum of the spray are as high as 22%. This causes no problems for the performed visualization experiments. However, it is importantto realize that due the asymmetry of the nozzles other (future) measurements with the same typeof nozzles cannot be compared one on one.Measurements with a blocked nozzle showed that it produces sprays with a higher momentum flux

compared to the sprays of a unblocked nozzle. The difference is about 8 to 10 %. The increaseis caused by the increased sac volume pressure. A blocked nozzle has better visual access but itcompromises the spray characteristics. In the main measurements presented in Part II and III noblocked nozzles were used.The performed mass flow measurements are not reliable due the drift in the pressure signal of theinjection pressure sensor. Also the mass flow measurements can only be conducted on a blockednozzle (the high pressure pump cannot maintain the necessary rail pressure when all holes areopen). However, it is unknown what influence the blocking of the holes has on the flow charac-teristics inside the nozzle. The unreliability in the mass flow determination effects the calculatedvalues Cd, Cv and Ca. Due to these factors the nozzle characteristics presented in table 4.4 coulddeviate somewhat from reality.

In Part I and II visualization experiments will be presented. There is no direct relation of thevisualization experiments with the momentum flux or mass flow measurements. But it is estab-lished , that substantial variations exist between the individual sprays of the holes of a nozzle.There are differences between two nozzle of the same type. Therefore the results in Part I and IIare unique for hole 3 of nozzle C.

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Part II

Penetration and dispersionresearch of non-reacting

evaporating diesel sprays

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Chapter 6

Behavior of the evaporating spray

For engine designers insight in the behavior of an evaporating fuel spray is of great importance.Improvements in injection equipment reduce emissions and increase power by a more effectivecombustion process.The most essential aspect of the spray behavior is the dispersion and the penetration of the spray.The angle of the spray is a measure for the dispersion of the spray. This can be related to the airentrainment in the spray:

Air entrainment a d0 Uf tan(/2) (6.1)

where a is the density of the ambient air, d0 is the orifice diameter, Uf the velocity of the injectedfuel and is the spray dispersion angle. The location of the spray tip as function of time is used as ameasure for the penetration of the spray. In [NS96] results for both dispersion and penetration arepresented and thoroughly analyzed, with the emphasis on the influence of the ratio a (ambient air

density. Therefore [NS96] is extensively used in this part to compare the results. In section 6.1 thetrend according to various literature of the dispersion angle of non-evaporating will be lined out.Also the difference between trends of non-evaporating and evaporating sprays will be emphasized.In section 6.2 trends and correlations according literature sources are provided for non-evaporatingsprays. The difference between non-evaporating spray penetration and evaporating spray pene-tration is shortly lined out. In chapter 7 the methods used for conducting the experiments aredescribed. Also the methods used for analyzing the measurement results are described includinga statistical analysis. The results of the main measurements from which the dispersion angle andpenetration are determined are presented in chapter 8. Further discussion and comparison withthe results presented in Part III, where the liquid core of the spray is investigated, are given inchapter 12.

6.1 Dispersion angle of non-evaporating and evaporatingsprays

As the spray progresses, air entrainment causes the spray to grow in diameter, which is alsoreferred to as the dispersion of the spray. The air entrainment occurs with a constant rate whichresults in a constant growth of the spray. Therefore the spray is cone shaped and the angle ofthis cone is a measure for the dispersion of the spray. There is no appropriate model availablewhich can determine the dispersion angle. The measurements conducted at the TU/e can only becompared with results from other investigations. In [Sie99] the following correlation is presentedfor the dispersion angle:

tan(/2) = 0,260 a

f0,19 0,0043

f

a

(6.2)

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where a and f is the ambient air density and fuel density, respectively. It can be noticed thatthe correlation Eq. 6.2 is independent on the temperature. In [HIY96] the following correlation isused:

= 0,05

a dpnozzle d202a

0,25(6.3)

where dpnozzle is the pressure drop across the nozzle orifice, d0 the nozzle orifice diameter anda the dynamic viscosity of the ambient air. The in Eq. 6.3 depends both on the ambient airdensity and temperature.Research on the spray angle is mainly concentrated on non-evaporating sprays. Hiroyasu and Arai[HA90a] conducted experiments with ambient air densities up to 30 kg/m3 and fuel pressures upto 800 bar. They identified a complete spray regime in which the spray dispersion angle is mainlydependent on orifice parameters and the af ratio. The dependence of the dispersion angle on

the ambient air density was 0,26a . Varde [VPV84] found in a similar research, with ambient air

densities up to 40 kg/m3

and injection pressures between 500 and 1500 bar, a dependence of thedispersion angle on the ambient air density of 0,33a . In another investigation Wakuri [WFAT60],with densities less than 22 kg/m3 and injection pressures between 400 and 750 bar, an dispersionangle dependence of 0,4a is found. With injection pressures up to 1200 bar and with densitiesbetween 15 and 55 kg/m3 a dispersion angle dependence of 0,19a is established in [BV94].Spray dispersion under evaporating conditions has not been extensively explored. In [SNH93]there are indications that there might be an increase in the spray dispersion angle as result of thevaporization. These measurements were executed at an ambient air density of 12,5 kg/m3 and atemperature of 773 K.

0.004 0.01 0.03 0.1 0.3

0.1

0.2

0.3

0.4

a/

f

tan(/2)

Figure 6.1: The dispersion angle versus theaf

ratio for non-evaporating sprays which are

presented in [NS96]. The upper blue line is thepower fit for the measurements with the noz-zle with d0 = 340 m (triangle data points).The lower red line is the power fit for the mea-surements with the nozzle with d0 = 257 m(cross data points) and with d0 = 198 m

(circle data points). Ta 450 K and Ta 300 K .

0.004 0.01 0.03 0.1 0.3

0.1

0.2

0.3

0.4

a/

f

tan(/2)

Figure 6.2: The dispersion angle versus theaf

ratio for evaporating sprays which are pre-

sented in [NS96]. The dashed line are thepower fit curves from Fig. 6.1. The upperblue line is the power fit for the measurementswith the nozzle with d0 = 340 m (trian-gle data points). The lower red line is thepower fit for the measurements with the noz-

zle with d0 = 257 m (cross data points)and with d0 = 198 m (circle data points).Ta 1000 K.

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In Fig. 6.1 the results of [NS96] are shown for an non-evaporating spray. The measurementwere conducted with mainly Ta 450 K and Ta 300 K. Three different nozzles were used inthese experiments. One nozzle has a hole diameter of d0 = 340 m. The other two nozzles have

a d0 = 257 m and d0 = 198 m. The measurements with the latter two nozzles produce similarresults regarding the dispersion angle. This is probably caused by a difference in the geometryof the nozzle which compensates for the smaller d0 = 198 m. An angle dependence of

0,19a is

found for these non-evaporating sprays which is similar to that what can be found in [BV94]. Itis suggested that with a high af ratio the spray behaves more like an incompressible jet. This

research also showed that the influence of the temperature on evaporating sprays seemed to benegligible. In Fig. 6.2 the results of experiments with evaporating sprays are compared to theresults of the non-evaporating sprays. These measurements are mainly conducted at Ta 1000 Kbut also two measurements are conducted at Ta 600 K and four measurements at Ta 1400 K.At low af ratios the evaporating sprays have considerable smaller angles compared to the non-

evaporating sprays. This difference is up to 30 %. As the af ratio goes up the difference of the

dispersion angle betwee

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Verslag Final Version Roel Peters