Optimization of fuel ignition resistance to achieve Optimization of fuel ignition resistance to achieve

combustion stability and ultra-low emissions

in CIDI engines

A. J. Smallbone, A. Bhave, A.R. Coble

cmcl innovations, Cambridge, U.K.

N. Morgan, G.T. Kalghatgi

Shell Global Solutions, PO Box1, Chester, UK

1

Towards clean diesel engines....

(a) using more premixed combustion(a) using more premixed combustion

(b) modifying the fuel?

(c) after-treatment solutions

2

modelling fuels, combustion and emissions

Stochastic Reactor Models

• CPU time seconds to minutes

• predictive combustion and emissions

• turbulence, heat transfer, MDI, EGR,

fuel volatility

1D multi-cycle software tools

breathing, valve train and

engine optimisation

• CPU time seconds/cycle

• poor predictive combustion

• poor predictive emissions• properly account for chemical kinetics

3D CFD software tools

In-cylinder optimisation

• CPU time days/cycle

• predictive combustion

• predictive emissions in

some cases

• limited by CPU time

• integration into 1D cycle tools

• more efficient solution for combustion

optimisation

• properly account for chemical kinetics

i.e. ignition, extinction, misfire, flame

propagation and emissions

3

Modelling challenges in combustion

Thermodynamics

•compression/ expansion

• heat transfer

Mixture preparation

•injection events

•evaporation

•turbulent mixingCI

•turbulent mixing

Combustion chemistry

•Ignition (delay)

•Flame propagation

•Local extinction

•(gas phase) emissions

Advanced particle model

•Soot formation & oxidation

•Coagulation

SI

ignition

principles of the model

Stochastic Reactor Model

•Represent in-cylinder composition as 100 representative particles (fuel-air parcels)

•Heat transfer with walls

•Mixing

•Solution of detailed chemical kinetics (~200 species 1000 reactions)

•Injection

Particle Model (PBM)

•soot chemistry includes a variety of unsaturated HCs and PAHs

•interaction of soot chemistry with the gas phase chemistry

•validation carried out in fuel-rich flame and engine experiments•validation carried out in fuel-rich flame and engine experiments

•CPU time 6-90 mins/engine cycle

reactive primary particles

agglomeration of complex particle aggregates

10 nm 10 nm

Using more premixed combustion

6

different modes of combustion

Mode DISI advanced CIDI

SOI [aTDC] -100 -100 -2

EOI [aTDC] -90 -90 25

C.R. 11 15.0 15.0

PIVC [bar] 0.75 1.2 1.2

TIVC [K] 450 450 550

Fuel gasoline diesel diesel

Fuel [mg] 10.0 10.0 10.0

1500 RPM ~2.62BMEP 30% EGR

Fuel [mg] 10.0 10.0 10.0

PPCI/LTC/HCCI CIDIDISI7

Animations available at http://www.cmclinnovations.com/products/srmsuite/phi-t-movies.html

Modifying the fuel

8

engine specifications

Compression ratio (CR) 15.9:1

Displacement 0.537 l

Bore 88 mm

Stroke 88.3 mm

Connection rod length 149 mm

84 PRF n-heptane

RON 84 0

MON 84 0

vol. % of iso-octane 84 0

vol. % of n-heptane 16 100

Engine specifications Fuel properties

Objective: Fuel-engine correlations for PPCI combustion using physics-based simulation tool

9

Connection rod length 149 mm

Inlet valve open (IVO) 362 CAD

Inlet valve close (IVC) 595 CAD

Exhaust valve open (EVO) 143 CAD

Exhaust valve close (EVC) 385 CAD

vol. % of n-heptane 16 100

C 7.83 7.0

H 17.67 16.0

LHV (MJ/kg) 44.4 44.6

Validation against engine operation •Parameterisation (500 resolutions of model)•Blind testing (heat release, NOx) (50 resolutions)

Fuel and engine parametric sweep•Optimise injection timing for 10 fuels (2000 resolutions)•Cycle-to-cycle variations (200 resolutions)

Alternative CFD technology (3 to 210 years on 1 PC)

model calibration

Speed 1200 RPM

Manifold pressure 1.0 bar (a)

Manifold

temperature65 deg C

Exhaust pressure 1.0 bar (a)

Engine operating point

10

Exhaust pressure 1.0 bar (a)

IMEP 4.0 bar

Injection pressure 650 bar

Equivalence ratio 0.370

Air mass flow rate 6.03 g/s

Example: impact of fuel Fuel 84PRF N-hept

SOI [aTDC] -8 -8

EOI [aTDC] -4 -4

1200 RPM 4bar iMEP5% EGR

n-heptane

Animations available at

84 PRF

Animations available at http://www.cmclinnovations.com/products/srmsuite/phi-t-movies.html

model blind testing - I

12

Combustion Delay Peak pressure

model blind testing - II

13

CO emissionsuHC emissions

model blind testing - III

14

NOx emissions PM emissions

criteria for optimal fuel specification for PCCI

Combustion characteristics

50%MFB @5CAD

15

Combustion delay

Local composition and emissions 50%MFB @5CAD

16

Local composition at ignition Emissions

criteria for optimal fuel specification for PCCI50%MFB @5CAD

5% perturbations in

(a)TIVC

(b)PIVC

17

Combustion stability

(b)PIVC

(c)Total fuel injected

optimal combustion delay for PCCI?

• How do we exploit this?

• Do we really need

another fuel standard?

Increase CR?

18

• Increase CR?

• How about other load-

speed points?

19

On-going development: aftertreatment

Particle modelling

model schematic

srm suite plug-flow plug-flow

Cu-Cr-Ag-K-Ce-Zr-Al catalyst(Prasad and Bella, 2010)

DPF

Addition of PM/catalytic reactions to chemical kinetic mechanism...ongoing coagulation

BCs: Temperatures, pressures and residence time from standard GT-Power simulations

results

srm suite plug-flow plug-flow

1108K 958K

900K

results

srm suite plug-flow plug-flow

Experiment: 20% reduction of PM

22.9%

DOC parametric study – catalyst material

Light off temperaturelargely independent of k0

summary

advanced analysis tools More premixed combustion

Integrated after-treatment

solutionsPM-combustion stability trade-off

Other fuel/engine optima

Thank you for listening...any questions?

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