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
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Towards clean diesel engines....
(a) using more premixed combustion(a) using more premixed combustion
(b) modifying the fuel?
(c) after-treatment solutions
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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
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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
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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
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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
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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
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Combustion Delay Peak pressure
model blind testing - II
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CO emissionsuHC emissions
model blind testing - III
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NOx emissions PM emissions
criteria for optimal fuel specification for PCCI
Combustion characteristics
50%MFB @5CAD
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Combustion delay
Local composition and emissions 50%MFB @5CAD
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Local composition at ignition Emissions
criteria for optimal fuel specification for PCCI50%MFB @5CAD
5% perturbations in
(a)TIVC
(b)PIVC
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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?
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• Increase CR?
• How about other load-
speed points?
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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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