Optimization Of Fuel Ignition Resistance To Achieve Combustion

Transcript

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 (b) modifying the fuel? (c) after-treatment solutions 2 modelling fuels, combustion and emissions 1D multi-cycle software tools breathing, valve train and engine optimisation • CPU time seconds/cycle • poor predictive combustion • poor predictive emissions 3D CFD software tools In-cylinder optimisation • CPU time days/cycle • predictive combustion • predictive emissions in some cases • limited by CPU time Stochastic Reactor Models • CPU time seconds to minutes • predictive combustion and emissions • turbulence, heat transfer, MDI, EGR, fuel volatility • properly account for chemical kinetics i.e. ignition, extinction, misfire, flame propagation and emissions • integration into 1D cycle tools • more efficient solution for combustion optimisation 3 Modelling challenges in combustion Thermodynamics •compression/ expansion • heat transfer CI Mixture preparation •injection events •evaporation •turbulent mixing Combustion chemistry •Ignition (delay) •Flame propagation •Local extinction •(gas phase) emissions SI ignition Advanced particle model •Soot formation & oxidation •Coagulation 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 •CPU time 6-90 mins/engine cycle reactive primary particles 10 nm 10 nm agglomeration of complex particle aggregates Using more premixed combustion 6 different modes of combustion 1500 RPM ~2.62BMEP 30% EGR 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 gasoline diesel diesel 10.0 10.0 10.0 Fuel Fuel [mg] Animations available at http://www.cmclinnovations.com/produ cts/srmsuite/phi-t-movies.html DISI PPCI/LTC/HCCI CIDI 7 Modifying the fuel 8 engine specifications Objective: Fuel-engine correlations for PPCI combustion using physics-based simulation tool Engine specifications Compression ratio (CR) Displacement Bore Stroke Connection rod length Inlet valve open (IVO) Inlet valve close (IVC) Exhaust valve open (EVO) Exhaust valve close (EVC) Fuel properties 15.9:1 0.537 l 88 mm 88.3 mm 149 mm 362 CAD 595 CAD 143 CAD 385 CAD RON MON vol. % of iso-octane vol. % of n-heptane C H LHV (MJ/kg) 84 PRF 84 84 84 16 7.83 17.67 44.4 n-heptane 0 0 0 100 7.0 16.0 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) 9 Alternative CFD technology (3 to 210 years on 1 PC) model calibration Engine operating point Speed Manifold pressure Manifold temperature Exhaust pressure IMEP Injection pressure Equivalence ratio Air mass flow rate 1200 RPM 1.0 bar (a) 65 deg C 1.0 bar (a) 4.0 bar 650 bar 0.370 6.03 g/s 10 Example: impact of fuel n-heptane Fuel 84PRF N-hept SOI [aTDC] -8 -8 EOI [aTDC] -4 -4 1200 RPM 4bar iMEP 5% EGR Animations available at http://www.cmclinnovations.com/produ cts/srmsuite/phi-t-movies.html 84 PRF model blind testing - I Combustion Delay Peak pressure 12 model blind testing - II uHC emissions CO emissions 13 model blind testing - III NOx emissions PM emissions 14 criteria for optimal fuel specification for PCCI 50%MFB @5CAD Combustion characteristics Combustion delay 15 Local composition and emissions Local composition at ignition 50%MFB @5CAD Emissions 16 criteria for optimal fuel specification for PCCI 50%MFB @5CAD 5% perturbations in (a)TIVC (b)PIVC (c)Total fuel injected Combustion stability 17 optimal combustion delay for PCCI? • How do we exploit this? • Do we really need another fuel standard? • Increase CR? • How about other loadspeed points? 18 On-going development: aftertreatment Particle modelling 19 model schematic srm suite plug-flow plug-flow DPF Cu-Cr-Ag-K-Ce-Zr-Al catalyst (Prasad and Bella, 2010) Addition of PM/catalytic reactions to chemical kinetic mechanism...ongoing coagulation BCs: Temperatures, pressures and residence time from standard GT-Power simulations results plug-flow srm suite 1108K plug-flow 958K 900K results srm suite plug-flow plug-flow Experiment: 20% reduction of PM 22.9% DOC parametric study – catalyst material Light off temperature largely independent of k0 summary advanced analysis tools PM-combustion stability trade-off Other fuel/engine optima More premixed combustion Integrated after-treatment solutions Thank you for listening...any questions? www.cmclinnovations.com