Browse Publications Technical Papers 2019-01-0211

Effect of injection timing on the ignition and mode of combustion in a HD PPC engine running low load 2019-01-0211

This work aims to study the effect of fuel inhomogene-ity on the ignition process and subsequent combustionin a compression ignition Partially Premixed Combustion(PPC) engine using aPrimary reference Fuel(PRF) in lowload conditions. Five cases with injection timings rangingfrom thestart of injection(SOI) at -70 crank angle degrees(CAD) to -17 CAD have been studied numerically and ex-perimentally in a heavy duty (HD) piston bowl geometry.Intake temperature is adjusted to to keep the combustionphasing constant. Three dimensional numerical simula-tions are performed in a closed cycle sector domain usingthe Reynolds Averaged Navier-Stokes (RANS) formula-tion with k-turbulence closure and direct coupling of fi-nite rate chemistry. The results are compared with engineexperiments. The predicted trends in required intake tem-perature and auto-ignition location for a constant combus-tion phasing are consistent with experiments. The simu-lations show that the auto-ignition is critically dependenton both fuel and temperature stratification. The ignitionoccurs in fuel-lean regions but the mixing of the fuel withthe cylinder gas and the cylinder gas temperature stratifi-cation (prior to injection) determines the ignition location.A higher heat release rate is observed in the later injec-tion cases, which is attributed to the higher equivalenceratio of the mixture inside the bowl. Negative temperaturecoefficient (NTC) heat release behaviour of the studiedfuel plays a role in shortening the ignition wave propaga-tion but the impact of the effect varies among the injectioncases. A sensitivity study of combustion efficiency withregard to the intake temperature is performed on two ofthe cases (SOI of -30 CAD and of -63 CAD). While thecombustion phasing is slower and correctly predicted inthe simulations of the advanced injection cases the com-bustion efficiency is found to be very sensitive to the intaketemperature. This is attributed to the high sensitivity of theignition delay time to equivalence ratio and temperature.


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