Enhancement of in-cylinder flow and combustion in a methane port injection engine by introducing gasoline direct injection

초록

This study investigates the combustion and emission characteristics of a methane port fuel injection (PFI) engine assisted by supplementary gasoline direct injection (DI). Experiments on a 398 cc single-cylinder spark-ignition engine (1,500 rpm, stoichiometric) were combined with validated CFD of flow, turbulence, and mixture formation. The fuel ratio and gasoline injection timing were varied to test whether small gasoline DI can promote combustion. All dual-fuel conditions showed higher indicated mean effective pressure than methane-only (M100) operation and faster combustion than both single-fuel cases, with the highest IMEP case (M30G70, BTDC 300 degrees) exceeding M100 by 3.18 %. Injection timing governed charge motion: intake-stroke injection enhanced tumble and turbulence, whereas excessively early injection weakened it through counter-flow with the incoming charge. Total hydrocarbon emissions increased with gasoline fraction, while nitric oxide emission decreased with increasing methane fraction. Notably, low-gasoline-fraction operation (M70G30, BTDC 240 degrees) shortened combustion duration (CA10-90) by similar to 3.6 % and advanced the start of combustion (CA10) by similar to 0.7 degrees CA, and reduced particulate number emissions about 31 % below M100 through stronger flow and faster combustion. For the 10 % gasoline energy fraction (LHV basis), an upward injection strategy, in which the side-mounted spray is tilted upward from its conventional direction to align with the tumble flow, was most effective at intermediate timing (BTDC 90 degrees), raising IMEP from 5.78 to 5.9 bar (2.1 %) over the reference injection while reducing CO emissions from 1.61 to 1.27 mg/cycle (21 %). These results demonstrate that methane PFI assisted by small gasoline DI is a promising dual-fuel strategy for improving combustion with low particulate emissions.

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