Influence of twin spark on performance and emissions of methanol fueled direct injection engine under multi-injection approach

A numerical investigation is done from the inlet valve closing to the exhaust valve opening at three different fuel injection timings with 0° and 2° crank angle dwell timings. Injection timing is advanced from −23° to −31° crank angle after top dead centre (CA ATDC) at fixed spark timing of −2° crank angle under a compression ratio of 17.3, having an engine speed of 1200 revolutions per minute (RPM). The performance, combustion, and emission characteristics of single and dual spark plug-assisted direct injection spark ignition methanol engine, are compared under pilot (1): main (3) injection approach. Indicated thermal efficiency is higher for dual spark plugs than single spark-plug under both dwell timings. Carbon monoxide, hydrocarbons, and unburned methanol emissions decreased for dual spark plug (SP) than single spark plug (SP); however, NO_x emission is observed to be higher due to a higher rate of peak pressure rise and combustion temperature under both dwell timings. This study also demonstrates the influence of dual spark plugs on swirl, tumble, air-fuel mixing behaviour, and flame speed under a pilot-to-main injection mass ratio of 1:3. Instead of showing any noticeable enhancement in swirl motion, dual spark plug (DSP) encourages tumble motion, which may be an appropriate reason for improved combustion, which further increases indicated thermal efficiency and reduces exhaust emissions.