Influence of ignition timing on combustion and emissions of a spark-ignition methanol engine with added hydrogen under lean-burn conditions

Ignition timing is an important parameter that impacts flame formation, early combustion process, and emissions of spark-ignition (SI) engines. Hydrogen as an auxiliary fuel may improve combustion and emission characteristics of SI engines. In this study, we experimentally investigated the effects of ignition timing on combustion and emissions of an SI methanol engine with added hydrogen at different engine speeds. At low engine speeds with various ignition timings, increasing hydrogen decreases indicated mean effective pressure, maximum cylinder pressure, maximum heat release rate, and combustion duration. While at high engine speeds with different ignition timings, more hydrogen increases the indicated mean effective pressure, maximum cylinder pressure, maximum heat release rate, and decreases the ignition delay, combustion duration, and COVimep. By comparison with cases without hydrogen, the COVimep can be respectively reduced by 21.5% and 36.8% with hydrogen ratios of 3% and 6% at engine speed of 2400 rpm and ignition timing of 28 °CABTDC. In addition, hydrogen additive decreases the carbon monoxide (CO) and hydrocarbon (HC) emissions at low engine speeds, but increases the nitrogen oxides and soot emissions at high engine speeds under various ignition timings.