Experimental study on combustion and emission characteristics of a hydrogen-enriched compressed natural gas engine under idling condition

This paper investigates the effect of various hydrogen ratios in HCNG (hydrogen enriched compressed natural gas) fuels on combustion and emission characteristics of a turbocharged spark ignition natural gas engine at idling conditions. The experiments were taken at hydrogen fractions of 0%, 30%, 55% and 75% by volume and were conducted under various operating conditions including different excess air ratio λ and spark timing θig. It is found that under various λ and θig, the addition of hydrogen can significantly reduce CH4 emission and CO emission, although NOx emission increased with the hydrogen addition, it was relatively low at idle conditions compared to other emissions. Meanwhile the addition of hydrogen can significantly reduce COVimep (coefficient of variation of the indicated mean effective pressure), extend the lean burn limit, decrease the combustion duration, achieve higher thermal efficiency and reduce fuel consumption.