Experimental investigation of effect of compression ratio and fuel composition in a port fuelled methane-hydrogen diesel engine

Fossil fuel sources diminish together with increasing energy demand in process of time. In order to meet global energy requirement alternative fuels have been used in transportation and industrial area for a long time. Natural gas, among the alternative fuels, is used as an energy source for transportation, industrial and in domestic usage nowadays. Because natural gas is firstly economic and environment-friendly fuel with respect to pollutants, it has rapidly found a widespread usage area in vehicles. However, natural gas technically came across some problems in the case of used in diesel engines. When the literature studies were examined, especially at low load it was seen to be highly surpassed the unburned hydrocarbon emissions, specific fuel consumption and observed poor brake thermal efficiency while knock, smoke and NOx formation were observed at high load. In this study, a diesel engine with common-rail fuel injection system used in a light-duty driving car was tested at different loads and compression ratios in a constant speed. For alternative fuels, port fuelled methane and hydrogen enriched methane of 5% and 10% by volume were used. In order to ignite the compressed charge, low amount of the diesel fuel was used as pilot fuel. Compression ratio was changed by using cylinder gaskets between cylinder head and block. Results of the diesel and alternative gas fuels obtained at different operation conditions were compared with each other. Results of the study showed that severe knocking operation and higher smoke emission at original compression ratio-high load condition were observed but greenhouse gas and unburned HC emissions were decreased. By decreasing the compression ratio, knocking decreasing, fuel economy improvement, lower NOx, smoke, CO2 and unburned HC emissions were remarkably observed at high test load. Hydrogen addition in methane was also resulted in lower unburned hydrocarbon and carbon dioxide emissions as well as higher engine effective efficiency and lower specific fuel consumption.