Effects of hydrogen-enriched biogas on combustion and emission of a dual-fuel diesel engine

Abstract

ABSTRACTIn recent years, due to stringent emission regulations, vehicle manufacturers have been compelled to cut down noxious pollutants released from diesel engines. Different alternative solutions have been recommended to achieve this challenging task. One of these alternative solutions is the utilization of biogas in addition to the use of liquid diesel. In this regard, the current study investigates the combustion characteristics and exhaust emissions of a turbocharged, direct injection, diesel engine operating at constant speed (1800 rpm) and under dual-fuel mode with diesel as the pilot fuel and biogas (generated from pig manure and corn straw) enriched by various H2 percentages (5-20% by vol.). The impacts of hydrogen addition in biogas on combustion and pollutant emissions were investigated and compared with those of biogas-diesel dual-fuel operation. Numerical simulations were carried out at two different engine loads corresponding to brake mean effective pressure (BMEP) of 0.425 and 1.7MPa. The findings revealed that Hydrogen addition in biogas resulted in a substantial rise in heat release rate (HRR) and pressure peak due to the rapid combustion during the premixed combustion stage, as compared to biogas-diesel fuel operation. The peak pressure and maximum HRR occurred earlier than that of biogas-diesel fuel operation. Concerning the emissions, the results indicated that CO2 emissions were found to be lower for the hydrogen-enriched biogas (HEBG) as compared to biogas-diesel fuel operation at all engine loads. Significant reductions in CO2 emissions of up to 56% were observed with 20% of H2 in biogas. However, the addition of hydrogen in biogas increased NOx, CO, and hydrocarbon emissions. NOx emissions increased when the percentage of H2 was increased in biogas.