Effects of Hydrogen Enrichment Biogas on Performance and Emissions of Honda GX200 Engine

Biogas and hydrogen are renewable fuels but their properties are very different. Biogas contains CO2 with a different component, so its calorific value and flame rate are low, affecting the quality of the combustion process of the engine. Hydrogen has a flame spread rate 10 times higher than methane. On the other hand, hydrogen can burn with a very poor mixture, with low ignition energy. Because of this property, hydrogen will help improve the combustion quality of biogas engines. In this research, we will simulate the influence of the equivalence ratio, biogas composition, and hydrogen content in the mixture on the indicated engine cycle work and CO, HC, and NOx emissions on the Honda GX200 engine. The optimal equivalence ratio changes from 1.05 to 1.01 as the CH4 composition in biogas increases from 60 to 80%. The rate of heat generation and NOx emissions increases with the hydrogen content of the fuel mixture and the volumetric hydrogen content of the methane mixture of about 20% is optimal to achieve the harmonic between engine performance and emissions. Under optimal operating conditions, the addition of 20% hydrogen content into biogas is found to improve the indicated engine cycle work by 6%, to reduce CO and HC emissions by 5–10 times. However, it increases NOx emission by 10–15% compared to neat biogas fueling mode.