Studying the effects of manifold pressure boosting and EGR on combustion and NO_x emission of hydrogen-fueled SI engine

Aiming to the global energy insecurity due to extensive dependence on fossil fuels, hydrogen is supposed to provide relief by researchers. However, employed to combustion engines, this green fuel leaves hazardous NO_x and limits output due to low volumetric energy content. Hence, improving operating parameters like compression ratio and manifold pressure, and NO_x mitigating technique like EGR may prove a boon. Therefore, in the present study, combustion and NO_x emission behavior of the SI-engine is studied under variable manifold air pressure (MAP) (up to 130 kPa) and EGR (up to 15%) at compression ratio 14:1. The outcomes shows the flame development increased by 1.24%, while flame propagation is increased by 1.63% by MAP boosting due to increased air and fuel supply. Cylinder pressure and heat-release rate (HRR) are also surged due to the increased fuel supply to maintain excess-air ratio (λ). However, peak cylinder pressure is retarded due to elongated combustion. The exhaust gas temperature (EGT) is increased by 19.4%, while elevated T_max is observed to shoot up NO_x by 40%. Combustion in improved at low EGR due to reduced λ, and also the specific NO_x. At higher EGR rate deteriorated combustion due to increased heterogeneity by high dilution, increasing combustion duration, cooling losses and reducing cylinder pressure, T_max and EGT. A 9.33% and 5.67% increase in CA10 and CA10–90 respectively is observed for 130 kPa at 15% EGR than no EGR. The rapid reduction in oxygen and higher heterogeneity reducing residence time, resulted in rapid drop (33% at N/A to 42.68% at 130 kPa for 15% EGR) in NO_x by EGR. The coefficient variation is reduced by boosting MAP but increased severely at higher EGR, which restricts operating EGR rate.