Analysis of the degree of constant volume and cooling loss in a spark ignition engine fuelled with hydrogen

Abstract

This study analyses factors influencing the thermal efficiency of a homogeneous charge spark ignition (SI) engine fuelled with hydrogen, focusing on the degree of constant volume and the cooling loss. The cooling loss from the burning gas to the cylinder walls in a homogeneous charge SI engine is quantitatively evaluated by analysing the cylinder pressure diagram and the exhaust gas composition. The degree of constant volume burning and the degree of constant volume cooling are also obtained by fitting the Wiebe function to the rate of heat release calculated using the cylinder pressure diagram. A comparison of combustion and cooling characteristics between hydrogen and methane combustion reveals that the cooling loss in hydrogen combustion is higher than that of methane combustion due to a thinner quenching distance and faster burning velocity for hydrogen combustion. It is also made clear that the higher cooling loss in hydrogen combustion results in lower thermal efficiency of hydrogen combustion as compared to that of methane combustion.