Second law analysis of hydrogen–air combustion in a spark ignition engine

Besides its renewable nature and low emission advantage, hydrogen has higher exergetic efficiency of combustion compared to hydrocarbon fuels. This makes it an attractive alternative fuel for internal combustion engines. The present work concerns the estimation of irreversibilities associated with various sub-processes occurring during combustion in a hydrogen fueled spark ignition engine. A quasi-three zone phenomenological combustion model is used for predicting the pressure and temperature histories of a single cylinder, four stroke spark ignition engine operating at equivalence ratios of 0.3–0.75 in the speed range 1500–3500 rpm. For each sub-process, the history of availability destruction during combustion and the effects of operating conditions are discussed. Measures are proposed for improving the exergetic efficiency by mitigating availability destruction. It is observed that chemical reaction is the major contributor to irreversibility generation, followed by pressure equilibration and heat loss to walls. While more than 94% of the fuel supplied undergoes combustion, nearly 20–30% of the reactant availability is destroyed. Charge preheating, product mixing and piston motion are observed to have negligible effects on irreversibility generation.