A thermodynamic analysis of the use of exhaust gas recirculation in spark ignition engines including the second law of thermodynamics

Abstract

This work examines results from a thermodynamic engine cycle simulation of a spark ignition engine with exhaust gas recirculation (EGR). EGR is a common feature of today's engines and is an effective technique to reduce combustion temperatures and nitrogen oxide emissions. Results were obtained for an automotive engine using isooctane. These results are presented as functions of EGR for constant load and speed, and as functions of load and speed for constant EGR level. For both a cooled and an adiabatic EGR configuration, the thermal efficiency first increased, reached a maximum, and then decreased as the EGR levels increased. The thermodynamic gains were largely due to favourable thermodynamic properties, reduced cylinder wall heat losses, and, for part-throttle operation, reduced pumping losses as the EGR level increased. The destruction of availability during the combustion process was highest for the cooled EGR configuration. For the cases examined, the destruction of availability due to combustion ranged from about 18 per cent to 22 per cent of the original fuel availability.