A Study on EGR Utilization in Natural Gas SI Engines Using a Two-Zone Combustion Model

In this study, a computer model of the four-stroke, spark-ignition natural gas engine thermodynamic cycle was developed. This model was constructed based on the mass and energy conservation principles and the combustion process was analyzed using a two-zone combustion model. The combustion angle was calculated by using relationships derived from a turbulent model. In addition, a kinetic model based on the extended Zeldovich mechanism was developed in order to show the ability of Exhaust Gas Recirculation (EGR) on reducing NO emissions. Furthermore, a knocking model was incorporated with the two-zone combustion model in order to predict any auto-ignition that might occur. The aim of this study is to investigate the effect of adding EGR to a stoichiometric mixture on engine performance and NO emissions under several inlet conditions. It was found that using EGR in cooled supercharged inlet conditions (333 K and 250 kPa) can reduce both NO emission and fuel consumption by about 80%, and 19 to 27% (depending on engine speed) respectively compared to a stoichiometric non EGR mixture condition.