In-cylinder studies of the effects of CO2 in exhaust gas recirculation on diesel combustion and emissions

This paper reports the results of the effects of CO2 in exhaust gas recircu lation (EGR) on diesel combustion and emissions. The experiments were carri ed out on a specially designed single-cylinder diesel engine. In-cylinder m easurements were obtained from the optically accessible swirl chamber using high-speed shadowgraphy, the two-colour method and laser extinction. Furth ermore, in-cylinder pressure measurements from the combustion chambers were used to derive the heat release rates during combustion. Two experiments were carried out on the effects of CO2 on diesel combustion and pollutant formation. In the first series of experiments, CO2 was used to replace some of the oxygen in the intake mixture, which simulated the di lution effect of conventional EGR. This so-called replacement EGR method wa s characterized by the typical NOx and smoke trade-off, where NOx reduction was accomplished at the expense of exhaust smoke. In the second series of tests, CO2 was added to the intake charge so that the oxygen concentration in the combustion chamber was not affected. In this additional EGR method, CO2 was found to suppress both NOx and smoke emissions. The mechanisms of t hese two different EGR modes on diesel combustion and emissions were examin ed using the above in-cylinder measurement techniques and exhaust emission analysis.