In-cylinder studies of the effects of CO 2 in exhaust gas recirculation on diesel combustion and emissions

Abstract

Abstract

This paper reports the results of the effects of CO₂ in exhaust gas recirculation (EGR) on diesel combustion and emissions. The experiments were carried out on a specially designed single-cylinder diesel engine. In-cylinder measurements were obtained from the optically accessible swirl chamber using high-speed shadowgraphy, the two-colour method and laser extinction. Furthermore, 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 dilution effect of conventional EGR. This so-called replacement EGR method was characterized by the typical NO_x and smoke trade-off, where NO_x 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 NO_x and smoke emissions. The mechanisms of these two different EGR modes on diesel combustion and emissions were examined using the above in-cylinder measurement techniques and exhaust emission analysis.