Combustion and emissions of a direct-injection diesel engine during cold start under different exhaust valve closing timing conditions

Abstract

The residual gas fraction has significant effects on combustion in a diesel engine. However, few researchers have studied the effects of the residual gas on startability and emissions of a diesel engine during cold start, in which the components of the residual gas fraction were very different from those under normal operating conditions. Through experiments conducted on a single-cylinder direct-injection diesel engine, this paper investigated the combustion and emissions characteristics during cold start under different exhaust valve closing (EVC) timing conditions. The results show that an appropriate increase in the residual gas fraction could promote ignition of the first firing cycle and combustion stability significantly during cold start. Residual gas also had significant effects on the emissions during cold start. Opacity during cold start, especially during the initial phase, could be reduced significantly by properly advancing the EVC timing. Owing to the strong thermal effect of residual gas, nitrogen oxide (NO _x ) emissions during cold start tended to increase as the EVC timing was advanced.