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.

A novel method to improve the cold starting ability of a low compression ratio diesel engine through recompression of the charge

“…This is because of the increase in the concentration of the fuel vapor/partially burnt products trapped in the cylinder. 14,15 Several theoretical studies have been done for increasing the peak compression temperature by retaining some of the hot compressed air in a pre-chamber located in the combustion chamber 16 or by increasing the effective CR by closing the intake valve at bottom dead center (BDC). 17 In summary, there is still need to develop a robust and fast method for starting a diesel engine under cold conditions which can be used irrespective of the engine size.…”

Influence of nozzle geometry on ignition and combustion for high-speed direct injection diesel engines under cold start conditions

“…In spite of all the improvements made in diesel technology to date, engine starting is still a problem for current light-duty engines at low ambient temperature and it is a limiting factor for future design trends. Depending on ambient temperature, the starting process of a diesel passenger car engine may result in long cranking periods with a large amount of pollutant emissions [1,2,3,4] or in the complete incapability of starting the engine. These problems are caused by poor conditions for auto-ignition: relatively low peak compression temperature and pressure.…”