A method of reducing the exhaust emissions from DI diesel engines by the introduction of a fuel cut-off system during cold start

摘要

This paper reviews the exhaust emissions from direct injection (DI) diesel engines in the initial period following start-up. The tests were undertake in "cold start" mode (the temperature of the cooling water and lube oil being equal to the ambient temperature) and "warm start" modes (after achieving a state of equilibrium). The results from both states are compared. Exhaust emissions in the period from cold start is very important and must be improved in order to satisfy present day standards worldwide. A significant emission decrease during cold start can be achieved by incorporating selective fuel cut-off during the few seconds directly after beginning of engine crank. Compared to the acceptable gaseous pollutant concentrations, it was observed that an almost 50% reduction in hydrocarbon emission and a 30% reduction in carbon monoxide emissions were obtained (3 minutes of idle run). For the other test variants (warm start and heated catalyst) products of incomplete combustion were eliminated as the result of catalyst reactor action - carbon monoxide emission was minimal, and HC and PM emission was considerably restricted. The decrease in emissions was the result of higher engine temperature and hence better combustion conditions. The upward trend in the exhaust emission levels was caused by a gradual decrease in catalyst temperature caused by engine idle.