Impact of DME as an Oxygenated Alternative Fuel on Combustion and Emissions Reduction in a Transportation Vehicle at Low Load Condition

Abstract

This study investigates the impact of dimethyl ether (DME) on the combustion and exhaust emission characteristics at low engine load operating and pilot injection conditions in a four-cylinder diesel engine that was modified for DME application. The combustion characteristics were analyzed based on the combustion pressure, the rate of heat release, the accumulated heat release, and the premixed combustion characteristics. The emission characteristics were analyzed through the analysis of the nitrogen oxides (NOx), soot, hydrocarbon (HC), and carbon monoxide (CO). The heat release amount per unit crank angle in DME combustion is higher than that in diesel combustion in a pilot injected combustion mode. The accumulated heat release of DME during the main combustion is higher than that of diesel fuel. The pilot injection combustion of DME fuel started earlier than single-injection combustion does. The advanced pilot injection timing caused a decrease of premixed combustion duration and a retardation of premixed combustion phasing. As the pilot injection timing moved to top dead center, the total combustion duration and the heat release amount per unit crank angle decreased. In the emission results, advances of the pilot injection timing caused the decrease of indicated specific (IS) ISNOx emission in both diesel and DME fuels. The advanced pilot injection timing caused a significant increase of HC and CO emission because of an increase of the overmixed region and incomplete combustion.