Effect of a dimethyl ether–soybean methyl ester blend as an alternative fuel on the combustion and the distributions of nitrogen oxide emissions and soot emissions in a passenger car diesel engine

Abstract

This paper investigates the effect of a dimethyl ether-soybean oil methyl ester blend as an alternative fuel on the combustion and the spatial distributions of nitrogen oxide emissions and soot emissions in a diesel engine using experimental and numerical approaches. The results obtained from the combustion and the emission characteristics (such as the heat release, the nitrogen oxide emissions, the soot emissions, the carbon monoxide emissions and the hydrocarbon emissions) of a dimethyl ether-soybean oil methyl ester blend are compared with the results from a conventional diesel fuel. The test fuels used in this investigation were dimethyl ether-soybean oil methyl ester blend, dimethyl ether and a conventional diesel fuel. The dimethyl ether-soybean oil methyl ester blend is a mixture of 80wt % dimethyl ether and 20wt % biodiesel fuel. A numerical calculation was conducted to analyse the combustion characteristics, the spray behaviours, the mixture formation, the emissions characteristics and the spatial distributios of nitrogen oxides and soot for the dimethyl ether-soybean oil methyl ester blend in a cylinder by using the AVL FIRE program. The numerical results showed that the combustion characteristics of the dimethyl ether-soybean oil methyl ester blend and diesel fuel were in good agreement with the experimental results, such as the combustion pressure and the rate of heat release. It was found that the effect of the dimethyl ether-soybean oil methyl ester blend on the combustion characteristics in an engine resulted in a shorter ignition delay and advanced ignition compared with those using conventional diesel fuel. In addition, the combustion duration of the dimethyl ether-soybean oil methyl ester blend was shorter than that of diesel fuel. The combustion effect of the dimethyl ether-soybean oil methyl ester blend on the concentration of the exhaust emissions indicated that the carbon monoxide emissions and the hydrocarbon emissions were lower than those from diesel fuel. On the other hand, the nitrogen oxide emissions of the dimethyl ether-soybean oil methyl ester blend slightly increased in comparison with those from diesel fuel. The soot emission concentration was nearly zero for the entire test range.