Effects of different aromatics blended with diesel on combustion and emission characteristics with a common rail diesel engine

Abstract

Aromatic hydrocarbons are thought to be the important components of diesel surrogate fuel. The studies on the effects of different aromatic hydrocarbons on diesel combustion process are of great significance. In this paper, experimental study was carried out on a modified single cylinder diesel engine to analyze the influences of different aromatics blended with diesel on the combustion and emission characteristics. Four typical aromatics (toluene, n-butylbenzene, tetralin and 1-methylnaphthalene) were selected and blended with commercial diesel fuel in 30% volume fraction to form the test fuels, respectively. Studies showed that the blending of aromatics resulted in the higher density and lower viscosity compared with traditional diesel fuel. Toluene lowered the distillation temperature of the mixed fuel to a large extent. The increases in both the ignition delay and the peak values of heat release rate were found in the experiments. The combustion duration was shortened especially for the multi-ring aromatics. It also increased maximum pressure rise rate remarkably at medium and high loads. As for the pollutant emissions, the higher CO emissions were detected at low loads for aromatics/diesel blends. The CO emissions of the multi-ring aromatics were higher than those of the single-ring aromatics and commercial diesel. HC emissions of the multi-ring aromatics were higher than those of diesel, while the single-ring aromatics had similar HC emissions to those of diesel. Blending aromatics leaded to the higher NOx emissions at medium-high loads. Smoke emissions were improved due to the longer ignition delay. The peak value of particle number/size distribution curve was shifted to the small-size sides after blending aromatics, in which the single-ring aromatics showed higher particle emissions than multi-ring aromatics.