Experimental investigation of the effects of diesel fuel properties on combustion and emissions on a multi-cylinder heavy-duty diesel engine

Abstract

Fuel properties play important roles both in the physical process of fuel air mixing and chemical process of combustion in the cylinder of diesel engines. There are many parameters to represent physical and chemical properties of a diesel fuel, which may affect combustion of diesel engine to different degrees. It is valuable to deeply understand the effects of fuel properties and the relations between some major properties as well. Therefore, the effects of diesel fuel properties on combustion and emissions have been experimentally investigated on a heavy-duty diesel engine in this study. In addition, the relationships among some major properties have been discussed. Twelve fuels with different fuel properties, which were produced by different refining processes from different refineries in China, were selected to ensure that the tested fuels have a wide representative. The results show that there is a strong correlation between fuel density and other fuel properties such as cetane number, aromatic hydrocarbon fraction, heat value, etc. Especially, the linear regression model between density and cetane number shows a certain reference significance. The cetane number of fuel with high density is low, which results in the delay of combustion and the rise of peak heat release rate at low load. There is no significant difference in brake thermal efficiency (BTE) for fuels with different fuel properties in the current study. However, the brake specific fuel consumption (BSFC) increases with the increase of fuel density because of the decrease in heat value. As the fuel density increases, the NOx emissions increase accordingly and the soot emissions roughly show an increasing trend as well. At low load, both CO and HC emissions obviously increase with the increase of fuel density. For example, at low load and low speed, CO and HC increase by 256%, 158% respectively as the fuel density increases from 800 kg/m3 to 920 kg/m3. Nonetheless, CO emissions remain a low level and show no obvious changes at medium and high loads, which is different from HC emissions that increase gradually especially for high speed conditions. The results of the European Steady-state Cycle (ESC) show that weighted BSFC and weighted emissions exhibit strong correlations with fuel density. When fuel density is bigger than a certain value (about 845 kg/m3), a rapid increasing trend is presented in the emissions of NOx, soot, CO and HC.