Effect of the properties of several fuels on the injection and combustion process in HSDI diesel engines

The interrelation between the physical properties of three alternative fuels and their effect on the combustion process in a HSDI Diesel engine has been studied, by comparison with standard gas-oil. The fuels are based on blends of automotive gas-oil with Fischer-Tropsch synthetic fuel, with rape-oil methyl ester and on an emulsion of water in gas-oil. The characteristics of the fuel spray have been investigated in an injection test rig, with the target of evaluating the evaporation and mixing phenomena. These results have been used to interpret the observed changes in the combustion process and in the pollutant emissions. In this regard, engine tests have been performed in a HSDI Diesel engine at some significant operation points. A key distinction has been made between points at low and high load, that is, low and high in-cylinder temperature prior to injection. The results of the study have shed light on the links between the basic physical and chemical fuel properties, the macro and micro-characteristics of the spray, the combustion evolution and the emission of pollutants.