The necessity to solve problems of limiting fuel resources and the
environmental pollution caused by the engine emissions enforces the scientists and engine manufacturers to investigate the possibility of using alternative fuels.
However, there are wide variations in the effect of using alternative fuels on both performance and environmental impacts of the engines. These variations are mainly owing to the differences of physiochemical properties for these fuels over those of traditional fuels (benzene and diesel fuels). The alternative fuels have distinguishable properties over traditional fuels; including molecular structure (as the existence of oxygen and absence of sulfur in addition to very low aromatic compounds), but they suffer from lower heating value. In this study the effect of alternative fuels and their stability have been studied. Moreover, the burning velocity of different fuels used as engine fuel is considered. The investigation of the effect of alternative fuels on the mechanical and environmental performance of the diesel engine was performed with special concern in the use of rapeseed oil methyl ester (RME). The test target contains the diesel engine setup equipped with all necessary instrumentations, and the test program follows the 8-mode test cycle of Regulation #96-02. The use of RME in mixture with diesel fuel leads to remarkable reduction in both particulate matter and unburned hydrocarbons (with rate increasing as the percent of RME in the fuel mixture increases reaching from 10% to 70%). However, a slight increase of both NOx and specific fuel consumptions is observed with no effect on the CO emission. The fuel mixture stability is a very important for both fuel transportation and storing. This property has been proved for different fuel mixtures (containing from 10 to 70% RME); there are no changes in color or odor for long time (up to 3 years), moreover mixture stratification was not observed.
Moreover, the burning laminar velocity as one of the major combustion
characteristics that directly affects the burning rate and emission formation for different alternative fuels has been studied. The burning velocity was determined using cylindrical closed combustion chamber with central ignition at the minimum ignition energy. The effect of fuel saturability and oxygen compound in its structure has been observed. Generally, as the degree of unsaturation increases, the burning velocity increases. The oxygenated fuels have higher values (by 5-10%) of burning laminar velocity comparing with those of conventional fuels having similar number of carbons. There is data about ambiguous influence of application alternative fuels on technical and ecological indicators of the diesel engines. This is mainly due to the effects of physical and chemical characteristics of fuels. |
