Effects of Aromatic Hydrocarbons on Fuel Decomposition and Oxidation Processes in Diesel Combustion

The chemical behaviors of diesel fuel and the effects of aromatic content on combustion characteristics and NO_x histories were experimentally investigated using a rapid compression machine and a total-gas sampling device. The aromatic content was changed under constant cetane number. Composition of the individual hydrocarbons, inorganic gases and NO_x under various ambient temperatures and fuel injection pressures were analyzed with aromatic-free and aromatic-containing fuels. The results indicate that injected fuel is rapidly decomposed and dehydrogenated during the ignition delay period. The decomposed low boiling-point hydrocarbons consist of mainly unsaturated hydrocarbons such as C₂H₄, C₂H₂ and C₃H₆ at the initial combustion phase. At the diffusion combustion phase, the low boiling-point hydrocarbons consist of mainly CH₄. The aromatic-containing fuel is decomposed with difficulty because of the lower decomposition rate of not only aromatic component but also other heavy saturate hydrocarbons, resulting in higher concentration of low-boiling point hydrocarbons after the ignition than that in aromatic-free fuel. Aromatic-containing fuel gives long NO_x formation duration and high final NO_x concentration than those of aromatic-free fuel.