Takaaki Kitamura

Mechanism of smokeless diesel combustion with oxygenated fuels based on the dependence of the equivalence ration and temperature on soot particle formation

Abstract The equivalence ratio φ and temperature T are well known to have a significant effect on the quality of particulate formation, such as the soot volume fraction, particle diameter and number density. The purpose of this work is to clarify the φ-T dependence of soot formation for various kinds of fuels, including paraffinic hydrocarbon, aromatic hydrocarbon and oxygenated hydrocarbon, and to discuss a possibility for smokeless diesel combustion considering particulate size and number density. The sooting φ-T map, showing the tendency to generate soot particles as a function of φ-T and T, was made using a detailed soot kinetic model. The computational results show that oxygenated fuel reactions lead to a lower soot yield, smaller particle diameter, lower number density and narrower sooting φ-T region than those of aliphatic and aromatic fuels, due to the notable reduction in production of both acetylene and polycyclic aromatic hydrocarbons (PAHs). Furthermore, this lower sooting tendency is emphasized as the fuel oxygen content increases. It was also found that the leaner mixture side of the soot formation peninsula on the φ-T map, rather than the lower temperature side, should be utilized to suppress the formation of PAHs and ultra-fine particles together with a large reduction in particulate mass.

Extraction of the suppression effects of oxygenated fuels on soot formation using a detailed chemical kinetic model

Abstract The influence of oxygenated fuels on the soot formation process inside a burning diesel jet plume was examined using a detailed chemical kinetic reaction mechanism. Normal heptane was selected as a representative diesel fuel, and methanol, ethanol and dimethyl ether were used as oxygenated fuels. It was found that the production of soot precursors, such as small unsaturated hydrocarbons and PAHs, are dramatically reduced by the use of oxygenated fuels, leading to “soot-free” diesel jet flame. Furthermore, there are remarkable differences in soot suppression effects between oxygenated fuels, which have the same molecular formula but different structures of atomic bonded oxygen.