In order to evaluate the feasibility of coal derived middle distillates as diesel-powered automobile fuels, mass emission of CO, HC, NOx and particulate matter, and content of soluble organic fraction (SOF) in particulate matter were measured by operating two types of automobiles under 10 mode driving cycle, idle condition and constant speed conditions at 20, 40 and 60km/h. One of the automobiles was conformed to Japanese emission standard in 1982 and the other to standard in 1986 which required more stringent permissible limit for NOx. The middle distillate was obtained from liquefaction of Illinois subbituminous coal followed by catalytic hydrogenation. The test fuels were prepared by mixing the middle distillate and a commercial gas oil, and adding a cetane booster to mixing fuel.
The mass emission of CO, HC and particulate matter, and the content of SOF emitted from the automobiles increased with the increase of the middle distillate content in the test fuels, but the mass emission of NOx hardly increased. The emission from the automobile which was conformed to more stringent emission standard for NOx showed stronger dependency on the middle distillate content than the other automobile. Addition of the cetane booster to the mixed fuel improved the ignition quality of the mixed fuel, and decreased the mass emission of CO, HC and particulate matter.
Although exhaust emission characteristics of the mixed fuel containing the coal derived middle distillate were improved by adding the cetane booster, it is necessary to make basic property of the middle distillate, such as aromaticity, distillation characteristics and so on., closer to petroleum derived fuel in order to use the middle distillate under more stringent emission standard.
