Effects of fuel properties, in terms of the 90% boiling point (T90) and the polycyclic aromatic hydrocarbon (PAH) content, as well as oxidation catalysts on diesel exhaust emissions have been examined using three direct injection (DI) diesel engines and two diesel passenger cars equipped with oxidation catalysts.
The diesel emission tests using two series of test fuels, one for examining the effects of the T90 and another for polycyclic aromatic hydrocarbons, have indicated that total hydrocarbons (THC) and particulate matter (PM) decrease as the T90 is reduced. PM and THC were also found to be on a declining trend with a decreasing content of polycyclic aromatic hydrocarbons. The extent of these effects of fuel properties on exhaust emissions varied with engine and car models, and appeared to be smaller in engines or cars having lower exhaust emissions.
Tests using three catalyst-mounted diesel engines conducted to determine the effect of oxidation catalysts on the exhaust emissions have shown significant reductions both in THC and PM. The declining trends for THC and PM have also been observed in tests using the two passenger cars with oxidation catalysts.
The above mentioned findings have suggested that the contribution of oxidation catalysts in reducing THC and PM is evidently much larger than that of fuel properties such as reduction of the T90 or polycyclic aromatic hydrocarbons.