The Effects of Fuel Properties on Emissions from a 2.5gm NOx Heavy-Duty Diesel Engine

The engine selected for this work was a Caterpillar 3176 engine. Engine exhaust emissions, performance, and heat release rates were measured as functions of engine configuration, engine speed and load. Two engine configurations were used, a standard 1994 design and a 1994 configuration with EGR designed to achieve a NO_x emissions level of 2.5 gm/hp-hr. Measurements were performed at 7 different steady-state, speed-load conditions on thirteen different test fuels. The fuel matrix was statistically designed to independently examine the effects of the targeted fuel properties. Cetane number was varied from 40 to 55, using both natural cetane number and cetane percent improver additives. Aromatic content ranged from 10 to 30 percent in two different forms, one in which the aromatics were predominantly mono-aromatic species and the other, where a significant fraction of the aromatics were either di- or tri-aromatics.

The results indicated that there were significant differences in the emissions levels of the two engine configurations, where the EGR engine had NO_x levels that were on average 50% lower than the corresponding 1994 engine. There were, however, no significant differences in the emissions that could be related to changes in the targeted fuel properties. It is speculated that the lack of fuel sensitivity of the test engine is related to the fact that the engine design incorporates a fuel injection rate that results in very little pre-mixed burn fraction and very little sensitivity to cetane number.