Fuel and Maladjustment Effects on Emissions from a Diesel Bus Engine

Substantial efforts have been made to reduce emissions from future heavy-duty diesel engines by control of selected fuel properties. U.S. diesel fuel for transportation use is scheduled by EPA to have low sulfur (≤ 0.05 wt. %) and a minimum cetane index of 40 by 1994 to reduce emissions. In addition, California has mandated that low sulfur diesel fuels contain less than 10 volume percent aromatics by 1994.

Relative to emissions impact, diesel engine design and state-of-tune are perhaps even more important than proposed changes to diesel fuel. The work reported here examined emissions from a 1986 DDC 6V92-TA bus engine using fuels with variation in cetane number, aromatic level, 90 percent boiling point, and sulfur content. The engine was run on these fuels with selected maladjustments to examine their interactive effects on bus engine emissions. Except for HC emissions, regulated emissions were affected more by state-of-tune than by variation in test fuel properties. However, fuel properties did have significant effects on regulated emissions such that lower emissions were generally favored when the fuel had a low 90 percent boiling point, low aromatic content, high cetane number, and low sulfur level.