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Four commercially available low-sulfur diesel fuels were additized with two chemically different cetane improvers. Both neat and additized fuels were evaluated in a 1991 prototype heavy-duty diesel (HDD) engine using the EPA Hot Start Transient Cycle. Hydrocarbon (HC), carbon monoxide (CO), nitrogen oxide (NOx), and particulate emissions were determined for each of the 18 fuel formulations tested. Results show that cetane improvers lower HC and CO emissions and, in some cases, NOx and particulate emissions. CO and HC emissions decreased as cetane number increased. The use of cetane improvers should help refiners design diesel fuel formulations which meet California requirements and assist original equipment manufacturers (OEM's) in meeting their emission targets.

A program to explore the effects of natural and additive-derived cetane on various aspects of diesel performance and combustion has been carried out. Procedures have been developed to measure diesel engine fuel consumption and power to a high degree of precision. These methods have been used to measure fuel consumption and power in three heavy-duty direct-injection diesel engines. The fuel matrix consisted of three commercial fuels of cetane number (CN) of 40-42, the same fuels raised to CN 48-50 with a cetane improver additive, and three commercial fuels of base CN 47-50. The engines came from three different U.S. manufacturers and were of three different model years and emissions configurations. Both fuel economy and power were found to be significantly higher for the cetane-improved fuels than for the naturally high cetane fuels. These performance advantages derive mainly from the higher volumetric heat content inherent to the cetane-improved fuels.

The effects of the cetane improvers* 2-ethylhexyl nitrate (EHN) and di-tertiary-butyl peroxide (DTBP) on regulated exhaust emissions from a 1993 Detroit Diesel Series 60 heavy-duty diesel engine were studied. EHN and DTBP were added to two commercially available fuels at concentrations ranging from 500 to 12,000 ppm by volume. Both additives reduced CO, NOx, and particulate emissions as measured in the hot start portion of the FTP heavy-duty transient emissions cycle. A comparison of the emissions response of the two additives shows that the nitrogen in EHN does not contribute to NOx emissions at typical treat rates.