Effects of Cetane Number, Aromatics, and Oxygenates on Emissions From a 1994 Heavy-Duty Diesel Engine With Exhaust Catalyst 950250

A Coordinating Research Council sponsored test program was conducted to determine the effects of diesel fuel properties on emissions from two heavy-duty diesel engines designed to meet EPA emission requirements for 1994. Results for a prototype 1994 DDC Series 60 were reported in SAE Paper 941020. This paper reports the results from a prototype 1994 Navistar DTA-466 engine equipped with an exhaust catalyst.

A set of ten fuels having specific variations in cetane number, aromatics, and oxygen were used to study effects of these fuel properties on emissions. Using glycol diether compounds as an oxygenated additive, selected diesel fuels were treated to obtain 2 and 4 mass percent oxygen. Cetane number was increased for selected fuels using a cetane improver.

Emissions were measured during transient FTP operation of the Navistar engine tuned for a nominal 5 g/hp-hr NO_x, then repeated using a 4 g/hp-hr NO_x calibration. To determine models for estimating fuel effects on emissions, multiple linear regression analysis of the emissions data was conducted. For this catalyst-equipped engine, the models indicated that increasing cetane number reduced HC, CO, and NO_x emissions. Increased cetane number reduced PM emissions for the 4 g/hp-hr NO_x calibration, but had no statistically significant effect on PM for the 5 g/hp-hr NO_x calibration. For both NO_x calibrations, increasing aromatic content increased PM emissions, and increasing oxygen reduced PM emissions.

THE EFFECTS OF oxygenated diesel fuels and other selected fuel properties on engine emissions have been investigated on engines that meet 1991 and 1994 EPA emissions regulations. (1, 2, 3, 4, 5, 6 and 7)* By incorporating engine design changes that control both HC emissions and the soluble organic fraction (SOF) of total particulate emissions, most heavy-duty diesel engines meet the 1994 regulations without using an exhaust aftertreatment device, such as a catalytic converter. For those diesel engines that require the use of a catalytic converter to meet emissions regulations, the relationship between fuel properties and exhaust emissions may be different than engines without a converter. The Coordinating Research Council-Air Pollution Research Advisory Committee (CRC-APRAC) developed the VE-10 Project to investigate the effects of cetane number, aromatic content, and oxygen level on regulated and selected unregulated emissions from a Navistar DTA-466 engine equipped with a catalytic converter. This engine was calibrated for 1994 emission regulations limiting NO_x emissions to 5 g/hp-hr and PM to 0.1 g/hp-hr. This engine was adjusted to approach 4 g/hp-hr NO_x by retarding fuel injection timing to further investigate fuel effects on emissions for combustion processes limited to lower NO_x.

Under the VE-10 program, similar test work was performed using a Detroit Diesel Corporation (DDC) Series 60 engine without a catalyst. Test work on the DDC engine was published in SAE Paper 941020. Conclusions about that engine indicated that increasing cetane number decreased CO and NO_x emissions, but had no significant effect on PM emissions. Increasing aromatics increased NO_x emissions for the Series 60. Adding oxygen to diesel fuel decreased CO and PM levels, but slightly increased NO_x emissions.

For purposes of this paper, discussions of emission results and the associated statistical analysis are limited to the Navistar engine.