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Transient emission tests were performed to compare emissions using fuels produced by the Sasol Slurry Phase Distillate Process, to those with US diesel fuels. A heavy-duty, four stroke, 1991 emission level diesel engine was used. Two variations of the Sasol Slurry Phase Distillate (SSPD) fuels were tested, along with fuels meeting the US 2-D and CARB specifications, as well as three blends comprising various concentrations of SSPD fuel in the 2-D fuel. It was found that the SSPD fuels produced significantly lower emissions than the 2-D and CARB fuels in all four regulated emission categories. The blended fuels generally reduced emissions in proportion to the amount of SSPD fuel in the blend. Tests were also performed at retarded injection timing settings with the SSPD fuel, which has a cetane number in excess of 70. It was found that a further reduction in NOx emissions could be obtained, without significantly compromising particulate emissions or specific fuel consumption.

Comparative exhaust emission tests were performed on Japanese light- and heavy-duty vehicles fuelled with a Fischer-Tropsch diesel derived from natural gas and two crude oil-derived reference diesels. Both vehicles were tested without and with an oxidation catalyst fitted to the engine. In the case of the light-duty vehicle a current Japanese specification diesel and a future specification low sulphur diesel were used as reference while in the case of the heavy-duty vehicle only the low sulphur diesel was used as reference. The emission tests were performed using the standard Japanese emission test cycle applicable to that vehicle type. In addition certain selected modes from a special test cycle representative of congested traffic patterns encountered in the Tokyo inner city environment were used for both the light- and heavy-duty vehicles. In general, Fischer-Tropsch diesel reduced all the regulated emissions compared to both crude derived diesels.

Comparative exhaust emission tests were performed with five diesel fuels, namely a Sasol Fischer-Tropsch diesel, a fuel meeting the CARB diesel fuel specification, a fuel meeting the US 2-D diesel fuel specification, and two blends of the Fischer-Tropsch diesel and the 2-D diesel. Hot-start and cold-start heavy-duty transient emission tests were performed using a 1999 model year DDC series 60 engine. Regulated exhaust emissions with the Fischer-Tropsch diesel were significantly lower than with the 2-D and CARB diesel fuels, in both the hot-start and cold-start tests. When compared with test results obtained previously with a 1991 engine, it was found that the reduction in NOX with the Fischer-Tropsch fuel was smaller in the 1999 engine, while the reduction in PM was greater.