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The factors governing fuel effects on diesel emissions are complex. Previous studies have demonstrated that interactions between fuel physical properties and the engine control system can result in engine calibration changes (primarily injection timing and EGR) despite the use of sophisticated electronic controls. In standard production engines, fuel effects on emissions can be strongly influenced by these interactions, making it impossible to determine the effects of fuel changes on the in-cylinder mixing and combustion processes. This paper describes fuel effects on engine-out emissions from a European light-duty diesel engine. The calibration effects were eliminated using a sophisticated test bed control system to maintain timing and EGR rate accurately at the design settings. By these means, fuel effects on the in-cylinder process could be accurately determined.

The effect of fuel sulphur on emissions from a lean-burn G-DI passenger car homologated according to German D3 specifications was investigated over the European drive cycles. In addition some tests over US Federal cycles were conducted. No statistically significant deterioration in tailpipe emissions was detected with the leanburn G-DI technology using a selective reduction type de-NOx catalyst at fuel sulphur levels from 30 to 300 mg/kg. The emission response to fuel sulphur level was essentially flat, and the sulphur effect was less than that seen in the EPEFE fleet. Tests were conducted applying a rigorous test protocol including four repeats with each fuel and a desulphation procedure between fuel changes. Approximately 15-20% improvement in fuel economy over comparable MPI cars was predicted based on the CO2 results from the current programme and German type approval data. Increased particulate mass emissions were observed, compared with typical MPI cars.