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Diesel engines are prime movers on a world wide scale for heavy duty trucks. Their market share in passenger cars, however, varies considerably between countries; depending on fuel prices, local fuel/car taxation and acceptability to private motorists. Pressures to reduce fuel consumption (CO2 emissions) and operational costs have increased the market share of diesel engines in new car sales to over 40% in some countries. At the same time diesel engine technology for trucks, buses and passenger cars has improved considerably with significantly higher performance, lower emissions and excellent customer acceptance. To reach all these goals, fuels, lubricants and coolants must meet high quality standards. In this respects fuel additives can contribute considerably to such performance aspects, and improve fuel quality in a cost effective manner.

Shell companies* and Mercedes-Benz have investigated the effect of diesel fuel properties on exhaust emissions in an advanced European IDI passenger car and a modern commercial vehicle DI engine. The experimental programme identified the key fuel properties that influence diesel engine emissions with specific emphasis on NOX and particulates emissions. The fuel properties investigated were density, sulphur, distillation range, cetane number, mono aromatics and polyaromatics content. With regards to the polyaromatics content, the fuels were not designed to differentiate between the effect of di- and tri+ -aromatics. It is concluded that the fuel properties which account for the observed fuel effects on particulates emissions are sulphur, density and polyaromatics content. Monoaromatics content, cetane number and the distillation, as described by T10E, T50E and T90E, were found to have no effect on particulates emissions.

European Diesel engine design, test facilities and test costs has created the necessity for test procedures designed to evaluate the performance of engine lubricants in European engine test laboratories. This situation may be compared with the application of Caterpillar engine test procedures in the U.S.A. In this discussion the MWM-B, CEC L-12-A-76 procedure, is reviewed under the following headings: Outline of test method Discrimination between reference and European commercial oils Correlation with field service requirements of production multi-cylinder Diesel engines Application of the MWM-B procedure and comparison of results obtained with singlegrade and multigrade Diesel engine oils.