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The influence of fuel quality on oxidation exhaust catalyst (OEC) efficiency in decreasing emissions of carbon monoxide, total hydrocarbons and total particulate matter (PM) from diesel cars has been investigated. Both in-house test results and further interpretation of published chassis dynamometer data have been utilised. Intrinsic OEC activity, which depends on exhaust gas temperatures, is shown to be largely unaffected by fuel quality, other than sulphur content. OECs affect PM emissions by changing the ratio of the soluble organic fraction to fixed carbon within engine-out PM. This ratio is strongly influenced by engine design and operation mode and to a lesser extent by fuel cetane number.

As a result of increasing concerns over air quality, environmental legislation has led to more stringent emissions limits for diesel engines and vehicles. This has affected both engine manufactures and fuel suppliers. Whereas in the US, only the fuel requirements for heavy-duty diesel engines are of key interest, in Europe light-duty diesel applications are also important since diesel-powered passenger vehicles are accepted by customers and their market penetration has increased rapidly. This paper gives an update of Shell's ongoing research on correlations between diesel fuel quality and particulate emissions in both heavy- and light-duty applications. In heavy-duty testing (both steady-state and transient), sulphur is the dominant fuel property affecting particulate emissions. After sulphur correction, fuel effects are small and can best be described by a combination of cetane number and density.