TRL was commissioned by the Department for Transport to review the approach used in the National Atmospheric Emissions Inventory (NAEI) for estimating emissions from road vehicles, and to propose new methodologies. This Report describes the effects of fuel properties on exhaust emissions. The main topics covered in the Report are: (i) the effects of fuel sulphur content on exhaust emissions; (ii) the effects of other fuel parameters; (iii) the effects of biofuels; (iv) the modelling of fuel effects; and (v) the implications in terms of the UK emission factors. The reduction in fuel sulphur content from 50 ppm (“ultra-low sulphur”) to 10 ppm (“sulphur-free”) seems unlikely to bring substantial emission benefits for current Euro 3/III and 4/IV vehicles. The main exception may be PM emissions. It is possible that older petrol vehicles could show some degree of catalyst recovery (i.e. lower emission levels) when used on sulphur-free fuel. However, such effects are rather difficult to quantify as there seems to be little interest in testing old vehicles on new fuels. Changes in other fuel properties can also result in small, but sometimes significant, changes in emissions. In order to derive fuel composition scaling factors, an adapted version of the method presented in COPERT III/4 is proposed. Fuel composition scaling factors are given for all light-duty and heavy-duty vehicles, and these should be used in conjunction with the emission factors which have been derived in the project. From the evidence it appears that emission scaling factors for biodiesel and ethanol are not required in the UK.

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