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Future US emissions limits are likely to mean a sophisticated nitrogen oxide (NOx) reduction technique is required for all vehicles with a diesel engine, which is likely to be either NOx trap or selective catalytic reduction (SCR) technology. To investigate the potential of SCR for NOx reduction on a light duty vehicle, a current model vehicle (EUII M1 calibration), of inertia weight 1810 kg, was equipped with an urea-based SCR injection system and non-vanadium, non-zeolitic SCR catalysts. To deal with carbon monoxide (CO), hydrocarbon (HC) and volatile organic fraction (VOF), a diesel oxidation catalyst was also incorporated into the system for most tests. Investigations into the effect of placing the oxidation catalyst at different positions in the system, changing the volume of the SCR catalysts, increasing system temperature through road load changes, varying the SCR catalyst composition, and changing the urea injection calibration are discussed.

Reduction of nitrogen oxides in Diesel exhaust gas is a challenging task. This paper reports results from an extensive study using Pt-based catalysts involving synthetic gas activity testing (SCAT), engine bench testing and tests on passenger cars. Preliminary SCAT work highlighted the importance of Pt-dispersion, and both SCAT and bench engine testing yielded comparable NOx conversions under steady state conditions at high HC:NOx ratios. On passenger cars in the European cycle without secondary fuel injection NOx conversion was lower than obtained in the steady state tests. Better conversion was obtained in the FTP cycle, where secondary injection was employed. Higher HC:NOx, ratios and more favourable temperature conditions which were present in the exhaust contributed to this higher conversion.