Abstract
Abstract
A particulate after-treatment system has been developed and applied to a 2.51 direct-injection diesel engine. The base exhaust system configuration included an oxidation catalyst; to this has been added a compact heat exchanger believed to have the potential for promoting particle growth, followed by four inclined reverse-flow cyclones in parallel. Emission measurements have shown that the system is capable of reducing exhaust particulate mass concentrations by up to 70 per cent compared with the base configuration. For the same engine speed and load, and with uncooled or cooled exhaust gas recirculation levels from zero to 50 per cent, particulate reductions were achieved without an increase in NOx emissions. Only a modest deterioration in particulate separation was found on bypassing the heat exchanger; this result might be explained by processes in the catalyst and adjacent muffler leading to significant particle growth, although no direct evidence of this is yet available. Measurements of the change in unburned hydrocarbon (HC) vapour concentration through the exhaust system components indicated that HC adsorption or condensation onto particulates is unlikely to be the predominant growth mechanism which allows inertial separation by cyclones. The feasibility of a cyclone-based after-treatment system for production vehicles is discussed.
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