Effect of an Oxidation Catalyst on Exhaust Emissions of a DI Diesel Engine Operating with a Partial Fumigation of the Intake Air with Fuel 2002-01-1726

Results showed the influence of the oxidation catalyst on exhaust emissions from a DI diesel engine due to the partial premixing, fumigation of the intake air with diesel fuel. Exhaust emissions of NO_x, CO, UHC, TPM, SOF and Carbon were measured and quantified on upstream and downstream of a low light off temperature (250 °C) oxidation catalyst. Two methods of diesel fumigation of the intake air with fuel were used. The difference between these two methods was the degree of premixing of diesel fuel with the intake air. The first technique used a high-pressure fine diesel spray onto a glow plug and the second technique used an electric vaporizer for prevaporised superheated diesel fumes at 350 °C. A low emissions version of Perkins 4-236 engine with squish lip piston was run both with and without fumigation at two speeds 1200 rpm and 2200 rpm. Roughly covering both city and highway running conditions. As the engine speed was increased from 1200 rpm to 2200 rpm, the average temperature of exhaust gases inside the oxidation catalyst was increased by about 50 °C at any given fumigation rate. It is also observed that at 1200 rpm, the oxidation catalyst showed a definite reduction of NO_x emissions of 10% probably due to correspondingly longer residence time inside the catalyst. The catalyst also reduced emissions CO by 80%, UHC by 65%, TPM and SOF up to 25%. However, the catalyst possibly due to correspondingly higher sulphur content of the fuel did not substantially affect emissions of Carbon at the time of experiment. When the engine speed was increased from 1200 rpm to 2200 rpm, the emissions of TPM, Carbon, SOF and UHC were also reduced by more than 70% at the downstream of the catalyst. It was also observed that the effect of the degree of premixing of fuel in the form of fully vaporised superheated fuel vapour in comparison to that of fine spray with the intake air is similar to that at the upstream of the oxidation catalyst.