Effect of an Oxidation Catalyst on Exhaust Emissions of a DI Diesel Engine Operating with Fumigation of the Intake Air with Superheated Steam

An oxidation catalyst was fitted on a DI diesel engine for an experimental study involving an oxidation catalyst and the use of superheated steam for fumigating the intake air. Results are compared with that of the influence of low level of fumigation of the intake air with superheated 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. The technique used an electric vaporizer for producing superheated steam and prevaporised superheated diesel fumes at 350 °C, respectively. 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 temperature of exhaust gases inside the oxidation catalyst was not reduced at any given fumigation rate of the intake air with superheated steam. Emissions of TPM, Carbon, SOF and UHC were also reduced by more than 70%, 70%, 60% and 50%, respectively at the exit of the catalyst due to an increase in the engine speed from 1200 rpm to 2200 rpm and the intake air was fumigated with superheated steam. The performance of the catalyst when the intake air was fumigated with superheated steam was similar to that with the fumigation of the intake air with fuel vapor. The catalyst 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 could not substantially affect emissions of Carbon at the time of experiment. These reductions in emissions were accompanied by substantial reduction in NO_x emissions at 1200 rpm and 2200 rpm due to the fumigation of the intake air with steam. The net influence of the fumigation of the intake air with the steam on emissions of NO_x was almost the same as that on the upstream of the catalyst i.e. 1% reduction in NO_x for every 1.5% water to fuel ratio (W/F) increase in superheated steam in the intake air.