Reduction of NOx with Superheated Steam in a DI Diesel Engine

Reduction of NOx was achieved in an experimental study in a DI Diesel engine. Results are presented, which show the comparison of the influence of partial fumigation of the intake air with superheated diesel fuel vapour and that of steam on the exhaust emissions and the engine performance parameters. Exhaust emissions of NO_x, CO, UHC, TPM, SOF and Carbon were measured and quantified. The technique used for fumigating the intake air with fuel and steam consisted of an electric vaporizer for producing perfectly prevaporised superheated diesel fumes and steam at 350°C. A low emissions version of Perkins 4-236 engine with squish lip piston was run with the fumigation of the intake air with superheated fuel vapour and that of steam at two speeds 1200 rpm and 2200 rpm, roughly covering both city and highway running conditions. Results showed that the onset of premixed combustion after the completion of ignition delay was not advanced with the increase in the fumigation rate of the intake air with steam. This showed that the presence of steam with the premixed charge during the ignition delay period neither influences the ignition delay period nor the start of premixed combustion. As the engine speed was increased from 1200 rpm to 2200 rpm, the emissions of TPM, Carbon and UHC were reduced by more than 70% and that of SOF were reduced by more than 50%. 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 steam on emissions of NO_x was 1% reduction in NO_x for every 1.5% (W/F) increase in dry saturated steam in the intake air, which is similar to that observed by other investigators. Results of the fumigation of the intake air with dry saturated steam were also compared with that of premixing of fully vaporized superheated fuel vapour in terms of the emissions of CO, UHC, TPM, SOF and Carbon, which were not substantially influenced due to the fumigation of the intake air with steam.