Effect of Partial Fumigation of the Intake Air with Fuel on a DI Diesel Engine Emissions

Results of an experimental study of a DI Diesel engine are presented, which show the influence of partial premixing fumigation of the intake air with diesel fuel on the exhaust emissions and the engine performance parameters. Exhaust emissions of NO_x, CO, UHC, TPM, SOF and Carbon were measured and quantified. Engine performance parameters include the event of the start of combustion and fuel consumption besides other parameters, which were published elsewhere. The study also showed that during a “normal operation” of a DI diesel engine, no emissions trade-off exists between NO_x and TPM. Rather these emissions need separate technological measures for their specific control. Two methods of diesel fumigation 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 producing perfectly 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. Results also showed that the onset of premixed combustion after the completion of ignition delay was advanced due to corresponding reduction in the ignition delay with the increase in the fumigation rate. 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 knocking tendency of the engine due to partial premixing of fuel with the intake air. Results were also compared with other published results which also showed the advantage of partially premixed fumigation over that of fully premixed fumigation in terms of the emissions of CO, UHC and engine efficiency, It was also observed that the degree of premixing of fuel in the form of fully vaporized superheated fuel vapor in comparison to that of fine spray with the intake air also reduced NOx by 45%, UHC by 50%, TPM by 40%, SOF by 50% and Carbon by 40%.