Effect of Injection Pressure and Swirl Motion on Diesel Engine-out Emissions in Conventional and Advanced Combustion Regimes

The fuel injection pressure and the swirl motion have a great impact on combustion in small bore HSDI diesel engines running on the conventional or advanced combustion concepts. This paper examines the effects of injection pressure and the swirl motion on engine-out emissions over a wide range of EGR rates. Experiments were conducted on a single cylinder, 4-valve, direct injection diesel engine equipped with a common rail injection system. The pressures and temperatures in the inlet and exhaust surge tanks were adjusted to simulate turbocharged engine conditions. The load and speed of the engine were typical to highway cruising operation of a light duty vehicle. The experiments covered a wide range of injection pressures, swirl ratios and injection timings. Engine-out emission measurements included hydrocarbons, carbon monoxide, smoke (in Bosch Smoke Units, BSU) and NOx. Exhaust Gas Recirculation (EGR) rates were varied to cover the engine operation from the conventional to the low temperature combustion regime, up to the misfiring point. The reduction in NOx and the penalty in BSU, HC, CO and indicated specific fuel consumption (ISFC) were determined over the whole EGR range. A comparative analysis is made between the effects of increasing the fuel injection pressure and swirl ratio on the autoignition reactions, cool flames, premixed combustion fractions and the trade off between NOx and BSU.