The Effects of Intake Pressure on High EGR Low Temperature Diesel Engine Combustion

Diesel engine emissions of NO_X and particulate matter (PM) can be reduced simultaneously through the use of high levels of exhaust gas recirculation (EGR) to achieve low temperature combustion (LTC). These reductions are highly dependent on the oxygen concentration in the combustion chamber. This paper investigates varying the intake pressure to adjust the oxygen concentration and the corresponding impacts on emissions for EGR rates up to 65%. An engine operating condition corresponding to 600 kPa gross-indicated mean effective pressure (gimep) at 2500 rpm is investigated using a 0.51-liter single-cylinder high-speed direct-injection (HSDI) diesel engine. This facility is equipped with independent control of the intake pressure and temperature, the EGR rate and the exhaust back pressure. This work focuses on investigating the potential of increasing EGR tolerance at medium load by increasing the boost pressure from 120 kPa to 180 kPa (absolute), while keeping PM and NO_X emissions at acceptable levels. This paper also presents an investigation into the effects of injection timing and injection pressure on diesel LTC. The combined effects of EGR rate and intake pressure on PM, NO_X and HC emissions are reported along with gross-indicated specific fuel consumption (gisfc).