Simultaneous Reduction of NOx and PM Emissions through Low Temperature EGR Cooling in Diesel Engines

In this paper, Authors tried to investigate the influence of Low Temperature EGR (LtEGR) on NOx, PM emissions and fuel efficiency in NEDC 120 cycle. Sports Utility Vehicle (SUV) less than 3.5T vehicle selected for investigation of LtEGR. The existing water cooling circuit modified to suitable to handle the LtEGR concept without changing the existing EGR cooler. Cooled EGR technology has two benefits in terms of handling high EGR ratios and more fresh air within the engine displacement. Under this assumption separate LtEGR layout was prepared for the evolution of superior EGR cooling technologies and low pressure EGR. For the same volume of exhaust gas, higher mass of LtEGR is possible without change in fresh air mass as well LtEGR has advantage to occupy the less volume space for the same EGR mass fraction and thereby it is possible for higher fresh air; and engine to digest high amount of EGR or air depending upon the trade off and substantially improve the heat carrying capacity of exhaust gas. Attempt has been made here to downstream temperature of EGR. For this, the source for coolant has been taken from radiator outlet unlike the conventional location of cylinder block. The tuning of LtEGR done in part throttle performance zone on test bed and final evaluation trials were performed on vehicle as per NEDC 120 cycle. About 2 to 50C EGR temperature reduction was observed in major operating points. Significant reduced NOx and smoke emissions were observed in throughout the cycle. Interesting lower THC emissions due to high mass flow rate of fresh air lead to improved combustion. The same data set used in vehicle and test conducted as per NEDC120 cycle. The cumulative result of LtEGR is 16.14% lower in NOx and 23.33% lower PM emissions for the same fueling. Over the ECE and EUDC phase of NEDC cycle, EUDC showed a significant reduction in NOx and smoke. The NOx peaks at the time of acceleration were reduced which clearly showed that at higher torque region lower temperature of EGR helped in reducing the in cylinder temperature. The combustion heat release curves showed a uniform combustion in cylinder with low temperature EGR.