Study of implementation of hybrid EGR during transient operations on diesel engine to reduce NOx emissions with fast emission measurement system

Knowing the importance of EGR, to control the emissions from internal combustion engines and to cope with future emissions standards, it is necessary to investigate the influence of EGR on diesel engines. Specially, the need of studying transient operations, playing vital role in newly developed driving cycles like WLTP and RDE is getting prominent. This study consists a utilization of high pressure and low pressure exhaust gases with different rates to reduce the instantaneous emission of NOx at transition phase and full load part of the load transient. This paper focuses on different kind of such load transients experienced by a vehicle on road. The engine has to go through certain predefined load to no load and again to full load at the end. Likewise, it has been tested with similar test procedure and environment inside the test cell at a particular engine speed. The EGR valves and exhaust throttle movements were synchronized manually during the transition from no load to full load to avoid the regulation of valves by Engine Control Unit. The NOx and CO2 emissions are measured at exhaust and intake manifold respectively with high time-resolution measurement system. The temporal transport delays of HP and LP EGR are quantified with instantaneous CO2 measurement. Comparison of normal transients (without EGR at full load) with transients (using HP EGR and LP EGR) is carried out. A hybrid strategy with both Low and High pressure EGR have been proposed to reduce NOx emissions. At last the advantage of using LP EGR over HP EGR has been quantified during this load transient operation.