Effect of cooled EGR on modified light duty diesel engine for combustion, performance and emissions under high pressure split injection strategies

Abstract

Environmental concerns demands light duty Engines to satisfy the stringent Euro VI emission norms. The aim of this study is to present the effect of cooled exhaust gas recirculation (EGR) on emission reduction. Tests are conducted on a modified single cylinder light duty diesel engine to run on high pressure common rail direct fuel injection. Diesel is injected directly in to the engine cylinder for both retarded and split injections at pressures of 200, 230, 250, 300 and 350 bar respectively. Cooled EGR is circulated along with intake air in to the inlet manifold of the engine for flow rates of 5% and 10%( wt/wt) of injected air respectively for both retarded and split injections. Single injection is retarded at−11° ATDC and split injection consists of pilot injection at −54°ATDC of 10% mass share and main injection at −11°ATDC of 90% mass share. The result shows split injection (MPFI) decreases the ignition delay, In-cylinder combustion temperature and peak pressure for higher EGR flow rates compared to retarded single injection (SI) for all Injection pressure. Split injection reduced NOx from 1400 ppm to 200 ppm for 10% EGR flow rate at 350 bar injection pressure at full load operating conditions. Split injection at high Injection pressure decreases smoke by 10% as compared to retarded single injection. Test results show that there is trade-off exists between retarded and split injections at 350 bar injection pressure at full load conditions. Retarded injection has 33.61% brake thermal efficiency while split injection exhibits only 29.06% for 5% EGR flow rates. But higher EGR flow rates of 10% both retarded and split injection has nearly same brake thermal efficiency of 30.11%. Split injection reduced the combustion duration, ignition delay and exhaust gas temperatures for higher EGR flow rates compared to single retarded injection. The present research reveals that there exists an injection pressure map between the design operating pressure and maximum injection pressure. MPFI system under CRDI mode is very effective in reducing the NOx emissions with 10% EGR flow rates for maximum Injection pressure. While retarded SI injection is effective for moderate Injection pressure with the same EGR flow rates.