Combustion analysis of modified light duty diesel engine under high pressure split injections with cooled EGR

Abstract

The aim of the present research work is to study the combustion phenomenon in modified light duty diesel engine to run on Common rail direct injection (CRDI) system under cooled exhaust gas recirculation (EGR). The test engine is single cylinder 3.7 kW@1500 rpm direct injection diesel engine capable of injecting high pressure fuel for both retarded and split injections. The engine is fitted with separate electronic variable timing fuel injection kit instead of conventional fuel supply system. Retarded injection consists of single injection at 11° before top dead centre (BTDC) and split injection consists of both pilot injection at 54°BTDC of 10% mass share and main injection at 11°BTDC of 90% mass share. 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 for flow rates of 5% and 10% (wt/wt) basis. The experimental set up is capable of delivering precise control of fuel and EGR flow rates at all operating conditions. 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 34% brake thermal efficiency while split injection exhibits only 32.1% for 5% EGR flow rates. But higher EGR flow rates of 10% both retarded and split injection has nearly same brake thermal efficiency of 30.1%. Split injection reduced the combustion duration, ignition delay and exhaust gas temperatures for higher EGR flow rates compared to single retarded injection. Keywords: EGR, High pressure injection, Split injection, Retarded injection, Combustion, Ignition delay, NOx