Effects of exhaust gas recycle loop layout and retarded intake valve closing on variations in combustion in a heavy-duty diesel engine

Abstract

To improve engine response and decrease exhaust smoke and NOx emission during transient operations, variations in cycle-to-cycle and cylinder-to-cylinder combustion were investigated in a two-stage turbocharged, exhaust gas recirculation heavy-duty diesel truck engine. Variations in combustion were confirmed to be caused by insufficient mixing of the exhaust gas recirculation with intake air. And steady operation, by increasing the length of the mixing path, coefficient of variation of the exhaust gas recirculation rate in cylinder 1 declined from 8.12% to 3.68%, while that for the other cylinders decreased from approximately 4.0% to 2.98%. These improvements also caused reductions in coefficient of variations for indicated mean effective pressure and crank angle of 50% fuel burned (CA50). By using an intake valve closing timing retarding actuator system, coefficient of variation of the exhaust gas recirculation rate for cylinder 1 was further decreased from 3.68% to 2.82%. It was interesting to find that EGR/air mixing length revealed a great effect on soot and NO_x emissions during transient operations, especially those involving sudden increases in load. By using long mixing path instead of short mixing path combined with suitable fuel injection strategy and exhaust gas recirculation rate, transient response of load was reduced by 10% and transient smoke spike decreased from 0.8m-1 to 0.5m-1.