An investigation on the effects of late intake valve closing and exhaust gas recirculation in a single-cylinder research diesel engine in the low-load condition

Abstract

The effects of late intake valve closing and exhaust gas recirculation on the emissions and the engine performance of a single-cylinder diesel research engine were observed. Two cam profiles (symmetric and asymmetric) were implemented using an offset angle at various intake valve closing timings to characterize the engine performance and the emissions. The injection timings were swept at every condition to evaluate the optimal operating conditions. The highest indicated mean effective pressure was observed once the combustion phasing was tuned to the optimum crank angle (in degrees) by varying the injection timing. The indicated mean effective pressure exhibited a slight penalty when both exhaust gas recirculation and late intake valve closing were used in comparison with the base intake valve closing timing with no exhaust gas recirculation. However, an appropriate combination of the exhaust gas recirculation with late intake valve closing was effective in reducing the nitrogen oxide emissions owing to the decreased in-cylinder temperature. The prolonged ignition delay with exhaust gas recirculation and late intake valve closing also contributed to the improvement in the nitrogen oxides–smoke trade-off relationship. The potential for further reduction in the smoke emissions with the asymmetric cam profile was observed. An increase in the in-cylinder swirl motion was expected, which enhanced the air–fuel mixing process.