Influence of Intake Port Structure on the Performance of a Spark-Ignited Natural Gas Engine

Abstract

Spark-ignited natural gas engines have received increasing attention in the heavy-duty market due to their low cost and reliability advantages. However, there are still some issues with natural gas engines retrofitted from 10 to 15 L diesel engines, which is a valuable medium-term goal for the automotive industry. In this work, the effect of intake port structure on the performance of a spark-ignited heavy-duty natural gas engine was investigated by multidimensional numerical simulations. A newly designed intake port was proposed, with strengthened in-cylinder turbulent kinetic energy and homogeneous air-fuel mixtures. Bench tests show that the proposed intake port has impressive thermal efficiency, cycle variation, and acceptable emissions performance. The effective thermal efficiency improves from 41.0% to 41.4%, and the cycle variation is 36% lower than traditional schemes. However, with the accelerated flame propagation, the in-cylinder temperature and NOx emission of the mixed-flow port increase while the CO emission decreases. In summary, a proper balance of in-cylinder swirl and tumble flow can significantly affect the economy and stability of natural gas engines. The proposed structure solves the inherent problems of slow natural gas flame propagation and harmful cyclic variations.