Cyclic variation of large-bore multi point injection engine fuelled by natural gas with different types of injection systems

Influence of mixing process optimization in the manifold on mixture formation and cycle-to-cycle variation (CoV) was studied in a large-bore MPI natural gas engine. The study was explored by adjusting injection nozzle shape and location as well as end-of-injection timing (EOI). Gas was induced to intake valve seat with elbow and four types of elbows with different nozzle shape and location were designed. Compared to single elbow situation, twin elbows improved the quality of mixture formation and the CoV was decreased obviously. It was also found that natural gas spraying to the surroundings had better effect than that spraying along air flow direction. The fourth type of elbow was employed to study the influence of injection duration on the CoV. With the data collected, it can be seen that the CoV was decreased due to the improvement of mixture formation quality when extending injection duration. While partial gas could not flow into cylinder when the injection duration was extended too long and this was unfavorable for mixture formation and combustion. Quality of mixture could be improved by optimizing the mixing process in the intake manifold and this could partly compensate for weak airflow motion in the large bore cylinder. (C) 2016 Elsevier Ltd. All rights reserved.