Numerical and Experimental Investigation of Cyclic Variability of a Large Bore Spark-Ignited Natural Gas Engine

摘要

Two-stroke engines are known to be prone to having cyclic variation. The cyclic variation of a large bore spark-ignited natural gas engine has been numerically and experimentally investigated. COV_(IMEP) (coefficient of variability of IMEP) of 300 consecutive cycles has been used to quantify cyclic variation through experimental investigations. Through experiments it has been discovered that at rated speed, the engine has close to 2-3% COV_(IMEP) at full-load, and close to 60-80% COV_(IMEP) at half-load conditions. CFD analysis was used to try to find out the culprit for this much cyclic variation. It has been revealed that the swirl ratio and tumble ratio in the cylinder, and the turbulent kinetic energy (TKE) around the spark plug are the most influential factors, contributing to the cyclic variation. This means that the scavenging (gas exchange) process, which is responsible for the flow development in the main chamber is the most important process to be modified to reduce the cyclic variation of this engine. Further analysis of the combustion chamber flow field is required for additional information.