The Combustion Phenomena in the Pre-Combustion Chamber of Micro-Pilot Gas Engine

摘要

The gas engine is in the spotlight for reasons of high efficiency and low emission. This engine serves an important role in stationary power generation markets. The micro-pilot pre-combustion chamber is one of the ignition systems for large gas engines. This micro-pilot ignition system injecting a small quantity of diesel fuel or marine diesel oil into the pre-combustion chamber can provide higher ignition energy than conventional spark ignition systems. Therefore, the micro-pilot gas engine has high potential to ignite also low calorific fuel efficiently. For effective utilization of energy resource such as low calorific fuel and improvement of efficiency and emission, it is more important to optimize and improve the pre-combustion chamber. However, the phenomena in the pre-combustion chamber consisting of pre-mixture motion, diesel spray atomization, auto-ignition of diesel fuel, combustion of lean pre-mixture, etc. are more complex. This paper focuses on the combustion stability of micro-pilot gas engine and discusses the combustion phenomena in the pre-combustion chamber experimentally. In the experiment, a Rapid Compression and Expansion Machine (RCEM) was used to simulate the high pressure and high temperature conditions of a real gas engine. RCEM is useful for visualizing the combustion phenomena in the pre-combustion chamber and main combustion chamber. The spray behavior, ignition, and flame propagation were observed with high-speed video camera. This experimental research showed that the combustion unstable appears at a specific value of equivalence ratio. The mechanism, namely the relationship between equivalence ratio and ignition instability, is discussed. In addition, as a result of visualization, it was realized that the high-speed pre-mixture motion in the pre-combustion chamber affects the spray behavior and combustion. In this paper, the relationship between these interactions of pre-mixture motion and combustion instability is described.