3-D CFD Simulation Of The Working Process Of A Marine Gas Engine

Natural gas (NG) is a promising alternative fuel because of its economic and environmental benefits. Meanwhile, natural gas is abundant and reliable in long-term supply. Promoting gas engines can effectively reduce the consumption of conventional gasoline and diesel oil, and reduce global CO2emission. In order to meet the current and proposed emission regulations and avoid abnormal combustion, gas engines should adopt lean burn strategy. However, due to lean mixture characteristics of slow burning speed, conventional open-chamber gas engines face to many problems such as slow combustion rate, combustion instability, cycle-by-cycle variations and reduction of thermal efficiency, even misfire. These problemes are more serious in large gas engine. To overcome these problems, the pre-chamber combustion system with enrichment strategy was designed to gain stable ignition and quick flame propagation. With the enrichment injection, the fuel concentration in pre-chamber is controlled independently and the turbulence intensity is largely increased. This paper investigates issues relating to a lean burn marine gas engine. The working process of a lean burn marine gas engine was simulated with a3-D CFD software package AVL-FIRE. This study was conducted to simulate the intake, compression and lean mixture process of a large marine gas engine. The charge motion and fuel-air mixing process were simulated. The structure and behavior of flame jets from the pre-chamber and flame propagation in the main chamber, combustion phenomena and ignition characteristics were investigated. Different enrichment strategies were compared. The simulation results were compared with literatures relating to lean burn gas engine. Based on the simulation results, the enrichment strategies were optimized and the structural optimization of the combustion system was proposed.