As a result of the excavation of unconventional sources of natural gas, which has rich reserves, has attracted attention as a fuel for use in natural gas engines for power generation. From the viewpoints of efficient resource utilization and environmental protection, lean burn is an attractive technique for realizing a higher thermal efficiency with lower NOx emissions. However, ignition systems have to be improved for lean-burn operations. Laser ignition, which is expected to serve as an alternative to spark plug ignition, can decrease the heat loss and has no restriction on the ignition location because of the absence of an electrode.
Consequently, an extension of the lean-burn limit by laser ignition has been demonstrated. In this study, we investigated the effects of the location and number of laser ignition points on engine performance and exhaust emissions. Laser ignition was also compared with conventional spark plug ignition. The investigation was conducted using a single-cylinder NA gas engine, which used CH4 for fuel. The results showed that the use of two-point laser ignition can extend the lean-burn limit compared to two-point spark plug ignition or single-point laser ignition. In addition, the laser ignition achieved a higher thermal efficiency with lower NOx emissions than two-point spark plug ignition.
