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Technology for the enhancement of compression ignition for a natural-gas homogeneous charge compression ignition (HCCI) engine was developed using nonthermal plasma. Specifically, nonthermal plasma was utilized to enhance the ignition of the methane/air premixture by irradiating it in an intake tube. The effect of the irradiation on compression ignition was investigated using a rapid compression and expansion machine; the ignition delay was found to shorten by the influence of irradiation. The dependence of the ignition delay time on the temperature at the end of compression was determined. Chemical analysis of the plasma-processed gas was performed using a gas detection tube as a simple method and ion-attachment ionization mass spectrometry (IAMS) as a novel method. A chemical kinetic simulation was also conducted to examine the temperature dependence of the ignition delay.

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.