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We developed a novel ignition method called laser breakdown-assisted long-distance discharge ignition (LBALDI) that combines laser breakdown with a discharge to realize lean combustion. The creation of laser breakdown plasma between electrodes for discharge enables discharges over longer distances than those of conventional sparkplug as inferred from laser-triggered lightning or laser-triggered gas switches. This method should help realize volumetric ignition through the creation of a long-distance discharge. Experiments on the fundamental discharge and ignition of methane/air mixtures were conducted. The optimum incident time of the laser prior to the application of a high voltage was found to reduce the sparkover voltage and markedly reduce the voltage required by LBALDI under pressurized air conditions. In the ignition experiment, LBALDI showed the fastest heat release rate at the lean flammable limit.

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.