燃料噴霧中のレーザー励起ブレイクダウン着火に関する研究 (第二報 燃料噴霧中でのレーザー励起ブレイクダウンおよび着火特性の調査)

抄録

In order to ignite fuel spray directly by a laser beam, it is necessary to investigate the characteristics of laser-induced breakdown ignition and generation of plasma as ignition sources in fuel spray. This study conducted experiments of laser-induced breakdown ignition in an steady ethanol/air premixture and ethanol spray flow by using third harmonic of the Q-switched Nd:YAG laser. For evaluation of breakdown occurrence and ignition probability, the flame and the plasma images were obtained. And laser beam incident energy was also measured. Although probability of the breakdown occurrence and the ignition increased with the increase of incident energy, there are great difference between the breakdown threshold and the minimum ignition energy in the case of spray flow. Also, in spray flow, plasma was generated at multiple points and its number, size and position are different from pulse to pulse. The initial flame kernels generated by these plasmas were growing while being affected by each other. It is suggested that the behavior of the fuel droplets around the initial flame kernel affect the ignition probability since the ignition probability with increasing number density of droplets is decreased.