Optical diagnostics of nanosecond and nanometer ignition and quenching mechanism

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The laser-induced breakdown was generated by focusing a 532-nm nanosecond pulse from a Q-switched Nd:YAG laser. In this research, 1) Laser ignition charcteristics, such as, shape of laser-induced plasma, emission spectra, breakdown threshold energy, flame kernel development, minimum ignition energy, 2) Effect of ambient pressure on laser-induced plasma, 3) Shockwave from laser-induced plasma, and Flow structure around hot kernel, 4) Application of laser-induced breakdown spectroscopy (LIBS) on premixed flame and exhaust gas from spark-ignition engine, were investigated. The results provided information about the different stages of laser-induced breakdown; with a specific attention on the transition from flame kernel to self sustain flame. The plasma shape and emission spectrum were very reproducible. The differences in flame kernel size and radicals emission evolution were analyzed in case of mixture firing or misfiring. Under higher ambient pressure conditions, energy for making laser-induced plasma decreases. Based on the flame kernel size evolution the Taylor Blast wave theory has been utilized to plot the location of the shock. The location was calculated with the laser supported detonation (LSD) Model. Furthermore, a very good correlation has been observed with the hot gas ignition process. The atomic spectrum intensity of the exhaust gas changed with preset A/F. When A/F becomes larger (lean condition), C and Fl spectrum intensity decreased because these atomic decreased because these atomics comes from fuel (regular gasoline) in premixed flame and exhaust gas from SI engine. Atomic spectrum intensity ratios of H/0 and C/O correlated with preset A/F.