Abstract
The mechanism of air breakdown for engine ignition was investigated with the high-brightness pulse lasers. After the conformation of double pulses and ultrafast short pulse effects for laser induced breakdown, we have designed a compact (spark plug size), diode-pumped, passively Q-switched Nd:YAG/Cr4+:YAG micro-laser for ignition of engines. The output energy of 2.7mJ per pulse and totally 11.7mJ (sum of 4 pulses) was obtained at the pump duration of 500μs with the optical-to-optical conversion efficiency of 19%. The pulse width and M2 value were 600ps and 1.2, respectively. The brightness of the micro-laser was calculated to be 0.3PW/sr-cm2 and the optical power intensity of 5TW/cm2 was estimated at the focal point of ignition. The enhanced combustion by the micro-laser ignition was successfully demonstrated in a thermostated constant-volume chamber with room temperature and with atmospheric pressure. The cross-section area of the flame kernel generated by the laser ignition is 3-times larger than the spark plug at 6ms after ignition in a stoichiometric mixture (A/F 15.2) of C3H8/air, even though the ignition energy of the laser is 1/3 of that of a spark plug. The real automobile engine ignition has been also successfully demonstrated by using this high-brightness, low energy micro-laser.
