Laser Spark Plug Development and Engine Testing - Design of a diode side pumped solid state passively Q-switched laser for use as an ignition source for a lean-burn stationary natural gas engine

To meet the ignition system needs of future lean- burn natural gas engines a diode side pumped passively Q-switched Nd:YAG laser was developed and tested. Laboratory experimentation used a wide range of input parameters that when combined produced brilliant sparks in air. The results show a strong dependence of the output on the output coupler reflectivity Q-switch initial transmission and gain media dopant concentration. The results show peak power levels of up to 3MW and peak focal intensities of up to 560 GW/cm2. Engine testing was performed on a Ricardo Proteus single cylinder research engine. The engine testing consisted of a comparison of the in-cylinder and emissions behavior. All engine parameters were kept as constant and the equivalence ratio was varied between 0.8 0.9 and 1.0. The test laser was constructed with a 30% output coupler 32% Q-switch initial transmission and a 0.5% Nd concentration rod all pumped by approximately 1000 Watts of optical power. The test laser single mode output pulse had an energy of 23 mJ with a pulsewidth of 10 ns and an M2 value of 6.55. This output produced focal intensity of 270 GW/cm2.