Lean-Burn Stationary Natural Gas Engine Operation With a Prototype Laser Spark Plug

An end pumped passively $Q$-switched laser igniter was developed to meet the ignition system needs of large bore lean burn stationary natural gas engines. The laser spark plug used an optical fiber coupled diode pump source to axially pump a passively $Q$-switched Nd:YAG laser and transmit the laser pulse through a custom designed lens. The optical fiber coupled pump source permits the excitation energy to be transmitted to the spark plug at relatively low optical power, less than 250 W. The $Q$-switched laser then generates as much as 8 mJ of light in 2.5 ns, which is focused through an asymmetric biconvex lens to create a laser spark from a focused intensity of approximately $225GW/cm2$⁠. A single cylinder engine fueled with either natural gas only or hydrogen augmented natural gas was operated with the laser spark plug for approximately 10 h in tests spanning 4 days. The tests were conducted with fixed engine speed, fixed boost pressure, no exhaust gas recirculation, and laser spark timing advance set at maximum brake torque timing. Engine operational and emissions data were collected and analyzed.