On Comparative Engine Performance Testing With Fiber Delivered Laser Ignition and Electrical Ignition

Laser ignition of natural gas engines has shown potential to improve many facets of engine performance including brake thermal efficiency, exhaust emissions, and durability as compared with traditional spark ignition. We present proof of concept of a novel fiber optic delivery approach using solid core multimode step index silica fibers with large cladding diameters (400 m core, 720 m cladding). The fibers were able to deliver high beam quality 25 nanosecond pulses of 1064 nm light with 7–10 mJ energy; sufficient to consistently ignite the engine at various air-fuel ratios and loads. Comparative tests between the laser spark plug and a traditional J-gap spark plug were performed on a single cylinder Waukesha Cooperative Fuel Research (CFR) engine running on bottled methane. Performance was measured in terms of the Coefficient of Variation (COV) of Net Mean Effective Pressure (NMEP), fuel specific efficiency, and emissions of oxides of nitrogen (NO_x), carbon monoxide (CO), and total hydrocarbons (THC). Tests were run at three different NMEPs of 6, 8, and 12 bar at various air-fuel ratios. Results indicate successful operation of the fiber and improved engine performance at high NMEP and lean conditions.