Key requirements for state of the art industrial gas engines are high engine thermal efficiency, high engine brake mean effective pressure (BMEP), low NOx emissions, and acceptable spark plug life. Fundamentally, as engine thermal efficiency and power density increase, along with the requirement of reduced NOx emissions, the pressure at the time of ignition increases. This results in a higher spark breakdown voltage that negatively affects spark plug life. This problem is resolved with a smaller electrode gap and high spark energy to overcome quenching effects during ignition kernel development. High flow fields in the spark gap region are required to assure the spreading of the discharge, which reduces the rate of electrode erosion. In addition, these high flow fields overcome mixture inhomogeneities by developing large ignition kernels. These large ignition kernels, inside the prechamber spark plug, produce high velocity flame jets into the main chamber enhancing combustion, which results in thermal efficiency gains at lower NOx levels and higher BMEP. The advanced combustion system solution discussed in this paper is the combination of high-energy ignition and a prechamber spark plug with flow fields at the electrode gap. Future developments include improved ion signal quality detonation detection resulting in additional gains in thermal efficiency.
Effect of single-contact spark plug electrode gap on composition of engine exhaust emissions
