Influence of initial electric arc root position on electric arc behavior with spark plugs in large lean burn spark ignited gas engines

Increasing efficiency while reducing emissions leads to high mean effective pressures, high compression ratios and increasingly lean operation for spark ignited large gas engines. Despite these boundary conditions, gas engines must be operated between knocking and misfiring at low cycle-to-cycle fluctuations. The excess air ratio and the ignition process of the lean mixture greatly influence the stability of the combustion process. To enable sufficiently low cycle-to-cycle fluctuation of the combustion process despite the ever increasing excess air ratio levels, it is necessary to understand and investigate the sub-areas of the engine process, for example, ignition, flow condition and mixture formation. This paper focuses on one sub-area of conventional spark ignition, the influence of the electric arc root position on the origin and stretching of the electric arc, because electric arc behavior is considered important in the subsequent combustion process. The results show that electric arc roots on the downstream end of the electrodes tend to enable a longer electric arc length at the first electric arc short circuit (i.e. the first abrupt shortening of the electric arc during its spark duration) than electric arcs with electric arc roots on the upstream ends of the electrodes.