Experimental studies on spark stability in an optical combustion vessel under flowing conditions

Besides mixture formation and combustion, ignition and robust flame kernel formation are the main parameters needed to realize the otto-cycle process. During much of the development history of combustion systems, the requirements on the ignition system have steadily increased but could always be fulfilled by the inductive ignition system. In contrast, some current developments in gasoline engine combustion concepts focus on the increase of cylinder charge which is often associated with supercharging or the increase of exhaust gas recirculation and/or air dilution. In such cases, the ignition and flame kernel formation becomes challenging. The increase of specific power by charging leads to higher gas densities at ignition requiring high ignition voltages of up to 40 kV which have to be covered by the ignition system. At part load conditions the ignition voltage demand is considerably lower, however the ignition conditions are much more critical due to low gas temperatures at ignition point and low chemical reactivity of lean mixtures. The electrical properties of the spark plasma, such as spark current, spark energy and spark duration as well as the interaction of the spark plasma with the internal engine flow are key factors in order to meet the aforementioned challenges.