Experimental investigations on a pre-chamber spark plug with variable heat range by integrating a controlled hot surface

In gasoline engines, pre-chamber spark ignition systems are used to achieve high efficiency and low NOx emissions when operating under lean conditions. While a cold pre-chamber spark plug can lead to misfiring and flame quenching under cold start or part load operation, a hot pre-chamber can result in uncontrolled pre-ignition phenomena under full load operation. This paper presents an approach to adjust the heat range of a pre-chamber spark plug and thus, the temperature of the mixture in the pre-chamber, according to the operating condition. Furthermore, higher mixture temperatures in the pre-chamber are intended to enhance the inflammation under lean conditions and to extend the lean limit. For this purpose, a glow plug is integrated into the pre-chamber, whose temperature can be controlled as a function of the operating point. A real-time closed-loop control strategy was applied by using the correlation between the glow plug tip temperature and its electrical resistance. The developed ignition element is called Hot Surface Assisted Spark Ignition (HSASI). In addition to a functional test, a variation of the engine temperature was performed on a single-cylinder, gasoline fueled research engine at the Karlsruhe University of Applied Sciences. In the first step, the influence of the glow plug assistance on the flame development angle and the combustion stability was determined. Subsequently, the air-fuel equivalence ratio λ was varied and the lean limit of unassisted and glow plug assisted spark ignition were determined. Experimental investigations for a constant air-fuel equivalence ratio and a constant ignition timing show that a higher glow plug resistance and thus a higher glow plug temperature shortens the flame development angle and shifts the center of combustion to earlier crank angles. Furthermore, the positive influence of the active glow plug on the flame development angle and the combustion stability increases with retarded ignition timing. With λ = 1.5 and a constant center of combustion (8 °CA after top dead center firing), the ignition timing can be retarded by 4.5 °CA. When operating with lower coolant temperature, an active glow plug increases combustion stability and extends the lean limit by Δλ = 0.1.