Efficient Post-Processing Method for Identification of Local Hotspots in 3D CFD Simulations 2022-37-0005

Knocking is one of today’s main limitations in the ongoing efforts to increase efficiency and reduce emissions of spark-ignition engines. Especially for synthetic fuels or any alternative fuel type in general with a much steeper increase of the knock frequency at the KLSA, such as hydrogen, precise knock prediction is crucial to exploit their full potential. This paper therefore proposes a post-processing tool enabling further investigations to continuously gain better understanding of the knocking phenomenon. In this context, evaluation of local auto-ignitions preceding knock is crucial to improve knowledge about the stochastic occurrence of knock but also identify critical engine design to further optimize the geometry. In contrast to 0D simulations, 3D CFD simulations provide the possibility to investigate local parameters in the cylinder during the combustion. Measurement of auto-ignition yields challenges regarding the small time frame of the phenomenon and the required optical access to the combustion chamber. However, manual identification of auto-igniting hotspots within 3D CFD simulations is extremely time-consuming and not reasonable if a multitude of engine cycles or operating conditions have to be evaluated. This paper, therefore, introduces a post-processing method that allows automated identification of auto-igniting areas named hotspots. The method is developed based on LES data of 100 engine cycles at a single operating point and uses a geometrical comparison of the propagating flame front at different times to distinguish cells of a hotspot from the spark-ignited flame front. Two calibration parameters allow tuning of the method to make it applicable for various engines. The results show reliable identification of auto-igniting hotspots. The proposed method consequently provides an efficient tool for the investigation of local parameters related to auto-ignition that helps to improve understanding of the knocking phenomenon and consequently improves the engine development process.