Properties of Ignition Kernel Generated by a Sunken Fire Igniter

Environmental regulations imposed stringent requirements, including the adoption of biofuels and the reduction of fuel consumption. As these measures are integrated, reliable engine operation, particularly for in-flight re-ignition and high-altitude ground ignition, must be ensured. Flame development and propagation in annular combustion chambers strongly depend on kernel characteristics generated by the igniter used and their interaction with a surrounding environment that is typically challenging to ignite. Therefore, a more detailed understanding of ignition kernel properties under adverse conditions is essential. The primary objective of the present study is to characterize ignition kernel properties using a real helicopter igniter, focusing on the characteristic times at the onset of the ignition phase during spark generation, a stage for which fine-scale data are currently lacking. Such information is crucial for accurately initializing numerical simulations dedicated to predicting ignition success or failure in the engine. To this end, several diagnostic techniques have been employed, including microcalorimetry, schlieren visualization, and filtered plasma chemiluminescence. The results indicate a decrease in energy transfer efficiency and an increase in final ignition kernel volume as initial pressure decreases. An existing simple model has been evaluated for its ability to predict the experimentally obtained results.