Stochastic Modeling of Non-Premixed GH2/LOX Autoignition Under Transcritical Conditions

In a hydrogen–oxygen rocket engine with a fuel-rich staged combustion cycle, high-temperature products from the fuel-rich preburner (mainly including gaseous hydrogen, GH2) and cryogenic liquid oxygen (LOX) are separately injected into the main combustor at supercritical pressure. In this context, non-premixed GH2/LOX autoignition would occur under transcritical conditions, which remains a challenging problem due to the interaction between autoignition chemistry, turbulence, and real-fluid thermodynamics. This study aims to fill part of this gap by exploring the autoignition behavior using a partially stirred reactor (PaSR). The PaSR configuration has the potential to mimic the stochastic autoignition process and investigate intricate interactions between turbulent mixing and chemical reactions by varying mixing/residence timescales, as well as global equivalence ratios. The mixing time (τ_mix) isfound to have a significant impact on autoignition dynamics. Specifically, both fast and slow mixing would delay transcritical autoignition. There is an optimal mixing time range, i.e., 0.05 ms < τ_mix < 0.5 ms, in which autoignition is very fast and is not sensitive to changes in residence time and/or global equivalence ratio. Moreover, residence time plays a critical role in promoting a fuel-rich environment that facilitates autoignition, while the global equivalence ratio can significantly affect autoignition dynamics in the mixture fraction space.