Modeling of lifted turbulent flame by the flame edge theory and its implication in liquid rocket combustion instability

Partial quenching structure of turbulent diffusion flames in turbulent mixing layer is investigated by the method of flame hole dynamics. The essence of flame hole dynamics is derivation of the random walk mapping, from the flame-edge theory, which governs expansion or contraction of flame holes initially created by local quenching events. The numerical simulation for flame hole dynamics is carried out in two stages. First, a direct numerical simulation is performed for constant-density fuel-air channel mixing layer to obtain the background turbulent flow and mixing fields. The Lagrangian simulation of the flame hole random walk mapping projected to the scalar dissipation rate array, extracted from the DNS dada, yields temporally evolving turbulent extinction process as well as its statistics on partial quenching characteristics exhibiting that the chance of partial quenching is more strongly influenced by the crossover scalar dissipation rate than by the extinction scalar dissipation rate. In addition, the heat-release oscillations, associated with oscillating lift-off height in the region close to the injector face, can give an estimate to the acoustic amplification rate to liquid rocket engines' acoustic instability.