On flame speed enhancement in turbulent premixed hydrogen-air flames during local flame-flame interaction

Abstract

Given the need to develop zero-carbon combustors for power and aircraft engine applications, Sd of a turbulent premixed flame, especially for H2-air, is of immediate interest. The present study investigates 3D DNS cases of premixed H2-air turbulent flames at varied pressures for different Ret and Ka with detailed chemistry to theoretically model Sd at negative curvatures. Prior studies at atmospheric pressure showed Sd˜ to be enhanced significantly over SL at large negative κ due to flame-flame interactions. 1D simulations of an imploding cylindrical H2-air laminar premixed flame used to represent the local flame surfaces undergoing flame-flame interaction in a turbulent flame at the corresponding pressure conditions are performed to understand the interaction dynamics. These simulations emphasized the transient nature of the flame structure during flame-flame interactions and enabled analytical modeling of Sd˜ at these regions of extreme negative κ of the 3D DNS. The JPDF of Sd˜ and κ and the corresponding conditional averages from 3D DNS showed a negative correlation between Sd˜ and κ. The model successfully predicts the variation of ⟨Sd˜|κ⟩ with κ for the regions on the flame surface with κδL≪−1 at all pressures, with good accuracy. This shows the aforementioned configuration to be fruitful in representing local flame-flame interaction in 3D turbulent flames. Moreover, at κ=0, on average Sd˜ can deviate from SL, manifested by the internal flame structure, controlled by turbulence transport in the large Ka regime. Thus, the correlation of ⟨Sd˜⟩/SL with ⟨|∇cˆ|c0⟩ at κ=0 is explored.