Flame structure analysis of turbulent premixed/stratified flames with H2 addition considering differential diffusion and stretch effects

Abstract

In this work, the flame structures of the recent Darmstadt turbulent premixed/stratified flame series with 20% volume fraction H2 addition (Schneider et al., PCI, 2019) are analyzed using flamelet tabulated manifolds. Three different methane/hydrogen flames (MHFs) with increasing complexity are studied. The effects of differential diffusion, stretch and stratification on the applicability of the flamelet model are investigated in detail. Specifically, to investigate the differential diffusion effects, three different modeling approaches are considered, in which the diffusion fluxes are calculated using the multi-component (MC), mixture-averaged (MA) and unity Lewis number (Le1) approaches. To investigate stretch effects, a strained premixed flamelet (SPF) model is proposed, in which the flame’s internal response to stretch is characterized with an additional tabulation coordinate. A double-conditioning analysis is conducted for different flame series. The dataset is conditioned on both the local equivalence ratio and local stratification to analyze the coupling effects of stratification and differential diffusion on the flame structure. Overall, the flamelet predictions are consistent with the experimental findings for all flames.