Effect of hydrogen addition on the variations of heat release rate in a t urbulent stratified swirl methane-air flame

Three-dimensional RANS simulations with reduced mechanism were performed to investigate the effect of hydrogen addition on the heat release rate (HRR) spatial variations in premixed and stratified cases of a t urbulent stratified swirl methane-air flame. k-ω SST turbulent model and PaSR combustion model were used while considering the differential diffusion with different Schmidt numbers. Variations in the combustion intensity in a globally lean and turbulent flame were studied with 40% hydrogen addition (on the volume of fuel basis) to the fuel and compared to the reference methane-air combustion under two operational conditions: fully premixed and stratified. Results reveal that H2 addition increases HRR in both stratified and premixed cases compared to pure methane combustion; however, the peak HRR in stratified case occurs in upstream locations (near the burner exit) which, can be related to higher burning velocity in stratified case. Also, while adding H2, HRR profiles move outward, especially in downstream locations showing that the flame expands radially. All in all, stratification intensifies the changes in temperature, local equivalence ratio, and HRR.