Flame stretch and flame thickening in turbulent stoichiometric hydrogen/methane premixed jet flames

The impact of hydrogen addition on flame stretch, strain, and thickness is examined for turbulent premixed jet flames fuelled with stoichiometric hydrogen/methane mixtures. A Direct Numerical Simulation (DNS) dataset with four cases (0, 10, 50, and 80% hydrogen by volume) at a fixed jet Reynolds number of 10,300 is analysed. Keeping the Reynolds number constant causes the Karlovitz number to decrease with hydrogen addition. The results show that flame thickening varies with the Karlovitz number, with the highest Karlovitz case ( K a = 75 ) exhibiting thickening similar to cases with much higher Karlovitz numbers, indicating that other parameters such as turbulent Reynolds number can play a role, as recently suggested in the literature. Hydrogen addition leads to non-monotonic behaviour in the stretch Probability Density Function (PDF), driven by the normal strain rate contribution. Finally, the joint PDF of stretch and its components reveals a strong correlation between normal strain rate and stretch, reinforcing trends observed in pure methane flames. • Flame stretch and thickening in hydrogen/methane premixed flames are studied. • Flame thickening is governed by Karlovitz number and possibly Reynolds number. • Hydrogen addition leads to non-monotonic behaviour in the stretch distribution. • There is a strong correlation between stretch and normal strain rate. • A suitable non-dimensionalisation explains hydrogen addition effects.