The influence of turbulence on the burning velocity of premixed CH4-H2 flames with different laminar burning velocities

Abstract

The influence of the turbulence on the turbulent burning velocity S T of a premixed flame, characterized by a flat flame front stabilized in a stagnation flow was investigated using a two component Laser-Doppler-velocimetry (LDV) technique. The use of different CH 4 -H 2 combustion mixtures enabled the laminar burning velocity S L : to be varied between 0.18 m/s and 0.72 m/s. The turbulence intensities u ′ generated in the experiments ranges from 0.1 m/s up to 1.2 m/s. The turbulent burning velocity could be precisely determined due to the simple configuration of the flat flame front. The results show that, for lean flames and for low u ′ values S T linearly increases with u ′, the slope of this function being dependent on S L and increasing approximately proportional to S τ = S L + 5.3 ⋅ S L 1 / 2 ⋅ u ' . Furthermore, the data obtained from lean flames within the present investigations comply well to the relationship: S T =S L +5.3·S L 1/2 · u ′ No noticeable differences could be observed regarding different CH 4 -H 2 mixture compositions, provided S L remained constant. Initial measurements of rich flames have shown that the effect of turbulence intensity on rich flames is different from that on lean flames. A dependence of the turbulent burning velocity on turbulent length scales could not be found for the stagnation flame system.