Effects of combustion progress variable and Karlovitz number on the scalar dissipation rate of turbulent premixed hydrogen-enriched methane-air flames: An experimental study

The scalar dissipation rate plays a key role in the modeling of turbulent premixed flames. Despite the above, our knowledge concerning the effects of several parameters, such as the combustion progress variable, Karlovitz number, and fuel composition on the scalar dissipation rate requires to be developed. This is carried out experimentally here. Two mixtures, methane-air (Lewis number of unity) and hydrogen-enriched methane-air (Lewis number of 0.8), are examined. Three passive (perforated plates) and one active turbulence generators are used, leading to a wide range of turbulence intensities with the corresponding Karlovitz number changing from 0.1 to 34.5. The hot-wire anemometry and the Rayleigh scattering techniques are used separately to study the background non-reacting turbulent flow and the reacting scalar dissipation rate, respectively. Three models that are available in the literature for estimating the Favre-averaged scalar dissipation rate are experimentally assessed. Using experimental results obtained in this study, it is shown that moving from fresh reactants towards combustion products increases the above modeling parameters by 2-3 times, depending on the tested Lewis number. For each tested Lewis number, empirical formulations that include the effects of both the Karlovitz number and combustion progress variable on the modeling parameters are proposed. Care must be taken in extending the proposed models of the present study to test conditions that are not examined here.