Comparison of the Reactive Scalar Gradient Evolution between Homogeneous MILD Combustion and Premixed Turbulent Flames

Moderate or intense low-oxygen dilution (MILD) combustion is a novel technique that can simultaneously improve thermal efficiency and reduce emissions. This paper focuses on the differences in statistical behaviours of surface density function (SDF = magnitude reaction progress variable gradient) between conventional premixed flames exhaust gas recirculation (EGR) type homogeneous-mixture under MILD conditions using direct numerical simulations (DNS) data. The mean values SDF cases were found to be significantly smaller than those corresponding flame cases. Moreover, behaviour response variations turbulence intensity compared cases, are explained terms strain rates induced by fluid motion ones arising from displacement speed. It was effects dilatation rate much weaker reactive scalar gradient preferentially aligns with most compressive principal strain-rate eigendirection. By contrast, aligned extensive eigendirection within considered here, but extent this alignment weakened increasing intensity. gave rise predominantly positive value normal flames, whereas remained negative, its increased component speed assumed non-negligible for broader range variable, flames. unburned side burned decreased middle before mildly towards side. These significant propagation effective rate, which explains evolution variation tangential fluid-dynamic values, it overcome negative curvature stretch yield both dependence findings suggest local eigendirections need addressed modelling EGR-type combustion.