Analysis of EDC constants for predictions of methane MILD combustion

Abstract

The indisputable wide use of the Eddy Dissipation Concept (EDC) indicates that the mean reaction rate is reasonably modeled for MILD (Moderate or Intense Low-oxygen Dilution) and conventional combustions. However, RANS (Reynolds-Averaged Navier-Stokes) modelling with the standard EDC constants tends to over-predict maximum temperatures when applied to the MILD combustion regime. Therefore, there is a modification need of the EDC constants to predict properly the mean reaction rate, and then the maximum temperatures. The relation of the mean reaction rate and the EDC constants, including the primary and the secondary, is presented. A lab-scale methane MILD combustion furnace (MCF) with non-preheated air from literature is chosen for the validation of the EDC constants. The modification is done with one of the secondary EDC constants ranging from 1 to 28 where the primary constant is kept at CD1=0.1357. Predictions with the secondary EDC constant of 4 agree quite well with the measurements of the MILD combustion in this furnace. The modified EDC constant of 2 are suggested for the predictions of the conventional combustion in this furnace. Finally, based on the excess temperature or the normalized root mean square excess temperature (NRET), a criterion for the attainment of MILD combustion in this furnace is suggested.