The Delft Jet-in Hot Coflow (DJHC) burner is used to investigate flameless combustion by imitating the recirculation flow characteristics appearing in a real complex furnace via a hot diluted coflow[1]. A welldefined stream of high temperature, low oxygen concentration combustion products is injected around the fuel jet as oxidizer in order to obtain ‘Moderate and Intense Low-oxygen Dilution (MILD)’ combustion conditions. For a range of jet and coflow conditions detailed experiments were made [2] and also several numerical validation studies, see e.g. [4,5]. The Eddy Dissipation Concept (EDC) model for turbulence chemistry interaction modeling has been widely used for modeling MILD combustion. EDC is providing a closure for the mean chemical source term based on a proposed microstructure of the reacting flow following from energy cascade concepts. It assumes that chemical reactions can only happen in the smallest eddies, whose size are of the same order of magnitude as the Kolmogorov scales, the so-called fine structures. Thus, the fraction of fine structure 훾훾∗ and mean residence time 휏휏∗ (the reciprocal of it denotes the mass exchange between reactants inside fine structure and the surrounding) are necessary for EDC simulation. They are related to turbulent kinetic energy 푘푘 and eddy dissipation rate 휀휀 (which are calculated from turbulent models) via two constants 퐶퐶퐷퐷1 and 퐶퐶퐷퐷2 . It has been confirmed that 휀휀 = 2퐶퐶퐷퐷1푢푢∗3/퐿퐿∗ = 4퐶퐶퐷퐷2푢푢∗2/3퐿퐿∗2.

We report on a comparative study of model predictions of jet-in-hot-coflow flames. TheDelft Jet-in-Hot- Coflow (DJHC) burner was built to mimic the important characteristics of flameless combustion without the complications of a real furnace [1,2]. The DJHC burner has been used to create a turbulent diffusion flame of Dutch Natural Gas in a coflowing oxidizer stream of high temperature with low oxygen concentration. The experimental database contains the results of high speed chemiluminescence imaging, velocity statistics from LDA measurementsand temperature statistics from CARS measurements. In recent years several computational studies have been made using the DJHC burner as validation database [3-9]. It has been shown before that predictions are sensitive to the coflow radial profiles of temperature and oxygen concentration, to there presentation of effects of entrained air, and to turbulence-chemistry interaction and this is also the focus of the present study