Modelling ethylene-hydrogen jet flames in the MILD combustion regime

Abstract

Moderate or Intense Low oxygen Dilution (MILD) combustion is a particular combustion regime which offers improved thermal efficiency and a reduction of nitrogen oxide (NOx) pollutants and soot. In this paper computational fluid dynamics (CFD) is employed to model turbulent jet flames issuing into a hot and di- luted coflow stream, with a view to develop fundamental level understanding of the MILD combustion regime. Reynolds averaged Navier-Stokes (RANS) simulations are coupled with the Eddy Dissipation Concept (EDC) turbulence-chemistry model and the computational results are compared with experimental measurements. For the turbulent ethylene-hydrogen (C2H4/H2) fuel jet, a modified k- turbulence model, the standard Reynolds Stress Model (RSM), Shear Stress Transport (SST) model, k-! models, and a modified RSM are considered. Results show that a mesh, constructed with 53610, primarily rectangular, elements with a characteristic length of 0.950mm, is sufficient to model the combustion processes in the MILD configuration of the JHC burner. The most accurate reacting flow field is predicted using the modified RSM, by adjustment of the factor C1 to 1.6 from the default 1.44. The RSM is the most computationally expensive model, being an anisotropic exten- sion of the standard k- model, however the increased computational cost is small in comparison to the cost of solving the detailed, finite-rate chemistry required for modelling MILD combustion. The modified RSM is therefore deemed to be superior in this application in comparison to the other turbulence models investigated.