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An a priori assessment of the Partially Stirred Reactor (PaSR) model for MILD combustion

par Iavarone, Salvatore ;Pequin, Arthur ;Chen, Zhi X.;Doan, Nguyen Anh Khoa;Swaminathan, Nedunchezhian;Parente, Alessandro
Référence Proceedings of the Combustion Institute, 38, 4, page (5403-5414)
Publication Publié, 2020-09-01

Article révisé par les pairs

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Résumé :

Moderate or Intense Low-oxygen Dilution (MILD) combustion allows prevention of the thermo-chemical conditions prone to the formation of pollutant species while ensuring high energy efficiency and fuel flexibility. MILD combustion is characterized by a strong competition between turbulent mixing and chemical kinetics so that turbulence-chemistry interactions are naturally strengthened and unsteady phenomena such as local extinction and re-ignition may occur. The underlying physical mechanisms are not fully understood yet and the validation of combustion models featuring enhanced predictive capabilities is required. Within this context, high-fidelity data from direct numerical simulation (DNS) represent a great opportunity for the assessment and the validation of combustion closure formulations. In this study, the performance of the partially stirred reactor (PaSR) combustion model in MILD conditions was a priori assessed on DNS of turbulent combustion of MILD mixtures in a cubical domain. Modeled quantities of interest, such as heat release rate and reaction rates of major and minor species, were compared to the corresponding filtered quantities extracted from the DNS. The filtered chemical source terms of three main species, CH4, CO2, and CO, and the intermediate OH, were considered. Different submodels for the key model parameters, i.e., the chemical time scale τc and the mixing time scale τmix, were considered and their influence on the results was evaluated. The results revealed that the mixing time scale is the leading scale in the investigated cases. The best agreement with the DNS data regarding the prediction of heat release rate and chemical source terms was achieved by the PaSR model that uses a local dynamic approach for the estimation of the mixing time scale. An overestimation of the OH species source terms occurred in limited zones of the computational domain, characterized by low heat release rates.