Effect of Replacement of Air N2 by H2O on Internal Structure and Pollutants Formation in an Opposed Jet Diffusion Combustion of a Hydrogenated Biogas in Flameless Regime

Nowadays, combustion intervenes in more than 80% of primary energy consumption, the control of the combustion process is essential. Fuel consumption, emissions reduction and energetic efficiency increasing are challenges to which researchers are faced. The most interesting invention that meets nearly all these prerequisites is the flameless combustion regime. This regime is based on the dilution and preheating of reactants by recirculated exhaust gases. This regime is well adapted for the low calorific fuels such as biofuels. In this context, this work presents a contribution to flameless combustion which differs from the conventional one by its low emissions and high efficiency. This numerical study considers the effects of air contained nitrogen substitution by water vapor, the oxygen volume concentration in the oxidizer stream and hydrogen doping of the fuel. To simplify analysis, the opposed jet configuration is adopted with a full diffusive transport approach. The MILD combustion is described by the well-known Gri 3.0 mechanism. It has been noticed that oxygen reduction within a range of 4% to 6%, which is a characteristic of flameless combustion, reduces significantly temperature and emissions whereas hydrogen addition to the fuel, which increases temperature and emissions, has a lower impact. Dilution by water vapor reduces temperature and emissions by thermal and chemical effects except OH radical.