Numerical Investigation of Dilution with H2O/CO2 and Strain Rate Effects on Laminar Diffusion Flames in Counter-flow Configuration: Analysis for Biogas-Syngas Mixture.

Abstract

Environmental problems linked to the use of fossil fuels are inevitable at least in the medium term. It is therefore essential to optimize combustion systems in order to reduce harmful emissions. To achieve this goal, we combine two techniques during combustion: the use of biofuels and their dilution. The impacts of several factors, including the type of diluent (H₂O and CO₂), the volume of diluent (0% to 40%), and the site where the diluents are injected (oxidizer or fuel side), radiation losses and injection velocity (strain rate from ignition to extinction limit), are examined to obtain the maximum benefits of combustion. The oxidizer is composed of air (0.21O₂+0.79N₂) while the fuel is composed of an equimolar mixture of biogas and syngas ((0.25CH₄+0.25CO₂) +(0.25H₂+0.25CO)). The configuration of an opposed jet flame is used with constant atmospheric pressure. The chemical kinetics is described by the Gri-Mech 3.0 mechanism. The results are in good agreement with the literature data. It is found that CO₂ is more effective than H₂O in reducing maximum temperatures, NOx, CO, C₂H₂ emissions, and other soot; whether it is added to the air or fuel side. Furthermore, the maximum temperatures and extinction limits (i.e., flame resistance) for the fuel-side dilution are higher than those for the oxidant-side dilution. Nevertheless, the latter is still preferred in applications not requiring a high injection velocity. In this study, the zero-emission limit is approached for 10% of the CO₂ oxidant side dilution.