Combustion characterization of the mixtures biogas-syngas, strain rate and ambient pressure effects

Abstract

The use of biofuels in applications of interest requires knowledge of behavior of their flames under various working conditions. This paper aims at demonstrating the effect of strain rate and ambient pressure on laminar diffusion flames structure and extinction temperature limits of biogas-syngas mixtures. Opposed-flow configuration is adopted over a wide interval of strain rate (nearly from ignition to extinction) and ambient pressure (from 1 to 10 atm). Chemical kinetics is described by GRI-Mech 3.0 mechanism and Chemkin program used to solve the problem. Results revealed that increase of hydrogen volume in syngas highly enlarges strain rate extinction limits and keeps extinction temperature nearly constant. On the other hand, methane volume augmentation in biogas preserves approximately extinction strain rate and improves extinction temperature. Besides, it has been observed that increasing strain rate enhances non-equilibrium effects and radical production; whereas, it reduces temperature and final combustion products. It has been established that ambient pressure has opposite role of strain rate except for flame thickness. Results showed that in this kind of flames, for the cases of low strain rate and pressure or high strain rate and pressure, the NO species production is governed by the NO2 route. For the other cases, the prompt route is preferred and the thermal path is the least favored and disabled at elevated pressures. Reaction zone thickness is almost constant for all compositions; however, it is reduced by pressure and strain rate augmentations.