Exhaust gas recirculation effects on flame structure and laminar burning speeds of H2/CO/air flames at high pressures and temperatures

Abstract

Experimental studies have been performed in conjunction with a novel differential based multi-shell model to investigate the flame structure and measure laminar burning speeds of H2/CO/air/diluent premixed flames at high pressures and temperatures. This paper focuses on synthetic gas (syngas) as the fuel blend, which is a mixture of H2 and CO, and investigates the effect of synthetic exhaust gas recirculation (SEGR) as the diluent on flame structure and laminar burning speed. SEGR is a mixture of 14% CO2 and 86% N2. In these experiments two different SEGR concentrations of 5% and 10% have been used. The experiments were performed in two constant volume spherical and cylindrical chambers. The cylindrical chamber was set up in a schlieren system equipped with a high speed CMOS camera, capable of taking pictures up to 40,000 frames per second, which was used to study the structure and stability of the flame. The laminar burning speed of the combustion process was calculated from the pressure rise measurement during flame propagation in spherical chamber. Power law correlations have been developed for laminar burning speeds of smooth H2/CO/air/SEGR flames over a wide range of temperatures (298K up to 450K), pressures (from sub-atmospheric up to 5.5atm), equivalence ratios (ϕ=0.6–3) and three different hydrogen concentration of 5%, 10% and 25% in the fuel mixture. SEGR lowers the laminar burning speed and has significant effect on the flame stability compared to H2/CO/air, especially for very lean and very rich mixtures. Experimental burning speeds of H2/CO/air/SEGR mixtures have been compared with available measurements as well as computed values obtained by 1D free flame simulations using two chemical kinetics mechanisms. Very good agreements have been observed with the experimental data available in the scientific literature as well as computational burning speeds.