An experimental and kinetic modeling study on the effects of reformate gas addition on the laminar burning velocities of natural gas

The present study focuses on evaluating the effects of reformate gas (RG) (i.e. 10% CH4, 20% H2, 5% CO, 13% CO2 and 52% N2 by volume) addition on the laminar burning velocity (LBV) and Markstein length of natural gas (NG) fuel. The experimental measurements were performed using a 5.86-L cylindrical constant volume combustion chamber and a schlieren photography system equipped with a high-speed camera was used to record the spherical flame propagation. The numerical simulations were obtained using CHEMKIN-PRO software and six kinetic mechanisms. Measurements were compared with simulations and the FFCM-1 model shows a better prediction with the present experimental data. The experimental measurements and numerical simulations were conducted for NG/RG-air mixture at an initial temperature of 298 K, a pressure of 0.1 MPa and equivalence ratios ranging from 0.7 to 1.3 with varying the RG proportions from 10 to 90%. Results show that the LBV of NG-air flame decreases with the increase of the RG content due to the decrease of adiabatic flame temperature. Moreover, for equivalence ratios ranging from 0.7 to 1.1 and increasing the RG content, the instability of laminar NG/RG-air flames increases due to the increase of CO2 and N2 concentrations. The sensitivity analysis implies that R1 (H + O2 = O + OH) and R15 (H + O2 (+M) = HO2 (+M)) are the most important reactions affecting the LBV as the RG content increases. The analysis of radical concentration shows that the active radical production is deteriorated by 38.38% for OH, 24.47% for H and 34.94% for O when the RG content increased from 10% to 90% in the mixture while the reaction pathway has little changes. The present study demonstrates that the addition of a small percentage of RG is a viable approach to maintain flame stability and reactivity.