Ignition and flame propagation in methane/O_2 mixtures diluted with CO_2 are studied. A laser ignition system and dynamic pressure data are utilized to ignite the mixture and to record the combustion pressure, respectively. The laminar burning velocities (LBV) are obtained at room temperature and atmospheric pressure in a spherical combustion chamber. Flame initiation and propagation is recorded by using a high-speed camera in select experiments to visualize the effect of CO_2 proportionality on the combustion behavior. The laminar burning velocity is studied for a range of equivalence ratios (Φ =0.8-1.3, in steps of 0.1), and oxygen ratios, D=O_2/(O_2+CO_2) (26-38% by volume). It was found that the LBV decreases by increasing the CO_2 proportionality. It was observed that the flame propagates toward the laser at a faster rate as the CO_2 proportionality increases. Current experiments are in very good agreement with existing literature data. The premixed flame model from CHEMKIN PRO software and two mechanisms (GRI-Mech 3.0 and ARAMCO Mech 1.3 ) are used to simulate the current data. In general, simulations are in reasonable agreement with current data though the mechanisms predict slower flame speeds. The LBV values obtained by the ARAMCO 1.3 mechanism are closer to the experimental values. Additionally, sensitivity analysis is carried out to understand the important reactions that influence the predicted flame speeds. Improvements to the GRI predictions are suggested after incorporating latest reaction rates from literature for key reactions.
展开▼
