Laser Ignition and Flame Speed Measurements in Oxy-Methane Mixtures Diluted With CO2

Abstract

Ignition and flame propagation in methane/O2 mixtures diluted with CO2 are studied. A laser ignition system and dynamic pressure transducer are utilized to ignite the mixture and to record the combustion pressure, respectively. The laminar burning velocities (LBVs) are obtained at room temperature and atmospheric pressure in a spherical combustion chamber. Flame initiation and propagation are recorded by using a high-speed camera in select experiments to visualize the effect of CO2 proportionality on the combustion behavior. The LBV is studied for a range of equivalence ratios (ϕ = 0.8–1.3, in steps of 0.1) and oxygen ratios, D = O2/(O2 + CO2) (26–38% by volume). It was found that the LBV decreases by increasing the CO2 proportionality. It was observed that the flame propagates toward the laser at a faster rate as the CO2 proportionality increases, where it was not possible to obtain LBV due to the deviation from spherical flame shape. Current LBV data are in very good agreement with existing literature data. The premixed flame model from chemkin pro (Reaction Design, 2011, CHEMKIN-PRO 15112, Reaction Design, San Diego, CA) software and two mechanisms (GRI-Mech 3.0 (Smith et al., 1999, “The GRI 3.0 Chemical Kinetic Mechanism,” http://www.me.berkeley.edu/gri_mech/) and ARAMCO Mech 1.3 (Metcalfe et al., 2013, “A Hierarchical and Comparative Kinetic Modeling Study of C1–C2 Hydrocarbon and Oxygenated Fuels,” Int. J. Chem. Kinetics, 45(10), pp. 638–675)) are used to simulate the current data. In general, simulations are in reasonable agreement with current data. 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.