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Effects of propane or ethane additives on laminar burning velocity of methane-air mixtures Hung, Jocelyn


Laminar burning velocities of stoichiometric methane-air, ethane-air, propane-air as well as methane with propane and ethane additives have been determined from pressure-time records during combustion in a constant-volume spherical combustion bomb with central ignition. Additives up to 20 volume percent were used. Initial pressure ranged from 1 to 8 atm. Results show that these additives increase the burning velocity of methane-air by an amount depending on the concentration and initial pressure. Ethane appeared to be more effective than propane for the same volume percent. Two analytical methods were used to deduce the laminar burning velocity: Metghalchi and Keck (M and K) model and linear model. The M and K model is a procedure to satisfy the conservation of mass and energy for a mixture consisting of two homogeneous regions, burnt and unburnt, separated by a flame of negligible thickness. The linear model, from the assumption that the fractional pressure rise is linearly proportional to the fractional mass burnt, calculates the burning velocity based on the mass conservation equation. Results from these two methods agree to within 5%. Dissociation reactions, when neglected, were found to give values of burning velocities that are 10% too low. Ionization probes were used to detect flame arrival times at specific radial locations. Experimental and calculated results agree to within 2%.

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