Effect of propane-methanol blending ratio on the stretched and unstretched flame speeds at elevated initial temperatures

The unstretched flame speed of the premixed propane-methanol/ air flames has been studied experimentally in a constant volume combustion chamber with central ignition. The experiments were done at atmospheric pressure and stoichiometric air/fuel ratio. Various blending ratios of methanol (0%, 20%, 40%, 60%, 80%, 100%) by volume, and different elevated initial temperatures (348 K, 373 K, and 398 K) were used in this study. In general, the results indicated that the unstretched flame speed increased with increasing both methanol blending ratio and initial temperature. For M60 the increment value of unstretched flame speed at Ti=398K was about 9% compared with that of pure propane and by elevating the initial temperature for the same blend ratio (M60) from 348 K to 398 K the increment value was about 8.8%. It is also noticed that Markstein length decreased with increasing both initial temperature and blending ratio, which is indicate that flame instability increased with increasing these parameters.