Experimental and kinetic study on the laminar burning speed, Markstein length and cellular instability of oxygenated fuels

摘要

The laminar burning speed, Markstein length and cellular instability of three oxygenated fuels, polyoxymethylene dimethyl ether 3 (PODE3), dimethyl carbonate (DMC) and n-butanol (NB), were experimentally studied using spherical flame propagation method. Both of the three fuels are potential alternatives for petrochemical gasoline and diesel. Laminar burning speeds and Markstein lengths were measured at ambient pressure and elevated temperature (363 K-423 K) with three extrapolation models including linear and non-linear employed to extract the unstretched flame speed. Onset of flame cellular instability of the three fuels was determined at high pressure (0.5–0.75 Mpa) which was favored to the occurrence of cellular instability. Three well-validated mechanisms for PODE3, DMC and NB respectively were used to numerically analyze the flame structure and then understand the underlying effect of the molecular structure of oxygenated fuels on laminar flame propagation. Results show that PODE3 has the highest laminar burning speed among the three, supporting by both thermal effect and kinetic effect. While the laminar burning speed of NB is higher than that of DMC, which is due to the combined effect of thermal factor and kinetic factor. The molecular structure of oxygenated fuels exerts an influence on the laminar flame propagation through the fuel-specific cracking pathway and resulting formed intermediates with different reactivity. The absence of C–C bond within PODE3 and DMC leads to the formation of substantial oxy-intermediates (CH2O) with high reactivity during fuel decomposition. PODE3 has the most stable flame among the three because of the strong stretching of PODE3 flame. The flame stability of DMC and NB is approximately similar especially at high initial pressure.