Experimental study on premixed combustion of spherically propagating methanol-air-nitrogen flames |
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Authors: | Xiangang Wang Zhiyuan Zhang Zuohua Huang Xibin Wang and Haiyan Miao |
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Affiliation: | (1) Consultant Engines and Future Fuels, formerly Daimler AG, Research Division, 71065 Sindelfingen, Germany;(2) Work carried out at Institut f?r Physikalische Elektronik, University of Stuttgart, Germany |
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Abstract: | The outward propagation and development of surface instability of the spark-ignited spherical premixed flames for methanol-air-nitrogen
mixtures were experimentally studied by using a constant volume combustion chamber and a high-speed schlieren photography
system. The laminar burning velocities, the mass burning fluxes, and the Markstein lengths were obtained at different equivalence
ratios, dilution ratios, initial temperatures, and pressures. The laminar burning velocities and the mass burning fluxes give
a similar curve versus the equivalence ratios. They increase with the increase of initial temperature and decrease with the
increase of dilution ratio. The laminar burning velocity decreases with elevating the initial pressure, while the mass burning
flux increases with the increase of the initial pressure. Markstein length decreases slightly with the increase of initial
temperature for the rich mixtures. High initial pressure corresponds to low Markstein length. Markstein length increases with
the increase of dilution ratio, which is more obvious when the mixture becomes leaner. Equivalence ratio has a slight impact
on the development of the diffusive-thermal cellular structure at elevated initial pressures. The initial pressure has a significant
influence on the occurrence of the flame front cellular structure. At the elevated pressures, the cracks on the flame surface
branch and develop into the cell structure. These cells are bounded by cracks emitting a bright light, which may indicate
soot formation. For very lean mixture combustion, the buoyancy effect and cooling effect from the spark electrodes have a
significant impact on the flame propagation. The hydrodynamic instability, inhibited with the increase of initial temperature
around the stoichiometric equivalence ratio, is enhanced with the increase of initial pressure and suppressed by mixture dilution. |
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