Effect of Non-Luminous Flame Radiation During Methanol Droplet Combustion

Abstract

The effect of non-luminous thermal radiation on the combustion of a suspended methanol droplet in a low temperature (300 K) and low pressure (1 atm) environment is discussed in detail. Numerical results are obtained using a predictive, transient, two-phase, axisymmetric numerical model that includes surface tension effects. Radiation is modeled using the optically thin approximation with the product species CO₂ and H₂O as the radiating species. Results for combustion in a nearly quiescent atmosphere (initial Reynolds number 0.01) and initial droplet diameters in the range of 0.43 mm to 3 mm are presented. In agreement with the reported literature, it is shown that the effect of flame radiation is negligible when the initial droplet diameter is less than approximately 1 mm and becomes increasingly important for larger droplets. As a result, the average evaporation constant decreases with the initial droplet diameter. Radiation and surface tension combined as well as surface tension alone have a significant effect on the predicted extinction diameters of methanol droplets. However, when surface tension is neglected, radiation alone has a negligible effect on the prediction of the extinction diameter. The extinction diameter presents a non-linear variation with the initial droplet diameter for initially large droplets. The agreement with experimental results available in the literature is very good.

Keywords:

• Droplet combustion
• Methanol
• Non-luminous radiation
• Surface tension

This research was funded by NASA EPSCoR under grant NCC5-572. Computational resources were provided by the Thermal-Fluids computational facility and the Research Computing Facility at the University of Nebraska – Lincoln.