Mathematical Modelling on Chemically Reacting Boundary Type Flow under Reduced Gravity Conditions

A numerical study was performed to give a quantitative description of a heavily sooting, non-premixed laminar flame established in a shear boundary layer in microgravity. The competition between fuel pyrolysis rate, radiation loss due to soot formation and oxygenside diffusion creates a number of unusual phenomena. A three-dimensional, laminar diffusion flame over plate in low-speed concurrent flow was formulated and solved. The model consists of full Navier-Stokes equations for mass, momentum, energy and species. Gas radiation associated with soot formation is included. The PAH inception model, which is based on the formation of two and three-ringed aromatic species, reproduces correctly the measured soot from a laminar ethylene diffusion flame. The flame standoff distance is beyond the boundary layer thickness, while soot resides always within the boundary layer. The fraction of the total energy released by the flame to the surface increases with a rise of pyrolysis rate due to increase in the flame volume. The zone of the high heat flux increases noticeably when the flame becomes most obviously dual on the cross-stream section due to development of the counter-rotating vortex.