Ignition of a combustible gas near heated vertical surfaces

✍ Scribed by L-D. Chen; G.M. Faeth

• Publisher: Elsevier Science
• Year: 1981
• Tongue: English
• Weight: 902 KB
• Volume: 42
• Category: Article
• ISSN: 0010-2180
• DOI: 10.1016/0010-2180(81)90143-7

✦ Synopsis

A theoretical investigation of the ignition of a combustible gas by a heated vertical surface is described. Laminar, natural convection conditions were treated by numerical solution of the nonsimilar boundary layer equations, assuming an ideal gas and a one-step reaction and neglecting radiation. The plume above the surface was also analyzed, so that the ignition criterion could be specified as the least severe surface condition where a deflagration wave develops in the plume. Heated surfaces included both isothermal and constant heat flux boundary conditions. Plume conditions involved free-standing surfaces and surfaces along a wall. In the latter case, wall boundary conditions included adiabatic and isothermal (equal ambient and wall temperatures) wall plumes. Isothermal surfaces required less severe conditions for ignition than constant heat flux surfaces having the same maximum temperature. The required severity of surface conditions for ignition increased as plume conditions varied in this order: adiabatic wall plume, free-standing plume, isothermal wall plume. The frequently used ignition criterion for heated surfaces, which assumes that ignition occurs where the temperature gradient normal to the surface becomes zero, is shown to overestimate the severity of surface conditions required for ignition in some circumstances. Other limitations of this earlier criterion are that it cannot be applied to either constant heat flux or high-temperature surfaces.