Piloted ignition of solid fuels at low ambient pressure and varying igniter location

In order to investigate the effects of ambient pressure and igniter location on piloted ignition of solid fuels, the ignition mass flux of PMMA was experimentally determined for locations of the igniter between 6 and 70 mm above the solid surface, under two external heat fluxes of 21.2 and 25.4 kW/m2. The experimental results show that the ignition mass flux decreases as the igniter approached the solid surface until it reached a minimum, and then the ignition mass flux remains nearly constant followed by a slight increase with a further decrease of the igniter location. In addition, in another series of experiments the ignition mass flux for elm wood decreases by a factor 0.6 at reduced pressure 0.67 (Tibet 0.67 atm) compared to the ignition mass flux at normal pressure (Hefei, 1.0 atm). The results of this work are explained well by a numerical piloted ignition model which also explains recent observations on the ignition mass flux at reduced pressures in a forced-flow ignition and flame spread apparatus.