The development of liquid fires commonly accompanies with the external heat radiation. This subject concentrates on the laboratory-scale experiments (100 cm x 4.4 cm x 2.0 cm) on flame spread over jet fuel of RP-3 with radiant heat fluxes of 1.1, 1.69, 2.25, 2.8 and 3.6 kW/m(2). The results show that the flame behaviors, subsurface flow and heat transfer mechanism depend strongly on the intensity of external heat flux. The measurements of flame pulsation frequency and flame spread rate verify that they increase significantly initially but augment slightly afterwards with the externally applied heat flux, indicating that the heat flux is principally used for raising the liquid's temperature in the initial stage of flame spreading. The heat exchanges involving flame spread process, namely, external heat radiation, convective heat flux, conductive heat flux, flame radiation, and re-radiant heat losses are analyzed. The energy calculation model confirms that the total heat flux is approximately equal to the sum of heat fluxes from radiant panel and convective flow. The scaling analysis of velocity of subsurface flow proves that it should be linearly related to the externally applied heat flux in the correlation of u(s) similar to (q)over dot(er)(2/3). (C) 2020 Elsevier Ltd. All rights reserved.