Experiments were conducted on IDFs burning butane. The flame holder has a central air jet surrounded by 12 circumferentially arranged fuel jets. The flame consisted of a short entrainment zone and a long mixing and combustion zone with intense combustion. The temperature profiles of the flame showed a cool core at low flame heights, which disappeared at high flame heights. The stagnation point heat flux and radial heat flux distribution of the same flame, upon impinging on a flat plate, also indicated a cool core at low nozzle-to-plate distance but disappeared at high nozzle-to-plate distance. (C) 2004 Elsevier Ltd. All rights reserved.