"Combustion is a dynamic and complex chemical reaction that research scientists must try to explain and understand. The simple, traditional descriptor of the 'fire triangle' or the more modern 'fire tetrahedron' may serve as simple verbal shorthand to explain combustion to a lay person, but clearly they are not sophisticated enough to describe the intricate chemical decomposition and simultaneous physical changes that occur where oxygen, heat, and fuel merge into that phenomenon we call 'fire.' In the research world, even flame 'types' are described differently: there are 'premixed' flames and 'diffusion' flames. A premixed flame occurs when the fuel gas and oxygen or air are mixed before ignition. A familiar example is the flame from an oxyacetylene cutting torch. The acetylene and oxygen are mixed at the nozzle and ignited by a spark or other source to produce a concentrated, high-temperature, and efficient flame. Other examples in day-to-day life include laboratory Bunsen burners and the burners for a hot water tank or a gas-fire stovetop."
Coffee Break Training - Fire Protection Series No. 2008-47
United States Fire Administration: http://www.usfa.fema.gov/