Flame

A flame is the visible, gaseous portion of a fire, produced when a fuel reacts with an oxidizer in an exothermic process. It consists of hot, reactive gases that emit light as chemical intermediates and, in many hydrocarbon flames, incandescent soot particles radiate energy. The light-emitting species typically include radicals such as H, O, OH, and, in certain flames, carbon-containing fragments like CH and C2.

Flames are categorized by how combustion occurs and how the reactants mix. Premixed flames have fuel and oxidizer mixed before ignition, as in a gas stove or Bunsen burner. Diffusion flames rely on the mixing of fuel and oxidizer at the flame surface, as in a candle flame. Flames can also be classified as laminar, with smooth, orderly structure, or turbulent, where wrinkled, chaotic flow enhances mixing and flame speed.

Color and temperature are influenced by combustion efficiency and soot formation. Blue flames generally indicate hotter, more complete combustion, while yellow or orange flames often reflect soot incandescence. The flame color may also shift with fuel type, pressure, and surrounding air.

Peak flame temperatures in hydrocarbon–air flames typically reach about 1,600–2,000 °C (approximately 2,900–3,600 °F), though local temperatures vary with geometry and mixing. The flame is central to many applications, including heating, cooking, propulsion, and industrial processing. It is also a focus of safety concerns due to burn hazards and the risk of house fires, and it is studied scientifically through flame spectroscopy and measurements of flame speed and temperature.