The Shchelkin spiral is a device that assists the transition from

deflagration Deflagration (Lat: ''de + flagrare'', "to burn down") is subsonic combustion in which a pre-mixed flame propagates through a mixture of fuel and oxidizer. Deflagrations can only occur in pre-mixed fuels. Most fires found in daily life are diffu ...

(subsonic combustion) to

detonation Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with ...

in a pulse detonation engine. The spiral is named after

Kirill Ivanovich Shchelkin Kirill Ivanovich Shchelkin (russian: Кирилл Иванович Щёлкин ) (17 May 1911 – 8 November 1968) was a Soviet physicist born in Georgia, with armenian origin, the former Soviet program of nuclear weapons who made theoretical ...

, a Russian physicist who described it in his 1965 book ''Gas Dynamics of Combustion''. In pulse detonation engines, direct detonation of the combustible mixture can be relatively straightforward, but require more energy than when detonation is preceded by deflagration. The

deflagration to detonation transition Deflagration to detonation transition (DDT) refers to a phenomenon in ignitable mixtures of a flammable gas and air (or oxygen) when a sudden transition takes place from a deflagration type of combustion to a detonation type of explosion. Descri ...

(DDT) must however occur within the length of the detonation tube, which can be solved by providing the Shchelkin spiral. The Shchelkin spiral acts as an obstacle by creating a partial blockage of the detonation tube, effectively shortening the distance along the detonation tube in which the transition occurs..

References

{{reflist Ignition systems Russian inventions Soviet inventions Spirals