Deflagration vs Detonation
Both of these are types of exothermic processes occurring in slightly different natures. The term ‘exothermic’ refers to the release of energy to the surrounding. Both deflagration and detonation are ways of how the flow of heat and energy is being directed when dealing with combusting reactions. Combustion is a “chemical reaction where the substance reacts rapidly with oxygen with the production of heat and light” (as given in the Oxford Dictionary of Chemistry).
The word ‘deflagration’ comes from a Latin origin and literarily means ‘to burn down’. In deflagration, the heat of the combustion reaction is transferred layer by layer; from a hot layer to the neighbouring cold layer making it hot and then from it to the cold layer lying next to it. This causes ignition and many fires in our daily life are caused by this process of heat transfer. Deflagrations range from flames to small scale explosions. However, in general the heat propagation method involved in here is relatively slow and happens at subsonic speeds. The term ‘subsonic’ refers to any speed slower than the speed of sound and a subsonic event essentially occurs via a sound propagating medium.
Due to the relatively slow transfer of heat, deflagrations are often under control and do not cause sudden and massive explosions where a lot of gas pressure is released in addition to heat. Therefore, this process has been extensively used in many internal combustion engines due to its safety. Also, the ignition of gun powder, fireworks, lighting of the gas stove etc. are all due to deflagration.
Furthermore, this process has been used in the demolition of stone caves in the mining industry as a healthy alternative to high energy explosives due to the relative ease in controlling the process. However, certain sudden short-duration deflagrations can cause harm due to the massive amount of energy released during a short time and due to the pressure impact. These short-duration deflagrations more closely resemble the detonations. When these occur in combustion engines where ideally the deflagration process is what expected to happen, engine knocking takes place with sudden plunges and this causes the loss of power and the excessive heating of certain parts of the engine.
In French, the word ‘detonation’ means ‘to explode’. In this process, heat is transferred via a shock wave front driven by a high energy exothermic reaction trailing behind, which in this case is a combustion reaction. Detonation occurs at supersonic speeds (speeds faster than the speed of sound) and due to the shock wave front it causes massive turbulence in the medium of propagation releasing a lot of pressure along with heat.
Mostly, in bombs and other explosives, this technique is being used since its origin itself, shock waves travel faster through media than an ordinary wave. Also, due to the highly directional nature of the shock wave, energy is being released towards one direction; generally forward direction. Detonation is also used for other less destructive purposes such as depositing coatings on a surface, cleaning old equipment, and propelling aircrafts.
What is the difference between Deflagration and Detonation?
• Deflagration means ‘to burn down’, whereas detonation means ‘to explode’.
• Deflagration is a relatively slow process when compared to detonation which happens at supersonic speeds.
• Detonation releases more energy than a deflagration process during a shorter time.
• Heat and energy propagation in a detonation process occurs via a shock wave front whereas, in a deflagration process, heat transfer happens by heat escaping from layer to layer in the medium.
• In a detonation process, high pressure gas is released in addition to heat, but in deflagration it is mainly heat that is released and causes relatively less release in pressure.