Deflagration

Deflagration is a process of subsonic combustion that usually propagates through thermal conductivity (hot burning material heats next layer of cold material and ignites it).

Deflagration is different from detonation which is supersonic and propagates through shock compression.

Flame Physics

We can better understand the underlying flame physics by constructing an idealized model consisting of a uniform one-dimensional tube of unburnt and burned gaseous fuel, separated by a thin transitional region of width δ in which the burning occurs.

The burning region is commonly referred to as the flame or flame front. In equilibrium, thermal diffusion across the flame front is balanced by the heat supplied by burning.

There are two characteristic timescales which are important here.

The first is the thermal diffusion timescale τd, which is approximately equal to $\tau_d \simeq \delta^2 / \kappa$ where $\kappa \;$ is the thermal conductivity.

The second is the burning timescale τb, which is approximately equal to $\tau_b \simeq \epsilon / \dot {w}$ where ε is the total energy released by burning per unit mass, and $\dot {w}$ is the burn rate (eg, the rate of increase of specific thermal energy).

In equilibrium, these two rates are equal:

The heat generated by burning is equal to the heat carried away by heat transfer.

This lets us find the characteristic width $δ$ of the flame front:

$\tau_b \simeq \tau_d$

$\delta \simeq \sqrt {\epsilon \kappa / \dot {w}}$

Now, the thermal flame front propagates at a characteristic speed $S l$ , which is simply equal to the flame width divided by the burn time:

$S_l \simeq \delta / \tau_b \simeq \sqrt {\kappa \dot {w} / \epsilon}$

This simplified one-dimensional model neglects the possible influence of turbulence.

As a result, this derivation gives the laminar flame speed -- hence the designation $S l$ .

Applications

In engineering terms, deflagrations are easier to control than detonations.

Consequently, they are better suited when the goal is to move an object (a bullet in a gun, or a piston in an engine) with the force of the expanding gas.

Typical examples of deflagrations are combustion of a gas-air mixture in a gas stove or a fuel-air mixture in an internal combustion engine, a rapid burning of a gunpowder in a firearm or pyrotechnic mixtures in fireworks.

In astrophysics, flame fronts are believed to play a crucial role in Type Ia supernovae.

There, the energy is supplied not by chemical processes as is the case with all terrestrial flames, but rather by thermonuclear burning.

Deflagration is a process of subsonic combustion that usually propagates through thermal conductivity (hot burning material heats next layer of cold material and ignites it). Deflagration is different from detonation which is supersonic and propagates through shock compression. Flame Physics We can better understand the underlying flame physics by constructing an idealized model consisting of a uniform one-dimensional tube of unburnt and burned gaseous fuel, separated by a thin transitional region of width δ in which the burning occurs. The burning region is commonly referred to as the flame or flame front. In equilibrium, thermal diffusion across the flame front is balanced by the heat supplied by burning. There are two characteristic timescales which are important here. The first is the thermal diffusion timescale τd, which is approximately equal to $\tau_d \simeq \delta^2 / \kappa$ where $\kappa \;$ is the thermal conductivity. The second is the burning timescale τb, which is approximately equal to $\tau_b \simeq \epsilon / \dot {w}$ where ε is the total energy released by burning per unit mass, and $\dot {w}$ is the burn rate (eg, the rate of increase of specific thermal energy). In equilibrium, these two rates are equal: The heat generated by burning is equal to the heat carried away by heat transfer. This lets us find the characteristic width $δ$ of the flame front: $\tau_b \simeq \tau_d$ $\delta \simeq \sqrt {\epsilon \kappa / \dot {w}}$ Now, the thermal flame front propagates at a characteristic speed $S l$ , which is simply equal to the flame width divided by the burn time: $S_l \simeq \delta / \tau_b \simeq \sqrt {\kappa \dot {w} / \epsilon}$ This simplified one-dimensional model neglects the possible influence of turbulence. As a result, this derivation gives the laminar flame speed -- hence the designation $S l$ . Applications In engineering terms, deflagrations are easier to control than detonations. Consequently, they are better suited when the goal is to move an object (a bullet in a gun, or a piston in an engine) with the force of the expanding gas. Typical examples of deflagrations are combustion of a gas-air mixture in a gas stove or a fuel-air mixture in an internal combustion engine, a rapid burning of a gunpowder in a firearm or pyrotechnic mixtures in fireworks. In astrophysics, flame fronts are believed to play a crucial role in Type Ia supernovae. There, the energy is supplied not by chemical processes as is the case with all terrestrial flames, but rather by thermonuclear burning. °	Deflagration is a process of subsonic combustion that usually propagates through thermal conductivity (hot burning material heats next layer of cold material and ignites it).	La deflagrazione è un processo di combustione subsonica che solitamente si propaga per mezzo della conduttività termica (il materiale caldo che sta bruciando riscalda lo strato vicino di materiale freddo e gli dà fuoco).
	Deflagration is different from detonation which is supersonic and propagates through shock compression.	La deflagrazione è diversa dalla detonazione che è supersonica e si propaga attraverso una compressione d’urto.
	Flame Physics	Fisica della fiamma
	We can better understand the underlying flame physics by constructing an idealized model consisting of a uniform one-dimensional tube of unburnt and burned gaseous fuel, separated by a thin transitional region of width δ in which the burning occurs.	Possiamo meglio capire la sottostante fisica della fiamma costruendo un modello idealizzato costituito da un tubo uniforme e unidimensionale di combustibile gassoso sia incombusto, sia combusto, separati da una sottile regione di transizione di ampiezza δ nella quale avviene la combustione.
	The burning region is commonly referred to as the flame or flame front. In equilibrium, thermal diffusion across the flame front is balanced by the heat supplied by burning.	La regione che sta bruciando è comunemente definita fiamma o fronte di fiamma. In condizioni di equilibro, la diffusione termica attraverso il fronte di fiamma è bilanciata dal calore fornito dalla combustione.
	There are two characteristic timescales which are important here.	Ci sono due scale di tempo caratteristiche che sono importanti in merito.
	The first is the thermal diffusion timescale τd, which is approximately equal to $\tau_d \simeq \delta^2 / \kappa$ where $\kappa \;$ is the thermal conductivity.	La prima è la scala di tempo τd, relativa alla diffusione termica, che è approssimativamente uguale a $\tau_d \simeq \delta^2 / \kappa$ , dove $\kappa \;$ è la conduttività termica.
	The second is the burning timescale τb, which is approximately equal to $\tau_b \simeq \epsilon / \dot {w}$ where ε is the total energy released by burning per unit mass, and $\dot {w}$ is the burn rate (eg, the rate of increase of specific thermal energy).	La seconda è la scala di tempo della combustione, τb, che è approssimativamente uguale a $\tau_b \simeq \epsilon / \dot {w}$ , dove ε è l’energia totale rilasciata dalla combustione per unità di massa, e $\dot {w}$ è la velocità di combustione (per esempio, la velocità di incremento dell’energia termica specifica).
	In equilibrium, these two rates are equal:	In condizioni di equilibrio, queste due velocità si equivalgono:
	The heat generated by burning is equal to the heat carried away by heat transfer.	il calore generato dalla combustione è uguale al calore asportato per trasferimento di calore.
	This lets us find the characteristic width $δ$ of the flame front:	Questo ci permette di trovare δ, l’ampiezza caratteristica del fronte di fiamma:
	$\tau_b \simeq \tau_d$	$\tau_b \simeq \tau_d$
	$\delta \simeq \sqrt {\epsilon \kappa / \dot {w}}$	$\delta \simeq \sqrt {\epsilon \kappa / \dot {w}}$
	Now, the thermal flame front propagates at a characteristic speed $S l$ , which is simply equal to the flame width divided by the burn time:	Ora, il fronte termico di fiamma si propaga con una velocità caratteristica $S l$ , che è semplicemente uguale all’ampiezza della fiamma divisa per il tempo di combustione:
	$S_l \simeq \delta / \tau_b \simeq \sqrt {\kappa \dot {w} / \epsilon}$	$S_l \simeq \delta / \tau_b \simeq \sqrt {\kappa \dot {w} / \epsilon}$
	This simplified one-dimensional model neglects the possible influence of turbulence.	Questo modello semplificato unidimensionale trascura la possibile influenza della turbolenza.
	As a result, this derivation gives the laminar flame speed -- hence the designation $S l$ .	Come risultato, questa deduzione dà la velocità laminare della fiamma, da qui la designazione $S l$ .
	Applications	Applicazioni
	In engineering terms, deflagrations are easier to control than detonations.	Dal punto di vista ingegneristico, le deflagrazioni sono più facili da controllare delle detonazioni.
	Consequently, they are better suited when the goal is to move an object (a bullet in a gun, or a piston in an engine) with the force of the expanding gas.	Di conseguenza, sono più appropriate quando lo scopo è quello di muovere un oggetto (una pallottola in una pistola, o un pistone in un motore) con la forza di un gas in espansione.
	Typical examples of deflagrations are combustion of a gas-air mixture in a gas stove or a fuel-air mixture in an internal combustion engine, a rapid burning of a gunpowder in a firearm or pyrotechnic mixtures in fireworks.	Tipici esempi di deflagrazioni sono la combustione di una miscela gas–aria in una stufa a gas o di una miscela combustibile–aria in un motore a combustione interna, la combustione rapida della polvere da sparo in un’arma da fuoco o le miscele pirotecniche nei fuochi d’artificio.
	In astrophysics, flame fronts are believed to play a crucial role in Type Ia supernovae.	In astrofisica, si pensa che i fronti di fiamma giochino un ruolo cruciale nelle Supernove di Tipo Ia.
	There, the energy is supplied not by chemical processes as is the case with all terrestrial flames, but rather by thermonuclear burning.	In quel caso, l’energia è fornita non da processi chimici come nel caso di tutte le fiamme terrestri, ma piuttosto da combustioni termonucleari.