Let's assume somebody show you a combustion and ask you that what kind of combustion is it? How do you show that it's Detonation or Transient or Deflagration?
I've read some stuff on the net, e.g.
https://www.quora.com/What-is-a-detonation-and-what-is-a-deflagration-in-terms-of-fire
https://www.quora.com/What-is-the-difference-between-deflagration-combustion-and-detonation-combustion-in-CI-engines
https://www.quora.com/How-do-I-explain-the-difference-between-deflagration-and-detonation
But it looks like knowing the type of combustion is a challenge. For example in the first link you can see this paragraph:
"Keep in mind, though, that a fast deflagration is STILL an explosion! Black powder deflagrates, but that is still an explosion. Detonation takes place in high explosives like TNT or dynamite."
Is there any formula or equation that show us a combustion is Detonation or Transient or Deflagration?
Please post your answer for two cases. Experimental and numerical simulation. I mean how do you know when they show you the real combustion and when they show you the numerical simulation of the combustion?
The Chapman-Jougeut equations or, more precisely, the ZND models describe both detonation and deflagration events and provide quantitative estimates of how they are distinguished. These equations are widely published. These include the following conditions, which can be experimentally or numerically explored
1. A detonation proceeds at sonic velocity or higher relative to the unburned gases. A deflagration proceeds slower than this, generally much slower.
2. Detonations produce much higher peak pressures.
3. Detonations generally proceed through pressure-driven decomposition of the reacting gases whereas deflagrations proceed via chemical reaction.
4. Detonations release the same amount of energy as deflagrations of the same material, but the energy release is much faster.
Colloquially, any explosion is generally called a detonation. However, most are actually deflagrations. Since both can be highly destructive and both generally lead to explosions of something, they are often equated or at least not distinguished. Deflagrations produce lower overpressures and therefore less dramatic changes in all gas properties and less overall chaos than detonations of the same material. Detonations and deflagrations commonly produce shock waves that propagate from their point of reaction, but these waves are, themselves, not detonations or deflagrations unless they are driving reactions in the materials in front of them. They may be generated by deflagrations and detonations, but the technical use of these terms supposes there is some sort of heat release occurring as the event proceeds. Therefore, a shock wave, regardless of strength, is not a detonation or a deflagration, though it may be caused by either one of these.
Deflagration-based explosions generally result from reaction in some sort of closed vessel, which overpressures the vessel to the point of physical and catastrophic failure. This failure produces a shock wave and is the explosion. A detonation can do this as well, but a detonation does not require any closed container. It propagates through the reactants with increasing Mach number without the need for a confining chamber to establish sonic or supersonic velocities or pressure ratios.
In SI engines, Detonation or abnormal burning, in combustion gives more rate of energy release, more temperature and pressure and adversely affect thermal efficiency whereas In CI engines, knock occurs because of ignition lag in combustion of fuel. As this ignition lag increases, in combustion, excessive amount of energy is suddenly released causing high rate of pressure rise. Ignition lag affects starting up, warming up and produces exhaust smoke.
- Badges
- Science topic
- Similar topics
- Linguistics
- Composition Studies
- Publications