Does diesel 'explode' in a diesel engine cylinder?

[Sojourner]

I'm having a discussion with someone, and he's wanting to know if diesel is 'explosive' and asserts that what happens in a diesel engine. I say diesel expands when it burns rapidly under extremely high compression and that diesel is not explosive (whereas gasoline or LGP definitely has explosive potential under the right circumstances).



Could any of you RKIs please provide the skinny on the process?



TIA

 

[JMoberly]

You got it right. Diesel is injected into a cylinder of highly compressed air which then burns. There is no spark and the fuel begins to spontaneously burn as it enters the cylinder. This is what allows for greater torque and multiple injection events.



There are plenty of diagrams to be found on google.

 

[DCaswell]

all explosions including gun powder are the result of very rapid burning

 

[JFaughn]

You have define the words first , the way I look at it is that explode is not really a usable word , everything that is refured to as an explossion is really burning , so even a wood fire is not exploding , the defference is the rate of burn , there are now explosives , read a blaster handbook , even so called high explosives are just faster burning , at a fast enough rate of burn there is some sort of word magic , now at no set speed is there any mention of when the word explosive starts .

 

[Vaughn MacKenzie]

Diesel does and does not explode in the cylinder. It depends on how it's introduced. Throw it in there all at once and it'll explode. Spray it smoothly and evenly over the course of several degrees of crank rotation and you mostly have an even burn.

Outside of an engine diesel generally isn't explosive, it's hard to ignite. But if you get a semi or a locomotive in a big wreck it can easily create a fireball.

 

[Forrest Nearing]

You have define the words first , the way I look at it is that explode is not really a usable word , everything that is refured to as an explossion is really burning , so even a wood fire is not exploding , the defference is the rate of burn , there are now explosives , read a blaster handbook , even so called high explosives are just faster burning , at a fast enough rate of burn there is some sort of word magic , now at no set speed is there any mention of when the word explosive starts .

what he said...



and I believe that the diesel/air mixture burns fast enough to be considered an explosion... it's enough to cause a shock wave that rattles against the piston crown

 

[AKaiser]

They are both explosions, but neither is a detonation (high-order explosion), but a deflagration (low-order explosion), under ideal conditions.



Below lies proof that wikipedia isn't without usefulness.



"An explosion is a sudden increase in volume and release of energy in a violent manner, usually with the generation of high temperatures and the release of gases. An explosion causes pressure waves in the local medium in which it occurs. Explosions are categorized as deflagrations if these waves are subsonic and detonations if they are supersonic (shock waves). "



"Deflagration (Lat: de + flagrare, "to burn") is a process of subsonic combustion that usually propagates through thermal conductivity (hot burning material heats the next layer of cold material and ignites it). Deflagration is different from detonation which is supersonic and propagates through shock compression. "



"Detonation is a process of supersonic combustion in which a shock wave is propagated forward due to energy release in a reaction zone behind it. It is the more powerful of the two general classes of combustion, the other one being deflagration. "

 

[tgordon]

In terms of iginition, it is the atomization that causes it to burn. Gasoline will atomize under atmospheric conditions, get rid of the vapors and one can throw a match into a container of it and the match will go out I do not recomend unless you know what you are doing



Take a injector tester and place a lit candle in front of it and one can make a neat fireball as the injetor atomizes the fuel for combustion. :-{}

 

[mhenon]

They are both explosions, but neither is a detonation (high-order explosion), but a deflagration (low-order explosion), under ideal conditions.



Below lies proof that wikipedia isn't without usefulness.



"An explosion is a sudden increase in volume and release of energy in a violent manner, usually with the generation of high temperatures and the release of gases. An explosion causes pressure waves in the local medium in which it occurs. Explosions are categorized as deflagrations if these waves are subsonic and detonations if they are supersonic (shock waves). "



"Deflagration (Lat: de + flagrare, "to burn") is a process of subsonic combustion that usually propagates through thermal conductivity (hot burning material heats the next layer of cold material and ignites it). Deflagration is different from detonation which is supersonic and propagates through shock compression. "



"Detonation is a process of supersonic combustion in which a shock wave is propagated forward due to energy release in a reaction zone behind it. It is the more powerful of the two general classes of combustion, the other one being deflagration. "

You beat me to it! It looks like, by definition, it's an explosion:

ex·plo·sion /ɪkˈsploʊʒən/ Pronunciation Key - Show Spelled Pronunciation[ik-sploh-zhuhn] Pronunciation Key - Show IPA Pronunciation

–noun 1. an act or instance of exploding; a violent expansion or bursting with noise, as of gunpowder or a boiler (opposed to implosion).

2. the noise itself: The loud explosion woke them.

3. a violent outburst, as of laughter or anger.

4. a sudden, rapid, or great increase: a population explosion.

5. the burning of the mixture of fuel and air in an internal-combustion engine.

6. Phonetics. plosion.



I wouldn't have considered it an explosion but what do I know.

Mike

 

[AKaiser]

You beat me to it! It looks like, by definition, it's an explosion:

ex·plo·sion /ɪkˈsploʊʒən/ Pronunciation Key - Show Spelled Pronunciation[ik-sploh-zhuhn] Pronunciation Key - Show IPA Pronunciation

-noun 1. an act or instance of exploding; a violent expansion or bursting with noise, as of gunpowder or a boiler (opposed to implosion).

2. the noise itself: The loud explosion woke them.

3. a violent outburst, as of laughter or anger.

4. a sudden, rapid, or great increase: a population explosion.

5. the burning of the mixture of fuel and air in an internal-combustion engine.

6. Phonetics. plosion.



I wouldn't have considered it an explosion but what do I know.

Mike

Crap I learned in Artillery School finally paid off. :-laf



Of course, mix it with Ammonium Nitrate, and you get a higher order explosive (ANFO: Ammonium Nitrate-Fuel Oil), add blasting caps, and you get a detonation.

 

[GHarman]

You still have a measureable propagation rate that is longer and has more energy than the pressure/time/energy curve of gasoline. What do I know, I'm just a retired welder. :-laf GregH

 

[Rotty]

So what is a nuclear explosion?

Is it detonation, explosion or just a big bang?

 

[AKaiser]

So what is a nuclear explosion?

Is it detonation, explosion or just a big bang?

It's a detonation for sure, as it involves a shock wave, but an exotic form of detonation. It's started by colliding two pieces of fissile material together at a rapid speed, usually using some form of explosive charge. This type was used at Hiroshima. Alternatively, there is another process called "implosion," which was used at Nagasaki. See http://www.cartage.org.lb/en/themes...nReaction/nuclfissionbom/nucllfissionbom.html



Fusion (thermo-nuclear) bombs are actually activated via a fission explosion, which gives off X-rays and heat (hence "thermo-nuclear"), which then creates the conditions for fusion. See http://science.howstuffworks.com/nuclear-bomb1.htm



From http://www.blastgardintl.com/td_explosion_terminology.asp



"Nuclear Explosion - In fission processes, a fissionable nucleus absorbs a neutron, becomes unstable, and splits into two nearly equal nuclei. In an atomic weapon the number of neutrons producing additional fission is greater than 1, and the reaction increase rapidly into a runaway explosion. In the process a small proportion of fissionable material is converted into huge amounts of energy: E = mc2, where "E" is energy, "m" is mass, and "c" is the speed of light.

 

[rbattelle]

Here's a good report on the subject.

Another good one.

Excellent.

Those papers tell much of the story (and they're FREE!). I also always give a plug for Taylor's book. Volume 2 has an excellent discussion of the compression ignition process. Here's an quick excerpt:

Since both the pressure and temperature of the cylinder contents at the time of injection are very high, some chemical reaction undoubtedly begins as soon as the first droplet of injected fuel enters the cylinder. However, this chemical reaction starts so slowly that the usual manifestations of combustion, namely the appearance of a visible flame or of a measurable pressure rise, occur only after the expiration of an appreciable period of time called the delay period. Thus, for diesel engines, it is convenient to define ignition as the moment when a flame visible to the eye or to a photographic film, just appears or when the pressure starts to rise appreciably as the result of combustion.
... It has been shown that in a well-mixed and evaporated fuel-air mixture the reaction rate following autoignition can be extremely rapid. The fact that the maximum reaction rate in the compression-ignition engine is often slower than that of autoignition in a premixed charge of similar composition is due to the retarding effects of incomplete mixing of fuel with air and of incomplete fuel vaporization.

This stuff is great reading.

Ryan