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Author Topic: Dieseling  (Read 230 times)

Offline Novagun

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Dieseling
« on: April 26, 2018, 09:04:50 AM »
The following is a thread borrowed from the GTA forum.  I could not bring across the Tom Gaylord video so perhaps someone can do that. ------

Hey guys I was watching some Airgun Academy videos on YouTube, and Tom Gaylord was talking about lubricating piston seals when he claimed that it is normal for the air gun to diesel and produce some smoke in the barrel that you can blow out after firing it, but that "detonation" is what most people are talking about when there's a loud bang.

But it doesn't seem like having smoke wafting through your barrel is really optimal either, and it seems to be where there's smoke, there was fire.

So what should I think about this?

 My reply is as follows :-

Dieseling is normal  - probably so with leather seals lubricated with hydrocarbon oil. Not so the silicon oil. However you look at it dieseling is undesirable.
With use of silicon oil and grease it can be eliminated and of course Krytox.
I think the important point is that silicon is not a good lubricant for steel to steel contact but is good for steel to synthetic.
Tom Gaylord was not wrong but it would have been interesting to hear his views on the Krytox type lubricants.

Looking at the video the smoke seems excessive for an acceptable amount of dieseling and the gun did go off with a crack. As an aside in New Zealand an air gun that is dieseling and more so detonating becomes, by legal definition, a firearm for which you need a licence.

Nevertheless an interesting and worthwhile video.

Of interest,  I have just read an article in an old South African magazine about velocity inconsistency in an airgun of 20 fps.  It said that over a range of 30 yards the pellet drop caused by the velocity drop is one ten thousandsth of an inch. So how much extra velocity do you get from dieseling and how much variation between each incident of dieseling.

Does it matter?


« Last Edit: April 26, 2018, 09:10:13 AM by Novagun »

Offline Dvlnme

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Re: Dieseling
« Reply #1 on: April 26, 2018, 05:56:29 PM »
Have done lot reading on this one over the years,n cant make my mind up on it eh!!used be springers
 that were ether injected specifically to get that explosion and the increase in velocity it caused,so go
 figure on that one,so obviously the exploding ether prob wouldnt be much different to exploding oil  as far
 as the effect went eh!!as a kid we had one these german ether injected rifles and the same rifle without it.
,no chronos in those days so never knew if velocity actually increased,but muzzle blast was certainly
 louder from ether injected rifle,cant remember if accuacy was any different tween the two rifles tho.
 but seems to me that for accuacy to remain the same with a rifle thats dieselling,it would have to be
 dieseling for every shot,other wise as oil gets burnt away the performance would change,would it not????
 To me the jury still out on this one eh!!as have seen no proof either way from what i have read on the
 issuse,most of it is really just opinions,not backed up by any creditable proof.
 but interesting topic anyway
 cheers mike

Offline Novagun

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Re: Dieseling
« Reply #2 on: April 26, 2018, 07:05:16 PM »
Someone voiced an opinion that for detonation to occur you had to have ignition but not for dieseling.

Here is my reply:-
To get dieseling I think you must have ignition. That is how a diesel engine works. The diesel vapour burns to make the propulsive force on the piston. It burns relatively slowly compared to an explosive force. Detonation of a lump of grease I  think is caused by an abundance of grease and high temperature and pressure. I wonder if detonation is the precise term that should be used. Maybe it is just a bigger dieseling burn causing a higher pressure in the compression tube that causes the crack and a lot of smoke.
Perhaps the video showed what we know as detonation because there are times when an airgun fires and does not make a crack and does not puff smoke but still has a burnt hydrocarbon smell at the breach. It could be just a matter of degree.
Of course it could be that the initial dieseling burn increases temperature and pressure over and above normal to cause the rapid burn of the rest of the grease. After all it is the rapid oxidation of the hydrocarbon that causes the unwanted effect.

To add to that, I don't think even powder burners detonate their charge. I think it is a rapid burn. Explosives like cortex and dynamite explode and bust thinks up but what would a .303 cartridge full of dynamite do to your breach?

PS. I have a can of black powder for my miniature cannon. On the label its says it is not an explosive but it goes off with a decent bang.
« Last Edit: April 26, 2018, 07:11:42 PM by Novagun »

Offline Novagun

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Re: Dieseling
« Reply #3 on: August 07, 2018, 10:33:09 AM »
There is a fresh discussion going on in the Gateway to Airguns forum; airgungate. There are some people who I guess are scientificly qualified and then there are the rest trying to understand or at least come to a reasonable explaination.
It is well worth following the thread if dieseling interests you. Very complicated topic and even the scientists only understand it in theory because there do not appear to have been any practical experiments performed to take measurements.

There is a paper by a Russian called Zeldowich that has been translated to English by NACA that is refered to.
Read and understand it if you can.  Equations, you will see.
« Last Edit: August 07, 2018, 01:05:12 PM by Novagun »

Offline Akzle

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Re: Dieseling
« Reply #4 on: August 07, 2018, 10:35:35 PM »
There were airguns, quite some years back now, that you added oil to, to deliberately "diesel" for increased poaer, or so the sales brochure went.
I have done it to more than a few low-end air guns, either a puff of crc, or a bit of mum's 3n1. Certainly hits harder, but havent done any tests to overall accuracy, or longevity of seals etc. I don't think it would do damage unless it was a real shit gun. But if you had a good gun you wouldnt bother.

Offline Novagun

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Re: Dieseling
« Reply #5 on: August 08, 2018, 12:34:28 PM »
Still trying to put together a very basic description of dieseling and detonation in spring powered airguns to answer concisely the question,what is dieseling.
Here is my effort so far and I post it for criticism.

Dieseling is a deflagration of hydocarbon fuel. That is application of heat to cause rapid burning. This is caused by the rapid compression of air to provide heat to ignite hydrocarbon fuel in the compression chamber.  This results in a subsonic propagation of a flame front through the gaseous medium from the point of ignition in a not completely uniform mixture of air and fuel. This is dieseling; a comparatively mild event.

The onset of this burning rapidly increases the pressure and temperature in the compression tube and when there is sufficient fuel present these increases cause the propagation of the flame front to increase to supersonic speed with an associated shock wave that is both heard and felt as excessive recoil. Smoke can be seen from both levels of ignition but maybe not from a very mild dieseling event. In both instances some burning smell is present.

Because the reaction of the fuel in the airgun is dependant on the presence of suffient oxygen in the air for the burning of the fuel, if either the fuel or oxygen are completely expended then the burning ceases.  The fuel is present in the form of hydrocarbon lubricants, the quantity of which is randomly dependant on the excess present in the compression tube of the gun. The quantity of oxygen present is uniform in each event because it depends only on the amount ingested when the piston is retracted against the spring when cocking the gun. Detonation depends on sufficient fuel being available.

The comparison between the chemical reaction in a diesel engine and that which occurs in an airgun should be differentiated in that the measurement of the ratio of fuel to air is precisely regulated in an engine designed to do exactly that and produce sustained power. The burning of fuel in an airgun is unregulated and depends on the amount of fuel being available and is consequently inconsistent. 

Offline Akzle

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Re: Dieseling
« Reply #6 on: August 08, 2018, 03:50:40 PM »
Have done lot reading on this one over the years,n cant make my mind up on it eh!!used be springers
 that were ether injected specifically to get that explosion and the increase in velocity it caused,so go
 figure on that one,so obviously the exploding ether prob wouldnt be much different to exploding oil  as far
 as the effect went eh!!as a kid we had one these german ether injected rifles and the same rifle without it.
,no chronos in those days so never knew if velocity actually increased,but muzzle blast was certainly
 louder from ether injected rifle,cant remember if accuacy was any different tween the two rifles tho.
 but seems to me that for accuacy to remain the same with a rifle thats dieselling,it would have to be
 dieseling for every shot,other wise as oil gets burnt away the performance would change,would it not????
 To me the jury still out on this one eh!!as have seen no proof either way from what i have read on the
 issuse,most of it is really just opinions,not backed up by any creditable proof.
 but interesting topic anyway
 cheers mike

doh! you pretty well beat me to any kind of point i had!

Offline Akzle

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Re: Dieseling
« Reply #7 on: August 08, 2018, 03:52:31 PM »
To add to that, I don't think even powder burners detonate their charge. I think it is a rapid burn. Explosives like cortex and dynamite explode and bust thinks up but what would a .303 cartridge full of dynamite do to your breach?

PS. I have a can of black powder for my miniature cannon. On the label its says it is not an explosive but it goes off with a decent bang.

quite right, powders are considered propellants, not explosives.

Offline Novagun

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Re: Dieseling
« Reply #8 on: August 08, 2018, 11:22:05 PM »
To continue the discussion and I quote information gleaned from others more informed than I.

Dieseling will increase the velocity of a pellet markedly and often well above the speed of sound. That in itself introduces another problem for accuracy. The primary problem though is getting the exact amount of fuel per shot and to get it to burn at the same rate in an unregulated mixture of air and hydrocarbon to give the same velocity boost each time is impossible so accuracy suffers.
All dieseling reduces accuracy.

In the circumstance where detonation occurs there is a reduction in pellet velocity. This occurs because much of the energy of detonation is dissipated by way of heat going into the metal of the gun, smoke being made, the piston and spring being forced back, vibration of the spring and every other part of the gun that will wobble. Again the detonation per shot is inconsistent and reduces accuracy. There is a further or contributory loss where the discharge gas gets blocked or retarded at the restriction of the transfer port.

Detonation can occur either in the compression tube or behind the pellet only or both.  I am unsure if the detonation occurs only behind the pellet and in front of the transfer port if that produces a force that accelerates the pellet to supersonic speeds but I suspect it would.

In the New Zealnd situation the deliberate introduction of excess fuel into the firing cycle even by loading the pellet skirt with oil, or ether, turns an air gun into a firearm as it is using the combustion of fuel to create a discharge by way of explosive force. It just happens that the fuel is not Pyrodex or whatever they use in bullets and the ignition is compressed air instead of a primer.

As Akzle rightly said it is a complicated process. On top of that those with more knowledge than I state that the description is conceptual as actual measurements have not been done. Maybe the reality is not too far removed from the concept. The mathematics involved just is.


« Last Edit: August 09, 2018, 05:57:07 AM by Novagun »