The role and value of dieseling in springers

[bennedose]

For those who don't know, let me first explain what "dieseling" means. "Dieseling" is when an oil (or vapour) explodes when it is suddenly compressed. Sudden compression causes heating and that heating can set the oil on fire (provided there is oxygen) to cause an explosion. This is called "dieseling" because this is EXACTLY what happens in diesel engines. Diesel engines have no spark plug and the compression causes the fuel to burn.

In the compression chamber of a springer, exactly the same thing can happen. I want to talk about the "how and when" of this phenomenon

We spend inordinate amounts of time trying to ensure that no flammable oils enter the springer's air compression chamber. We speak of moly paste for lubrication and other measures to remove oil. I am gradually beginning to feel that a lot of this is only marginally useful. Here are certain unavoidable facts

1. There is a small amount of diseleing that occurs during every shot fired in a springer no matter what lubricant you have used. This was proven by Cardew and Cardew (I will post the relevant page later)
2. The fact that dieseling is normal is mentioned in other sources (like Umarex.com)
3. Whether we like it or not diseling adds a certain amount of "firepower" to a springers action by burning anything that can burn
4. When the piston compresses the air in the springer chamber, the temperature briefly rises to 1000 degrees C and even silicone oil will burn at this temperature. Even Molybdenum paste has a flash point that is less than this. Almost anything will catch fire in the presence of oxygen when such high tempereatures are reached. It is no use trying to go overboard to stop it - you can't.

The only thing to do is to accept it and ensure that it is not excessive.

What is "excessive" dieseling?
1. White smoke and a foul smell after each shot
2. Very loud sound
3. Obviously high velocity - more than noarmal

What can excessive diseling do?
1. Damage the piston seal
2. Break the spring
3. Carbon deposits on piston seal

How to avoid excessive dieseling
1. try and use non Hydrocarbon based lubricants. Oils are allowed. They will diesel a bit
2. Don't use too much - once in 1000 shots is enough.
3. Never use diesel, kerosene or petrol

In my experience I find that just because my springer has some loss of power it does not mean that the spring and seal need changiong. It needs servicing. Barrel cleaning and lubrication. Some of that lubricant gets into teh compression chamber. There may be diseleing for 2-3 shots after servicing, but if it is more than that you have put too much oil.

The charm of spingers comes from the fact that they are "living animals". they can get moody and down and need a little love after which they pick up and shoot marvellously. If you don't like moody springers and want connsistent performance, go for a PCP.

Here is a screen grab of a relevant page of Cardew and Cardew where they showed that the ONLY thing that stopped deseling was removing ALL oxygen. That caused a drop in power. Dieseling is an essential part of life with a springer. We need to accept it and use it with care

cardew-diesel.jpg

[Basu]

The experiment of Cadrew clearly proves that ARs are subjected some dieseling even if no oil is given in the compression chamber.Essentially the lubricants that is used to avoid friction....gets into the chamber....may be at least qty.but affect the velocity.
I remember, during my early days I used to put Shinger oil in transfer port to enhance power.
I used to be under impression that reduction of friction was responsible for extra energy....
but I was partly correct.....
It can be presumed that even with the advent synthetic seal , the chances of dieseling might have reduced but can not be eliminated.

Basu

[kshitij]

In whatever videos i have seen, dieseling is artificially/purposely achieved by putting a small drop of oil in the skirt of the pellet in a break barrel rifle. In this scenario, the ignition is happening right behind the pellet and not inside the compression chamber.
But if the dieseling is happening in the chamber like you say, wonder how much of it is impacting the pellet velocity. Infact I feel it must be doing more damage than good.

[bennedose]

But if the dieseling is happening in the chamber like you say, wonder how much of it is impacting the pellet velocity. Infact I feel it must be doing more damage than good.

I am not saying it. This information is there in the image I have posted - a page from Cardew and Cardew

No dieseling (due to absence of Oxygen) - there is a 45% reduction in muzzle velocity.

[bennedose]

This is what Umarex has to say about diseleing
http://blog.umarexusa.com/dieseling-air-rifles/

Dieseling in an air rifle is natural due to the lubrication required for smooth operation, but too much lubrication can be damaging to your airgun, and may even result in injury to you or others. This is why we stress you follow the RWS recommended air rifle 1000 shot maintenance schedule (also see 100 shot schedule) and specified amount of lubrication for all of your air rifles.

BB Pelletier in Pyramidair says:
http://www.pyramydair.com/blog/2007/5/w ... an-part-1/

The Cardews warned of the danger of creating an intentional detonation, but they did it to learn as much as possible. They also proved beyond a doubt that all powerful airguns support combustion with every shot. That is the same as saying all powerful spring-piston airguns diesel with every shot.

[bennedose]

http://www.charliedatuna.com/airgun_doc ... nation.doc

There are a lot of airgun people out there that claim dieseling will damage or destroy a springer airgun. That is absolutly not true. The problem is they do not know the difference between dieseling and detonations as the terminology applies to springer airguns. Because of their lack of knowledge and understanding or lack of research on their part, they state misinformation.

“ Cardew” The standard reference (the bible of airgunning)

The Airgun from Trigger to Target written by G.V. and G.M. Cardew is the best source for most of what is known within the field of airguns.

The Cardews did extensive research and experimentation in this field, and they published the complete results, including their test designs. If anyone doubts what someone says, this is where to begin if he wants to prove them wrong. To date, very few have taken up the challenge to prove the Cardews wrong and those that have, has failed.

This book is an excellent airgun reference and is difficult to find.

So….just what does the Cardew’s have to say??????

The four phases of spring-piston guns

The four "phases" refers to how much velocity is generated and also how that velocity is obtained. The phases are:

 Blowpipe

 Popgun

 Combustion (dieseling)

 Detonation


 Blowpipe

This is the weakest of all spring-piston guns. The power plant doesn't generate much compressed air, and the loose-fitting projectile doesn't make good use of what there is. The Marksman 2000K pistol is a modern example of a blowpipe gun, though there have been numerous other examples throughout history. The "Gat" pistols are another example, as is the vintage Quackenbush line of airguns (not the big bores made today by Dennis Quackenbush). The blowpipe is really just a mechanical device that emulates a common pea-shooter or blowgun.

 Popgun

The popgun phase begins when there is more compressed air, but it doesn't generate enough heat for combustion. The pellet fits the bore tightly and makes maximum use of the air pressure. Though the name sounds degrading, all the spring-piston target rifles and some of the pistols are actually popguns. The FWB 300 rifle generates velocities of less than 550 f.p.s. in .177. Since there is no combustion (I will address this in a moment), the popgun is usually the most well-regulated of all spring-piston guns, not varying in velocity by more than a few feet per second. The IZH 53M is a good example of a modern popgun pistol, while the IZH 61 is an example of a popgun rifle.

 Combustion!!! (Dieseling)

This is the phase that almost all adult sporting airguns are in. When the piston compresses the air, the heat it generates is so high that it ignites any small droplets of lubricants that may be present in the compression chamber. What the Cardew’s proved by their testing is that all powerful spring-piston guns burn fuel to generate their power. The power that's added by combustion depends on the amount and combustion quality of fuel available. This is where some badly-tuned spring guns shoot at all different velocities. Ten years ago, I was advised by the importer of some Chinese air rifles to liberally lubricate the compression chamber with corn oil. He said the wax in the oil would leave deposits on the walls of the compression chamber and make the piston seal fit tighter, raising velocity. In fact, the corn oil was a very good fuel! The treated guns jumped by 100 f.p.s., or so. [I bet I've just started a race to the kitchen to "borrow" the Wesson Oil!]


The Cardews maintain that all powerful spring-piston airguns are in the combustion phase. They also say that isn't a bad thing. As long as the combustion is controlled and small, it benefits us all. In other words - all guns diesel. But when it gets out of hand, we move up to the next and final phase.

 Detonation!!!

This is where the so called ”dieseling damage” occurs.

This is the phase you DON'T want to be in! An abundance of fuel in the compression chamber no longer burns - it explodes! You get much higher velocities out the muzzle - and broken mainsprings, swollen compression chambers and guns that sometimes actually re-cock themselves at the other end! All combustion-phase airguns are capable of detonating, so the shooter has to severely limit any fuel-like substance that is introduced into the compression chamber.

When you hear a loud BANG! and sometimes see a bright light coming from the muzzle (flames in the barrel!), you have a detonation. Since all combustion-phase guns can detonate, the thing to do is to reduce the number of detonations to as few as possible. Just having smoke in the barrel is not a detonation, but the byproduct of a normal combustion.

For an excellent guide and to learn and undestand more about airguns and as well as learn more about their experiments, get Cardew’s book.

[mercury]

the Cardew's use the term combustion. is combustion dieseling ?? well, yes at one level it is. but..

i would think there is a difference between combustion and dieseling ; as there is between dieseling and detonation. combustion is a given...a liberal use of combustible lubes can lead to dieseling....excessive use of said lubes could lead to detonation. dieseling or detonation MAY also take place if a spring air gun is dry fired; for sure in magnum springers.

as to the benefits...it does give the extra fps. as to a loss in accuracy ...i am going to stick my neck out and say no ! dieseling ...when some smoke follows the pellets exit from the barrel...MAY/MAY NOT cause a loss in accuracy. if accuracy can be equated to shot consistency ( fps).....and assuming that the piston seal and breach seal have no leak and a quality spring is in place...then the only reason for inconsistent shots and loss in accuracy can be due to excessive lube. it is the movement of the excessive lube and not necessarily the dieseling associated with it that can lead to inconsistent fps and a loss in accuracy.

i am not in any way supporting dieseling...excessive dieseling will hamper accuracy and ruin the internals ; continuous detonation will not only ruin the gun but the user runs the risk of severe injury.

both my guns do not have a wisp of smoke in the barrel after each shot. the BSA is sub 12ft lbs and the 350 is 23+ft lbs and the accuracy excellent..for me at least...over the respective distances for their different power levels.

when combustion is a constant then the benefit comes with controlling the extent of the combustion.

[ganeshn]

@bennedose thanks for uncomplicated and clear explaination on the dieseling in air guns, for most part I never imagined it actually happens and the elegant experiment by cardew to nail it.
what was surprising is the effienincy of a little oil to sustain increase in power, guess it begs a new specification just for lube oil recommended for air guns

[bennedose]

@bennedose thanks for uncomplicated and clear explaination on the dieseling in air guns, for most part I never imagined it actually happens and the elegant experiment by cardew to nail it.
what was surprising is the effienincy of a little oil to sustain increase in power, guess it begs a new specification just for lube oil recommended for air guns

I am currently using WD 40

[brihacharan]

"mercury" wrote....
The Cardew's use the term combustion. is combustion dieseling ?? well, yes at one level it is. but...i would think there is a difference between combustion and dieseling ; as there is between dieseling and detonation. combustion is a given...a liberal use of combustible lubes can lead to dieseling...

> IMHO - The term 'Dieseling' is the result of Rudolph Diesel's discovery of the combustible oil(named after him) when crude oil is subjected to fractional distillation,,,,
> Unlike petrol which requires a spark for ignition, Diesel Oil requires high compression (a principle on which diesel engines work)
> Hence any lube that remains in the receiver of an air rifle when subjected to high pressure when the AR if fired (the piston released with high force) results in the combustion of the lube....
> This action / reaction Pressure & Combustion) probably came to be known / termed as 'Dieseling'
> In reality the combustion must be taking place at the junction of 'the transfer port & breech' = because diesel ignites only when compressed & suddenly released through a smaller aperture (when diesel vaporizes) - This is the principle on which diesel engines are designed & built....
> It can therefore be surmised that if at all any damage to the AR caused due to dieseling happens at the breech area / breech seal / barrel - receiver joint....while carbon deposits occur within the barrel....
Briha

[bennedose]

While searching for information on dieseling I came across several board discussions with contradictory stuff. It looks like teh same myths and the same facts are recycled over and over again. Unfortunately Cardew remains a single point source and until someone comes up with further studies we have to accept Cardew's work.

One myth seems to be that you can stop excess dieseling by shooting heavy pellets. About 2 years ago I had loaded an air rifle full of oil and it was smoking and detonating like the world was going to end. I then shot off about 50-60 of the world's worst pellets - Mastershot Hunt. No doubt the dieseling was less - but ultimately I took the rifle apart and washed it in hot detergent water (Henko washing powder!) to get all the oil and grease off.

Actually that rifle had a useless powerful new spring and the weapon became really sweet after I cut off 6 coils from the spring.

[timmy]

May I horn in here, please?

This isn't so much related to air guns as it is to what is happening in the phenomena you all are describing here.

First, I suspect that "Combustion (dieseling)" and "Detonation" are variations of the same phenomenon: Combustion (in the author's definition) is the ignition of a little bit of fuel (whatever kind or oil or grease is used for lubrication) and Detonation is a larger quantity, which is reacting with a larger quantity of air in the gun when compressed.

The whole business is related to what is known in chemistry as "collision theory." All molecules have a certain shape. In what we are acquainted with for fuels, such as diesel fuel or gasoline, there are a variety of hydrocarbon chains, and the predominance of longer chains in diesel fuel molecules cause them to be known as "heavy oil engines" as compared to gasoline, which tends to have shorter chains.

Regarding gasoline, the primary concern is "octane rating." Actually, the rating is known as iso-octane or, more properly, 2,2,4-Trimethylpentane, but lets keep things simple here. Octane is formed by eight carbon atoms that are bonded with single bonds to each other - as if you put eight coins in a row on the table and made one connection with a string through them all. Then, you would attach two smaller coins to the top and bottom of each "carbon" coin, so there would be 8 carbon coins and 16 small coins, representing hydrogen. Finally, you could also put a small coin on each end, connecting it with the end carbons with a string. So, you would end up with 8 carbons and 18 hydrogens. The molecule of octane would look like this:



Because of the orbits of electrons, the carbon atom actually will attach a hydrogen in a tetrahedral shape, like this:



so the whole octane molecule will have a zig-zag appearance in three dimensions.

iso-octane is an isomer of octane, where the chain of carbon atoms is arranged a little differently, but you get the ideal. Gasoline is typically composed of octane (and its isomers) heptane, which is seven carbon atoms and 16 hydrogens -- a shorter chain, in other words, hexane, which has six carbon atoms (and is a component of WD 40) and pentane, which has five carbon atoms and twelve hydrogens.

The shorter forms of these hydrocarbon chains, methane - one carbon, ethane - two carbons, propane - three carbons, and butane - four carbons (like your cigarette lighter fluid) are in gaseous form at room temperature and pressure.

The idea of "octane rating" for your car engine is that iso-octane is rated at 100 for its resistance to detonation under pressure (it allows a high compression ratio in your engine) and heptane (seven carbons, remember?) is rated at 0 in resistance to detonation under pressure.

All of these short hydrocarbon chains will ignite relatively easily when they are subjected to pressure or high temperature.

Now, for diesel fuel, the hydrocarbon chains are longer and harder to "detonate." Where with a car engine, you want the fuel to resist detonation so you can run higher compression, the opposite is true for diesel -- you want it to ignite as soon as the fuel is sprayed into the combustion chamber, and the long, heavy hydrocarbons in diesel fuel resist detonating, even under the very high compression of diesel engines. Diesel fuel has a "cetane rating" which works the opposite of octane rating: it measures how easy the fuel is ignited. Cetane is a long hydrocarbon with 16 carbons in a row and 34 hydrogens and it is rated at 100. There is a zero end of this scale, too, but describing this is too complex, so let's pass it by.

When the pressure in the chamber of the gun rises, some of the lubricant will be vaporized, and floating around in the chamber as a gas with oxygen and the other components of air. As the air becomes increasingly compressed, it gets hotter and hotter -- which means that the molecules, both oxygen and hydrocarbon (the lubricant) move about faster and faster, and in the more confined space, they begin to slam into each other more often and with greater force. "Collision Theory" holds that, in order for a reaction to take place, one molecule that will react with another (oxygen and hydrocarbon, in this case) have to collide in the right orientation and with enough force to break them and recombine into different compounds, which releases energy.

Of course, this release of energy enables other molecules to collide and react, raising the pressure and temperature even further, in a chain reaction.

The pressure and temperature are sufficient in a diesel engine to cause the fuel to ignite as soon as it is sprayed into the combustion chamber.

The gasoline and air are compressed together in an ignition engine, and a spark plug is fired at the proper moment to initiate a small reaction -- the spark heats a small amount of air/fuel as it ionizes a discharge path, and this burning fuel initiates a chain reaction.

So, this is what is going on in a springer when the compression pressures are sufficient to ignite the lubricant.

Incidentally, Rudolf Diesel's first engines were designed to run on coal dust -- this is extremely explosive when mixed with oxygen and is likely to have contributed to the sinking of the Lusitania in WW1. Diesel's coal dust engine was not a success, as the combustion could not be controlled and the explosion wrecked the engine. Diesel was successful in developing an engine using vegetable oil -- so much for new biofuels!

Anyway, pardon my digression, but I hope that this aids some interested party in understanding what goes on when an air/fuel mixture is ignited by compression.

[bennedose]

Regarding gasoline, the primary concern is "octane rating." Actually, the rating is known as iso-octane or, more properly, 2,2,4-Trimethylpentane,

That's interesting. I didn't know that and assumed it was a straight chain. Maybe I am wrong but this "compact" molecule seems to offer up more opportunities for the Hydrogen atoms to bump into nearby Oxygen atoms and go bang!

[ganeshn]

I am currently using WD 40

Does it show signs of dieseling.
Is it better than the usual barell oil.

That's interesting. I didn't know that and assumed it was a straight chain. Maybe I am wrong but this "compact" molecule seems to offer up more opportunities for the Hydrogen atoms to bump into nearby Oxygen atoms and go bang!

The compactness of the molecule stabilizes the free radical more hence it tempers the runaway combustion which otherwise becomes a detonation in a gasoline IC engines.


in diesel engines the detonation does not take place due to direct injection of fuel.

[bennedose]

Does it show signs of dieseling.
Is it better than the usual barell oil.
.

WD 40 is "better" in the sense that I can get away with a short spray at the transfer port rather than directly into it or dropping a full drop of oil into the port. That way I get a bit of smoke for 2 shots and that's all. If you put a drop of oil in you get detonation for 10 or 15 shots.

I had bought a Weihrauch HW 35 in the UK in 1984 and the seller had given me a bottle of silicone oil, expressly advising me to put a drop of silicone oil through the transfer port every 100 shots or so. I did that religiously for nearly 30 years but back then I would shoot 100 shots in one year. Nowadays it is 100 shots in a week. Of course I no longer have the Weihrauch.

Reading Cardew and Cardew - you find that they have great praise for leather seals. He points out that they are tough, and they swell up to hold a seal well. This goes against conventional wisdom that demands synthetic seals. Synthetic seals are no doubt good, but I suspect they are not as forgiving as leather seals. GSmith still sell high quality leather seals