What does dieseling mean? – Part 1

by B.B. Pelletier

Sometimes, I have to be reminded that not everybody understands all the terms I use in my postings, and last week someone asked for an explanation of the term dieseling. This term is almost always used when talking about spring-piston airguns, though there is such a thing as a dieseling event with a precharged gun, as well. That’s something you NEVER want to witness. But, the most common use of the term dieseling applies to spring guns.

What it means
In 1894, Rudolph Diesel designed a working internal combustion engine that ignited the vaporized fuel by means of heat generated by compression, alone. It did not rely on a sparkplug, which meant that an entire engine subsystem was eliminated. The diesel engines of today are based on the work he started that long ago.

A spring-piston airgun generates a very small amount of highly compressed air to power a pellet or BB. When the air is compressed by the piston, the temperature rises to very high levels (Beeman has said 2000 degrees F) that can ignite tiny oil droplets, created when the lubricated piston seal scrapes the walls of the compression chamber. Thus, the diesel effect happens. Because the amount of “fuel” is very small, the force of the resulting ignition is usually also very small, but the presence of smoke in the barrel after a shot has been fired is one telltale indicator.

Read your Cardew
G.V. and G.M. Cardew wondered about the same things we do, so in the 1970s they conducted a series of experiments to determine what things were happening when airguns fire. Their book, The Airgun From Trigger To Muzzle, was a report on these experiments. In 1995, they updated their work and published The Airgun From Trigger To Target. The approach they took makes it obvious to me that they had read Dr. Frank Mann’s seminal work on firearm ballistics of nearly a century before, The Bullet’s Flight From Powder To Target. Like Mann, the Cardews used ingenious ways of testing various airgun principles, and I think that nowhere did they do better than when they described dieseling. You can buy this book here at Pyramyd Air. If you are curious about all technical aspects of airguns, this is one you really need.

Four phases of a spring-piston airgun
They categorized four phases of spring-piston power, based on what happens when the guns fire. Those phases are blowpipe, popgun, combustion and detonation. We are only concerned with the two most powerful phases; combustion (the Cardews call dieseling combustion in their second book) and detonation. Combustion is a true diesel event, but there isn’t enough fuel present to make a mighty bang. The reason they did not use the term dieseling for this phase is because the detonation phase is also a dieseling event. The difference between the two is the amount of fuel available.

A detonation is a very strong combustion. You will hear a bang and, in the most extreme instances, guns can recock themselves and even blow apart! Jess Galan wrote about this in Airgun Digest Vol. 2, when he wrote about “Oil-Can Louie.”

Obviously, there will be a lot of smoke with detonations, too; but with a detonation, you will sometimes see a small flame coming out of the muzzle of the gun! It helps to be in a very dark place to see this phenomenon. 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.

Tomorrow, I will tell you how they did it, and also give you some hint as to how certain sly airgun manufacturers can cheat their velocities.

What about a PCP diesel?
When you charge a precharged gun from a scuba or carbon fiber tank, the rapid compression of air generates heat – a LOT of heat, as a matter of fact. So much heat that there have been a few accidents attributed to this heat and the presence of petroleum-based lubricants that do not belong in precharged reservoirs. These accidents are nearly always catastrophic, and at least one resulted in the death of the person filling the airgun. Another accident happened with a vintage big bore airgun, where lard is used inside the reservoir to trap airborne contaminants. These reservoirs were made at a time when scuba tanks and 3,000 pound pressures did not exist, so lard was not the danger we think it is today. But, if someone fills a vintage tank from a scuba tank, even though they are careful not to exceed the vintage pressure of 500 or 600 psi, the speed at which the air is introduced is enough to create sufficient heat to ignite the lard. When it did, the tank was blown off the connection, fortunately, injuring no one but resulting in this cautionary tale.

19 thoughts on “What does dieseling mean? – Part 1”

  1. BB,my point is this,when diesling tackes place, does it burn off just whats present in the chamber,and if this gets burnt of in one combustion, and there was no more fuel to combust,and no contamination from oil getting in to the piston chameber,then how can they say that high powerd spring guns relie on it for part of ther power source?

  2. Hello B.B.,

    I have noticed you have mentioned “The Airgun from Trigger to Target” before in some of your other posts.

    This is definitely going to be on my list of things to buy with my next Pyramid Air order. Seems like it will undoutably aid in my understanding of certain topics, and I won’t have to air them here.

    Very useful.

  3. BB,

    Tying back to your post last week on breaking in a new gun, I assumed dieseling was a new gun phenomenon.

    I had assumed that due to manufacturing process there is excess oil in the gun and these would “burn off” over time.

    After your explanation, it seems that dieseling is always present since the pressure to cause it is always there. So is the presence of smoke just due to excessive oil?

    And to nathan’s point earlier, does the residue from the event pose any harm to the gun?

    New Mendoza RM-200 Owner

  4. I am looking to purchase a CO2 pistol, and I have a few options that meet my requirements of looks, capacity, price, and power. Here are the 5 candidates that I have whittled down:
    Crosman C11
    Crosman Pro 77
    Gamo PX107
    Magnum Research Baby Desert Eagle
    Walther CP-99 Compact

    I have read you reviews that I can find of the guns listed above. I am currently leaning toward the Gamo due to its rifled barrel (shooting only lead balls in that one) and looks, both of which seem to give it an edge over the competition. What is your opinion of this list? My reason for purchasing is to learn handgun use before I purchase a “real” gun, and to have a good target/plinking/fun gun. Thanks for running such a great blog, it helps make PyramydAir the best air gun site on the web

  5. Hello, i know this is the wrong place to post this, but i dont know where else to put it.
    Ibe been trying to contact your sales department via e-mail and your contact form, about some questions for an order im about to place, but i NEVER get any reply from them.
    ibe heard nothing but good comments about pyramyd air´s customer service, so im very surprised im not getting any response, considering im placing an order for almost $1,200 dollars.
    I would appreciate it if someone could attend my request, or if for some reason they cant, at least tell me that they wont so i can shop somewhere else.

    The order information request i sent via e-mail (twice) is called “Im buying a PCP from you” and its about a fully equiped Condor + accesories that is to be sent to Laredo Texas.


    Ernest Dallet

  6. ernest,
    i bought a condor from them and i spent about 1250, i ended up using stuff from my house and have a 2 grand condor rig.

    I have sent many emails to p air and not had any response. I dont know what to tell you. This blog is more for the discution of airguns, not for complaints. This blog is held by pyramydair but whatever is on here is not a reflection of their opinions. I am not affiliated with pyramydair but i can still post here, just like you did and im doing at this moment.

    If you know this is not the correct place to post why would you.


  7. I was wondering if a recoil pad and wearing some heavily insulated work gloves would reduce the amount of heard sound from a springer. I also wonder if covering the barrel in tape would tune the sound down. What if your face did not come in contact with the gun? Would any of this do anything besides making you miss? I am not conserned with sound but i am curios much like george.


  8. BB said
    “how certain sly airgun manufacturers can cheat their velocities.”

    I say
    Gamo Gamo Gamo Gamo Gamo Gamo Gamo Gamo Gamo Gamo Gamo Gamo Gamo Gamo Gamo Gamo
    1600 fps? NO!

    I guess they did not false advertise they simply wanted the airgun to be a firearm so they could advertise firearm velocity.

    They were dishonest in a couple ways.
    1. the hunter extreme is not a new gun, its the same as the 1250 but giving it a new name is the only way they could almost get away with false ad.
    2. the pba pellet does not increase aything but velocity.
    3. they have not responded to this problem

    Note: this is not a complaint. It is relivent to bbs post.


  9. jandj,

    The guns you have selected all work fine, but none of them is good for target shooting, unless you mean big targets that are very close.

    You would be better off with a Colt M1911A1 or a Walther CP88, because they can hold a one-inch group at 25 feet.

    But if you really like the Gamo, go for it. Any gun is better than none.


  10. Ernest,

    I have contacted Pyramyd Air and they tell me their new email program may list your service provider (ISP) as a spammer. In that case, you are blocked, but you may not get any notification of it.

    Can you call them?



  11. Sumo,

    Most of the sound comes through the bones in your face, but I do believe some must come through the shoulder, as well. When I hold a TX200MkIII away from my face and shoulder, it sounds less loud – almost like other people hear.


  12. sumo said: “If you know this is not the correct place to post why would you.”
    Well, like i said in the post, i dont know where else to report this.

    B.B. Thanks for your help, i cant call them because i dont live in the US (it would cost me as much as the rifle jejeje), but I am placing an order to be delivered TO the USA, to Laredo Texas in fact i know that they dont ship guns to other countries, but this order will be delivered within the USA (ill personally travel to Laredo to pick up the gun).
    You think they might get my message if i write to them from another email account? say yahoo or hotmail?


Leave a Comment