Do PCPs diesel?

[igolfat8]

I thought I read where PCPs don’t diesel but I can’t find anything in the search function. If they don’t diesel, why not? And why do Springers diesel? I recently waxed some pellets with bicycle chain wax and have been shooting them today but did not experience any dieseling like I remember from a springer I had many years ago.

[oldnamvet]

Somewhere I read that the springers generate more pressure for a brief millisecond and that ignites any oil or lube.

[CraigH]

Somewhere I read that the springers generate more pressure for a brief millisecond and that ignites any oil or lube.

I imagine the caveat is, if petroleum oils are used.   

PCP users are always cautioned to only use silicon oils and greases to preclude the issue.

I don't know about transient dynamic conditions, or the precise points of combustion for various lubricants.

[PakProtector]

PCP users are always cautioned to only use silicon oils and greases to preclude the issue.

No...pcp users are cautioned to use silicone or Teflon(Fluro-polymer, like Krytox ) oils because the behavior of air as an oxidizer at high pressure is *MUCH* more energetic.

Also, do something foolish like fill with O2, and charge to the usual firing pressures, and all sorts of bad things can happen with the usual flammable contaminants in silicone.
cheers,
Douglas

[ShakySarge]

A PCP should never diesel or detonate. As Pakprotector stated, Lubricants should only be silicone or Krytox and the like.

[FuzzyGrub]

A springer compresses air rapidly, when fired, very similar to a diesel engine, and can ignite compostable substances, such as oils.

A pcp compresses air when you fill it, slowly compared to the above, and gives off some heat in the process.  When fired, the air expands and causes a cooling effect. 

[rsterne]

A pcp compresses air when you fill it, slowly compared to the above, and gives off some heat in the process.  When fired, the air expands and causes a cooling effect.

That is correct.... There may be a transient spike in temperature in the transfer port very early in the shot cycle.... but with the overall cooling effect of the expanding air, I have never heard of dieseling in a PCP....

Bob

[igolfat8]

Thanks for the clarification and additional information.

[jackssmirkingrevenge]

I've had ignition inside a pumper having gone overboard with silicone oil inside the chamber and subsequently pumping vigorously, there was a muffled "PFFFT" and some smoke and a subsequent disassembly of the chamber revealed it to be coated in black soot.

[rsterne]

I have melted a Delrin FTP in a pumper, too.... from a high compression ratio and a ridiculous amount of pumping.... The heat came from the pumping, and not from firing the gun.... Did your "PFFFT" occur during the pumping stage, or when you fired it?.... Since you said it was a muffled "PFFFT", I assume you achieved a detonation while pumping that caused a failure in a seal?....

This would not be unlike a PCP igniting some oil during the filling process.... I assume the OP meant dieseling during firing.... but then you know what happens when I assume anything.... 

Bob

[FuzzyGrub]

I have "baked" the o-ring in the Huma regulator by trying to feed air quickly, to seal the poppet valve.  That is still far from dieseling. 

[rsterne]

Yeah, that is just overheating the O-ring from the sudden compression of the air around it, with no fuel (other than the rubber of the O-ring) to combust.... I can see it oxidizing and becoming hard and cracked from that, however....
Bob

[jackssmirkingrevenge]

Did your "PFFFT" occur during the pumping stage, or when you fired it?.... Since you said it was a muffled "PFFFT", I assume you achieved a detonation while pumping that caused a failure in a seal?....

Yes, it was during pumping, not firing.

[rsterne]

Sounds like you are lucky a seal failed, or either the valve could have come flying out, or the pump are driven back out of your hand by the detonation.... Could have been ugly.... I wonder how many thousands of psi occurred for that brief instant before the "PFFFT"....

Bob

[Ribbonstone]

For sure, can get a detonation during filling (increasing pressure/increasing heat) with air if something volatile has been used as a lube.

I've not seen direct evidence of a detonation from firing.  Basically decompressin the system (lower temp). TRUE, the released air does recompress at the base of the pellet (at least until the air pressure over comes inertia/friction and starts the pellet movoing down the barrel).

As I've never soaked a pellet in gasoline or ether (or something equally easy to light off), can't 100% swear that that recompression couldn't light it off...but I really suspect not.



A PCP shot can atomize and stray liquid between the valveand blow a vapor out the barrel....see plenty of vids with a little condenstation cloud at the muzzle. 

[Kinetic45^]

I have no proof but I did get a single experience back a while ago that I posted about.

I was given some 220gr SWC cast bullets for my 1858 Remington black powder revolver from Kaido's Ojamaa's design n molds that were lubed in the grooves with a blend of vegetable oil and coconut oil (which is a solid at room temp but melts in your hand).  Very greasy on the base too since they had been pan lubed and removed from that with a Lee 'hole cutter' punch.

While at the range shooting and chronying, I decided to shoot some in my Texan which was running 4500PSI (NOT a AF bottle!!!!! Do NOT overfill the aluminum bottle!!!) and the first shot kicked harder than I had ever had before and my friend immediately said "I thought that was an air rifle... a small jet of flame just came out the barrel!"  and the chrony had a very high reading, way over what any air rifle could produce. When I questioned him he said he saw a "2 inch jet of pink/orange out of the muzzle for a fraction of a second as you fired"
The O-ring on the valve was also ruined and I did not / could not shoot it any more that day.

So although everyone says it's not possible SOMETHING strange happened that day.
I think it DID diesel.

When cleaning and inspecting the rifle that night the patches came out absolutely black and sooty.
Here is a pic that has some of the bullets I shot and on the right you can see the Coconut oil/vegetable oil lube.

[rsterne]

It is possible you managed to get it to diesel.... The Air Force rifles have a VERY large volume between the valve seat and the base of the bullet, so there is a lot of air there to be compressed when the valve opens.... We all know what happens when we fill a gun too fast, the reservoir gets hot.... As I said, there is a possibility of a temperature spike in the transfer port at the instant of firing, although the overall effect is cooling of the gas as it expands.... DomingoT wrote a paper on PCPs where he calculated the temperature rise in the transfer port, so the mechanism exists for it to happen, but if I remember correctly, the temperature rise should not have been enough to cause ignition.... Maybe the lube used had a volatile carrier with a very low flash point....

Bob