Do Paintball Guns 'Diesel'

[Toestr]

I'm rebuilding a Daisy 853 air rifle which has a built in single stroke pneumatic pump that feeds a poppet valve (Sheridan style layout) for one shot's worth of pressure. In the disassembly videos I'm watching the guy is talking about cleaning out the black residue in the hammer area/valve/compression tube from 'dieseling'. Except I didn't think this type of rifle would do that. I know I've wiped similar black residue from the lower tube of blowbacks but I always just thought it was dirt/residue from wearing parts mixing with the oil.

I understand that dieseling occurs from the heat of a rapid compression of an air/fuel mix causing combustion and can see how this would be a concern in a sprung piston air rifle.

However this rifle is basically just like any poppet valve marker in that a hammer hits a valve which releases air vs compressing it like a spring piston air rifle. And I don't think the pump is causing particularly much heat because it's not moving particularly fast (it compresses to approximately 1200psi in about a second based on some quick volumetric difference calculations).

So would the rapid release of pressure cause dieseling? I know a bit of dieseling is commonplace in spring piston air rifles, but I didn't think a poppet valve would cause any. Would the type of oil used be able to reduce this?

[Jordan]

Nope. Decompression doesn't cause dieseling.

If you have dirty oil in the compression tube or hammer tube, it's from component wear and oil additives doing their job by cleaning and suspending dirt.

[Pyrate Jim]

Had to ask around, but the consensus was that the black residue is primarily carbon. Non-flammable, so there is no mixing of air and fuel like dieseling, it's all just air.
Air being compressed increases temperature, air expanding loses temperature. (known as "Charles Law" in hydrodynamics)
Certain brands of oil contain solvents. It is possible to compress air to the ignition point of those solvents.

I try to use grease on moving parts, not oil. White Lithium wheel bearing type.

[JeeperCreeper]

As far as I know, dieseling in pellet rifles and such comes from people adding combustible oil in the breech to intentionally make it ignite and shoot hot. Never heard of it just happening from normal use and maintenance.