Air rifles don't use a combustion process to fire the pellet unlike a powder loaded round of ammunition.
I know nothing about dieseling in air rifles.
I knew nothing about it, prior to using this one, referring to the Ruger .22
While awaiting arrival I read about it, and studied it a bit more in-depth. It is a phenom that occurs from the sudden and extreme compression of air behind the pellet, with both spring, and nitro-piston types. It is supposed to get hot enough with that instantaneous compression that it ignites vapors from the guns internal lubrication, in the same process that drives diesel motors, sparkless ignition due to compression.
I did witness this when I was sighting the Ruger. It only happened after shooting several rounds in a row (was shooting 5, then inspecting the group, and changing targets). I opened the breach, and, out came smoke. I've not seen it in one-off rounds.
explained:
Spring-piston air guns (or simply "spring guns" or "springers") operate by means of a
coil spring-loaded
piston pump assembly contained within a compression chamber separate from the
gun barrel. Before shooting, the user need to manually cock the gun by flexing a lever connected to the pump assembly. The cocking drives the pump piston backwards and compress the spring until its rear engages the
sear. The act of pulling the
trigger disengages the sear, allows the spring to decompress and release the
elastic potential energy stored within it, and pushes the piston forward thereby compressing the air in the pump cylinder. Because the pump outlet (located to the front of the pump) is directly behind the pellet sitting in the barrel
chamber, once the air pressure has risen enough to overcome any static friction and/or barrel restriction holding back the pellet, the pellet is propelled forward by an expanding column of pressurized air. All this takes place in a fraction of a second, during which the air undergoes
adiabatic heating to several hundred degrees and then cools as the air expands. This can also cause a phenomenon referred as "dieseling", where flammable substances in the compression chamber (e.g. petroleum-based lubricant) can be
ignited by the compression heat like in a
diesel engine, and lead to an
afterburner effect with (often unpredictable) additional thrusts, as well as combustion smoke coming out of the muzzle upon firing. Most spring-piston guns are
single-shot breechloaders by nature, but multiple-shot
repeaters with
magazine feeders have become more common in recent years.
https://en.wikipedia.org/wiki/Air_gun