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I'm researchigng a spitfire crash near my home town 1944 . The pilot did not survive the crash. Now I'm writing his story. The pilot reported engine trouble. During my research I found followin data:

  1. His wingman reported later (quote) "I saw black regular streams of boost smoke comming from the aeroplane, indiciating he was priming his way".
  2. There is a change that the radiator was hit by FLAK and was leaking, resulting in a cooling problem and raising the engine temperature.
  3. the radiator was black, mostlike set on fire

Trying to find possible cause of the crash, I have questions (I'm not an engineer)

  • can priming the engine (kigass) reduce the engine temperature to avoid overheating
  • can a cooling radiator set on fire? For example after being hit by flak or because of (extended) priming ? best regards
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    $\begingroup$ What is KiGass? $\endgroup$
    – Ralph J
    Feb 8 at 13:55
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    $\begingroup$ Please pretend your question is going to your editor and edit your question for spelling, grammar and clarity... $\endgroup$
    – FreeMan
    Feb 8 at 14:57
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    $\begingroup$ Kigass is the name of the company that made primer pumps for Spitfires. Apparently, "Kigassing" became slang for injecting fuel into the engine in that manner. $\endgroup$ Feb 8 at 20:25
  • $\begingroup$ Bullet number 2: change or chance? $\endgroup$
    – CGCampbell
    Feb 9 at 12:54

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His wingman reported later (quote) "I saw black regular streams of boost smoke coming from the aeroplane, indiciating he was priming his way".

The point is that the engine was apparently not getting any (or sufficient) fuel through the normal means, so the pilot was using the primer to deliver fuel to the engine. Not that the pilot was trying to cool the engine by priming. The "regular streams" of "boost" (perhaps should read "black"?) smoke from the engine were due to the primer delivering a rich mixture, not due to a fire that the priming was intended to extinguish.

can a cooling radiator set on fire?

Ethylene glycol is combustible. See for example https://www.cdc.gov/niosh/ershdb/emergencyresponsecard_29750031.html#, click on "emergency response", "fire fighting information".

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  • $\begingroup$ This is about what I was thinking. $\endgroup$
    – John K
    Feb 8 at 19:50
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    $\begingroup$ If the account was a transcript of a verbal debriefing then "blue" might be a better interpretation of "boost". $\endgroup$ Feb 8 at 22:07
  • $\begingroup$ Although glycol is flammable, it's mixed with water in engines, including the Merlin XII by 1939 (per Wikipedia. Normally there's more water than glycol because water has higher specific heat capacity (only slightly higher volumetric heat capacity). Glycol alone, however, has a higher boiling point (lots of relevant data at engineering toolbox, but unfortunately not the flash point of a mixture $\endgroup$
    – Chris H
    Feb 9 at 14:52
  • $\begingroup$ ... but see DSIAC - even pure glycol, not used in the Spitfire by '44 would be a low risk, and with 30% in water, no risk $\endgroup$
    – Chris H
    Feb 9 at 14:53
  • $\begingroup$ It's notable that running rich causes cooler cylinder temperatures than running lean, so injecting extra gas into the cylinders, even if they were already running, would cause cooler cylinders and (I think) lowered exhaust gas temps as well. For a modern example of this phenomenon, piston engine airplanes are typically run full rich during takeoff to reduce the high cylinder temperatures caused by full power. $\endgroup$ Feb 9 at 19:15
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To your specific questions:

First, dumping fuel into an engine by priming to cool it by evaporation does not work. In an operating engine a rich mixture runs cooler than a lean mixture, but this is because the lean mixture burns slower and exposes the cylinder to high heat longer. The result is measured in tens of degrees in cylinder head temperature while the flame in the cylinder is ~2000 centigrade. If the pilot was indeed priming the engine, he was trying to keep it running in the belief it was not getting fuel.

Second, it was not coolant from the radiator catching on fire. The spitfire radiator is wing mounted near the belly and nowhere near the engine, so black residue here was either always there or may have been smoke residue from an already burning engine.

enter image description here

Also, though ethylene glycol is slightly flammable any water mixed in needs to be driven off before it will ignite. The spitfire uses 70% water 30% EG, so this is not easy to do without a nearby, already burning, heat source.

An initial review of a few papers examining both antifreeze and pure ethylene glycol seem to indicate that there is a low risk of the coolant being either an initial fire source or a primary fuel source. As expected, the water and the phase change required to evaporate it is a strong deterrent to igniting the coolant due to heat losses, and since ethylene glycol has a boiling point of 388 °F (198 °C), the water will preferentially be evaporated first before significant ethylene glycol vapors can be generated.

You did not specifically ask for the cause of the crash but if a pilot reported engine trouble in an aircraft emitting smoke after possibly being hit by flak, it is likely the engine had mechanical damage and either oil or fuel was starting to burn. The reference to your "boost smoke" statement to gather context would be helpful, as to my knowledge this is not a thing.

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Running richer mixture will lower the engine temperature to a certain degree, but I'm not sure, given the information availlable, this is why priming was used in this case. As quiet flyer suggested, the pilot may have attempted to feed the engine fuel by priming to keep it running.

The "boost smoke" may also have been a small fire in the engine bay, since the radiator was covered in soot. Then again, are you sure the radiator was not painted black? This is sometimes used in automotive applications to increase heat transfer in low flow conditions (black surfaces both emit and absorb heat more efficiently).

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    $\begingroup$ Black is no better than silver in radiation at engine cooling temperatures. This heat is radiated at mid IR wavelengths, outside the visible spectrum. Black absorbs visible wavelengths better than silver which is the source of the misunderstanding. $\endgroup$
    – Pilothead
    Feb 8 at 22:47
  • $\begingroup$ IR emission, unless temps are very high, is negligible compared to heat rejected by conductive/convective transport. It's why you insulate buildings for convective heat loss, not IR, and painting heat exchangers black to get their emissivity near 1 has no detectable effect, more than offset by the insulation of the paint. The same reality is a problem for the global warming narrative. IR absorption by greenhouse gasses from earth's surface is less than 10% of energy absorption by the atmosphere. It's nearly all conduction/convection and water evaporative transport. $\endgroup$
    – John K
    Feb 9 at 5:53
  • $\begingroup$ I've seen studies/tests where there is a measurable difference between black and bare metal emissivity, I'll try and find them. I'll reiterate these were automotive applications involving stationary air (iirc). $\endgroup$
    – Jpe61
    Feb 9 at 6:33
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    $\begingroup$ As noted by Pilothead, the radiator is not inside the 'engine bay' so that part makes no sense. $\endgroup$
    – MikeB
    Feb 9 at 8:15
  • $\begingroup$ There is, as it turns out, plenty of evidence that painted surfaces radiate heat with greater intesity than polished metal. Now, radiator rarely are polished, so in that sense my comments are senseless (pun intended). but anyway. $\endgroup$
    – Jpe61
    Feb 9 at 13:27

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