Late Bf109 exhaust grime

[Moose]

Exhaust grime is very noticeable in SOME photographs of later Bf109's, mostly high-altitude fighters like the G-6/AS. Makes me wonder... could the pilots adjust the air/fuel mixture in flight?... or would it just become richer at higher altitudes, resulting in heavier exhaust? Could it also be due to late-war fuel quality?

 

[Bretoal2]

Exhaust grime is very noticeable in SOME photographs of later Bf109's, mostly high-altitude fighters like the G-6/AS. Makes me wonder... could the pilots adjust the air/fuel mixture in flight?... or would it just become richer at higher altitudes, resulting in heavier exhaust? Could it also be due to late-war fuel quality?

Exhaust grime is more often related to oil consumption...

 

[Crimea_River]

Also seen on 190D's. I'm no expert but would suggest a combination of factors including fuel and oil quality plus minimal time for harassed ground crews to keep their aircraft clean.

 

[Casor]

Those 109's appear to be late models and the Germans were forced to use synthetic fuels late in the war during the bombing and these fuels were particularly dirty.

 

[Deleted member 68059]

Those 109's appear to be late models and the Germans were forced to use synthetic fuels late in the war during the bombing and these fuels were particularly dirty.

They were using synthetic fuel almost exclusively from about Jan 1941 onwards, for which they had been developing a huge hydrogenation industry to provide for, for a decade beforehand. Their development and use of synthetics had absolutely nothing to do with being subjected to bombing. There is nothing dirty at all about them that doesn't apply to all AVGAS.

 

[Deleted member 68059]

Exhaust grime is very noticeable in SOME photographs of later Bf109's, mostly high-altitude fighters like the G-6/AS. Makes me wonder... could the pilots adjust the air/fuel mixture in flight?... or would it just become richer at higher altitudes, resulting in heavier exhaust? Could it also be due to late-war fuel quality?

As stated this is more of a symptom of oil consumption, because all aero engines run rich at maximum power.

Later in the war to save time and fuel in testing, they dramatically cut the running-in hours that new factory engines were allowed, and then finally stopped running them in
on petrol at all, and used propane.

Consequently the planes were sent out with very badly bedded in piston rings, and this may well have been more visible in effect in those engines using higher boost, as they put a lot of stress on the upper piston ring. This (along with general bad build quality and reduction in assembly standards) is probably the main cause in my opinion.