Luftwaffe pressing more & earlier towards water-alcohol injection (ADI) than towards high-octane fuel?

z42 · Mar 1, 2025

Shortround6 said:
Some of the Fw 190s had system were they could inject (dump?) raw fuel into the air intakes and get around 140hp extra and use 8.8lbs of boost instead of 5.5lbs. (figures from Janes so they converted to British measure). Now why did they resort to a system like that? Maybe because the standard injection pump could not flow the required amount of fuel? Maybe because the fuel being sprayed into the inlet duct/s in front of the supercharger impeller cooled the intake charge somewhat?

IIRC in Calum's book it was mentioned that they ran out of capacity in the original injection pump, and rather than design a new pump with bigger capacity they just added a 15th pump to inject fuel into the supercharger inlet.

z42 · Mar 1, 2025

Luft.4 said:
One should keep in mind that the 601N could not efficiently combust the C3 fuel because the fuel did not fully evaporate. Additional cooling could further worsen the problem. DB 601N + C3 + MW does not appear to be a good combination.
C3 worked in the BMW 801D because this air-cooled engine had worse cooling, allowing for the C3 to fully evaporate in the combustion chamber.

AFAIU the problem wasn't that the 601N couldn't efficiently combust C3 per se, but rather that minute amounts of fuel found their way past the rings into the crankcase (as happens with all engines to some extent), and because of the high boiling point it didn't evaporate away, and over some time as the concentration of fuel in the oil increased the lubrication qualities decreased until either the bearings were damaged or even the engine seized outright.

The composition of C3 was changed over time as well to shift the distillation curve downwards, C3 in 1940 wasn't the same thing as C3 in 1944. But by then the 601N had long been withdrawn from service.

Luft.4 · Mar 2, 2025

z42 said:
AFAIU the problem wasn't that the 601N couldn't efficiently combust C3 per se, but rather that minute amounts of fuel found their way past the rings into the crankcase (as happens with all engines to some extent), and because of the high boiling point it didn't evaporate away, and over some time as the concentration of fuel in the oil increased the lubrication qualities decreased until either the bearings were damaged or even the engine seized outright.

The composition of C3 was changed over time as well to shift the distillation curve downwards, C3 in 1940 wasn't the same thing as C3 in 1944. But by then the 601N had long been withdrawn from service.

Evaporation occurs during combustion. If you want to get really nit-picky with what I wrote then the 601N could not fully evaporate the C3 during its combustion cycle which then caused oil dilution problems.
AKA could not efficiently combust C3... meanwhile the BMW 801D did not have this problem.

z42 · Mar 2, 2025

Luft.4 said:
Evaporation occurs during combustion. If you want to get really nit-picky with what I wrote then the 601N could not fully evaporate the C3 during its combustion cycle which then caused oil dilution problems.
AKA could not efficiently combust C3... meanwhile the BMW 801D did not have this problem.

My point was that the 801D would also suffer from minute amounts of fuel getting past the rings into the crankcase. But since the temperature there was higher than in the 601N that fuel did evaporate (and eventually get out through the crankcase ventilation system) rather than mixing with the oil and wrecking the engine.

tomo pauk · Mar 2, 2025

Wrt. the earlier introduction of water-alcohol injection on the LW - the beneficiaries of that should've also been the other users of the German engines, like Italians and other Axis AFs. A MC.200 with MW 50 might've been even more of a tough cookie before 1943.
Obviously, the Bf 109E/F/G also fall in this category.

Luftwaffe pressing more & earlier towards water-alcohol injection (ADI) than towards high-octane fuel?

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