Beatrice Schilling's innovation...

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It was very clever. Still, why didn't RR use fuel injection? I can't remember which BoB book I read it in but didn't someone have a German fuel injection system "on a shelf somewhere gathering dust".
 
Bretoal2 said:
Fuel evaporation in intake manifold lowers mixture temperature and gives better power.
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In fact this effect (at least in single stage engines, it probably did keep most of the gains at high altitude in the 2stg machines) totally vanishes by 35,000/40 feet because the incoming air temperature is so low that the fuel stops evaporating through the supercharger (dicovered by the Royal Aircraft Establishment when they did artificial altitude bench tests of a Merlin-46 supercharger). The rest of the benefit vanishes due to needing chokes. (The required flashback arrestors dont help either)

You can get all those same evaporation benefits at lower altitudes anyway by putting an extra injector in front of the supercharger anyway, like the BMW801, then it works even better because you have no chokes.

In my view the continued droning on about fuel through the supercharger being so wonderful by various RR people post-war, was really just a desperate attempt to salvage some good news from an otherwise deeply embarrasing mistake by RR & associated industries in going to war without even a pressure carburettor, let alone a proper injection system. They realised what an error it was when they tested the first captured German direct injection engines during the Battle of Britain from the "Lammermuir Heinkel" then RR realised that the stupid reports from the RAE by Dr Morley during the 30`s about injection not being any better were garbage. By then it was too late to do very much about it, other than develop their own carburettor (which never worked) or their own injection system (which only just entered service at the very end of the war, and I think never saw combat).

The situation was at least partially rectified from the Merlin-66 onwards by fitting American pressure carburettors, which at least didnt cough and splutter. These problems were in fact known about for years before 1940, but appear to have been basically ignored in Britain. Even American civilian airline pilots knew in the 30`s because they had to often use runways which were so bumpy that they sometimes had engines fail right on take-off as the floats bumped up and down so much it cut the engine !

The float carburettor has no place on any really serious aeroplane, and should have been binned in the 1920`s by all developed nations.
 
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SaparotRob said:
It was very clever. Still, why didn't RR use fuel injection? I can't remember which BoB book I read it in but didn't someone have a German fuel injection system "on a shelf somewhere gathering dust".
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I had nothing to do with the title of the video, which is a little bit... "markety" but this answers that question.


View: https://youtu.be/DOSe4lmy8S4?si=cg9AXgAl1YytJxG_
 
Bretoal2 said:
Carb icing is mostly due to choke, not fuel evaporation.
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You are not discussing the thread here are you? So, do you want to argue about Gas-Laws? Or about the thread?
WRT aircraft float carburetors, the Venturi effect is designed to be a minimum for the sole function of raising fuel from the float bowl, otherwise the restriction becomes very limiting on airflow and creates great losses in the air massflow, with consequent restrictions on possible power. So, temperature drop after the Venturi will be in the region of 2 degrees C per 35mb pressure drop after the Venturi. However, temperature drop of an effective Gasoline/Air mixture is around 25 degrees C.
So, carb icing is primarily caused by fuel evaporation.
You might note that the Bendix Pressure carbs have chokes, they do not suffer from carb icing because the fuel is usually introduced into the eye of the supercharger.

Eng
 
Snowygrouch said:
In fact this effect (at least in single stage engines, it probably did keep most of the gains at high altitude in the 2stg machines) totally vanishes by 35,000/40 feet
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If you integrate the effect of increasing mass charge over altitude, you can see that its contribution allows you to reach 30,000 feet in less time. Moreover:
At this stage we must add that although the full temperature drop due to evaporation cannot be allowed before the eye of the supercharger at high altitudes, yet by the time the petrol has passed through the supercharger and has been subjected to the corresponding temperature rise evaporation will be complete. Hence the induction pipe temperature of the charge (T_ci) is reduced by the full 25°C. at all altitudes.
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Cited from "The Performance of a Supercharged Aero Engine" by S.Hooker, H.Reed and A.Yarker, March 1941

Although the late Wright R-3350 already used direct injection, the P&W R-4360 was fitted with an injected carburetor, which led to icing problems (mainly due to the engine being installed backwards, not fuel evaporation). Noticed while visiting the New England Air Museum. I assume, if you have a good pressured (injecting) carburetor and high quality fuel the need of direct injection is questionable.

P.S. I suspect that the Soviet VK-4 carburetor on the Ash-73 engine was actually a copy or further development of the Bendix Model PR58P3 injection carburetors fitted to the R-3350. I would be very grateful if someone could share a link to information about the VK-4.

I found a photo that could be considered as proof that the K-4 (not VK-4) carburetor on the Ash-73 is a copy of the Chandler-Evans carburetor from the R-3350, and not the later Bendix-Stromberg injection carburetor.
 
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Engineman said:
You might note that the Bendix Pressure carbs have chokes, they do not suffer from carb icing because the fuel is usually introduced into the eye of the supercharger.
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Only if the engine was not mounted backwards. :)
 
bf109xxl said:
Only if the engine was not mounted backwards. :)
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Hi, I am guessing that is on the B-36? There is the possibility of ice forming in some types of ducting and intakes, in specific circumstances and conditions. I am not aware of the R-4360 problem, but more info would be interesting.

Eng
 
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