Jumo-213A for Dora - Page 3 - ED Forums
 


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Old 09-19-2013, 09:21 AM   #21
MACADEMIC
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Good to see these graphs, and thank you for your kind words Yo-Yo. It is incredibly interesting and rewarding to work with you.



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Old 09-19-2013, 09:33 AM   #22
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Jumo 213 A with 1770 PS against Jumo 213 J with 2250 PS
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Left: PS; Below: height in km; Right: specific fuel consumption

From: Junkers Flugtriebwerke; Reinhard Müller; Aviativ Verlag
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Old 09-19-2013, 09:38 AM   #23
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So if the FW190 is getting MW50 then does it mean P51D will get access to 150 Octane fuel? Afaik it is not currently modelled in DCS Mustang.

Sorry if that's not related to FW190, just jumping on the occassion to ask that question
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Old 09-19-2013, 09:50 AM   #24
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Its interesting to see the tech stuff behind the models, thanks for this.

Nice to see the 190D getting the MW50
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Old 09-19-2013, 12:17 PM   #25
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Nice read, thanks for sharing this. It´s always great to get these snippets from ED´s work process and I certainly enjoy to read (watch) it all.
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Old 09-19-2013, 12:29 PM   #26
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I should have placed this materials before... but better late than never. It's a translation from the Russian part of the forum. Maybe some aspects of the engine performance will become more clear. Hope you will enjoy the esse...

Quote:
Due to numerous requests from the workers, food prices will be increased ... Ooops, sorry... gradually we will begin to talk about the Dora and its features. As it was for the Mustang development, the story will not be just for sake of being told, but to show what depths of modeling we climb to modelling similar to the real-world aircraft.

Because apparently after the Mustang release, the workers would ask for its historical rival, the BMW-801 was developed in my spare time, and the new engine (take my word) would have been made from the Merlin for relatively low cost, even though Komandogerat must be developed.
Important note: “workers” and their “requests” was the lovely stamp of Soviet propaganda I hate and thus often recall.

And then quite suddenly the information fell from somewhere that the next aircraft would be the Dora… and it was not good news at all... at least for me.
As you know, the D9 used the Jumo-213A engine. And the Junkers motors had a great feature that almost led me first into a light stupor. Look at the engine performance vs altitude charts - you'll understand. (Look for yourself – there are at least two available diagrams, plus a manual, and all a bit different).
For Jumo engines, as altitude decreases below the full throttle or critical altitude, power remains constant or even increases, although for the engine with plain supercharger automatically maintaining constant boost pressure below critical altitude, its power decreases with decreasing altitude.Power drops due to excess pressure ratio of the blower below the critical altitude. The air is compressed and heated, then the excessive pressure is throttled, but the air keeps excessive temperature. There are several subseqent reasons to get less power: overheated air has less density at the same pressure (engine power is proprtional to air mass flow, i.e. density at the same volume flow that is considered constant at certain rpm), the excessive power to this overheating is stolen from the engine. There is another one disadvantage of low altitude throttling - overheated air is prone to detonation.
The ideal way to solve this problem is to have variable pressure ratio blower.

German engineers successfully solved the problem: for the DB-60X - between the first and second critical heights - gradually increasing the blower speed, and Junkers engineers solved the problem in general by creating a supercharger with variable pressure ratio due to special vanes at the blower inlet. Additionally, as the vane throttle could not work in full range of required power settings, the engine was equipped with a throttle of traditional type to control low power range.
To have engine performance vs altitude near perfect, thus, having no saw-teeth, the designers used the automatic adjustment not just for boost pressure, but for the air mass flow.
Hydro-mechanical MBG was an analogue of BMW Kommandogerat, provided almost the same functions, combining and defining a common coordinated program for the prop governor, boost controller, ignition timing and fuel injection pump. An interesting detail: the Germans were able to combine in the same unit with common aneroid sensor controllers for air mass flow and fuel flow, thus, simplifying the device and avoid possible mismatches in air-to-fuel ratio, as two separate aneroid controlled units would meter air and fuel separately.
MBG also automatically switched the blower speed at the certain altitude.
If oil pressure used for MBG automatics dropped, it shifted to manual mode and the auxiliary throttle began to work in full range providing MP control.

Emergency power

There are a lot of legends and myths regarding these modes. There are several reasons for it: they have never, in my opinion, been truly modeled in simulations, popular books and articles contain sometimes contradicting, sometimes not true facts, and really accurate technical information only can be found in the authentic German manuals.
The most well-known system - MW-50 that made possible to boost the supercharged engine without the risk of detonation. As the British and American engines used air cooling system (inter-and aftercooler) requiring to increase the area and mass of radiators, pipelines, having an additional pump, tank and coolant, the Germans chose a different way - the water-alcohol mixture. Of course, both ways have their advantages and disadvantages, so it’s difficult to say for sure which one was right. Probably, it was done regarding technology allowance, the opportunities to place system parts in the aircraft, etc. Moreover, regarding the features of the fuel metering, injection of 40-50% water-alcohol mixture in Merlins would simply be unprofitable waisting of alcohol. Why so - it will become clear later.

Even if you just inject poor water into the supercharger it increases the power, because at constant boost pressure it increases the density of the air entering the cylinders. A similar effect is achieved due to inter / aftercooler. Lowering of the temperature increases the manifold pressure detonation begins at providing an additional opportunity to further manifold pressure safe increasing.
As you probably remember, automatic injection type Bendix-Stromberg carburetor used in Merlin meters the fuel by measuring the air mass flow (venturi tube determines the volumetric flow rate, gas-filled aneroid - a function of air density, and a needle of special form in an air pass from the venturi tube works as a computer, multiplying these values). If you inject pure water, carburetor correctly determines that additional fuel is required and fuel-air ratio (alpha) is kept. Water-alcohol mixture itself contains a sufficient amount of fuel, so the rich mixture at high power rates will become richer only increasing the amount of unburned fuel in the cylinders.
The Junkers engine MBG, as MW-50 was engaged, automatically readjusted the blower controller to the increased air flow. As the additional amount of fuel supplied with MW-50 was not sufficient to maintain the desired mixture strength, MBG fuel pump for the engines allowing MW-50 was reconfigured for more fuel flow.
The blower controller switch shifting up maximal limit was made in a very simple way: methanol (sometimes ethanol!) vodka fed an injector passing from the tank under pressure of the air taken after the supercharger. This pressure moved a piston driving an oil valve that opens oil passage to the servo-piston. The servo-piston shifts maximal boost limit to the new position adjusted to get desired increased boost.
The system was sensitive not only to the fluid pressure but also to the pressure of propellant air after emptying the tank. On the one hand it required constant pilot’s attention to avoid "dry running" at emergency power boost that could ruin the engine, and on the other, it possibly could be a reason to implement reduced "dry" boost rate (1900 hp) that was considered safe.

Why Germans used methanol…(we will not discuss the matter what is better to drink… methanol gives the same effect but only once in somebody’s life). The real reason is that methanol has slightly higher latent heat of vaporization, so it’s better cooler, and it has higher octane number.
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Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

Last edited by Yo-Yo; 09-19-2013 at 12:31 PM.
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Old 09-19-2013, 01:55 PM   #27
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Quote:
Originally Posted by Yo-Yo View Post
I should have placed this materials before... but better late than never. It's a translation from the Russian part of the forum. Maybe some aspects of the engine performance will become more clear. Hope you will enjoy the esse...
Thanks for finally posting this on the English side, I hope my pestering wasnt too much
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Old 09-19-2013, 01:59 PM   #28
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Quote:
Originally Posted by SiThSpAwN View Post
Thanks for finally posting this on the English side, I hope my pestering wasnt too much
Is the text now more readable than it was after Google translator?
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Ніщо так сильно не ранить мозок, як осколки скла від розбитих рожевих окулярів
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Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 09-19-2013, 02:01 PM   #29
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Quote:
Originally Posted by Yo-Yo View Post
Is the text now more readable than it was after Google translator?
Much better
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Old 09-19-2013, 02:33 PM   #30
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You are right, its not really on topic, but it would be nice to see options for fuel types, but I am not sure how easy that would be to add, maybe its something they could do on the DCS WWII side...


Quote:
Originally Posted by Endy View Post
So if the FW190 is getting MW50 then does it mean P51D will get access to 150 Octane fuel? Afaik it is not currently modelled in DCS Mustang.

Sorry if that's not related to FW190, just jumping on the occassion to ask that question
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