Ethanol as fuel for German emergency figher aircraft program?

[davebender]

267 million liters. 1938 German ethanol production.
752 million liters. 2010 German ethanol production.
Per Wikipedia the V2 rocket program consumed about a third of total German ethanol production.

What if Germany cancelled the V2 rocket program and used the ethanol for their emergency fighter aircraft program? You cannot run the entire Luftwaffe with ethanol but perhaps you can power two or three Jagdgeschwader dedicated to air defense.

Alcohol has only about half the BTUs of gasoline so you need an airframe such as the Me-309 which held 770 liters of internal fuel. Plus drop tanks.

Jumo 213 engine was in mass production during 1944. Make a variant with modified compression ratio, valve timing etc. that takes full advantage of the high octane fuel.

 

[msxyz]

The biggest problem of ethanol, aside from increased consumption as a consequence of lower energy content and different stoichiometric ratio, is that it's more difficult to vaporize. That's why in biofuels it's mixed with a small (15%) amount of gasoline. In cold weather, gasoline amount is actually increased to 25% to 30%.

Let's say that the Germans opted for some blend in the 20-40% range. Other problems that might have arisen:

Ethanol octane rating is about 105; octane rating of gasoline / ethanol mixture is not a direct proportion of the octane ratings of the two components. By 1944, Germany was able to synthesize, via the Bergius process, gasoline substitutes with octane ratings above 100 and above what was possible to obtain with ethanol alone.

In harsh cold (such as that encountered at high altitudes) ethanol - gasoline blends tend to separate. Ethan gasoline blends are also hygroscopic and, as the water content increases, separation of the two substances becomes more likely. Hence why biofuels use anhydrous ethanol, because it has a lower water content to begin with. Unfortunately, anhydrous alcohol needs to be refined further than standard (4% water content) alcohol in an energy hungry process.

A better substitute of ethanol is butyl alcohol. Butyl alcohol is a byproduct of the process used to create acetone, hence was readily available (acetone is used in quantities in the making of explosives). Butyl alcohol has an energy content which is closer to that of gasoline, vaporizes better and it also promotes better mixing of ethanol and gasoline.

In the closing months of the war, the Japanese were stockpiling fuel in preparation for the invasion of their home islands. Thus, they experimented with alternative fuels to use in training aircrafts and elsewhere but front line units. In addition to preparing gasoline substitutes using turpentine oil as a basic component, they experimented with several gasoline-ethanol blends. In the end, they came up with a fuel which was 50% ethanol 10% butyl alcohol and the rest gasoline. This was far from an ideal substitute, but it worked. Sort of.

 

[Shortround6]

And training and transport aircraft at 15,000ft and under is a whole different story than combat aircraft at 25,000-30,000ft.

Even in Brazil some cars have small gasoline tanks for staring the engine in colder weather/areas and then switching to the Ethanol.

 

[FLYBOYJ]

I installed an ethanol conversion kit on my Honda Civic. Engine ran smoother but lost between 3 to 5 mpg. It was also hard to start in the cold.

 

[model299]

My son switched to E85 on his Mitsubishi Eclipse hot rod. He buillt his own engine management computer to run it, and run it did. It was quite the screamer. Mileage did go down, but detonation problems disappeared, and it ran noticeably cooler in the summer. He didn't drive the car in the winter, so cold weather drivability wasn't an issue.

 

[Milosh]

The Germans had a hard enough time getting petro fuel to the points that required it. Having another fuel would only complicate deliveries more. To have such a fuel viable, the Germans would have had to switch to alcohol fuel by at least the time of Barbarossa.

It might have been useful for training a/c.

The Germans were low on petro fuel late war but not that low. The biggest problem was getting the fuel to the points that required it.

 

[davebender]

1944 Germany could still make diesel just as they could still make jet fuel. Diesel engines wouldn't be my first choice for a fighter aircraft but they were desperate by the fall of 1944. What could be done if the program had unlimited funding and peacetime safety standards were set aside?

 

[Shortround6]

dead end.

You don't think the Germans just might have thought of this themselves? and rejected it.

Diesel engines have higher peak pressures inside the cylinder even if the average or mean pressure is lower than an equivalent gasoline engine. This means the pistons, piston rods, crankshaft, cylinder walls, head or block attachment bolts,etc all have to be stronger (heavier) than an equivalent powered gas engine. If you try to shave the strength (peacetime safety standards ?) you wind up with a lot of wrecked engines an/or engines that don't last as long as the gasoline engines. With some German gas engines lasting less than 100 hrs between overhauls this doesn't sound like a good idea.
Granted some flying is better than no flying ( no fuel) but with "unlimited funding" another plant for the production of synthetic gasoline would have been a better bet.
Especially considering the 3-5 years to get an engine into production.

 

[msxyz]

The Luftwaffe used some two stroke, opposed piston diesel engines in certain bombers and long range transports but that's all. I think also the high altitude variant of the Ju-86R used diesel engines with an extra one in the fuselage moving a huge blower that fed all the three engines.

For the "Amerika bomber" program they even developed the concept further with the Jumo 224, a 24 cylinder 48 piston two stroke engine. In the end they got it running at 4800 rpm and with a specific fuel consumption that wasn't far from modern common rail engines (Jumo diesels used unit injector pumps and the opposed piston geometry creates a near ideal combustion chamber with minimal thermal losses and very good swirl). Specific power was also impressive, more than 50 HP per liter, better than any gasoline engine of big displacement used during the war.

Unfortunately, the bomber never materialized and the engine was too big and heavy for any fighter. The sole completed example of the engine fell in soviets hands. Opposed piston diesel engines are still used in marine applications, on locomotives (the famous British Napier Deltic is an offspring of the Jumo 205 which was licensed by Napier before WW2) and I think also a few US submarines used engines of similar design built by Fairbanks-Morse. Some soviet tanks still use to this day flat-six, two stroke opposed piston engines because they're compact and have better specific power than four stroke diesels.

Back to topic, since diesel engines don't run on stoichiometric ratio but usually in excess air, losses at altitude would be better manageable. In addition to that, diesel turbochargers ares less stressed than in a gasoline engine because of lower temperatures of the exhaust, thus they could have been made of lower grade steel. The big problem of diesels is that they have to withstand higher pressures so they need to be made heavy, so the trade-offs aren't really worth for small aircrafts. The Germans were far ahead in diesel engines development even before WW2; had it been possible to create a suitable diesel engine for a fighter, they would have investigated the possibility.