It seems modern fighter aircraft are rather sensitive to what you put in their fuel tanks.

According to local media, the fuel used by the German Tornado fleet appears to have been mixed with ‘too much bio-diesel’.

According to news site Frankfurter Allgemeine, this was noticed during a routine check last Monday:

“The tolerance values ​​are minimally exceeded,” said Colonel Kristof Conrath of the Tactical Air Force Squadron 51. “It’s not that the aircraft would fall from the sky. For safety reasons, all tanks of the aircraft must be flushed.”

It is understood that this breakdown is particularly annoying for the Luftwaffe, as training of new Tornado pilots is already three months behind.

There’s more at the link.

I didn’t know that the Luftwaffe was using biodiesel in its jet aviation fuel – presumably as an additive, just as we’re using ethanol as a gasoline additive in the USA.

Automobiles are a bit sensitive to what’s in their tanks, too.  My father served in the Royal Air Force during World War II.  At the start of the war in 1939, the RAF began to switch to 100-octane fuel for its high-performance aircraft engines (previously it had used 87-octane).  Gasoline rationing was introduced at about the same time for all civilian vehicles.  He used to tell us stories of how airmen, who couldn’t get enough gasoline coupons to make the trip to London and back, would “borrow” a few gallons of 100-octane fuel from the bowser to top up their tanks.  The engines of the time simply couldn’t handle the hotter combustion temperatures of the aircraft fuel, and would burn out their valves, leading to drunken airmen stranded by the side of the road in the small hours of the morning, unable to get back to base.  Misuse of “official” fuel was considered a serious offense, so many of them simply accepted the punishment for being late to return from liberty – then proceeded to repair their engines using RAF maintenance facilities as well!  He used to laugh about that.



  1. There is very sound reason I spend the extra money on non-oxygenated (NO ethanol!) gasoline for the snowblower – I need it to *work* *every* *time*.

  2. THe issue is that the higher levels of Bio gells up at colder temps. Even a few percent over.

    You can fix the gelling issue with other additives, but they too have consequences for the engines and/or performance.

  3. Another potential problem with biodiesel is that unless you're very careful, it can apparently get a bit too biological. A while back, Berkeley, California had problems with fungus in the biodiesel used by a number of city service vehicles. The fungus clogged the fuel injectors.
    Bad enough in a truck being driven around a small city. In a high performance jet fighter…

    Maybe German biodiesel is better quality, though.

  4. I placed some large areas of paving in a bio-diesel refining facility. It was somewhat strange of a facility, since most all equipment was on skids. I assumed, since it was obvious subsidies were involved, or tax breaks, the equipment could easily be loaded on a truck and removed.

    On some days, we smelled rancid grease. On others, the odor of french fries was strong. Trucks would bring in the raw products, the fuel was made, and the fuel was hauled for blending by oil refineries.

    I had a chance to speak with someone with knowledge about the product. According to them, bio-diesel isn't a reliable fuel, and too much may cause problems with an engine. The solution by refiners was a percentage too small to cause problems with blends. Considering how small the percentage must be, there must be a financial gain somewhere to deal with what is obviously an operation not cost effective.

  5. Our company make a fuel dilution meter for the USN. It measures fuel that ends up lubricating oil. We can do 2104, 9250 or commercial diesel with out any problems but no one has a good way to measure bio-diesels for the reason Jess mentioned, batch to batch variability.


  6. Not to be a pedantic ass, but that's not how I octane works. I am absolutely convinced that those guys returning from leave burned up their engines, but it's impossible to burn up an engine by using too high an octane.

    Most Aviation engines during World War II used 115 octane, not 100. When they could only get 100, they could not use the full power of their turbocharged engines because the fuel would ignite to easily or detonate at lower octane. Higher octane fuel actually ignites more slowly.

    The reason high octane fuel is used in high-performance engines is so that you can jam more fuel and more air into the same piston at a higher compression ratio before blowing the engine apart. Lower octane fuel is what blows up engines. Been there, done that, helped replace the cylinder heads on the engine.


  7. Peter's correct. The RAF started on 87-octane gas and then transitioned to 100-octane fuel in 1940–41. Not sure when they went to 115-octane, but it was probably '43 or so.

  8. According to General "Jimmy" Doolittle (MOH for the '42 Tokyo Bomber Raid), The Germans never produced those high-octane fuels during WW2. He claimed that it was a significant advantage for our forces. (He worked for Shell Oil prior to the war, and was involved in developing it.)

    I'm not sure what they used, but their aircraft tended to have very large capacity engines. When you listen to their FW-190 and Me-109 engines idling, they sound like very radical old hotrods/racers from the 60-70's. Lots of valve overlap cam timing. "Lumpy" sounding is one of the old terms from back in the day.

  9. I imagine the only thing worse than having your Check Engine light come on when you are three miles in the air is to have the light come on when somebody is shooting at you.

  10. "Higher octane fuel actually ignites more slowly. "

    Isn't it the slower flame that permits excessive heat into the valves and head? Since a regular octane engine would still ignite the fuel earlier at the lower pressure, unless they also adjusted the timing, there is more time for the heat to dissipate into the cylinder head before being exhausted along with the longer burn time from the slower flame front.

  11. Alge likes to grow in regular diesel, that's not a biodiesel specific problem.

    the biggest problem with biodiesel is that it will gell at higher temps than more purified fuel (including more purified bio-diesel)

    not a good thing to have in aircraft flying to high altitudes

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