Diesel motors are great...but?

[pycoed]

Hundreds , if not thousands, of German aircraft ran on diesel engines in WWII: the Junkers JUMO 204(?)range.
I well remember my parents telling me of the characteristic vibrating drone of their bombers during air raids, so different from the petrol engined British bombers.

 

[John_Mc]

Yes. Many people liked the 100 octane in high compression engines. It was low lead, so back then, they added a lead additive.

If they were adding a lead additive, they were wasting their time. !00 LL was only "low lead" in comparison to the old 100 or 100/130 avgas. !00 LL still had about 3 times the lead of the leaded auto fuel of that time. In more recent years, the lead content of 100 LL has been trimmed a bit further, but it still has more leasd than the leaded auto fuel used to have.

 

[GManBart]

If they were adding a lead additive, they were wasting their time. !00 LL was only "low lead" in comparison to the old 100 or 100/130 avgas. !00 LL still had about 3 times the lead of the leaded auto fuel of that time. In more recent years, the lead content of 100 LL has been trimmed a bit further, but it still has more leasd than the leaded auto fuel used to have.

Exactly what I was thinking. Current 100LL has around 2 grams of TEL per gallon, and that number has dropped from what it used to be. At it's peak automotive fuel with lead only got to around 3 grams per gallon with some of the premium, high octane blends...but avgas of the time was much higher.

 

[GManBart]

As far as high altitude goes, large jet aircraft have a number of systems to keep the fuel from gelling. Most have heat exchangers that the fuel flows through in the engine, and then there are a number of ways the fuel in the tanks and lines is kept warm. One, they'll sometimes have a hydraulic fluid heat exchanger that uses fuel as a coolant. Sometimes they'll run the large bleed air line (hot air from the engine) for the wing anti-ice systems next to fuel lines to transfer heat. Another is putting a fuel tank near the air conditioning compressors which get quite hot. All airliners are pressurized and that creates heat, so they're always running air conditioning systems. I think that some tanks do have immersion heaters in them, but it's been a long time since I was up on any of that stuff. I'm sure there are other ways I'm not aware of, but those are some of the common methods.

I've hand flown a piston engined airplane at just under 18K feet...no problem at all, but it had twin turbos and pressurization.

 

[Rock knocker]

All airliners are pressurized and that creates heat, so they're always running air conditioning systems.

Last time I was in an airliner, the outside temperature was minus 70º F. I'm thinking the AC was off

 

[GManBart]

Last time I was in an airliner, the outside temperature was minus 70ｺ F. I'm thinking the AC was off

Nope....the AC was on. When you pressurize air, you create a lot of heat. When you're at high altitude the pressurization system is working to keep the cabin level at approximately 4-8,000ft. When outside air makes it to the bleed valves it'a already at high pressure, and around 400*F. It has to be run through AC packs (heat exchangers and air cycle machines) to keep temps reasonable in the cabin.

In simple terms, when pilots make the cabin warmer, they're simply turning down the amount of AC being used.

 

[tcartwri]

Geophysics company I used to work for has three of these. They really like them.

Diamondaircraft DA42

 

[k0ua]

So the answer is yeah diesel engines are great and plenty of aircraft in the past and present do use them, and more are likely to in the future.

 

[Industrial Toys]

Always nice to hear the "EXPERTS" talk about stuff most of us have never heard of!

No wonder aircraft are so darn expensive!

Curious. IF the air at altitude is so thin, do the compressors have to work very hard to compress it to cabin pressure?

 

[k0ua]

Always nice to hear the "EXPERTS" talk about stuff most of us have never heard of!

No wonder aircraft are so darn expensive!

Curious. IF the air at altitude is so thin, do the compressors have to work very hard to compress it to cabin pressure?

let's put it this way, without the pressurized cabin at 30,000 feet you are not going to last long..