Would diesel engines make sense for planes?

Tabnabs

Well, the German's certainly thought it worth a shot.

A nice piece on a little remembered era of aviation history

http://www.dieselpunks.org/profiles/blogs/s-a-m-11-diesel-mail

Delta Kilo

There are some aircraft using diesel engines, i think skytrace in weston have a couple of them on their light training aircraft.

I think the issue is that you cant get a high rpm from a diesel engine, as diesel engines are by nature high torque, low rpm. Torque is useful for pulling trailers on the ground, but not much use to you in the sky, hence why most light aircraft use a petrol derivative.

xflyer

I saw one of the C172 diesel conversions recently. One of the two photo aircraft buzzing around our skies this summer. It was exceptionally quiet complete with three blade propellor. The three blader would compensate for the lack of RPM I assume. The crew told me it had a nine hour endurance although they didn't.:o It did seem to take a lot of runway to get airborne but then again it may have been heavy with fuel.

pclancy

9 hours would be a lot of pee-bottles rolling around on the floor by landing.

Run_to_da_hills

Delta Kilo wrote: »

There are some aircraft using diesel engines, i think skytrace in weston have a couple of them on their light training aircraft.

I think the issue is that you cant get a high rpm from a diesel engine, as diesel engines are by nature high torque, low rpm. Torque is useful for pulling trailers on the ground, but not much use to you in the sky, hence why most light aircraft use a petrol derivative.

Torque could also be good for towing gliders.

Delta Kilo

Run_to_da_hills wrote: »

Torque could also be good for towing gliders.

Nope, not at all.

All forward motion of an aircraft is provided by the aerodynamic shape of the propellor, not the torque of the engine.

The idea is to have that propeller spinning fast to produce more thrust, which will help tugging a glider.

Maybe if there was some extremely dense air, the diesel engine might give enough power to keep the propellor turning!

Torque is turning power, so for example in a truck, the engine can still turn the wheels despite 44tons impeding it. A petrol engine would not be able to do that.

Kumsheen

I suppose the Germans were looking for endurance at the time which is why they developed diesels, but history does prove them to be of limited success.
But they are regaining in popularity again so you never know.

amen

A petrol engine would not be able to do that

surely with the correct gear ratio you could move the 44tons with a petrol engine?
might not be very efficient but you could do it after all steam engines move more then 44t

Carawaystick

Compression ignition engines traditionally were heavier than otto cycle engines as the block and head needs to be stronger to cope with the higher compression ratio
Alloy blocks are now lighter so better suited for aircraft

What sort of revs do props spin at? Modern automotive diesels redline at around 75-90% of petrol engines

Diesel has a higher volumetric energy density than petrol, dunno about by weight though

Stinicker

I'm not that well up on this subject but do the smaller planes that are piston driven do they use a special petrol fuel or unleaded similar to cars? I read once that Kerosene for jets is not taxed and is the same Kerosene (paraffin) that is used for home heating oil or is it a special blends for planes.

The reason I ask was that a former ex boyfriend of my sisters was a trainee mechanic in shannon around 10 years and had a boyracer type car (integra or Skyline I can't remember) and he said he used to get airline fuel cheaper for it. The same fella was full of tall stories so I never knew whether to believe him or not.

Ald

Carawaystick wrote: »

Compression ignition engines traditionally were heavier than otto cycle engines as the block and head needs to be stronger to cope with the higher compression ratio
Alloy blocks are now lighter so better suited for aircraft

What sort of revs do props spin at? Modern automotive diesels redline at around 75-90% of petrol engines

Diesel has a higher volumetric energy density than petrol, dunno about by weight though

In a C152 you're talking about 2200 rpm in the cruise.

xflyer

The reason I ask was that a former ex boyfriend of my sisters was a trainee mechanic in shannon around 10 years and had a boyracer type car (integra or Skyline I can't remember) and he said he used to get airline fuel cheaper for it.

He was full of it, airline fuel is Jet A, Kerosene or Paraffin type fuel. Not far off Diesel. Diesels are what is known as multifuel engine. It wouldn't work in a petrol car. You could modify a diesel to run almost anything. Chip shop fat being one.

But a petrol car can only use petrol.

However by changing the word airline to aircraft fuel and you have aviation gasoline, Avgas which is petrol with added lead. Older cars ran on leaded fuel. You can get more power out of an engine with leaded fuel. But modern car engines and that includes engines ten years ago would be killed stone dead by leaded fuel. Particularly any Japanese car of the era.

Plus it's way more expensive than car fuel or mogas. If he was getting it cheaper it was because he was stealing it. Jet A is cheaper than Avgas or petrol. But you can't use in petrol cars, diesels are different.

The typical aircraft piston engine is a very old fashioned design so need to use Avgas, although it can use Mogas with limitations.

Run_to_da_hills

Diesel compression engines are popular with model aircraft.

http://www.eifflaender.com/enginepics.htm

leeroybrown

We'll probably see a resurgence of diesel engines for planes. Most of the reasons why avgas engines were developed instead of diesels have been overcome with the resurgence of diesel engine technology in recent years. When you take those issues out of the equation you suddenly have the advantage that diesel has a higher energy density than avgas which is a nice advantage to have on your side.

Delta Kilo

Im not all too convinced with the resurgence of diesel in aviation...

There are more variables involved than people think.

Most modern diesels rely on turbochargers for performance, however when you reach altitude, then it is a different kettle of fish altogether.

Air density, pressure and temperature change and you will find that engines start to operate with decreased performance. Granted it is probably not a significant amount under 4-5,000ft, but still.

I reckon, but am not certain, that a diesel engine would suffer more performance wise than a petrol engine running with increased lead in the petrol.

Delancey

During WW2 the Soviet Air Force had a 4 diesel-engined heavy bomber which was supposed to be used to bomb Berlin.
It was a total disaster with the aircraft hacked from the sky with ease - so easy to shoot down that the more experienced German pilots used to allow their inexperienced colleagues the practice of shooting them down .

Flyer1

Thielert do a diesel conversion for 172's, PA28's, DA40's. Lots of different aircraft use these engines. They are derived from the 1.7 mercedes A class diesel engine.

Have flown a couple of them, not sure how viable they will be in the future.

BEASTERLY

Flyer1 wrote: »

Thielert do a diesel conversion for 172's, PA28's, DA40's. Lots of different aircraft use these engines. They are derived from the 1.7 mercedes A class diesel engine.

Have flown a couple of them, not sure how viable they will be in the future.

That engine has been plauged with problems has it not?

Stovepipe

Hi all,
Given that Jet A-1 is cheap, I think aero diesels will be around for a while yet. Personally, I think they should concentrate on getting them to run on regular diesel, which is infinitely more plentiful than Jet A1.Failing that, work to bring down the price of turbine engines, which, in essence, are easy to manufacture and build (think of every turbo in every car, truck and train in the world) so that they can replace the outdated aircooled Lycomings and reduce the amount of accidents that happen because of ancient technology engines.
regards
Stovepipe

airsofter.adam

maybe on a light prop, but i couldnt see an a380 running on a diesel engine. The diesel engine have high power with low RPM which wouldnt work for a large/heavy aircraft.

Delta Kilo

Stovepipe wrote: »

Hi all,
Given that Jet A-1 is cheap, I think aero diesels will be around for a while yet. Personally, I think they should concentrate on getting them to run on regular diesel, which is infinitely more plentiful than Jet A1.Failing that, work to bring down the price of turbine engines, which, in essence, are easy to manufacture and build (think of every turbo in every car, truck and train in the world) so that they can replace the outdated aircooled Lycomings and reduce the amount of accidents that happen because of ancient technology engines.
regards
Stovepipe

airsofter.adam wrote: »

maybe on a light prop, but i couldnt see an a380 running on a diesel engine. The diesel engine have high power with low RPM which wouldnt work for a large/heavy aircraft.

Different ball game altogether really. The thread so far has been dealing with light piston engine aircraft.

A turbofan engine is used to power bigger aircraft like the a380. Maybe the turbofan engines could be adapted so that they can burn diesel, I dont know, but there must be a valid reason why it isnt done. I wouldnt be a favour of it, because I drive a diesel car, and I wouldnt want the price of diesel to sky rocket because of the increased demand from all the airliners buying thousands of gallons of it!

Turbofan engine manufacturers are looking at ways of reducing fuel burn. The new LEAP-X engine from cfm, powering the new A320neo, incorporates a gearbox on the main shaft of the engine that runs down the middle of the engine, the LPT shaft. The idea is you can get your fan blades spinning at the same rate by using less burning in the core combustion chamber due to the gearbox increasing the speed of the LPT shaft.

Stovepipe

Hi all
@delancey, with regard to the Soviet Pe-8 bombers, the airmen pleaded directly to Stalin to have the diesels replaced with radials, which he sanctioned and the Pe-8s became successful bombers. They were very heavily armed and feared by the Luftwaffe pilots who had to attack them.
With regard to diesel being used in large aircraft, the difference in diesel for auto use and kerosene in jet aircraft is actually very little. Kerosene for aircraft use is treated with biocide so that microbiological growth from absorbed water doesn't corrode the wing from within and it is also treated so that it doesn't freeze at the typical -56 degrees C encountered at the altitudes jets fly at. Kerosene in a jet aircraft is also preheated before it is passed into the fuel control unit and into the combustion section of the jet engine. Kerosene does not contain the sulphur that road diesel does contain. Industrial jet engines, which are often direct copies of aviation units, routinely run on diesel, kerosene, heavy marine diesel, natural gas, gas from landfills and other types of waste gases and any other fluid that can be sufficiently vapourised and provide a decent energy return. Military helicopters that use turbine engines are even allowed to use diesel or even paraffin or even a percentage of petrol in an emergency. Diesel engines are also routinely capable of running on the same stuff. If it can be vapourised, a diesel or a turbine will run on it. Nowadays, given how efficient the auto industry has made the small diesel, I reckon they will supplant the aircooled petrol-driven piston engine.
regards
Stovepipe