Fuel economy in the air (diesel airplanes?)

[thatguitarguy]

Jet fuel is basically kerosene which is very similar to diesel.



from wikipedia:


Piston engine use

Jet fuel is very similar to diesel fuel, and in some cases may be burned in diesel engines. The possibility of environmental legislation banning the use of leaded avgas, and the lack of a replacement fuel with similar performance has left aircraft designers and pilot's organizations searching for alternative engines for use in small aircraft.[5] As a result, a few aircraft engine manufacturers, most notably Thielert, have begun offering diesel aircraft engines which run on jet fuel. This technology has potential to simplify airport logistics by reducing the number of fuel types required. Jet fuel is available in most places in the world, whereas avgas is only widely available in the few countries which have a large number of general aviation aircraft. A diesel engine may also potentially be more environmentally-friendly and fuel-efficient than an avgas engine. However, very few diesel aircraft engines have been certified by aviation authorities, and widespread use of diesel aircraft engines is still years in the future.

Jet fuel is often used in ground support vehicles at airports, instead of diesel. The United States military makes heavy use of JP-8, for instance. However, jet fuel tends to have poor lubricating ability in comparison to diesel, thereby increasing wear on fuel pumps and other related engine parts.[citation needed] Civilian vehicles tend to disallow its use, or require that an additive be mixed with the jet fuel in order to restore its lubricity. Jet fuel is also significantly more expensive than diesel, so using it in ground vehicles is considered by some to be wasteful.

Jet fuel - Wikipedia, the free encyclopedia

[jamesqf]

I know they have been used - years ago, I used to work for a rancher who had several radial diesel engines that he'd converted to drive irrigation pumps. (The guy was something of a mad inventor type. I particularly remember his homebuilt forklift, which worked quite well except for the fact that it steered backwards - turn the wheel right, it went left.)

As for why there aren't many diesels, or much emission regulation, in prop planes, consider the size of the market and the cost of getting ANYTHING certified under the FARs. Most general aviation planes were built in the 1960s, if not earlier, using engine designs from the '40s and '50s.

[dremd]

Originally Posted by Christ

That's why they make chokes.

Design the engine to run efficiently at high alt, and at low alt, it'll probably blow up, so you either set it up to only use a max amount of fuel, which is pig-rich at low alt, and perfect at high alt, or you set it up with a choke, so that it runs as a smaller displacement engine (effective displacement) at low alt, and runs "normally" at high alt.

I hate making these post.

That is the beauty of a Diesel engine, runs good from 500:1 - 10:1 AFR

Choke on a diesel is useless. Advance injection timing for cold starts.MKI VW diesels had a lever to advance pump for cold starts.

Best way to adjust effective displacement is with forced induction, turbo would be easiest IMO. Just have to keep cylinder pressures acceptable at takeoff power to maintain durability.

[Christ]

Originally Posted by dremd

I hate making these post.

That is the beauty of a Diesel engine, runs good from 500:1 - 10:1 AFR

Choke on a diesel is useless. Advance injection timing for cold starts.MKI VW diesels had a lever to advance pump for cold starts.

Best way to adjust effective displacement is with forced induction, turbo would be easiest IMO. Just have to keep cylinder pressures acceptable at takeoff power to maintain durability.

I know how they work, but I like to give up the obscure options before the obvious ones.

[dremd]

I guess the inherent question is what is the thrust hour/ pound (I just made that unit up) for each powerplant (diesel, gasoline, Turbo Jet, Turbo Fan, Turbo Prop, ram jet, something else I'm forgetting).

Only reason I'm not saying GO DIESEL is that Dick Routan didn't use diesel power for his round the world on 1 tank plane. Maybe the high octane of AV gas makes it more practical, I totally don't know.

[dremd]

Originally Posted by Christ

I know how they work, but I like to give up the obscure options before the obvious ones.

Alright.

[Christ]

For instance, if I can ever find the reference (I'm terrible at bookmarking anything I read, if you can't tell), there were a couple air-throttled diesel compression ignition engines back in the 40's, maybe 50's (?).

They used a throttle and had a vacuum fuel control on the IP, but were still compression ignition. My guess (I don't know anything about them) is that they were either unreliable, or unrealistic (in terms of fuel use/power/etc.), and didn't have an expert marketing team backing them up like Soccer Mom's and SUV's.

[dremd]

Originally Posted by Christ

For instance, if I can ever find the reference (I'm terrible at bookmarking anything I read, if you can't tell), there were a couple air-throttled diesel compression ignition engines back in the 40's, maybe 50's (?).

They used a throttle and had a vacuum fuel control on the IP, but were still compression ignition. My guess (I don't know anything about them) is that they were either unreliable, or unrealistic (in terms of fuel use/power/etc.), and didn't have an expert marketing team backing them up like Soccer Mom's and SUV's.

I must admit I have worked on a few air "throttled" diesels.

1) friends 80's Benz 5 cylinder Diesel with Vacuum operated EVERYTHING. would close a throttle valve (firmly) when you put your foot on the brake, and be spring loaded at (all?) times to generate vacuum. Why they didn't have a vac pump I have no idea. When you tied the thing open the car got much faster, but nothing worked.

2) Anything in the oil field has a "rig saver" on it. Basically a throttle valve that closes automatically when the engine over revs, or an operator forces shut down. Issue is that flammable gas can easily be released in range of the engine causing an unintentional over throttle situation and Run-Away which can very easily create an ignition source for the flammable gas floating around. All of these I have seen are only on/ off and have to be reset manually.

3) My Golf Has an "Anti Shudder" valve that closes when the key is turned off (maybe other times as well?).

4) I **THINK** that newer "clean" diesels have a throttle valve to keep the Air Fuel Ratio in some range. (no evidence/ sources here at the moment)

[Christ]

Any information you have will probably trump whatever source I can come up with, honestly. I'd be interested to see what you come up with.

[Silveredwings]

It seems to me aviation diesels have been in development for as far back as I remember in hopes of taking advantage of lower cost and highly available Jet-A fuel. Applications seem to be limited to retrofits into STC'd airframes (FAA-approved replacements of avgas piston engines).

Lycoming IO-720 400 hp Diesel


Economic Comparison of a 200 hp Diesel to an IO-360 200 hp Lycoming