Alternative Fuels and Aircraft

[HForrest]

I'm beginning to have a real interest in aviation. I plan to start taking pilot lessons within the next year or two, and I hope to own aircraft in the future. However- Airplanes and Helicopters use significant amounts of fuel, and I do believe that within my lifetime, petroleum will completely cease to be an option for power.

Cars and the like have already been converted to run on H2, Ethanol, etc. So, my question is this: would this be feasible for aircraft conversions? Piston powered planes and helicopters are essentially the same idea as car engines as I understand it... the same concept at least. Furthermore, what about jets? Would any non-petrol fuels work in jets, specifically turbine-powered helicopters?

[Sylvilagus Aquaticus]

I've read about a Cessna 172 (maybe a 150) converted to a Stirling cycle powerplant. It exceeded the spec engine at all altitudes and had a higher service ceiling than the internal combustion engine. Better fuel per hour rating than the Continental/Lycoming, too, IIRC.  Interesting thing about Stirlings- at higher altitude, they become more efficient and of course, you can run them on anything...even sunlight.

Then for the truly adventurous, there's DeltaHawk, who makes an aviation diesel engine.

http://www.deltahawkengines.com/


As far as non-petroleum based fuels for jet turbines, I think it has a lot to do with vapor pressure dynamics.  I've seen plenty of ramjets that would run on propane, LNG, LP and the like, but I don't know of you could do the same with a compressor turbine.  My estimation is that methanol or ethanol isn't thermodynamically efficient enough to run a turbine engine, but I've been wrong before.  I doubt that H2 storage technology is advanced enough to use as a fuel for jet aircraft to allow sufficient fuel load capacity for extended flight.  It'd just be a huge flying Thermos bottle.


Regards,
Rabbit.


(edited for spelling. Dang cats.)

[Ben]

Diamond is already using diesel in the European DA-20s and plans on selling them here as well (if they haven't already started). I assume, like with cars, they could eventually go biodiesel.

[cfabe]

Combat, there are some planes out there that are fuel-efficency comporable to cars. Look at the RV line of kit planes, some of those will get the equivalent of 20mpg. Not too bad. Given that fuel is a much lower percentage cost of running an airplane than it is running a car, alternative fuels for airplanes will probably be slower coming. Eventually it will happen, I'm sure.

[Jamisjockey]

Wombat:
Just remember, Controllers are god.

[Brad Johnson]

Diamond is already using diesel in the European DA-20s and plans on selling them here as well (if they haven't already started). I assume, like with cars, they could eventually go biodiesel.

Dang, somebody beat me to it!

Brad

[Gewehr98]

Skip the pistons.

Jet engines, including high-bypass turbofans, can be tuned to run just fine on all sorts of liquid hydrocarbons.  I'd wager that the food-grade vegetable oil that resourceful folks are now filling their Volkswagen and Mercedes diesels with would be just fine in a turbofan.  Problem is, I doubt the restaurant industry could keep the airline industry adequately fueled. Maybe supplemented and mixed with Jet A/JP-8, but that's about it.

[Stickjockey]

Diesel has been used to greater or lesser effect in aviation several times. Jet-A is actually closer to diesel or kerosene than to AvGas.

[Sergeant Bob]

Diesel has been used to greater or lesser effect in aviation several times. Jet-A is actually closer to diesel or kerosene than to AvGas.

Indeed. When I was stationed in Panama, the only thing we burned in our diesels was JP-5.

[mfree]

Biodiesel == bad mojo in aircraft, unless you're heavy with antigelling and freeze temp lowering additives... like lots of petrodiesel.

It'd kind of be bad to fall out of the sky because half the fuel in your wing tanks solidified because it's below freezing at altitude...

Another 3 cents, diesel engines would be *perfect* for light prop aircraft IF, IF IF they can be made light (as with the delta engines) and still be as strong. The power curve matches prop curve very well, you could get away without needing a gearbox, you could have a two-stroke diesel without oil consumption for even more power in a light package.... actually, i think that's what the Deltas are, two-stroke.

Other than that, seems turboprop is the way to go.

[Art Eatman]

If you computerized the air/fuel mix (using fuel injection) and the ignition timing on a standard Lycoming, you'd get a helluva lot better power curve and fuel economy.  It can be done, of course, but then you're "Experimental".

Art

[K Frame]

Both the Germans and Soviets built aircraft that used diesel engines before and during WW II. Not sure whether any saw combat or not.

[Stickjockey]

It can be done, of course, but then you're "Experimental".

This is the reason it's not done more often. FAA standard certification = mucho $$$.

[grampster]

Someone mentioned cats and buttered bread (in another thread) producing electrical power.  Skinny cats, low fat margarine solves a weight problem.

[thorn]

Jet engines, including high-bypass turbofans, can be tuned to run just fine on all sorts of liquid hydrocarbons.  I'd wager that the food-grade vegetable oil that resourceful folks are now filling their Volkswagen and Mercedes diesels with would be just fine in a turbofan.  Problem is, I doubt the restaurant industry could keep the airline industry adequately fueled. Maybe supplemented and mixed with Jet A/JP-8, but that's about it.

more than anyting, formn what i saw on a tv show, it is the FAA won't allow comercial use of untested fuels- and it takes ten years of tests to prove a fuel is safe.

so no one invests the $$ to get better stuff going , like biodiesel.

as it is jet fuel is practically diesel

[Antibubba]

To ask a question that puts us back on the ground:  Why don't I see diesel engines on motorcycles?

[DustinD]

I hang out at www.homebuiltairplanes.com which is a pretty good source of information about aviation possibilities.

The reason there is almost no R & D in aircraft piston engines is due to the several years and millions of dollars it takes to certify airplane engines. That and the fact that after turbine engines where developed towards the end of WWII they got all of the attention and development dollars. The situation has gotten to the point where a $2,000-$6000 car engine such as the Mazda rotary, Chevy LSx, VW, etc can out preform a $30,000 1940's tech airplane engine.

There are some low bypass turbo fans that are being certified and should sell for about $30,000. Sadly those guys will not sell to the experimental crowd, they said in their e-mails that we can thank the trial lawyers for it. I guess the turbine manufactures have too deep of pockets to risk a lawsuit after someone dies after doing acrobatics at  low altitudes, runs out of gas, or knowingly flies into bad weather and sues them for all they are worth. Note that those three causes of death account for 95% of general aviation fatalities.

As for current aviation planes and engines, many have STCs for using the cheaper auto fuels. Many STCs do not require any modification to run reliably. If you can get electronic ignition to replace one of the magnetos you can up to an 11% decrease in fuel consumption. Fuel injection will also beats carburetors but I not know for sure how much. Not having ice form on your carbs is pretty nice too.

If you are flying an experimental engine you can even mix diesel with gasoline and run that in standard spark fired engines if you are careful to watch gel temps and flash points to make sure you can start the engine and keep it from stalling.

Jet engines do run well on many fuels including hydrogen. The original concept for the SR-71 Blackbird was to use hydrogen, but the horrible range it would have gotten prevented that from happening. The only trouble with hydrogen is trying to store enough onboard, and that it can cause some metals to turn brittle and fail.

Some airplanes do get over 50 mpg. I expect some more to be on the market in the coming years. My favorite concept is a pressurized, UNducted fan, pusher, that can fly mach .86 IIRC at altitude and probably still get over 50 mpg.

Also note that helicopters will not get as good of fuel efficiency as fixed wing airplanes.

Antibubba: Until recently diesels had horrible power to weight ratios. Power to weight is very important on motorcycles, and diesels still can not beat gas engines in that regard. There also was the trouble with vibration that was only recently solved. I did hear about a diesel powered motorcycle that got something like 160 mpg and could still do wheelies at 80 mph. I found some diesel bikes by doing a google search. I guess there is not much of a demand for them yet for more.

[Antibubba]

Oh.  Thanks, I'll do a search.

[HForrest]

In terms of H2 storage onboard airplanes and jets... how did they propose the hydrogen to be stored on the SR-71? If you've ever heard of United Nuclear, they've converted cars to run on hydrogen and are working on a commercial product. They apparently store the hydrogen bonded to metal hydrides, and their tanks look pretty small, definitaly could be fit into an aircraft... said the range is about 450 miles with 4 tanks in a... I think it's a Mitsubishi SUV. 'Course, AFAIK, jets use a frickin' ton of fuel.

[Brad Johnson]

The main problem with diesels is that, until now, diesel engine technology has been focused on long-life, brute strength engines for big trucks, trains, and heavy-duty pickups. As a result the engines are big, rugged, dependable, and HEAVY.

They don't have to be. A piston engine certified for aircraft use is required to be torn down every 1500-2000 hours. At 70 mph, 2000 hours only equals 140,000 miles. Truck engines regularly exceed 1,000,000 (that's one MILLION miles) and are subject to all kinds of extreme abuse - shock loading, extreme and rapid rpm changes, etc. that aircraft engines do not see. Since the aircraft engine is only expcted to run safely and reliably for far less time than a truck engine, and expected to perform within a specific set of extremes, engineering for a much lighter powerplant should be no problem.

The best part of a diesel aircraft powerplant would be economy. According to the the petroleum section of the official web site of Nebraska, Gasoline has 125,000 btu per gallon and diesel has around 138,000. That's 10.4% more energy per gallon or. That equates to a 10.4% increase in range on a given amount of fuel or, from another view, 10.4% more power on the same amount of fuel (higher speed).

The biggest problem will be fuel. At around 0 deg F number 2 diesel fuel quickly takes on the consistency of Vicks Vaporub. Dissolved parrafins solidify and turn the fuel into a slimy guck. You can use #1 fuel to lower that temp significantly, but the anti-gelling properties are accompanied by the drawbacks of having fewer btu per gallon and having less lubricity (equates directly to reduced pump life).

Brad

[mfree]

Combat-Wombat;

They proposed to store the LH2 like you'd store LH2 in anything in 1958..... as a cryogenic liquid.

[DustinD]

What kind of energy densities (energy/hydrogen per pound) can metal hydrides get? I think they are way too heavy for airplanes, and possibly too heavy for cars that want decent range unless there was a breakthrough that I missed.

I tried to find the article that I read about the making and designing of the SR-71. It was a good read, but I can not find it anywhere. I did find some references online to a hydrogen airplane concept that lost to the SR-71 due to it's low range.

One idea that will not go over well in the present political climate is nuclear powered jet liners. I think the concepts used isotope or some other "clean" friendly reactor type.