Cubdriver

In my thread "Future 737" I post newsclips on biofuel and alternative fuel development for transport category aircraft, airliners and turboprops. The thread also includes developments in high efficiency turbines, since the two go together.

But there is another front that needs to be covered: the development, testing, and certification of biofuels, alternative fuels, and new engines for General Aviation (GA) aircraft. This thread will move a little slow because there is less money in the field. But it is topic that will have a definite impact on flight school aircraft, light commercial aircraft, and all other aircraft in the category. Diesel and turbo-diesel engines will be covered here as well if it relates.

From today's AOPA EPilot-

Another step taken in search for alternate fuel


Teledyne Continental Motors and Hawker Beechcraft have joined forces to move the search ahead for an alternative to 100LL by testing a 94-octane “no lead” aviation gasoline in flight. A Beechcraft G36 (Garmin G1000-equipped) Bonanza flew several flights, the longest to date lasting one hour, with 94 unleaded fuel that was specially blended for aviation purposes. Although this was heralded by Continental President Rhett Ross as another of his company’s impressive aviation firsts, there may still be a long road ahead in the alternative fuel search. Read more and watch the Bonanza’s first flight with unleaded fuel >>

From AOPA Pilot Dec. 2008-

FAA Tech Center evaluates future fuels

By AOPA ePublishing staff


When it comes to the future of aviation fuels, there’s one place to turn for definitive analysis—the FAA’s Alternative Aviation Fuel and Engine Test Facility, part of the WJH Technical Center, located in New Jersey.
Engineers at the facility are dedicated to working with industry to evaluate fuel options, including possible successors to 100LL avgas.
“I think our facility has been a leader in the area of research to help find a solution—a safe, environmentally friendly solution—to what we all know will eventually go away,” said Dave Atwood, an engineer at the facility who works with a team of seven people to test possible alternatives for leaded avgas.
Not only do they analyze potential fuels developed by universities and oil companies, they also provide guidance that can be used to help develop new fuels to test.

From AOPA Pilot Nov. 2008-

Goodbye Big Blue? The future of avgas

by Dave Hirschman


Pilots have been forewarned of the imminent demise of leaded avgas for many, many years and the blue fuel is still plentiful. So it’s easy to dismiss talk of its looming disappearance now as alarmist rhetoric.
But regulatory and market forces are combining in powerful new ways that may someday force 100LL into extinction. And general aviation companies, including engine and airframe manufacturers, electronics, and petroleum firms, are taking steps to prepare new products designed to allow piston airplanes to keep flying into the future.
“After 20-plus years of research, no silver bullet replacement fuel has yet been found to satisfy the needs of the entire general aviation fleet,” said Rob Hackman, AOPA’s senior director of regulatory affairs. “So a second option that appears more likely would include some sort of engine modification for a portion of the fleet in addition to an unleaded fuel. It remains to be seen whether a bolt-on, FAA-certified, aftermarket solution will become available at a realistic price. AOPA members are the end user, and we’re going to continue to make sure their interests are protected. Whatever the industry agrees upon as a replacement to 100LL, it’s got to be safe and legal for the entire fleet to use and allow as much time as needed for the industry to transition.”

rickair7777

Could LL engines be modified with new valves and seats and run on unleaded with an octane booster? It is RELATIVELY cheap to pull heads on those things.

Ewfflyer

I do like the work Cont. Eng's are doing, hopefully something comes of it. I'm still concerned as mentioned above with Valves and detonation issues, but they've put 4-5 flights on the plane so far and it hasn't fallen out of the sky yet!

ryan1234

wonder how they'll handle the STCs for everyone...
also... I wonder if a switch to a new, slightly cheaper fuel will give the ammo for a tax on aviation use fuel possibly bringing the price up to par with 100LL?

Cubdriver

Rick-

In a word, no they can't. There is no drop-in octane booster additive that does everything TEL (tetra-ethyl-lead) in 100LL does. In addition, the piston aircraft engine industry does not have the kind of money and resources to launch an attempt to develop and certify drop-in cylinder head replacements for the existing piston engine fleet. This was possible for the auto-industry in the 1970s. The business case the automobile industry enjoys for this is a very different scenario.

1) The TEL (tetra-ethyl-lead) additive in 100LL Avgas is put there to boost the octane of the fuel. Airplane piston engines need a higher octane rating fuel because they run high-compression engines. High compression engines operate at a higher percentage of their total operating speed range. They need the higher octane and compression to permit higher mass flow rates used with supercharged and turbocharged engines, and to avoid the potential damage from detonation. Cars do not have these features although some of them are used in racing cars. In a word, aviation engines are high performance engines and they need high compression fuel.

2) High octane fuel gives less detonation. Less detonation gives better power extraction from the fuel, better burn performance, less wasted energy, and less damage and stress to the engine. Aircraft engines are safety critical engines. They need the extra reliability afforded by high compression, low detonation engines.

3) You can't run high octane engines on low octane fuels or damage will result. Some low-compression aircraft engines can, with a host of caveats and considerations, obtain an STC to operate with auto gasoline or mogas. As we know, the airplanes designed for use with 100 and 100LL tend to have very long service lives. They do not phase themselves out the way cars phase themselves out over a decade or so. You need to have an octane booster to replace TEL (100LL) if you want these engines to survive for multiple decades. To date, no such replacement has been invented. A large percentage of the existing fleet can use 91/96 unleaded gasoline, perhaps even 70%, but there is a large number of airplanes not served by this substitute fuel. Those engines are true high performance engines that need the high performance characteristics associated with the TEL additive.

4) For decades TEL was used to boost the octane of fuels used in cars and trucks across the modern world and allowed the production of very strong engines. High compression engines made before the ban on leaded automotive fuels are still prized by performance car enthusiasts for the extra horsepower they put out. In 1973 the toxic effects of TEL were shown to be the case, and as a result of this and the fact that lead interferes with the action of catalytic converters used for emission reduction the EPA won regulation against the use of leaded automotive fuels. That's a good thing supposedly because lead in the atmosphere is a very harmful, a topic for other discussion. Engines went to lower compression ratios at an expense in the millions in terms of research and redesign for engines for cars. Avgas remained exempt from the law because developing new cylinder heads for small aircraft engines would have cost more than any of the major engine manufacturers could bear. There are high design, manufacturing, and certification costs associated with aircraft engines and they tend to change very slowly in comparison with automobile engines. It is a smaller industry and it cannot afford to accomodate the rapid changes imposed on the auto industry. At this time, a drop-in replacement for 100LL fuel is what is really needed.

5) TEL in 100LL also cools valve seats and prevents corrosion in the engine. Carmakers had to come up with tougher valves and valve seats that could withstand the higher temps of detonating fuels and the corrosive effects of unburned mixtures. This could be done for aviation engines as you suggest, but it's really not the main issue. High compression ratio-compatible fuel is what is needed at this point.

6) There is a lot of hope in this regard. Funding for alternatives to 100LL is ongoing and is fairly well funded. Some notable programs are the Swift Fuel invention from Purdue University, and the FAA research on the subject being conducted at their New Jersey facility.

Here's a little bit of sleep-inducing material on the subject.

AOPA on leaded gas
AOPA on 100LL
Wiki on aircraft engines
Wiki on avgas
Wiki on gasoline
Wiki on octane

Cubdriver

Future Power Under the Microscope

Thomas A. Horne (AOPA)

A panel discussion at AERO focused on the opportunities and challenges of the proposed alternative propulsion systems of the future. The views were as enlightening as they were divergent. Mike Kraft of Lycoming engines emphasized that traditional spark-ignition engines remain the most efficient at transforming avgas into power. Lycoming has been conducting tests with biomass fuels, but so far Lycoming has concluded that it will be difficult to anticipate the exact nature of future general aviation fuels. “We’re anticipating the software and strategies that we may have to use,” Kraft said, adding, “If we go to a fuel that doesn’t have the current energy properties of avgas, traditional engines won’t behave the same. So airframe manufacturers, engine manufacturers, and fuel suppliers must all cooperate in developing a future fuel.”



German firm debuts hybrid LSA engine

from AOPA Online/ AvWeb (4/5)

German manufacturer Flight Design has unveiled a new hybrid engine for its CT line of light sport aircraft. The new design uses an electric engine for takeoff and climb, before the traditional, 130 hp gasoline engine takes over for cruising. Flight Design says the hybrid feature increases safety, since the electric engine can take over during an emergency, increasing the aircraft's glide time for a safe landing.

mshunter

Very well writen, but I would not consider 8.5 to 1 compression ratios (i.e. IO-550) to be high compression. The main reason why we use leaded gas in aviation is because of it's "cushoining" effects and cooling effects. Being a former Auto tech, the majority of engines produced today are 9.0 to 1 and higher. Motorcycle engine are 12.5to1 and higher. They all can run on 91 octane. The auto makers have figured out how to make power with unleaded fuels, and higher compressions mostly with valve timing. If you can get the valve timing events right, you can make just as much power on lower octane ratings, with higher compressions.

Also, aircolled engines tend to operate at higher tempatures than liquid cooled engines. Have you ever heard an auto "diesel" when it shuts down? This is basically due to the fact that either the timing was to high causing excessie heat in the cumbustion chamber, carbon on top of the piston and in the cyl. heads cumbustion chamber being red hot and continueing cumbustion, or the temp of the engine being to high, causing again, the cumbustion chamber to be to hot and not stoping the ignition cycle.

On to the catalic convertor issue. Don't run leaded gas in anything with a cat convertor. Like you have stated, it will ruin the convertors efficency, but the EPA is misguided. Remember what the lead does to the valves and seats? It cools them. So it does the same thing to the convertor. A cool convertor works less efficently than a hot one. But what it also does is plug it up. A pluged convertor simply won't let the exhaust flow.

Now, my opnion on a need for alternative aviation fuel. It simply is not needed. The lead 100LL fuel accounts for in the atmosphere is less than 1%. But, if they want to make it work, it can be done without completely re-enginering aviation engines. So what happened to all the auto's with the improper valves and valve seats. Some of them are still on the road. What about 100 (green fuel). It contains no lead, and we can still run it in our airplanes with no ill affects. It's a simple matter of octane.

What exactly is the affect of higher octane? In it's simplest terms, the higher the octane, the slower the burn. The higher the cyl. pressure (i.e. compression ratio), the faster the burn. So a compression ratio of 10to1 will require a higher octane, or if turbocharged (increased cyl. pressure and heat) will reauire a higher octane for a given compression ratio (8to1 non-turbo=87 octane, 8to1 turbo=93octane). The more pressure an engine makes with the cumbustion process, the more heat it makes, which we have already established will lead to detonation. If we increase the octane rating of the fuel (i.e. go to 130 octane), we should not need the lead in the fuel any longer. Take the lead out, the fuel gets less expensive. Increase the octane, it gets more expensive. Back to square one with price now.

In my opnion, there is too much thought going into our fuel, when the fix is rather simple. Increase the octane that is availible(which will cool things down), take the lead out, and the problem solved.

It's late, and I have much more to type, but it's time to stare at the backside of my eyelids.

jonnyjetprop

There is on going research into electricon ignition systems that would allow big bore engines to run on a special aviation fuel. It's unleaded gas that I think is around 93-94 octane. The issue is that the ignition system would detect knocking and adjust the timing.

On a second note, it's problematic to run a low compression engine on auto gas. You can't use fuels that have ethanol mixed in it.

mshunter

On the contrary. Ethanol is used as a detonation buffer. It takes much more ethanol to make the same power as a petrol based fuel, but it also generates significantly less heat, which is one reason why the lead is added to av-gas. I for one, am against an ethanol based fuel, because it costs energy to make it (more energy goes into making than it yields).

The reason why we don't add ethanol to av-gas is because of the what the engine cases are made of. There is a measurable amount of magnesium in the case (block) of opposed engines to save weight. Ethanol corrodes magnesium, and the unburnt fuel that makes it way past the rings would corrode the case over time.

We can do it without completely overhauling the system. If we increase the octane (which will generate less heat) and eliminate the lead, in theory, problem solved.

Cubdriver

It seems like a contradiction that aircraft engines have lower compression ratios than the average car. The numbers may differ, but so do the operation regimes. Aircraft engines operate at a higher percentage of their total operating range. Airplane at cruise= 85% or more of total RPM range, versus a car cruising down the highway may be at about 35%. Agreed.
Same story here- these engines do not operate at a very high percent of their respective RPM ranges. In addition, the higher compressions you see today are the result of lots of R&D. Back in 1971 when automakers backed off compressions for the first time, values around 8-9 were common. Only later was it possible to bump it back up as engines were redesigned, something which was very expensive to do.
Agreed- and this is the operating principle behind PRISM (pressure-reactive intelligent spark management system) from GAMI of Ada, Oklahoma. It is not in use due to high certification costs.
Agreed in general, especially for cylinder head temps. I will have to look into the flame temps and exhaust gas temps but I think they are similar for the two engines. Cooler cylinder walls can affect the burn quality for the better. A Continental O-520 may run at about 1400F EGT and 400F cylinder wall temps at full thrust. The cylinder wall temps are a lot more than in a water cooled engine. I do not think the flame temps are very different however. Higher cylinder walls would seem to indicate higher octane fuels are needed, because there is more available activation energy (heat). Yeah I have heard of it. Aviation engines will do it a little bit too even with low lead gas.
Ok. I am not sure about the EPA being misguided... but it doesn’t matter to aviation.
EPA agrees as well, hence the exemption we have for aviation using leaded fuels past the 1996 deadline for cars and trucks. But it’s not just about the EPA. Leaded gas is only made by one small company and they could go out of business at any time. Or the EPA could rescind our exemption on leaded avgas. We need to get another fuel ready. Well, 70% of them do not need re-engineering to work to run on lower octanes, but the other 30% do and they are the root of the problem. And the cost of re-engineering them would be very high. Who is going to pay for it? They do not sell enough to spread the cost out and they are already very expensive engines as they are.And most of them are not. So you are saying there was never a need for re-engineering auto engines to run on no-lead gasoline? You are not correct. There was, and it was done at a cost of many millions by US automakers in the 1970s.
No- it has even more lead. Avgas 100 Green has about .85 grams per liter lead, while Avgas 100LL Blue has about .56 grams per liter of lead. Agreed as long as we are speaking in generalities. It’s more about the evenness of the flamefront during the burn cycle but close enough. Actually octane is not the problem. There are many fuel additives that can provide high enough octane numbers, ethanol for example. But all of them have problems such as cooling properties, toxicity to the environment, cost per gallon, low energy density content, and so on. If it were simple problem to develop a replacement for TEL (lead) a major petroleum manufacturer would have done it decades ago.
I am not sure what your point is here?
Taking the lead out will destroy 30% of the piston engine aviation fleet, which may seem to be a good solution when you're at the end of a 4 day trip. This exact strategy used by Detroit in the 1970s to dispose of most of the existing cars that ran on leaded gas in previous ages. But do you as the owner of a brand new $50,000 Lycoming TIO540 airplane want the engine destroyed in say, five or ten years while the rest of the airplane is perfectly fine? Of course not, and this is why there is a big fuss being made over finding a "drop in" replacement for leaded avgas.