Fuel-cells and Electric Motors for Props?

[Jonfliesgoats]

I was thinking about how propulsion in aerospace tends to become simpler and more efficient over time.  We went from twelve cylinder, sleeve-valved reciprocating Rube Goldberg motors with short service lives to turbojets with, essentially, one moving part.

Anyway, electric propellers seem to be en vogue for solar applications.  What is the feasibility of using fuel cells and electric motors in the 200hp (150kw) range?  

Preliminary math to follow:

Edited December 10, 2016 by Jonfliesgoats

[Streetwind]

Some people are examining this in real life: http://phys.org/news/2016-09-world-seater-fuel-cell-plane-germany.html

One thing to take note of is that if you size the fuel cells to deliver enough power for take-off, then you are carrying a woefully oversized power stack all flight long. The plane in the link above has batteries for additional take-off power instead, which comes out lighter.

[Jonfliesgoats]

Very cool!  

I think it would be conceivable to come up with firewall-forward kits to re-equip existing reciprocating airplanes with fuel-cell electric kits.  The service life and overhaul costs would be much lower and the airplanes could use a wider variety of hydrocarbon or other fuels. 

I am having a little difficulty finding figures on weights and efficiencies of existing hydrocarbon fuel cells.

http://newatlas.com/jet-fuel-electricity-room-temperature-fuel-cell/34594/

I am stuck on hydrocarbon fuel cells for now because it will be a while before hydrogen infrastucture is widely built out.

Edited December 10, 2016 by Jonfliesgoats

[Jonfliesgoats]

My antique airplane has a Continental C-85-12f motor which weights 180lbs along with another 60lbs of accessories and 20lbs of propeller.  For now, let's exclude accessories and propellers.

Anyway, figure 60kw for 90kg of engine.  It's got to be easy for fuel-cell electric combinations to beat that.

In terms of efficiency, the specific fuel economy of most reciprocating airplane engines is about .45lb/hp*hr or 280g/kw*hr.  I don't have these numbers for emerging fuel cells.

Also, this:

https://www.technologyreview.com/s/426252/gasoline-fuel-cell-would-boost-electric-car-range/

[wumpus]

Cool, can't say I'm impressed with anything that needs hydrogen infrastructure.  I wonder what happened to methanol fuel cells?  They were supposed to be all the rage for mobile (and nearly shipped), but eventually people realized that charging by mains beat paying for fuel (in tiny little batches) every single time.

Replacing ethanol blends with methanol is non-trivial, but nothing like the requirements for hydrogen.

[Jonfliesgoats]

Yeah, and when you look at investments required for hydrogen infrastructure in the developing world, things start getting silly.  I really like the methanol/ethanol idea for localized fuel distillation.  The economics of how much biomass you need for a given energy demand aren't as unfavorable as people initially thought.

There are articles out there, but fuel cell development hasn't made the news in a while.  

[Eklykti]

16 hours ago, wumpus said:

I wonder what happened to methanol fuel cells?

Methanol is too toxic for everyday use. There are some research on ethanol fuel cells, which will be lot safer, but probably that's far from being really useful yet.

[Jonfliesgoats]

University of Wisconsin and Tom Jeffries, along with a host of others, work(ed) hard on getting ethanol yields up, especially from stuff with lignocellulose (woody stuff).  I could imagine fuel cells with home-distilled ethanol suplying household power demands.  

For firewall-forward kits and existing airplanes, I would be happy with anything that uses existing hydrocarbons. There is growing concern with the use of tetraethyl lead in aviation fuel.  Getting anything aside from jet fuel in most of Africa is a challenge.  Overhauls costs for reciprocating engines run around 15-20 thousand dollars along with cylinders, etc.  The price advantage of turboprops disappears below a certain power output.  Developing this is a costly and time consuming process, but the economic incentives are there.  

This would be really useful for medium sized UAV/RPV too.

[magnemoe]

59 minutes ago, Eklykti said:

Methanol is too toxic for everyday use. There are some research on ethanol fuel cells, which will be lot safer, but probably that's far from being really useful yet.

How toxic compared to gasoline? 
Butane would be nice for small fuel cells, not planes but the powerpack / small generator segment. 

Has been interest in hybrids for STOL/ VTOL, in that you can easy use the electrical powered propellers for takeoff and landing. They use an piston engine or gas turbine for power. 
 

[Jonfliesgoats]

I am kind of excited to see how these fuel cells develop.

[wumpus]

On 12/11/2016 at 11:22 AM, magnemoe said:

How toxic compared to gasoline? 
Butane would be nice for small fuel cells, not planes but the powerpack / small generator segment. 

Has been interest in hybrids for STOL/ VTOL, in that you can easy use the electrical powered propellers for takeoff and landing. They use an piston engine or gas turbine for power. 
 

Methanol eats through most car fuel lines, and takes a bit of work to modify cars to run on the stuff.  I doubt that it is more toxic to humans (I loved the Aussie press screaming about the carcinogenic properties of xylene (when gas cost more than xylene), all the while ignore just how nasty benzene (and other chemicals commonly found in gasoline).

I suspect that the biggest problems for such things (ignoring the regulatory issues of multiple motors) would be the aerodynamic issues of the VTOL/STOL bits (assuming you have extra propellers and such).  I think that the way such things are manufactured, electric motors would allow redundancy (5-6 or more motors in case one fails) with little added cost (except in terms of aero inefficiency, which would be difficult to control in ways that kept the chances of failure independent).

If you are interested in STOL, check out http://odec.ca/projects/2004/flor4a0/public_html/freewing.htm
(unfortunately, if you want to fly such a beast it creates nearly as many problems as it solves.  It was designed as a drone/UAV).

[Jonfliesgoats]

Regulatory issues for building replace,nets to reciprocating engines to install on existing airplanes are significant, but far from insurmountable.  Aerodynamically, the kits could fit with very little modification into existing cowlings, even with existing engine mount geometry.

Of course, my vision is nowhere near as ambitious as those pushing V/STOL capability.  Existing airplanes with existing (fixed pitch) propellers etc. are in my mind.  

Using existing constant speed propellers becomes a little bit more challenging.  These props use engine oil, so an oil-accumulator system would have to be supplied to existing high-pressure pumps and governors.  Those governors themselves would have to interact with a new shaft system.  None of these challenges are beyond simple engineering, but the costs of development and certification get s lot steeper.

I am also taking cheap, reliable, hydrocarbon fuel-cells for granted.  That tech. Is the real meat and potatoes (Beans and squash!! Yum!) of any sort of development in this vein.  

Also, good discussion on toxicity and chemistry in general, guys!  Methanol is nasty and bad for rubber, but so is ethanol.  This is why many auto fuel STCs (STC=supplemental type certificate) for light airplane are no good with oxygenated fuels (ethanol, mtbe), making the STC less useful.

Ideally an fuel cell electric prop STC for existing planes would use materials that are durable for heavy and light fuels and resistant to polar, hydrocarbon solvents.  Jets and turboprops, for example, can run on gasoline, kerosene based fuels, aviation fuel, etc.  The engines themselves tolerate the variety in fuels well, but  decreased maintenance intervals are required to monitor filters, pumps, etc.  Replacing high octane reciprocating engines with fuel-cells would bring this versatility to smaller aircraft.

In terms of toxicity, benzene, MTBE, tetraethyl lead and aromatics in general are pretty nasty.  We need to consider health effects relative to other options in addition to health effects generally.  

Its safe to say that when hydrocarbon fuel cells become viable, my vision will be one of the least ambitious applications of the tech out there.

Edited December 12, 2016 by Jonfliesgoats

[Jonfliesgoats]

Looks like Boeing has a modified Diamond flying on hydrogen power already.

[PB666]

On 12/10/2016 at 0:23 PM, Jonfliesgoats said:

I was thinking about how propulsion in aerospace tends to become simpler and more efficient over time.  We went from twelve cylinder, sleeve-valved reciprocating Rube Goldberg motors with short service lives to turbojets with, essentially, one moving part.

Anyway, electric propellers seem to be en vogue for solar applications.  What is the feasibility of using fuel cells and electric motors in the 200hp (150kw) range?  

Preliminary math to follow:

I think the Wright 3350c was an 18  cyclinder engine that was the primary powerplant on long distance high capacity aircraft before the 707 (I don't count the comet as it was more of a prototype than an actual production model and had a very short life). It was indeed complicated, it was difficult to keep cool and maintain performance at high altitude. Many of the biggest planes like the DC7 used four of them (meaning they had 72 cylinders a bangin away to keep the bird aloft). The largest of which, the R-3350-42WA : @ 2,830 kW (that is 2.8 MW, something to think about when we talk about generators in space that long to produce 200 kW of power, such as for the VAS IMR powerplant needed). A run of the mill airliner from the late 1950s could produce 8000 kW. The 3350c got about 1/6th of its power from recycling engine heat using steam generator. Unfortunately the original design used a DC4 wing, which really was underdesigned for an engine of that power or the added weight it could carry.

While the engine is quite beloved there were a number of incidences involving loss of airframe because of the engines. They were quite finicky with regard to resonance, and bad resonance has been blamed on a couple of airframe losses. Due to the higher power they could be flown for small periods of time over the NGO altitude, but this could result in engine overheating and other problems. Now a days if a jet engine goes bad (excepting the concorde) you turn around and return to the nearest compatible runway. If you read the incident report for the DC6 and DC7 you find a number of losses due to catastrophic engine failure.

Here are some kerbalesce things to mill over. (remember there were only 343of these produced). http://www.airliners.net/aircraft-data/douglas-dc-7/191,  Seventeen DC-7s remained on the U.S. registry in 2010,

loss of airframe and life when the number two propeller separated and penetrated the fuselage.

loss of airframe and life after an engine caught fire

sinking of an airframe a successful water landing in Sitka Sound just before 1 p.m. local time after struggling with propeller problems for 45 minutes

write-off of airframe do to off-runway landing after feathering malfunction (might have been pilot error). Another one of these occurred with DC6. In the models I flew, I found it extremely difficult to get DC6 and 7 off the ground when loaded with fuel, their angle of attack is laughably below the stall point for the wing as they come off the ground, the only reason they life off is because of the added ground affect, you gain 5 knts more of IAS and the nose needs to go down scraping those tree tops as you fly by. Landing is equally difficult with fuel. One airframe was lost because a commercial firm overloaded the aircraft, the combined engine and weight of the craft split the wings off the plane on a fly-out of Miami. On the longest range flights, the loss of weight due to fuel made the aircraft rather prone to lift and problems for 3nm:1000 ft FA vector, the spoiler takes care of this problem on the 7.

Heres the DC6. (pratt and whitney R2800) 18  cylinder engine was more reliable, but not near as powerful as the 3350c (Var 15A, 16B, and 17B) up to 1900 kW power.

A number of airframes were lost due to engine fire.

engine vibrations which forced the crew to return to Manaus. On the ground one of the right hand engines burst into flames. The fire spread to the fuselage causing the dea

the number three propeller separated and struck engine four, causing the aircraft to break up

crashed seven miles off course while attempting to land on the blue ice runway at Patriot Hills airport in Antarctica. There were no fatalities but damage was extensive and the aircraft was written off. Not to many jet aircraft can place this one in their incidence report list.

[Jonfliesgoats]

Great reference regarding the DC-7!  There are DC-6s flying in Alaska to this day, but DC-7s are quietly collecting dust and mouldering in Cotonou  and N'djamena. They are relics of the JCA airlift into Biafra from the late 60s. 

Here's a link to the constellations parked at São Tomé from the airlift.  They were more reliable than DC-7s, but faced similar economic pressure from simpler jets with higher thrust and power loadings.  These planes still have the fish in their tails from JCA.  The DC-7s and 6s rotting in nearby airports were likely left over from the airlift, but I can prove their heritage.  Still, you see them rotting at the corners of W. African airfields along with BAC 1-11s, a handful of Tridents and growing numbers of 727s.

 

Edited December 14, 2016 by Jonfliesgoats

[mikegarrison]

Fuel cells are often quite sensitive to what goes into them. Like catalytic converters, their membranes and catalysts can be poisoned by unexpected additives or impurities in the fuel. So I wouldn't expect them to be more flexible than current engines about what fuel gets used.

The other issues is, as always, power to weight ratio. If the powerplant itself weighs more, then it has to save a lot of fuel in order to make up the difference. This is a trade today's turbofans face. Higher bypass ratios tend to give better SFC but also require heavier engines (and have more drag). The trades get complex and differ depending on whether the plane is designed for longer missions or shorter missions.

Many fuel cells run very hot (as do combustion engines), so there are still cooling and fire safety issues to deal with.

[PB666]

23 hours ago, Jonfliesgoats said:

Great reference regarding the DC-7!  There are DC-6s flying in Alaska to this day, but DC-7s are quietly collecting dust and mouldering in Cotonou  and N'djamena. They are relics of the JCA airlift into Biafra from the late 60s. 

Here's a link to the constellations parked at São Tomé from the airlift.  They were more reliable than DC-7s, but faced similar economic pressure from simpler jets with higher thrust and power loadings.  These planes still have the fish in their tails from JCA.  The DC-7s and 6s rotting in nearby airports were likely left over from the airlift, but I can prove their heritage.  Still, you see them rotting at the corners of W. African airfields along with BAC 1-11s, a handful of Tridents and growing numbers of 727s.

 

DC-7 was a respectable plane, if it had as many builds as 737 they would have worked out most of the kinks. Although if I could have a plane it would be a 6B, see if I could have a spoiler installed (heh-heh).  As long as the old planes weren't horsed you probably could do a minor rebuild on the engines and replace the hydrolic fuel connectors and get them back in the air again. But at 18 cylinders and 2800 kW you really are pushing capacity. The comet was not . . . ., unfortunately for in-wing mounted jet technology, the technology was blamed for the accidents, but in fact it was due to poor fuselage design.

Sometime the popularity failure of a nameplate is often due more to perception than reality.

DC7 could have been improved. Just take a look at the differences between the 737-300 and the 737-Max, its hardly the same aircraft. The DC8 and 707 were not really great aircraft, but they were the jet-set attraction. The 8 was noisy, it produced alot of smoke, and inefficient. Within a few years after initial production all the engines of aircraft in use were replaced, and even the replacement engines are not efficient by modern standards (would not meat current 1st world airport pollution control standards). The real threat to DC7 usage was the DC9, it could take off on many of the DC7 runways or shorter, it was efficient to run precisely the same routes with about the same number of passengers and make a profit. But Douglas simply stopped DC6 and 7 production although it was widely popular, that immediately makes the future of the aircraft one of obsolete. You could still justify a very low rate of production of the type, even DC3s still have uses, but you won't find any manufacturer willing to produce.

 

[Jonfliesgoats]

Agreed, PB666.  Economics killed the DC-7 as jets became more sustainable.  

People are knocking the motor more than the airframe (get it?  Knocking the motor!  I amuse me!).  That said, extracting more power from reciprocating engines lead to increasing complexity in props and other devices.  By the time you have have turbo-supercharged, with umpteen or tens of cylinders, hydromechamical controllers for auto-mixture, waste gates, and other things you have a pretty complicated piece of gear with lots of points for failure.  Honestly, I am amazed we didn't see more troubles with fires, uncontained supercharger failures, etc.  I repeat myself, though.  

Also, along the lines of the DC-7 getting a bad wrap, other prop liners with more successful reputations fell out of the first-world market around the same time.  Constellations and Stratoliners were off long-haul routes only a short time later.  Short-haul recips, like Convair 440s, lasted a while longer until turboprops made it onto the scene with decent reliability.  The C-46, which came out some years earlier, had some pretty bad teething problems associated with fires and en electromechanical propeller system.  We did work through those problems until the C-46 was relatively safe and reliable.  So timing is certainly a factor.

 

Was production of reciprocating airliners ended early?  I don't know.  

You mention some of the cost and teething problems associated with the DC8 and 707.  At the time it was obvious, due to power and thrust loading, that jet power was the future.  You can extract more thrust from an engine weighing only a fraction of the equivalent reciprocating engine AND the jet engines liked high altitudes better than similar props.  So getting an early start pushing your next generation of plane makes some sense, considering the difficulty in setting up production lines, etc.

What wasn't obvious was the maintenance reliability and safety of jets at the time.  Only a few years earlier the DeHavilland Comet was crashing.  It would have been reasonable, considering the high temperatures and stresses involved in turbine engines, to expect some more catastrophic events from, what was then, a technology new to the commercial market.  So a decision to  keep making propliners would not have been unreasonable.

Early jets after the Comet did pretty well, it turns out.  Yeah, there were noise and pollution issues.  The ability to load more people and bags onto these planes drastically reduced the cost per seat per nautical mile, however.  D.C.-8s stopped flying for UPS not ten years ago.  The last D.C.-9 stopped flying for Delta only two years ago while MD80s and 90s keep flying.  727s and other craft can still be found on freight ramps and in the third world.  Sadly, Convair's 880 never quite made it and the company eventually disappeared.  The only 880 I can find is in Graceland, only a few miles from where I type now.

Reciprocating engines aren't dumb.  We got a lot of know-how from making complicated reciprocating motors during the Second World War and Postwar years.  The huge, complicated messes of systems that made for very high performance reciprocating engines, contra-rotating propellers, and elaborate control systems display a lot of brilliance in solving problems.  

Perhaps, when electric props are the norm, people will say similar things about the reduction gear boxes and accessory systems associated with turboprops?

 

Edited December 16, 2016 by Jonfliesgoats

[kerbiloid]

Methanol is very toxic, it can kill or at least blind you if swallow a glass of it, while a glass of petrol or ethanol would just make you drunken and give a headache.
And you can't distinguish methanol and ethanol organoleptically, so can easily miss.
(Btw, ethanol is the main antidote against methanol poisoning, because it gets digested faster than methanol and allows to make the methanol be digested slowly and get neutralized. )

Ethanol has twice less calorific capacity than petrol. So, it by definition is a very poor replacement,

Edited December 16, 2016 by kerbiloid

[Jonfliesgoats]

This conversation reminds me of old men telling me about going blind from drinking wood alcohol.  Interesting point regarding the treatment of methanol ingestion with ethanol too.

I think, when people look at ethanol they are looking less at the energy density of the fuel than its sustainability.  There are a number of reciprocating ethanol powered airplanes out there and all of them consume about 3/2 more fuel for a given power output.  With fuel cell-battery-electric props, one could imagine a variety of fuels working, but, as you point out specific fuel economy would vary based on fuel used.

 

[magnemoe]

5 hours ago, kerbiloid said:

Methanol is very toxic, it can kill or at least blind you if swallow a glass of it, while a glass of petrol or ethanol would just make you drunken and give a headache.
And you can't distinguish methanol and ethanol organoleptically, so can easily miss.
(Btw, ethanol is the main antidote against methanol poisoning, because it gets digested faster than methanol and allows to make the methanol be digested slowly and get neutralized. )

Ethanol has twice less calorific capacity than petrol. So, it by definition is a very poor replacement,

Ok I tough petrol was more toxic than that. 
That you can mistake it for ethanol is an serious issue at least in places moonshine and other pure alcohol is common. You can markers to it to warn people however this need to be strong and would be pollution for the fuel cell. Note that methanol is used now but not sold from gas pumps everywhere. 

[AeroGav]

The thing about fuel cells is that smaller ones operate at low temperatures (under 150C IIRC) so require exotic and expensive catalysts to work.     Higher temperature (500, 600 C) ones don't , but weren't being considered for the automotive industry, rather industrial applications.

The other thing to remember is that fuel cells are most efficient at low load.  This suits automotive use quite well, because it takes less than 30hp to propel a family car at 75mph  and most cars have > 5x that much available.  However aircraft tend to cruise much closer to full power.    They climb to high altitude for cruising flight where the thin air reduces engine power such that the engine is >60% throttle just to maintain level flight.     This suits internal combustion engines quite well, which loose efficiency at part load, and gas turbines even better, which loose even more efficiency when throttled back.

Then there's the problem that hydrogen, the beverage of choice for fuel cell stacks, is a crummy aviation fuel, being difficult to store.

Finally, you got to deal with the horrendous inefficiency of the hydrogen supply chain.   Major losses electrolysing water to make H2,  then compressing/refrigerating it,  then in the fuel cell again at the other end.   If we had unlimited zero carbon electricity of course it'd still be worth it, but we're not there yet .   For automotive use it's better to just take the electricity that would have been used to create H2 and feed it to an EV directly.  300 mile range EVs are commercially available,  with sufficient fast charging infrastructure that'd be enough for most users.

[wumpus]

I guess a second comparison would be methanol vs. ethylene glycol (another chemical associated with being part of moonshine and assorted dodgy alcohol).  It is also fairly toxic and used in fairly large quantities in gas (and diesel) engines.  Of course, it isn't a consumable, but you have even more leakage issues than fuel (thanks to overheating threats).

In the US, the EPA has clamped down amazingly hard on gasoline evaporation.  I suspect that the existing infrastructure would pretty much eliminate the toxic hazards of methanol.  I've been assuming that methanol would be an effective biofuel (and production of ethanol from similar stocks has failed, but that might be fixed with more advanced yeast engineering).

PS: don't ask what's in the water in Corpus Christi, Texas.  But it is petroleum based and you shouldn't drink it, wash with it, or touch it.  Don't even look at it to be safe.
http://www.bbc.com/news/world-us-canada-38320675  Simple methanol plants seem less likely to cause this type of thing, but with *efficient* plants, who knows (well, other than any chemical engineers who might be luriking in this thread who have built a methanol plant).

[Jonfliesgoats]

Good information, Aerogav.  So, right now, one would need a seriously overpowered fuel cell, even with a fuel-cell-battery-motor combination?  Ideally some numbers regarding continuous amperage available from a given weight hydrocarbon fuel cell will be available.  Additionally, I don't know how bulky these things are.  I imagine a device the size of a shoe box or microwave, but that is nothing more than a guess.

Also, I agree about hydrogen infrastructure.