Siemens and Airbus To Push Electric Aviation Engines (networkworld.com)

coondoggie quotes a report from Networkworld: Siemens and Airbus teamed up today to develop electric and hybrid electric/combustion engines for commercial and private aircraft. The companies said they would amass a joint development team of about 200 employees that would jointly develop prototypes for various propulsion systems with power classes ranging from a few 100 kilowatts up to 10 and more megawatts, for short, local trips with aircraft below 100 seats, helicopters or unmanned aircraft up to classic short and medium-range flights. Hybrid-electric propulsion systems can significantly reduce fuel consumption of aircraft and reduce noise. European emissions targets aim for a 75% reduction of CO2 emissions by 2050. These ambitious goals cannot be achieved by conventional technologies, the companies stated. Airbus has developed a 2-seat electrically powered aircraft, known as the E-Fan. Siemens too has been developing an electric aircraft engine.

Comments

Energy density per kg

[NotInHere]

Is the energy density per kg of batteries really that much better than the energy density of methane gas, or liquid hydrogen?

Re:Energy density per kg

[R3d M3rcury]

I would imagine not. On the other hand, there are other ways of storing energy than batteries (like hydrogen fuel cells).

Get the electric airplane engine working. Let someone else worry about storing the electricity to power it.

Re:Energy density per kg

[Brett Buck]

Not at all. Kerosene is a very good fuel.

    The problem with methane, or even worse, liquid hydrogen, is that while the energy content per pound is good, the energy content per unit volume it terrible. That means very large fuel tanks, meaning more drag and more airframe mass, which leads you to making the wings bigger, which leads to you needing and even bigger tank, which leads to more drag, etc. Liquid hydrogen is one of the worst fuels imaginable for an airplane.

      Liquid hydrogen is only about 4.4 lbs/ cu ft and lerosene is something like 55 lb/cu ft. You simply can't make the airplane big enough.

Re:Energy density per kg

[Solandri]

If I remember from last time an article about these showed up, they're not planning to power the aircraft with 100% electric. It's a hybrid. During ascent it can run the engines at full fuel burn like is done now. During cruise, instead of throttling back, it continues to run the engines at full burn for a while, partly to move the plane forward, partly to charge the batteries. Then it switches the fuel off and runs the engines off the batteries for a while. When the batteries are depleted, run off fuel at full burn again. Repeat.

Run this way, the engines can be optimized for maximum efficiency at just a single RPM (max thrust), instead of having to be optimized across a wide range of RPM. The fuel you save from the higher efficiency of optimizing for a single RPM can more than makes up for the extra weight of the batteries. The point of this project is to figure out what combination of battery size and RPM optimization profile yields the greatest overall fuel savings.

Re:Energy density per kg

[Lisandro]

The engine is the easy part. We already have plenty options for efficient electric engines on any power range you'd like. I recall a group called "Bye Electric" fitting a C172 with a 200hp electric engine with little issues.

Power storage is everything. Every single option to store electric energy onboard an aircraft is orders of magniture less power-density efficient than gas.

Re:Energy density per kg

[Lisandro]

This was actually tried in the past: both the USA and the ex-USSR experimented with nuclear powered engines. Instead of electric engines they used regular jet engines, with the combustion chamber using heat from the reactor instead of burning fuel. It worked fine, the problem was they were unable to properly shield the crew from the reactor's radiation without adding too much weight.

Re:Energy density per kg

[jcr]

If the hydrogen is from a carbon neutral source, which I assume it must or it's a waste of time,

There are other advantages to hydrogen as a transport fuel besides the tree-hugger appeal.

would it not be more efficient to just burn the hydrogen in a traditional jet engine?

Nope. When you burn anything in an internal combustion engine, more than half of the energy from the reaction is lost as exhaust heat. If hydrogen fuel cells can be made with a similar power to weight ratio, then the ability to capture 70% or more of the chemical energy of the 2H2+O2 -> 2H20 reaction beats jet engines all to hell. A fuel cell/electric fan drive train would be far cheaper, require less maintenance, and much lower noise than today's aircraft.

-jcr

Re:Energy density per kg

[Harlequin80]

Energy density for liquid hydrogen needs to be measure in MJ/L for you to really see why it sucks to use. LH2 is 5.6MJ/L and a LiPo is 2.28 MJ/L.

While batteries are probably a long way from being capable of driving aircraft liquid hydrogen is a non starter because it takes up too much space. Standard Kerosene jet fuel has an energy density of 37MJ/L and has none of the painful storage or explosive risks of hydrogen.

Re:Energy density per kg

[blindseer]

There are other advantages to hydrogen as a transport fuel besides the tree-hugger appeal.

There are also many disadvantages. Hydrogen eats steel and aluminum. It has a much poorer energy density by weight and volume than jet fuel. I could come up with more if I wasn't so tired right now but those two alone really kills hydrogen as aviation fuel, especially if derived from a very useful fuel like natural gas (which is mostly just methane) or propane.

Since the entire goal of using this system is to improve the efficiency of burning the jet fuel then producing hydrogen from a fossil fuel sounds like you'd be going backwards. Part of the energy of the fuel is in the carbon hydrogen bonds, if you break those bonds on the ground to make the hydrogen then it is not contributing to the movement of the plane in the air.

Unless you can show me where I've gone wrong, or something I missed, I still think that hydrogen fuel for airplanes is a very bad idea with the possible exception of hydrogen derived from cracking water with power derived from nuclear fission. I won't even consider wind, solar, or geothermal good alternatives since they currently cost more than nuclear power.

Nope. When you burn anything in an internal combustion engine, more than half of the energy from the reaction is lost as exhaust heat.

That would be relevant if the aircraft in question did not have an internal combustion engine. What they want to do is run a generator with an internal combustion engine, then use that electricity to run a motor that drives a ducted fan. While you caught me on the thermal efficiency angle since they claim to reduce fuel consumption by 25% with this system they also hope to gain on efficiency by having batteries be part of the airplane structure. That is not a simple task and they know it.

Their claim of these efficiency gains comes from the hope that they can develop an electric storage system suited to power an aircraft. Since we have not even found a suitable storage system for the much simpler problem of electric cars and trains I believe they are not going to find that solution soon. If they do then perhaps we can see internal combustion cars get beat out by pure electric and electric hybrid cars on every price point, not just luxury cars and tree hugger magnets.

If I use the definition of efficiency to refer to it's cost and complexity, and not it's ability to convert fuel to forward motion, then a common jet engine is more efficient than the hybrid. For an airline this is a make or break matter, they run on total cost of ownership. For a personal vehicle this might not be so critical since a hybrid might offer other advantages such as comfort, performance, or just bragging rights, that a common jet engine would not have.

Re:Energy density per kg

[Harlequin80]

They are both equally important. Especially in things like aircraft. To carry the amount of energy required the size of the hydrogen tanks would be stupidly large. So large that it you wouldn't have any room for anything else. The 777s cary 181,300 L of fuel, this is 6,708,100 MJ of energy. If you assume the same efficiency for a hydrogen burning engine you will need 1,197,875L of liquid hydrogen fuel.

When you then consider that the 777 is 73.9m long and has a cabin diameter of 5.87m which, if treated as a cylinder is 1,362,000 L you start to see the problem. Even if you assume that all 181k of jet fuel is carried in the wings, you have cut your cabin space down to just 345m3 from the original 1362m3 just to hold the extra fuel volume. And this would be an over estimate as it is based on the plane being a tube.

Re:Energy density per kg

[Anonymous Coward]

Liquid Hydrogen would work well in Commercial jets - massive reduction in fuel mass reduces structure weights. It doesn't matter much that have to store fuel in fuselage tanks (just make a bigger fuselage), because so much of plane power use is to lift 1/3rd of takeoff mass in kerosene and bigger engines to accelerate it at takeoff.

EG 787-8 takeoff kerosene is 130tonnes dry, 100tonnes out of total 230tonnes needing about 125m for average mission weight of 180 tonnes.
LH2 would be about 140 tonnes for 25% power or energy saving, needing about 24 tonnes of fuel (engine and landing gear and structure would be lightened) and needing about 350m (tanks about 3.5 tonnes) in a fuselage length of 14m (which is roughly difference between the 787-8 and the 787-10).

If necessary you can just make your jet fly higher to reduce relative size of fuselage compared to larger wings, gives benefit of more internal volume for comfort.

Liquid Hydrogen is probably the best fuel for supersonic use - as it cuts fuel weight by about 75% (about 40-50% of takeoff weight) lowering structural loads and weights, lowering thrust needed proportionally and lowering boom noise by up to half (perhaps more if flying higher), and can easily give global range (eg see lapcat). Also possible advantages in improving gas turbine efficiency through pre or intercooling or using a superheated rankine cycle on the LH2 for even bigger fuel savings. Can also cool passengers.

LH2 would also be fine in Trucks and Ships. What it really sucks at is intermittent small applications like cars motorbikes etc where small scale long term storage issues and close proximity to humans make it dangerous. Fortunately batteries are good enough for that.

So in a post fossil fuel world LH2 is pretty attractive for all sorts of transport, as long as we can find cheap methods of manufacture (ideally nuclear or perhaps southern ocean floating wind turbines or around Antartica to use collosal power available in katabatic winds there.)

Re:Energy density per kg

[Hognoxious]

Not currently (sorry). Maybe that's why they're targeting short haul flights - it's limited by the length of the cable.

Re:Energy density per kg

[jcr]

It has a much poorer energy density by weight and volume than jet fuel.

Volume yes, weight no. There's a reason why hydrogen was used in the first stage of the Saturn V.

-jcr

Re:Energy density per kg

[phayes]

Aircraft are only now beginning to use turbines to generate electricity which is then used in electric motors but is is a very widely used technology in many ships -- especially large warships.

A first application for adding an electric engine to the tail end of an airliner to re-energize the fuselage boundary layer airflow. As the plane flies through the air it slows down some of the air which ends up as drag. By putting a ring around the end of the fuselage directing the boundary layer airflow to an electric engine powered from the main turbines, drag goes down to the point that smaller diameter engines are needed (also diminishing drag). The major design change needed is that with the ring and engine, the horizontal stabilizers must be moved to a T tail.

Both NASA & Airbus are studying this for future designs: see here.

Re:Energy density per kg

[religionofpeas]

Don't liquefy it then. Do I have to do all the thinking round here?

Good idea. Let's put all the fuel in a big cigar shaped tank that you carry on top of the plane. By virtue of being so light, it also helps to create extra lift.

Re:Energy density per kg

[plover]

I'm amazed that in all humanity, nobody's tried it.

"Oh, all the humanity!"

Re:Energy density per kg

[blind biker]

Hydrogen eats steel and aluminum.

I noticed there is a strong groupthink on Slashdot that is against hydrogen fuel cell technology. And one of the (blatantly incorrect) statements is that hydrogen is impossible to store. And yet, there are multiple car manufacturers that make viable hydrogen-powered cars, and the hydrogen storage is not the problem at all. The problem is the current common methods of producing hydrogen, and the (non) availability of gas stations.

I swear that the collective Slashdot IQ falls through the floor when fuel cells, especially hydrogen fuel cells, are the topic. The dumbest, least researched statements, get the most upvotes. It's embarrassing to watch.

Re:Energy density per kg

[Rei]

I assumed they meant to say "wasn't" ;)

Indeed, to sum up:

Mass density: excellent
Volumetric density: horrible
Thrust: poor (though probably not an issue for passenger jets)
Ease of ignition: easy. Burns aggressively in almost any fuel-air mixture, requires only a trivial spark to ignite, and burns can accelerate from deflagrations to detonations in many circumstances.
Ease of accidental ignition: likewise, easy.
Liquid storage: very difficult. High boiloff rate (liquefies air outside its tank), lots of energy goes into creation (incl. ortho/para conversion), entrained air freezes out as a highly explosive ice, subpar compatibility with composites, metal embrittlement over long periods. Boiloff gases pool under overhangs / enters pipes & follow them to their destinations.
Gas storage: difficult. Requires very high pressures for even low densities; high leakage rate and metal embrittlement over long periods. Leaked gas pools under overhangs / enters pipes & follows them to their destinations.
Airflow required for stoichiometric burn: high (~17kg air per kg kerosene, ~40kg air per kg H2)

Basically: as a fuel, hydrogen is both wonderful and terrible.

Use the US Navy seawater to jet fuel tech instead

[blindseer]

The US Navy has been experimenting with the technology that can extract carbon and hydrogen from seawater, connect those elements together in long hydrocarbon chains, with heat and electricity from nuclear fission. They've shown it works. This technology makes aircraft carbon neutral without any modifications to the aircraft itself.

The use of an electric hybrid aircraft would still require hydrocarbon fuels. If that fuel is dug from the ground then it is still adding carbon to the air. I suppose we could combine the two technologies, synthetic hydrocarbons and hybrid planes, but it would still require that we invest in synthetic hydrocarbons.

These electric planes are interesting I suppose but they would not solve the problem like synthesized fuels would.

Re:not going to work

[MightyYar]

Not to mention that the hydrocarbon-fueled aircraft gets lighter and more efficient as it burns fuel, while batteries stay the same weight that they were at takeoff.

Re:not going to work

[SirSlud]

I'm sure this is all new information to them.

In other news..

[JustNiz]

Siemens and Airbus just formed a partnership to develop a 4000 mile long power cord.

Re:The cylinder is heavy, not the gas, but where f

[ChrisMaple]

Due to traction limitations of steel-on-steel, locomotives are heavy by design and the diesel-electric weight is not a disadvantage. The same does not apply to airplanes.

Who said it was battery powered?

[WoTG]

This sounds a lot like the diesel-electric "hybrids" that power trains. Diesel generators generate electricity to power electric propellers. It makes sense to me... of course I know nothing about this stuff. If my assumption is correct, a nice benefit would be that aircraft could use cheaper fuel rather than jet fuel (which I assume costs more per litre... I think it does, if only because of lower volumes).

Re:not going to work

[Lisandro]

Yeah, but to a much lesser degree. Aircraft engines are usually optimized for a given altitude range - normal piston engines decrease power with altitude. Turbochargers improved on this, but they suffer the same issue. Turbofan engines used on airliners have peak efficiency at cruise altitude but suck when flying low.

In general, air density is the main factor impacting aircraft performance, because it impacts on three separate thing: how the engine runs, how much lift can the wings generate and how much air can a propeller push or a jet can suck. Of those, the first one is by far the most important, as it in it can compensate (to a degree) for the rest.

Re:not going to work

[shawn2772]

You nailed it. IDIOTS are pushing this. Void of any comprehension of engineering realities.

Yeah, Siemens and Airbus aerospace engineering teams tend to contain lots of idiots.

Well, either that or slashdot tends to contain lots of arrogant blowhards.

Which is the case here is left as an exercise for the reader.

Re:Use the US Navy seawater to jet fuel tech inste

[blindseer]

And you failed to understand what a Hybrid Electric System is. It's a Combination of Internal Combustion engine with an Electric Drive Motor

A true hybrid allows for power from more than one energy source. An internal combustion engine driving a generator, and the generator driving a motor, is not a hybrid. That would make an electric drive train.

The Fucking Chevy Volt uses such a setup.

No the fucking Chevy Volt has a battery pack and a mechanical transmission. While it might not be able to go in reverse or slow speeds without the electric drive train it is capable of going highway speeds without it. These proposed aircraft do not claim to have a mechanical link from the on board internal combustion engine to the ducted fans. If they did then I might be impressed since that would be an engineering feat.

Locomotives are also Hybrids

Very few trains are true hybrids. Some are capable of using a "third rail" for power, those are hybrids. Even using capacitors or batteries on board would not make them hybrids since all the energy to drive the train comes from the fuel oil.

many of the latest cruise ships are using the same tech

Yes they do, but unless those ships use under water extension cables to power the ship at sea they are still just diesel powered with electric drives.

so why in hell can't you get it through your tiny little mind that Hybrid does not mean Fuel Cells and Batteries.

Because I actually looked up what "hybrid" means.

It's about Bypass Ratio Improvement

[monkeyxpress]

Wow, all the comments on this article have completely missed the point of this. IDIOTS are not pushing this - the concept offers very real efficiency improvements.

The primary constraint in modern jet aircraft efficiency is the propulsive efficiency - turning the mechanical shaft power into forward thrust. This is fundamentally limited by the size of your fan for a given airspeed. If you make the fan swept area a little bit bigger, you can get major improvements in the overall efficiency of the aircraft. This is why newer airplanes always have bigger and bigger engines (787 vs 767, 737NG, A320NEO).

However there are limits to how big you can go. One problem is physically fitting a large diameter engine into existing airframe designs. On the 737NG they had to raise the nose landing gear to accommodate the new engines. There are practical limits to how much you can keep doing this sort of thing without having to create a completely new airframe (the 737 is a 1960s airframe). The other problem with larger fan blades is that the tip speed increases with diameter, which means the fan RPM must reduce to prevent supersonic airflow. This then creates a compromise on the turbine section of the engine. The newest generation of engines are now using gearboxes so that the turbine can run at a higher speed than the fan, which lets them go to larger bypass ratios. The cost, however, is in weight and complexity.

The big benefit that hybrid electric could offer is being able to effectively increase the fan area by distributing fans along the wing. This could create massive efficiency gains, and bring jet aircraft closer to the efficiency of turboprops. Imagine a 737 with two large electric fans next to each other. This could double the swept area on the same fuselage. Further, the concpept could make boundary layer ingestion designs practical, and these also offer big advantages in terms of efficiency for future airframe designs.

This is not about making battery powered aircraft. It is about re-arrangement of the aircraft systems to provide better propulsive efficiency.