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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.
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.
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.
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
The only title of honor that a tyrant can grant is "Enemy of the State."
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.
Fuel cells are not all that great either. One of the biggest problems is that they're low power density. And the more power you try to get out of them, the lower their efficiency gets. Plus, aircraft jet engines - when operating at high throttle - are actually pretty efficient to begin with.
A hydrogen fuel cycle - between electrolysis losses and fuel cell losses is much less efficient than an electric cycle. When it comes to cars, usually 1/4 to 1/2 the system efficiency; for aircraft it'd be in the ballpark of 1/2. It also represents far higher capital costs (if you think batteries are expensive, try pricing fuel cells some time) and shorter lifespans (yes, fuel cell lifespans are generally pretty terrible - even in passenger car usage). Fuel cells also demand very high purity fuel, which means that you can rule out the cheapest hydrogen (NG-reformed) - it has to be (extremely expensive) electrolysis H2. Electricity, by contrast, is extremely cheap - much cheaper than jet fuel.
The biggest advantages for switching to electricity for an aircraft come on the ground and during landing. While jet engines are very efficient at high throttle, they're very inefficient at low throttle, and burn a lot of fuel when idling, too. So there's already a lot of work on electrifying the landing gear for taxi, for example.
When it comes to hybrid engines, there's two big targets. One is an electric fan feeding the engine. The other is direct electric drive of the compressor, with the nacelle as the stator and the compressor as the rotor. The latter option lets you entirely eliminate the turbine, which is an expensive piece of hardware that adds significant parasitic drag and reduces combustion efficiency. So moving energy consumption to electric not only lets you save on fuel - one of the biggest costs of an airline - but also engine purchase cost and maintenance. This of course comes at the cost of batteries, but their prices keep dropping (and with how much Tesla is going to need to scale up to meet their orders, they're going to drop even more than expected)
If I ever become wealthy and mad, I'll leave Companion Cubes on desert islands for shipwreck survivors.
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.
Do you ever fly?
APUs have been in aircraft in various forms since World War 1. Modern APUs are turbines that burn jet fuel.
Next time you are close to a big plane, look for a small-ish vent on the wing or the tip of the fuselage. Large planes (and lighter than air aircraft) have had these for a century already.
Your article does have some interesting ideas about using drag envelopes to gain an efficiency advantage, but the idea there haven't been separately powered generators on aircraft before is false.