Carbon Free Aircraft: Feasible Possibility or Wishful Thinking?

[dmehling]

We have all been hearing plenty of things in the last decade about the development of carbon free cars. Although someone impractical right now, it is certainly doable. However, I have not really heard anything about alternative fuels for aircraft. It seems reasonable to expect that we could develop carbon free subsonic aircraft, since we could use electrically powered props. But is there any research out there on either carbon free or low carbon propulsion systems that would enable supersonic air travel? Is this a feasible possibility at some point in the future or just wishful thinking?

 

[alxm]

The problem there is that aircraft require massive amounts of power, and that batteries and fuel cells (as of yet) are very bulky and heavy.

I suspect that for the foreseeable future, the only viable 'green' option is renewable, carbon-neutral fuel.

 

[dmehling]

I understand what you are saying about batteries and such, which will require more research to boost efficiency and reduce weight. But, I think the possibility of such aircraft at subsonic speeds would certainly possible. What I really want to know is if carbon free supersonic travel is even physically possible, regardless of how long it would take to develop.

By the way, when you say carbon neutral, are you referring to the use of carbon offsets?

 

[alxm]

What I really want to know is if carbon free supersonic travel is even physically possible, regardless of how long it would take to develop.

Well, there are plenty of rocket engines that already accomplish that.
As for supersonic flight powered by electricity, that's a different story. I'm skeptical; The only design we know of today would be a propeller plane, and no prop plane has ever broken the sound barrier. And modern jet engines tend to be more efficient than piston engines as well. It's a very different situation from electric cars.

By the way, when you say carbon neutral, are you referring to the use of carbon offsets?

No, I just mean getting the fuel from non-fossil sources. If it comes from renewable sources, it doesn't lead to a net increase in CO2. (provided the fuel has more energy than is used making it, which is of course the case for any serious alternative).

Virgin Airlines already ran a commercial flight on 20% biofuel. This was of course mostly a PR stunt, as it's 1) not financially viable yet and 2) the current sources of biofuels aren't very sustainable.
But that's being addressed through a lot of research into e.g. algae biodiesel, which is probably the most promising alternative for renewable, carbon-neutral jet fuel.

 

[dmehling]

Are you saying that rocket engines are carbon free? I guess as a layman, my assumption is that the use of a controlled explosion to produce thrust in a rocket would produce a lot of carbon, even if it's not a fossil fuel. Is that a wrong assumption? What kinds of rockets would be carbon free?

 

[kgbgru]

All of our chemical engines use oxygen in the atmosphere or a stored oxidizer, usually LOX or NOS, to burn fuel. Gas and most jet fuels are made of hydrocarbons, chains of carbon atoms covered with hydrogen. That is where we get the carbon emissions. Combustion of these hydrocarbons releases carbon dioxide and carbon monoxide. This is not the case for a popular rocket fuel. The space shuttle main engines burn LOX and liquid hydrogen. This combustion reaction produces only water vapor, very hot water vapor. Most designs for hypersonic vehicles use liquid hydrogen as a fuel. You should check out Reaction Engines design called Skylon. Is is a design for a "space plane" that is fueled by liquid hydrogen. Single stage to orbit with no carbon emissions, now that's tight.

 

[Strat-O]

While it's feasible to operate most any jet engine on liquid hydrogen with only minor modifications it is still an exotic fuel when it comes to aircraft. Hydrogen is problematic any way you consider it. It doesn't compress well and while liquefied hydrogen can be contained it slowly boils away. You can compress it but it requires very high pressure tanks for storing useful amounts. There are ways to liquefy hydrogen in the form of anhydrous ammonia but any fuel leak or crash would probably release a huge cloud of rather toxic gas. That said, I think the problem will be solved before too long.

As far as electric aircraft, You will no doubt see more propeller driven aircraft but I think that there will also be electrically driven fans that look pretty much like today's turbo fans.

Marlin

 

[Topher925]

As far as electric aircraft, You will no doubt see more propeller driven aircraft but I think that there will also be electrically driven fans that look pretty much like today's turbo fans.

Marlin

How so? As of right now the energy density of a battery is no where near that of any aircraft grade fuel. As far as I know the future for "green" aircraft is looking pretty dim. Even if we develop zero emission cars I would still suspect that aircraft will be flying with petroleum based fuels for decades to come.

 

[sophiecentaur]

The greenest / lowest carbon air journey is the one you don't take.

 

[Strat-O]

How so? As of right now the energy density of a battery is no where near that of any aircraft grade fuel. As far as I know the future for "green" aircraft is looking pretty dim. Even if we develop zero emission cars I would still suspect that aircraft will be flying with petroleum based fuels for decades to come.

Did I mention batteries? There are other ways that electricity could be used in aircraft. One idea is ground-based lasers that beam the energy to the aircraft. The big advantage there is that you don't have to carry any fuel load so payload efficiency goes up.

Marln