Aircraft and Carbon Dioxide Emissions

Climate change requires significant changes to our lifestyle, and one of the more tricky problems to solve is air travel. Interestingly, you will find many environmentalists always telling everyone to cycle, but then spend tens of thousands of air miles going to environmental conferences. So, what can we do?

One solution is to reduce air travel. And there is no need in principle to adopt Greta Thunberg’s solution of sailing over the Atlantic. With a bit of investment, high speed rail can get you between the centres of reasonably close cities faster than aircraft, when you include the time taken to get to and from airports, and time wasted at airports. We can also reduce travel, but only so far. At first sight, things like conferences can be held online, but there are two difficulties: time-zone differences encourage doing something else, and second, the major benefit from conferences is not listening to set talks, but rather meeting people outside the formal program. For business, facing each other is a far improved way of negotiating because the real signals are unspoken. 

Some airlines are trying to improve their environmental credentials by planting trees to compensate for the carbon dioxide they emit. That is very noble of them, but apart from the fact it is their money doing it (and often it is not – it is the passengers who feel conscious stricken to donate more money for planting) it is something that should be done anyway. 

There has been talk of building electric aircraft. My personal opinion is this is not the solution. The problem is in terms of unit weight, jet fuel contains at least thirty times the energy density of the best batteries available. Even worse, for jet fuel, as you go further, you get lighter, but not with batteries. You could make a large aircraft fly, say, 1,000 to 2,000 km, as long as you did not want to carry much in the way of passengers or cargo. With thirty times the fuel weight for a long distance flight your aircraft would never get off the ground. However, the Israeli firm Eviation has developed a small electric aircraft for a load of 9 persons (plus two crew) powered by 920 kWh batteries with operating costs estimated at $200/hr. The range is about 540 nautical miles, or about 1,000 km. That could work for small regional flights, and it will be available soon.

Another option to be offered by Airbus is the E-Fan-X project. They will take a BAe 146 craft, which usually carries about 100 passengers, and which usually is powered by four Honeywell turbofan engines, and replace one of the inner ones with an electric-driven 2 MW propulsion fan motor. The idea is the takeoff, where the most power is required will use the normal jets, but the electric motor can manage the cruise. 

An alternative is to reduce fuel consumption. One possibility is the so-called blended wing, which is being looked at by NASA. This works; an example is the B2 bomber, however while it reduces fuel consumption by 20% it is most unlikely to come into commercial use any time soon. One reason is that there is probably no commercial airport that could accommodate the radically different design. It would also have to have extensive examination because so far the design has only had military applications, in which only very specific loads are involved. In principle, this, and other designs can reduce kerosene usage, but only by so much. Maybe overall, 25% is achievable, which does not solve anything.

Uranium 235 has an energy density that leaves kerosene for cold, but which airport wants it, and would you board it anyway? It could presumably be made to work, but I can’t see it happening anytime soon because nobody will take the associated political risk.

That leaves hydrogen. 1 kg of liquid hydrogen can provide the same energy as 3 kg of kerosene, so weight is not the problem, but keeping it cold enough and maintaining pressure will add weight. It cannot be stored in the aircraft wings because of the volatility. To keep it cold it is desirable to have minimum surface area of the tank. However, it is reasonably clean burning, giving only water and some nitrogen oxides. For a Boeing 747-400 aircraft, the full fuel load is 90 tonne less, but because the tanks have to be in the fuselage, they occupy about 30% of the passenger space.

That may work for the future, but the only real way to power current aircraft is to burn hydrocarbon fuel. More on that next week.

6 thoughts on “Aircraft and Carbon Dioxide Emissions

  1. Corrupt Airline Industry Should be Forced Make Hybrid, Hydrogen Planes
    Civilizations decay when taken over by plutocracy, which makes first their thinking heads decay (the question of why this didn’t happen in Medieval Europe is of the utmost interest; it has much to do with ferocious competition between the potentates, especially Paris and London).

    The French engineer and inventor Ader created the first planes (he had also created the first wireless stereo). Adler used new technology, the lightest steam engines ever made. He took off on 9 October, 1890. However, in the following decade, higher performing gasoline engines were invented. Between Ader’s first flight and the first jet engines, half a century. Eighty years to land on the Moon. Since then, we have pretty much stagnated.

    Hybrid propulsion for aircraft should be feasible with existing battery technology (or the one just around the corner, with twice the energy density; let alone solid state lithium, which is on the verge of industrial production).

    The point of aircraft hybrid propulsion is that much power is used during ascent or emergency (all engines on). Hybrid can recover much of this energy during descent (with appropriate large slow propellers working as air brakes in the back of the plane). Due to aviation needs batteries could be much improved (going to solid state, forgoing much of the present weight for cooling and isolation of the present flammable cells; in a car, battery mass is not that important).

    One can easily sketch what should be done. But it would require vastly different airframes (large propellers in the back, etc.).

    Hydrogen planes are obviously feasible, as large hydrogen rockets routinely fly (as Ariane V). They just require a massive “green” hydrogen infrastructure, which is needed anyway (to store sustainable energy such as solar PV).

    Once again, different airframes would be needed. Airbus has been using the same airframe on the A320 for 40 years…. And Boeing for nearly 60 years on the 737… The whole airline industry has become corrupt, resting, fat and content, over huge subsidies, packing passengers like disease laden sardines, flying them all over the world for no good reason…

    Ader, who invented so many things, electric or not, also created the words “avion” and “aviation”… Coronavirus is showing us that flying people like sardines should be against the law. Airline subsidies should also be against the law, be they for not paying a fuel tax, for business jets, etc. High speed or not, AWE, pollution and energy cheaper electric trains should be subsidized instead.

    It goes without saying that the cruise ship industry should also be forced to go hybrid and sailing (omnidirectional sails exist)… And also slower. One large cruise ship (ironically made in France) was demonstrated to cause, anchored in Marseilles, France, as much pollution as two million cars. It should be all electric, and if that means nuclear engines, so be it.
    We know, from 99.99% sure paleontological record, and 100% from elementary geographical thermal logic that at 450 ppm CO2, oceans should be 30 meters (100 feet) higher. Now we are already at 500 ppm in CO2 equivalent. However, coronavirus is going to curb the human CO2 input this year (that may help us see how much CO2 augmentation is caused by human activity). Just as with viruses, humanity has been under the belief that this sort of thing happens to others. However, elementary logic and basic geography show we could have a breakup of the iceshileds within a few decades.

    So we need to shut down CO2 production. Air travel was expected to become a most major contributor, within a few year… Thanks, SARS-CoV2!

    Patrice Ayme

    • Removal of air transport may not be as beneficial as some people think. After 9/11 the reports are the ground temperatures in the US increased by almost 2 degrees C. Th reason – the jets leave ice crystals at 35,000 feet and they reflect sunlight, thus raising the albedo. There may be no winners out of this additional corona virus

      • Yes, well, indeed, sometimes. It depends upon the conditions for the formation of crystals (do you have a link? I didn’t know the effect was that strong). In any case that sure is not true for cruise ships, with its ground level pollution…

        The effect you are talking about is computed in exobiology. For example high altitude methane blocks a star’s energy at high altitude: this is why the surface of Titan is so cold. So low altitude methane augments the greenhouse, high altitude CH4 does the opposite.

        This effect, in reverse, by destruction of high altitude methane from solar flares, is expected to rise the temperature of Proxima B planet… And make it Earth like, temperature-wise.

  2. Hello Patrice. Sorry, it was something I aw once and it stuck in my mind, but I can’t provide a reference. As for Titan, I would think it was the smog that gives this effect. There are an awful lot of different chemicals up there thanks to any methane getting up there tending to photolysed by the hard UV, and the reacting with nitrogen.

    Proxima B should be tidally locked, so it will have a range of temperatures. Whether is methane in an atmosphere is unknown. It may not even have an atmosphere, as it could be condensed out on the cold side, or blown away by the solar sputtering.

    • If there could be high altitude methane on Proxima b, for example as on Titan, or from (some) life. That high CH4 absorbs star energy, from reverse greenhouse, preventing it to reach the ground. However, flares from the Red Dwarf would make hydroxide destroying the high altitude CH4… thus warming the planet. It’s true the flares could strip the atmosphere… Except if there is a magnetic field… I don’t believe it would condense; looking at Pluto…

      • It may be the case on Proxima b. Methane is not stable in our solar system because the UV in the sunlight destabilises it. There is very little methane in Titan’s atmosphere and most of that is below the smog (which is made from photolysing methane) and it is replaced by emissions from the ground. However, the red dwarf emits very little if any UV, so just maybe a methane atmosphere could live. If it did, because the red dwarf mainly emits infra red light, you should get that inverse greenhouse effect.

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