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Thread: Hydrogen a worse fuel for aircraft?

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    Hydrogen a worse fuel for aircraft?

    I see that Airbus has shown off some concept pictures of zero emission aircraft. They propose using hydrogen as a replacement fuel for the turbine engines. Having recently come across reports that contrails at high altitude contribute more than CO2 towards global warming, would hydrogen be the worst possible solution?

    I'm under the impression that the only emission from burning hydrogen is water, which of course makes the contrail problem worse.

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    Quote Originally Posted by headrush View Post
    I see that Airbus has shown off some concept pictures of zero emission aircraft. They propose using hydrogen as a replacement fuel for the turbine engines. Having recently come across reports that contrails at high altitude contribute more than CO2 towards global warming, would hydrogen be the worst possible solution?
    I doubt it would be the worst, but I would think the practical issues would lead to air travel being one of the last things getting a major structural change. I believe air travel accounts for about 3% of CO2 emissions, and there are much easier/cheaper targets on the ground. Hydrogen is extremely bulky (requiring different aircraft design) and a hard fuel to handle. It is also expensive when produced from fossil fuels - and then you still need to deal with the CO2, or you lose much of the advantage of using it. It is more expensive still when split from water using energy from non-carbon energy sources. There are still gains to be made reducing aircraft fuel use, and ground transport can substitute for some of that, though that can be costly too (California is building a high speed train that has ballooned in cost and is taking longer to build than expected - many consider it to be a boondoggle).

    For the foreseeable future, it might make more sense just to have offsets for air travel.

    I'm under the impression that the only emission from burning hydrogen is water, which of course makes the contrail problem worse.
    Oxides of nitrogen (NOx) are also produced when you burn hydrogen at high temperature.

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    I don't think water vapor has the persistence in the atmosphere that CO2 does. It forms clouds and becomes rain. CO2 just continues to hang around.

    <citation needed>. I'll see if I can find something.

    ETA: From Wikipedia:
    Water vapor accounts for the largest percentage of the greenhouse effect, between 36% and 66% for clear sky conditions and between 66% and 85% when including clouds.[22] Water vapor concentrations fluctuate regionally, but human activity does not directly affect water vapor concentrations except at local scales, such as near irrigated fields. Indirectly, human activity that increases global temperatures will increase water vapor concentrations, a process known as water vapor feedback.[86] The atmospheric concentration of vapor is highly variable and depends largely on temperature, from less than 0.01% in extremely cold regions up to 3% by mass in saturated air at about 32 °C.[87] (See Relative humidity#other important facts.)


    The average residence time of a water molecule in the atmosphere is only about nine days, compared to years or centuries for other greenhouse gases such as CH4 and CO2.[88] Water vapor responds to and amplifies effects of the other greenhouse gases. The Clausius–Clapeyron relation establishes that more water vapor will be present per unit volume at elevated temperatures. This and other basic principles indicate that warming associated with increased concentrations of the other greenhouse gases also will increase the concentration of water vapor (assuming that the relative humidity remains approximately constant; modeling and observational studies find that this is indeed so). Because water vapor is a greenhouse gas, this results in further warming and so is a "positive feedback" that amplifies the original warming. Eventually other earth processes offset these positive feedbacks, stabilizing the global temperature at a new equilibrium and preventing the loss of Earth's water through a Venus-like runaway greenhouse effect.[86]
    I would also expect the mass of water vapor produced by a hydrogen fueled airplane to be pretty minimal compared to natural and other human sources.
    Last edited by Trebuchet; 2020-Sep-21 at 10:24 PM.
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    I think the science is settled that we have too much CO2 partly from planes. The water vapour is a potent greenhouse blanket and it gets worse as the near surface atmosphere warms, but CO2 is the extra factor in anthropogenic warming so setting aside the technical challenges, hydrogen is surely part of the solution both as burn fuel and fuel cells. Personally I would like to see hydrogen airships brought back with appropriate technology.
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    Quote Originally Posted by profloater View Post
    I think the science is settled that we have too much CO2 partly from planes. The water vapour is a potent greenhouse blanket and it gets worse as the near surface atmosphere warms, but CO2 is the extra factor in anthropogenic warming so setting aside the technical challenges, hydrogen is surely part of the solution both as burn fuel and fuel cells. Personally I would like to see hydrogen airships brought back with appropriate technology.
    I would think flying aircraft will become battery operated. Perhaps to start in 10 years.
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    Quote Originally Posted by Copernicus View Post
    I would think flying aircraft will become battery operated. Perhaps to start in 10 years.
    Batteries have far worse energy density than even hydrogen, and that is worse than jet fuel by a large margin. Battery capacity will improve, but a doubling or tripling of capacity would still result in a poor energy density for an aircraft, and that would be revolutionary for battery technology.

    Battery planes might eventually be practical for some short range prop plane applications, but not to replace jetliners.

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    Quote Originally Posted by Copernicus View Post
    I would think flying aircraft will become battery operated. Perhaps to start in 10 years.
    Yes small aircraft already but international needs the energy to Weight to be better. Hydrogen will be an order or two more effective than lithium and way cheaper. Current fuels 20 times better than lithium for energy stored/weight. Efficiency of electric motors makes up a little but long range remains a challenge. Cars can get range, just about, if charging can be fast, like cup of coffee fast, but for planes and ships, hydrogen beckons.
    sicut vis videre esto
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    I don't understand this at all.

    Clouds have a net cooling effect. Water vapour trails are just long clouds, they ought to reflect sunlight back into space.

    The soot and NOx might well be warming, but surely not the water droplet contrails per se.

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    Quote Originally Posted by kzb View Post
    I don't understand this at all.

    Clouds have a net cooling effect. Water vapour trails are just long clouds, they ought to reflect sunlight back into space.

    The soot and NOx might well be warming, but surely not the water droplet contrails per se.
    Water as droplets forms reflective clouds. Water vapor, after the droplet evaporates, is a potent greenhouse gas, transparent to human eyes. Water from the surface does not normally reach the altitudes of jet airliners much, so it's not a natural problem. Once the vapor gets up there it takes a while to come down, spreading apart and insulating heat that whole time; and contrails are too narrow to reflect much sunlight away when it's still in droplets.
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    Quote Originally Posted by Noclevername View Post
    Water as droplets forms reflective clouds. Water vapor, after the droplet evaporates, is a potent greenhouse gas, transparent to human eyes. Water from the surface does not normally reach the altitudes of jet airliners much, so it's not a natural problem. Once the vapor gets up there it takes a while to come down, spreading apart and insulating heat that whole time; and contrails are too narrow to reflect much sunlight away when it's still in droplets.
    The fact that the initially hot jet exhaust water vapour quickly condenses shows that the air up there is saturated with respect to water. It's usually something like -20 C 6 miles up.

    Clouds and particulate in the atmosphere are generally taken to have a climate cooling effect. They increase the average albedo of the planet.

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    Quote Originally Posted by kzb View Post
    The fact that the initially hot jet exhaust water vapour quickly condenses shows that the air up there is saturated with respect to water.
    Er, that's wrong. That's not how condensation works.

    Believe the explanation or don't, it's no skin off my nose.
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    Quote Originally Posted by Noclevername View Post
    Er, that's wrong. That's not how condensation works.

    Believe the explanation or don't, it's no skin off my nose.
    I'm reserving judgement on it at the very least.

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    Quote Originally Posted by profloater View Post
    Yes small aircraft already but international needs the energy to Weight to be better. Hydrogen will be an order or two more effective than lithium and way cheaper. Current fuels 20 times better than lithium for energy stored/weight. Efficiency of electric motors makes up a little but long range remains a challenge. Cars can get range, just about, if charging can be fast, like cup of coffee fast, but for planes and ships, hydrogen beckons.
    Liquid hydrocarbons have greater hydrogen density per unit volume than does liquid hydrogen itself.

    You'd be better off making synthetic jet fuel from hydrogen and waste carbon sources, as long as the hydrogen was made using low-carbon energy.

    Also has the advantage there is no large technical step-change, with all the safety cases that would entail.

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    Quote Originally Posted by kzb View Post
    You'd be better off making synthetic jet fuel from hydrogen and waste carbon sources, as long as the hydrogen was made using low-carbon energy.
    Or biofuels. That’s been done already as a test, but currently is too expensive compared to fossil fuel to be competitive. Hydrogen would be worse, though. I just don’t see hydrogen fuel becoming important for airliners. As long as fossil fuels are economical to produce, for aircraft, offsets make more sense. After fossil fuel gets too expensive, bio or artificially made hydrocarbons make more sense. If the purpose is to reduce total CO2 in the air, there are easier approaches. It just isn’t that huge a part of CO2 emissions (2%).

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    Quote Originally Posted by Van Rijn View Post
    Or biofuels. That’s been done already as a test, but currently is too expensive compared to fossil fuel to be competitive. Hydrogen would be worse, though. I just don’t see hydrogen fuel becoming important for airliners. As long as fossil fuels are economical to produce, for aircraft, offsets make more sense. After fossil fuel gets too expensive, bio or artificially made hydrocarbons make more sense. If the purpose is to reduce total CO2 in the air, there are easier approaches. It just isn’t that huge a part of CO2 emissions (2%).
    Offsets are a con. Can I ignore the requirement to get an electric car as long as I "offset" my 15 mpg SUV then?

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    Quote Originally Posted by kzb View Post
    I'm reserving judgement on it at the very least.
    Well, at least judge the fact that condensation happens at thermal contrast boundaries, like cold upper air hitting jet engine exhaust.

    Anyway, derailing, subject dropped.
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    Quote Originally Posted by kzb View Post
    Offsets are a con.
    You’re sure of that, in every case? So methods of extracting CO2 from the air are inherently a con? Choosing more practical methods for countering CO2 is always a con?

    Can I ignore the requirement to get an electric car as long as I "offset" my 15 mpg SUV then?
    If you have a more practical and economical method for reducing CO2, why not? However, ground transportation accounts for a much larger percentage of CO2 production and is easier to deal with than jetliners, so probably is a poor example.

    Agriculture accounts for 18% of greenhouse gas production, concrete accounts for 8%, aircraft 2%. General industrial and general transport are above all that. It is most practical to target the sources that give you the most bang for the buck. Rather than disrupting air travel, why not offset using better options?

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    Quote Originally Posted by kzb View Post
    Liquid hydrocarbons have greater hydrogen density per unit volume than does liquid hydrogen itself.
    But what they don´t have is energy density per unit mass.

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    Quote Originally Posted by kzb View Post
    Liquid hydrocarbons have greater hydrogen density per unit volume than does liquid hydrogen itself.

    You'd be better off making synthetic jet fuel from hydrogen and waste carbon sources, as long as the hydrogen was made using low-carbon energy.

    Also has the advantage there is no large technical step-change, with all the safety cases that would entail.
    But that releases CO2
    sicut vis videre esto
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    Quote Originally Posted by chornedsnorkack View Post
    But what they don´t have is energy density per unit mass.
    Yes, liquid hydrogen does win out on energy per unit mass.

    But I'm not comparing with that, I am comparing with batteries.

    Hydrocarbons twenty times better than Li-ion batteries (by energy/mass) according to Post #7.

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    Quote Originally Posted by profloater View Post
    But that releases CO2
    . . . and? The atmosphere isn’t CO2 free, the concern is the total CO2 in the atmosphere.

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    Quote Originally Posted by profloater View Post
    But that releases CO2

    Living does, too.

    But kzb's suggestion releases a lot less CO2 than petroleum. It's a start.
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    Quote Originally Posted by profloater View Post
    But that releases CO2
    It doesn't release NET CO2, provided the synthetic hydrocarbon is made using a zero-CO2 energy source.

    HC's are a more concentrated hydrogen storage medium than any hydrogen storage medium.

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    Methods to extract CO2 from air to use as a feedstock for hydrocarbons are a growing area of research. Plants do it for free, but they're relatively slow and inefficient. Human engineers might be able to improve on the process, using it for more than fuel; plastics and building materials could perhaps be a good and useful form of sequestering atmospheric carbon.

    But all the successful methods so far are expensive and small scale. So the research continues.
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    In other news....
    The world's first hydrogen-powered commercial aircraft has taken to the skies above Bedfordshire.

    The only thing that the six-seater Piper M-class plane emits is water vapour - and ZeroAvia, the company behind the technology, says its aim is to make hydrogen planes available commercially in three years.

    "What we're doing is replacing fossil fuel engines with what's called hydrogen electric engines," ZeroAvia founder and chief executive Val Miftakhov told Sky News.
    The article doesn't say, but would a "hydrogen electric engine" be a fuel cell?


    https://news.sky.com/story/amp/world...shire-12080886

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    This article, https://www.aviationtoday.com/2020/0...ric-turboprop/ , from July 7th, 2020 gives a bit more information about ZeroAvia's hydrogen powered aircraft.

    The final design goal is indeed a hydrogen fuel cell powered electric aircraft. The test flight that the article headrush linked to was, if I understand correctly, the first with a fuel cell as a power source. They've conducted many previous tests with electrical systems and motors but with a battery instead of a fuel cell. Some excerpts from the article . . .

    The series of 10+ test flights, completed beginning June 23 at Cranfield University’s airport, used a Piper Malibu Mirage turboprop modified with a 300-kilowatt (kW) battery electric power system . . . [confusing use of "turboprop"]
    We recorded the most economic cruise from the flight occurring at 2,000-RPM prop speed, 90 kts indicated and that was with 75 kW of consumption.
    ZeroAvia and its partners for Project HyFlyer are now preparing for the next round of flight-testing using the hydrogen electric powertrain that they ultimately want to use for zero emissions passenger carrying aircraft. In that system, the power inverters and electric motors still drive the propeller, however the electricity is provided by the hydrogen fuel cell system in place of the battery.
    . . . Mifthakhov said, adding that the biggest cost savings for their preference of hydrogen to battery power is the limited lifespan of batteries compared to the life of the aircraft.
    Additionally, the energy density of the hydrogen electric system is “five times better than battery power,” as the weight of the hydrogen fuel cell system is significantly lower, according to Mifthakov.
    Project HyFlyer’s ultimate goal is a 300-nautical mile flight in the hydrogen-powered Mirage taking off from the Orkney Islands in Scotland.

    While the 2023 goal is a 19-passenger Twin Otter capable of 500-mile regional flights, their next goal will target larger regional turboprops like Bombardier’s Dash-8 or the ATR 500 series by the end of the decade. Mifthakov said the team believes it can achieving operating costs that are half of what are required for a jet fuel powered Twin Otter.
    They seem to think that they can make both the hydrogen storage and hydrogen fueling infrastructure issues work. Neither of the articles mention how the hydrogen will be produced, though in the article headrush linked to ZeroAvia founder and chief executive Val Miftakhov is quoted as saying, "We also have a fueling infrastructure set up that ensures zero emission production of hydrogen itself."

    I wonder how the costs and longevity of the hydrogen fuel cell compares with batteries.

  27. #27
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    H fuel cell plane flew today, 6 passengers 350 mile range. Flying wing shape.
    sicut vis videre esto
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    Mentour Pilot on Airbus H fueled ideas!

    Disclaimer: I spent my last five years of my aerospace career in Boeing's "Product Development" and "Advanced Concepts" departments. I very much enjoyed that time. But ten years later, you can count on the fingers of one foot how much of that work has come to fruition. I doubt that Airbus's comparable departments are much different.
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    I hope they are.

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    Quote Originally Posted by publiusr View Post
    I hope they are.
    We need the Tesla of aircraft to jettison the main players into action.
    The moment an instant lasted forever, we were destined for the leading edge of eternity.

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