7 ms·
The challenges of hydrogen for airliners, part 2: ecosystem
- jandrese 6y agoI'm not seeing much advantage of running off of H2 instead of a biofuel like ethanol, especially if we get switchgrass or other less energy intensive forms of biofuel production off of the ground. H2 has so many storage and handling challenges that are going to be compounded when weight is an issue that its hard to see its future in the airline industry.
- supernova87a 6y agoYes, I'm curious to know how much of a weight penalty H2 incurs in required heavy pressure vessels, compared to typical liquids?
- wcoenen 6y agoOnly gaseous hydrogen is stored in heavy tanks under high pressure. As explained in the article, gaseous hydrogen has been deemed infeasible for aviation and the idea is to use liquid hydrogen. No high pressure involved.
- supernova87a 6y agoWell, liquid hydrogen requires some pretty heavy insulating/cooling equipment, doesn't it?
- wcoenen 6y agoThe insulation would likely be some type of spray-on foam over aluminum tanks, so not a lot of weight penalty there. Cooling likely wouldn't be done, I assume any excess hydrogen boil-off that couldn't be burned immediately would be allowed to escape through an overpressure vent. (So ideally top it up right before taking off. There could still be a problem if the plane needs to queue a very long time for a congested runway.)
- sradman 6y ago> Liquid hydrogen has about four times the volume for the same amount of energy of kerosene based jet-fuel. In addition, its highly volatile nature precludes storing the fuel in the wings, as with conventional transport aircraft. Therefore, most liquid hydrogen aircraft designs store the fuel in the fuselage, leading to a larger fuselage length and diameter than a conventional kerosene fuelled aircraft. This lowers the performance due to the extra wetted area of the fuselage. The larger fuselage size causes more skin friction drag and wave drag. On the other hand, hydrogen is about one-third of the weight of kerosene jet-fuel for the same amount of energy. This means that for the same range and performance (ignoring the effect of volume), the hydrogen aircraft would have about one-third of the fuel weight. For a Boeing 747-400 type aircraft, this would reduce the takeoff gross weight from 360,000 to 270,000 kg (800,000 to 600,000 lb). Thus, the performance of a hydrogen-fueled aircraft is a trade-off of the larger wetted area and lower fuel weight. This trade-off depends essentially on the size of the aircraft. [1] [1] https://en.wikipedia.org/wiki/Hydrogen-powered_aircraft#Properties_of_hydrogen_aircraft https://en.wikipedia.org/wiki/Hydrogen-powered_aircraft#Prop...
- jandrese 6y agoFrom what I understand a considerable amount of the weight savings for H2 is lost when you add in the mass of the fuel tanks and piping. The other problem is that the reduction in wing area needed (due to lower weight) is offset by the increase in drag of the fuselage so the savings are modest if they even materialize.
- p_l 6y agoThe problem with biofuels in aviation is that the most common available forms have... problems with storage and weight of the system. Because ethanol evaporates too fast, which is the same reason why aviation still uses leaded gasoline, and why ethanol additives are very limited. Remember, aviation fuels need to work way above 10km above sea level.
- jandrese 6y agoThis seems like an easier problem to solve than converting to H2.
- jeffreyrogers 6y agoI'd assume ethanol would be converted to something like kerosene, since that's what jet engines burn anyways. But without regulation I don't see the incentive to use biofuels. They're significantly more expensive and don't offer any performance benefits. Hydrogen has the same problems btw.
- woodandsteel 6y agoOne gigantic advantage for synfuel kerosene that is carbon-neutral because it is produced with renewable energy, is you can continue to use the present airliner fleet. With hydrogen you have to spend many trillions of dollars replacing it. Furthermore, replacing all the planes would take many decades, while synfuel kerosene might go into production much sooner. Do the hydrogen airliner boosters take all that into account?
- avmich 6y ago> Do the hydrogen airliner boosters take all that into account? Sure, and other things too, like combustion benefits and hazards. But regarding your money worries - they don't need to happen overnight, just like electric cars don't replace gasoline ones suddenly. Hydrogen fundamentally more potent fuel than kerosene - both by energy density and heat characteristics. Like with other commercial technologies, to be accepted it has to change traditions somewhat, which isn't easy. Safety is another important matter - it remains to be seen if hydrogen can be safely brought onboard to regular commercial liners, though advancements demonstrated by Toyota Mirai remind that progress doesn't stand still.
- jaywalk 6y agoI realize that this very different, but hydrogen is very negatively associated with aviation.
- kozak 6y agoLet's say "it already has a track record in aviation" instead.
- jandrese 6y agoDon't worry, nothing could ever go wrong with pressure vessels filled with heavily compressed explosive gas, especially in an accident.
- ggm 6y agoOf all the explosive gases, hydrogen is not the worst. It floats, and it's combustion products tend to be less toxic. I really don't think rocketry experiences inform commercial aviation choices. Has the hydrogen storage associated with spaceflight been responsible for significant explosions. Flight vessels are made as thin walled as possible for a reason. Land bound containers don't have the same weight penalty.
- ncmncm 6y agoThus, don't compress it.
- nomad543 6y agoFunny that while you are saying this, Teslas are catching fire spontaneously.
- jeffreyrogers 6y agoI like hydrogen and support trying it in aviation (the Soviet Union actually had an airliner that ran on liquid hydrogen, so this isn't really that new of an idea), but I really don't see how hydrogen can compete on economics with fossil fuels.
- jandrese 6y agoThus far several companies have experimented with H2 aircraft and come to the conclusion that it doesn't make sense with current technology.
- jeffreyrogers 6y agoYeah, I think hydrogen is a few decades too early. Maybe if there is real regulation limiting GHG emissions or high oil prices hydrogen will make sense, but until then I don't see how it can be made to work.
- sandworm101 6y agoOthers have concluded that it doesn't make sense even with future technology. The energy density of hydrogen, while better than batteries, just isn't worth all the headaches. For a similar cost to an extensive LH2 infrastructure, various diesel-from-air solutions could produce simple non-cryogenic hydrocarbon fuels. (CO2 + H2 = CHC + O2)
- ncmncm 6y agoNew insulation technology changes the balance. Practical aerogel production means that heavy, shape-constrained high-pressure tankage is no longer needed, so that tanks may now be light and have the most convenient shape. Furthermore, recent advances in catalysts for hydrolysis, some directly from sun exposure with no detour through electric form, make production of hydrogen from water and light practical. New airframes with lifting-body designs, already better than those used now, have more room for tankage as a side benefit. The practicality of any idea can change very, very rapidly, as details of solutions to engineering problems change. Recently solar and wind power were impractical. Now they are cheapest, and coal-fired power is impractical.
- bfuclusion 6y agoBring back the Zeppelins:) There's lots of missions they can do besides passenger carrying, and they do it better than aircraft.
- woodandsteel 6y agoTwo sorts of questions for those who support this idea 1) If is is so workable, then why don't we have hydrogen test planes flying today? Are there any technological problems that remain to be solved? 2) How is hydrogen supposed to be better than synfuel kerosene produced with renewable energy? And note than any argument must include the cost of replacing every current airliner with an all new hydrogen one, as opposed to keeping the present airliners.