From the CAMBRIDGE UNIVERSITY PRESS and the “those who don’t pay attention to history are condemned to repeat it” department. See the money quote about kerosene below, bold mine.
Liquid hydrogen may be way forward for sustainable air travel
Professor Hermans from Leiden University’s famous Huygen’s Laboratory acknowledges that oil-based liquid fuels such as gasoline, diesel and kerosene will be hard to beat when it comes to how much energy they pack in relation to their volume and weight–not to mention the sheer convenience of using them to get from A to B.
The author of popular books such as Physics is Fun (2012) and Energy Survival Guide (2011) acknowledges that achieving sustainable transport in the post-fossil fuel era will be a huge challenge–but finds that liquid hydrogen could offer a potential solution for future air travel.
“Given the severe weight limitations for fuel in aircraft, liquid hydrogen may be a viable alternative in the long run,” he argues:
- First, handling of liquid hydrogen would be carried out by professionals, which reduces the safety issues involved with liquid hydrogen to the same level of risk involved in handling kerosene.
- Second, liquid hydrogen itself is very light (in fact, it is in a gaseous state at ordinary temperatures), which is an important advantage for air travel.
- Third, the disadvantages of “boil off” (created by the low boiling point of liquid hydrogen) would be reduced in air travel because of the low outside temperature at cruising altitudes.
Hermans discounts the use of solar power for air travel without revolutionary changes in the airplane concept, but concludes that it seems wise to extend the availability of oil products as long as possible. However, he argues that the low cost of kerosene is a huge disincentive in this respect:
“It is a defect that kerosene is so irrationally cheap, which triggers much unnecessary air travel,” he writes. “A worldwide tax on kerosene–if at all politically possible–should be something to pursue.”
For road transport, Hermans argues that liquid hydrogen is not a viable option due to safety issues around handling it. He finds that electric vehicles offer the most promising solution. However, the challenge is to improve the performance of batteries to prolong the driving time for electric cars, as well as improving the performance of supercapacitors for more rapid charging of the batteries, he argues.
Direct driving using solar power is difficult, Hermans finds, even under a clear sky. However, students from Eindhoven University of Technology are among those that have taken up the challenge; they built a four-seater solar-powered family car that can be driven indefinitely under clear skies at a speed of about 43km/h. The only drawback is that the car is just over 1m tall and is not very comfortable. Hermans concludes that solar family cars will be feasible in future if consumers are willing to sacrifice on comfort.
Alternatively, Hermans writes, the most efficient way for us to reduce energy use in future is to reduce our mobility, for example, by having shorter distances between the workplace and home. “In other words, urban planning provides an important key,” he concludes.
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MRS E&S, a journal of the Materials Research Society and Cambridge University Press, encourages contributions that provide viewpoints and perspectives on the all-important issue of how humankind can work towards, and build, a sustainable future.
The contents of this press release refer to the following article which is freely available
The challenge of energy-efficient transportation, by Professor Jo Hermans
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I am embarrassed that a physicist wrote this. Let’s run some numbers.
Note: I am assuming that the author only intends to use hydrogen as the fuel source, not as a flotation mechanism. If he is proposing a return to dirigibles, other objections will apply.
A 747 consumes approximately 36,000 gallons of jet fuel on an intercontinental flight. That works out to:
4813 cu ft, 4.32E9 BTUs and 240,600 lbs of fuel.
To get the same BTUs, you would need 75,800 lbs of H2. That’s only .31 the mass so that’s a savings. However, at 1 atm, that mass of H2 occupies 1.35E7 cu ft – or about 2800 times the total volume of the 747 itself. Since the dominant driver of airline fuel cost is air resistance and air resistance is dominated by the cross-sectional area component, you’re either going to go very slowly or have a VERY long airplane (that will still have much higher resistance).
So presumably, he’s not proposing gaseous H2. Liquid H2 has a density of 4.423 lbs/cu ft so our international trip would require a bit over 17,000 cu ft of liquid H2. For scale, that’s about 4 railroad tankcars worth of liquid H2. That works out to about 3.6 times the volume of the existing jet fuel tanks. It’s not quite as absurd but it will still have a significant effect on design and aerodynamics of the plane.
Note, however, that’s just the raw fuel weight and volume. We also have to consider the difference in container weight between something that can store jet fuel at ambient temperature and pressure (basically, any plastic or metal bag) and something that can keep H2 liquified at 20K or below. The external tanks on the Space Shuttle might not be bleeding edge technology anymore but they’re probably still pretty close. Scaled down to the volume needed for a single intercontinental flight, you’d have to add back about 20,000 lbs and a bunch more volume just for the containment vessel and control mechanisms.
On net, you might with proper design be able to build a jet that can use H2 at or near parity with conventional fuels. But why would any sane engineer take on all the additional risks and costs of manipulating liquid H2 just to get back to about the same performance?