Whittle’s legacy
I enjoyed reading the Forward Thinkers article “Sir Frank Whittle, inventor of the turbojet engine” (Professional Engineering No 6, 2022.)
In reality, my father was not entirely happy being described as “the inventor of the turbojet engine,” not due to any German claim to the same fame, but due to the 1921 turbojet proposal of Maxime Guillaume. The significant difference between the two proposals was that FW demonstrated feasibility by calculation, whereas Guillaume was simply countering the then popular conception that jet propulsion might be created by employing the exhaust of the piston engine. He created a drawing of a turbojet that had little functional merit.
Your article mentions that, in the US, General Motors were the recipients of the technology in 1941 when, in fact, it was General Electric… oops!
Ian Whittle
Hazards from hydrogen
I agree with R T Holmes that batteries can only be a stopgap solution to the problem of storing energy on a moving vehicle for all the reasons stated (Your Voice, Professional Engineering No 3, 2022).
However I am not sure that his solution, using hydrogen to directly power the vehicle, is not just another stopgap. The main disadvantages are the large volume, even at very high pressure, which could be difficult to accommodate and the containment vessel and pipework which would need to be very strong and heavy to withstand accident damage and general abuse in long-term use. The other, less frequently mentioned, disadvantage is the possibility of leakage.
Even NASA cannot guarantee keeping hydrogen on the right side of the seals, as evidenced by the delayed launch of the Artemis space mission, so what chance has the average user in long-term operation? Parked in an enclosed space, an explosive mixture could easily result from a minor leak unnoticed in the open air.
I don’t think many would dispute the fact that chemical energy storage in a liquid fuel which is stable unpressurised at normal temperature would be the best solution for weight, volume, safety and general convenience. It could be used in either a combustion engine or a fuel cell, thus covering existing vehicles and new designs, providing much faster total decarbonisation than introduction of the other alternatives on new vehicles only.
The problem is how to produce a carbon-neutral liquid fuel in large quantities and, if that is solved, all other alternatives would suddenly become less attractive. It must be possible with large amounts of intermittent wind and solar electricity available and green hydrogen from seawater, perhaps even extracting carbon from the air making it totally carbon neutral.
John Hardaker,
Skipton, North Yorkshire
When hydrogen takes flight
I was pleased to learn that the Farnborough airshow returned accompanied by weather competing with that of Texas (“Farnborough returns,” Professional Engineering No 5, 2022).
The prospect of a future hydrogen-fuelled aircraft and achieving superconductivity in combination with cryogenic fuel storage (liquid hydrogen) caught my eye. The developers are likely aware that energy storage challenges abound. Liquid hydrogen is a particularly cold cryogen. Its saturation temperature is only 21º warmer than absolute zero and it boils continuously, generating vapour with a particularly wide explosive limit. Irrespective of the cold temperatures, the tendency for hydrogen to also embrittle steels can be potentially catastrophic. Presumably the intention is to perform distributed cooling of electrical machines and runs of semiconductor enhanced powerbus.
Space applications may have mitigated these risks for one-shot flights but, for commercial flights, flying with a distributed vat of hydrogen seems a terrifying prospect.
A supervisor once mentioned that an interesting milestone will occur when superconductivity is achieved in materials operating at the saturation temperatures of liquid natural gas. Liquid natural gas is also a cryogen but is nearly 100º warmer than hydrogen, even warmer than liquid nitrogen, and is more favourable all round in terms of safety.
It’s amazing that these properties change so much through the addition of one carbon to bind four hydrogen atoms to make methane – the main constituent of natural gas. If the origin of the carbon to achieve this is controversial, it can always be synthesised from renewable resources and added along with hydrogen.
Stefan Parfitt,
McGregor, Texas
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.