Those are amazing engines. It's a pity that in the future we'll just be using magnets and coils, there something about these designs that moves me in a way that nothing electrical ever will. And I'm a great fan of renewable energy, and realize that the pollution that has been created (and is still being created) is absolutely unsustainable.

About 12 years ago they used to use 55022 as a shunter at Springburn yard, because it was "road legal" and could couple up to older carriages that were being taken in for refurbishment. Nice cushy retirement job, easy shifts and a well-appointed engine shed to park up it at night ;-)

I used to hear it all the time, working in a nearby industrial site. I'd maybe just take five minutes to sit outside and drink my coffee, listening to that weird shimmering howl.

There are no good recordings of it on Youtube and I suspect like a lot of things you have to experience it for yourself.

A series of 10 "baby deltics" were built and ran for some years, although they weren't particularly successful on the whole.

> avid train spotter at Waverley station in edinburgh

We probably met. I was there every day traveling to and from school but did casual trainspotting on the side. Oblivious someone would one day write a book with that title..

Gas turbines aren't generally noted for their efficiency, but rather:

- Power-to-weight ratios. Critical in aerospace applications.

- Long duty cycles. Everything spins, reducing wear-and-tear relative to reciprocating designs. Maintenance on piston engined aircraft during WWII was a major logistical concern.

- Raw speed. Supersonic flight requires high rotary speeds, and the few propeller-driven aircraft which achieved this had ... issues. Ground crews and pilots suffered health effects from the noise alone, and notoriously often flat refused to work with the XF-84H "Thunderscreech": <https://en.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech...>. At near-supersonic speeds and above, propeller blade tips themselves break the sound barrier, losing aerodynamic flow over the blades, making quite a racket, and greatly reducing efficiency.

Propeller-driven planes remain more efficient than jets in many instances, though last I checked US military forces rely on turboprops over reciprocating engines in virtually all instances, possibly excepting some civilian-based (e.g., Cessna / Piper, etc.) trainer or observer variants.

Those exhaust driven turbines didn't just drive the compressor like is typical with turbochargers, but was also mechanically linked to the crank shaft so the turbine contributed to the overall power output of the engine directly, not just by forcing more air into the cylinders. That's what made them "turbo-compound."

The youtube channel "Greg's Airplanes and Automobiles" has a nice video about turbo compound engines.

Speaking of turbines and fire apparatus, back in the 60's a few jet turbine powered engines and one ladder truck were made: https://www.aeroflap.com.br/en/when-fire-trucks-used-boeing-...

Napier Nomad is one of my favorite engine designs. More info at https://oldmachinepress.com/2019/08/05/napier-nomad-compound...

They're still in use by our UK navy. Nine minesweepers still on active duty.

Scavenging here means getting the exhaust from the previous cycle out of the cylinder and replacing it with fresh air. Technically all internal combustion engines do it one way or another, but usually you hear the word in relation to two stroke engines. Two strokes don't have discrete "suck" and "blow" steps so those need to be done at the same time. With two stroke diesels, that was done using blowers to basically force out the exhaust by blowing in fresh air.

Generally speaking at least, two stroke diesel engines weren't super efficient, but did offer great power output relative to their size.