Apparently they really don't scale well. I found this reddit post explaining it better:
> Gas turbines scale extremely poorly. They rely on small clearance between the rotating blades and the housings for efficiency. The smaller the turbine, the greater the relative clearance and the more energy is lost. Gas turbines, at least with established technology, make very little sense below 300ish HP. As a real life comparison: A Robinson R44 piston helicopter and an R66 turbine Helicopter have almost identical design, dimensions, and weights. Power is around 250 / 300hp. The former burns between 50-60L of gas per hour at cruise, the latter around 90-110L of Jet fuel.
They did come about, in the late 60s. Williams worked on these to varying degrees of success. One of their designs became quite famous. The F107 powers the BGM-109 Tomahawk and AGM-86 ALCM.
There are companies that have tried, like Capstone (formerly Capstone Turbine, then Capstone Green Energy). Capstone declared chapter 11 bankruptcy last year (since emerged and continuing under new leadership.)
There's no reason to have a generator that charges the pack in a hurry. It really only needs to cover the maximum sustained average draw - driving up an extended grade at high speed. That's a lot less than 300 hp - it's probably not more than 80 hp or so at most.
I remember back in the 90's in auto shop we calculated that you'd only need 15-25hp continuous to essentially power all of a car's needs if you could smooth demand for power from the peaks over the length of the trip. It stuck with me as a surprisingly small number, but it mathed out, even including heating and AC. Cars are both larger and more aerodynamic nowadays; I wonder if the amount would still be the same?
Will car owners be allowed to run their (25 hp) range extenders unattended? It could be useful to allow it to top up battery while parked, and the car could detect its in an enclosed garage.
For many 'standard' driving patterns (relatively 'flat' urban commutes with approx balanced medium length up and down grades) there are lightweight optimal solutions for EV's that can minimise both battery pack size (and weight) and the need to draw on a small rotary engine for recharge.
The UK's drone engines come in light and small with models that range from 5 BHP to 120 BHP with 40 BHP being suitable for broad swathe of "typical" driving.
Here's his video on his 1960's one, which is worth watching and some neat animation footage from the period talking about the design: https://www.youtube.com/watch?v=b2A5ijU3Ivs
You can tell Jay genuinely loves cars and the history of the auto world. He's indulging his hobby interest in a way that will preserve these vehicles for future generations to see and learn about. As far as ways rich people can spend their money that's a pretty cool one in my book.
He said that they had to put really big brakes on it. I guess for some reason you can't just have a clutch. Personally if I was going for eco I'd want something more clever than "bigger brakes" but maybe building something like a Hybrid Synergy Drive is harder than building a turbine.
Also: While Leno seems to be very interested in restoration, he also is clearly very interested in staying alive. He's got a ton of old cars that have been modified to have very good, modern disc brakes.
The EcoJet is just one of many examples of his cars that have been improved in this way.
The reason jet engines have that sort of exhaust is because the primary purpose of the gas turbine there is to dump all the excess energy into the exhaust to make it go fast (so that the plane can be pushed ahead by the reaction force). They produce very little power, just enough to power the Auxiliary Power Unit (that manages the plane electronics, air-conditioning etc.).
If you want to use a gas turbine for producing power, you will set it up such that most of the energy goes into the work generated, rather than the exhaust, so it would be a cooler, slower exhaust, similar to an IC-engine.
Other people have already mentioned the distinction between turbojets (what you’re describing) and turbofan engines, but I think there’s another inaccuracy:
> They produce very little power, just enough to power the Auxiliary Power Unit (that manages the plane electronics, air-conditioning etc.).
The APU is a completely separate gas turbine that doesn’t rely on the main engines. As a consequence, the APU on an airplane will also have its own exhaust.
> If you want to use a gas turbine for producing power, you will set it up such that most of the energy goes into the work generated, rather than the exhaust, so it would be a cooler, slower exhaust, similar to an IC-engine.
Yes, obviously. At the same time, I was under the impression that turboprops and turboshafts on airplanes and helicopters still produced enough jet exhaust to represent a safety hazard, and in those applications you would also expect that most of the energy would go into the work generated rather than the exhaust. So is it just that this residential generator is even more efficient than the main engine of a heavy-lift helicopter? Is it because it’s a less powerful machine in the first place? I could continue to speculate about this but I don’t actually know.
It's because to extract all the energy from the exhaust, you need huuuuuge turbine blades to extract the last little bit of energy from very slow moving air.
So instead you extract most of the energy, and then use the last little bit as extra thrust in a plane/helicopter.
Depending on the plane and engine. Big jetliners have high-bypass turbines where they do intentionally produce a lot of torque, to spin a large compressor fan, but most of the fan air does not go through the combustion step, it's just used to react off of.
Gas turbines are economically effective when larger than about 300hp. This border with time slow lowered, but I don't know, when it will appear somewhere about 50Kw of most popular automobiles (Toyota Corolla, WV Golf, Ford Focus).
When scaling down, gas turbines become much more expensive than ICE. For example on small planes market, exist many dual-powered models (in range 200-300hp), and with gas turbine it typically priced twice of ICU-powered with very similar parameters. Range of 1000hp+ on planes are near totally gas turbines.
AFAIK I think there is some difficulty in getting turbines to scale down efficiently with a need of a recouperator to maintain a higher core temperature for better efficiency. The recouperator is additionally expensive on top of the already expensive turbine cost.
Having a rotary with a turbo should be able to work better at a lower scale for a pretty cheap production cost.
Want to comment explicitly, though I upvoted a similar comment ... a gas turbine in a consumer car will be a maintainability nightmare (where do you find the technicians that can do anything with it?), at least in the current automotive ecosystem.
