Seems like a good time to ask this question that has been bugging me forever, since all the HN jet nerds will be drawn to this thread:
Why hasn't anyone made a hybrid car that uses a gasoline-powered turbine generator to charge its batteries instead of a piston engine?
I'd imagine that hooking up such an engine directly to the drivetrain like in a Prius would be difficult, but surely a small turbine with one hell of a muffler running a generator (similar to a natural gas power plant), both running only at their peak efficiency RPMs, would yield a very efficient car that could still use the extant gasoline infrastructure.
I'm sure there are very interesting reasons, either due cost, noise, reliability, or durability, that this idea hasn't taken off, and I'm very interested to hear y'all's thoughts on the subject. Or maybe there has been progress in this area, and I'd love to see some links!
I've been wondering about this very same question a lot myself and accidentally stumbled across the answer just a few days ago:
Efficiency of turbines smaller than grid scale is simply not anywhere close to what piston engines can do at e.g. car size. Even at naval scale, turbines only win in use cases where power density is more important than fuel efficiency. Helicopters are deep in the (specific) camp of power density beats efficiency because carrying a heavier but more efficient engine would easily eat the fuel savings. Fixed wing aircraft gain range by climbing high, but up there both efficiency and power density of piston engines decreases dramatically with decreasing air density, so they are also in the camp of power density over efficiency (turbines are also affected, but not quite as much).
Note that despite all this, the Otto Aviation 500L that is all about fuel efficiency at high altitudes uses a piston engine (they probably put a lot of effort into their turbocharger, those can lessen the impact of thin air)
> Why hasn't anyone made a hybrid car that uses a gasoline-powered turbine generator to charge its batteries instead of a piston engine?
Because turbine engines have some pretty serious downsides. Compared to a piston engine, they guzzle fuel [1], they're pretty complex to repair (which is one of the problems Ukraine is facing), they spin at absurd RPMs which means that they need some serious housing to not turn into a shrapnel dispenser in case of an engine failure or accident, and they produce an awful lot of hot exhaust gas at high velocity that needs to be dissipated somewhere - down isn't OK because it will melt the asphalt, sideways is not OK because it will melt or injure anyone and anything next to the car, and upwards carries serious risks as well (e.g. if you're in a tunnel).
I worked for a company that did this in the 1990's. Small gas turbine, the size of two show boxes (200hp) powering a generator, which charged the batteries and/or electric motors.
The advantages are efficiency, low weight and no gearbox is needed, as the turbine spun at over 100,000 rpm and the generator was fine with that.
The main disadvantages were noise and turbines need more maintenance than piston engines. No LiIon batteries back then either.
One not mentioned was someone in Southern California who got an old aircraft APU (probably a Solar T-62[1] or similar) and made an electric hybrid back in the 1980s. The APU charged the battery, and shut down when the battery was full. Worked OK, apparently.
The trouble with turbine engines is that, below bizjet size, they don't seem to get any cheaper. Not for lack of trying in the 1990s. NASA, Williams International, and Eclipse tried hard. There were a few prototype planes, but no commercial success. There are today what are called "very light jets", but this means 4-6 people and and a price around $2 million.
General aviation is still mostly piston-powered. There are tiny jet engines for R/C planes, but they have very short operating lives.
Having an ICE that drives a generator (alternator?) to power a traction motor(s), without being mechanically linked to the drivetrain, is how diesel locomotives operate. I believe the concept also has been (is being?) explored for linehaul trucks. But I'm not sure what constraints there are on passenger vehicles though... I'm also curious.
If I had to guess, I would bet that the constraints are more commercial than physical... hybrids are already very efficient, so the market for such a vehicle would probably not justify the engineering costs. But that's just a guess!
Wrightspeed did this a while (10 years?) ago. It looks like they have since pivoted to fully electric powertrains for buses, but when they first started they were doing range-extending hybrid powertrains for heavy trucks. I found an article the describes the system at the time:
With a range-extender hybrid system, you can keep the turbine closer to its peak-efficiency operating point, since it only has to handle steady-state load while the battery takes up the spikes. Not sure how it would do up a long grade, but I imagine they designed for that.
i think even the tiny, model jet engines used in radio control planes are both very hot, and move lots of air. both of which are hard to tame to the point of making them comfortable to coexist with on a city street in large herds.
I still want one. direct the exhaust forward, dump in a little extra fuel, and instant snowblower / flamethrower. Makes that pesky crosswalk crowd just melt away.
I think someone is making this, or maybe I misunderstood your question. The Ariel Hipercar uses a jet engine to power it’s 4 electric engines. I think it’s just used as a range extender, and last I saw they didn’t have it working yet. It’s been a while since I checked up on the car.
Arnold Schwarzenegger’s Hummer from the early 2000’s is setup like this — 100mpg with bio-diesel. I think this is the original article I read about his car’s creator, Johnathan Goodwin, from years ago.
You'd be better off with an engine specifically designed to be efficient. Turbines are great at many things, but they are complex and don't scale down very well. They were primarily used where high torque and power is required, and they just aren't practical outside of that.
A better option would be a constant speed ICE engine running at it's peak efficiency (like a diesel-electric train).
>Why hasn't anyone made a hybrid car that uses a gasoline-powered turbine generator to charge its batteries instead of a piston engine?
The current engine formula (2014-) in Formula 1 racing might be of interest to you.
> During acceleration of a Formula 1-car, the turbo charger is performing at its peak and is spinning at about 100,000 rpm. The MGU-H (Heat) functions at that moment as a generator. This is connected to the turbo charger and converts the energy, generated by the turbo, into electricity; that, in turn, is stored in a battery or sent directly to the MGU-K.
> This MGU-K (Kinetic), connected straight to the crankshaft of the turbo engine, acts as an electric motor that supplies extra power to said engine. This MGU changes into a dynamo, which stores the energy that is released during braking in the battery. This stored energy, can later be used to support the turbo engine during acceleration or overtaking.
As mentioned in a sibling comment, turbines don't scale down very well. Boundary layer friction gets relatively worse for smaller turbines, and AFAIU small turbines have relatively larger inefficiency due to air leaking past between the blades and the casing, etc.
There's a couple of companies working on recuperated turbine engines for small aircraft in the few hundred kW range, remains to be seen whether any of these will succeed.
I don’t have the source at hand, but a gas turbine is ridiculously inefficient for variable loads. At idle, fuel consumption can be ~35% of what it is at full power.
It would only need to charge for short time, and subsequently shut off. When a charge top-up is required, startup would be another rigamarole.
> You have to give the California Department of Motor Vehicles (the DMV) credit for creativity on this one. A DMV insider has disclosed to me that the DMV has made a formal request to a federal agency to rule if my Beetle constitutes a threat to national security based on what could happen if it got into the wrong hands. This raises three questions in my mind: #1 Does this mean I’m the right hands? #2 If someone with the name "b_laden13" is the highest eBay bidder for my Beetle can I refuse his offer even if he has the prestigious eBay Red Shooting Star feedback rating (the highest)? #3 Would this affect my eBay rating?
Wonder if they ever found a way to give the guy a ticket.
We live in a society where things are legal by default. Why would adding a jet engine to a car be a priori illegal? If he harms somebody or otherwise causes damage, that itself is what's illegal and he'd be liable regardless of motor vehicle regulations. If this mod became a larger trend, especially consumer-available, then regulations would be implemented to head it off. But for a few lone instances it's not particularly necessary.
Jet exhaust doesn't need to be high pressure. It depends. For example a turboprop engine doesn't provide any jet thrust and usually the exhaust is even pointed away from the direction of flight.
But it is very hot so exhausting it close to the ground or people is a serious problem.
The scooter seems like it could be a poor idea due to asymmetric thrust, and I have to wonder if he just mocked it up in jest. It does look pretty awesome though.
This is wild, but I would strongly disagree on the aesthetic of it. In my opinion, he picked pretty much the worst possible car for this. Managed to make a jet-powered vehicle look... lame, somehow.
Imagine an El Camino or even an AMC Eagle with this contraption in the bed, how much cooler that would look? But really, how could you not use a Delorean as the base for this project??
It would be legal to run it on the factory engine, at which point the jet is just cargo. If you start the jet on a public road, it could be considered a public nuisance, reckless driving, etc.
If a the vehicle presents a clear and present danger of any kind it is a-priory a ticketable offence at least. With the jet off, it poses no such danger.
"The car has two engines: the production gasoline engine in the front driving the front wheels and the jet engine in the back."
Careful wording to give the impression that the drive shaft of the helicopter turbine would be connected to the rear wheels, without actually claiming that it is. So it's a car with a large flame thrower in the back, minor The Boring Company vibes.
Well possible that the author might have had more fun writing than building/driving. (I do love the incredulous tone of "#1 Does this mean I’m the right hands?")
I would rather not follow a car like that on the road, hell, even driving by it.
The looks don't signal the intent. Guess what will it do next when either light starts blinking, or both? There is no known signal for kicking on the jet engine! From the back it looks like a gigantic cannon too, BeachBuggyRacing kind.
Just for kicks, I'd also put a "Student Driver" decal on the rear window :).
Awesome project, but are there any actual videos of it running the jet engine?
He says the jet engine moves 11,000 CFM of air, but that air can only come through the windows and the sunroof. Pulling 183 cubic feet of air per second through those little openings while sitting in the drivers seat isn't going to work. Just try to do the math on how fast that air would have to be moving through those windows.
> The Beetle was chosen because it looks cool with the jet and it shows it off well.
Subjective, but I would argue that the Beetle is a terrible choice and makes the jet engine look like a pole sticking out of a ball. A flat sports car would probably fit the look much better and mimic the aerodynamics of an aircraft.
nice... does anyone remember a K Car with a supercar engine? that was not quite as crazy as this one, no jet engine, but it was nice. i can't seem to find it but i remember reading about this "sleeper car".
[+] [-] hrichards|2 years ago|reply
Why hasn't anyone made a hybrid car that uses a gasoline-powered turbine generator to charge its batteries instead of a piston engine?
I'd imagine that hooking up such an engine directly to the drivetrain like in a Prius would be difficult, but surely a small turbine with one hell of a muffler running a generator (similar to a natural gas power plant), both running only at their peak efficiency RPMs, would yield a very efficient car that could still use the extant gasoline infrastructure.
I'm sure there are very interesting reasons, either due cost, noise, reliability, or durability, that this idea hasn't taken off, and I'm very interested to hear y'all's thoughts on the subject. Or maybe there has been progress in this area, and I'd love to see some links!
[+] [-] usrusr|2 years ago|reply
Note that despite all this, the Otto Aviation 500L that is all about fuel efficiency at high altitudes uses a piston engine (they probably put a lot of effort into their turbocharger, those can lessen the impact of thin air)
[+] [-] mschuster91|2 years ago|reply
Because turbine engines have some pretty serious downsides. Compared to a piston engine, they guzzle fuel [1], they're pretty complex to repair (which is one of the problems Ukraine is facing), they spin at absurd RPMs which means that they need some serious housing to not turn into a shrapnel dispenser in case of an engine failure or accident, and they produce an awful lot of hot exhaust gas at high velocity that needs to be dissipated somewhere - down isn't OK because it will melt the asphalt, sideways is not OK because it will melt or injure anyone and anything next to the car, and upwards carries serious risks as well (e.g. if you're in a tunnel).
[1] https://www.augsburger-allgemeine.de/politik/panzer-vergleic...
[+] [-] RachelF|2 years ago|reply
The advantages are efficiency, low weight and no gearbox is needed, as the turbine spun at over 100,000 rpm and the generator was fine with that.
The main disadvantages were noise and turbines need more maintenance than piston engines. No LiIon batteries back then either.
The project only built 1 finished prototype.
[+] [-] Animats|2 years ago|reply
One not mentioned was someone in Southern California who got an old aircraft APU (probably a Solar T-62[1] or similar) and made an electric hybrid back in the 1980s. The APU charged the battery, and shut down when the battery was full. Worked OK, apparently.
The trouble with turbine engines is that, below bizjet size, they don't seem to get any cheaper. Not for lack of trying in the 1990s. NASA, Williams International, and Eclipse tried hard. There were a few prototype planes, but no commercial success. There are today what are called "very light jets", but this means 4-6 people and and a price around $2 million.
General aviation is still mostly piston-powered. There are tiny jet engines for R/C planes, but they have very short operating lives.
[1] https://en.wikipedia.org/wiki/Solar_T62
[+] [-] clucas|2 years ago|reply
If I had to guess, I would bet that the constraints are more commercial than physical... hybrids are already very efficient, so the market for such a vehicle would probably not justify the engineering costs. But that's just a guess!
[+] [-] jgable|2 years ago|reply
[+] [-] h2odragon|2 years ago|reply
I still want one. direct the exhaust forward, dump in a little extra fuel, and instant snowblower / flamethrower. Makes that pesky crosswalk crowd just melt away.
[+] [-] salty_biscuits|2 years ago|reply
https://en.m.wikipedia.org/wiki/Jaguar_C-X75
Turbines get more efficient as they get bigger.
[+] [-] thebutcher|2 years ago|reply
EDIT: I just read this article from 2023 that says the turbine engine still isn’t working: https://www.evo.co.uk/ariel/206120/ariel-hipercar-prototype-...
[+] [-] TuesdayNights|2 years ago|reply
https://www.autoblog.com/amp/2007/10/20/biodiesel-turbine-su...
[+] [-] Lanrei|2 years ago|reply
A better option would be a constant speed ICE engine running at it's peak efficiency (like a diesel-electric train).
[+] [-] Hinrik|2 years ago|reply
The current engine formula (2014-) in Formula 1 racing might be of interest to you.
> During acceleration of a Formula 1-car, the turbo charger is performing at its peak and is spinning at about 100,000 rpm. The MGU-H (Heat) functions at that moment as a generator. This is connected to the turbo charger and converts the energy, generated by the turbo, into electricity; that, in turn, is stored in a battery or sent directly to the MGU-K.
> This MGU-K (Kinetic), connected straight to the crankshaft of the turbo engine, acts as an electric motor that supplies extra power to said engine. This MGU changes into a dynamo, which stores the energy that is released during braking in the battery. This stored energy, can later be used to support the turbo engine during acceleration or overtaking.
[+] [-] iancmceachern|2 years ago|reply
https://apps.dtic.mil/sti/citations/ADA515623
My guess the answer to your question would be cost.
[+] [-] jabl|2 years ago|reply
There's a couple of companies working on recuperated turbine engines for small aircraft in the few hundred kW range, remains to be seen whether any of these will succeed.
[+] [-] Scene_Cast2|2 years ago|reply
[+] [-] xattt|2 years ago|reply
It would only need to charge for short time, and subsequently shut off. When a charge top-up is required, startup would be another rigamarole.
Now, rotary engines, that’s a different story…
[+] [-] symmetricsaurus|2 years ago|reply
[+] [-] mixmastamyk|2 years ago|reply
[+] [-] historyTeach123|2 years ago|reply
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[+] [-] latchkey|2 years ago|reply
Jet Powered Volkswagen Beetle https://news.ycombinator.com/item?id=28349589 (August 29, 2021 — 2 points, 1 comments)
Ron Patrick's Street-Legal Jet Powered Volkswagen Beetle (2006) https://news.ycombinator.com/item?id=16513835 (March 4, 2018 — 156 points, 60 comments)
Street-Legal Jet Powered Volkswagen Beetle https://news.ycombinator.com/item?id=5384390 (March 15, 2013 — 6 points, 2 comments)
Street Legal Jet Powered Beetle (2006) https://news.ycombinator.com/item?id=831185 (September 18, 2009 — 76 points, 23 comments)
[+] [-] dang|2 years ago|reply
(I just added it to https://news.ycombinator.com/highlights)
[+] [-] overlyambitious|2 years ago|reply
[+] [-] generalizations|2 years ago|reply
Wonder if they ever found a way to give the guy a ticket.
[+] [-] smohnot|2 years ago|reply
https://www.autoevolution.com/news/get-yourself-the-iconic-j...
[+] [-] stergios|2 years ago|reply
[+] [-] omginternets|2 years ago|reply
[+] [-] mindslight|2 years ago|reply
[+] [-] dzdt|2 years ago|reply
[+] [-] wkat4242|2 years ago|reply
But it is very hot so exhausting it close to the ground or people is a serious problem.
[+] [-] nikanj|2 years ago|reply
[+] [-] xrd|2 years ago|reply
[+] [-] mindslight|2 years ago|reply
[+] [-] btbuildem|2 years ago|reply
Imagine an El Camino or even an AMC Eagle with this contraption in the bed, how much cooler that would look? But really, how could you not use a Delorean as the base for this project??
[+] [-] ynoxinul|2 years ago|reply
[+] [-] K0balt|2 years ago|reply
If a the vehicle presents a clear and present danger of any kind it is a-priory a ticketable offence at least. With the jet off, it poses no such danger.
[+] [-] ralfd|2 years ago|reply
https://news.ycombinator.com/item?id=16513835
[+] [-] JoblessWonder|2 years ago|reply
[+] [-] brk|2 years ago|reply
[+] [-] usrusr|2 years ago|reply
Careful wording to give the impression that the drive shaft of the helicopter turbine would be connected to the rear wheels, without actually claiming that it is. So it's a car with a large flame thrower in the back, minor The Boring Company vibes.
Well possible that the author might have had more fun writing than building/driving. (I do love the incredulous tone of "#1 Does this mean I’m the right hands?")
[+] [-] zoomablemind|2 years ago|reply
I would rather not follow a car like that on the road, hell, even driving by it.
The looks don't signal the intent. Guess what will it do next when either light starts blinking, or both? There is no known signal for kicking on the jet engine! From the back it looks like a gigantic cannon too, BeachBuggyRacing kind.
Just for kicks, I'd also put a "Student Driver" decal on the rear window :).
[+] [-] Aurornis|2 years ago|reply
He says the jet engine moves 11,000 CFM of air, but that air can only come through the windows and the sunroof. Pulling 183 cubic feet of air per second through those little openings while sitting in the drivers seat isn't going to work. Just try to do the math on how fast that air would have to be moving through those windows.
Cool show piece though.
[+] [-] grecy|2 years ago|reply
Surely when you strap a jet engine to a Beetle you need to find out how fast it goes!
[+] [-] ed_mercer|2 years ago|reply
Subjective, but I would argue that the Beetle is a terrible choice and makes the jet engine look like a pole sticking out of a ball. A flat sports car would probably fit the look much better and mimic the aerodynamics of an aircraft.
[+] [-] rmason|2 years ago|reply
[+] [-] Miserlou57|2 years ago|reply
[+] [-] avg_dev|2 years ago|reply
[+] [-] brucethemoose2|2 years ago|reply
https://www.youtube.com/watch?v=A52W20Z38Bw
https://www.youtube.com/watch?v=D6SZuionhqQ
A turbine is relatively exotic, if only because they are even more impractical.
[+] [-] unknown|2 years ago|reply
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[+] [-] unknown|2 years ago|reply
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