Turbine series hybrid car

[thestankinator]

A few months ago the thought came to me that it'd be neat to have a turbine powered car. It was kinda out of the blue, but I have always liked unique/odd stuff like that. The vision in my head has changed quite a bit over time in order to make it more feasible for my budget/skills, but as of now it's this: get a cool jet age car in so-so condition (I've more-or-less settled on a 1961-1963 Ford Thunderbird as being the ideal starting point), remove the factory drivetrain, put in an electric motor and as small a battery as you can find with enough voltage, and use a small gas turbine as a range extender.

The electric drivetrain components are another story for another time (and as a number of people have attempted similar electric power conversions, it doesn't look like it'd be that hard to figure out), but I don't know what to do about the turbine. Initially I was thinking I'd use an aircraft APU, but those are mostly beyond my budget and make more power than I'd need (somewhere around 25kW would probably be ideal to charge the battery just faster than the motor discharges it in normal highway driving). I've heard of people making jet engines out of automotive turbochargers before, and that certainly seems likely to be more budget friendly, but it requires a lot more design/fabrication work out of me, and I'm not even sure it's a feasible idea in the first place. If anyone could answer the following questions, it'd be extremely helpful:

• Is it even possible to get that amount (25kW-ish) of power out of such an engine? What about two? If it'd need more than two, it's probably not worth pursuing.
• If so, what kind of turbo would give me the most bang for my buck?
  
• How would I go about attaching a generator to it? I imagine I'd need to make sure whatever I do is extremely well-balanced given the speed the engine would be turning.
  
• Is it possible to muffle the exhaust at all? I know these engines are typically extremely loud, and while I wasn't expecting the car to be quiet, I don't want to be unable to drive it even in the middle of nowhere.
• What sort of fuel consumption should I expect?
  
• Are there any other considerations you would make?
• Is this just a terrible idea unlikely to end any way other than me being hurt or killed?
  

Thank you!

[thestankinator]

I've seen the DIY Turbines thread before, but I assumed all the links were broken when the pictures didn't load. I looked through it again just now and it looks like some of the answers I'm looking for might be in there. Still, if you can help with the above questions, I'd much appreciate it!

[racket]

25Kw isn't a lot of power , so easily produced

Fuel burn rates are terrible :-(

No worries about exhaust noise

[thestankinator]

I did a little more research and it looks like typical power use for a Tesla Model 3 on the highway is somewhere around 20kW, so with a less aerodynamically refined car and possible energy use for a cabin/battery heater I might want more like 30 or 35kW. I'm having a hard time following all the math that goes into these turbines - could you suggest what size range I should be looking at for the gas producer and power turbine?

Thanks!

[racket]

LOL ................theres a lot of variables that you need to consider and then make a decision on which way to proceed .

Firstly you need to find what generator to use , what RPM etc etc , this will influence the gearbox and freepower options/variables , then we might think about the gas producer which is the easy part .

[thestankinator]

Heh, good point. I got so excited by the turbine part of the project I totally forgot about the generator part. Come to think of it, it might be easier to make it a parallel hybrid and use the motor's regen to charge the batteries. The downside to that, of course, is that charging wouldn't be effective at low speeds. If I were to go that route, though, the rear axle would be turning about 900 RPM at highway speed, so I'd definitely need a lot of gear reduction. I'll have to think about this a little more before I'm ready to talk about turbine design....

[racket]

A 30-35 Kw turbine wheel won't generally be very large , so RPM would be high , probably in the >40,000 range if you want to run it efficiently , this will need either a high speed generator with minimal gearing or a low speed one with lotsa gearing, gearing of turbines is "problematic"

LOL.............if your proposed project was easy , there'd be plenty of them already built

[enginewhisperer]

Here's one with a more "off the shelf" model turboprop engine driving the generator:

www.youtube.com/watch?v=tCxW9I-Ifdw


A parallel hybrid using the main motor to charge the batteries would work, but then you have the worst possible gearbox requirements for your turbine engine.
If you can use a high rpm generator you can get away with a much simpler gear reduction - but you'll have more complex electronics and control systems to sort out.

[thestankinator]

racket, why do you say "gearing of turbines is 'problematic'"? I hope I didn't give the impression I thought this would be easy (heck, my relatively normal racecar has taken over a year and it still doesn't have a rollcage); I think it will be quite a challenge, but not one that is insurmountable. That said, I'm very much in the "I don't know what I don't know" phase.

I've seen that RX-7 before, but those model turbines cost a lot more than I want to spend, and they're too shiny. I want to take this car to some 24 Hours of Lemons events (not races, but rallies and maybe a concours) so it needs to look a bit "thrown together as inexpensively as possible." Heck, now that I think of it, maybe "it only charges effectively on the highway" is just the right energy for such a project.

This brings up a new question, though: where do I even look for a generator? If I Google "30kw generator" I get lots of results for stuff meant to power buildings. I guess the obvious answer if I want to do a bunch of sketchy stuff myself (like the turbine engine that was the original subject of this thread) is probably to get another electric car motor and drive it with the turbine. That seems less than ideal, but I suppose it could give me the option if I want to be extra ambitious to add a clutch so I can hook it up to the drivetrain for extra power when the battery is topped off.

[enginewhisperer]

yeah the RX7 is just an example of the same thing being done.
A turbo based engine can be done to replace the model turboprop. It'll just be much larger and heavier (but can also require a lot less maintenance!)

Any electric motor is also a generator (or alternator). Something that runs at high rpm like a large RC brushless inrunner motor is a possible option, especially if you do it without a reduction gearbox.
Rectifying the 3 phase AC output with a simple diode bridge is not super efficient, so you need to oversize the generator or run active rectification (a motor controller), which is expensive.


For racing you may be better off using the turbine to drive the wheels with the electric motor as a power boost - but with a small battery you'll probably only get a lap or so out of it.
It's very hard to get useful regen braking energy on the race track (braking times are too short and the system can't handle the high currents needed for decent braking performance)

[racket]

LOL..................that turbine engine being used in the RX7 is kinda small , it looks like this one tomahawk-aviation.com/eu/motorsengines/turbines/turbineturboprop-engines-1740-spt15-rx-2-shaft-turboprop-engine-set-helicopter-software-version-optional.html 14 Kw with both exhaust pipes open , with one closed and greater backpressure , probably a bit less , certainly not 60 HP , and they've "magnified" the exhaust noise :-(

[enginewhisperer]

yeah the 60hp is probably the main drive motor's output.

[thestankinator]

Well, initially my idea was, in fact, to build a turbine powered race car, but anything that makes enough power to not be dangerously slow would be out of budget and use too much fuel. I still wanted a car that goes "whoosh" instead of "vroom" though, so eventually that idea morphed into what I described above. When driving on the road, since peak power is only needed for short bursts and most of the time actual power use will be below 30ish hp, the electric drivetrain can handle acceleration and the turbine only has to make just more power than the average used to keep the battery topped off. Sure, it'd still burn a lot of fuel, but it wouldn't cost $1800 per weekend just in fuel!

RC motors are an interesting idea for a generator, but surely they couldn't handle nearly that much power? It seems to me the best bet would be another electric car motor with a 4:1 or so reduction gear. Nissan LEAF motors can be had for fairly cheap and can handle at least 10,000rpm.

[racket]

I think we need to sort out your budget before going any further, ..................just how small is it ??

[thestankinator]

"Budget" is a generous word. I'm at Army training at the moment so I've got lots of time to daydream about stuff like this and not much time for anything else. It started to intrigue me enough that I started looking up the constituent components I'd have to figure out and realized it might be something I could actually do. In addition to limited actual money, I'm trying to do it as cheap as possible in part to show how it can be done and in part because that's the sort of thing 24 Hours of Lemons goes for, and I think I could win a prize or two if I could actually make the car work.

I just had a look at my cost estimate spreadsheet and realized I'd forgotten how expensive the electric drive bits are going to be; I was hoping to get everything done for $10k or so, but $20k looks like a much more realistic figure unless I somehow get a lot of stuff donated, and coming up with that much money will be tough, so this might have to wait a few years. Maybe I'll try my hand at a turbine powered go kart like yours before I try to tackle anything this big. That would certainly be a lower-stakes way to test my turbine constructing ability, and I figured something like that as a test bed would be a first step in this project anyway. In that case, I could maybe justify throwing $1000-2000 at it.