Gas-turbine-series-hybrid vehicle?

I had an idea recently about an electric car that would use a gas turbine powerplant to charge the batteries and power the motor. This turbine powerplant wouldn't be connected to the car's mechanical drivetrain, it would only be used to charge the batteries or provide power to the electric motor, enabling the turbine to be optimized to run a generator at a very small range of RPMs, allowing the turbine to be designed to be as efficient as possible. A gas turbine could theoretically run off a number of different fuels, including gasoline, diesel, ethanol, natural gas, hydrogen, propane, cooking oil, and for the fuel type that it's designed for, it could run much more efficiently as a powerplant than an equivalent IC engine. If the electric drivetrain is fairly efficient, a car could conceivably be much more efficient this way. In fact, this concept isn't too far off from the Chevy Volt concept, except instead of an IC engine like they propose, it'd be a gas turbine powerplant. Such a vehicle would run on batteries for about 40 miles (a bit over an average American's commute to work), and could be recharged from the wall, meaning that in a typical workweek, no fuel needs to be burnt! For longer trips, the driver could forgo long periods of battery charging by letting the generator kick in and operate the car. Fueling would be done just like any ordinary car at a fuel station.

Such a vehicle could have the massive torque an electric motor can afford, and as long as the motor is efficient at higher speeds, it can sip gas at a sustained highway speed. The electric drivetrain would be much easier to maintain than an ordinary car, as many critical components such as the transmission and the engine itself are replaced by much simpler electrical systems. The turbine engine would require very little maintenance as it may only have a few moving parts, maybe even only one major part if it's a one-stage engine with the turbine directly driving the compressor which is also hooked to the generator. If a centrifugal engine designed is used rather than an aircraft-typical axial engine configuration, little thrust will be placed on the bearings, minimizing their stress and allowing them to last longer than aircraft turbine bearings, and much, much longer than the bearings in an IC engine (correct me if I'm wrong on that, but I think the smooth operation of a turbine engine is easier on the bearings than the multi-stroke operation happening in an IC engine). The turbine components would likely be cheaper in a centrifugal configuration as these engines do not usually require the vanes to be airfoils, flat surfaces are the norm.

Here's the wiki for a centrifugal turbine, a.k.a. a radial turbine.
http://en.wikipedia.org/wiki/Radial_turbine

Another advantage of the vehicle from a standpoint of technological evolution is that the turbine powerplant is hooked up to the car only by fuel lines, electrical connections, and some computer plugins, there is no major mechanical interface. This allows the turbine powerplant to be interchanged with, say, a hydrogen fuel cell and hydrogen tank, another set of batteries, more cargo space, whatever. It could be an option the car manufacturer offers at sale.

Of course, after a mere few minutes of searching online, I found out that my idea, as I expected, wasn't that creative, many have thought of it, which leads me to question why this type of system hasn't received some real attention by major automakers... I've collected some neat links...

The somewhat publicized EV-1 had a prototype variant that used a gas turbine APU placed in the trunk. I hear the wiki article as a whole has a few factual errors, so don't take it totally blindly, but look at the "EV1 series hybrid" part...

http://en.wikipedia.org/wiki/General_Motors_EV1


Here's what appears to be a sleek-n-sexy (albeit probably expensive in practice due to it's demand for composite parts) sports car concept that uses the turbine-series-hybrid concept to get 200 MPG while still being able to do 0-to-60-MPH in 3 seconds and a top speed of 200 MPH. A gorgeous look to it too...

http://www.sema.org/main/semaorghome.aspx?ID=57239


A similar build being done on a Hummer to get about 60 MPG while still having 600 HP at hand.

http://www.autobloggreen.com/2007/10/20/biodiesel-turbine-super-capacitor-series-hybrid-hummer-60/


It makes me wonder where I can buy a 60 kW turbine APU and a good electric car, lol. I thought it'd be cool to hear people's thoughts on this. How would you like to have a car that could daintily sip on a number of diverse fuels, can scream out of intersections and onto freeways at breakneck accelerations, would likely last a long time, be straightforward to maintain, would be easy to modify with future technology, and probably wouldn't cost too much more than a current hybrid vehicle of the same size? It almost sounds too good to be true, which is why I'm wondering what the silver bullet is... I'd image the turbine's expense is where it's at, but I think an economically designed APU designed for a single RPM setting might be economically competitive.

What do yall think?

 

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You wouldn't need a 60kW APU, you'd only need about 20kW. With EEstor supercaps, based on barium titanate as dielectric, being developed that have around twice the energy density and much higher power density than lithium batteries you can get all your acceleration you'd ever need from those. 20kW is more than enough to maintain highway speed in a aerodynamic vehicle.

 

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Ever since i saw a gas turbine engine on a Canadian navy frigate i have often wondered how hard it would be to shrink it to fit inside a car
could you imagine an F1 car with a gas turbine engine?

 

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There's a guy doing this already, he creates custom hybrid hummers for enviroguilty movie stars. I think he was in Wired or Discover.

 

I looked up that EEstor supercapacitor thing today, it seems like there's a bit of controversy around those, but if they do what they say, then yeah, that'd be killer! You probably wouldn't need to replace them as often as batteries, and they probably wouldn't generate as much heat as a battery during high discharge or charge. I wonder how they hold up in extreme temperatures though, maybe better than batteries but these seem like a far cry from normal capacitors.

I'm actually trying to find my thermodynamics and compressible flow textbooks to see if it's theoretically possible to make a cheap and very efficient gas turbine system. I'm still in college, and don't take aerospace propulsion till this coming semester, so I might just wait till then to figure out the nitty-gritty of this kind of system.

The big problem with turbine engines is that upon shrinking them, it gets harder and harder to make them thermodynamically efficient because heat moves quicker through thinner and smaller components than it does larger components. Also, a gas turbine engine in a full-scale municipal power plant and maybe on that Canadian frigate use a separate steam powerplant to try to use some of the waste heat. For a car, this wouldn't be very feasible, but an intercooler and a second stage just might make this work...

These are my brainstorms, feel free to chime in and correct me or whatever. I'm kinda looking for someone to jump up and shoot this concept down, because so far it just seems, i dunno, obvious.

 

That last one about the wave rotor got my attention, it sounds like just a heat exchanger, I'm not sure why it helps, guess I'll have to look into it...

 

I don't know what anyone would want the turbine for. Just take an off the shelf diesel or gasoline engine that develops enough power. It's a hell of a lot cheaper.

 

In my mind, if a large car company had retooled to mass produce turbine engines for use in APUs, the cost per unit would be less than a same power ICE (internal combustion engine), since it's fewer components involved. The only reason an ICE still maintains foothold is cause of mechanical drivetrains. In a Electrical drivetrain the turbine would be operating at constant RPM and thus be more efficient than an ICE.

Mark my words; we are going to see a big move from ICE to turbines as soon as series hybrids catches on. The Chevy Volt will be the spark that will kick-start the change.

 

You could always gear it down.

 

It has potential. I've heard very tiny gas turbines are being explored for use as a power source for cell phones and computers.

 

The neat thing is that this doesn't need the technological jump of a micro-scale engine, the engine only needs to be small enough to fit in part of a car's hood, not a laptop battery compartment, at least in this application (although that would be kinda neat if they make that happen). The technology seems to already exist to let this work without high-end materials and frequent maintenance.

You sure could use IC engines in the same application, it'd be cheaper initially for sure, but a turbine has the promise of being much more efficient than an IC engine while potentially being cheaper in the long-run in terms of maintenance and future production costs.

Maybe. I dunno, this is speculation, I'm not really ready to do the math yet.

 

Would it need to be? In a gas turbine engine, the compressor and compressor turbine reach those blistering RPMs, but the power turbine, spinning on its own shaft, does not. The PTO speed of all modern turboshaft engines is independent of engine speed itself.

 

I had the idea that the power turbine WAS the main turbine, like the compressor, turbine, and generator were on the same shaft. You suggesting having an extra stage in the turbine for the generator, while the other turbine stage is only hooked to the compressor? I'm not sure how this is done in real life, but this does sound more feasible. Echo, is this how it's normally done?

 

The cycle efficiency of a recuperated minitrubine (20-40kw) tops out ~35% better then gasoline but less then diesel. Even so in theory a turbine engine could run on diesel, kerosene, ethanol, gasoline or any blend of which as well as natural gas, propane and hydrogen.

 

Yeah, very few turboshaft engines have their power turbine on a common shaft with the rest of the engine. Actually I think the only application that uses a common shaft for the PTO is some turboprops.

Case in point: the General Electric LM2500. You can find one or more of these in the engine rooms of surface combatants in navies all around the world. All it is is a CF6 turbofan with a power turbine stage bolted onto the back of it. The CF6 core functions as a gas generator, with the bypass air from the fan merged into the turbine exhaust. During operation, the engine's exhaust is forced through a power turbine on a different shaft, which windmills in the exhaust and gives you 33,000 shaft horsepower @ 3600 RPM.

I don't know what the compressor and turbine speeds are of a CF6 at full throttle, but they're definitely spinning a hell of a lot faster than 3600 RPM.