Volt should use a turbine..?

[SabrToothSqrl]

So, now that the Volt (and BTW I hate GM), has decoupled a physical driveline from the engine, I got to thinking, is a "normal" car engine, that's been designed to output rotational energy across a varying RPM, the best way to convert gasoline to electricity? Obviously that's a bit oversimplified, but wouldn't a turbine actually be the best, most efficient way to get electrons from oil? It has WAY fewer moving parts, etc. etc.

and yes, I'm aware of the Chrysler car, but many of those issues were most likely related to its mechanical drive system.

If if this has been talked about before, sorry, it just came to me the other day. It goes against my belief that these cars are a waste of engineering time that could be used to further battery cars, but why not? Lol

ideas?

 

[jerry33]

I believe noise and maintenance would be a problem.

 

[Saghost]

Actually the second generation volt engine is always connected to the wheels.

Having said that, I do believe a micro turbine would make a great range extender in an i3 type car.

Something like the Capstone 30kW would be a great choice - no fluids except the fuel, no timing, one moving part (a single single that connects the motor-generator, compressor, and turbine, spinning on air bearings.)

It'll run about equally well on any liquid hydrocarbon (or with minor changes to the fuel system and injection, any gaseous hydrocarbon) and is small, light, and reliable.

The noise issue shouldn't be hard to address - with a single operating rpm, it'll always be one frequency, which means well designed echo chambers can damp it out quite efficiently.

The one challenge is cost - I think Capstone sells them for $20-30k each, though I'm not sure why they are so expensive since the mechanical parts are much the same as your average small turbocharger and the electronics not much different from typical modern EV drive systems. It might be an economy of scale thing.

 

[GSP]

Gas turbine engines can be much smaller and lighter than piston engines. They also can run much longer between overhauls. No reciprocating parts make them extremely smooth, and they made sexy high rpm noises.

However, they cost a lot more than piston engines, and their efficiency is significantly worse, even at their best efficiency torque and speed point. This results in a significant mpg hit compared to a Volt or Prius with piston engines.

Big turbine engines can match piston engines for efficiency, using exotic materials such as single crystal turbine blades, precision machining for very tight clearances, and many stages for both compressor and turbine sections. The result is a 25 MW machine that costs millions and is way to big for a car.

GSP

 

[Saghost]

However, they cost a lot more than piston engines, and their efficiency is significantly worse, even at their best efficiency torque and speed point. This results in a significant mpg hit compared to a Volt or Prius with piston engines.

Capstone uses regenerators to preheat combustion air with exhaust heat, and they claim ~29% efficiency from fuel to electricity - which considering the (1st generation) Volt's ~33% peak thermal efficiency and ~88% peak motor-inverter efficiency is right in line with a Volt running in Series.

Of course, in highway cruising the Volt is able to avoid the double conversion from mechanical to electric and back for much of the energy used, which means it'd still have an edge. Also, the Atkinson engine of the newer Priuses can reach ~37% thermal efficiency. (I haven't seen real numbers on the 2016 Volt or the 2016 Prius yet, but both are likely a little better.)

From an engineering standpoint, I'd argue that the advantages of a microturbine more than outweigh the drawbacks for a series hybrid and possibly for any range extender implementation - provided it can be made cost competitive, of course.

Marginally lower fuel efficiency can be traded off against the lack of maintenance and smaller, lighter device (which makes the car more efficient under all operating conditions, including the 90% of miles that are driven without using fuel.)

 

[RDoc]

But wouldn't a 30kW turbine cost north of $10K?

 

[Saghost]

But wouldn't a 30kW turbine cost north of $10K?

That's the part I don't understand. You're right, that's what you'd pay for one right now.

However, aside from the air bearings and a shaft to the drive motor, the turbine is identical to a typical $500 car turbocharger. Combustion chamber and injector design is critical, but the construction and materials aren't terribly exotic. The motor-generator has to operate at very high speeds, but I don't think it's terribly different from other modern AC synchronous motors for EVs or RC aircraft.

The only parts I haven't mentioned yet are the regenerator, which is just a high temperature heat exchanger from the post turbine exhaust (700F?) to the post compressor intake air (300F?) - which again shouldn't require anything terribly exotic in terms of design or construction, the ignitor (typical spark plug), and the control computer/programming (and associated sensors.)

So as an engineer, I don't understand why building a microturbine should cost so much given the pieces that make it up (and assuming it is using a solid disk single stage centrifugal compressor and turbine - which the Capstones do.)

 

[Bangor Bob]

Wrightspeed is using turbines for their PHEV garbage trucks. They say they aren't as fuel-efficient as a diesel, but the maintenance is lower, they're inherently flex-fuel, and exhaust after-treatment is simple and inexpensive compared to diesel engines.

The worst aspects of the 1G Volt have to do with vibration & noise from the ICE, and the "delay/lurch" when it changes modes when running on the ICE and lots of torque is demanded (eliminated in the 2nd-gen). A turbine would eliminate both - along with some ICE-specific maintenance like oil changes.

On the costs - it has to be purely production scaling/experience curve issues. ICE's are hugely more complex and take a lot more equipment and tooling to build than a 30kW turbine, but a 30kW ICE can be sold for < $2000 if you're not too fussy about the weight/noise/emissions.

 

[S'toon]

I know there was a rumour a couple of years ago that the range extender would be a rotary engine. The reasoning being it's small and fuel efficient. Turbines are not fuel efficient. The M1A1 tank uses a turbine engine and uses WAY more fuel than other tanks.

 

[SabrToothSqrl]

What do diesel electric trains use?

what if we used like 10 model aircraft turbines driving 10 small generators?

 

[Bangor Bob]

I know there was a rumour a couple of years ago that the range extender would be a rotary engine. The reasoning being it's small and fuel efficient. Turbines are not fuel efficient. The M1A1 tank uses a turbine engine and uses WAY more fuel than other tanks.

It is run in load-following mode rather than at peak efficiency, that puts a serious hurt on fuel consumption.

Actually, with the price of batteries today and going forward, it's essentially a moot point. GM should make the 3rd-gen Volt a BEV - it would cost them less than making it a PHEV.

 

[Jeff N]

Also, the Atkinson engine of the newer Priuses can reach ~37% thermal efficiency. (I haven't seen real numbers on the 2016 Volt or the 2016 Prius yet, but both are likely a little better.)

Toyota claims 38.5% peak efficiency in their previous Prius engine and now 40% in the new one. Hyundai claims 40% in the new engine in the Ioniq model coming out this fall. Honda has claimed at least 39% I think for their latest Accord hybrid engine. I'm not aware that GM has made a claim for the 2016 Volt engine or the different 2016 Malibu hybrid engine. Since the new Malibu hybrid engine gets about the same EPA 47 mpg as the Accord hybrid in a similar class of vehicle it most likely can also do 39%-ish efficiency.

In a car like the Volt where you are using the engine for only a small percentage of miles, the maintenance levels between an ICE and turbine become fairly equivalent. I've got 124,000 miles on my Volt and, following GM's recommended maintenance schedule, I've only had 2 oil changes in 5 years. And I drive way more on gasoline than most Volt owners due to my long commute and some road trips. I've only managed to keep gas miles down to 37% of my total driving while most Volt drivers on the road today manage 25-30% overall. The new Volt, with 50% longer battery range than my 2011 Volt, will result in even fewer gasoline miles.

 

[S'toon]

Actually, with the price of batteries today and going forward, it's essentially a moot point. GM should make the 3rd-gen Volt a BEV - it would cost them less than making it a PHEV.

I disagree. There is a place for the Volt, places where there's no charging infrastructure. I live in the big EV black hole. The nearest Supercharger is over 500km/300miles away. The nearest CCS/Chademo charging station is even further. If I were to buy a car right now, it would be a Volt. I'm hoping that by 2018 Tesla will have made some move to build Superchargers, but I'm not holding my breath. Tesla has shown no interest whatsoever in expanding their network in Canada. They think we're a bunch of buck-toothed hicks or something.

 

[McRat]

...

However, aside from the air bearings and a shaft to the drive motor, the turbine is identical to a typical $500 car turbocharger. ...

Turbine efficiency is related to the pressure ratio map of the compressor segment. A modern jet engine is about 22:1? But only through a certain operational range. When it falls below the 22:1 it gets thirsty really quick.

Steady state power production at the "meaty" part of the map is efficient, but outside that region it falls very, very quick.

Automotive turbochargers are terrible at more than 4:1 pressure ratio. You'd have to run compound turbocharging to even get jet fuel to ignite. It doesn't burn for crap at 4:1. Too slow to be useful. Yeah, you could use crappy fuel like gasoline or ethanol and it would run at low pressure ratios, but it would not run efficiency at high pressure ratio where the good shiit is.

BTW - This issue with the pressure ratio mapping is being addressed by 2 speed high bypass jet engines. Wider operating range for less fuel consumption.

 

[wws]

In the case of a car like the i3 ReX, there is a pretty clear separation of the range extender engine and the electric drive train. However in the case of the Volt, they are much more tightly integrated. When the Gen 1 Volt runs in charge sustaining mode (i.e., gas engine running), there are both serial and parallel "power split" hybrid modes. The latter when cruising on highways at speed to get more efficiency. The Gen 2 Volt has three CS modes - low extended, fixed ratio, and high extended, none of which are true serial hybrid. So using a turbine would not really match the general direction GM is taking the Voltec.

http://gm-volt.com/2015/02/20/gen-2-volt-transmission-operating-modes-explained

My thoughts are that a Diesel engine might be interesting - provided noise and weight could be handled. Given that many Volt owners go for months at a time without using gas, Diesel fuels lower volatility might be an advantage too.

 

[AndreN]

I know there was a rumour a couple of years ago that the range extender would be a rotary engine. The reasoning being it's small and fuel efficient.

Rotary (Wankel) engines may be small and have great power-to-weight ratios, but they are most definitely not fuel efficient. I had a 1988 RX-7 with a 1.3 liter, 146hp engine, and it got 18mpg. The Renesis engine in the RX-8 was better but still not great (still 1.3l, 212hp, 16mpg city, 19mpg highway for the 2011 model). A Honda S2000 with 237hp got 18/25 mpg for example.

 

[Saghost]

Turbine efficiency is related to the pressure ratio map of the compressor segment. A modern jet engine is about 22:1? But only through a certain operational range. When it falls below the 22:1 it gets thirsty really quick.

Steady state power production at the "meaty" part of the map is efficient, but outside that region it falls very, very quick.

Agreed. Turbine efficiency off peak is pretty poor, idle is horrible (often close to 50% of peak fuel flow,) and they take 15 seconds or more to start. Which is why I'd think a range extender is a natural fit, where the engine can easily be operated at the peak point for nearly all operation, incurring only the slight losses of sending some power on a battery round trip at lower speeds.

Automotive turbochargers are terrible at more than 4:1 pressure ratio. You'd have to run compound turbocharging to even get jet fuel to ignite. It doesn't burn for crap at 4:1. Too slow to be useful. Yeah, you could use crappy fuel like gasoline or ethanol and it would run at low pressure ratios, but it would not run efficiency at high pressure ratio where the good shiit is.

BTW - This issue with the pressure ratio mapping is being addressed by 2 speed high bypass jet engines. Wider operating range for less fuel consumption.

Okay, I'm missing something here. The boiler that warms my house has no problem getting complete combustion of home heating oil (basically diesel fuel, largely similar to Jet A) at atmospheric pressure, let alone the higher pressures you describe. And we've certainly seen enough cases of diesel cars and trucks burning, though it is harder to ignite than gasoline. I wouldn't expect the turbine to depend on spontaneous combustion of the fuel - all the jets I know much about have ignitors (glorified spark plugs) to initiate (and sometimes sustain) combustion.

I'll grant that lower compression ratios put theoretical limits on the efficiency of a heat cycle machine, but Capstone is using single stage centrifugal compressors and turbines, and is demonstrating quite competitive efficiency levels with "regeneration" (heat exchange between post turbine exhaust and pre combustion air,) if not quite up to the best in the ICE business this year.

 

[eloder]

I disagree. There is a place for the Volt, places where there's no charging infrastructure. I live in the big EV black hole. The nearest Supercharger is over 500km/300miles away. The nearest CCS/Chademo charging station is even further. If I were to buy a car right now, it would be a Volt. I'm hoping that by 2018 Tesla will have made some move to build Superchargers, but I'm not holding my breath. Tesla has shown no interest whatsoever in expanding their network in Canada. They think we're a bunch of buck-toothed hicks or something.

Pretty soon though, you'll just be paying a huge premium for not buying a BEV that meets all your daily needs, and renting a car the few times a year you need to go further. The extra cost of the Volt's generator requires many, many renting days a year before it becomes better off.

I personally have a Leaf as my sole commuter vehicle. I don't take it on trips even if I had the charging infrastructure between big cities. Even now it works out for me because I would have had to shell out a few thousand more for a Volt--two weeks of car rentals a year won't come close to that lifetime price gap even ignoring the extra maintenance having an ICE requires.

 

[Requiem]

Using a turbine to generate electricity is exactly what Tesla co-founder Ian Wright thought of too, so he created Wrightspeed

 

[Gerardf]

Just rn into this :

Chinese company tests turbine-driven electric super car - Roadshow