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Wrightspeed unveils new turbine range extender for medium- and heavy-duty electric powertrains; 30% more efficient than current microturbine generators

Wrightspeed Inc., a developer of range-extended electric vehicle powertrains for medium- and heavy-duty vehicles (earlier post), has unveiled the Fulcrum, a new proprietary turbine generator for use in its Route family of electric powertrains (Route for Class 3-6, Route HD for Class 7-8). The new 80 kW Fulcrum is a radial inflow, axial turbine, intercooled and recuperated. Fulcrum is a single shaft machine, the generator runs at turbine speed (~100,000 rpm). Weighing in at 250 lbs (113.4 kg), the Fulcrum is approximately 1/10th the weight of its piston generator counterparts and it is designed to have a 10,000-hour lifetime.

The Route extended range electric powertrains incorporate a range-extending genset designed to recharge the high-power battery pack (currently from A123 Systems) and Wrightspeed’s own geared traction drive (GTD) (earlier post). Wrightspeed, founded by Ian Wright, one of the original co-founders of Tesla Motors, has used a 65 kW Capstone microturbine in earlier Route powertrains. The 65 kW Capstone unit weighs 300 lbs (136.1 kg), for a power-to-weight ratio of 478 W/kg; by comparison, Wrightspeed’s new Fulcrum microturbine offers a power-to-weight ratio of 750 W/kg. With Fulcrum, on which the company has been working for about 3 years, Wrightspeed now owns 100% of the Intellectual Property of its powertrain products.

F-lowres
Rendering of the 80 kW Fulcrum microturbine generator. The recuperator and combustor are at left; the generator with integrated power electronics at right. The two tubes lead to and from the intercooler, which is not shown in this rendering. Click to enlarge.

A two-stage compression process and novel recuperation design make the Fulcrum 30% more efficient than existing turbine generators, while tripling usable power, Wrightspeed says. Its multi-fuel capabilities allow it to burn diesel, CNG, LNG, landfill gases, biodiesel, kerosene, propane, heating oil, and others. In addition, the Fulcrum will make for a smooth, comfortable ride for drivers and a quiet, clean experience for neighborhoods because of its ultra-low vibration.

While piston generators rely on catalytic converters to reduce their emissions by 10x to meet ever-increasing California Air Resources Board standards, the Fulcrum turbine generator is so much cleaner, that it meets emissions standards without adding to its weight and complexity.

Noise, said Wright, is mostly intake and is high frequency, much smaller than than from a jet engine; the recuperator also acts as a buffer. There is no vibration, he added. Spinning at 100,000 rpm, it has to be very precisely balanced, or it would come apart.

Route HD

Route HD
Top: Tandem drive truck with Route powertrain using Fulcrum turbine. The turbine unit is just behind the cab, sitting atop the high-power battery pack. The intercooler (yellow) is shown, but not connected to the turbine. Bottom: Close-up of turbine. Click to enlarge.

Microturbines operate on the Brayton Cycle. Atmospheric air is compressed and heated (usually by introducing and burning fuel); these hot gases then drive an expansion turbine that drives both the inlet compressor and a drive shaft. Other than the size difference, microturbines differ from larger gas turbines in that they typically have lower compression ratios and operate at lower combustion temperatures.

To increase efficiency, microturbines can recover a portion of the exhaust heat in a heat exchanger (recuperator) to increase the energy of the gases entering the expansion turbine—thereby boosting efficiency. “Without a recuperator,” said Wright, “efficiency is just horrible.

The use of microturbines in autos has been explored for a long time, with a number of manufacturers actively exploring the potential shortly after World War II: these included Rover in the UK; Fiat’s Turbina, introduced in 1954; a Chrysler Plymouth prototype turbine car also introduced in 1954; GM with its Firebird prototypes, also introduced in the early 1950s; and the limited production run Chrysler Turbine Cars, introduced from 1962-1964.

The Japanese began a 100 kW automotive ceramic gas turbine (CGT) project in 1990 and concluded it in 1997. The US Department of Energy (DOE) in the 2000s ran a cooperatively funded, multi-path technology development program called the advanced microturbine system (AMTS).

None lasted, although interest in the approach—now especially for hybrid vehicles—is still strong, with one of the most recent OEM examples being the Jaguar C-X75 gas micro-turbine extended range electric vehicle concept in 2010. Jaguar was using a turbine from Bladon Jets. (Earlier post.)

There have been a number of problems with automotive applications of turbines, Wright noted, among them fuel economy and efficiency, and cost.

While turbines have seen great success in aviation, a fundamental challenge with the use of a turbine as the main traction engine in an on-road vehicle is that turbines are not efficient at low-load points; they are only efficient at full power, noted Wright. In other words, fuel economy is a significant problem. However, he added, the advent of the range-extended EV architecture alters the operational requirements significantly; instead of coping with varying load, the turbine can operate at its most efficient point—similar to the high efficiency large-scale turbines used in power generation—to produce power for the battery pack, which in turn powers the electric motors.

The automotive industry is in the midst of a fundamental disruption, with electric vehicles merely symbolizing the beginning of the movement. The Fulcrum, together with our range-extended EV architecture, is perfectly suited for achieving maximum efficiency in extremely high-power stop-and-go applications, such as garbage trucks. For many of the same reasons that aviation changed from piston engines to turbines decades ago, we believe turbines will begin to replace piston engines in range-extended electric vehicle applications.

It doesn’t matter what the driver is doing, you operate the turbine only at its most efficient point. It’s only 250 lbs, incredibly clean and also multi-fuel. It has all those advantages.

—Ian Wright

Further, Fulcrum’s design with its intercooler, recuperator and pressure ratio enables a higher efficiency than usually seen in this class of turbine, Wright said.

A further disadvantage for turbines in automotive applications has been cost. Wrightspeed addressed that by deliberately designing Fulcrum for low cost manufacturing, leveraging turbocharger technology with great economies of scale at this point.

Wrightspeed emphasizes the use of high-power batteries rather than high-energy batteries in its powertrain.

One of the things that enables the story is that the batteries have become extremely reliable and long life, even when at high power. We use the smallest pack we can. In general, we save fuel in three separate ways: first is with a grid charge; second is regenerative braking—we run very high power regen, much, much higher than anyone and we pretty much avoid the use of friction brakes; and third is running the engine at the sweet spot.

—Ian Wright

None of those three approaches work very well in long-haul trucking in which the big rigs with optimized engines and gearing are cruising for long stretches at an optimal, constant speed. On the other hand, a big rig in an urban environment is just horrible at fuel efficiency, Wright said. As a result, the Route extended range electric powertrain is ideally suited for urban environments. FedEx, which is already running a couple of trucks using the Route powertrain, has ordered 25 more.

Resources

  • Shah, R.M.A.; McGordon, A.; Amor-Segan, M.; Jennings, P., (2013) “Micro gas turbine range extender - Validation techniques for automotive applications,” Hybrid and Electric Vehicles Conference 2013 (HEVC 2013), IET , vol., no., pp. 1,6, 6-7 doi: 10.1049/cp.2013.1913

  • Fanos Christodoulou, Panagiotis Giannakakis and Anestis I. Kalfas (2010) “Performance Benefits of a Portable Hybrid Micro-Gas Turbine Power System for Automotive Applications” J. Eng. Gas Turbines Power 133 (2), 022301 doi: 10.1115/1.4002041

Comments

mahonj

Might be good for urban buses and bin trucks.
It would be pretty cool on a Tesla!

That way, you could drive all day with the AC on at 80mph.

Musk makes rockets - how hard would it be to add a microturbine to a Tesla (model ST).

DavidJ

Thought the comment about aviation was revealing. Power unit ffficiency might not match that of a diesel but the improved power to weight allows for lower mass and so better system efficiency in stop-go applications.

Nick Lyons

So it is 30% more efficient than something; just how efficient is it? I'm guessing a small diesel would have significantly higher thermal efficiency for this application, albeit with a significant weight penalty. The other question is cost: turbines are expensive in part because expensive materials are needed to cope with the constant high combustion temperatures. Hotter = more efficient, also more expensive. I wish them luck, and would be interested to see cost and efficiency info.

Engineer-Poet

The smallest Capstone unit ekes out 26%, the next larger (C60?) gets 30%.

gorr

Im deceive that it is less efficient at constant speed on the highway. When are we gonna replace ships, airplanes, trains, tractor-trailer trucks.

Till then im trying to save fuel by keeping my old small gasoline car that I drive slowly. Keep on rolling slowly.

jzj

I'd like to be corrected if I'm wrong, but give or take a few percentage points this is my understanding of various engine efficiencies:
1. conventional gasoline internal combustion: 20%
2. variable value timing gasoline internal combustion: 25%
3. direct-injection turbocharged gasoline internal combustion: 30%
4. microturbines: 30%
5. diesel: 35%
6. high-pressure injection turbocharged diesel: 40%
7. various split-cycle internal combustion engine designs: 45%
8. Stirling engine: 50%

As it relates to engines for electric vehicle extended range generators, the larger the battery pack then the less the engine is used, and the less important its efficiency and the more important that it is light, small, and cheap.

mahonj

@jzj
I agree with you, a range extender does not have to be that efficient, because it won't be used very much.
On the other hand, it should be small and light and require little maintenance as it is mostly just dead weight that you have to carry around with you.
Note that a chemical engine includes the exhaust and emissions control equipment which can also weigh a lot. Thus, you have to look at the total extra mass and volume.
Thus a generator which requires very little exhaust aftertreatment has a further benefit.

Alex_C

What about oil change interval for turbines - do they need any lubricant change and how often?
What type of lubricant do they use - is it just for bearings?

Engineer-Poet

The Capstone units use air bearings.  Seems hard to wear them out in operation, though the number of start-stop cycles would appear to be an issue.

Thomas Pedersen

One major downside with a turbo diesel is the component count - of which many are expensive: engine block, turbo, intercooler, oil cooler, water cooler, fuel pump, injection nozzles, etc.

A GT has no cooling, aside from a small oil cooler. Unless the turbine rides on air bearings, which this one does not appear to do, given that it leverages standard turbo charger technology.

What is the function of an intercooler, if there is only one compression stage?..

cujet

I'm missing something obvious here. Why have an intercooler and a recuperator? Is the idea to simply cool off the compressed air, then use waste exhaust heat to re-heat it prior to combustion? I don't follow the logic.

gryf

The addition of the intercooler is interesting. Has WrightSpeed considered adding an Organic Rankine Cycle Waste Heat Recovery (WHR) System? One could add a system similar to the Cummins Super Truck which has a mechanical coupling of the WHR to the engine that would eliminate the addition of another generator. Though this would still add 600 lbs additional weight, efficiency would be improved.

Engineer-Poet
What is the function of an intercooler, if there is only one compression stage?

There are 2 compression stages.  The intercooler reduces the back-work from the second stage, and reduces the compressor outlet temperature so that more energy is recovered in the recuperator.

Has WrightSpeed considered adding an Organic Rankine Cycle Waste Heat Recovery (WHR) System?

It's probably not a good fit for the light/cheap goals of the exercise, and additional heat recovery would probably be done better by adding another stage of compression and intercooling so that the recuperator has an even lower inlet temperature to work with and can recover more exhaust heat.

You raise a point, though.  I've wondered this about the intercooled GE LM100 gas turbine.  The intercooler options include air-to-water and air-to-air... but the public GE documents don't have anything on BTU output, outlet temperature or anything else that would indicate suitability for heat recovery.

Roger Pham

IMHO, a 4-cylinder piston engine running Atkinson cycle capable of 38-40% thermal efficiency at constant output would be unbeatable in this application. This type of efficiency is available in a wider output range means that the engine can be directly clutched to the drive train at cruise to realize even higher efficiency due to elimination of electrical resistive losses in the motor and generator.

The Prius' 1.8-liter engine capable of 98 hp or 73 kW would not weigh a lot more than the 250-lb weight of this turbine engine, and would return higher efficiency at lower cost.
If more power is required, the 2.4-liter Atkinson-cycle engine from the Camry hybrid would be suitable, or apply a turbocharge on the 1.8-liter engine to run it on Miller cycle for higher power.

Piston gasoline engine running Atkinson-cycle are low in cost, light in weight, low in emission, and durable due to the higher expansion hence lower operating temperature. The real-life durability and reliability of the Prius' engine has been amply proven.

gryf

Thanks E-P you are correct, a combined cycle is not a good fit for this system. What about a ceramic turbine hot section and a ceramic recuperator? Found research at ARPA-E using microturbines, as well as info on Brayton Energy (their ICR-350), Paccar, and a recent patent by ICR Turbine Engine Corp (US8669670). Ceramic turbines are definitely feasible (cost?). Also work by HRL Labs in architected 3D materials would be a good candidate for future ceramic recuperators. Efficiencies of these microturbines could approach 50% and the WrightSpeed approach may even be feasible for Class 8 trucks.

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