Walmart showcases WAVE tractor-trailer at MATS; micro-turbine range extended electric vehicle with 45.5 kWh Li-ion pack
28 March 2014
Walmart showcased its Walmart Advanced Vehicle Experience (WAVE) at the Mid-America Trucking Show (MATS) in Louisville, Ky. WAVE is a tractor-trailer combination that features leading edge aerodynamics; an advanced turbine-powered range extending series hybrid powertrain; electrified auxiliary components; and control systems.
The project aims to demonstrate a wide range of advanced technologies and designs Walmart is considering in an effort to improve the overall fuel efficiency of its fleet and lower the company’s carbon footprint. Although the prototype currently runs on diesel, its turbine is fuel-neutral and can run on compressed or liquid natural gas, biofuels or other fuels.
|Walmart Advanced Vehicle Experience. Click to enlarge.|
The prototype is the result of collaboration between Walmart and many vendors, including Peterbilt, Roush Engineering, Great Dane Trailers and Capstone Turbine.
Tractor. Walmart and Peterbilt have collaborated on aerodynamic, hybrid, electrification and alternative fuel projects in the past, each with incremental gains in fuel efficiency and emission reductions. The Walmart Advanced Vehicle Experience tractor combines many of these projects in a single vehicle.
Powertrain. WAVE is a Range Extending Series Hybrid that features a microturbine Range Extender generator developed by Capstone Turbine Corporation. The micro-turbine is fuel neutral and produces very low emissions without the need for aftertreatment. Turbines are also appealing because of their few moving parts, low maintenance requirements and lighter weight.
Range extending hybrids are a synergy between electric trucks and series hybrids, and their design reduces the energy storage size required for trucks to run on batteries alone.
With Walmart Distribution Centers now located closer to metropolitan areas, transport vehicles have shorter transit times to their delivery destinations. These shorter trips reduce the vehicles’ average trip speed and create more opportunities to recover energy through regenerative braking. The generator and energy storage on the truck are scalable based on the range desired.
Capstone also engineered the truck’s integrated hybrid drivetrain solution. The use of a hybrid powertrain allows the turbine to remain at optimum operating rpm, while the electric motor/energy storage handles acceleration and deceleration. A longer-range version of this powertrain would feature a larger turbine and smaller energy storage system.
Vancouver (Canada)-based Corvus Energy is the Energy Storage System supplier for the truck. In each truck, there are 7 lithium polymer battery modules (96V) to provide 650 VDC for a total of 45.5 kWh. The system includes both the traction, braking, and control elements. The energy storage system is also used to supplement the generator and buffer the power for the accessory systems.
The batteries are sized to provide power for the truck’s systems when the vehicle is waiting for a few hours to drop off a load. Batteries also power the vehicle in a pure electric mode (w/o generator) for limited miles of stop and go driving, such as what might be found in a busy shipping terminal or traffic jam.
Component Electrification. With automobiles moving to electrified accessories such as power steering and air conditioning, this truck scales those systems up for use on a larger vehicle. These electrified components are used only when needed and at peak efficiency.
Aerodynamics. Designers used extensive computational fluid dynamics (CFD) analysis to optimize the truck’s styling. The truck’s shape represents a 20% reduction in aerodynamic drag over Walmart’s current Peterbilt Model 386. By placing the cab over the engine, the truck’s wheelbase is greatly shortened, resulting in reduced weight and better maneuverability.
Further, with the air-cooled microturbine, there is no need for a large radiator in front of the vehicle.
Walmart relied on product development supplier Roush Engineering to carry out the vehicle’s construction.
Trailer. The vehicle’s trailer, manufactured by Great Dane Trailers, offers a host of fuel-saving features. The trailer body is built almost exclusively with carbon fiber, including one-piece carbon fiber panels for the roof and sidewalls, saving nearly 4,000 pounds (1,814 kg) when compared to traditional designs. The trailer’s convex nose also enhances aerodynamics while maintaining storage space inside the trailer.
Other special features of the trailer include special low-amperage LED lighting strips, composite trailer skirts, aerodynamic disc wheel coverings, a Posi-lift suspension, and a one-piece, fiberglass-reinforced floor panel with a 16,000 lb (7,257 kg) forklift rating.
A number of vendor partners were involved in the design and creation of the Walmart Advanced Vehicle Experience. Key partners—in addition to Peterbilt Motors Company, Roush Engineering, Capstone Turbine Corporation and Great Dane Trailers—include Qualnetics Corporation; Allison Transmission; Transpower; New Eagle; Fiber-Tech Industries; Grote Industries, Inc.; Laydon Composites Ltd.; Isringhauser Seats; Graykon, LLC; Dometic Corp; RealWheels Corp; Corvus Energy; Parker Hannifin; Accuride; Milliken Chemical; SAF-HOLLAND USA Inc.; and Whiting.
In 2005, Walmart, one of the nation’s largest private fleet operators, announced its goal to double fleet efficiency by 2015. As of last year, the company had achieved an 84% improvement in fleet efficiency over its 2005 baseline.
Walmart is continually looking for innovative ways to increase our efficiencies and reduce our fleet’s emissions. The Walmart Advanced Vehicle Experience is a bold step in transportation technologies that, although not on the road in its current form, will serve as a learning platform for the future that will accelerate our progress toward our goals.—Tracy Rosser, senior vice president of transportation at Walmart
A hand to Walmart to get involved in the development and operation of advanced more efficient trucks.
The same approach would give improved results with large inter-city and city buses (with larger batteries)
Posted by: HarveyD | 28 March 2014 at 08:55 AM
...and "we" are saying that Walmart is bad. I am not sure that Capstone is a very good choice due to efficiency of range extender but the power density is very high (higher than diesels). If one needs to hide the whole power train - this is the way to go. Again, the efficiency of Capstone is...
Posted by: CarCrazy | 28 March 2014 at 09:20 AM
45.5 kWh! how far can a class 8 truck travel on that?
Posted by: dursun | 28 March 2014 at 09:59 AM
Walmart should be commended for it's efforts to reduce truck fleet fuel consumption. The Capstone C65 (65kw) turbine has an efficiency of 25-28% (ref: Essentials of Natural Gas Microturbines, Valentin A. Boicea). Use of a recuperator and effective use of the electric power train will improve this significantly. The Capstone turbine is a widely used and reliable micro turbine, so that was reason for this choice.
GE has recently patented (US 20120251899) a unique combined cycle of a SOFC and gas turbine that has over 70% efficiency. This is accomplished by reforming natural gas - H2 for the fuel cell and using the rest of the reformate gas for the gas turbine.
One could imagine using a smaller Capstone C30 turbine and a Redox Power Systems 25kw SOFC that would achieve 70% efficiency and it would still weigh less than a diesel.
Posted by: Account Deleted | 28 March 2014 at 11:05 AM
dursan, it's a series hybrid, not EV.
Walmart has reach the saturation point typical of all big box stores, like K-mart. Their only way to continue to grow is through technological advancement, and moving production to cheaper copuntries. Although, it's hard to believe they could find anything cheaper than china. So, really, they need to change the technology of operations. It would be nice too if they could get the toxic fume smell out of their stores. It's one thing to sell toxic waste because some people think it makes them smell better, it's another to expose all your customers to a high dose of toxic brain rotting fumes as they seek less toxic products.
Posted by: Brotherkenny4 | 28 March 2014 at 11:10 AM
Over 50% of the energy used in USA (and in many other countries) is wasted, doubling harmful emissions.
Ground, air and sea transports are responsible for a big piece of the pie. Partial and/or full electrification has the potential to cut energy consumption by 50% to 75% and emission by as much as 80% with current technologies and even more in the not too distant future.
Of course, electricity will have to be produced without burning fossil or bio-fuels.
Posted by: HarveyD | 28 March 2014 at 11:42 AM
The other use for the batteries and capstone is to provide power for heating & cooling when the driver is resting.
Posted by: citizen | 28 March 2014 at 12:18 PM
Perhaps this is done for publicity stunt and free advertising for Walmart...but technically, this project falls short! It is very tough to beat existing state-of-the-art efficiency of aerodynamic-optimized turbo-diesel semi-truck-trailer at 10 mpg. Think about it: a full-size pickup truck weighing less than 1/10th of an 80,000-lb semi can achieve perhaps 15-18 mpg on the freeway!
The Capstone turbine can obtain 28-30% thermal efficiency at best, and from which, the electric drive train is only 80% efficient at best. 30% x 80% = 24%...while modern turbo-charged, turbo-compounded HDV diesel can deliver 48% thermal efficiency. During Hwy cruise, a turbo-diesel semi operates at or very nearly at its peak thermal efficiency.
For city operation of a turbo-diesel tractor, only a modest level of electrification will be needed. Perhaps a 100 kW electric motor/regenerator can be coupled to the transmission to recuperate kinetic energy during stop-and-go city trips. A 5-10 kWh battery operating at 10-20C can serve as energy storage, also to provide comfort to the cab during extended stops without having to idle the engine extendedly and thereby wasting diesel fuel and polluting the environment.
Consider the 300-400kW power level that a semi is equipped with, adding only a 100 kW of electric motor/regenerator and a 5-10 kWh battery, while perhaps downsizing the engine by 100 kW, will result in very little additional cost, all of which will be recovered in a few years from fuel cost savings.
Posted by: Roger Pham | 28 March 2014 at 03:08 PM
Roger, like you I cannot believe a series hydrid Gas Turbine/Electric could beat the SFC of a modern diesel AT CRUISE. If that were true why haven't we seen GE shift from Diesels to gas turbines in their locomotives?
Posted by: Herman | 29 March 2014 at 01:17 AM
Good point, Herman. Check out http://www.aqmd.gov/tao/ConferencesWorkshops/ZeroEmissionFreightForum/20_SSamuelsen_print.pdf.
GE is a funding partner.
Posted by: Account Deleted | 29 March 2014 at 07:59 AM
I'm with CarCrazy and Herman. Something like the HyperBar boosted low-compression diesel would have a substantial efficiency advantage over a Capstone. Heck, you might be able to use a Capstone C30 as its turbocharger. The batteries would eliminate the need to operate at low load very much (if at all).
Posted by: Engineer-Poet | 29 March 2014 at 09:28 AM
Thanks, gryf, for the tip. Back in a past life when I was working with UTC, I remember sitting in a conference room when several of us sketched a similar idea, although it was focused on a NatGas fuel. I don't think anything like it was ever done -- if so nothing came of it (UTC sold their fuel cell business last year).
I am not fuel-cell literate beyond the basic physics. Riddle me this, if you would: do you think a reformer capable of sufficient H2 flow to run a locomotive would package in the volume shown in the referenced presentation? This isn't a rhetorical question. I am clueless. It just seems that there is so much complexity to the typical Diesel blend (from sulfur to numerous C-H-O molecules) this would be a tough putt. I could see NatGas -- while I don't know of one, I could imagine the possibility of a membrane that would pass the CH4, which is a MUCH easier molecule for the fuel cell complex to manage.
Anyhow, thanks again and if you have some good links on modern reformer architectures I'd be much obliged -- search engine results are wearing me out.
Posted by: Herman | 29 March 2014 at 09:03 PM
I see a lot of focus on just the microturbine vs the diesel engine. It just may be the overall machine makes it more efficient. I noticed it was air bearings, so there is no motor oil needed for lubrication. This would be a cost savings in maintenance. No intake for a radiator was needed resulting in 10% efficiency gain in fuel mileage. The diesel engine needs a radiator intake which lowers the efficiency of the truck going down the road. Another seems to be lower emissions, although I see no specs on this yet. As I look at a capstone website, they are looking at 25 million hours of reliability. That would be a big cost savings to Walmart there. The turbine seems to be quite simple. Is it possible to use waste heat and turn it into useable energy for refrigeration, further propulsion.
Posted by: Jeffgreen54 | 29 March 2014 at 10:19 PM
Looking at the whole truck design as a complete system is the correct way.
You have to understand that the narcissists and ego maniacs on this site always have to be right and every one else wrong. If they are proven wrong they change the rules and claim that they were misunderstood.
Posted by: SJC | 30 March 2014 at 07:00 PM
The radiator of a semitractor takes up only a small portion of the total frontal drag. As such, it can easily be blended into the frontal area without incurring any drag penalty. The portion of air that flows thru the radiator is very small in comparison to the total amount of air that is deflected and passed on by, so, the radiator contributes very little to the overall aerodynamic drag of a semi truck, on order of less than 1% in my estimation.
Let's wait and see the mpg figure of this new hybrid design, if they will ever release the mpg figure at all. Our prediction is that the efficiency of this new Walmart contraption will fall far short of the 10-mpg that the state-of-the-art Diesel + aerodynamic-optimized semitruck is capable of!
Fuel cell + reformer + gas turbine + electric drive train seems way too complicated for the 60% efficiency quoted on the referenced link. Advanced turboDiesel with turbocompounding is hitting close to 50% efficiency already.
Future trucks will just simple use carbon-free H2 in tanks + FC stack at ~60% efficiency and be done with.
Posted by: Roger Pham | 31 March 2014 at 03:05 AM
The rule of thumb for aerodynamics on cars is of an even split (1/3, 1/3, 1/3) between cooling, underbody and visible surfaces.
In other words, cooling systems contribute more-or-less 33% of drag on cars. I'm sure that the numbers are different for tractor trailers, but I would be surprised if the difference was as big as your estimate.
Posted by: Bernard | 31 March 2014 at 06:09 AM
Of course, if the gas turbine is paired with something like an organic Rankine cycle engine bottoming cycle to generate useful power from the waste heat, you've got to have a condenser and the cooling drag problem is right back in your face.
Posted by: Engineer-Poet | 31 March 2014 at 06:39 AM
Some of the commenters seem to have missed the key point that Walmart's "transport vehicles have shorter transit times".
This means more stop-and-go, and less time spent at freeway speeds where conventional diesels reach their peak efficiency. A turbine generator that only operates at its (lower) peak efficiency will be better than an idling big diesel.
Posted by: Bernard | 31 March 2014 at 06:58 AM
There are many examples of fuel cell reformer research on the web. Most involve SOFC and Natural Gas, e.g. Bloom, Tokyo Gas, Redox Power Systems, Ceramic Fuel Cell Systems - BlueGen, and UTC. If the fuel cell is a PEM or HT-PEM they could use alcohol based fuels, possibly using a reformer similar to the Monsanto exhaust driven reformer (http://www.greencarcongress.com/2013/08/20130820-sall.html).
NOTE: Diesel efficiency gains have usually involved adding waste heat utilization (check Directions in Engine-Efficiency and Emissions Research (DEER) proceedings) or other fuels - Reitz, Bengt Johansson (Lund U.), this adds more complexity, e.g. Turbocompounding or a Rankine bottoming cycle.
Delphi has spent years researching an SOFC APU for Class 8 trucks using diesel fuel reformers (http://www.hydrogen.energy.gov/pdfs/review13/h2ra002_hennessy_2013_o.pdf).
and http://www.netl.doe.gov/publications/proceedings/01/seca-workshop/pdf/mukerjee.pdf) and could be added to the Walmart truck.
Even if H2 is the fuel (we hope produced using solar energy or renewable fuel), the best approach is to reduce the size of the fuel cell like the GE bus (http://gofuelcellbus.com/uploads/GE_IFCBW_2011.pdf) or the Vision Motors Tyrano truck and use batteries for the predominant energy source, remember all FCEV are electric vehicles.
Finally, the GE patent also discusses using the fuel cell with an ICE (described here http://spectrum.ieee.org/energywise/energy/fossil-fuels/ge-to-muscle-into-fuel-cells-with-hybrid-system).
Posted by: Account Deleted | 31 March 2014 at 09:23 AM
One more reference. This one also with a fuel cell plus ICE. Check out Chris Edwards work at Stanford (here http://gcep.stanford.edu/events/symposium2013/docs/Poster2013_CarolRegalbuto.pdf and here http://gcep.stanford.edu/pdfs/Understanding_the_Path_to_High-EfficiencyChemical_Engines.pdf).
Posted by: Account Deleted | 31 March 2014 at 09:47 AM
Let's review: Advanced Diesel = diesel engine, e.g. Cummins ISX12 (3000 lbs) + SCR (think reformer) + turbocompound (think gas turbine w/o burner). Still needs a 1000 lb transmission and gets 50% efficiency. Or fuel cell + reformer (1000 lbs) + gas turbine (250 lbs) + battery (~1000 lbs) and nearly 70% efficiency.
Posted by: Account Deleted | 31 March 2014 at 10:21 AM
NB: if the bulk of the vehicle's time is spent at low speed, the ρv² term of air drag is much reduced and the thermal efficiency of the powerplant would weigh more heavily than a radiator or lack thereof.
Posted by: Engineer-Poet | 31 March 2014 at 04:04 PM
The 1/3 rule of thumb was formulated when air was allowed to flow into and out of the radiator regardless of cooling needs. A radiator is sized for much much higher cooling needs (120 kW of engine power) than for just the power used at hwy cruise, or just barely about 15kW of power. New cars with controllable louvers to drastically reduce air flow into the radiator are realizing significant reduction in aerodynamic drag. In a semitruck, the trailer is formidable in size and contributes the bulk of aerodynamic drag.
The SCR and the turbocompounder are tiny and are included in the wt. of the engine.
On the FC + reformer + Gas turbine + battery, you forgot to mention the electric motor and motor controller. The latter items probably won't weigh any more than the transmission, however, they are much more costly. For trucking use, cost is more important than weight. However, for aircraft use, weight is more important than cost.
Posted by: Roger Pham | 31 March 2014 at 04:20 PM
Another good reformer reference uses JP8.
Precision Combustion does a lot of DoD work.
Posted by: Account Deleted | 31 March 2014 at 09:22 PM
Cooling needs are proportional to overall drag. That's because the engine is creating the torque to overcome that drag. Think about it: the trailer creates tremendous drag. The engine generates enough power to overcome that drag. The engine is less than 50% efficient, so over half of the fuel's energy is dissipated as heat, using radiators. Radiators are air-cooled, which creates drag.
The 1/3 rule applies at speed (no one cares about drag at idle!). Variable radiator louvers lower drag somewhat, but not by >97%, as you assumed. The efficiency gain is in the single digit range.
Then again, if you really have worked-out a system that limits cooling drag to under 1%, you should patent it and let the planet benefit. You will make millions, and the world will save billions.
Posted by: Bernard | 01 April 2014 at 06:10 AM