Today when we talk about percentage of improvement, we're used to hearing single digit numbers, usually on the lower side of 5. Often, it's fractions of a percent we're chasing. When Cummins and Peterbilt unveiled their SuperTruck project, they boasted almost unheard of gains of 68% in freight efficiency over a 24-hour duty-cycle, a 50% improvement in freight efficiency on an 11-hour drive-cycle and a 20% improvement in the thermal efficiency of the engine.

Those terms may sound somewhat nebulous, but they are meaningful. Freight efficiency (or ton-miles per gallon) is a measure of how much freight can be moved over a given distance by a given amount of fuel. It's a more descriptive measurement than miles-per-gallon because it accounts for the amount of work being done with the fuel consumed.

In lay terms, Cummins and Peterbilt succeeded in moving more freight (by lightening the truck and trailer) over a given distance on less fuel (by reducing the amount of fuel consumed by the truck and trailer) in an 11-hour driving cycle (a typical day's driving in a highway application).

The companies also saw sizable gains in a 24-hour duty cycle, which is more representative of a sleeper operation with hotel loads on the system as well as in-cab climate control. Like before, they accomplished all this using less fuel than a current truck would use in a similar situation.

The gains in thermal efficiency speak to the engine's ability to convert the chemical energy contained in a gallon of fuel to motive power at the driveshaft.

David Koeberlein, Cummins' Principal Investigator on the SuperTruck project, says they managed to improve the thermal efficiency of the engine from today's typical 42% to 50%.

"The difference between 42 and 50 percent may seem small, but it's a 20% gain," he says. "And it's all the more remarkable when you consider historic gains in thermal efficiency have been measured in single-digit steps."

Showcase for ideas

The Peterbilt-Cummins SuperTruck is pretty neat looking, but its beauty is more than skin deep. There's a lot of brand new technology here, and some hardware that has never been installed on a truck before. The idea behind the SuperTruck project was not to build a truck that fleets would be lining up to buy. Rather, it's a showcase for some unique prototype components and systems that have now been validated and will soon appear on the showroom floor.

In the previous article in the magazine, we covered some of the aerodynamic and lightweighting features of the SuperTruck (you can view a photo gallery highlighting some of those advances here). Now, let's dig into how Cummins and Peterbilt managed to make this truck so much more efficient.

But before we go much further, it should be noted that cost wasn't really a design constraint for this exercise. Some of what is on-board the SuperTruck is still in the science-project realm. Ken Damon, SuperTruck Project Manager at Peterbilt, stresses that many but not all of the new components on the truck can be commercialized fairly easily. Others, not so easily.

"In lightweighting the truck, we used some rather exotic components, such as magnesium crossmembers and the aluminum-matrix brake drums," he says. "They certainly have commercial potential, but they probably wouldn't be readily accepted by industry. Our next challenge is in making those things commercially viable."

The same goes for Cummins' Waste Heat Recovery system.    

Waste Heat Recovery

Peterbilt's chief engineer, Landon Sproull told us the engine contributed about 20% while the aerodynamics and light-weighting contributed about 30% of the overall 50% improvement is freight efficiency in the straight driving cycle. An actual mile-per-gallon number was never mentioned, but the WHR system accounted for nearly half of the overall gain.

Schematic illustration of the Gen 3 version of Cimmins' Wast Heat Recovery system,

Schematic illustration of the Gen 3 version of Cimmins' Wast Heat Recovery system,

WHR systems are fairly common now in stationary diesel engines, but Cummins says this is the first time such a system has been successfully installed in a heavy truck. As you'll see in the photos, it's still in the prototype stage -- note the hose clamps and the engineering test leads all over the engine.

Briefly, WHR uses an organic Rankine Cycle to transform thermal energy into mechanical energy (in this case). Using a series of heat exchangers, evaporators, turbines and recuperators, a fluid with a fairly low boiling point is heated by various sources of heat from the engine. As it boils and vaporizes into a gas it spins a turbine that is eventually linked mechanically to the engine where it delivers a certain amount of energy to the powertrain. The potential gains from such installations are compelling.

Here are short videos to illustrate roughly how a waste heat recovery system (organic Rankine cycle) works. One is a stationary application, the other is from Cummins.

"In our case, we put the power generated by the turbine back into the front accessory drive belt of the engine," says Koeberlein. "It is a mechanical link between the turbine and the engine. Our turbine is spinning at 35,000 RPM. We have a gear train pulling that down 10:1. Then our belt drive is pulling that down 3:1. So overall, we have about a 30:1 ratio between engine speed and turbine speed. And those are approximate numbers."

Cummins ISX15 with WHR. from the left side.

Cummins ISX15 with WHR. from the left side.

Koeberlein says the energy could be used to drive engine accessories but Cummins found the most efficient use of the recovered energy is to drive the wheels.

"We had experimented with converting the energy to electricity to drive other components, but found the mechanical system to be much more efficient," he says. "As it stands now, we are not driving any accessory components with this system. All the energy is going to the wheels."

Cummins ISX15 with waste heat recovery from the front-right side

Cummins ISX15 with waste heat recovery from the front-right side

Despite the apparent complexity of the system and the additional weight of the boilers, heat exchangers, recuperators, turbines, etc., the system is still a net gain for the truck.

Koeberlein says the total weight of the WHR system, today, is about 600 pounds. But it's important to remember that even with the WHR system, the rest of the weight-reduction efforts on the SuperTruck resulted in a vehicle that is 1,300 pounds lighter than a traditionally equipped baseline, 2013 truck.

Among the other benefits of the system are reduced EGR temperatures and reduced load on the cooling system. That results in very little if any fan-on time, even when the engine is pulling a hill at low speed where ram air is minimal. On a recent test drive of the SuperTruck, the only fan-on time we experienced was when idling with the air conditioner running. The fan never came on while we were driving.

The cooling module consists of three units, the WHR condenser cooler, the charge-air cooler and the engine radiator, in that order.

"The radiator core is actually smaller than one we use in a production truck because there's less heat for it to reject," Damon says. "It sits much lower between the frame rails, and there's a large opening in the front bumper to improve the ram air flow through the condenser. The design was actually very carefully calibrated in order to be able to cool it with ram air and not let the fan come on at highway operation."

There were other modifications made to the engine to improve efficiency, though less dramatic. They include increasing the compression ratio, refining the shape of the piston bowl, a lower-pressure EGR loop, reduced cylinder friction and more. And like some of the other components on the truck, some of this work will find its way into production engines in the near future, some will not.

"Many of the modifications we've made here come with some associated cost and therefore we'll have to do a cost benefit analysis," Koeberlein notes. "I do know that some of these technologies will make it into our next generation products. We’ll have to see what actually shakes out from our due diligence on cost and what we can eke out of what we initiated here on SuperTruck."

Hotel Loads, HVAC & More

As we noted, part of this exercise was to demonstrate improvements in an over-the-road type of duty cycle (the 24-hour cycle), complete hotel loads, overnight air conditioning, etc.

U.S. Express helped Peterbilt develop a realistic load profile for the system based on the needs identified by its own drivers, including the need to power a CPAP machine for a full night.

"One of the things that we learned in developing this was the high usage of CPAP machines in the truck industry," Damon says. "Some company safety boardshave very strict requirements that guys have to carry a CPAP machine on board, so we needed to accommodate that load as well. This system allows you run air conditioning very generously for a full 10 hours as well as using a microwave a couple times, running gaming systems, movies, charging accessories like phones and heating water. I call it a very trucker-friendly system."

Trailer side skirts retract with the flick of an air switch. Future models could be deployed automatically based on wheel speed.

Trailer side skirts retract with the flick of an air switch. Future models could be deployed automatically based on wheel speed.

The SuperTruck used an electric climate control system powered by four 3300-watt-hour lithium-ion batteries for a total of 13.2 KW-hour, which is significantly higher than current systems that are supporting just HVAC. That proved more than adequate for a full night's use, but they found they needed about six full hours at highway speed the following day to fully recharge the batteries.

To validate the battery system, the SuperTruck and the baseline truck were tested side-by-side with exactly the same load profile.

"Our 24-hour duty-cycle test was pretty much a two-day operation in the way we tested," Damon says. "The first day we would apply the hotel loads to our baseline truck, and then to the SuperTruck which was running its battery-based APU. The same exact load profile for 10 hours and then we shut it down. The next day we would start the drive-cycle portion of the test. So both trucks would start with their batteries depleted. The minute we left our test lab the truck was recharging."

Engineers made no modifications to the actual cab or sleeper to improve its ability to maintain an internal temperature.

"On the first version of the SuperTruck, not this one, we tried some UV resistant glass for the windshield as well as all the side glass, and we also put in some advanced insulation," says Damon. "When we did the CFD analysis on the insulation, we found that because parts of the cab structure interfered with where the insulation could go, the insulation wasn't as effective as you might have presumed.

"In other words, there is a lot of leakage where you have structure supporting a roof or back wall or something. Even with all that insulation in place, the bang-to-hype ratio wasn’t there," notes Damon. "All that would have come with a weight and a cost penalty for sure. So, on our second truck we did not take those measures."

All That, and Technology Too

We've talked a lot about the physical attributes of the truck, the nuts and bolts than make the improvement. In addition to the massive amount of technology and engineering involved in the WHR system, engineers also developed a sophisticated "cycle efficiency management" system for the truck. It's cruise control on steroids.

The cruise system on the truck is quite advanced," Koeberlein tells us. "It seeks to maintain the road speed by looking forward and calculating how much power it will take out of the engine to move up a grade. And we’re seeking best vehicle speed that keeps the engine at the most efficient operating point."

The Advanced Cruise Control display tells the driver what the system is doing. A similar display may not be used in production versions.

The Advanced Cruise Control display tells the driver what the system is doing. A similar display may not be used in production versions.

The system is loaded with GPS and terrain data so it knows the road profile. Like a driver, it "sees" a hill coming through the GPS, and it knows the grade, knows the weight and speed of the vehicle. It will negotiate the grade not trying to maintain a pre-set speed, but optimizing fuel consumption within a time parameter. It will give up some speed in order to get over the hill as efficiently as possible.

The way Damon describes it, the system is designed to take the truck over a specified route, sort of the way a pilot programs way points into a flight navigation system. The system then runs the trip from origin to destination and bases many of its decisions on predetermined trip time. It will give up speed (and time) where it makes fuel consumption sense, knowing it will make up the time at some later point coasting downhill when the extra speed is free. When the driver sets the cruise control (really the cycle efficiency management system) for 62 mph, the truck accepts that as a trip time benchmark, not a road speed benchmark.

We have tried to cover the major developments of this truck. There's more of course, but some are incremental improvements of existing equipment. It's useful to remember that this SuperTruck, and the others that will be revealed in the coming months, are demonstration projects; platforms to demonstrate technologies and innovations that will help fleets operate more efficiently in the future.

As we have explained, all of the additions to this truck have been validated. They work as intended, though they may not make it into a production vehicle for some time to come. The WHR system, for example, has demonstrated its effectiveness, contributing a little less than half of the overall efficiency gains chalked up by the truck. But as Cummins readily admits, it's still way too expensive to bring to market.

"The waste heat recovery system currently in its Gen 3 configuration is too costly," admits Koeberlein. A key objective with Gen 4 will be getting the cost structure within an 18- to 24-month payback for the customer."

The same applies to the magnesium crossmembers and aluminum matrix brake drums. They are presently more expensive than most customers would tolerate, but field trials suggest there's lots of potential there.

Aluminum matrix brake drums save 50 pounds per wheel, but they might be too expensive for some fleets.

Aluminum matrix brake drums save 50 pounds per wheel, but they might be too expensive for some fleets.

"We haven't extensively tested those brake drums yet," Damon reminds us. "This wasn't a brake testing truck, but the test we have done shows they are very good with stopping distance, and they don’t retain heat the way cast iron brakes do -- even with the fairings covering the wheels. We have run the truck at 80,000 pounds over a very brake-intensive route in Arkansas with thermocouples on the brakes and heat retention wasn't a problem. The brake drums performed very well and they are almost 50 pounds lighter per drum than cast iron. There's certainly value there, but the price point and customer acceptance haven't been determined."

Whatever else this truck might be, it's no longer science fiction. While it was not part of the official demonstration project, Cummins and Peterbilt did some real-world work with the truck. Real loads, real roads, real shippers.

"I want to really emphasize the collaboration we had with our shipper partner on this project and that we were consulting with them on a regular basis on technologies to make sure we weren’t off in the weeds somewhere," says Damon. "We had them actually carry commercial freight on our first truck -- our Demo-One truck -- a year ago. We loaded up their freight at their loading dock. We took it from Irving, Texas to Laredo; about a 900-mile round trip. And just to make sure the operations, the aerodynamics, the trailer-tail and everything else were functional in field operations."

That's really what SuperTruck is all about. It's a demonstration project, and it has successfully demonstrated some pretty advanced technology. Our guess is some of what we see on SuperTruck today will be on the showroom floor much sooner than you might expect.

Don't forget to check out the SuperTruck photo gallery to see the truck up close. We took those photographs on a recent test drive of the truck. We'll run that story in the August issue of Heavy Duty Trucking.