Fuel-Efficient Trucks Coming Down the Road
By Tom Gibson
Nigel Clark, the George B. Berry Chair of Engineering at West Virginia University (WVU) has a birds-eye view of heavy-duty truck technology and sees the advances made in tractor-trailers. As an expert and researcher in the field, he sits on the Committee to Assess Fuel Economy Technologies for Medium- and Heavy-Duty Vehicles. “If you look over the last ten years, you’ll see there’s been a steady progression of improvements,” he remarks.
WVU typifies the research going on with trucks, Clark reveals. As one of its signature facilities, the school has a mobile laboratory so big it takes two tractor-trailers to move it. They can measure the efficiency and emissions from a truck or bus as it is driven on the road to get real-world measurements of fuel consumption and CO2 production and then compare them with models.
“Engineering students at universities get involved in this research. Many of them go on to work for engine and truck manufacturers,” Clark adds. “We do a lot of engine work in conjunction with engine manufacturers,” working through WVU’s Center for Alternative Fuels, Engines, and Emissions.
This may sound encouraging, but we’re going to need facilities like this around the country to step up even more in coming years. The U.S. EPA and National Highway Traffic Safety Administration have jointly proposed regulations to cut greenhouse gas emissions from heavy-duty trucks, requiring that their fuel economy increase up to 40 percent by 2027 compared with 2010 levels. The rules, which cover almost any truck larger than a standard pickup, come as part of President Obama’s Climate Action Plan and will form an integral part of his environmental legacy.
A tractor-trailer now averages five to six miles a gallon on diesel fuel; the new regulations would set the bar at nine miles a gallon. The proposals could cut millions of tons of carbon dioxide pollution while saving millions of barrels of oil. This will require extensive investment and innovation, with engineering schools playing a key role in the research effort.
Tom Wallner, manager of the Fuels, Engine & Aftertreatment Research Department in the Center for Transportation Research at Argonne National Laboratory in Lemont, IL, says recent goals have been to improve the freight fuel efficiency of heavy-duty trucks by at least 50 percent in miles per gallon. A sub-goal was to improve the engine efficiency to a peak of 50 percent with a pathway to achieving 55 percent. “All three are very challenging goals.”
How will researchers reach such lofty goals for truck fuel efficiency? John Woodrooffe, a research scientist and mechanical engineer at the University of Michigan Transportation Research Institute, says, “I don’t think there’s a silver bullet. It’s going to be a systems approach. The four major elements are the engine and drive line, aerodynamics, rolling resistance of tires, and size and weight regulation.” Actually, the fourth component depends on whom you talk to. Clark says, “The fourth piece is sophisticated integration of control of all the components.” Either way, it involves a piecemeal cumulative approach, meaning adding many small gains from all different facets of the trucking realm.
Aymeric Rousseau, manager of the Systems Modeling & Control Group at Argonne National Laboratory, explains how the systems angle plays out. “We do a lot of work on the engine side on the modeling and simulation and testing. It’s important to take the entire system approach and maximize the efficiency of the entire power train.” This highlights one of the main challenges in researching heavy-duty trucks and a major reason for computer simulation: “There is an incredible number of combinations.” For each application, there are many technologies and ways you can combine them, leading to thousands or tens or even hundreds of thousands of combinations. “Using either full simulation or a mix of hardware and software, we can go through a wide range of iterations quickly and efficiently.”
As perhaps the lowest hanging fruit in the systems approach and a prime example of it, Clark says, “People have been looking at selecting gear ratios more carefully to match the engine and looking at the whole power train as an integrated unit.” Improved control of transmission shifting and careful gear selection can yield a few-percent increase in fuel efficiency.
Woodrooffe points out that this can work hand in hand with changes in the way trucks are manufactured. Traditionally, truck companies procure components from varied sources and assemble them according to customer orders. “There was not a lot of room for R&D there. Now, we’re getting more into vertical integration. This can be something as simple as matching the engine to the transmission.” Clark adds, “We have worked with truck and engine manufacturers, and they have become more integrated. There are more companies producing both trucks and engines.”
Over the past 30 years, great strides have been made to improve the efficiency of engines, and experts consider them mature. But areas to tweak remain. One is getting engine friction even lower, meaning better, lower-viscosity lubricants that result in lower energy loss. Another area involves downspeeding of engines, making them more capable when running at only partial load, at lower speed.
Fuels comprise another area of study. Wallner says Argonne is developing a hybrid system that uses dual fuels. “The efficiencies we achieve by combining gasoline and diesel are above that for a single fuel.” The fuels are fed to the engine at various ratios depending on engine load and speed.
A relative newcomer to the fuel mix is natural gas. Compressed natural gas is better suited to short-haul business, meaning vehicles like refuse trucks, buses, and delivery trucks, while liquefied natural gas has been adopted for long-haul applications because you can store more fuel on board. Either approach involves further developing the infrastructure and vehicle components needed to handle the gas.
At the University of Dayton Research Institute, their multiscale composites and polymers division is developing compressed gas storage vessels for the trucking industry. Their goal is an affordable, lightweight, high-strength fuel tank that can be mass-produced.
Another area of engine improvement involves capturing waste heat from exhaust streams. Researchers can run separate loops with Rankine cycles that use waste heat like you might harness steam from a boiler and recover the energy. You can run a generator and recapture it as electric energy, for example, to offset electrical energy use.
In explaining Argonne’s role in truck research, Rousseau, says they have developed a simulation tool they have licensed, and licensees include about 175 universities worldwide. “We work very closely with some universities. There are a lot of national programs that DOE and Argonne are involved with. One of the unique abilities of national labs is that we have a wide range of expertise that encompasses the areas that require simulation. At the university level, they may be very good in specialized areas, but they may not have a large group like we have here. We leverage and complement that specific expertise.”
Wallner cites an example of a program. Eco Car involves 17 universities from the U.S. and Canada, with 30-40 students from each university. Argonne partners with several universities on engine projects, and in some cases, students are assigned to work at Argonne for a year or so, and they can use research results for their own thesis. “That’s mutually beneficial since they get access to cutting-edge data, and we get access to the students and their knowhow as well as their facilities at the university.” Argonne works with and recruits from schools like Michigan, Michigan Tech, Mississippi State, Wisconsin-Madison, Cal Berkeley, Ohio State, Purdue, Clemson, and Stony Brook. Another strong school in truck fuel efficiency is the University of California Riverside, and work goes on at the Texas Transportation Institute, part of the University of Texas system.
Trucks Becoming Slipperier
Most engineers know that the aerodynamics of a moving vehicle relates heavily to its drag coefficient, a measurement of how stealthily it slips through the air. Woodrooffe reports, “The tractor side of the vehicle has added considerable focus in the last 20 years to optimize the shape of the cab to reduce speed drag coefficient. That has been remarkably successful.” You see many truck cabs on the road with fairings or spoilers on the roof that smooth the airflow transition between the cab and trailer.
But an area that hasn’t seen as much attention is the trailer, Woodrooffe adds. This is because trailers are utilitarian, and the owner of the tractor doesn’t necessarily own the trailer. Therefore, the trailer modifications to make it slipperier don’t accrue to the trailer owner because they don’t pay the fuel bill. “Call it a disconnect in the incentive system, a primary area for regulatory action to help encourage trailer manufacturers to optimize the aerodynamics of the trailers.” One improvement that has come about is the skirt placed under trailers to improve airflow.
When it comes to tires, the industry has long strived to produce designs with lower rolling resistance by improving both the carapace and the tread. Now they’re going to what they call the wide-base single tire, which replaces the dual-tire group typically seen on trucks. Energy is lost in sidewall deflection, and in the wide-base tire, you’ve eliminated two sidewalls compared to a dual. In turns, you use energy trying to force dual tires to turn a radius because they’re locked together, and one tire is rolling on a different radius than the other.
It is expected that the new rules will add $12,000 to $14,000 to the manufacturing cost of a new tractor-trailer, although EPA studies estimate that cost will be recouped after two years by fuel savings.
Rousseau says, “I think there has been a lot of progress. Remember maybe ten years ago, I don’t think we would see trucks with skirts on the road. Now, it’s pretty much a given. And you’re starting to see single tires more.” An indication that, piece by piece, the savings will add up and the research efforts of engineering schools across the country will bear fruit.
Based in Milton, PA, Tom Gibson, P.E. is editor and publisher of Progressive Engineer, an online magazine and information source (www.ProgressiveEngineer.com).