What is Being Done to Improve the Efficiency of Class 8 Long-Haul Trucks?

Class 8 long-haul tractor-trailers represent approximately 2% of the total on-road population in the United States, 6% of the total vehicle miles traveled, 80% of the goods hauled in the US and 20% of the fuel consumed for transport according to the 2013 U.S. Energy Information Administration (EIA) data.  Because these vehicles have a total weight of 33,000-80,000 + lbs, every mile per gallon gained in fuel economy is worth thousands of dollars in fuel cost savings per truck per year.  Fuel efficiency is currently about 6-7 miles per gallon which leaves room for improvement.  

To address this issue, the US Department of Energy (DOE) has initiated one of the largest precompetitive R&D programs to improve the freight-hauling efficiency of heavy-duty Class 8 long-haul tractor-trailer trucks.  The program is monitored and managed by the Vehicle Technologies Office which is responsible for developing and deploying efficient and environmentally friendly highway transportation technologies, thus enabling Americans to use less petroleum.  

Department of Energy “SuperTruck” Program

The Department of Energy has provided $284 million in funding for this initiative.  The program is about,  “expediting the development of advanced heavy-duty vehicle efficiency technologies” and is an initiative to achieve the looming fuel standards for heavy duty trucks to be effective in 2020.  The program is not to design a commercially viable vehicle but rather to accelerate the development of advanced efficiency technologies.  Using a “best in class” 2009 model year baseline truck, the program objective is to develop and demonstrate a 50% improvement in overall freight efficiency, noting that 30% of the vehicle efficiency improvement must come from the tractor and trailer and the other 20% must come from the engine.  

In addition each vehicle’s engine must show a 50% brake thermal efficiency (BTE).  This is defined as break power of a heat engine as a function of the thermal input from the fuel. It is used to evaluate how well an engine converts the heat from a fuel to mechanical energy. Other requirements mandate compliance with existing US Environmental Protection Agency (EPA) emissions standards and all the vehicle safety and regulatory requirements that apply to commercial tractor-trailers. 

Who Are the Players?

Four industry teams were competitively selected for this program. These industry teams consist of leading vehicle and engine manufacturers in the North American market who together account for more than 75% of the Class 8 market in the US.  Each team is composed of a number of partners consisting of engine, truck and trailer manufacturers, suppliers, fleet owner, universities and national laboratories.  Each SuperTruck team focuses on different technologies and uses independent technology approaches, which in the end, produce four unique paths and multiple solutions toward the same objectives.  The four teams and their focuses are:

Cummins Inc. – an advanced organic Rankine cycle waste heat recovery system (WHR) and developing an aerodynamic Peterbuilt tractor-trailer combination including various load reduction technologies.

Daimler Trucks North America LLC – focus on hybridization, engine downsizing/downspeeding, WHR and improved aerodynamics as well.

Navistar Inc. – main focus on aerodynamics and hybridization as well as combustion efficiency and turbocompounding. 

Volvo Technology of America Inc. – (joined in 2011) focus is on engine downsizing/downspeeding, tractor-trailer aerodynamics, WHR, and turbocompounding.

Team Progress

Since 2010, the Cummins and Peterbuilt team has demonstrated 20% in engine efficiency and a 70% increase in freight efficiency registering 10.7 miles per gallon under typical Class 8 driving conditions,  which is up from the typical 5.8 miles per gallon.  These gains were achieved by reducing tractor-trailer weight, increasing aerodynamics and “thermal efficiency,” and converting the chemical energy from a gallon for fuel to power at the driveshaft.

(Photo by Sarah Gerrity, Energy Department)

The second truck to exceed the goal in March 2015 was Daimler Trucks North America’s Freightliner which broke another record by achieving a 115 percent freight efficiency improvement by reaching 12.2 miles per gallon.  This efficiency breakthrough was achieved by using a variety of technologies including engine advancements, aerodynamic revisions, wider low-rolling resistance tires, a long-haul hybrid system and engine waste heat recovery improvements.

(Photo captured from the April 2, 2015 Office of Efficiency & Renewable Energy Article)

Navistar is working on achieving a 70% improvement, which is comprised of 30% aerodynamic improvements, 25% engine efficiency improvements, 10% weight reduction and 5% reduction in parasitic loads.  They have been working with wind tunnels for the past nine months working with the whole tractor-trailer combination.  Engine work has been more challenging..  So far, the project is at 47.5% BTE.  This is up from the 42% baseline but still short of the 50% project goal.

A latecomer entering the SuperTruck Program in 2011, Volvo is concentrating on full vehicle integration to achieve the 50% fuel efficiency. Optimization of the total tractor-trailer is being achieved through computational fluid dynamic simulation, balancing powertrain cooling, and aerodynamic requirements.  A drag reduction of 20% provided a 10% freight efficiency improvement when tested under normal road conditions.  A 40% drag reduction (targeted) would yeild a 16% freight efficiency improvement.  When using low-rolling resistance tires,  a 20% reduced load relative to the baseline would provide a 5% improvement in freight efficiency. 

Some Program Barriers

Some of the fuel-saving technologies such as aerodynamic design or waste heat recovery systems could add substantial weight to the vehicle which would affect the ton-miles per gallon.  Challenges are also created when these systems are integrated into the vehicle.  Prototypes need to be built because modeling and simulation play an important role in the integration of these complicated systems.  The design of the trailer cannot be ignored as a non-aerodynamic trailer could hurt the overall efficiency of the vehicle.  The last barrier is end user acceptance.  Some issues in this category could be vibration and noise due to engine downspeeding, safety and reliability when “engine braking”, use of ethanol in the waste heat reduction systems and issues in the design itself making mechanical inspection more difficult with trailer skirts and other physical aerodynamic improvements.

There is a potential savings of thousands of gallons of fuel and thousands of dollars annually for each long-haul truck driver if they drove a SuperTruck instead of a conventional truck.  Specifically, if all Class 8 vehicles in the U.S. were SuperTrucks, we would consume close to 300 million fewer barrels of oil and spend nearly $30 billion less on fuel each year. It is estimated that because long-haul trucks drive so far and consume so much fuel, each long-haul truck driver could save about 5,000 gallons of fuel and $20,000 annually driving a SuperTruck instead of a conventional truck.

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