However, the transportation of goods and people today is mostly powered by fossil fuels, which emit greenhouse gases (GHG) when burned. In the US, the transportation sector accounted for 28% of the overall GHG emissions in 2018 – and the US Environmental Protection Agency reports that 23% of that sector emission came from medium and heavy-duty trucks. This makes the trucking industry a major player in the effort to minimize tailpipe emissions of GHG.
At Volvo Trucks, care for the environment is one of our core values. We believe in sustainable transport solutions. Although electric trucks are here, we know that their widespread adoption may take some time. Therefore, in addition to our investment in electric and hydrogen-powered trucks, we are also focused on reducing the tailpipe GHG emissions of our diesel-powered trucks, to carry society through this transition period.
For the past decade, we have done some of that work as part of the US Department of Energy’s “SuperTruck” program to improve the freight efficiency – measured in ton-miles per gallon (or ton-mpg) – of diesel-powered, heavy-duty Class 8 tractors. These trucks, which account for only 4% of the vehicles on US roads, use about 20% of US transportation fuel.
In the original SuperTruck program (ST1), participants were challenged to improve the freight efficiency by 50% over a 2009 baseline. Among all competitors, the “average” 2009 baseline offered 90 ton-mpg. A 50% improvement, therefore, would have achieved a freight efficiency of 135 ton-mpg.
Determined to challenge ourselves, we chose as our baseline the Volvo VNL 670 – our most efficient highway tractor in 2009, offering 100 ton-mpg (at 65,000 pounds Gross Vehicle Weight). Ultimately, Volvo’s ST1 delivered a freight efficiency of approximately 188 ton-mpg – an 88% improvement over our baseline.
“After hundreds of tweaks and dozens of iterations [with our virtual twins], we were able to reduce the overall aerodynamic drag of SuperTruck 1 by 40%, yielding a 20% direct improvement in fuel economy.”
Three main factors contributed to the improvement: reducing the weight of the tractor and the trailer, improving the efficiency of the powertrain, and drastically reducing the aerodynamic drag, for which my team was responsible.
To improve on the aerodynamic design of our baseline required extensive experimentation. Fortunately, Volvo Trucks is an advanced user of virtual twin technology (known generically as “digital twin” technology). This powerful combination of virtual 3D design and multi-physics CFD (Computational Fluid Dynamics) simulation allows us to experiment in the “Digital Wind Tunnel” with real-life accuracy, testing thousands of variations in a fraction of the time and cost that would be required for testing with physical prototypes in physical wind tunnels.
Our virtual twin process also offers detailed visual insight about the airflow around the vehicle. This is critical, as it drives our iterative design process; every design change is based on learnings from the previous iteration, thereby continuously improving the aerodynamics until we reach diminishing returns. After hundreds of tweaks and dozens of iterations, we were able to reduce the overall aerodynamic drag of ST1 by 40%, yielding a 20% direct improvement in fuel economy.
On the heels of ST1’s success, the DOE initiated the SuperTruck II (ST2) program and doubled the challenge: a 100% improvement over the same 2009 baseline. The project is still ongoing as we enter the final build phase. However, the tractor-trailer design is now frozen. This time, using the same virtual twin technology, we reduced the overall drag by 50% over our 2009 baseline – almost 20% better than we achieved in ST1.
Coupled with the improvements achieved by our powertrain colleagues, Volvo’s ST2 is expected to deliver a 120% improvement over our baseline, achieving 220 ton-mpg. The validation of our virtual twin results with the physical prototype, currently under construction, should happen in the coming months.
As a demonstrator, SuperTruck is similar to a concept car; while many of the improvements already are or soon will be incorporated into our commercial offerings, others need more work to bring down their cost. And SuperTruck II isn’t the end of the journey: the recently announced SuperTruck III program will focus on battery-electric and fuel-cell-powered vehicles – the designs that will move the trucking industry from a transitional period of lower tailpipe GHG emissions to one with zero tailpipe emissions.
PROFILE: Raja Sengupta is Lead Engineer for Aerodynamics at Volvo Trucks North America, responsible for aerodynamic certification for CO2 of the company’s product portfolio. He also led Volvo Trucks’ aerodynamics development team for the US Department of Energy’s SuperTruck I program, and currently leads Volvo Trucks’ aerodynamics team for the SuperTruck II program. He has a doctoral degree in aerospace engineering from the University of Cincinnati, and previously worked for NASA Langley, the motorsports industry, and for a simulation software developer, where he specialized in simulation for engine cooling and full-truck simulation.
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