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New path to increasing heavy-truck efficiency with state-of-the-art research engine

08/17/2022

University of Michigan researchers have contributed to Volvo’s demonstration engine that will achieve a peak of  55% brake thermal efficiency, meaning high fuel efficiency.  U-M studies showed a 35% reduction in nitrogen oxides (NOx) emissions for heavy-duty trucks using extreme Miller cycle with high intake boost while enabling higher thermal efficiency.

“The research findings identify future pathways and practical considerations for improving energy efficiency while reducing emissions from heavy-duty transportation. The relatively simple, cost-effective Miller cycle valve strategy studied in this research can be readily and broadly implemented in Class 8 trucks to reduce harmful NOx emissions without penalizing fuel conversion efficiency,” said Andre Boehman, professor of mechanical engineering heading the project at U-M.

Transportation is the second-largest cause of greenhouse gas (GHG) emissions in the United States with heavy-truck emissions being the second largest contributor of the section at 24% according to the EPA in 2019. This is only going to increase as we already see the rise in demand for goods across the nation, putting more pressure on transportation to move more products. 

The research’s main focus, the Miller cycle, is an engine’s intake valve actuation strategy that leaves the intake valve open during part of the engine’s compression stroke, making the engine compress the cylinder charge against the pressure of the intake manifold rather than the pressure of the cylinder walls for the initial portion of the compression stroke. Their recent paper published in the International Journal of Engine Research demonstrates that late intake valve timings and elevated turbocharger efficiencies are needed to increase efficiency compared to a conventional diesel engine.  Elevated intake manifold pressures are necessary for extreme Miller cycle strategies to provide worthwhile benefits over conventional intake valve profiles. Under high boost operation, conventional diesel engines are plagued by sharp increases in peak cylinder pressures and NOx emissions. At these high boost conditions, the effective compression ratio of Miller cycle strategies offers reduced friction losses and reduced NOx emissions without compromising fuel consumption.

“By analyzing the effects of Miller valve timings across a series of constraints, this research provides a thorough understanding of how to leverage the tradeoffs associated with Miller cycle to develop more efficient heavy-duty vehicles to support a more sustainable transportation system,” said Boehman.

This research has been a collaboration with Volvo Technology of America and other partners, including ExxonMobil Research and Engineering, Delphi Automotive, and Federal Mogul, as part of the Department of Energy Supertruck II project relying on a state-of-the-art research engine at the Walter E. Lay Automotive Laboratory. The paper published in the International Journal of Engine Research is titled, “Extreme Miller cycle with high intake boost for improved efficiency and emissions in heavy-duty diesel engines.”