Familiar to many, the 2011 SuperTruck program was a five-year challenge set by the U.S. Department of Energy to create a Class-8 truck that improves fuel efficiency by 50 percent. Hoping for even more groundbreaking achievements this time around, the Department of Energy has initiated a second five-year program to bring further fuel-efficiency advancements and near closer to eventual commercialization. Cummins, Peterbilt, Daimler Trucks North America, Navistar, and Volvo Group remain the five teams involved in this R&D endeavor. Michael Berube, head of the Energy Department’s vehicle technology office mentioned “SuperTruck II has set goals beyond where the companies think they can be.” SuperTruck II is looking for a 100 percent increase in freight-hauling efficiency and a new engine efficiency standard of 55 percent. With such lofty goals, the SuperTruck II development teams will need to tackle improvements in freight efficiencies from all sides.
Material considerations, body aerodynamics, low-resistance tires, predictive torque management using GPS and terrain information, combustion efficiency, and several other improvements methods on the first iteration have demonstrated how the SuperTruck II will require a multi-phase and integrated systems approach to achieve equally successful numbers. However, with an engine efficiency target that is 31 percent above the SuperTruck’s first go around, special attention will be required on engine advancement to achieve an efficiency standard of 55 percent.
One of the main methods apart from auxiliary load and friction reduction is a comprehensive waste heat recovery (WHR) system dedicated to the engine. From the existing works devoted to waste heat recovery, the following methods of efficiency increase can be highlighted:
- Addition of the internal heat recuperation to a WHR cycle
- Appropriate working fluid selection
- Increment of initial parameters of bottoming cycle up to supercritical values
- Maximize waste heat utilization due to the usage of low temperature heat sources
- Bottoming cycle complexification or usage of several bottoming cycles with different fluids
With regards to fluid selection, no universal organic fluid exists that is suitable for a wide range of ORC applications. For this reason, each WHR project requires an extensive fluid selection analysis as one of the main design steps. In general, working fluids are selected based on their thermodynamic properties, thermal stability, and environmental impact/safety. Amongst the most popular options are water, ethanol, R245fa, and R134a. Once the proper design range it set for the waste heat cycle, the designer can successfully set which fluid may be the best for its given application.
Later in the design process, the engineer must consider how to design a turbine that will create the optimal amount of power for the selected fluid type and operating ranges. With high efficiency targets on the SuperTruck II, the proper experience and resources are required to create high-efficiency ORC turbines that can achieve these targets. It is will be interesting to see what kind of engine advancements and technologies will be utilized from each design team throughout the outset and final completion of the SuperTruck II. If you would like to learn more about SoftInWay’s AxSTREAM platform for design ORC Turbines in WHR cycles, please visit: http://www.softinway.com/software-applications/heat-balance-design-analysis/