Fleet Management News & Business Info | Commercial Carrier Journal
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60 COMMERCIAL CARRIER JOURNAL | MARCH 2015 EQUIPMENT: WASTE HEAT RE COVERY hybrid vehicle's brakes are applied, kinetic energy is captured by the onboard electrical motors. When the vehicle starts moving again, the electric motors use the captured energy for acceleration. "That's a highly effi cient design, assuming you can design an economic and compact system to capture and reuse that energy," Granger says. In most proposed waste heat recovery systems, the boilers are either the exhaust system or the exhaust gas recirculation system. If the waste heat recovery system is in the exhaust stream, it has to be behind the selective catalytic reduction system to work correctly. "At that point, you have to connect the heat exchangers to some sort of expansion device," Granger says – a turbine, a piston or any number of machines that can take pressurized gas and convert it to usable power. Once that process is complete, that power can be harnessed and sent to an electric generator to either run vehicle acces- sories or for gearing to convert it to mechanical power. Over the last 20 years, waste heat recov- ery increasingly has been used in station- ary applications such as power plants to boost effi ciency and reduce GHG effects. Only recently has the technology been demonstrated in laboratory environ- ments as a viable means to improve fuel economy in heavy trucks. The Peterbilt-Cummins SuperTruck team integrated a waste heat recovery system in two demonstration vehicles as part of its 50 percent effi cient engine package. "Waste heat recovery was a key contributor to the program results that achieved a peak 75 percent improvement in fuel economy over a baseline 2009 production truck," says Ken Damon, manager of Peterbilt Motors' vehicle performance group. For vehicle applications, this approach has been investigated in laboratories for decades, and recent research and devel- opment has enabled implementation of functional prototypes on line-haul heavy trucks, says Mark Groeneweg, director of Daimler Trucks powertrain engineering for the company's NAFTA region. "Technology demonstrations facili- tated by the U.S. Department of Energy SuperTruck program are a successful example of that," Groeneweg says. "It is a promising technology to boost commer- cial vehicle fuel economy." One size won't fi t all Despite the promise that waste heat recovery technology holds, there are signifi cant barriers to implementing it in trucking applications. "Kenworth and Paccar are constantly evaluating new technologies that pro- vide benefi t to customers," says Kevin Baney, Ken- worth chief engineer. "As engines continue to gain effi ciency through mea- sures such as downspeed- ing, reduced friction and parasitics, we also recognize the potential of waste heat recovery systems." But that potential, ac- cording to Baney, depends heavily on the engine's duty cycle, and such systems also add cost, complexity and weight to the vehicle. "When customers evalu- ate fuel-effi cient features, they typically expect a payback of no more than two to three years that considers additional maintenance and upfront acquisition costs," he says. "At present, we do not see an economically based application for waste heat recovery in our vehicles, but we will continue to evaluate its viability." Greszler says waste heat recovery systems theoretically could provide fl eets with up to a 4 percent boost in fuel economy – assuming they operate in the right applications. It's more likely a vehicle would net only an overall increase of 2 percent because of lost aerodynamic effi ciency, he says. "These are sizeable systems, and packaging will be problematic." The systems also present lag-time is- sues, Greszler says. Because it takes time for a waste heat recovery system to get fl uids up to temperature, fl eets running in mountains or hills won't be able to access the additional power when they need it most – during the uphill portion of a climb. "It's technology that will work This Cummins illustration shows a proposed waste heat recovery system. In most, the boilers are either the exhaust system or the EGR system. If the waste heat recovery system is in the exhaust system, it has to be behind the SCR system to work correctly.