PowerDriver simulations predict thermoelectric exhaust waste heat recovery output of 300W, -2.5% in fuel consumption; prototyping begins
The European Union-funded PowerDriver project—a two-year, €3-million (US$4-million) research project initiated in February 2012 to turn exhaust gas waste heat into electricity using thermoelectric generator (TGEN) technology—has completed simulation work on on a potential automotive application. Results suggest TGEN output of 300W and equivalent fuel saving over the NEDC drive cycle of 2.5%
The PowerDriver project is a collaborative research initiative involving Jaguar Land Rover Ltd and Rolls-Royce PLC together with supply chain and research and development partners and universities. Jaguar Land Rover Ltd is interested in technology capable of being applied to gasoline engine passenger cars while Rolls-Royce PLC is interested in marine applications related to diesel engines.
PowerDriver’s basic objective was overcome the limitations relating to the production of an automotive and marine power generation system by integrating advanced nano-structured silicide and functionally graded telluride thermoelectric materials into a heat exchanger assembly that will enable electrical power to be generated from the exhaust system without affecting back-pressure or engine balance.
From a technological perspective the PowerDriver project has a number of challenges, the partners note. For example, the thermoelectric materials under consideration for the automotive application—both n-type and p-type, to form a couple—are silicide-based materials. These have a potentially low cost base but need further development to achieve the performance and thermal stability required for the application. This is not least due to the fact that the TGEN is located within the exhaust line and is subject to significant thermal cycling.
In addition, the lead-telluride-based thermoelectric materials being investigated for the marine application have a proven track record in similar applications but present financial and thermal stability issues which need to be overcome. Furthermore, the thermoelectric generators require electronic controls which also need to be developed to maximize output efficiency. The joining of current conductors to the thermoelectric material also presents issues which will need to be overcome.
Engineering simulation modeling work is necessary to design both the TGEN and the heat exchangers to obtain the optimum system performance (cost/watt) and thermal stability using Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) techniques, in addition to achieving volume and weight constraints for the target vehicle.
Currently this work suggests that a prototype TGEN design can be achieved with a predicted performance output of 300W, based on the NEDC operating cycle, which would provide a potential fuel saving of up to 2.5% with a comparable reduction in carbon footprint.
With the completion of simulation work, the PowerDriver project will now continue to progress the production of a prototype TGEN design for a Jaguar passenger car, which will provide a reduction in fuel consumption and a corresponding decrease in carbon dioxide emissions.
In parallel, designs will also be developed for two marine diesel applications—again, achieving a reduction in fuel consumption and carbon dioxide emissions. Both the marine and automotive installations will be designed to enable their implementation at a commercially viable cost.
During the remainder of the project, activity will be directed at the production of a prototype for evaluation on a hot air test rig to confirm the projected power output performance; the cost/watt of power for a complete commercial system will also need to be established. This will validate the commercial potential of the system before more costly in-vehicle testing is undertaken.
The lead telluride thermo electric materials used for the marine application have proved challenging, however, the developed n-type material has achieved electrical performance suitable for taking forward into a TGEN design, although cost difficulties have resulted in a change to the selected p-type material. Remaining work will center on the development and characterization of the new material, including the confirmation of a viable manufacturing process. The final thermoelectrical material couple may include functionally graded materials (FGM) which consist of a sandwich of materials in which the individual layers are tuned to the temperature profile being experienced.
Given the imperative to reduce vehicle carbon dioxide emissions and improving fuel economy, Ricardo is actively pursuing a range of new technologies aimed at making the combustion engine of the future cleaner and more efficient. Waste heat lost through the exhaust system is one of the greatest sources of inefficiency in current engines and thermo-electric generation offers a potentially attractive means of harnessing this in the form of usable electrical power. We look forward to working with our partners on the PowerDriver project to create viable prototype designs for cost-effective implementations of this technology.—Ricardo chief technology and innovation officer Professor Neville Jackson