Combustion engines, the engines in gas-powered cars, only use a quarter of the fuel’s potential energy while the rest is lost as heat through exhaust. Now, a study published in ACS Applied Materials & Interfaces demonstrates how to convert exhaust heat into electricity. The researchers present a prototype thermoelectric generator system that could reduce fuel consumption and carbon dioxide emissions — an opportunity for improving sustainable energy initiatives in a rapidly changing world.
Fuel inefficiency contributes to greenhouse gas emissions and underscores the need for innovative waste-heat recovery systems. Heat-recovery systems, called thermoelectric systems, use semiconductor materials to convert heat into electricity based on a temperature difference. However, many existing thermoelectric device designs are heavy and complex, requiring additional cooling water that’s used to maintain the necessary temperature difference. Now, a team of researchers led by Wenjie Li and Bed Poudel have developed a compact thermoelectric generator system to efficiently convert exhaust waste heat from high-speed vehicles like cars, helicopters and unmanned aerial vehicles into energy.
The researchers’ new thermoelectric generator contains a semiconductor made of bismuth-telluride and uses heat exchangers (similar to those used in air conditioners) to capture heat from vehicle exhaust pipelines. The team also incorporated a piece of hardware that regulates temperature, called a heatsink. The heatsink significantly increases the temperature difference, which directly influences the system’s electrical output. Their prototype achieved an output power of 40 Watts, about enough to power a lightbulb. Importantly, the results indicate that high airflow conditions, like those found in exhaust pipes, enhance efficiency, thereby increasing the system’s electrical output.
In simulations mimicking high-speed environments, the waste-heat system demonstrated great versatility; their system produced up to 56 W for car-like exhaust speeds and 146 W for helicopter-like exhaust speeds, or the equivalent of five and 12 lithium-ion 18650 batteries, respectively. The researchers say their practical system can be integrated directly into existing exhaust outlets without the need for additional cooling systems. As the demand for clean energy solutions escalates, they add that this work could pave the way toward practical integration of thermoelectric devices into high-speed vehicles.
The authors acknowledge funding from the Army Rapid Innovation Fund Program; the National Science Foundation Industry-University Cooperative Research Centers Program through the Center for Energy Harvesting Materials and Systems; and the Office of Naval Research.
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