Waste Heat Recovery

The waste heat recovery research and development (R&D) focuses on technologies that can recover and convert engine waste heat to electrical energy to improve the overall engine thermal efficiency and reduce emissions. Recovery of energy from the engine exhaust represents a potential for at least a 10% improvement in the overall engine thermal efficiency. The efficiency of turbochargers used to recover part of this energy could be increased from the current 50% to 58% to about 72% to 76% with enhancements such as variable geometry. An electrically driven turbocharger with increased transient response would be another approach. Turbocompounding and direct thermal-to-electric conversion could also improve the overall thermal efficiency. Bulk semiconductor thermoelectric devices are currently 6-8% efficient. However, recent developments in quantum well thermoelectrics suggest a potential improvement to over 20% is possible.

Research Goals

Long-term, researchers seek to develop technologies that can recover and convert engine waste heat to useful energy and improve the overall thermal efficiency of diesel engines to greater than 55% while reducing emissions to near-zero levels. Specific goals include the following:

  • By 2010, enable commercially viable turbocompound units that can produce more than 10 kilowatts (kW) of additional power from light-duty engine waste heat.
  • By 2012, enable commercially viable turbocompound units that can produce up to 40 kW of additional power from heavy-duty engine waste heat.
  • By 2012, achieve at least 21% efficiency in quantum well thermoelectric devices for waste heat recovery.

Research in this area also supports the overall engine efficiency goals of the FreedomCAR Partnership and the 21st Century Truck Partnership.

Approach

Iterative test and redesign efforts are conducted for electric turbocompound systems to validate the electric power produced and the resulting overall engine efficiency gains. Low-speed torque will be improved to reduce engine size for improved efficiency with the same performance.

For commercially competitive thermoelectric devices for transportation, the approach is to develop quantum well thermoelectrics (or nano-thermoelectrics) into devices that can perform power generation or heating and cooling for vehicle applications with the cost criteria for commercial production.

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