Waste Heat Recovery

[Due to the increasing size of the archives, each topic page now contains only the prior 365 days of content. Access to older stories is now solely through the Monthly Archive pages or the site search function.]

Researchers Demonstrate Quantum-Coupled Thermal to Electric Conversion With Efficiency as High as 40% of Carnot Limit, With Calculated Potential of Up to 90%

November 18, 2009

Basic scheme of the quantum-coupled converter. Shaded boxes indicate electron reservoirs. Arrows represent couplings. Letter U represents the electrostatic interaction while letter V represents the tunneling. Source: Hagelstein, 2007. Click to enlarge.

Researchers from MIT, with colleagues from IISc in Bangalore, India and HiPi Consulting in Maryland have experimentally demonstrated the conversion of heat to electricity using thermal diodes with efficiency as high as 40% of the Carnot Limit. Their calculations find that this new kind of system could theoretically reach as much as 90% of that ceiling.

By contrast, current solid-state thermoelectric devices only achieve about one-tenth of the Carnot Limit, according to MIT Associate Professor Peter Hagelstein, co-author of a paper on the new concept published 13 November in the Journal of Applied Physics.

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GM Receives $2.7M ARPA-E Award to Explore Thermomechanical Waste Heat Recovery Using SMA Heat Engine

October 28, 2009

Concept diagram of an SMA heat engine for power generation from waste engine heat. Source: GM. Click to enlarge.

As one of 37 projects selected by the US Department of Energy’s ARPA-E (earlier post), General Motors R&D will receive $2.7 million (subject to final negotiation with DOE) to support building a prototype thermomechanical waste heat recovery system using a Shape Memory Alloy (SMA) heat engine to generate electricity from the heat in automotive exhaust. GM was the only automaker to receive an ARPA-E award in the first round of funding.

According to Jan Aase, Director of the Vehicle Development Research Laboratory at GM R&D in Warren, Michigan, the team calculates that they might be able to deliver up to a 15% improvement in fuel economy using as little as a 15-20 °C differential between hot and cold in the system. (Prior to joining GM R&D, Aase was at GE Global Research.)

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BMW Outlines Intelligent Heat Management Applications for Reducing Fuel Consumption and CO2; New Thermoelectric Generator Unit Integrated with EGR

October 12, 2009

Distribution of energy in the car. Click to enlarge.

BMW dedicated a portion of its recent Innovation Days 2009 event to the topic of Intelligent Heat management as a mechanism for reducing fuel consumption and CO₂ emissions. Among the projects discussed were reducing cold starts; using waste heat for different heating applications in the car; and a new implementation of a thermoelectric generator (TEG) for waste heat recovery.

Even a highly efficient combustion engine converts only about one-third of the energy in the fuel into traction actually propelling the car. The remaining two-thirds are lost as waste heat going into the environment through the car’s exhaust emissions and through the radiator.

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Ford Conducts Design of Experiment Investigating Thermoelectric Energy Regeneration

May 04, 2009

by Jack Rosebro

Conceptual schematic of direct thermoelectric generator mounted in a vehicle’s exhaust stream. Indirect configurations are also possible. Adapted from Hussain et al. Click to enlarge.

At SAE 2009 World Congress in Detroit last month, Ford Motor Company presented a research paper that detailed the results of an initial investigation, termed a Design of Experiment, into thermoelectric exhaust heat energy recovery in conjunction with a hybrid powertrain.

The investigation, conducted by Ford engineers Quazi Hussain, Clay Maranville, and David Brigham, used computer modeling to predict the performance of TE devices of various physical configurations, using average highway-speed exhaust gas flows and temperatures of a 2.5L engine with an Atkinson-cycle engine, as used in Ford’s Escape hybrid SUV.

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BMW Study on Rankine Cycle for Waste Heat Recovery Shows Potential Additional 10% Power Output at Highway Speeds

May 03, 2009

Energy utilization vs. complexity of different heat recovery systems. In this study, BMW focused on Rankine A (exhaust gas only) and Rankine B (exhaust gas and coolant). Adapted from Ringler et al. (2009) Click to enlarge.

BMW is exploring two pathways for waste heat recovery in vehicles: one thermoelectric, the other thermodynamic. In 2005, BMW Group Research and Engineering announced it was developing a steam-powered auxiliary drive—the Turbosteamer—to use the waste heat present in the exhaust gases and cooling system from a conventional gasoline engine as its source of power. The long-term development goal articulated at the time was to have a system capable of volume production within ten years.(Earlier post.)

At the recent SAE 2009 World Congress, BMW presented an analysis of two basic configurations of the Rankine cycle applied to a thermodynamic heat recovery system for a four-cylinder combustion engine. Based on bench test measurements, BMW has concluded that waste heat recovery can provide an additional power output of about 10% at typical highway cruising speeds.

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Cyclone Targets Small-Scale Co-Generation Market With External Combustion Waste Heat Engine

February 11, 2009

WHE unit. Click to enlarge.

Cyclone Power Technologies Inc., the developer of the external combustion Waste Heat Engine (WHE) (earlier post), has formed a separate division to market and manufacture WHE systems for applications such as small-scale cogeneration, solar thermal electricity production, biomass combustion, and engines for auxiliary power units for trucks and RVs.

The WHE is derivative of Cyclone’s external combustion Green Revolution Engine. (Earlier post.) Unlike its more powerful counterpart, the WHE operates in a low-pressure, low-temperature range. By contrast, the GRE employs super-critical pressure (3,200 psi, 22 MPa) and super-heated steam (1,200 °F, 649 °C).

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Waste Heat Recovery System Receives Powertrain Innovation of the Year Award

November 18, 2008

Cutaway diagram of the heat2power system mounted on an engine. Click to enlarge.

The Paris, France-based developer of a waste heat recovery (WHR) system, heat2power, won the Powertrain Innovation of the Year Award at the Professional Motorsport World Expo in Cologne (11-13 November) with its Thermal Energy Recovery System (TERS). heat2power says that its WHR system can provide fuel savings of 15-35% under all driving conditions at a cost of approximately 30% more than a comparable turbocharged gasoline engine.

The heat2power system uses one or more cylinders for the regeneration of waste heat. These cylinders can be in replacement of the combustion cylinders inside an existing engine or as an add-on module that is connected to the engine by means of a gear set or a belt drive. It is also possible to have no mechanical linkage between the combustion engine and the WHR unit in case the power from the regeneration unit is taken off electrically.

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