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GENSETS

Generators for Small Electrical and Thermal Systems

The GENSETS program aims to develop transformative generator technologies to enable widespread deployment of residential combined heat and power (CHP) systems. These small, natural gas-fueled systems can fulfill most of a US household's electricity and hot water needs, and if widely used could increase the overall efficiency of power generation in the US, and reduce greenhouse gas emissions.
For a detailed technical overview about this program, please click here.  

Aerodyne Research, Inc.

Single-Cylinder Two-Stroke Free-Piston Internal Combustion Generator

Aerodyne Research with partners from Stony Brook University, Precision Combustion, Inc., and C-K Engineering, Inc. will design and build a CHP generator based on a small single-cylinder, two-stroke free-piston internal combustion engine. Similar to an automotive internal combustion engine, the proposed system follows the same process: the combustion of natural gas fuel creates a force that moves a piston, transferring chemical energy to mechanical energy used in conjunction with a linear alternator to create electricity. The free-piston configuration used here, instead of a traditional slider-crank mechanism, has the potential to achieve high electrical conversion efficiency. Their design also includes a double-helix spring that replaces the crankshaft flywheel in conventional engines and can store 5-10 times the work output of the engine cycle and operates at high frequency, which is key to high energy density, compact size, low weight, and low cost. The system will also incorporate low temperature, glow plug-assisted homogeneous charge compression ignition (HCCI) combustion, which reduces heat loss from the engine and further increases efficiency.

Air Squared Inc.

A High Efficiency SACI 1 kW Generator System with Integrated Waste Energy Recovery

Air Squared with partners at Argonne National Laboratory, Purdue University, and Mississippi State University, will develop an advanced internal combustion engine (ICE) integrated with an organic Rankine cycle (ORC) for waste heat recovery. The ICE will use spark-assisted compression ignition (SACI) combustion, a turbulent jet ignition (TJI) fueling system, a high compression ratio, and aggressive exhaust gas recirculation to deliver a higher thermal efficiency with low emissions. Traditional internal combustion engines use the force generated by the combustion of a fuel (e.g. natural gas) to move a piston, transferring chemical energy to mechanical energy. This can then be used in conjunction with a generator to create electricity. SACI is an advanced combustion technique that uses a homogeneous mixture of fuel and air with spark assist to enable higher thermal efficiencies and lower emissions. The TJI combustion system further increases thermal efficiency by enabling reliable SACI combustion even with ultra-lean mixtures (i.e. high air to fuel ratio). The ORC design uses mostly the same components of a traditional Rankine cycle, but uses an ammonia/water mixture instead of steam, combined with a novel oil-free scroll expander.

American Superconductor

Sustainable Economic mCHP Stirling (SEmS) Generator

American Superconductor (AMSC) in collaboration with team members Qnergy, Alcoa Howmet, Gas Technology Institute (GTI), MicroCogen Partners, and A.O. Smith Corporation will develop a Free-Piston Stirling engine (FPSE) powered by an ultra-low-emissions natural gas burner for micro-CHP applications. A Stirling engine uses a working gas housed in a sealed environment, in this case the working gas is helium. When heated by the natural gas-fueled burner, the gas expands causing a piston to move and interact with a linear alternator to produce electricity. As the gas cools and contracts, the process resets before repeating again. Advanced Stirling engines endeavor to carefully manage heat inside the system to make the most efficient use of the natural gas energy. The ITC design features free-piston architecture using flexure bearings thus eliminating rubbing parts and allowing for long system life under continuous use. The team will also develop novel materials that enable high-temperature engine operation, further increasing the efficiency of the system.

Brayton Energy

1kW Recuperated Brayton-Cycle Engine Using Positive-Displacement Components

Brayton Energy, LLC will develop a 1 kW recuperated Brayton cycle engine to produce heat and electricity for residential use. To begin the cycle, compressed air is preheated in a recuperator before adding fuel, then the air-fuel mix is ignited in a combustion chamber. The high temperature exhaust gases then expand through the turbine, providing some of the work that drives the compressor and also produces electricity in a generator. Major project innovations include the use of a rotary screw-type compressor and expander that operate in a sub-atmospheric Brayton cycle i.e. below atmospheric pressure. In addition, Brayton will also use their innovative patented recuperator that is currently in production, and an ultra-low emission combustor.

MAHLE Powertrain

Advanced Lean Burn Micro-CHP Genset

MAHLE Powertrain with partners at Oak Ridge National Laboratory, Louthan Engineering, Kohler Company, and Intellichoice Energy will design and develop a CHP generator that uses an internal combustion engine with a turbulent jet ignition (TJI) combustion system. Similar to an automotive internal combustion engine, the proposed system follows the same process: the combustion of natural gas fuel creates a force that moves a piston, transferring chemical energy to mechanical energy used in conjunction with a generator to create electricity. The TJI combustion system incorporates a pre-chamber combustor, enabling the engine to operate in ultra-lean conditions (i.e. high air to fuel mixture), which results in significant improvement in engine thermal efficiency. The team will further increase the system's efficiency by using low friction engine components, while a low-temperature after-treatment system will reduce exhaust emissions.

Metis Design Corporation

Advanced Microturbine Engine for Residential CHP

Metis Design Corporation (MDC) with Lawrence Berkley National Laboratory will develop a Brayton cycle engine for residential use to produce heat and electricity. To begin the cycle, air is drawn into the system where it is compressed and pressurized. This compressed air is then heated in a recuperator and introduced in to the combustion chamber. Fuel is injected in to the combustion chamber and subsequently the air-fuel mixture is ignited. The high temperature exhaust gases then expand through a turbine, providing some of the work that drives the original compressor and the remainder produces electricity in a generator. Other innovations include adding a rotating vaneless diffuser to the compression process to reduce viscous losses that would normally reduce the efficiency of small compressors. The design also includes a high-efficiency recuperator to capture waste heat from the turbine exhaust and a low swirl burner to reduce emissions.

Mohawk Innovative Technology, Inc.

High-Speed Microturbine with Air Foil Bearings for Residential CHP

Mohawk Innovative Technology, Inc. (MiTi) and its partners at the University of Texas at Austin and Mitis SA will develop a 1 kW microturbine generator for residential CHP based on MiTi's hyperlaminar flow engine (HFE) design. Key innovations of the design include highly miniaturized components operating at ultra-high speeds and a viscous shear mechanism to compress air that is mixed with natural gas and undergoes a flameless combustion process that minimizes emissions. The hot combustion gas drives the turbine and generator to produce electricity and heat water for household use. Besides using the viscous shear-driven compressor and turbine impellers and flameless combustion, the turbogenerator uses permanent magnet generator elements and air foil bearings with very low power loss, all of which are combined into a highly efficient, low emission, and oil-free turbomachine for residential combined heat and power that requires little or no maintenance.

NanoConversion Technologies, Inc.

High-Efficiency Thermoelectric CHP

NanoConversion Technologies, along with researchers from Gas Technologies Institute (GTI), will develop a high-efficiency thermoelectric CHP system. This is a solid-state device that uses heat to create electricity and contains no moving parts, thus creating no noise or vibrations. Instead, this thermoelectric CHP engine uses a novel concentration mode-thermoelectric converter (C-TEC) to harness the heat of the natural gas combustor to vaporize and ionize sodium, creating positive sodium ions and electrons that carry electric current. The C-TEC uses this sodium expansion cycle to produce electricity using an array of electrochemical cells. The superadiabatic combustor technology from GTI provides a low emission external combustion heat source with 95% fuel-to-heat efficiency and a stable temperature compatible with the C-TEC units.

Sencera Energy, Inc.

Kinematic Flexure-Based Stirling-Brayton Hybrid Engine Generator for Residential CHP

Sencera Energy and Ohio University will develop a novel kinematic Stirling-Brayton hybrid engine using flexure based volume displacement in lieu of a conventional piston-cylinder Stirling engine. A Stirling engine uses a working gas housed in a sealed environment, in this case the working gas is helium. When heated by the natural gas-fueled burner, the gas expands causing a piston to move and interact with an alternator to produce electricity. As the gas cools and contracts, the process resets before repeating again. Advanced Stirling engines endeavor to carefully manage heat inside the system to make the most efficient use of the natural gas energy. The flexure-based design achieves the same function as a piston-cylinder set by simply changing the volume of the working spaces, as opposed to sliding a piston along the interior of a cylinder. The removal of pistons from the design eliminates the need for sliding seals such as piston rings or air/gas bearings, resulting in lower engine friction, less fluid flow loss and fewer dead volumes. It also lowers the potential fabrication cost compared to other heat engines. The proposed kinematic engine design provides easy coupling to existing rotary alternator designs, which allows the use of robust, mature, and cost-effective off-the-shelf alternator technologies and controllers.

Sunpower, Inc.

Free Piston Stirling Engine Based 1kW Generator

Sunpower, in partnership with Aerojet Rocketdyne and Precision Combustion Inc. (PCI), proposes a high-frequency, high efficiency 1 kW free-piston Stirling engine (FPSE). A Stirling engine uses a working gas such as helium, which is housed in a sealed environment. When heated by the natural gas-fueled burner, the gas expands causing a piston to move and interact with a linear alternator to produce electricity. As the gas cools and contracts, the process resets before repeating again. Advanced Stirling engines endeavor to carefully manage heat inside the system to make the most efficient use of the natural gas energy. New innovations from this team include the highly efficient and high frequency design which reduces size and cost and can be wall mounted. The heater-head assembly acts as the heat exchanger between the burner and the enclosed working gas, and the higher temperature allows for greater efficiency. Aerojet Rocketdyne will assist this effort by developing high temperature materials to use in this process, while PCI will add a novel catalytically-assisted, two-stage, burner to maximize heat transfer to the heater-head.

Tour Engine, Inc.

High Efficiency Split-Cycle Engine for Residential Generators

Tour Engine, in collaboration with Wisconsin Engine Research Consultants (WERC) will develop a miniature internal combustion engine (ICE) based on Tour's existing split-cycle engine technology. Traditional ICEs use the force generated by the combustion of a fuel (e.g. natural gas (NG)) to move a piston, transferring chemical energy to mechanical energy. This can then be used in conjunction with a generator to create electricity. Unlike a normal combustion engine, a split-cycle engine divides the process into a cold cylinder (intake and compression) and a hot cylinder (expansion and exhaust). This allows for independent optimization of the compression and expansion ratios, leading to increased thermal efficiency. A novel Spool Shuttle Crossover Valve (SSCV) is the key enabler for the Tour engine, as it transfers the fuel/air charge from the cold to hot cylinder.

West Virginia University Research Corporation

Advanced Stirling Power Generation System for Combined Heat and Power

West Virginia University Research Corporation (WVURC) and their partner, Infinia Technology Corporation, propose to demonstrate an advanced Stirling power generation system for residential CHP applications. A Stirling engine uses a working gas housed in a sealed environment, in this case the working gas is helium. When heated by the natural gas-fueled burner, the helium expands causing a piston to move and interact with a linear alternator to produce electricity. As the gas cools and contracts, the process resets before repeating again. Advanced Stirling engines endeavor to carefully manage heat inside the system to make the most efficient use of the natural gas energy. This project makes extensive use of additive manufacturing i.e. constructing components one layer at a time - similar to 3D printing. They propose using additive manufacturing because building the system as one piece minimizes interfacial heat losses and improves heat transfer, leading to increased efficiency.

West Virginia University Research Corporation

Oscillating Linear Engine and Alternator

West Virginia University Research Corporation (WVURC), along with its partners at ANSYS, Inc., Sustainable Engineering, Wilson Works, and Stryke Industries, will develop a CHP generator for residential use based on a two-stroke, spark-ignited free-piston internal combustion engine (ICE). Traditional internal combustion engines use the force generated by the combustion of a fuel (natural gas in this case) to move a piston, transferring chemical energy to mechanical energy, which when used in conjunction with a generator produces electricity. This free-piston design differs from traditional slider-crank ICE models by eliminating the crankshaft and using a spring to increase frequency and stabilize operation. The resulting design is compact with few moving parts and has reduced frictional losses. In place of a traditional alternator, this engine drives a permanent magnet linear electric generator.

Wisconsin Engine Research Consultants, LLC

Spark-Assisted HCCI Residential Generator

Wisconsin Engine Research Consultants (WERC) and its partners Adiabatics, Briggs and Stratton, and the University of Wisconsin-Madison will develop a generator using an internal combustion engine (ICE) that incorporates an advanced spark-assisted homogeneous charge compression ignition (SA-HCCI) system. Traditional internal combustion engines use the force generated by the combustion of a fuel (e.g. natural gas) to move a piston, transferring chemical energy to mechanical energy. This can then be used in conjunction with a generator to create electricity. SA-HCCI systems achieve combustion by compressing their fuel/air mix to the point of ignition, with a spark helping to initiate the process. These systems run very fuel lean and achieve high efficiency and waste less heat compared to conventional ICEs. In addition, the WERC team will further increase efficiency by incorporating thermal barrier coatings, an advanced boost system, and an optimized low-friction combustion chamber.
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