High Efficiency Split-Cycle Engine for Residential Generators

Tour Engine Image ARPA-E Project

San Diego, California
Project Term:
11/24/2015 - 07/31/2023

Critical Need:

In 2013, centralized U.S. power plants had an average electricity generation efficiency of only 33%, wasting 67% of primary energy as heat and emitting 2 billion tons of CO2, about 38% of U.S. total emissions. Further, 6% of electricity is generally lost during transmission and distribution from the power plant to the customer. An alternative to centrally produced power is distributed generation, in which electricity is generated at the point of use. Residential combined heat and power (CHP) systems can burn natural gas to produce electricity for a home while also using the waste heat for space and water heating. The potential energy efficiency for CHP systems is more than 80% and significant adoption of such systems would enable dramatic reductions in primary energy use and concurrent CO2 emissions. However, usage of small CHP systems is not widespread because systems currently on the market are limited by high price, low efficiency, and short lifetime. The GENSETS program seeks to develop 1 kW (electric) CHP generators that have high fuel-to-electricity generation efficiency, long life, low cost, and low emissions.

Project Innovation + Advantages:

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.

Potential Impact:

If successful, Tour Engine’s project will facilitate development and commercialization of economical, efficient, and durable CHP systems for residential use. These advancements support progress toward ARPA-E’s overall goals as follows:


Innovations developed in this project could help households and businesses become more energy self-reliant and less susceptible to energy-related outages through distributed, local generation of power and heat.


Widespread adoption of high-efficiency residential CHP systems could decrease overall primary energy consumption and therefore reduce CO2 emissions associated with electricity generation by up to 10%.


Cost-effective NG-fueled residential CHP systems could offer consumers lower electricity and heating bills.


ARPA-E Program Director:
Dr. William Horak
Project Contact:
Dr. Oded Tour
Press and General Inquiries Email:
Project Contact Email:


Next Step Engineering Solutions, LLC
Wisconsin Engine Research Consultants, LLC

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