Stirling Thermal Motors Inc


STM 4-120 engine The STM 4-120 Stirling Engine is the result of 15 years of Stirling engine development at Stirling Thermal Motors Inc. (STM) in Ann Arbor, Michigan, USA. The four cylinder, double acting STM 4-120 engine (4 cylinders each with a displacement of 120 cm3) is designed to meet industrial as well as automotive specifications. The designers claim a fuel efficiency equivalent to a Diesel engine, with ultra-low emissions and up to 90% less noise than a Diesel engine. The ST 4-120 uses a variable swashplate to change the stroke, and so in turn change the power at constant working gas pressure. This gives

  1. Exceptional part-load performance where the maximum efficiency is maintained over a broad load range.
  2. Fast transient response. The power changes from idle to full load in 1/3 of a second.
  3. Compact design, with constant thrust load on the swashplate, constant torque and very low vibration.


Stirling Thermal Motors has reciently been renamed as STM Power Inc

STM Power Inc. is a developer of on-site, electricity and cogen systems using a proprietary four-cylinder adaptation of external heat (Stirling-cycle) engine technology.

The Company refers to its products as PowerUnits. The Company believes that electricity and heat produced by its PowerUnits are expected to be more economical than other energy conversion technologies (fuel cells, microturbines and photovoltaic systems) competing in the distributed generation ("DG") market.

A 25 kW PowerUnit, which is based on the STM 4-120 engine, began testing in December 1999. A renewable DG product, the SunDish Solar system, has already been installed in five test facilities. To date, approximately $40 million has been invested in the Company.

Another product will be the 10 kW PowerUnit, based on the STM 4-70 engine, which is being developed as an adaptation of the engine that was built in conjunction with General Motors Corporation for use in GM's hybrid electric car.

Re-configured as a PowerUnit, it will be designed to deliver a rated capacity of 10 kW of electricity and 66,000 Btu per hour of heat. The 10 kW PowerUnit will measure approximately 3ft by 3ft by 2ft (about the size of a small residential air conditioning unit). Development of the 10 kW PowerUnit is estimated to begin in 2002.


STM Power was establised in 1990. The Company shut down in early 2007. The company was revieved under new ownership in mid 2007 as Stirling Biopower


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