3 kW Stirling engine for power and heat production

A new 3 kW Beta-type Stirling engine has been developed. The engine uses natural gas as fuel and is designed for use as a small combined heat and power plant for single family houses. The electrical power is supplied to the grid. The engine is made as a hermetic device, where the crank mechanism and the alternator are built into a pressurized crank casing. The engine produces 3 kW of shaft power corresponding to 2.4 kW of electric power. The heat input is 10 kW representing a shaft efficiency of 30% and an electric efficiency of 24%. Helium at 8 MPa mean pressure is used as the working gas. The crank mechanism is a combination of an upper and lower yoke, each forming half of a Ross mechanism. The upper yoke is linked to the displacer piston and the lower yoke to the working piston. The design gives an approximately linear couple point curve which eliminates guiding forces on the pistons and the need for X-heads. A grease-lubricated needle and ball bearings are used in the kinematic crank mechanism. The burner includes an air preheater and a water jacket which makes it possible to utilize nearly all of the heat from the combustion gases. The performance of the engine has been tested as a function of mean pressure and hot and cold temperature, and emissions and noise have also been measured.