Heinrici 80 mm hot air engine.

Heinrici 80 mm hot air engine.

Type: Closed (Stirling) cycle unpressurised hot air engine.
Piston Dia.: 80mm.  Stroke: 88mm. Swept volume: 442cc Flywheels diameter: 332mm.
Layout: Inverted vertical, concentric piston and displacer (beta configuration).
Power: Fractional; (50watts at 350rpm would be optimistic).

History: Collected (with two others) from Temuka, believed to have been used for pumping town gas.

Made in Zwickau, Germany, most likely around 1920 (there is no engine number).  

 It has a town gas burner (this model could also burn kerosene, wood or coal).

 Heinrici hot air engines are of the valveless, closed cycle type, generally called Stirling cycle engines, after Robert Stirling, the Scottish Presbyterian minister who pioneered their development in the early 1800’s.  They operate by alternate heating and cooling a quantity of air, called the working fluid, contained in the engine’s internal spaces.  Heat is applied externally and passes through the cylinder wall, heating the working fluid, which is then expanded against a piston to do mechanical work.  After heating and expanding, the working fluid is moved to a cool space where it cools and contracts before being returned to the hot space for the cycle to repeat. 

It has a displacer (just a loose piston), below and in the same cylinder as the power piston to which it is connected via cranks and linkages so as to lead by 90degrees of crankshaft angle.  The heated and cooled spaces are connected by the annular gap around the loose-fitting displacer so that the working fluid moves between these spaces and changes volume by the appropriate ratio as the engine rotates.  Because they have no valves and experience no sudden pressure changes, Stirling engines are noted for quietness and reliability.

 Most Heinricis in New Zealand were imported by Bradley Bros Ltd, a firm of Christchurch Glaziers in the early 20th century.  They re-badged them to the Bradley name.  Heinricis were made in Zwickau Germany from 1884 through to the 1930s.  By 1914 they had sold 21,000 engines in 12 sizes ranging from 26mm to 190mm bore.   Built to a high standard, their most popular engine was the 65mm bore model. Their smaller engines had insufficient power for most practical applications but were used to pump water or gas (including “petrol” gas used at some remote NZ sites) and to operate sewing machines and dentist’s drills. There are also 65mm bore and 55mm bore Heinricis in this collection.

This engine was collected and restored by Roger Mahan.  It has a wall mounted heater surround- thought to have been supplied by Bradleys, the importers.  It is currently mounted on a stand from a 5” Ericsson hot air engine.  

 Peter Lynn for the Mahan Heritage Centre, July 2023