Rotary Steam Engines: Page 9

Updated: 9 Apr 2009
Chapman engine
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With the introduction and development of the steam turbine, which could be regarded as the apotheosis- or more likely the nemesis- of rotary steam engines, the impetus behind the development of positive-displacement rotary engines must have been much reduced, but it did not disappear. The technology appears so seductive that it appears that people will be trying to come up with a workable rotary steam engine until the sun cools. Certainly the patents on rotary engines did not stop coming. See
here for some later patents in Britain and the USA.


Originator: Howard R Chapman (California, USA)

This engine was a "steam engine" powered by Freon. It was intended as part of a bottoming cycle to improve the efficiency of conventional IC engines.

The operation of the Chapman engine
Above: The Chapman engine attached to a conventional IC engine. The eccentric rotor does not rotate; radial sliding seals create six working chambers.

Inlet and exhaust are by multiple valves not shown here. The six things with a star at one end are the cranks that restrain the rotor from rotating; the stars represent the bevel gears that drive the rotary inlet valves- see picture just below. Each seal only wiped a small part of the periphery. They were pressed against the inside of the casing by compression springs.

Image from Popular Science, Jan 1976

The Chapman engine
Left: The Chapman engine mounted on its host internal-combustion engine, and coupled by chains to the output shaft. Note that the relatively low-speed Chapman engine needs to be geared up to match the IC engine output rpm.

Freon vapour is admitted by rotary valves, and leaves by poppet exhaust valves. The former were driven by gears on the multiple cranks restraining the rotor. How the exhaust valves were actuated is not known.

Image from Popular Science, Jan 1976

The Chapman engine
Above: The Chapman engine (green) in its bottoming cycle.

Three hot fluids- engine cooling water, lubricating oil, and the exhaust gases- pass through the boiler (heat exchanger A) and boil the Freon. This generates power as it expands in the Chapman engine. The Freon is then condensed in heat exchanger B by the engine cooling water that has just left the radiator.

Image from Popular Science, Jan 1976

Unlike some bottoming-cycle projects, the Chapman operation received no government funding. Its history is currently unknown, but it is clear that Chapman did not make thing easy for himself by attemping to make a satisfactory rotary engine at the same time as exploring the novelty of automotive bottoming cycles. At least one other bottoming-cycle project, by Thermo Electron, (which did receive government funding) used a three-stage turbine running at 60,000 rpm.

See United States Patent 3,743,451, "Rotary Engine", published 1973

This engine should not be confused with The Chapman Engine of 1810.


The internals of the Henry engine
Left: The internals of the Henry engine. Reproduced by permission.

The Henry engine is mainly aimed at exhaust heat recovery from combustion engines, ie a bottoming cycle.

The aims of the Henry Works are:

  • An engine with a higher efficiency than turbines of the same power rating.
  • A design which is less expensive to produce than a turbine.
  • Similar smooth running characteristics as a turbine.
  • A simple design which is easy to repair or service in the field.
  • Ability to handle wet steam due to its robust parts and slower speeds (3000 RPM).
  • Higher efficiency over much of its RPM range making speed control less critical than in turbines.

See The Henry Engine. (External link)

And now... some unique pictures of the Henry rotary engine prototype undergoing testing.

The Henry engine
Left: First run of the P-4 Henry engine in January 2000.

Personnel: Mike Taggett, George Gubler and Merrill Harker.

Reproduced by permission

The Henry engine
Left: Early field tests of the Henry engine at a boiler company in Tulsa, Oklahoma.

Reproduced by permission.

The Henry engine
Left: Mike Taggett with "Henry P-4" installed at an Ethanol plant in Minnesota.

The engine is powering a 7 HP pump. P-4 accumulated 250 running hours here in January, 2003.

Reproduced by permission.

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