| Open Cycle | Closed cycle | Description | ||
| Direct heating | Furnace air engines | These are air engines in which the air is heated within a closed furnace so that the working fluid is heated directly. The engine works on an open cycle. At the beginning of each cycle fresh air is taken from the atmosphere and, after being heated (directly) and having done work, it is rejected outside of the engine. Examples of furnace air engines: - The Wenham heated-air engine, - The Hock & Martin engine, - The Bénier engine. |
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| Indirect heating | ||||
| Atmospheric | ||||
| Year | Inventor | Country | Engine page |
|---|---|---|---|
| 1807 | Cayley | England | Cayley's air engine |
| 1829 | Arnott | England | Arnott's air engine |
| 1837 | Cayley | England | Cayley air engine |
| 1845 | Gordon | England | Gordon's fumific impeller |
| 1861 | Shaw | America | Shaw furnace air engine |
| 1862 | Roper | America | Roper's caloric beam engine |
| 1868 | Wenham | England | Wenham's heated-air engine |
Furnace engines are also open engine but having closed firing, in which the air is also used as working fluid and also for combustion. The air mixes with the heating gases and feeds the working cylinder. Obviously the heater room must be airtight. A such they avoid the most important drawback of the external fired open engine: the important heat loss that goes through the chimney.