Compound internal combustion engine

A typical arrangement for a compound ICE is that the fuel/air is first combusted and expanded in one of two alternating 4-stroke combustion high-pressure (HP) cylinders, then having given up heat and losing pressure, it exhausts directly into a larger-volume low-pressure (LP) cylinder, where it is re-expanded extracting more work from it.

The crankshaft is arranged so the two high-pressure cylinders have synchronized reciprocating motion, while the low-pressure cylinder throw is positioned at a 180-degree phase difference from the high-pressure throws causing opposing reciprocating motion between the high-pressure and low-pressure cylinders.

This design was likely created by then Deutz employee Gottlieb Daimler.

The Eisenhuth Horseless Vehicle Company produced a series of automobiles with compound ICEs from 1900 to 1908.

[2] In 2000 the design was "re-patented" as the five-stroke engine by Gerhard Schmitz.