Internal-combustion engines of the reciprocating type, but irrespective of other structural features, in which the combustible mixture is ignited in the working cylinder at or substantially at atmospheric pressure. The combustible mixture ordinarily begins to enter the working cylinder at the beginning of the working stroke in which case it is ignited at atmospheric pressure, as above, after a definite portion of the working stroke has been performed and the whole charge supplied, the engine thus working upon a two-stroke cycle without compression. The charge may, however, be drawn into the working cylinder by a distinct charging stroke, such stroke being followed by a stroke corresponding with the compression-stroke in four cycle engines during which the exhaust-valve is held open and the charge then ignited under atmospheric pressure at the beginning of the third or working stroke, in which case the engine works upon a four-stroke cycle without compression.
(1) Note. Engines in this subclass working on the two stroke cycle without compression, as above, differ from the majority of the engines occurring in subclass 68, and engines working upon a similar cycle occurring in subclass 61, only in the degree of pressure under which the charge exists before the ignition thereof.
