ENGINE. A motor or prime mover which is capable of utilizing natural forces, such as the pressure of steam or the expansion of a gas, and converting those forces into mechan ical energy in the form of motion, which may be employed for doing mechanical work, thus distinguishing it from a ((machine,l) which can receive motion only from a motor or engine external to itself.
The term engine was originally used in the sense of a machine, a usage which survives in rose-engine and cotton-gin (gin being simply a short form for engine). The first textile ma chines were called engines, and we still speak of engines of war. But when steam engine be came familiarly shortened to engine, the term was confusing, and gradually machine was sub stituted for the word engine in nearly all uses except for generation of power.
All heat engines act through the medium of a working substance which absorbs heat, con verts a portion of that heat into mechanical energy, which is represented by the work per formed by the engine, and rejects the remaining portion of the heat, still in the form of heat. The working substance may be a gas, a liquid or a solid. The various successful forms of heat engines may be conveniently grouped into three general classes — steam en gines, gas and oil engines, turbines and rotary engines.
Steam In ordinary forms of steam engines the working substance is sat urated steam, a fluid consisting of a mixture of water and steam in varying proportions, the expansive energy of which is utilized to drive or impart motion to a piston working within a cylinder.
Miscellaneous Many engines are named from some distinctive feature of their mechanism or a peculiarity of construction. Hence there is the automatic engine, one that is self-regulating, requiring little attention. In a stationary engine this would mean one that regulated its own speed or point of cut-off; in an automobile engine it would mean one that would run without attention, as long as the gasoline feed, carburetor, spark-plug, etc., were in order. A cut-off engine is one in which the steam or motive fluid is cut off before the end of the stroke. A quadrant engine is one
having a piston that moves in a quadrangular chamber. A reciprocating engine is the most ordinary type, in which the piston moves back and forth. A direct-connected engine is one that has the crank-shaft extended to form the main shaft of a dynamo. A multi-cylinder en gine is one having several cylinders operating on the same shaft, as a 6- or 8-cylinder auto mobile engine. A self-contained engine is one in which the engine and boiler are both housed in one framework. A screw or propeller en gine is a marine engine for driving a screw propeller. A series-expansion engine is one having several cylinders in which the steam or motive fluid is successively expanded. A twin finder engine is one having two cylinders formed in one casting or
One in which the piston speed is slow, according to some authori ties, less than 600 feet per minute.
One in which the pressure of the steam is exerted only on one side of the piston, which is forced back again by the pressure of the atmosphere on the other side against the vacuum produced by the con densation of the spent steam. They were merly used chiefly for pumping purposes, and in connection with steam hammers, but are now practically out of date.
One in which the steam in the cylinder is exhausted into the piston, either against the pressure of the air, or against the vacuum of the condenser. Origi nally, all engines were made single-acting, but nearly all modern steam engines are double acting.