What is "compound engine"

Compound \Com"pound\,

1. [OE. compouned, p. p. of compounen. See Compound, v. t.] Composed of two or more elements, ingredients, parts; produced by the union of several ingredients, parts, or things; composite; as, a compound word.

   Compound substances are made up of two or more simple substances.
   --I. Watts.

   Compound addition, subtraction, multiplication, division (Arith.), the addition, subtraction, etc., of compound numbers.

   Compound crystal (Crystallog.), a twin crystal, or one seeming to be made up of two or more crystals combined according to regular laws of composition.

   Compound engine (Mech.), a form of steam engine in which the steam that has been used in a high-pressure cylinder is made to do further service in a larger low-pressure cylinder, sometimes in several larger cylinders, successively.

   Compound ether. (Chem.) See under Ether.

   Compound flower (Bot.), a flower head resembling a single flower, but really composed of several florets inclosed in a common calyxlike involucre, as the sunflower or dandelion.

   Compound fraction. (Math.) See Fraction.

   Compound fracture. See Fracture.

   Compound householder, a householder who compounds or arranges with his landlord that his rates shall be included in his rents. [Eng.]

   Compound interest. See Interest.

   Compound larceny. (Law) See Larceny.

   Compound leaf (Bot.), a leaf having two or more separate blades or leaflets on a common leafstalk.

   Compound microscope. See Microscope.

   Compound motion. See Motion.

   Compound number (Math.), one constructed according to a varying scale of denomination; as, 3 cwt., 1 qr., 5 l

2. ; -- called also denominate number.

   Compound pier (Arch.), a clustered column.

   Compound quantity (Alg.), a quantity composed of two or more simple quantities or terms, connected by the sign + (plus) or - (minus). Thus, a + b - c, and bb - b, are compound quantities.

   Compound radical. (Chem.) See Radical.

   Compound ratio (Math.), the product of two or more ratios; thus ab:cd is a ratio compounded of the simple ratios a:c and b:d.

   Compound rest (Mech.), the tool carriage of an engine lathe.

   Compound screw (Mech.), a screw having on the same axis two or more screws with different pitch (a differential screw), or running in different directions (a right and left screw).

   Compound time (Mus.), that in which two or more simple measures are combined in one; as, 6-8 time is the joining of two measures of 3-8 time.

   Compound word, a word composed of two or more words; specifically, two or more words joined together by a hyphen.

A compound engine is an engine that has more than one stage for recovering energy from the same working fluid, with the exhaust from the first stage passing through the second stage, and in some cases then on to another subsequent stage or even stages. Originally invented as a means of making steam engines more efficient, the compounding of engines by use of several stages has also been used on internal combustion engines and continues to have niche markets there.

The stages of a compound engine may be either of differing or of similar technologies, for example:

• In a turbo-compound engine the exhaust gas from the cylinders passes through a turbine, the two stages being dissimilar.
• In a compound steam locomotive the steam passes from the high pressure cylinder or cylinders to the low pressure cylinder or cylinders, the two stages being similar.
• In a triple expansion steam engine the steam passes through three successive cylinders of increasing size and decreasing pressure. Such engines were the most common marine engines in the golden age of steam.

These examples and compound turbines are the main but not the only uses of compounding in engines, see below.