# compression ratio

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## compression ratio

[kəm′presh·ən ‚rā·shō]
(electronics)
The ratio of the gain of a device at a low power level to the gain at some higher level, usually expressed in decibels. Also known as compression.
(mechanical engineering)
The ratio in internal combustion engines between the volume displaced by the piston plus the clearance space, to the volume of the clearance space. Also known as compression.
(metallurgy)
Ratio of the volume of loose metal powder to the volume of the compact made from it.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

## Compression Ratio

the ratio of the volume of the working fluid at the beginning of compression in the cylinder of an internal-combustion engine to the volume at the end of compression. The working fluid in carburetor engines is an air-fuel mixture; in diesel engines it is air. An increase in the compression ratio causes a decrease in the volume of the working fluid at the end of the compression stroke; the pressure and temperature of the working fluid are increased correspondingly, combustion is accelerated, and heat losses are reduced. A higher compression ratio increases the power output of an engine and improves fuel economy. However, increases in the compression ratio are limited by the fuel’s ability to prevent detonation. Compression ratios for carburetor engines range from 6.5:1 to 9.5:1; those for diesel engines are between 16:1 and 21:1.

## Compression ratio

In a cylinder, the piston displacement plus clearance volume, divided by the clearance volume. This is the nominal compression ratio determined by cylinder geometry alone. In practice, the actual compression ratio is appreciably less than the nominal value because the volumetric efficiency of an unsupercharged engine is less than 100%, partly because of late intake valve closing. In spark ignition engines the allowable compression ratio is limited by incipient knock at wide-open throttle. See Combustion chamber, Internal combustion engine

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.

## compression ratio

i. The ratio of the volume of fuel-air mixture in a reciprocating engine when the piston is at the bottom dead center to the volume when it is at the top dead center. It is the ratio of the cylinder volume at the end of the intake stroke to the cylinder volume at the end of the compression stroke.
ii. The ratio of the compressor discharge pressure to the compressor inlet pressure. Also called compressor pressure ratio.

## compression ratio

The measurement of compressed data. For example, a file compressed into 1/4th of its original size can be expressed as 4:1, 25%, 75% or 2 bits per byte. See archive program and data compression.
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References in periodicals archive ?
In the compression zone, at a compression ratio of 2.2 (screw FF2), and in the feed zone, at a compression ratio of 2.75 (screw FF3), the long pellets were aligned at approximately 10[degrees] from the orthogonal direction to the flight inclination angle, decreasing the cohesion of the SB.
The relation between m and the compression ratio (CR) for the Boat image is shown in Fig.
A high compression ratio gives greater efficiency while a low compression ratio allows for greater power and torque.
Figures 15 shows the results of random vibration analysis, demonstrating the maximum values of the PCB in-plane principal strain according to the compression ratio of the pad in each case, respectively.
The performance of the adhesive interfaces is crucial in developing a monolithic action for the double-superposed shear wall under different axial compression ratios, especially under high axial compression ratio.
As a result the 15-liter engine with automatic compression ratio changes from 8 to 15:1 [20].
Data from the NH and eight HF SNHL groups in quiet were subjected to two-way repeated-measures ANOVA to test the effects of group and time compression ratio on speech recognition.

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