compression ratio

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Related to compression ratios: Lossy compression, Lossless compression

compression ratio

[kəm′presh·ən ‚rā·shō]
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.
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 It might be outdated or ideologically biased.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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

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.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved

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 ?
VC-Turbo engine of INFINITI QX50 is the world's first production-ready variable compression ratio engine, transforming on demand.
The VC-Turbo, the world's first variable compression ratio engine, was recognized with high scores at The International Engine + Powertrain of the Year Awards.
Visual Analysis of Plastication Process by Full-Flight Screws with Different Compression Ratios
The VC-Turbo engine is the worlds first production-ready variable compression ratio engine, transforming on demand.
On the other hand, the Haar transform [6] works well for high frequencies and achieves a high compression ratio while maintaining the quality of the image.
Figure 14 shows the variation of the first eigenfrequencies of PCB with various pad compression ratios in each case.
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 shown in Table 2, the pure-tone HF averages were significantly correlated with time-compressed speech recognition scores at compression ratios of both 0.6 and 0.8, and normal speech recognition scores (all p values < 0.05), under both quiet and noisy conditions.
Under lower compression ratios, when greater engine performance is the goal, the engine runs under the regular combustion cycle.