# 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.

## 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

## 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.
References in periodicals archive ?
A high compression ratio gives greater efficiency while a low compression ratio allows for greater power and torque.
As the angle of the multi-link arms changes, it adjusts the top-dead-center position of the pistons and the compression ratio with them.
In addition, the contribution of the reformed gas composition increase in the order of compression ratio, initial temperature, and equivalence ratio.
Lossy compression loosens the tolerable observation error margins to achieve the flexibility on trading off between reconstruction accuracy for higher compression ratio and less energy consumption, which can lengthen the lifetime of wireless sensors in turn.
The tolerance optimization for the compression ratio is reviewed briefy, the Gaussian process modeling approach is presented in detail, and the applied S-MDO method is also introduced.
3 The compression ratio according to the lifting-wavelet used
Higher compression ratios maximize the amount of power generated by a given amount of fuel, but only up to a point.
From these two figures it can be seen that the tendency of water sorption for compressed poplar rose gradually as the compression ratio increased during the second stage.
For the testing of the CsME on the engine the experimental setup was prepared, which consists of Variable Compression Ratio diesel engine, Exhaust gas analyzer, Smoke meter, data acquisition system to generate P-[theta].
And one of the key features affecting thermal efficiency is the compression ratio, which is always a compromise in fixed compression ratio spark ignition engines.
Once scanning resolution and compression ratio standards were established, the maps were scanned without making much effort in color balancing, image cleaning, or other changes in image processing software.
The old 3:1 or 4:1 compression ratio for plastics and 2:1 or 2.

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