compression ratio

(redirected from compression ratios)
Also found in: Dictionary.
Related to compression ratios: Lossy compression, Lossless compression

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 ?
Compression ratios of 32:1 can still produce images that are useful for some applications.
A higher compression ratio is able to achieve greater efficiency and improved fuel consumption; lower compression ratios offer greater power and torque, particularly in turbocharged engines, but are known for reduced fuel efficiency.
The experiments are carried out at a constant speed of 1500rpm on various loads under steady state conditions using neat diesel and different stable fuel blends (D85E5B10, D80E10B10, D75E15B10, D70E20B10 and D65E25B10) for the compression ratios of 15, 17 and 19.
Maximum compression ratios of softwoods produced in eastern Canada.
The free-piston configuration serves two purposes: It generates electric power and also controls the compression ratio by varying the rate of electrical generation.
In this study, we measured Young's modulus in the radial and tangential directions, and the shear modulus and Poisson's ratio in the cross section of compressed wood with various compression ratios, and examined the influence of compression ratio.