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 ?
Other variable compression ratio (VCR) systems currently developed are more complex and expensive.
72kW Speed 1500 rpm (25rps) Number Of Cylinders 1 Compression Ratio 15:1 TO 20:1 Bore 80 mm Stroke 110 mm Type Of Ignition CI Method Of Loading Eddy Current Dynamometer
From Figure 1, it is clear that the surface contact angle of the compressed poplar without resin increased as the compression ratio of the wood was increased.
The overall ODI Visual Analog Pain Scale (VAS) scores that measure lower back pain and anterior (front) body compression ratios (the length of the spine) did not differ significantly among the groups after 12 weeks.
It is also the first and only intelligent VCR engine with a floating compression ratio as it features integrated hydraulic actuators that provide a wide range, precise and continuous compression ratio control for each cylinder.
The system achieves GZIP compression ratios at an average of three to one.
The lowest NO emission is observed as 250 ppm for neat diesel under the compression ratio of 19 at the brake mean effective pressure of 0.
Compression ratio, press temperature and press holding time were given in Table 1.
A computer-controlled electric motor drives the main shaft," says Last, "and alters the compression ratio based on where the engine is on the curve, and what type of fuel it is running.
Since the screw had a relatively high compression ratio, the unmelted plastic in the compression section created a wedging action between the root of the screw and the barrel, resulting in screw deflection and metal-to-metal contact.
JPEG2000 is the latest still image compression standard available today, designed to increase the compression ratio and quality of digital still images and text, while maintaining the 24-bit color and multi-platform compatibility advantages of the current JPEG standard.
Four hours after finishing first in Sunday's race at Richmond International Raceway, Wallace's victory was put on hold as officials said Wallace's Ford Thunderbird engine had failed tests measuring compression ratio.