What is compression? (pistons)
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edit: I'm so bored....
The compression ratio is a single number that can be used to predict the performance of any engine (such as an internal-combustion engine or a Stirling Engine). It is a ratio between the volume of a combustion chamber and cylinder, when the piston is at the bottom of its stroke and the volume when the piston is at the top of its stroke. The higher the compression ratio, the more mechanical energy an engine can squeeze from its air-fuel mixture. Literally, high ratios place increased oxygen and fuel molecules into a reduced space, thus allowing for increased power at the moment of ignition. Higher compression ratios, however, also make detonation more likely.
The ratio is calculated by the following formula:
, where
b = cylinder bore (diameter)
s = piston stroke length
Vc = volume of the combustion chamber (including head gasket). This is the minimum volume of the space into which the fuel and air is compressed, prior to ignition. Because of the complex shape of this space, it usually is measured directly rather than calculated.
-Due to pinging (detonation), the CR in a gasoline/petrol powered engine will usually not be much higher than 10:1. Recently, with the addition of variable valve timing and knock sensors to delay ignition timing, one worldwide manufacturer is building 10.8 CR gasoline engines that use (U.S.) 87 octane fuel.
-In engines running exclusively on LPG or CNG, the CR may be higher, due to the higher octane rating of these fuels.
-IC racing engines burning methanol and ethanol often exceed a CR of 15:1.
-In engines with a 'ping' or 'knock' sensor and an electronic control unit, the CR can be as high as 13:1 (2005 BMW K1200S)
-In a turbocharged or supercharged engine, the CR is customarily built at 8.5:1 or lower.
-In an auto-ignition diesel engine, the CR will customarily exceed 14:1--and over 22:1 is not uncommon.
more... http://en.wikipedia.org/wiki/Compression_ratio
www.wikipedia.com
edit: I'm so bored....
The compression ratio is a single number that can be used to predict the performance of any engine (such as an internal-combustion engine or a Stirling Engine). It is a ratio between the volume of a combustion chamber and cylinder, when the piston is at the bottom of its stroke and the volume when the piston is at the top of its stroke. The higher the compression ratio, the more mechanical energy an engine can squeeze from its air-fuel mixture. Literally, high ratios place increased oxygen and fuel molecules into a reduced space, thus allowing for increased power at the moment of ignition. Higher compression ratios, however, also make detonation more likely.
The ratio is calculated by the following formula:
, where b = cylinder bore (diameter)
s = piston stroke length
Vc = volume of the combustion chamber (including head gasket). This is the minimum volume of the space into which the fuel and air is compressed, prior to ignition. Because of the complex shape of this space, it usually is measured directly rather than calculated.
-Due to pinging (detonation), the CR in a gasoline/petrol powered engine will usually not be much higher than 10:1. Recently, with the addition of variable valve timing and knock sensors to delay ignition timing, one worldwide manufacturer is building 10.8 CR gasoline engines that use (U.S.) 87 octane fuel.
-In engines running exclusively on LPG or CNG, the CR may be higher, due to the higher octane rating of these fuels.
-IC racing engines burning methanol and ethanol often exceed a CR of 15:1.
-In engines with a 'ping' or 'knock' sensor and an electronic control unit, the CR can be as high as 13:1 (2005 BMW K1200S)
-In a turbocharged or supercharged engine, the CR is customarily built at 8.5:1 or lower.
-In an auto-ignition diesel engine, the CR will customarily exceed 14:1--and over 22:1 is not uncommon.
more... http://en.wikipedia.org/wiki/Compression_ratio
Last edited by 19.3secS2K; Nov 29, 2006 at 06:05 AM.
