Berkeley CSUA MOTD:Entry 45018
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2006/10/27-30 [Uncategorized] UID:45018 Activity:nil
10/27   When people talk about engines, what exactly is the compression
        ratio and what is the significance?
        \_ http://en.wikipedia.org/wiki/Compression_ratio
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en.wikipedia.org/wiki/Compression_ratio
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. edit Saab Variable Compression engine Because cylinder bore diameter, piston stroke length and combustion chamber volume are almost always constant, the compression ratio for a given engine is almost always constant, until engine wear takes its toll. It does this by replacing the typical one-part engine block with a two-part block, with the crankshaft in the lower block and the cylinders in the upper portion. The Atkinson cycle engine was one of the first attempts at variable compression. Since the compression ratio is the ratio between dynamic and static volumes of the combustion chamber the Atkinson cycle's method of increasing the length of the powerstroke compared to the intake stroke ultimately altered the compression ratio at different stages of the cycle.