compression ratio
Noun
Meaning
(automotive) The ratio of the volume between the cylinder head of an internal combustion engine and the piston before and after the compression stroke.
(computing) The ratio of the size of compressed data to the size of the original uncompressed data.
Source: en.wiktionary.orgExamples
A bit rate of 128 kbit/s is commonly used, at a compression ratio of 11:1, offering adequate audio quality in a relatively small space.
A higher octane rating allows a higher compression ratio or supercharger boost, and thus higher temperatures and pressures, which translate to higher power output.
Also, increased mechanical efficiency is created by a higher compression ratio through the concomitant higher expansion ratio on the power stroke, which is by far the greater effect.
An Atkinson cycle engine uses the timing of the valve events to produce the benefits of a high expansion ratio without the disadvantages, chiefly detonation, of a high compression ratio.
Comparing the two formulae it can be seen that for a given compression ratio ( r ), the ideal Otto cycle will be more efficient.
Boost pressures can be higher on diesels than on petrol engines, due to the latter's susceptibility to knock, and the higher compression ratio allows a diesel engine to be more efficient than a comparable spark ignition engine.