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Superchargers in cars are bulky, expensive, consume considerable amount of engine's power and yet they generate only about 6-9 psi boost. On the other hand, modern common rail diesel engines inject fuel into the cylinder at 36,000 psi. Naturally, superchargers handle a much larger volume, but still the discrepancy is shocking. I suppose it is easier to generate pressure with a liquid which is not compressible, but why exactly is that?

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    $\begingroup$ Just consider the differences in volume flow rate, then think about density and viscosity... All the reasons are there. $\endgroup$
    – Solar Mike
    Sep 13 at 12:21
  • $\begingroup$ @SolarMike a lean air-fuel ratio is 14.7:1. But it is mass ratio. When we convert that to volume ratio, because of the air's 625 times lesser density (compared to gasoline), we get volume ratio of 9187.5:1. Okay, now I think I get it ;) $\endgroup$
    – ciamej
    Sep 13 at 12:51
  • $\begingroup$ Isn't 14.7:1 stoichiometric? $\endgroup$
    – Solar Mike
    Sep 13 at 13:16
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    $\begingroup$ Have you even looked at the size difference between a car and a rail locomotive? $\endgroup$ Sep 13 at 13:27
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    $\begingroup$ @CarlWitthoft I mean en.wikipedia.org/wiki/Common_rail $\endgroup$
    – ciamej
    Sep 13 at 13:49

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