Quote:
Originally Posted by cheesehawk
Interesting, cold air induction does have its merits, but never would have thought it mattered what point you introduced the cold. If it made a 25C difference at the supercharger intake, why couldn't it be the same 25C at the cylinder head?
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The supercharger compresses the charge adiabatically.
In the isentropic case, (T2/T1) = (P2/P1)^((gamma-1)/gamma)
Isentropic Supercharger work = W*Cp*(T2-T1)
Actual Supercharger work = (Isentropic work)/(Isentropic Efficiency)
Reducing the temperature upstream of the supercharger therefore reduces the supercharger work at fixed supercharger efficiency, and therefore increases the overall efficiency of the machine.
Furthermore, because the supercharger temperature ratio is > 1, it follows that the the temperature reduction in the induction manifold will be correspondingly greater than that due to the evaporation of the fuel alone (though in this case the 25 K figure was measured in the induction manifold, the point is that you wouldn't actually get a 25 K temperature drop from direct fuel injection at TDC).