For the compressor maps for automotive turbochargers, the Corrected mass flow rate (at inlet) is given as abscissa. However, I wish to know the mass flow rate at the outlet. What is the relation in between them, given the Pressure ratio (2.5)

  • $\begingroup$ @SolarMike So, is the work done by the compressor not raising the density of the fluid? I mean, the work done is going to be raising the static pressure of the fluid, as well as the dynamic pressure. Wont the rise in static pressure result in an increased density and thus reduced mass flow rate? $\endgroup$ – afterburner77 May 20 '20 at 11:36

The mass flow across a turbocharger is constant:

If X kilogrammes of air go in then X kilogrammes of air come out.

However if the pressure is twice the inlet pressure then the output volume is smaller and the density is higher as well as the temperature is increased. This is one reason there are intercoolers as having too high an inlet temperature reduces the volumetric efficiency.

A good reference for the concepts and formulae you need is Engineering Thermodynamics, Work and Heat Transfer by Rogers & Mayhew (still have my original copy bought some 30 years ago).

  • $\begingroup$ Thanks for the clarification. I reckon by that, I can imply that the output Volumetric Flow rate would increase by a factor of (P1/P2)x(T2/T1). (Through ideal gas law). Would that implication be correct? $\endgroup$ – afterburner77 May 20 '20 at 15:03
  • $\begingroup$ There is also the fuel. For gasoline, the mass ratio is about 14.7 air to fuel. For diesels, the mass ratio varies. Turbos often have dump gates that remove mass when activated, and some of them are a bit leaky. There are also small (and variable) corrections for crankcase venting. $\endgroup$ – Phil Sweet May 20 '20 at 15:51
  • $\begingroup$ No, ideal gas law does not apply because the species are changing. $\endgroup$ – Phil Sweet May 20 '20 at 15:52

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