Let's Talk ALGORITHMS

[atsakiri at ford.com]

> This is the equation Bicking gives for calculating Mass Flow Rate using
> speed-density.
> 
> Known		V   = Per-cylinder Nominal Displacement
> Known		Ra  = Gas Constant of Air
> Measured	RPM = Engine Speed
> Measured	Ta  = Intake Air Temperature
> Measured	P   = Intake Manifold Pressure
> 		n   = Volumetric Effieciency
> Calculated	Ma  = Mass Flow Rate
> 
> 
> 	Ma = (RPM)*V*n*P
> 	      ---------
> 	      (Ra)*(Ta)
> 

Two comments:

a) There's a "2" missing in this equation if it's for a four stroke
   engine.  There are 2 revolutions per cycle (i.e. 2 revs per V 
   displacement).  Beware of units trouble.

b) This will give the flow rate per cylinder (as opposed to total
   engine flow).

> Here are questions I have.
> 
> 1)  What is meant by the Gas Constant of Air?

Just thought I'd toss in the numbers I have at my desk.
These are from Heywood's Internal Combustion Engine Fundamentals.

 _
 R = universal gas constant = 8.3143 J/(mole K)


 Ra = gas constant for air

      _
    = R/M  (where M = molecular mass of air)


       8.3143 J    mole
    = ---------------------- = 0.287 J/(kg K)
       mole K     28.962 kg



---
Anthony Tsakiris

The opinions expressed are my own and not necessarily those of my employer.