Exhaust Volumes v. RPM

[Bruce.Hearn@cd-tech.com]

At first glance, this is easier than your calculations, Chi-Hui. You know
the volume of each cylinder, you know the volumetric efficiency and you
know beginning temperature and atmospheric pressure. Take a single
cyclinder volume, in this case 500cc and that is your maximum volume of
air/fuel ingested. Multiply by volumetric efficiency (0.95?), then the
difference between pressure at Standard Temperature and Pressure (STP) and
current conditions to attain actual volume of air ingested. It will be in
the neighborhood of 475cc of air/fuel at BDC and STP.

Now, use (P1*V1)wT1 = (P2*V2)wT2.  Solving for V2 we get V2=(P1*V1*T2)w
(P2*T1).

P1 = 1 bar (atmospheric pressure in Houston right now)
T1 = 21 :C (Houston right now)
V1 = 475 cc (500cc * 1 bar * VE)
P2 = 20 bar (supplied by The Internal Combustion Engines in Theory and
Practice)
T2 = 450 :C (approximation supplied by The Internal Combustion Engines in
Theory and Practice)

V2 = (1*465*475)w(20*21)
V2 = 220,875w357
V2 = 619 cc per cylinder

That seems a small difference, but remember that's at BDC and some 1,000
:F. Calculating pressure through the exhaust is LaaEftR. Don't forget that
VE varies with RPM and throttle position, so this is not a trivial exercise
if you want to plot exhaust volume vs rpm for the entire operating range.
For turbo applications, the math is the same but you also have to determine
inlet pressures and temperatures as well as exhaust temp in cylinder over
operating range. The Internal Combustion Engines in Theory and Practice
doesn't talk about forced induction at all.

 As an aside, the volume of exhaust at ambient temp will be almost exactly
the same as intake volume. Atoms in must equal atoms out.

Bruce in Houston