Design and Simulation of Two Stroke Engines

Chapter 2 - Gas Flow through TwO'Stroke Engines
Reference density Po " 287 x T (2.1.22)
It is interesting that these equations corroborate the experiment which you conducted
with your imagination regarding Fred's lung-generated compression and expansion waves.
Fig. 2.1 shows compression and expansion waves. Let us assume that the undisturbed
pressure and temperature in both cases are at standard atmospheric conditions. In other words,
po and To are 101,325 Pa and 20°C, or 293 K, respectively. The reference acoustic velocity,
an, and reference density, po, are, from Eqs. 2.1.1 and 2.1.3 or Eqs. 2.1.21 and 2.1.22:
a0 = Vl.4 x 287 x 293 = 343.11 m/s
Po
101,325 ,__.. , / 3
= 1.2049 kg/m J
287 x 293
Let us assume that the pressure ratio, Pe, of a point on the compression wave is 1.2 and
that of a point on the expansion wave is Pj with a value of 0.8. In other words, the compression
wave has a pressure differential as much above the reference pressure as the expansion
wave is below it. Let us also assume that the pipe has a diameter, d, of 25 mm.
(a) The compression wave
First, consider the compression wave of pressure, pe. This means that pe is:
Pe = Pe>