Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
Fig. 2.18 Inflow from a pipe to a cylinder or plenum.
C!=0 (2.17.1)
The case of subsonic particle flow will be presented first and that for sonic flow is given
in Sec. 2.17.1.
In Fig. 2.18 the expanding flow from the throat to the cylinder gives pronounced turbulence
within the cylinder. The traditional assumption is that this dissipation of turbulence
energy gives no pressure recovery from the throat of the port or valve to the cylinder. This
assumption applies only where subsonic flow is maintained at the throat.
Pt = Pl
(2.17.2)
On the other hand, the flow from the pipe to the throat is contracting and can be considered
to be isentropic in the same fashion as other contractions debated in Sees. 2.11 and 2.12.
This is summarized on the temperature-entropy diagram in Fig. 2.19 where the gain of entropy
for the flow rising from pressure pt to cylinder pressure pi is clearly visible. The isentropic
nature of the flow from pS2 to pt, a vertical line on Fig. 2.19, can also be observed.
The properties and composition of the gas particles are those of the gas at the superposition
point in the pipe. The various gas properties for cylinder inflow are defined as:
y = y2 R = R2 G5 = G< G7 = G?2 etc.
As usual, the analysis of flow in this context uses, where appropriate, the equations of
continuity, the First Law of Thermodynamics and the momentum equation. However, the
momentum equation is not employed in this particular analysis for subsonic inflow, as the
constant pressure assumption used in Eq. 2.17.2 reflects an even higher gain of entropy, i.e.,
energy dissipation due to turbulence, than would be the case if the momentum equation were
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