Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
As the mass flow is found from:
ms = psAcs = G5as(X! - X2)Ap0X G5
s
the transmitted pressure amplitude ratios, X\f and X2f, and superposition particle velocity,
csf, are related by:
x sf = ( x lf + x 2f " 1) and c sf = G 5 a o( x lf " x 2f)
The momentum and continuity equations become two simultaneous equations for the two
unknown quantities, Xif and X2f, which are found by determining csf,
?sf = cs + Psf " Ps (2.3.5)
Ps c s
i + xsf+- c ^
whence x G 5 a Q (2.3.6)
"If
and X2f=l+Xsf-Xif (2-3.7)
Consequently the pressures of the ongoing pressure waves pif and p2f after friction has
been taken into account, are determined by:
Plf = Po x Pf ? and P2f = Po x 2f ? < 2 - 3 - 8 )
Taking the data for the two pressure waves of amplitude 1.2 and 0.8 which have been
used in previous sections of this chapter, consider them to be superposed in a pipe of 25 mm
diameter with the compression wave pi moving rightward. The reference conditions are also
as used before at To is 20°C or 293K and po as 101,325 Pa. However, pressure drop occurs
only as a result of particle movement so it is necessary to define a time interval for the superposition
process to occur. Consider that the waves are superposed at the pressure levels
indicated for a period of 2° crankshaft in the duct of an engine running at 1000 rpm. This
represents a time interval, dt, of:
or dt = = 0.333 x 10" 3 s
6x1000
6 60 0
dt = x — = — s (2.3.9)
360 N 6N
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