Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
The values of X* X,, ao, ce, and q were 1.0264, 0.9686, 343.1, 45.3, and 53.9, respectively,
in terms of a positive direction for the transmission of each wave. In other words, the
properties of waves pe and pj are to be assigned to waves 1 and 2, respectively, merely to
reduce the arithmetic clutter both within the text and in your mind.
If pi is regarded as moving rightward and that is defined as the positive direction, and
consequently, p2 is moving leftward as in a negative direction, then Eqs. 2.2.1 and 2.2.2 show:
Hence,
Xs = Xi + X2 - 1 = 1.0264 - 0.9868 - 1 = 0.995
ps = xs 7 = 0.965 and ps = Psp0 = 0.965 x 101,325 = 97,831 Pa
cs = 45.3 + [-(-53.9)] = 99.2 m/s
Thus, the pressure transducer in the wall of the pipe would show little of this process, as
the summation of the two waves would reveal a trace virtually indistinguishable from the
atmospheric line, and exhibit nothing of the virtual doubling of the particle velocity.
The opposite effect takes place when two waves of the same type undergo a superposition
process. For example, if wave pi met another wave pi going in the other direction and in the
plane of the pressure transducer, then:
Xs = 1.0264 + 1.0264 - 1 = 1.0528 and Ps = xj = 1.0528 7 = 1.434
cs = 45.3 + [-(445.3)] = 0 m/s
The pressure transducer would show a large compression wave with a pressure ratio of
1.434 and tell nothing of the zero particle velocity at the same spot and time.
This makes the interpretation of exhaust and intake pressure records a most difficult
business if it is based on experimentation alone. Not unnaturally, the engineering observer
will interpret a measured pressure trace which exhibits a large number of pressure oscillations
as being evidence of lots of wave activity. This may well be so, but some of these
fluctuations will almost certainly be periods approaching zero particle velocity also while yet
other periods of this superposition trace exhibiting "calm" could very well be operating at
particle velocities approaching the sonic value! As this is clearly a most important topic, it
will be returned to in later sections of this chapter.
2.2.2 Wave propagation during superposition
The propagation velocity of the two waves during the superposition process must also
take into account direction. The statement below is accurate for the superposition condition
where the rightward direction is considered positive.
where, as = aoXs
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