Design and Simulation of Two Stroke Engines

The pressure amplitude ratio, Xj, is calculated as:
Chapter 2 - Gas Flow through Two-Stroke Engines
X; = 0.8^ = 0.9686
Therefore, the propagation and particle velocities, otj and q, are found from:
Oi = 343.11 x (6x0.9686-5) = 278.47 m/s
q = 5 x 343.11 x (0.9686-1) = 53.87 m/s
From this it is clear that the propagation of the expansion wave is slower than the reference
acoustic velocity but the air particles move somewhat faster. The expansion wave is
moving rightward along the pipe at 278.47 m/s and, as it passes from particle to particle, it
propels each particle in turn in a leftward direction at 53.87 m/s. This is deduced from the fact
that the numerical values of aj and q are of opposite sign.
The local particle Mach number, Mj, is defined as the ratio of the particle velocity to the
local acoustic velocity, a,, where:
From Eq. 2.1.12,
aj = aoXj
Hence, a} = 343.11 x 0.9686 = 332.3 m/s
and the local particle Mach number is,
M = Z^Z = _0.1621
332.3
The mass rate of gas flow, rh j, caused by the passage of this point of the expansion wave
in a pipe of area, Aj, is calculated by:
From Eq. 2.1.17:
rhj = piAjCj
Pi = Pixf = 1.2049 x 0.9686 5 = 1.2049 x 0.8525 = 1.0272 kg/m 3
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