Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
1.4
O 1.3 -
DC
DC
111
DC
CD
CO
CO
ID
DC
0_
1.2 -
I '•»
LU
DC 0.9 H
Q_
0.8
1.1
1.0
MEASURED
DIVERGENT TAPER
TIME, seconds
0.00 0.01 0.02 0.03 0.04 0.05 0.06
Fig. 2.44 Measured and calculated pressures at station 2.
MEASURED
DIVERGENT TAPER
TIME, seconds
0.9
0.00 0.01 0.02 0.03 0.04 0.05 0.06
Fig. 2.45 Measured and calculated pressures at station 3.
Actually, as it is a short, steeply tapered pipe there is a close resemblance between the
behavior of this pipe and the sudden contraction discussed in Sec. 2.19.3 and illustrated in
Figs. 2.34 to 2.37. The cylinder release conditions were identical in both cases so the exhaust
pulses which arrived at the discontinuity in areas was the same. Consequently there are great
similarities between Figs. 2.35 and 2.43 for the pressure transducer at station 1, and between
Figs. 2.36 and 2.44 for the pressure transducer at station 2. The records for the tapered pipe
look slightly more "peaky" in certain places. However, that effect is seen more strongly in
Fig. 2.45 where the onward transmission of the residual of the exhaust pulse is observed to
have developed a shock front as it passes the pressure transducer at station 3. In other words,
the tapered pipe has contributed to, and exaggerated, the normal distortion process of a compression
wave profile. It is also interesting to compare the amplitudes of the transmitted and
reflected waves, as the tapered pipe should be more efficient at this than a sudden expansion.
The peak of the suction wave from the tapered pipe undergoing superposition at 0.024 second
at station 1 is 0.68 atm; for the sudden expansion it is 0.74 atm or less strength of expansion
wave reflection. The peak of the transmitted wave from the tapered pipe passing station 3
undisturbed at 0.011 second is 1.08 atm; for the sudden expansion it is 1.05 atm or an exhaust
pulse of reduced strength is delivered farther down the pipe system.
182