Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
No.
1
2
3
4
5
Table 2.16.2 Output from calculations of outflow from a cylinder
Pr2
1.0351
1.036
1.554
1.528
1.538
Ps2
1.0351
1.036
1.554
1.672
1.392
TS2°C
999.9
999.9
486.4
492.5
479.9
Pt
2.676
2.641
1.319
1.546
1.025
Tt °C
805.8
787.8
440.0
469.5
392.9
ms2 g/s
3.54
3.66
85.7
68.1
94.3
Table 2.16.3 Further output from calculations of outflow from a cylinder
No.
1
2
3
4
5
Ct
663.4
652.9
372.0
262.9
492.7
M,
1.0
1.0
0.69
0.48
0.945
CS2
18.25
18.01
175.4
130.5
213.5
Ms2
0.025
0.025
0.315
0.234
0.385
aoi & aot
582.4
568.3
519.6
519.6
519.6
ao2
717.4
711.5
525.1
522.1
530.5
The input data for test numbers 1 and 2 are with reference to a "blowdown" situation
from gas at high temperature and pressure with a small-diameter port simulating a cylinder
port or valve that has just commenced its opening. The cylinder has a pressure ratio of 5.0 and
a temperature of 1000°C. The exhaust pipe diameter is the same for all of the tests, at 30 mm.
In tests 1 and 2 the port diameter is equivalent to a 3-mm-diameter hole and has a coefficient
of discharge of 0.90. The gas in the cylinder and in the exhaust pipe in test 1 has a purity of
zero, i.e., it is all exhaust gas.
The purity defines the gas properties as a mixture of air and exhaust gas where the air is
assumed to have the properties of specific heats ratio, y, of 1.4 and a gas constant, R, of 287 J/
kgK. The exhaust gas is assumed to have the properties of specific heats ratio, y, of 1.36 and
a gas constant, R, of 300 J/kgK. For further explanation see Eqs. 2.18.47 to 2.18.50.
To continue, in test 1 where the cylinder gas is assumed to be exhaust gas, the results of
the computation in Tables 2.16.2 and 2.16.3 show that the flow at the throat is choked, i.e., Mt
is 1.0, and that a small pulse with a pressure ratio of just 1.035 is sent into the exhaust pipe.
The very considerable entropy gain is evident by the disparity between the reference acoustic
velocities at the throat and at the pipe, aot and ao2, at 582.4 and 717.4 m/s, respectively. It is
clear that any attempt to solve this flow regime as an isentropic process would be very inaccurate.
The presentation here of a non-isentropic analysis with variable gas properties is unique
and its importance can be observed by a comparison of the results of tests 1 and 2. Test data
set 2 is identical to set number 1 with the exception that the purity in the cylinder and in the
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