
Ideal Adiabatic Analysis Lessons learned 
One of the first things I used the online program first was to try out
variations of the Ross90.dat engine. Here are the input data to the program :
Engine Type ( alpha, beta, gamma )
Gas
Average pressure [kPa]
Temp in heater [K]
Temp in kooler [K]
Volume Phase Lag [°]
Clearance volume, compression space [cm³]
Swept volume, compression space [cm³]
Clearance volume, expansion space [cm³]
Swept volume, expansion space [cm³]
Kooler volume [cm³]
Regenerator volume [cm³]
Heater volume [cm³]

alpha
air
200
923
300
95.5690
8.0
61.0450
10.00
61.045
31.21
34.8900
28.5100

All of the statements made below must be taken with the
thought in mind that the ideal adiabatic model used does not investigate
whether the heater, regenerator, and kooler can indeed facilitate the
calculated heats. It is implicitely assumed that they can. Heat transfer
calculations are an entirely new ball game.
Changing mean pressure and working gas
Changing the mean pressures doubles the value of all relevant parameters
except that of the efficiency which stays constant. This result could have
been already obtained by inspection of the governing differential equations.
Changing the type of gas is a little bit more complex. The data are
identical for air (the original version) and hydrogen, except for the mass
of gas inside the engine. The reason for having essentially no difference in
engine performance is related to the fact that both gases have two atoms
per molecule and with that the ratio of specific heat capacities is (nearly)
identical (1.4).
Helium and Argon give again identical performance values because they
are both monoatomic gases with a ratio of specific heat capacities of 1.667.
They have though slightly lower efficiency than the airH2 pair (0.5992 vs.
0.625) but at identical net work of 3.706 J. The penalty is a higher demand
for heat supplied by the heater ( 6.184 vs. 5.93 J ) and higher heat rejection
in the kooler ( 2.48 vs 2.22 J ). The most dramatic effect is on the
demands on the regenerator. The heat in and out of the regenerator has
dropped from 32.46 J for air/H2 to 22.91 J for the Helium/Argon pair.
 Ross90.dat  Double Pressure 
Hydrogen  Helium  Argon 
Net work [J]  3.706  7.412 
3.706  3.706  3.706 
Efficiency []  0.6251  0.6251 
0.6246  0.5992  0.5992 
Work, expansion space [J]  5.929  11.86 
5.934  6.184  6.184 
Work, compression space [J]  2.222  4.445 
2.228  2.479  2.479 
Heater, heat transfer [J]  5.928  11.86 
5.934  6.184  6.184 
Kooler, heat transfer [J]  2.222  4.445 
2.228  2.479  2.479 
Total mass of gas [g]  0.2496  0.4991 
0.01737  0.03460  0.3455 
Mean Pressure [Pa]  2.000e+5  4.000e+5 
2.000e+5  2.000e+5  2.000e+5 
Max Pressure [Pa]  2.733e+5 [Pa]  5.466e+5 
2.733e+5  2.761e+5  2.761e+5 
Min Pressure [Pa]  1.434e+5 [Pa]  2.867e+5 
1.433e+5  1.402e+5  1.402e+5 
Regenerator, heat into gas [J]  32.46  64.93 
32.17  22.91  22.91 
Regenerator, heat out of gas [J]  32.46  64.93 
32.17  22.91  22.91 
Changing the volume phase lag
We keep all the original ross90.dat except for the volume phase lag which in
the original version was at 95.569°. The remarkable feature of the table
below is that there is a wide range of possible angles without having to pay
a severe penalty as fas as net work is concerned. The volume phase lag
with the highest network of 3.711 J (not shown in the table) is at some 93°.
A little bit of surprise is that the efficiency is rising almost linearly
even over the entire range investigated, even beyond the point of highest
net work. Maximum and minimum mean engine pressure show similar behavior
and the heat demand on the regenerator increases steadily with increasing
volume phase lag.
Phase lag  75  85° 
95.569°  105°  115° 
Net work [J]  3.541  3.678 
3.706  3.628  3.439 
Efficiency []  0.6188  0.6218 
0.6251  0.6283  0.6317 
Work, expansion space [J]  5.722  5.915 
5.929  5.774  5.443 
Work, compression space [J]  2.182  2.237 
2.222  2.146  2.004 
Heater, heat transfer [J]  5.722  5.915 
5.928  5.774  5.443 
Kooler, heat transfer [J]  2.182  2.237 
2.222  2.146  2.005 
Total mass of gas [g]  0.2478  0.2487 
0.2496  0.2504  0.2512 
Mean Pressure [Pa]  2.000e+5  2.000e+5 
2.000e+5  2.000e+5  2.000e+5 
Max Pressure [Pa]  2.830e+5  2.784e+5 
2.733e+5  2.687e+5  2.639e+5 
Min Pressure [Pa]  1.376e+5  1.403e+5 
1.434e+5  1.462e+5  1.492e+5 
Regenerator, heat into gas [J]  26.75  29.65 
32.46  34.72  36.85 
Regenerator, heat out of gas [J]  26.75  29.65 
32.46  34.72  36.85 
Changing the ratio of swept volumes of compression and expansion space
The original ross90.dat version has a ratio of the swept volume
of the expansion space, V_{swe}, to that of the compression space,
V_{swc}, of 1. Here we change the ratio but keep the sum of the two
at a constant value of 2*61.0450 = 122.09 cm³.
Again, changes in all listed parameters are faiirly small over a wide range
of change in the ratio between compression and expansion space. The net work
produced peakes at a ratio of about 1.20. The efficiency seems to be increasing
monotonically with ever increasing burden on the regenerator.
V_{swe}/V_{swc}  0.75  1.00 
1.25  1.50  1.75 
Net work [J]  3.538  3.706 
3.731  3.680  3.589 
Efficiency []  0.6172  0.6251 
0.6298  0.6329  0.6353 
Work, expansion space [J]  5.733  5.929 
5.924  5.814  5.650 
Work, compression space [J]  2.195  2.222 
2.193  2.134  2.061 
Heater, heat transfer [J]  5.733  5.929 
5.924  5.814  5.650 
Kooler, heat transfer [J]  2.195  2.222 
2.193  2.134  2.061 
Total mass of gas [g]  0.2544  0.2496 
0.2455  0.2421  0.2392 
Mean Pressure [Pa]  2.000e+5  2.000e+5 
2.000e+5  2.000e+5  2.000e+5 
Max Pressure [Pa]  2.830e+5  2.733e+5 
2.668e+5  2.621e+5  2.585e+5 
Min Pressure [Pa]  1.379e+5  1.434e+5 
1.472e+5  1.501e+5  1.523e+5 
Regenerator, heat into gas [J]  31.07  32.46 
33.18  33.76  34.18 
Regenerator, heat out of gas [J]  31.07  32.46 
33.18  33.76  34.18 
Repeating previous investigation but at a heater temperature of 400 K.
Not much of a change here.
V_{swe}/V_{swc}  0.75  1.00 
1.25  1.50 
Net work [J]  0.6189  0.6467 
0.6434  0.6255 
Efficiency []  0.1493  0.1534 
0.1550  0.1554 
Work, expansion space [J]  4.143  4.215 
4.151  4.024 
Work, compression space [J]  3.524  3.569 
3.507  3.398 
Heater, heat transfer [J]  4.134  4.215 
4.151  4.024 
Kooler, heat transfer [J]  3.524  3.569 
3.507  3.398 
Total mass of gas [g]  0.3459  0.3440 
0.3423  0.3407 
Mean Pressure [Pa]  2.000e+5  2.000e+5 
2.000e+5  2.000e+5 
Max Pressure [Pa]  2.644e+5  2.613e+5 
2.603e+5  2.602e+5 
Min Pressure [Pa]  1.486e+5  1.504e+5 
1.511e+5  1.512e+5 
Regenerator, heat into gas [J]  8.644  9.572 
10.25  10.77 
Regenerator, heat out of gas [J]  8.643  9.572 
10.25  10.77 
