# piston.py (Source)

```"""
Two reactors separated by a piston that moves with a speed proportional to the pressure
difference between the reactors.

Gas 1: a stoichiometric H2/O2/Ar mixture
Gas 2: a wet CO/O2 mixture

-------------------------------------
|          ||                       |
|          ||                       |
|  gas 1   ||        gas 2          |
|          ||                       |
|          ||                       |
-------------------------------------

The two volumes are connected by an adiabatic free piston. The piston speed is
proportional to the pressure difference between the two chambers.

Note that each side uses a *different* reaction mechanism

Requires: cantera >= 2.5.0, matplotlib >= 2.0
Keywords: combustion, reactor network, plotting
"""

import sys

import cantera as ct

fmt = '{:10.3f}  {:10.1f}  {:10.4f}  {:10.4g}  {:10.4g}  {:10.4g}  {:10.4g}'
print('{:10}  {:10}  {:10}  {:10}  {:10}  {:10}  {:10}'.format(
'time [s]', 'T1 [K]', 'T2 [K]', 'V1 [m^3]', 'V2 [m^3]', 'V1+V2 [m^3]', 'X(CO)'))

gas1 = ct.Solution('h2o2.yaml')
gas1.TPX = 900.0, ct.one_atm, 'H2:2, O2:1, AR:20'

gas2 = ct.Solution('gri30.yaml')
gas2.TPX = 900.0, ct.one_atm, 'CO:2, H2O:0.01, O2:5'

r1 = ct.IdealGasReactor(gas1)
r1.volume = 0.5
r2 = ct.IdealGasReactor(gas2)
r2.volume = 0.1

# The wall is held fixed until t = 0.1 s, then released to allow the pressure to
# equilibrate.
def v(t):
if t < 0.1:
return 0.0
else:
return (r1.thermo.P - r2.thermo.P) * 1e-4

w = ct.Wall(r1, r2, velocity=v)

net = ct.ReactorNet([r1, r2])

states1 = ct.SolutionArray(r1.thermo, extra=['t', 'volume'])
states2 = ct.SolutionArray(r2.thermo, extra=['t', 'volume'])

for n in range(200):
time = (n+1)*0.001
if n % 4 == 3:
print(fmt.format(time, r1.T, r2.T, r1.volume, r2.volume,
r1.volume + r2.volume, r2.thermo['CO'].X[0]))

states1.append(r1.thermo.state, t=1000*time, volume=r1.volume)
states2.append(r2.thermo.state, t=1000*time, volume=r2.volume)

# plot the results if matplotlib is installed.
if '--plot' in sys.argv:
import matplotlib.pyplot as plt
plt.subplot(2, 2, 1)
plt.plot(states1.t, states1.T, '-', states2.t, states2.T, 'r-')
plt.xlabel('Time (ms)')
plt.ylabel('Temperature (K)')
plt.subplot(2, 2, 2)
plt.plot(states1.t, states1.volume, '-', states2.t, states2.volume, 'r-',
states1.t, states1.volume + states2.volume, 'g-')
plt.xlabel('Time (ms)')
plt.ylabel('Volume (m3)')
plt.subplot(2, 2, 3)
plt.plot(states2.t, states2('CO').X)
plt.xlabel('Time (ms)')
plt.ylabel('CO Mole Fraction (right)')
plt.subplot(2, 2, 4)
plt.plot(states1.t, states1('H2').X)
plt.xlabel('Time (ms)')
plt.ylabel('H2 Mole Fraction (left)')
plt.tight_layout()
plt.show()

else:
print("""To view a plot of these results, run this script with the option --plot""")
```