Example 10 from RP-1311
=======================

.. note:: The python script for this example is available in the `source/bind/python/cea/samples` directory of the CEA repository.

Here we describe how to run example 10 from RP-1311 [1]_ using the Python API.
This is a rocket problem assuming a finite-area combustor (FAC), using normalized mass flow rate :math:`\dot{m} /A_c` to define the combustor area;
the example is otherwise similar to :doc:`Example 9 <example9>`.

First import the required libraries:

.. code-block:: python

    import numpy as np
    import cea

Use :data:`cea.R` inline when normalizing enthalpy.

Declare the reactants and set their amounts and initial temperatures.
Currently, the Python API requires species names to be in bytes format, so we use the `b""` syntax to create byte strings.
The initial reactant temperatures, `T_reactant`, will be used later to compute the chamber enthalpy.
The amounts of each are specified through the `fuel_weights`, `oxidant_weights`, and `of_ratio` variables specified here.
Setting the `fuel_weights` array equal to `[1.0, 0.0]` means that `H2(L)` constitutes 100\% of the fuel, and similarly,
setting the `oxidant_weights` array equal to `[0.0, 1.0]` means that `O2(L)` constitutes 100\% of the oxidant.
These values will be used in conjunction later with `of_ratio` to compute the overall weight fraction array of the reactant mixture.

.. code-block:: python

    reac_names = [b"H2(L)", b"O2(L)"]
    T_reactant = np.array([20.27, 90.17])  # Reactant temperatures (K)
    fuel_weights = np.array([1.0, 0.0])
    oxidant_weights = np.array([0.0, 1.0])
    of_ratio = 5.55157

Next, set some states for the rocket analysis. We will pass these values into the :class:`~cea.RocketSolver` later.

.. code-block:: python

    pc = 53.3172  # Chamber pressure (bar)
    pi_p = [10.0, 100.0, 1000.0]   # Pressure ratio
    supar = [25.0, 50.0, 75.0]  # Supersonic area ratio
    mdot = 1333.9  # Mass flow rate (kg/s)

Instantiate the reactant and product :class:`~cea.Mixture` objects.
To create the product :class:`~cea.Mixture`, we pass the list of reactant names along with the flag `products_from_reactants=True`, which will return the full set of possible product species.

.. code-block:: python

    reac = cea.Mixture(reac_names)
    prod = cea.Mixture(reac_names, products_from_reactants=True)

Now instantiate the :class:`~cea.RocketSolver` and :class:`~cea.RocketSolution` objects.

.. code-block:: python

    solver = cea.RocketSolver(prod, reactants=reac)
    solution = cea.RocketSolution(solver)

Now we will use the reactant :class:`~cea.Mixture` object to compute the overall weight fraction array of the reactants:

.. code-block:: python

    weights = reac.of_ratio_to_weights(oxidant_weights, fuel_weights, of_ratio)

And compute the chamber enthalpy value based on the reactants weights and temperatures. We will pass this in later when we call :meth:`~cea.RocketSolver.solve`.
Note that this value is normalized by `R` here.

.. code-block:: python

    hc = reac.calc_property(cea.ENTHALPY, weights, T_reactant)/cea.R

Now we can solve the :meth:`~cea.RocketSolver.solve` function:

.. code-block:: python

    solver.solve(solution, weights, pc, pi_p, supar=supar, mdot=mdot, iac=False, hc=hc)

Finally, querry the solution variables and print them out:

.. code-block:: python

    num_pts = solution.num_pts
    T = solution.T
    P = solution.P
    rho = solution.density
    enthalpy = solution.enthalpy
    energy = solution.energy
    gibbs = solution.gibbs_energy
    entropy = solution.entropy
    M_1n = solution.M
    MW = solution.MW
    cp_eq = solution.cp_eq
    cp_fr = solution.cp_fr
    cv_eq = solution.cv_eq
    cv_fr = solution.cv_fr
    Mach = solution.Mach
    gamma_s = solution.gamma_s
    v_sonic = solution.sonic_velocity
    ae_at = solution.ae_at
    c_star = solution.c_star
    Cf = solution.coefficient_of_thrust
    Isp = solution.Isp
    Isp_vac = solution.Isp_vacuum

    print("P, bar         ", end=" ")
    for i in range(num_pts):
        if i == 1:  # Skip solution at infinity
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(P[i]), end=" ")
        else:
            print("{0:10.3f}".format(P[i]))

    print("T, K           ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(T[i]), end=" ")
        else:
            print("{0:10.3f}".format(T[i]))

    print("Density, kg/m^3", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(rho[i]), end=" ")
        else:
            print("{0:10.3f}".format(rho[i]))

    print("H, kJ/kg       ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.2f}".format(enthalpy[i]), end=" ")
        else:
            print("{0:10.2f}".format(enthalpy[i]))

    print("U, kJ/kg       ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.2f}".format(energy[i]), end=" ")
        else:
            print("{0:10.2f}".format(energy[i]))

    print("G, kJ/kg       ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.1f}".format(gibbs[i]), end=" ")
        else:
            print("{0:10.1f}".format(gibbs[i]))

    print("S, kJ/kg-K     ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(entropy[i]), end=" ")
        else:
            print("{0:10.3f}".format(entropy[i]))

    print("M, (1/n)       ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(M_1n[i]), end=" ")
        else:
            print("{0:10.3f}".format(M_1n[i]))

    print("MW             ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(MW[i]), end=" ")
        else:
            print("{0:10.3f}".format(MW[i]))

    print("Cp_eq, kJ/kg-K ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(cp_eq[i]), end=" ")
        else:
            print("{0:10.3f}".format(cp_eq[i]))

    print("Cp_fr, kJ/kg-K ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(cp_fr[i]), end=" ")
        else:
            print("{0:10.3f}".format(cp_fr[i]))

    print("Cv_eq, kJ/kg-K ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(cv_eq[i]), end=" ")
        else:
            print("{0:10.3f}".format(cv_eq[i]))

    print("Cv_eq, kJ/kg-K ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(cv_fr[i]), end=" ")
        else:
            print("{0:10.3f}".format(cv_fr[i]))

    print("Gamma_s        ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(gamma_s[i]), end=" ")
        else:
            print("{0:10.3f}".format(gamma_s[i]))

    print("Son. vel., m/s ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.2f}".format(v_sonic[i]), end=" ")
        else:
            print("{0:10.2f}".format(v_sonic[i]))

    print("Mach           ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(Mach[i]), end=" ")
        else:
            print("{0:10.3f}".format(Mach[i]))

    print()
    print("PERFORMANCE PARAMETERS")
    print()

    print("Ae/At          ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(ae_at[i]), end=" ")
        else:
            print("{0:10.3f}".format(ae_at[i]))

    print("C*, m/s        ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.2f}".format(c_star[i]), end=" ")
        else:
            print("{0:10.2f}".format(c_star[i]))

    print("Cf             ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(Cf[i]), end=" ")
        else:
            print("{0:10.3f}".format(Cf[i]))

    print("Isp, vac., m/s ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(Isp_vac[i]), end=" ")
        else:
            print("{0:10.3f}".format(Isp_vac[i]))

    print("Isp, m/s       ", end=" ")
    for i in range(num_pts):
        if i == 1:
            continue
        if i < num_pts-1:
            print("{0:10.3f}".format(Isp[i]), end=" ")
        else:
            print("{0:10.3f}".format(Isp[i]))

    print()

    print()
    print("MOLE FRACTIONS")
    print("")
    trace_species = []
    for prod in solution.mole_fractions:
        if np.any(solution.mole_fractions[prod] > 5e-6):
            print("{0:15s}".format(prod), end=" ")
            for j in range(len(solution.mole_fractions[prod])):
                if j == 1:
                    continue
                if j < len(solution.mole_fractions[prod])-1:
                    print("{0:10.5g}".format(solution.mole_fractions[prod][j]), end=" ")
                else:
                    print("{0:10.5g}".format(solution.mole_fractions[prod][j]))
        else:
            trace_species.append(prod)

    print()
    print("TRACE SPECIES:")
    max_cols = 8
    nrows = (len(trace_species) + max_cols - 1) // max_cols
    for i in range(nrows):
        print(" ".join("{0:15s}".format(trace_species[j]) for j in range(i * max_cols, min((i + 1) * max_cols, len(trace_species)))))

This results in the following output to the terminal:

.. code-block:: console

    P, bar              53.317     44.613     28.269      5.332      0.533      0.053      0.189      0.075      0.044
    T, K              3383.845   3341.127   3179.574   2595.058   1787.250   1136.019   1469.591   1220.872   1089.804
    Density, kg/m^3      2.410      2.044      1.372      0.324      0.047      0.007      0.020      0.010      0.006
    H, kJ/kg          -1026.05   -1238.93   -2206.45   -5291.52   -8467.22  -10561.95   -9526.82  -10306.49  -10698.76
    U, kJ/kg          -3238.68   -3421.28   -4266.22   -6937.12   -9592.53  -11277.13  -10452.00  -11075.09  -11384.84
    G, kJ/kg          -64163.7   -63757.2   -61701.8   -53849.5   -41909.8   -31818.8   -37025.4   -33151.1   -31090.9
    S, kJ/kg-K          18.659     18.712     18.712     18.712     18.712     18.712     18.712     18.712     18.712
    M, (1/n)            12.716     12.729     12.835     13.112     13.205     13.207     13.207     13.207     13.207
    MW                  12.716     12.729     12.835     13.112     13.205     13.207     13.207     13.207     13.207
    Cp_eq, kJ/kg-K       8.325      8.294      7.580      5.024      3.459      2.978      3.225      3.043      2.943
    Cp_fr, kJ/kg-K       3.934      3.926      3.894      3.748      3.414      2.978      3.221      3.043      2.943
    Cv_eq, kJ/kg-K       7.130      7.109      6.515      4.279      2.826      2.349      2.595      2.413      2.313
    Cv_eq, kJ/kg-K       3.280      3.273      3.246      3.114      2.784      2.349      2.591      2.413      2.313
    Gamma_s              1.145      1.144      1.146      1.170      1.224      1.268      1.243      1.261      1.272
    Son. vel., m/s     1591.47    1580.26    1536.49    1387.42    1173.46     952.30    1072.24     984.42     934.25
    Mach                 0.000      0.413      1.000      2.105      3.287      4.586      3.845      4.376      4.708

    PERFORMANCE PARAMETERS

    Ae/At                0.000      1.581      1.000      2.228     11.537     64.771     25.000     50.000     75.000
    C*, m/s            2331.00    2331.00    2331.00    2331.00    2331.00    2331.00    2331.00    2331.00    2331.00
    Cf                   0.000      0.280      0.659      1.253      1.655      1.874      1.769      1.848      1.887
    Isp, vac., m/s       0.000   3997.084   2877.055   3484.187   4149.463   4530.889   4347.670   4486.634   4554.328
    Isp, m/s             0.000    652.501   1536.487   2920.774   3857.762   4367.126   4123.290   4308.233   4398.342


    MOLE FRACTIONS

    H                 0.033498   0.032963   0.027157  0.0088902 0.00024165 1.3303e-07 1.5294e-05 5.7879e-07 5.3925e-08
    H2                 0.29479    0.29453    0.29418    0.29677    0.30037    0.30052    0.30051    0.30052    0.30052
    H2O                0.63456    0.63673    0.65176    0.68895    0.69934    0.69948    0.69948    0.69948    0.69948
    H2O2            5.6145e-06 4.7924e-06 2.5779e-06 1.2808e-07 6.6294e-11 6.6931e-17 3.5562e-13 9.1896e-16 1.3572e-17
    HO2             1.4937e-05 1.3033e-05 6.7146e-06 2.1556e-07 1.5477e-11 1.5329e-19 1.5833e-14  5.339e-18 1.7481e-20
    O                0.0020678  0.0019693  0.0012556 9.1657e-05 2.2451e-08 8.1616e-16 4.0804e-11 2.3271e-14 1.0437e-16
    O2               0.0017218  0.0016506  0.0010882 8.6583e-05  2.316e-08 9.8565e-16 4.4543e-11  2.721e-14 1.2863e-16
    OH                0.033341   0.032143   0.024545  0.0052119 4.1356e-05 2.1439e-09 1.0824e-06 1.4701e-08 6.5803e-10

    TRACE SPECIES:
    O3              H2O(L)          H2O(cr)

.. [1] McBride, B.J., Gordon, S., "Computer Program for Calculation of Complex Chemical Equilibrium Compositions and Applications II. Users Manual and Program Description: Users Manual and Program Description - 2",
    NASA RP-1311, 1996. [NTRS](https://ntrs.nasa.gov/citations/19960044559)