Opposed-flow diffusion flame

This example uses the CounterFlowDiffusionFlame function to solve an opposed-flow diffusion flame for Ethane in Air. This example is the same as the diffusion_flame.py example without radiation.

Tags: Matlab combustion 1D flow diffusion flame plotting

Initialization

clear all
close all

tic % total running time of the script
help diff_flame

runtime = cputime; % Record the starting time

Parameter values of inlet streams

p = OneAtm; % Pressure
tin = 300.0; % Inlet temperature
mdot_o = 0.72; % Air mass flux, kg/m^2/s
mdot_f = 0.24; % Fuel mass flux, kg/m^2/s
transport = 'mixture-averaged'; % Transport model
% NOTE: Transport model needed if mechanism file does not have transport
% properties.

Set-up initial grid, loglevel, tolerances. Enable/Disable grid refinement

initial_grid = 0.02 * [0.0, 0.2, 0.4, 0.6, 0.8, 1.0]; % Units: m
tol_ss = {1.0e-5, 1.0e-9}; % {rtol atol} for steady-state problem
tol_ts = {1.0e-3, 1.0e-9}; % {rtol atol} for time stepping
loglevel = 1; % Amount of diagnostic output (0 to 5)
refine_grid = 1; % 1 to enable refinement, 0 to disable

Create the gas objects for the fuel and oxidizer streams

These objects will be used to evaluate all thermodynamic, kinetic, and transport properties.

fuel = Solution('gri30.yaml', 'gri30', transport);
ox = Solution('gri30.yaml', 'gri30', transport);
oxcomp = 'O2:0.21, N2:0.78'; % Air composition
fuelcomp = 'C2H6:1'; % Fuel composition
% Set each gas mixture state with the corresponding composition.
fuel.TPX = {tin, p, fuelcomp};
ox.TPX = {tin, p, oxcomp};

Set-up the flow object

For this problem, the AxisymmetricFlow model is needed. Set the state of the flow as the fuel gas object. This is arbitrary and is only used to initialize the flow object. Set the grid to the initial grid defined prior, same for the tolerances.

f = AxisymmetricFlow(fuel, 'flow');
f.P = p;
f.setupGrid(initial_grid);
f.setSteadyTolerances('default', tol_ss{:});
f.setTransientTolerances('default', tol_ts{:});

Create the fuel and oxidizer inlet steams

Specify the temperature, mass flux, and composition correspondingly.

% Set the oxidizer inlet.
inlet_o = Inlet(ox, 'air_inlet');
inlet_o.T = tin;
inlet_o.massFlux = mdot_o;
inlet_o.setMoleFractions(oxcomp);

% Set the fuel inlet.
inlet_f = Inlet(fuel, 'fuel_inlet');
inlet_f.T = tin;
inlet_f.massFlux = mdot_f;
inlet_f.setMoleFractions(fuelcomp);

Create the flame object

Once the inlets have been created, they can be assembled to create the flame object. Function CounterFlorDiffusionFlame (in Cantera/1D) sets up the initial guess for the solution using a Burke-Schumann flame. The input parameters are: fuel inlet object, flow object, oxidizer inlet object, fuel gas object, oxidizer gas object, and the name of the oxidizer species as in character format.

fl = CounterFlowDiffusionFlame(inlet_f, f, inlet_o, fuel, ox, 'O2');

Solve with fixed temperature profile

Grid refinement is turned off for this process in this example. To turn grid refinement on, change 0 to 1 for last input is solve function.

fl.solve(loglevel, 0);

Enable the energy equation

The energy equation will now be solved to compute the temperature profile. We also tighten the grid refinement criteria to get an accurate final solution. The explanation of the setRefineCriteria function is located on cantera.org in the Matlab User’s Guide and can be accessed by help setRefineCriteria.

f.energyEnabled = true;
fl.setRefineCriteria(2, 200.0, 0.1, 0.2);
fl.solve(loglevel, refine_grid);

Show statistics of solution and elapsed time

fl.writeStats;
elapsed = cputime - runtime;
e = sprintf('Elapsed CPU time: %10.4g', elapsed);
disp(e);

Plot results

Make a single plot showing temperature and mass fraction of select species along axial distance from fuel inlet to air inlet.

z = fl.grid('flow'); % Get grid points of flow
spec = fuel.speciesNames; % Get species names in gas
T = fl.getSolution('flow', 'T'); % Get temperature solution

for i = 1:length(spec)
    % Get mass fraction of all species from solution
    y(i, :) = fl.getSolution('flow', spec{i});
end

j = fuel.speciesIndex('O2'); % Get index of O2 in gas object
k = fuel.speciesIndex('H2O'); % Get index of H2O in gas object
l = fuel.speciesIndex('C2H6'); % Get index of C2H6 in gas object
m = fuel.speciesIndex('CO2'); % Get index of CO2 in gas object

clf;
yyaxis left
plot(z, T)
xlabel('z (m)');
ylabel('Temperature (K)');
yyaxis right
plot(z, y(j, :), 'r', z, y(k, :), 'g', z, y(l, :), 'm', z, y(m, :), 'b');
ylabel('Mass Fraction');
legend('T', 'O2', 'H2O', 'C2H6', 'CO2');

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