Help with flammability limit calculation

[Shaun_com]

Hi all,

I am trying to write a Cantera script to plot the flammability limits of a fuel-air mixture.

The script goes as below.

I have declared reservoirs for fuel and air (r_f and r_a) along with a reactor filled with H ions where the streams from fuel and air reservoirs meet. The intention is to initiate reaction with the H ions.

ignitor = ct.Solution('gri30.yaml')
ignitor.TPX = 300, ct.one_atm, 'H:1.0'

fuel_conc = 10  # fuel concentration

reac1 = ct.IdealGasReactor(ignitor)  # reactor

# calculating fuel and air mass flow rates from the fuel concentration
fuel_mdot = fuel_conc/100*fuel.mean_molecular_weight
air_mdot = (1-fuel_conc/100)*air.mean_molecular_weight

mfc_fuel = ct.MassFlowController(r_f, reac1, mdot=fuel_mdot)
mfc_air = ct.MassFlowController(r_a, reac1, mdot=air_mdot)
                         
outlet = ct.Valve(reac1, downstream, K=1.0)

sim = ct.ReactorNet([reac1])

tfinal = 6.0
tnow = 0.0
while tnow < tfinal:
    tnow = sim.step()

I later define the mixture as being flammable if the resulting temperature is above the reservoir temperature

This is giving me values close to experimental values for most fuels but there are some deviations eg. CH4 upper flammability limit from the code is 17% instead of 15% and C2H6 upper flammability limit from the code is 18% instead of 13%.

Can you please take a look at this script and provide some feedback about the mistake here. Should I change the solution strategy or just some error in the code?

Thank you for your help.

[Bryan Weber]

Hi,

I don't see anything particularly wrong with the script. What are you comparing the flammability limits to? If you're comparing to experiments, you need to keep in mind that experimental facilities suffer from effects such as wall quenching and heat transfer that will tend to reduce the flammability limit compared to the ideal simulation. You also want to keep in mind the error bars on the experimental data points as well as the simulations (due to uncertainty in the kinetics parameters).

Best,

Bryan

[Shaun_com]

Hi Bryan,

Thank you for the help. Yes, I agree that the walls have a substantial effect in experiments. I was just going by the usual limits that are quoted in literature.

Kind regards,

Shaun