Modeling Secondary Air Injection in NH3/Air Combustion using FreeFlame — How to reflect staged injection?

[서준]

Hi all,

I’m trying to simulate NH₃/Air premixed combustion with staged air injection using the FreeFlame class in Cantera. Specifically:

What I’m trying to do

• Set primary equivalence ratio Φ₁ = 0.9 in the flame front before secondary air injection.

• Inject secondary air at 80 mm, resulting in a total equivalence ratio Φ_total = 0.8.

• Analyze the mole fractions (especially NO, NO₂) downstream (e.g., at 160 mm or 200 mm).

Setup

• Injector type: coaxial shear injector

  • NH₃ annular jet: inner diameter = 2.8 mm, outer diameter = 3.44 mm

  • Center air jet: diameter = 2.0 mm

• Reynolds number = 2000 for both streams

• T₀ = 300 K, P₀ = 1 atm

• Cantera version: [insert your version]

What I tried

I calculated the mass flow rates of NH₃ and air using the injector geometry and Re = 2000. I set the flame.inlet.mdotbased on the total flow rate per unit area:

But this only reflects the global condition, not the local equivalence ratio change due to secondary air at 80 mm.

What I want to ask

1. Is there a way to reflect the effect of secondary air injection at 80 mm in a FreeFlame simulation?

2. Would using FreeFlame + PlugFlowReactor be a good way to model such staged injection?

3. Can equivalence ratio or oxidizer composition vary along the flame domain in any way?

Any insight or suggestions would be greatly appreciated.

Thanks in advance!

[Ray Speth]

Hi,

There’s unfortunately no way to vary the mixture composition along the length of the 1D flame. If the conditions in the second stage are such that a plug flow assumption (neglecting streamwise diffusion) is reasonable, then I think that could work well. I would suggest looking at the surf_pfr_chain.py example as a starting point. This approach offers some flexibility so you could add the secondary air over some length of the PFR to approximate the mixing process, since the speed of that mixing will affect NOx formation.

Regards,
Ray

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