Learning Forum

[Zwernjayden]

Why is liquid-liquid dpm combustion only possible with species transport, and not non pre-mixed combustion model. Once the injections evaporate, why should it matter?

[Ren]

Hello, Jayden,

I'm not sure what you mean by "liquid-liquid dpm". But if you mean you have liquid fuel injected as dpm droplets into gases then you can use the non-premixed or the partially premixed combustion model.

I'm curious where/how did you get the impression that "dpm combustion only possible with species transport"? The Fluent documentations actually have some chapters on how to model solid and liquid fuels using the non-premixed model.

 

[Zwernjayden]

I mean liquid fuel and liquid oxidizer both being injected using DPM. I understand both combustion models can handle DPM but another Ansys employee implied that if both fuel and oxidizer were liquid you needed to use the species transport method instead of non pre-mixed combustion 

[Ren]

Apart from liquid fuel and liquid oxidizer, what are the other gases? How are the gases introduced into the domain?

 

[Zwernjayden]

The liquid fuel and liquid oxidizer should be the only components. I have tried mass flow inlets as well as dpm plain orifice atomizers. I want the liquid to vaporize into gas, then combust. 

[Ren]

In that case, I don't think the non-premixed combustion model can be used.

 

[Zwernjayden]

That is my question really. Why doesn't it work? Once the liquid vaporizes into gas, shouldn't it work? I read in the documentation you can only have fuel or oxidizer injected using DPM, not both, and I'm just unsure why

[Ren]

The issue is to do with the destination of the evaporated species. In the current implementation, the droplets are implicitly assumed to correspond to the fuel and consequently the evaporated species are all considered as the sources for the mixture fraction equation. This means that the evaporated oxidizer species will be considered as fuel as well. This is a limitation or restriction of the current implementation.

 

[Zwernjayden]

Ok that makes sense. And this is not the case for the species transport combustion models?

[Ren]

The species transport model should work. I suggest you try it out using a small test case.