Help with CFM Combustion... how to set initial and end fuel/oxidiser mixtures?
 

I'm trying to model a rocket engine combustion chamber, axisymmetric, premixed combustion of multicomponent gas (ethylene+oxidiser).

I'm using the Coherent Flame Model, with coupled energy+flow and standard K-epsilon turbulence... but I can't work out how to set my initial and end combustion gas component mixtures.

There's no node available in my inlet or outlet lists that allows me to assign what gases come in and go out, reactants or products.

The only thing available that's remotely relevant is the fluid stream: Unburnt Gas for which I can set mass ratios for the various gas profiles I listed in the multi-component gas .

I *had* assumed that the Unburnt Gas node referred to the amount of stuff left at the end - i.e. the combustion products plus any fuel/oxidiser that didn't get burned.
HOWEVER it doesn't seem so: when running my simulation with a scalar scene of Fuel Mass Fraction or Mass Fraction of C2H4 (my fuel), I can basically see an *inverse* of my gas being burnt: from the inlet, it goes from small blue area outwards to red which fills the rest of the chamber - so the amount goes *up* during combustion - to the value I specified in unburnt fuel. Which doesn't make sense, obviously.
How do I use the 'Unburnt Fuel' node correctly?

Any help understanding how to sort out fuel mixture specification with the CFM model would be greatly appreciated.

Thanks