Can't fix unwanted premature combustion
 

Hello there,

I'm trying to model a hydrogen combustion in a high pressure chamber with constant volume in STAR-CD 4.18. Oxygen and hydrogen in their gaseous form enter the chamber separately (filled with nitrogen).

For modeling the chemical reaction I started with the following settings
Reaction Type: Unpremixed/Diffusion
Reaction Model: EBU Standard
Ignition: Numerical (Time Step based Interval) in a defined cell type

Under "Scalar Boundaries" I set the mass fraction for the scalars "H2" and "MIX_FRAC_FUEL_1" to 1 in the hydrogen inlet. For the oxygen inlet I set the scalar "O2" also to 1.

My problem is, that as soon as hydrogen and oxygen mix, water is formed although the fluid conditions don't allow a self-ignition (1bar abs. and 300K) and the predefinied ignition hasn't been triggered. That is to say premature combustion.

The same problem also occurs if "Chemical Kinetics" instead of "EBU Standard" is chosen.

Help is very much appreciated. Thank you in advance.

This is due to you not selecting a property correctly. You need to tick a box which will use the products for the rate. This worked for me when I had a similar problem. The box is located in the physics continua tree as follows:

Reacting>Reactions>Reaction ??>Properties>EBU coefficients.

I hope that helps.

Tom