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Tim June 29, 2008 09:28

urgent: Combustion constant temperature

i'm running a diesel combustion simulation using dedecane of a constant volume cylinder. i have the temp and pressure set to 970K and 2.5e6Pa, and my combustion seems to be working as the products are appearing, but my temperature is staying constant throughout the transient simulation.

does anyone know whats going on??


Andrea June 29, 2008 13:50

Re: urgent: Combustion constant temperature
Hi, have you set on the temperature calculation? Does the combustion reaction accout for the conservation of thermal entalpy (or chemical...or similar!)? If yes it's ok...
And also what combustion model are you using? It's the temperature solver turned on? remember that the raise in temperature may follow the formation of the first combustion product of some c.a....depending on the rpm of the engine.

Tim June 29, 2008 14:01

Re: urgent: Combustion constant temperature
Its just a simple control volume model, injecting dodecane into a preheated cylinder. using transient, lagrangian multi-phase, chemical reaction (unpremixed/diffusion - chemical kinetics). Temp calc is on, and i have set dodecane to evap to C12H26. I am trying to model the soot and nox formations, but i think i haven't set the ignition model up properly. Would you recommend any type or settings for my conditions?

the reaction scheme i have set is c12h26+18.5O2->12CO2+13H2O

Andrea June 29, 2008 18:12

Re: urgent: Combustion constant temperature
You are using the chemical kinetics combustion model, so in the ignition model panel of the star-gui you can select only a "numerical" ignition model...that's not so pretty because there you must specify the cell type where the combustion can occour, the ignition temperature (you have to find the ignition temperature at costant pressure, assuming the initial pressure in your chamber, I suppose. You must refer to some database or some tabulated experimental data about costant volume combustion) and the burned gas fraction of leading reactanct that the ignition gives you (0.0 is default).
Note that the TIME or TIME-STEP option in the ignition model refer only to the time where is applied your ignition model, so defines the time where the ignition CAN occour... You can choose as starting time the time where the injection start and as end time a time very very distant from the end of your simulation...
Personally for Diesel combustion simulations I use the EBU LATCT model (Magnussen combustion model): in that model you can choose the Shell auto-ignition model (able to predict the double-delay ignition) that is simple to use. And with Magnussen you can also use the NOx model and the SOOT formation model of Mauss.

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