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alpha754293 May 28, 2012 17:48

How do I increase Newton Pressure Iteration Limit when used with CFX-RIF?
I ran into the same error that some other folks here have been getting with the "Newton Pressure Iteration Limit" error message and I've tried to see/find where I can add the extra expert control parameter for that.

Through the reading that I've done upto this point, someone pointed to the CFXPreRules.ccl and there I was able to find that it's a valid option for OBJECT: MATERIAL, under CONTEXT: {Homogenous binary mixture, Fixed Composition Mixture, ...}.

I am trying to simulate a spark ignition engine (one of the cylinders from a V8 engine). I've already created the chemical reaction using CFX-RIF (gasoline, as modeled by n-heptane and isooctane). (I'm using 0.13 n-heptane, 0.87 isooctane (by mass fraction).)

Oxidizer is 0.767 N2, 0.233 O2. No EGR. I've used the default values for the size of the table.

Whenever I try to add the fuel injection as a boundary condition (where the fuel injector port is) into my model - this is when I get the same error:

 |                    ****** Notice ******                          |
 | Newtons method failed to converge in  100 iterations.  This        |
 | occurred while computing the following variable:                  |
 |                                                                    |
 | Variable Name  : Total Temperature                                |
 | Location Name  : inj                                              |
 | Mesh location  : BELG57                                            |
 | Mesh entity    : VERTEX                                            |
 | Last 3 Changes :  2.42255E+01  2.42255E+01  2.42255E+01            |
 | Tolerance      :  1.0000E-02                                      |
 |                                                                    |
 | The Newton iteration was either slowly converging or has stalled.  |
 | The solver will continue with the variable set as it was on the    |
 | final iteration.  If this situation continues you might try        |
 | increasing the number of iterations allowed for Newtons method.    |
 | This can be changed by setting one of the parameters:              |
 |                                                                    |
 | Temperature : "Constitutive Relation Iteration Limit"              |
 | Pressure    : "Newton Pressure Iteration Limit"                    |
 |                                                                    |
 | for your mixture using the definition file editor.                |

From what people were saying, I'm supposed to add the expert control parameter into the MATERIAL object, but "Newton Pressure Iteration Limit" is not a valid option for pure substances, which are the materials that result from the CFX-RIF computation.

So, how do I go about increasing the Newton Pressure Iteration Limit?

I'm using total energy throughout for the heat transfer, and I've tried setting the Total/Static Temperature at 300 [K] and that didn't work. I even tried setting it to 500 [K] (because I thought that there might be a divide by subtraction in there somewhere as my fuel and oxidizer are also at 300 [K]) and that didn't work either.

The CEL that governs my injection sequence (as a pressure) is given by the following:

step((t-160*dt)/1[s])*20e6 [Pa] + step((170*dt-t)/1[s])*20e6 [Pa]
where dt is an expression (variable) that I define earlier.

It also doesn't seem like it matters whether I have it as that expression or as just straight constant 20e6 [Pa].

Any help would be greatly appreciated.

If you need additional information about how the model/simulation is set up, please do not hesitate to ask. Thanks.

dk_damo November 28, 2012 09:28

How do I increase Newton Pressure Iteration Limit when used with CFX-RIF?
did you manage to fix this problem you posted i am having the same error but cant find where to change this parameter.Thanks

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