NOx Emission Model Reference

Table 1. NOx Emission Model Reference
Theory	See NOx.
Provided By	[physics continuum] > Models > Optional Models
Example Node Path	Continua > Physics 1 > Models > NOx Emission
Requires	Material: Multi-Component Gas Reaction Regime: Reacting Reacting Flow Models: Reacting Species Transport or Flamelet
Properties	Key properties are: Source Enabled Trigger, Begin, Secondary Gradients, Convection. See NOx Emission Model Properties.
Activates	Initial Conditions	Nitrogen Oxide. See Initial Conditions.
	Boundary Inputs	Wall Combustion Scalar Option. See Boundary Settings.
	Solvers	NOx. See NOx Emission Solvers.
	Monitors	NO
	Field Functions	Mass Fraction of Nitrogen Oxide Emission. See Field Functions.

NOx Emission Model Properties

Source Enabled Trigger

Controls whether Simcenter STAR-CCM+ starts calculating the chemistry at the time-step, iteration, or physical time that you specify in the Begin property, or whether this model never contributes any sources.

Begin

Specifies the iteration, time-step, or physical time after which the reactions are activated. Before this iteration, time-step, or physical time, reactions are deactivated. Specifying a physical time [degCA] allows you to activate chemistry sources just before spark ignition. When specifying it as an expression which varies during the simulation, reactions are only active when the current iteration, time-step, or physical time is higher than the value provided by the expression.

Secondary Gradients

Neglect or include the boundary secondary gradients for diffusion and/or the interior secondary gradients at mesh faces.

On: Default value. Solves for interior and boundary types of secondary gradient.
Off: Does not solve for either type of secondary gradient.
Interior Only: Solves for the interior secondary gradients only.
Boundaries Only: Solves for the boundary secondary gradients only.

Convection

In transport equations, you can choose from a range of schemes that calculate the convection term at a cell face. This calculation requires Simcenter STAR-CCM+ to compute the face value of a quantity from the surrounding cell values. The method used for computing this face value has a profound effect on the stability and accuracy of the numerical scheme. For guidance on selecting a convection scheme, see Convective Flux.

1st-order: First-order convection scheme.
2nd-order: Second-order convection scheme.

Initial Conditions

Nitrogen Oxide: Allows you to set the profile for the mass fraction of the Nitrogen Oxide emission. For example, when simulating exhaust gas recirculation (EGR).

Boundary Settings

Any Boundary Type

Wall Combustion Scalar Option

Selects the scalars for the wall combustion calculation.

Method	Corresponding Physics Value Nodes
Zero Flux	None
Specified Value Allows you to specify the composition of species at a boundary.	Nitrogen Oxide

NOx Solver Properties

Under-Relaxation Factor: In order to promote convergence, this property is used to under-relax changes of the solution during the iterative process. If residuals show solution divergence or do not decrease, reduce the under-relaxation factor.
Solver Frozen: When On, the solver does not update any quantity during an iteration. It is Off by default. This is a debugging option that can result in non-recoverable errors and wrong solutions due to missing storage. See Finite Volume Solvers Reference for details.
Reconstruction Frozen: When On, Simcenter STAR-CCM+ does not update reconstruction gradients with each iteration, but rather uses gradients from the last iteration in which they were updated. Activate Temporary Storage Retained in conjunction with this property. This property is Off by default.
Reconstruction Zeroed: When On, the solver sets reconstruction gradients to zero at the next iteration. This action means that face values used for upwinding (Eqn. (905)) and for computing cell gradients (Eqn. (917) and Eqn. (918)) become first-order estimates. This property is Off by default. If you turn this property Off after having it On, the solver recomputes the gradients on the next iteration.
Temporary Storage Retained: When On, Simcenter STAR-CCM+ retains additional field data that the solver generates during an iteration. The particular data retained depends on the solver, and becomes available as field functions during subsequent iterations. Off by default.

Field Functions

Mass Fraction of Nitrogen Oxide Emission: Represents the mass fraction of NO. Since it is considered that NOx emissions consist only of NO, this is the transported scalar of the NOx Emission model.