Reactor Network Model Reference

You use the Reactor Network model to rapidly simulate detailed chemistry in a steady combustor.

Table 1. Reactor Network Model Reference
Theory	See Reactor Network.
Provided By	[physics continuum] > Models > Optional
Example Node Path	Continua > Physics 1 > Models > Reactor Network
Requires	Starting from a completely run steady-state reacting flow simulation. Material: either Multi-Component Gas or Multi-Component Liquid Time: Steady Reaction Regime: Reacting either: Reacting Flow Models: Reacting Species Transport Reacting Species Models: any Reacting Flow Models: Flamelet Flamelet Models: any and: Flow: any
Activates	Model Controls (child nodes)	[physics continuum] > Reactor Network See Reactor Network Chemistry Definition Clustering Reactor Type Numerical Settings Emissions
	Field Functions	RN Density, RN Index, RN Mass Fraction of [species], RN Soot Mass Density, RN Soot Mean Diameter, RN Soot Moment of [n], RN Soot Number Density, RN Soot Size Dispersion, RN Soot Volume Fraction, RN Temperature. See Reactor Network Field Functions.
	Simulation Operations	See Run Reactor Network.

You are recommended to use the Reactor Network model with the Steady model since the fluxes, and hence the reactors, are based on the instantaneous solution and not on a time-averaged solution.

[physics continuum] > Reactor Network

Here you specify the detailed chemistry mechanism that the reactor network model solves within the network of reactors. There are also several numerical parameters to set, in particular, the number of reactors that are in the network.

Reactor Network Right-Click Menu

Run Reactor Network: Runs the Reactor Network Solution. You can also run from previous reactor network solutions without clearing the solution first.
Stop Reactor Network Calculations: Stops solving the Reactor Network.
Clear Reactor Network Solution: Clears the existing Reactor Network Solution.

Chemistry Definition

The Chemistry Definition describes the chemical reaction mechanism, which is the collection of all species and their corresponding reactions, as well as the species thermodynamic properties.

Right-Click Actions

Import Complex Chemistry Definition (Chemkin format): Activates a standard Open dialog that imports files for the reactor network chemistry definition in Chemkin™format. Upon importing a chemistry definition, the reactions for the definition appear as sub-nodes of the Chemistry Definition node.
Delete Complex Chemistry Definition: Removes all the species and their reactions in the reactor network chemistry definition.

Chemistry Definition > Reactions

See Complex Chemistry

Clustering

See Chemistry Acceleration Properties: Clustering

Reactor Type

Reactor Option

Constant Pressure Reactor: The mass fractions in a reactor are calculated as the output of a 0D constant pressure reactor (CPR), where the input is the mass flux weighted average mass fractions from neighbor reactors (Eqn. (3828)). The integration time is the residence time in the reactor.
Perfectly Stirred Reactor: The mass fractions in a reactor are calculated as the output of a perfectly stirred reactor (PSR), which is a 0D steady-state equation system (Eqn. (3832)). The input mass fluxes into each PSR are the mass fluxes from neighbour reactors.

Temperature Option

Equation of State: The temperature is calculated by Eqn. (671).
Frozen from CFD: The reactors use the temperature from the CFD solution.
Enthalpy: The temperature is calculated from the CFD enthalpy field and the reactor network species.

Numerical Settings

Target Number of Reactors: The approximate number of reactors into which the computational domain is split by the Reactor Network model. Contiguous cells of similar composition are clustered into approximately this number of reactors. The accuracy of reactor network predictions, as well as the computational cost, increase with the specified Target Number of Reactors. Set this value to the largest value that you can afford with the available computational resources (serial or parallel) and run-time constraints.
Max Iterations: Maximum number of iterations for which the reactor network is solved. You can continue to run the reactor network solution from previous solutions by increasing this value—without clearing the solution first.
Residual Tolerance: The constant pressure reactor (CPR) or perfectly-stirred reactor (PSR) set of equations is iteratively solved until the residual is less than this value, or the maximum number of iterations are exceeded.
Absolute ODE Tolerance: Allows you to specify an absolute tolerance for the solver.
Relative ODE Tolerance: Allows you to specify a relative tolerance for the solver.
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.
Diffusion Flux Multiplier: The scaling factor for the internally calculated diffusion flux. The reactor network convective and diffusive fluxes are calculated from the steady reacting flow solution. Since there are usually far fewer reactors than cells, the predicted reactor network species fields can be overly diffusive. For example, combustion products in the flame zone can un-realistically diffuse upstream to the combustor inlets. This effect can be mitigated by reducing the Diffusion Flux Multiplier from 1 towards 0.

Emissions

Soot

When activated, provides the Soot Options sub-node with which you choose to account for soot emissions within the reactor network using either the soot moments method or the soot sections method.

Soot Options

Discretization Option


Discretization Option	Corresponding Sub-Node
Moments Accounts for soot emissions within the reactor network using the soot moments method, where the soot moment source term $ω_{M_{r}}$ is given by Eqn. (3672).	None.
Sections Accounts for soot emissions within the reactor network using the soot sections method.	Soot Sections Number of Sections Number of discrete sections in the particle size distribution function (PSDF). Maximum Soot Diameter Maximum diameter to which the soot particle grows. Small Diameter Fractal Dimension Surface growth fractal dimension of soot particles with a diameter $θ$ less than 20nm in Eqn. (3742) and Eqn. (3743). You can set this between 2.0 and 3.0. Large Diameter Fractal Dimension Surface growth fractal dimension of soot particles with a diameter $θ$ greater than 60nm in Eqn. (3742) and Eqn. (3743). You can set this between 2.0 and 3.0.

Nucleation Option

Only available as a property of the Soot Moments model or Soot Sections model when using the Complex Chemistry, Reactor Network, ECFM-3Z, or ECFM-CLEH combustion model. When using one of the Flamelet combustion models, you specify the nucleation option as a combustion table parameter.

Allows you to specify the Nucleation Option as either:


Nucleation Option	Corresponding Sub-Node
Single PAH Species (C16H10): See Eqn. (3679) and Eqn. (3680). The PAH precursor is recognised as any species which includes either A4 or A3R5 in the species name, or has the composition C16H10.	None
C2H2: See Eqn. (3682).	None
Multi PAH Species Allows you to select multiple PAH precursor species from those that are present in the chemical mechanism. Simcenter STAR-CCM+ recognises the chemical symbols of the PAH precursor species as described within the table for Multi PAH Species Nucleation. Available only when using the Complex Chemistry or Reactor Network combustion models.	PAH Species Components Lists the selected PAH precursor species—each displays its Sticky Coefficient property.

(Soot) Surface Chemistry Option


(Soot) Surface Chemistry Option	Corresponding Sub-Node
HACA The soot surface growth is modeled using the Hydrogen-Abstraction-C2H2-Addition (HACA) surface mechanism. Most appropriate when using the Complex Chemistry model. See HACA.	None
HACA RC The soot surface growth is modeled using the Hydrogen-Abstraction-Carbon-Addition-Ring-Closure (HACA-RC) surface mechanism. Most appropriate when using an ECFM model for diesel fuel. See HACA RC.	None

Steric Factor

Allows you to define a constant value for the steric factor

α

in Eqn. (3706).

Surface-growth Scale

Scales surface growth (part of

W_{r}

in Eqn. (3673)).

Nucleation Scale

Scales nucleation (

R_{r}

in Eqn. (3673)).

Oxidation Scale

Scales oxidation (part of

W_{r}

in Eqn. (3673)).

Two-Way Coupled Species

In soot reactions, gas phase species are transferred to and from the gas phase to the soot particles. When this property is activated, these gas-phase species are added and removed from the gas-phase simulation. Only available when using a reacting species transport model or the Reactor Network model.

Field Functions

RN Density: Density in the reactor.
RN Index: The index values of the reactors that the Reactor Network model creates.
RN Mass Fraction of [species]: The mass fraction of the [species] in the reactor.
RN Soot Mass Density: $M$ in [eqnlink] within the reactor.
RN Soot Mean Diameter: $d = {(\frac{6 M}{π N ρ_{s o o t}})}^{\frac{1}{3}}$ in the reactor.
RN Soot Moment of [n]: For the $i$ th reactor, $M_{r}^{i}$ in Eqn. (3831) for constant pressure reactors, and in Eqn. (3834) for perfectly stirred reactors.
RN Soot Number Density: $N$ in Eqn. (3674) within the reactor.
RN Soot Size Dispersion: $D_{s o o t} = \frac{(M_{2} M_{0})}{{(M_{1})}^{2}}$ in the reactor.
RN Soot Volume Fraction: $f_{v}$ in Eqn. (3675) within the reactor.
RN Temperature: The temperature in the reactor.