Operating Conditions

The following right-click actions and dialogs are available for operating conditions in Simcenter STAR-CCM+ In-cylinder.

Operating Conditions Right-Click Actions


Object	Right-Click Action
Operating Conditions	Edit Opens a dialog that allows you to set the properties of the operating conditions. See Operating Conditions Dialog.

Operating Conditions Dialog

RPM

Specifies the engine angular velocity in revolutions per minute.

Start Angle

Specifies the deg crank angle at which the simulation begins.

In general, you run an analysis over multiple engine cycles to reduce the effect of initial conditions on the final results. If your processing time is limited, you are advised to start the analysis some crank angles before the intake valve opens—for example at 300 deg crank angle. At this stage, you can assume that the flow in the cylinder is relatively steady compared to the intake and combustion phases.

Duration

Specifies the duration of the simulation in terms of deg crank angle interval. Therefore, the stopping crank angle is the Start Angle plus the Duration.

Reference Pressure

Specifies the reference pressure for the gas domain.

The reference pressure is simply a device that is used to reduce the numerical roundoff error in the numerical calculations involving pressure. This reduction in numerical error is necessary since the differences in pressure are important, and these differences can be small relative to the absolute value of the pressure (for example, in fully incompressible, or very low-Mach number flows). By subtracting a suitable constant reference pressure, a working pressure is obtained that is less prone to roundoff errors.

The reference pressure is used as in Eqn. (671) .Set the reference pressure to some ambient value such that the working pressures are small. The default value is 1.0 bar.

Default Wall Temperature

Specifies the temperature that is used as default value for the constant temperature setting on a wall, velocity inlet, or pressure outlet. See Engine Part Surface Reference.

Note	If you want to change a specific constant temperature setting to another temperature value, delete the $DefaultAmbientTemperature entry and enter the required value.

Constant Absolute Pressure Cylinder

(only for cylinder sector models)

For a closed-cycle analysis, specifies the absolute pressure in the cylinder. It is used to obtain density by the Ideal Gas Law, Eqn. (671).

Automatic Composition Initialization: When On, provides an automated approach to define the exhaust gas composition and the gas composition at the flow boundaries and for initialization. This approach calculates the gas composition as a function of the equivalence ratio at which the combustion takes place and of the exhaust gas recirculation (EGR) percentage.; For more information, see Automatic Composition Initialization.


Equivalence Ratio for Initialization
Definition	Sets the definition of the equivalence ratio. The following options are available: $Φ$ (Fuel/Air Ratio): sets the fuel-air equivalence ratio as given by Eqn. (591) $λ$ (Air/Fuel Ratio): sets the air-fuel equivalence ratio as given by Eqn. (592).
Initialization of Exhaust Gas Composition	Specifies the equivalence ratio of the fuel-air mixture (without EGR) in All Parts. See $Φ_{g l o b a l}$ in Automatic Composition Initialization—Exhaust Gas Composition.
Initialization of Unburnt Fuel/Air Mixture	For each zone in the engine—such as Cylinder, Intake port, and Exhaust port—specifies the local equivalence ratio of the premixed unburnt fuel-air mixture. See $Φ_{l o c a l}^{z o n e}$ in Automatic Composition Initialization—Gas Initialization and Boundary Conditions.


EGR
EGR	Sets the definition of the exhaust gas recirculation (EGR) level, depending on company practice. The following definitions are available: $\dot{E} / \dot{A}$ : sets the EGR as given by Eqn. (593). $\dot{E} / (\dot{A} + \dot{E})$ : sets the EGR as given by Eqn. (594). $\dot{E} / (\dot{A} + \dot{F})$ : sets the EGR as given by Eqn. (595). $\dot{E} / (\dot{A} + \dot{F} + \dot{E})$ : sets the EGR as given by Eqn. (596).
Cylinder	Specifies the exhaust gas recirculation for each zone in the engine —cylinder, intake port, and exhaust port—in %. See ${E G R}_{i}^{z o n e}$ in Automatic Composition Initialization—Gas Initialization and Boundary Conditions.
Intake (not for cylinder sector models)
Exhaust (not for cylinder sector models)