Flow Connection
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InjProfileConn Connection
This object describes an injector for simulations in which a fluid (fuel, water, etc.) is to be injected periodically with a profile specified by the user. Fluids may be injected into any cylinder, pipe, or flowsplit This is the injector that should typically be used for direct-injection engines.
Injected Mass The amount of fluid injected per cycle or the name of a dependency reference object.
Start of Injection Crank angle at start of injection relative to TOC firing or the name of a dependency reference object. Negative values indicate that the SOl occurs before TOC.
Reference Driver Definition of the TOC reference that is used for the Start of Injection timing angle. This attribute enables each injector to be phased according to firing order and interval without having to reassign the Start of Injection for each cylinder.
• For direct injection into 'EngCylinder' parts (i.e. diesel or GDI configurations), "def' may be entered.
• For injection into pipes or flowsplits (i.e. port injection), the corresponding cylinder number must be specified. This is the integer used in 'EngineCrankTrain' to define the firing order. (Note: this is
!!l!!the cylinder part name). Because each injector part will typically have a unique integer, it is typically convenient to specify •••••for the object, and to specify these values in each part using Part Override.
• For non-engine or unconventional engine simulations, the name of a 'Driver' reference object must be entered here.
Profile Type One of the following choices:
• presprof indicates that a profile of absolute injection pressure is entered.
• presdiff indicates that a profile of injection pressure above the cylinder pressure (P"'rP,y,) is entered. This option may only be used when injecting directly into a 'EngCylinder' component.
• massprof Indicates that a profile of mass flow rate is entered. The profile may have arbitrary units because the mass profile is automatically scaled to inject the proper mass of fuel per cycle as specified inInjected Massabove.
Angle Array Multiplier Multiplier to the Crank Angle Array in the Profile folder below. A dependency reference object is allowed. ("def'= I)
Pre.sure Profile Multiplier Multiplier to theProfile Arrayin theProfile folder below. WhenProfile Type is set to massprof, this multiplier will have no effect since the profile is always normalized to the amount of Injected Mass given above. A dependency reference object is allowed. ("def'= I)
Variable ProfileDep.Object The name of an 'RLTDependence' reference object that causes the injection profile to depend on one or two RLT variables. This allows the shape of the injection profile to automatically update during the simulation, for example depending on engine speed and injection rate. If there is no need for varying injection profiles, specify "ign".
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InjProfileConn
Flow Connection
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69
Injection Map Object
Fuel-Nozzle
Injected Ruld Temperature Fluid Object
Vaporbr8d Fuel Fraction
Alr.to-Fuel Ratio Limit
It is still necessary to enter a profile in theProfile folder of this object for use during the first cycle of the simulation (before RLT variables have been calculated).
In the 'RL TDependence' object, the Dependence Object attribute must point to either an 'XYTable' and 'XYZMap', depending if the dependency is on one or two RLT variables respectively ('XY.Function' objects are not permitted). Each cell in the 'XYTable' or 'XYZMap' object then names other 'XYTable' objects, each of which is an injection profile. If Profile Type is set to presprof or preadlff, then the pressure arrays (Y) in the 'XYTable' objects
must
always be in units of&
(The raw data itaelf can be in any unit so long as the Y Multiplier in that same object is used to convert the data to the proper unit.)Also, all of the 'XYTable' objects that contain profile data must be read before the object that points to them is read. There is no issue if the 'RLTDependence' object points to an 'XYZMap' object because 'XYZMap' objects are always read last, but if the 'RLTDependence' points to and 'XYTable', then this object must be ordered last. The order of reading is determined alphabetically by the object name. However, the reading order is unconventional' and inconsistent with the way they are listed in the object tree of the •. gtm file; they will be read in the order A, B, ... ,Y, Z, a, b, .... , y, z. Therefore, it is a good idea to precede the name of the object to be last with "z" (not "Z").
Name of an 'InjectionMap' reference object. This object may optionally be used to set the injection rate, timing, and profile according to a control algorithm similar to that used in the Engine Control Unit (ECU). When this object is used, the injection profile specified below in the Profile folder will only be used for the initial cycle(s) specified in the 'InjectionMap' reference object. This attribute will most typically be set to "ign" to impose the injection data specified in this object for the entire simulation. (This option also requires an extra "sensor" connection.
Please see the "Configuration" notes below.)
Temperatore of the injected fluid
Name ofthe 'FPropLiqIncomp' or 'FPropGasCombust' reference object defining the properties of the fluid to be injected.
Mass fraction of the injected liquid that will vaporize immediately after injection. For direct-injection into an 'EngCylinder' component, this attribute should typically be set to 0.0. (It
must
be set to 0.0 if the DUet combustion model is called by the cylinder.) For a typical port-injected gasoline engine, a normal value is 0.3. This attribute may be set to "ign"if an 'FPropGas.' fuel is injected. (Refer to the "Injection" section of the Users Manual for more details about evaporation after injection.) Minimum air-to-fuel ratio or the name of a dependency reference object.
The injected mass is dynamically reduced as necessary so that the
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70 InjProfileConn
Flow Connection
Injector Location
trapped air-to-fuel ratio does not fall below this limit. This variable is typically used for two pwposes:
• Simple smoke-limit simulation: this is useful for "load acceptance"
simulations of diesel engines.
• Imposing an air-to-fuel ratio: if the user sets Injected Mass to a very large value, the injection rate will be limited to the A1r-to-Fuel Ratio Limit at all times.
This option is only available for direct injection into an 'EngCylinder' component. The amount of available air is determined at the Start of Injection angle. If Start of Injection is before Ive (as is common for DISI engines), then the amount of trapped air in the cylinder will continue to change after the start of injection, and so this option will not work properly. In these situations, a limit can easily be imposed via the control components available within GT-SUITE. If no limit is desired, this attribute may be set to "ign".
The normalized location along a pipe where injection occurs. 0.0 represents the inlet end of the pipe, and 1.0 the outlet. If the injector is connected to a component other than a pipe, this attribute may be set to
"ign".
The following three a/tributes are especially important for simulations where Profile Type is set to ma88prof. This is because the injection pressure required to achieve the specified Injected Mass is back-calculated using the effective area from the data below. Therefore, if any of the three values are not very accurate, then the injection pressure will be very unrealisti~ften extremely large. This will result in poor combustion characteristics, especially if the 'EngCylCombDUet' combustion model or the 'EngCylCombDIWiebe' with "def'values is being used. However, the injection pressure can indirectly effect all types of combustion, even for pori injection, because the kinetic energy of the injected fluid is proportional to the square of the injection velocity, thus introducing very large amounts of energy into
the system.
If Profile Type is set to presprof or presdlff, then the Nozzle Discharge Coefficient specified below will be automatically calculated so that the specified Injected Ma88will always be achieved. These are generally "safer" techniques than massprof because the combustion rate is less sensitive to changes in the discharge coefficient than the injection pressure. In fact, the three attributes below will only effect the 'EngCylCombDUet'model.
Nozzle Hole Diameter Diameter of each nozzle hole.
Number of Holes per Nozzle Number of identical nozzle holes in the injector.
Nozzle Discharge Coefficient Nozzle discharge coefficient. The attribute is only used for the massprof option and should be set to "def' for pressure profiles.
Recommended values are 0.65-0.70. For pressure profiles, RLT variable for the discharge coefficient, "cnozz", should be monitored to verify that a realistic value (0.60 to 0.75) has been calculated. If the calculated value is not realistic, then there is an inconsistency between the Injected Mass, pressure profile, Nozzle Hole Diameter, and/or Number of Holes per Nozzla.
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71 InJProfileConn (;.:\
Flow Connection
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If a Variable Profile Dep. Object has been specified above, the profile entered here will only be used for the first cycle of the simulation. After the first cycle, RLT variables are calculated and the Variable
Profile Dep. Object will be used.
Profile
Crank Angle Array
Profile Array
Angle array for injection profile in crank-angle degrees. This array may start at any value because the code automatically shifts the array so that the first angle
in the array
coincides with Start of Injection specified~.
Injection profile array of pressure or mass (depending on Profile Type) corresponding to Crank Angle Array. Note that the pressure units above the array have no influence if a mass profile is specified because the array is always normalized to the Injected Mass.
Configuration: This connection may be attached to a pipe, flowsplil, or cylinder part by creating a link arrow from the injector to the component. The port number where this object attaches to the flow component must always be zero. (GT-ISE will correctly number the port if the linking arrow points from the connection to the component's port.) When Injection Map Object is being used, a link must also be drawnfrom the a pipe or flowsplit where the pressure and temperature are being sensed
dlred!y
to the 'InjProfileConn' part. (No 'SensorConn' part is necessary to use the 'InjectionMap'.) The port number where this link attaches to the pipe or flowsplit is arbitrary.Plotted and Sensed Variables:
Vqriqble Pressure Mass Flow Rate Volumetric Flow Rate Pressure Drop Across Nozzle Velocity
Cumulative Injected Mass
Plotted
Senmi• bar
• kglhr
• IIhr
•
• m/s
•
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72 InJRateConn.
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Flow Connection
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InjRateConnConneetion
This object describes an injector in which the instantaneous injection rate is to be specified. This injector is particularly convenient if a constant injection rate is to be imposed or if the instantaneous rate is to be controlled with an 'AetuatorConn'. Any fluid (fuel, water, etc.) may be injected with a 'InjRateConn' into a pipe or flowsplit.
Maaa Flow Rate
Injector Location
Injected Fluid Temperature Fluid Object
Vaporized Fuel Fraction
The mass flow rate of fuel through the injector or the name of a dependency reference object.
The nonnalized location along a pipe where injection occurs. 0.0 represents the inlet end of the pipe, and 1.0 the outlet. If the injector is connected to a component other than a pipe, this attribute may be set to
"ign",
Temperatore of the injected fluid.
Name of the 'FPropLiqIncomp' or 'FPropGasCombust' reference object defining the properties of the fluid to be injected.
Mass fraction of the injected liquid that will vaporize immediately after injection. For a typical port-injected gasoline engine, a nonnal value is 0.3. This attribute may be set to "ign" if an 'FPropGas.' fuel is injected.
(Refer to the "Injection" section of the Users Manual for more details about evaporation after injection.)
Cnnftguradon: This connection may be attached to a pipe or flowsplit part by creating a link arrow from the injector to the component. The port number where this object attaches to the flow component must always be zero. (GT-ISE will correctly number the port if the linking arrow points from the connection to the component's port.)
Plotted and Sensed Variables:
Vqrigble Mass Flow Rate Volumetric Flow Rate Cumulative Injected Mass
Plotted
Sensed
• kg/hr
• lIhr
•
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EngCylHeatTr Flow Reference
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EngCylHeatTr - Cylinder Heat Transfer Model
This object is used to describe parameters for the in-cylinder heat transfer models used to calculate heat transfer from 'EngCylinder' and 'EngCrankcase' parts.
Heat Transfer Model
User Model Object Name Convection Multiplier
Head/Bore Area Ratio
Piston/Bore Area Ratio
Radiation Multiplier
Normalized-hg Table
Must be set to one of the following:
• woschni indicates that the in-cylinder heat transfer will be calculated by the code using the Woschni model. This option is recommended when measured swirl data is not available.
• flow indicates that in-cylinder heat transfer will be calculated using flow detail provided by the 'EngCylFlow' reference object. This model is recommended when swirl coefficients have been specified in the valves.
• hgproflle indicates that in-cylinder heat transfer is calculated from an array of reduced cylinder-gas heat transfer coefficients versus crank angle. Such data would most typically come from in-cylinder CFD analysis.
• user indicates that a subroutine created by the user will be called to calculate in-cylinder heat transfer.
Name ofa 'UserModel' reference object if Heat Transfer Model is set to user. Set to "ign" if a user model is not used.
Multiplication factor for the convective heat transfer or the name of a dependency reference object. This factor is used to scale the convective heat transfer that is calculated by the code from the chosen heat transfer model. The 'ProfileAngle' reference object is a convenient means to customizing the woschni correlation. When 'ProfileAngle' is pointed to from this attribute, the angle-dependent multipliers will automatically be phased so that the 0 angle corresponds to TDC firing of each local cylinder part. ("def' =1.0)
Ratio of cylinder head surface area to cylinder bore cross-sectional area.
This ratio will be calculated automatically if the cylinder that calls this object is also calling an 'EngCylTWallSoln' reference object, in which case it may be set to "ign".
Ratio of piston surface area to cylinder bore cross-sectional area. This ratio will be calculated automatically if the cylinder that calls this object is also calling an 'EngCylTWallSoln' reference object, in which case it may be set to "ign".
Multiplication factor for in-cylinder radiation. This factor is used to scale the amount of in-cylinder radiation that is calculated by the code.
In-cylinder radiation is usually only significant for diesel engines, and should be set to "ign" in all other cases (usually 1.0 for diesel engines;
0.0 for all other engine types).
Name of a 'XYTable.' reference object that specifies an array of normalized-hg values (in the Y array) corresponding to an array of crank-angle degrees (in the X array). This attribute is only used when Heat Transfer Model is set to hgproflle, and so this attribute may be set
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EngCylHeatTr Flow Reference
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to "ign" for all other models. These values could be supplied, for example, by a CFD calculation. Normalized hg is defined as:
hg. =hg/(PVp
f75
where: hg. = normalized hg values hg = hg values
P fluid density Vp = mean piston speed
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EngCylCombDlWiebe Flow Reference
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EngCylCombDIWiebe - Direct-Injection Wiebe Combustion Model
This object imposes the combustion rate for direct-injection, compression-ignition engines using a three- term Wiebe function. This model should only be used when the fuel is injected directly into the cylinder with an 'InjProfileConn' connection. When the attributes below are imposed (i.e. Ignition Delayand the Fraction or Duration attributes are ill!! set to "def'), the injection profile will not influence the combustion rate. The only exception is that, at any instant, the specified cumulative combustion cannot exceed the specified injected fuel fraction (fuel injected to that time stepItotal fuel to be injected).
An Excel file named combustion. xIs is included in the installation directory of GT-SUITE and is useful in determining the Wiebe constants. The combustion spreadsheet has a feature to match the Wiebe constants to a heat release rate that has been calculated from measured cylinder pressure. (Please note that the 'EngCylCombProfile' reference object can be used to directly input the heat release rate calculated from cylinder pressure. Therefore, if the heat release rate has been calculated, it is not necessary to match the Wiebe parameters to it unless the Wiebe model is needed for a special purpose.) If the Ignition Delay or any of the Fraction or Duration attributes have been set to "def', this model becomes semi-predictive by trying to choose the attributes automatically. They are calculated from the injection profile, air-to-fuel ratio, pressure and temperature. Therefore, to obtain meaningful results when
"def' has been entered for any of these attributes, the injector geometry and injection pressure profile must be specified as accurately as possible because they will affect the combustion rate.
Ignition Delay
Pramixed Fraction
Tall Fraction
Premixed Duration
Main Duration
Tall Duration
Premixed Exponent
Main Exponent
Tall Exponent
Delay in crank-angle degrees between the start of injection (specified in the 'InjProfileConn' or 'InjectionMap' reference object) and the start of combustion or the name of a dependency reference object.
Fraction of fuel that mixes before the start of combustion and burns in the "premix" portion of the Wiebe function or the name of a dependency reference object.
Fraction of fuel that bums beyond the main diffusion bum or the name of a dependency reference object.
Duration in crank-angle degrees of the premix bum or the name of a dependency reference object The duration should exclude the first 10%
and the last 10% of the area under the premix curve, i.e. the tails.
Duration in crank-angle degrees of the main diffusion bum or the name of a dependency reference object. The duration should exclude the first 10% and the last 10"10of the area under the main bum curve, i.e. thetails.
Duration in crank-angle degrees of the tail bum curve or the name of a dependency reference object. The duration should exclude the first 10%
and the last I0% of the area under the tail bum curve, i.e. the tails.
Wiebe exponent for the premixed bum or the name of a dependency reference object. Larger values skew the curve to the right. ("def'=O.7) Wiebe exponent for the main bum or the name of a dependency reference object. Larger values skew the curve to the right. ("def'=O.9) Wiebe exponent for the tail bum or the name of a dependency reference object. Larger values skew the curve to the right. ("def'= 1.5)
EngCylCombDIWiebe Flow Reference
76
No.of Temperature Zones One of the following choices:
• two-temp specifies a two-zone combustion model. This option must be used if in-cylinder radiation is being modeled in the 'EngCylHeatTr' reference object.
• singl •. temp specifies a single-zone combustion model.
Combustion Efficiency The ftaction of fuel burned during combustion or the name of a dependency reference object. If a value less than 1.0 is specified, the unburned fuel will be removed proportionately from the combustion rate so that burn rate will have identical shape, but a lesser scale. ("def'= 1) NOll Reference Object Name of an 'EngCylNOx' reference object that may be used to model
NOx formation during combustion. If NOx predictions are not desired, this attribute may be set to "ign".