EngCylCombSIWiebe - SI Wiebe Combustion Model

Burned Fuel % at Duration Start Burned Fuel % ak Model Selection One of the following choices: • • • ign indicates that the user is not modeling knock or pre-ignition. standard indicates that the user wishes to use the knock models as defined in the ' EngCylKnock' reference object. standard-lastcycle indicates that the user wishes to use the knock models as defined in the ' EngCylKnock' reference object, but the calculation will be made for only the last cycle of each case. This option is recommended when the simulation is at steady state, the attributePost-Knock Combustion is off, and the attribute End Gas Zones is set to Multi-Zone in the 'EngCylKnock' reference object because the results of the knock model will not affect the rest of the model , and the calculation of knock will be computationally expensive. This option should not be used when the output of knock is used in a feedback control system (e.g., to control spark timing). This option cannot be used when the Post-Knock Comb Post-Knock Combustion is on, as that will affect the results and produce an incorrect result. user indicates that the user has created a knock model that should be called during combustion. (See Chapter 1 for more information about user models.)
Duration (def = 10% to 90%)
Wiebe Exponent
Options
Number of Temperature Zones Must be one of the following two choices: • two-temp indicates that temperature and composition will be independently calculated for the burned and unburned gases in the cylinder chamber. This option is recommended for most simulations and must be used to achieve meaningful NOx results with NOx Reference Object below. single-temp specifies a single-zone combustion model. This option is typically only chosen to maintain consistent results with other analyses that might assume only one temperature zone such as routines used to calculate heat release from measured cylinder pressure.
ENGINE (GT−POWER) REFERENCE TEMPLATES : EngCylCombSIWiebe − SI Wiebe Combustion Model
EngCylCombSIWiebe - SI Wiebe Combustion Model
This object imposes the combustion burn rate for spark-ignition engines using a Wiebe function. It can be used with any type of injection. If at any instant the specified cumulative combustion exceeds the specified injected fuel fraction for a direct-injected SI ( DISI) engine, the combustion rate will be limited by the amount of fuel available. Please note that if the imposed combustion rate starts before the cycle-start, all fuel prescribed to be burned prior to cycle-start will be burned on the second timestep of the cycle (resulting in a "spike" in the burn rate). An Excel file named WiebeComb.xls 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 using the 'EngBurnRate' template. However, note that the 'EngCylCombProfile' reference object can be used to directly input the burn rate calculated from cylinder pressure, and so it is not necessary to match the Wiebe parameters to measured combustion data. Please see the Engine Performance Manual section on “Calculating Burn Rate from Measured Cylinder Pressure” for details.
Air Burning Enhancement Factor
Burned Fuel % at Anchor Angle
Percentage burn point used for the Anchor Angle ("def"=50). This point must always be 0.1% higher than the duration start and 0.1% lower than the duration end to obtain a profile that will satisfactorily fit the defined points. Percentage burn point that signals the start of the Burn Duration attribute ("def"=10). Percentage burn point that signals the end of the Burn Duration attribute ("def"=90). This point must always be 10% higher than the duration start to obtain a profile that will satisfactorily fit the defined points.
Main
Anchor Angle (def = 50% Burn) Angle "anchoring" the Wiebe curve to TDC or the name of a dependency reference object specifying the angle. The specified angle is the number of crank angle degrees between TDC and typically the 50% combustion point of the Wiebe curve. The attribute Burned Fuel % at Anchor Angle below may optionally be used to change the burn point in the Wiebe curve from 50%. (Typical values are 5 to 12 degrees after TDC.) Duration of Wiebe combustion curve or the name of a dependency reference object specifying the burn duration. The duration by default excludes the first 10% and last 10% of the total combustion duration, but the attributes in the Options folder below may be used to set the burn points where the duration is measured. (Typical values are 25 to 35 degrees.). Wiebe curve exponent or the name of a dependency reference object. ("def"=2.0)