classGasolineEngineChp_EngineHousing
Information
Overview
The model of the motor housing uses a build-up scheme as a two-layer
wall with thermal transitions to a circulating cooling medium.
Assumptions were made to simplify the thermal simulation.
Assumptions
From individual cylinders, a total area (assumption: cylinder is at bottom dead center) is calculated and the heat conduction is modeled as a flat wall. This approximation of the unknown motor geometry with heat transfers to the environment and the cooling water circuit needs to be calibrated.
The engine block consists of a homogeneous material with known total weight and is divided into an inner and an outer part (default is grey cast iron)
For simplicity the oil circuit is considered as a capacity in the outer engine block that needs to calibrated as well. The cooling water circuit is assumed to run between these two parts (only the outer part interacts with the environment).
The thickness of the inner engine block is an essential, but unknown variable (literature indicates values around 5mm for car engines). Attachments and individual different material layers in the engine block are not taken into account for simplicity and can be approximated by calibration. The insulating housing of the power unit has no own capacity.
The heat transfer (cylinder wall to cooling water circuit) is calibrated and assumed to be proportional to the temperature difference because due to unknown cooling channel geometry the calculation of a convective heat transfer coefficient is not possible.
The temperature profile of the cylinder wall is homogeneously formed from the ambient temperature and the maximum combustion temperature (temperature curve in cylinder as a triangle with T_Amb - T_Com - T_Amb). Therefore a mean cylinder wall temperature is determinated using a bisector in the temperature profile as shown in the following figure.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Calibration properties | |||
| Modelica.Units.SI.Thickness | dInn | 0.005 | Typical value for the thickness of the cylinder wall (between combustion chamber and cooling circle) |
| Structure › Material Properties | |||
| AixLib.Fluid.BoilerCHP.Data.ModularCHP.EngineMaterialData | EngMatData | AixLib.Fluid.BoilerCHP.Data.ModularCHP.EngineMaterial_CastIron() | Thermal engine material data for calculations (most common is cast iron) |
| Modelica.Units.SI.ThermalConductivity | lambda | EngMatData.lambda | Thermal conductivity of the engine block material |
| Modelica.Units.SI.Density | rhoEngWall | EngMatData.rhoEngWall | Density of the the engine block material |
| Modelica.Units.SI.SpecificHeatCapacity | c | EngMatData.c | Specific heat capacity of the cylinder wall material |
| Structure › Engine Properties | |||
| Real | z | Number of engine cylinders | |
| Modelica.Units.SI.Thickness | dCyl | Engine cylinder diameter | |
| Modelica.Units.SI.Thickness | hStr | Engine stroke | |
| Real | eps | Engine compression ratio | |
| Modelica.Units.SI.Mass | mEng | Total engine mass | |
| Thermal | |||
| Modelica.Units.SI.ThermalConductance | GEngToAmb | 0.23 | Thermal conductance from engine housing to the surrounding air |
| Modelica.Units.SI.Temperature | T_Amb | 298.15 | Ambient temperature |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Real | nEng | Current engine speed | |
| Modelica.Units.SI.ThermalConductance | CalT_Exh | Calculation variable for the temperature of the exhaust gas | |
| Modelica.Units.SI.Temperature | T_Com | Calculated maximum combustion temperature inside the engine | |
| Modelica.Units.SI.Temperature | T_CylWall | Temperature of cylinder wall | |
| Modelica.Units.SI.Temperature | T_Exh | Inlet temperature of exhaust gas | |
| Modelica.Units.SI.Temperature | T_ExhPowUniOut | Outlet temperature of exhaust gas | |
| Modelica.Units.SI.MassFlowRate | m_Exh | Mass flow rate of exhaust gas | |
| Modelica.Units.SI.SpecificHeatCapacity | meanCpExh | Mean specific heat capacity of the exhaust gas | |
| Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a | port_amb | Heat port to ambient | |
| Modelica.Thermal.HeatTransfer.Components.HeatCapacitor | innerWall | Thermal capacity model of the cylinder wall | |
| Modelica.Blocks.Sources.RealExpression | realExpr1 | ||
| Modelica.Blocks.Sources.RealExpression | realExpr2 | ||
| Modelica.Thermal.HeatTransfer.Components.ThermalConductor | innerThermalCond | ||
| Modelica.Thermal.HeatTransfer.Sources.PrescribedHeatFlow | actualHeatFlowEngine | Heat flow from engine combustion | |
| AixLib.Fluid.BoilerCHP.ModularCHP.BaseClasses.BaseClassComponents.GasolineEngineChp_EngineHousing_CylToInnerWall | cylToInnerWall | Thermal model of the cylinder wall | |
| Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a | port_coo | Heat port to cooling circuit | |
| Modelica.Thermal.HeatTransfer.Sensors.HeatFlowSensor | engHeatToCoolant | ||
| AixLib.Fluid.BoilerCHP.ModularCHP.BaseClasses.BaseClassComponents.GasolineEngineChp_EngineHousing_EngineBlock | engineBlock | Thermal model of the engine block | |
| Modelica.Blocks.Sources.RealExpression | calculatedExhaustTemp | ||
| Modelica.Blocks.Interfaces.RealOutput | exhaustGasTemperature | Calculated exhaust gas temperature output to the mechanical engine model |
Contents
| Name | Description |
|---|---|
| Medium3 | |
| RotationSpeed |
Revisions
-
April, 2019 by Julian Matthes:
First implementation (see issue #667)