3. Refined Model (Three-way Pipe Junctions)
4.13. Assembled Elements
4.13.1. Air Cleaner
BOOST automatically creates a more refined calculation model of a plenum-pipe-plenum type for the air cleaner. This is used to model the gas dynamic performance of the air cleaner as well as the pressure drop over the air cleaner depending on the actual flow conditions.
4.13.1.1. General
The input of the total air cleaner volume, the inlet and outlet collector volumes and the length of the filter element is required. It is important to note that the length of the cleaner pipe is also used to model the time a pressure wave needs to travel through the cleaner. The physical diameter of the cleaner pipe is calculated from the specified pipe volume (Vpipe = Vtotal– Vinlet collector– Voutlet collector) and the specified pipe length (length of filter element).
By default the hydraulic diameter in Equation 2.4.9 in the Theory Manual is identical with the physical diameter. By activating the Hydraulic Settings option the hydraulic diameter can be specified by the user directly or via the hydraulic area.
4.13.1.2. Friction
There are two options to specify the performance (pressure drop) of the air cleaner:
Option 1: Target Pressure Drop
The air cleaner pressure drop is specified by means of a reference mass flow, the target pressure drop (defined as the static pressure difference at the inlet and the outlet pipe attachment) at the reference mass flow and the inlet air conditions (temperature and pressure), Figure 4-58.
Figure 4-58: Steady State Air Cleaner Performance
On the basis of this information, the wall friction loss of the model is adjusted by the program.
Option 2: Coefficient
The pressure drop of the air cleaner is calculated using the specified values for laminar and turbulent friction coefficients and the specified hydraulic diameter of the pipe as described in section 2.4 of the Theory Manual.
4.13.1.3. Flow Coefficients
Particular flow resistances at the inlet to and at the outlet from the air cleaner can be considered. The flow coefficients for the pipe attachments may be specified as a function of time in seconds, time in degrees crank angle or pressure difference at the pipe attachment.
For in-flow (flow into the air cleaner) the pressure difference is defined as the static pressure in the pipe minus the pressure in the air cleaner collector, and for out-flow as the pressure in the air cleaner collector minus the static pressure in the pipe. Refer to Flow Coefficients for details on standard values and directions.
4.13.2. Catalyst
Click on Aftertreatment or Linear Acoustics for relevant information.
As for the air-cleaner (refer to 4.13.1) BOOST automatically creates a more refined
calculation model of the catalyst. This is used to model the gas dynamic performance of the catalyst as well as the pressure drop over the catalyst depending on the actual flow
conditions.
4.13.2.1. General
) Note: The catalyst model in the BOOST cycle simulation can also be used in combination with chemical reactions. Please refer to the BOOST Aftertreatment Manual for additional information.
The input of the total catalyst volume (i.e. the monolith volume consisting of the gas and also the solid structure), the inlet and outlet collector volumes and the length of the monolith is required.
The specification of the honeycomb cell structure has a decisive effect on the pressure drop that is calculated for the catalyst:
• Square Cell Catalyst: The hydraulic diameter of the catalyst pipe is defined via a CPSI value and a wall and washcoat thickness.
• General Catalyst: The hydraulic diameter of the catalyst pipe is defined directly or via the hydraulic area of the catalyst front face (without solid part). The input of open frontal area (OFA) and geometric surface area (GSA) is relevant only if chemical reactions are active in this catalyst.
In order to simulate the chemical conversion behavior of the catalyst, activate the Chemical Reactions toggle switch in any case. Otherwise the catalyst is understood as flow element where only data about geometry and friction is required.
The basic geometry has to be defined by the following data:
Typical Values and Ranges Monolith Volume Determines the volume of the monolith in
comprising both, the volume of the gas phase and the solid substrate.
1–10 (dm3)
4.13.2.2. Type Specification
The cell structure of the monolith can either be defined assuming Squared Cell Catalysts in a simplified way or within any geometrical assumptions for General Catalysts.
If Square Cell Catalyst is selected, the following input data has to be defined:
Typical Values and Ranges Cell density
(CPSI)
Determines the type of monolith using the number of channels per in2.
100–900(1/in²)
Wall Thickness Determines the thickness of the monolith’s walls.
0.006–0.015 (in)
Washcoat Thickness
Determines the thickness of the washcoat. 0–0.003 (in)
If General Catalyst is selected, the following input data has to be defined:
Typical Values and Ranges Open Frontal
Area (OFA)
Determines the open frontal area (= fluid volume fraction) of monolith.
0.50–0.75 (-)
Hydraulic Diameter
(Hydraulic Area)
Determines the hydraulic unit or (diameter or area) of the monolith channels.
0.001–0.005 (m)
Geometric Surface Area (GSA)
Determines the geometric surface area. This surface is used for heat and mass transfer between the gas and the solid phase.
1500–4000 (m2/m3)
4.13.2.3. Friction
The friction of the catalytic converter model can either be specified by Target Pressure Drop or by a friction Coefficient. If the catalyst is simulated in the aftertreatment analysis mode only the specification of a friction coefficient can be used. For the case of a standard BOOST cycle simulation both input variants can be used.
If Target Pressure Drop is selected, the following data is required:
Typical Values and Ranges Inlet Mass Flow Determines the inlet mass flow, as reference
value for the evaluation of a friction coefficient.
Determines the inlet temperature, as
reference value for the evaluation of a friction coefficient.
300 (K)
Inlet Pressure Determines the inlet pressure, as reference value for the evaluation of a friction coefficient.
1 (bar)
Target Pressure Drop
Determines the pressure drop the element, as basis for the evaluation of a friction
coefficient.
0.003 (bar)
If Coefficient is selected, the following input data is required:
Typical Values and Ranges Laminar
Coefficient a
Determines a laminar friction coefficient according to Equation (23) in the
Aftertreatment Manual.
64 (-)
Laminar Coefficient b
Determines a laminar friction coefficient according to Equation (23) in the
Aftertreatment Manual.
-1 (-)
Turbulent (Friction Coefficient)
Determines a turbulent friction coefficient.
The friction coefficient can be specified as constant or table value (see typical values below). The latter value is defined as a function of the monolith length.
0.01–0.04 (-)
Friction Multiplier Channel Shape
Determines a dimensionless factor that
considers the influence of the channel shape in the case of laminar flow. The multiplier either can be chosen for different channel geometries (see section 3.4 of the Aftertreatment Manual) or setup completely free.
0.04–1 (-)
There are two options to specify the performance (pressure drop) of the catalyst:
Option 1: Target Pressure Drop Please see section 4.13.1.1 for details.
Option 2: Coefficient
4.13.2.4. Flow Coefficients
Please see section 4.13.1.3.