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Thursday, 12 September 2013

CFD simulation of the intake manifold


Mahmoud Moeini Sedeh

Department of Mechanical Engineering
Samuel Ginn College of Engineering, Auburn University
1418 Wiggins Hall, Auburn, Alabama 36849-5341, USA

Design and optimization of intake manifold
predesign of intake manifold
Pre-design of intake manifold is conducted based on 1D models in order to:
1- Maximize the air flow rate into cylinders to maximize the volumetric efficiency and output torque
2- Provide cylinders with equal amount of air (or air/fuel mixture) to have a smooth engine performance with minimum vibration and noise


The 1D model of the intake manifold including plenum and runners and effective dimensions

3D CFD Model of the Intake Manifold

The initial shape of the intake manifold is determined through considering the packaging of the engine compartment and with respect to the packaging of other components of the intake system such as intake pipe and throttle body. The initial dimensions are based on 1D model, which is not accurate enough to ensure the equal flow to each cylinder. Furthermore, 1D models are not able to predict details of the flow through the manifold such as separation and turbulent characteristics. As a result, a design modification (or optimization) is conducted after pre-design, using a sophisticated 3D CFD model developed based on the initial shape of the intake manifold, resulting from pre-design and packaging. 
The 3D CFD model of the intake manifold showing the interior of the intake manifold in a MPFI engine including plenum and runners


Unstructured Grid

The grid generation and grid independence study were performed for the developed model. The grid is unstructured due to the shape of the intake manifold.
A benchmark of turbulence models was also conducted using 1-equation, 2-equation and Reynolds Stress models prior to performing the transient simulation of flow through intake manifold for an entire cycle of the engine.   

The unstructured tetrahedral grid, generated for the intake manifold


Outlet Pressure The pressure at the end of runners (i.e. outlet boundaries of the manifold or inlet ports) changes dynamically depending on engine rpm and the valve arrangement (i.e. combustion arrangement or firing order).
There are different ways to obtain such pressure variation and adopt it into the CFD model as the boundary conditions. Thermodynamic (1D) simulation of the engine (including intake, combustion, exhaust and valvetrain) can yield such pressure variations.
For optimization purposes, the pressure can be measured experimentally using pressure transducers and high speed data acquisition systems.
Such pressure variation is applied to the CFD model as a transient boundary condition.
Variation of pressure at the end of the runners (i.e. inlet ports of the cylinders) at 4000 rpm


Pathlines_flow through cylinder 3CFD analysis results elucidate details of flow behavior through runners (such as flow separation, secondary flows, reverse flows, etc.) and the total mass flow rate can be integrated for each cylinder.
Based on CFD results several modifications will be proposed to enhance the intake manifold and the flow characteristics through the cylinders.
Flow pathlines (colored by particle ID) during the intake of cylinder #3 at 4000 rpm

Velocity Contours
Contours of velocity magnitude at selected time instants during the entire cycle of engine operation




References:


[1] M. Moeini, N. Ale-Ebrahim, (2003) “Three dimensional solution of turbulent fluid flow through the intake manifold of MPFI Engine,” 4th International Conference of R&D Centers, Tehran, Iran, 2003.
[2] M. Moeini, (2002) “Numerical investigation of 3D steady and transient flow through the intake manifold of I.C. engine,”The 17th Internal Combustion Engines Symposium, Japanese Society of Automotive Engineers, Tokyo, Japan, JSAE 20026084, Oct 9-11.
[3] B. Farhanieh, M. Moeini, (2002) “Numerical solution of steady and transient fluid flow through the intake manifold using finite volume method,” 2nd International Symposium of Internal Combustion Engines, Tehran, Iran, Feb 2002.

The numerical simulations were conducted using Fluent 6.0, Fluent Inc., 2001.

CFD simulation of the intake manifold

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