Modelling and simulation of flow through a flowbench

OBJECTIVE:

To create a 3D model of an IC engine flow bench geometry and perform a flow analysis. For a particular valve lift, carry out a grid dependency test and identify the best grid size. Further, using this grid size perform a parametric study to study the effect of valve lift on mass flow rate.

SOLUTION:

A flow bench geometry is a device used to study the internal aerodynamic qualities of an engine component. It is primarily used to test the intake and exhaust ports used in cylinder heads in an IC engine. It is also used to test the capabilities of other automotive components like air filters, carburettors, manifolds and so on.

In this project, the aim is to analyse the flow over a valve used in IC engines. A flow bench geometry of the engine with a single valve is modelled and the analysis is carried out. The analysis includes a grid dependency test and parametric study to better understand the effect of valve lift on the mass flow rate.

Step 1:

A simple IC engine flow geometry is created constituting a cylinder, intake valve with a fuel port. The cylinder dimensions are 100mm in diameter and 100mm in height. The fuel port has dimensions of 25mm in diameter and the valve is designed as shown in the figure. The cylinder and fuel port was given a shell thickness of 2mm. Since the flow analysis is internal, lids were created at the end of fuel port and at the bottom of the cylinder to ensure that the model is airtight.

Step 2:

The flow analysis is set up using the wizard option. A steady state internal flow using air as the working fluid was defined. The boundary conditions included defining the pressure values at the both lids. At the fuel port lid, a total pressure of 200000 Pa was defined and at the bottom lid of the cylinder static pressure of 101325 Pa was defined. Further, while meshing all surfaces along the valve was given a finer mesh, to capture the behaviour better.

Step 3: Grid dependency test

In this test, the valve lift was maintained constant at 5mm and three different grid sizes was used. The corresponding velocity, pressure and mass flow rates were analysed. The grid size was made fine to the maximum capability of the machine. Even though, the best mesh was not achieved due to the limitations in the capability of the machine, the finest possible mesh size of 5 was used for further calculations.

Parameter	Design point 1	Design point 2	Design point 3
Mesh size	3	4	5
Pressure (Pa)
Min	89203.72	83877.44	76619.68
Max	194933.76	196578.26	196704.81
Velocity (m/s)
Min	5.26	8.06	4.08
Max	214.576	211.546	304.69
Mass flow rate (kg/s)
Surface goal	0.0655	0.0651	0.0604

Step 4: Parametric Study

In the parametric study, the mass flow rate behaviour with varying valve lift values was analysed. The maximum and minimum valve lifts were defined as 8mm and 5mm respectively and the flow behaviour at 6 different values (between 8mm and 5mm) was analysed.

Parameter	Design point 1	Design point 2	Design point 3	Design point 4	Design point 5	Design point 6
Valve lift (m)	0.005	0.0056	0.0062	0.0068	0.0074	0.008
Mesh size	5	5	5	5	5	5
Pressure (Pa)
Min	76645.66591	80426.90951	81155.15805	86773.88061	83848.1609	88274.25573
Max	196704.1898	195216.1279	192893.2865	191792.969	188372.7185	186045.4591
Velocity (m/s)
Min	4.054893153	2.853253613	0.954976378	3.06444544	0.29586214	0.573207849
Max	304.6447322	317.7622228	322.807963	334.6007592	329.9762535	349.5916122
Mass flow rate (kg/s)
Surface goal	0.060411485	0.073595199	0.084789942	0.095057012	0.103377105	0.11048618

From the results it can be observed that considerable changes in flow patterns takes place with varying valve lifts. When the valve lift changes from 5mm to 8mm,

1. The mass flow rate increases continuously, 60.4 g/s to 110.5 g/s.
2. The value of maximum velocity increases from 304.6 m/s to 349.6 m/s
3. The maximum pressure value decreases from 196.7 kPa to 186.04 kPa.