Week 9: Project 1 - Surface preparation and Boundary Flagging (PFI)

Aim:-The aim of this project is to simulate the no hydro simulation for an IC engine and by surface preparation and Boundary Flagging.

Theory:-

The most widely produced internal combustion engines were of the Port Fuel Injected (PFI) design, where the fuel is sprayed into the intake ports to mix with incoming air. A four-stroke (also four-cycle) engine is an IC engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along with the cylinder, in either direction. The four separate strokes are termed as 

Intake, Compression, Expansion, and Exhaust.

The 4-stroke PFI (Port fuel injection) model is given to perform the no-hydro simulation it means that there will be no reaction and how the mesh was done & the movement of parts in the engine is working that will be checked.

Introduction:-

Fuel injection is the introduction of fuel in the internal combustion engine most commonly automotive engines by the means of an injector. Port fuel injections long ago replaced carburetors in cars because of their efficiency and lower maintenance requirements.

The fuel injector is installed in the intake manifold and they are cheap in production and do not have to withstand high pressure from the combustion chamber. The fuel injector injects the fuel into the combustion chamber through the intake valve owing to which the intake valve always remains and there is no carbon deposit in the intake valve. The major disadvantage with respect to the other injection system is that it lacks efficiency (better fuel economy) with respect to the other fuel delivery system.

Objective:- The task to be performed are as follows

1. Boundary Flagging.
2. Surface preparation.

After setting up the NO HYDRO case set up, make sure you create an animation for NO HYDRO and send it to us on Freshdesk ([email protected])

Make sure you are submitting a detailed report explaining the entire setup of NO HYDRO and showing all errors you came across and explain the meaning of each error.

Also, show the mesh on different slices at different time steps.

In an animation, all the valves and pistons should move accordingly to the crank angles and if it looks fine to us we will ask for the FULL HYDRO case set up.

We will run this FULL HYDRO case in our cluster and provide you with 3D OUTPUT FILES and Averaged output files so that you make use of them to post-process the results and get required plots respectively.

Surface Preparation:-

1. The STL file consisting of the geometry was loaded into CONVERGE.
2. A diagnosis was run to evaluate the quality of the geometry. The following errors in the geometry were noticed

       Intersections, Non-manifold Problems, Open Edges, Overlapping, and Normal Orientation

Normal Orientation

CONVERGE Studio requires that the normal for all the triangles be pointed inwards (towards fluid flow).  The Diagnosis tools can identify Normal Orientation issues by considering the directions of normals of the neighboring triangles since they need to be pointed in the same direction.

Prior to rectifying the errors in the geometry, boundaries were first identified as follows.

Piston:-

Inlet (Light Yellow Highlighted)

Liner (Yellow)

Cylinder Head

Exhaust Port

Outflow

Exhaust Valve Top

Exhaust Valve Angle (Red Highlighted)

Exhaust Valve Bottom (Green Colour)

 Intake Port (Divided into two portions)

Intake Bottom

 Intake Valve Angle

Intake Valve Top

Spark Plug

Spark Plug Terminal

Resolving Errors in Geometry:

Open Loop Edges- The Geometry comprised of Open Edges in Piston, Exhaust Port, and  Liner.  This was rectified using the following command

Geometry-Repair-Patch-Free Edge Loop- Edge Select- By Open Edge

Piston before rectification

Piston after rectification

A similar procedure was adopted to rectify the other open edges

2. Intersecting Edges

In the geometry, it was noted that the intake ports were interfering with the cylinder head. In the below snap, we can see that Intake port clashing with the cylinder head.

In order to rectify the above issue, The intake valve normal's were first computed. The normal vectors were noted. The intake valve was then translated by an amount of 0.005 to rectify this clash. The below command was used to rectify this problem

Geometry- Transform-Directional Vectors (Valve normal values inserted)- Translational amount.

Rectification of Normals- In the imported geometry all the normal vectors were pointing outwards.  This was rectified by using the 

Geometry-Transform-Normal-Propagate change from a single triangle.

This was done to ensure that the Normals pointed inwards in the direction of the flow.

Boundary Flagging:-

Application Type- Crank Angle based IC engine

Materials-

       Gas Simulation:- Defaults retained

Global Transport Parameters- Default retained

Reaction Mechanism- For the Reaction Mechanism, The mech.dat and therm.dat files provided were loaded into the simulation

Simulation Time Parameters:- Since the period of an  ICE engine cycle is 720 degrees, the start and end times have been set keeping this in mind

Solver Parameters (Default has been retained).

Regions and Initialization:-

The ICE engines were classified into four regions, namely Cylinder, intake1, intake 2, and exhaust region

i) Cylinder Region:- The mass fractions of the species were calculated based on the requirement for complete/stoichiometric combustion

ii) Intake 1- The mass fraction for the fuel-air mixture was inserted based on the typical composition for a standard ICE engine.

 iii) Intake_2:- Since air is taken in from intake port 2, the typical composition of air has been inserted.

iv) Exhaust Region:- Since whatever gas is to be exhausted through the exhaust region, comes from the combustion chamber, the composition of the exhaust gases is the same as that of the cylinder region.

Events 

 - To synchronize the cyclic opening of the intake and exhaust ports, events were created. The timing of the opening was obtained through the exhaust.in and intake.in files

Also the intake valves would be open throughout the combustion cycle. So a Permanent event was created.

- Permanent 

Boundary Conditions

 The component of the ICE engine was classified into different regions as shown below

The boundary condition for each component has been set as shown below.

- Piston:- Boundary Type- Wall

- Inlet:- Boundary Type- Inflow

- Liner:- Boundary Type- Wall

- Cylinder Head:- Boundary Type- Wall

- Exhaust Port:- Boundary Type- Wall

- Outlet:- Boundary Type- Outflow

Species:

The fuel we are using is iso-octane.

For the selection of species, we will write a stoichiometric equation for the reaction of iso-octane with air. 

C₈H₁₈ + ar*(O₂ + 3.76*N₂) = aCO₂ + bH₂O+ ar*3.76*N₂

Molecules	LHS	RHS
C	8	a
H	18	2b
O2	2ar	2a+b

Now from the above table, we have 3 unknowns with 3 equations hence solutions for unknowns are:

a = 8

b = 9

ar = 12.5

Final equation:

C₈H₁₈ + 12.5*(O₂ + 3.76*N₂) = 8CO₂ + 9H₂O+ 47*N₂

In the case of outflow, we are interested in products of the above stoichiometric reactions.

Converge takes the value in terms of the mass fraction so we should calculate the mass fraction of each product species and the sum of the mass fraction should always be ‘1’.

Products:

Molecules	Molecular weight	No of moles	The total mass of each molecule	Mass fractions
CO2	12+32 = 44	8	352	0.19235
H2O	2+16 = 18	9	162	0.08852
N2	28	47	1316	0.71912
		Total mass	1830	1

- Exhaust Valve Top:- Boundary Type- Wall, Movement as per exhaust_lift.in

- Exhaust Valve Angle:- Boundary Type- Wall. Movement as per exhaust_lift.in

- Exhaust Valve Bottom:- Boundary Type- Wall. Movement as per exhaust_lift.in

- Intake Port:- Boundary Type- Wall(Intake Port 1)

- Intake valve Bottom:- Boundary Type- Wall. Movement as per intake_lift.in

- Intake valve Angle:- Boundary Type- Wall. Movement as per intake_lift.in

- Intake Valve Top:- Boundary Type- Wall

- Spark Plug Terminal:- Boundary Type- Wall

- Spark Plug:- Boundary Type- Wall

- Intake Port:- Boundary Type- Wall (Intake Port 2)

- Turbulent Modelling:- RNG k-epsilon model is used.

- Base Grid:- An element size of 0.005 m has been selected,

-Fixed Embedding was enabled. This was done to ensure local refinement of the mesh so as to better capture the flow properties. Converge uses an octree data structure

a) Intake Valves: Embedding type Boundary, mode of embedding- Permanent. The scale factor is 4. This means the mesh cell size value at intake is 0.005/4=0.00125

b) Exhaust Valve= Embedding type Boundary, mode of embedding- Permanent. The scale factor is 4. This means the mesh cell size value at intake is 0.005/4=0.00125

c) Big Cylinder region:-Embedding type Boundary, mode of embedding- Permanent. The scale factor is 1

d) Small Cylinder region:-Embedding type Boundary, mode of embedding- Permanent. The scale factor is 2.

After setting the above, the input files were exported to a directory. In order to execute the simulation, the directory in which these input files were stored was accessed in Cygwin and the following command was typed "mpiexec.exe -n 4 converge.exe"
After the Simulation was executed, the results were converted into a form that would be compatible with Paraview. This was done using the "mpiexec.exe -n 4 post_convert.exe" command.

Results:-

at time step number 100

at time step number 150

at time step number 300

Animation

https://youtu.be/hrL3iJN4Zw8

Conclusion:-

In this project, the no hydrodynamic model was set up and observed in converge. The Valve motion and mesh refinement were found in accordance with the expected result.