Week 10: Project 1 - FULL HYDRO case set up (PFI)

Objective: To simulate the Full-hydro case setup of PFI.

• What is the compression ratio of the engine?
• Calculate the Combustion efficiency of the Engine.
• Determine the Power and torque of the engine by using an engine performance calculator.
• What is the significance of CA10, CA50, and CA90?
• Why do we need a wall heat transfer model? Why can't we predict wall temperature from CFD                 simulation?

 

Given parameters:

Engine Geometric Parameters

1. Bore =0.086 m
2. Stroke = 0.09 m
3. Connecting rod length = 0.18 m
4. RPM = 3000

Run parameters

1. Simulation mode: No Hydro

Simulation time parameters

1. Start time: -520 deg
2. end time: 120 deg

Boundary conditions

1. Piston temperature - 450K
2. Liner temperature - 450K
3. Head temperature - 450K
4. Spark Plug temperature - 550K
5. Spark Plug electrode temperature - 600K
6. Exhaust ports temperature  - 500K
7. Exhaust outflow - 1 bar
8. Exhaust outflow temperature - 800k
9. Exhaust species concentration - Calculate the stoichiometric condition
10. Exhaust valve top temperature - 525K
11. Exhaust valve angle temperature - 525K
12. Exhaust valve bottom temperature - 525K
13. Intake port - 1 temperature 425K
14. Intake port - 2 temperature 425K
15. Inflow pressure - 1 bar total pressure
16. Inflow temperature - 363K
17. Inflow species - Air
18. Intake valve top temperature - 480K
19. Intake valve angle temperature - 480K
20. Intake valve bottom temeprature - 480K

Initial conditions

• Intake port - 1 (closer to combustion chamber)
• ic8h18 - 0.025508
• o2 - 0.20157
• n2 - 0.77292
• Temperature - 390k
• pressure - 1 bar
• Intake port - 2 (away from combustion chamber)
• Air
• Temperature - 370K
• Pressure - 1 bar
• Cylinder
• Pressure - 1.85731 bar
• Temperature - 1360K
• Stoichiometric composition

Injection Parameters

1. Fuel flow rate = 7.5e-4 Kg/second
2. Injection start time = -480.0
3. Injection duration = 191.2
4. Fuel temperature = 330K

 

Nozzle positions

Nozzle diameter = 250 micrometer

Circular injection radius = Nozzle radius

Spray cone angle = 10

• Nozzle 0
• center 0.0823357 0.00100001 0.07019
• Align Vector -0.732501 0.210489 -0.647408
• Nozzle 1
• center 0.0823357 -0.00099999 0.07019
• Align Vector -0.732501 -0.210489 -0.647408
• Nozzle 2
• center 0.0823357 -0.0004 0.07019
• Align Vector -0.5 -0.2 -0.647408
• Nozzle 3
• center 0.0823357 0.0003 0.07019
• Align Vector -0.5 0.2 -0.647408

Spark Ignition Parameters

• Start of spark = -15 deg
• Spark duration = 10 deg
• Spark location = -0.003 0 0.0091
• Spark radius = 0.0005m

 

Geometry:

 

Simulation Case setup:

Application type:

• Crank angle based

 

Materials:

• Gas Simulation

• We select Parcel Simulation

•  Global Transport Parameters

• Reaction Mechanism

       therm.dat and mech.dat values loaded into the profile.

• Species

 

Simulation Parameters:

• Run Parameters

• Simulation time Parameters

• Solver Parameters

 

Regions and initialization

A region is a collection of boundaries used to differentiate different areas in the boundary.

• Cylinder region

• Intake Port 1

• Intake Port 2

•  Exhaust region

 

Boundary Conditions:

• Piston

 

• Inflow

• Liner

• Cylinder Head

• Exhaust Port

• Outflow

• Exhaust Valve Top

• Exhaust valve angle boundary

• Exhaust Valve Bottom

• Intake Port

• Intake valve bottom

• Intake valve angle

• Intake valve top

• Spark plug

• Spark plug terminal

• Intake port 2

 

Physical Models:

We select Spray modeling, Combustion modeling, Turbulence modeling, and Source/sink modeling.

 

• Spray modeling

        (a) General

        (b) Collision/Breakup/Drag

        (c) Wall Interaction

        (d) Injectors

 

• Combustion modeling

 

• Turbulence modeling

 

• Source/sink modeling

 

 

 

Grid Control:

We select Base grid, Adaptive mesh refinement, and Fixed embedding.

• Base grid

• Adaptive mesh refinement

• Fixed embedding

 

Results:

Compression Ratio

In a reciprocating engine, the piston oscillates between the Top dead center and the bottom dead center. These correspond to the minimum and maximum values respectively. The ratio between these two volumes is known as the compression ratio.

From the above graph we, note that

Maximum Cylinder Volume = `5.74186**10^(-4)` `m^(3)`

Minimum Cylinder Volume = `5.73996**10^(-5)` `m^(3)`

Compression ratio = `(5.74186**10^(-4))/(5.73996**10^(-5))`

Compression ratio = 10

 

Combustion efficiency of the Engine

Combustion efficiency is defined as the energy released by the burnt fuel to the theoretical energy content of the fuel.

 

`eta_(combustion)` = (Integrated Heat Release rate)/(mass of fuel * LHV)

Integrated Heat Release Rate= 1241.15 J

mass of fuel =  3x10^-5 kg

LHV = 43.4 MJ/kg

`eta_(combustion)` = `(1241.15)/(3**10^(-5) **43.4 **10^(6))` = 95.3 %

 

Need for Wall Heat Transfer model

Heat loss through the cylinder walls has a detrimental impact on the performance of the engine. Some of the undesirable effects include a reduction in volumetric efficiency, incomplete combustion, etc. The description of heat transfer in an ICE is a challenging task, considering the different systems (intake and exhaust ports, coolant circuit, lubricant oil subsystem), the different heat transfer mechanisms (convection, conduction, and radiation), and the rapid and unsteady changes that take place inside the cylinder. So there is a need to accurately model this phenomenon. Due to the complexity involved in a mathematical solution, there is a need to adopt suitable modeling.

 

Why we cannot use CFD  to predict wall temperature?

CFD can provide precise and instantaneous information about the flow within the engine (temperature, pressure, velocity distributions), but require temperature boundary conditions for the engine walls, which are typically assumed as being constant throughout the engine cycle. This will affect the combustion process, thus leading to inaccurate results  Imposing appropriate wall temperature boundary conditions is not an easy task, and may require some iterative process. However, such calculations with a given surface temperature are not sufficient when the focus is on analyzing the heat transfer within the engine. The heat flux and gas properties of the CFD are used as boundary conditions for the heat conduction calculation of the solid regions.

 

Significance of  CA10, CA50, and CA90

The CA10, CA50, and CA90  are defined as positions of the crank angle at which the cumulative heat release rate reaches 10%, 50 %, and 90%. The physical significance of CA10 is that it is used to signify the start of ignition in an engine, while CA 50 signifies the end of pre-mixed combustion and the start of diffusion combustion of fuel used in the engine. The greater the difference between CA10 and CA50, the higher the duration of combustion and vice versa.

 

Plots

• Cylinder Pressure

• Mean Temperature

 

Conclusion

In this project, a detailed simulation of the IC engine has been carried out. In the case setup, spray and combustion modeling was set up. The movement of piston, intake, and exhaust valves was created using regions and events. Mesh refinement techniques such as AMR and Fixed embedding were adopted to obtain finer results.

After simulation and post-processing, engine performance parameters such as compression ratio, power, and torque were computed and are listed below

Compression Ration=10.1

Power = 35.119 Kw

Apart from this, other aspects such as cylinder mean temperature and pressure, liquid particles, and emissions were studied as a function of a crank angle. Also, animations for temperature and spray modeling were examined.