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

Aim:-

To simulate the PFI engine with full hydro setup including spray and combustion model using CONVERGE and post processing the results.

Theory:-

1. Port Fuel Injection Engine:-

1. The fuel injection system for conventional spark injection engine inject the fuel into the engine intake system .
2. This section review system where the fuel is injected into the intake port of each engine cylinder.
3. Thus these system require one injector per cylinder, there are both mechanical and electronically injection system.
4. The advantage of port fuel injection are increased power and torque through improved volumetric efficiency and uniform fuel distribution and more rapid engine response to change in throttle position and more precises control of equivalence ratio during the cold start and engine warm up.
5. Fuel injection allow the amount of fuel injected per cycle, for each cylinder, to be varied in response to input derived from sensor which define actual engine operating condition.
6. It is the most widely produced internal combustion engine, where the fuel is sprayed into the intake port to mix with incoming air.
7. The fuel injector in PFI configuration are typically mounted in the intake manifold and the air fuel mixture is pulled into the cylinder head as the intake valve open.
8. In the port injection arrangement, the injector is placed on the side of the intake port, the injector spray gasoline into the air, inside the intake manifold.
9. The gasoline mixer with the air in reasonably uniform manner. This mixture of gasoline and air then passes through the intake valve and enter into the cylinder.
10. Port fuel injection devotes a separate injection nozzle to each cylinder, right outside it intake port therefore, the system is also called as port injection.
11. Shooting the fuel vapour this close to the intake port almost ensure that it will be drawn completely into the cylinder. The main advantage is that MPFI meter fuel more precisely than do throttle body injection design, better achieveing the desired air fuel ratio and improving all related aspect.
12. Also, it virtually eliminates the possibility that fuel will condense or collect in intake manifold. With carburettor, the intake manifold must be designed to conduct the engine heat, a measure to vapourize liquid fuel.

2. Spary and Turbulence:-

1. Accurate spray and turbulence modelling is critical for predictive diseal and gasoline combustion simulation.
2. In order to obtain result that are as realistic, as possible, CONVERGE contain a wider variety of spray and turbulence modelling, option CONVERGE include both Reynold-Averaged Navier Stokes (RANS) and Large Eddy Simulation (LES) turbulence model.
3. For spary, CONVERGE contain a host of option to simulate injection, breakup, vapourization and other spray related process.
4. All of the spray and turbulence model in CONVERGE are well validated and powerful.

Geometry:-

After importing the geometry in the form STL file, we get following error.

1. Intersection Error:-

The plane of one triangle passes through the plane of another triangle. Here the intake valve is closed too far that valve angle overlaps with the cylinder head and hence the error.

2. Non-Manifold Error:-

An edge that is shared by more than two triangle which does not include interface boundaries. This is an error in IC engine problem except to that of conjugate heat transfer problem.

3. Open Edge:-

Triangle with at least one edge that is not shared by another triangle can be repaired by sitch method or by creating new triangle.

4. Normal orientation:-

Triangle whose normal vector are approximately 180 degree different than the normal vector of adjacent triangle can be repaired by using normal open.

After solving all the error the geometry obtained as shown below

This geometry is proper for case setup and simulation purpose.

CASE SETUP:-

1. Application type:-

1. Crank angle based IC engine - On

2. Material:-

1. Gas simulation - On
2. Parcel simulation - On
3. Reaction Mechanism - On
4. Species - On

Species:-

3. Global Transport Parameter:-

1. Turbulent Prandtl Number - 0.9
2. Turbulent Schmidt Number - 0.78

4. Run parameter:-

1. Solver - Transient
2. Temporal type - Crank angle based engine simulation
3. Simulation mode - No Hydrodynamics
4. Gas flow solver - Compressible
5. Liquid flow solver - Incompressible

5. Simulation time parameter:-

1. Start time :- -520 degree
2. End time :- 120 degree
3. Initial time step - 1e-7
4. Minimum time step - 1e-8
5. Maximum time step - 1e-4

6. Boundary Condition:-

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. Exhaut outflow - 1 bar
8. Exhaust outlflow 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 temeprature - 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

7. Region and Initialization:-

Here we create region id to assign temperature and pressure to each region and initialize species, passive and turbulence in each region. By doing this we can highlight and isolate all boundaries associated to a region.

Combustion equation and mass fraction of species in the region

`C_8H_(18)+12.5(O_2+3.76N_2)rightarrow8CO_2+9H_2O+47N_2`

Species	Moles	Molecular wt (g/mol)	Mass	Mass Fraction
`CO_2`	8	44.01	352.08	0.192304
`H_2O`	9	18.01528	162.1375	0.088559
`N_2`	47	28.0134	1316.63	0.719137
		Total	1830.847	1

1. Combustion Chamber region:-

2. Intake Port region 1:-

3. Intake Port Region 2:-

4. Exhaust Port Region:-

8. Event:-

Using the event section is the only way to dicontinue flow between two region. To create custom CLOSE, OPEN or VALVE event between two or more region at defined interval.

1. Cyclic Event:-

2. Permanent Event:-

9. Spray Modelling:-

1. It can be used for both gas and liquid spray CONVERGE include state of art model for spray process including liquid atomization, drop breakup, turbulent dispersion and drop evaporation.
2. For PFI and direct injection system for IC engine, fuel spraying is taken into account.
3. Converge uses the Langragian solver to model discrete parcel and the Eulerian solver to model continuous fluid domain. It uses parcel into the domain of the injector. These parcel into the domain of the injector, these parcel are nothing but a group of identical drop and solves on per-parcel basis.
4. The drag force experienced by the spray are reason for their disturbance and cause primary and secondary breakup
5. The injection spray is in conical form and distribution uniformly throughout the cone is selected.

1. Evaporation Model:-

The evaporation model describe rate at which radius of drop shrinks and rate at which mass is being transferred in gaseous state added as source term in the species mechanism.

2. Collision Model:-

1. The NTC model involves stochastic sub sampling of the parcel within each drop. This result in much faster collision calculation.
2. In collision model, parcel in the same cell collide only leading to grid sensitivity.
3. Converge has adaptive collision mesh option to reduce grid sensitivity so that parcel can collide across grid cell.

3. Wall Interaction:-

1. In wall film drop action are calculated by hybrid approach based on particle based quantitie.
2. For this O'Rourke splash model is used that is based on Weber number, film thickness and viscosity.

4.Injector:-

Nozzle positions

Nozzle diameter = 250 micro-meter

Circular injection radius = Nozzle radius

Spray cone angle = 10

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

Calculation of Total Injected mass

• Rotation per min = 3000
• Rotation per second = 50
• Degree per second = 18000 degree/s
• Time per degree = 5.55556e-05 s
• Time per 720 degree = 0.04 s
• Fuel Flow rate = 7.5e-4 kg/s
• Fuel mass/cycle = (Time per 720 degree)*(fuel flow rate) = 3e-5 kg
• Therefore, the total injected mass = 3e-5 kg

Four nozzle are added from nozzle 0 to nozzle 3 . For each nozzle the configuration all the parameter listed above are given previously and it should be done for all the nozzle and are validated to check if they aer within the computational domain.

10. Combustion Model:-

1. Converge provided detailed combustion and simplified combustion. The detailed combustion takes lot of computational time to accurately model ignition and laminar flame propogation.
2. On the other hand, generally less computationally expensive and less predictive. This may be used if we want to use global parameter correctly or just find out the maximum combustion temperture.
3. Here, we use SAGE detailed chemistry solver that are local condition to calculate reaction rate based on principle of chemical kinetics.

• Fuel species name - IC8H18
• Under relaxation for steady state combustion - 0.25
• Temporal type - Cyclic
• Cyclic period - 720 degree
• Start time - -17 degree
• End time - 130 degree
• Region - Not region dependent
• Combustion temperature cut off - 600

11. Turbulence Model:-

12. Source /Sink Model:-

1. Two energy source that is spark plug and its terminal. This is the source in the energy equation responsible for increase of temperature of species.
2. In the first 0.5 degree of total 10 degree of energy source is 20 million Joule combining for 40 million Joule in first 0.5 degree and after those 20 million Joule for the rest angle.

Spark Ignition Parameters

1. Start of spark = -15 deg
2. Spark duration = 10 deg
3. Spark location = -0.003 0 0.0091
4. Spark radius = 0.0005m

Source 1 parameter

Source 2 parameter

Spark Plug with Source

GRID SIZE:-

dx = dy = dz = 4 mm

1. Adapative Mesh Refinement:-

It eliminates the need to mesh the whole model finely Adaptive mesh refinement provides such a dynamics programming environment for adapting the precision of the numerical computation based on the requirement of a computation problem in specific areas which need precision while leaving the other region at lower level of precision and resolution.

2. Fixed Embedding:-

1. Inlet and Exhaust Valve embedding:-

Inlet Valve Embedding

Exhaust Valve Embedding

Here, for the intake valve, the boundary type embedding is used. The embedding is used to get the refinement near the intake valve angle and the Boundary ID is given the same. The scale is 3 and the mesh size will be 0.5 mm. It is fixed and the same for Exhaust Valve also.

2. Combustion Chamber Embedding:-

Big Cylinder Embedding

Small Cylinder Embedding

To capture the combustion precisely, the combustion chamber is made with the cylindrical embedding. The small and big cylinder are used with mentioned sizes with of 1 and 2 with mesh size 2 mm and 1 mm respectively.

3. Spark Plug Embedding:-

Large Sphere Embedding

Small Sphere Embedding

To understand precisely the spark flame propogation embedding sphere of radius 1 and 3 mm with scale of 4 and 3 are used with start and end time.

4. Injector Embedding:-

For injection, the injector type embedding is used. The injector 0 is the injector ID and the radius 2, 4 mm and length are given. The scale is 4 on the mesh size will be 0.25 mm.

PLOT:-

1. Pollutant:-

Soot

Amount of Hiroy Soot estimated around 2.54e-8 kg

NOx

Amount of NOx estimated is around 1.28e-6 kg

CO

Amount of CO estimated is around 7.127e-6 kg

1. Pollutant such as CO, NOx and soot which is generally formed as an unwanted by product of incomplete combustion.
2. Soot generated within flames consist essentially of aggregates of sphere of carbon.

2. Pressure:-

1. The pressure plot show how the pressure varies inside the combustion chamber. The pressure start to increase rapidly during start of injection and is highest in the phase of combustion process.
2. The maximum pressure in the cycle is observed about 0.834 MPa

3. Temperature:-

1. As pressure varies inside the combustion chamber, the temperature also varies since they both are directly proportional that is due combustion, the temperature increase.
2. The maximum temperature observed during the cycle is about 1689.64 K

4. Otto Cycle:-

1. An Otto Cycle (P-V) is an idealized thermodynamics cycle that describe the function of a typical spark ignition piston engine.
2. The Otto cycle is a description of what happen to a mass of gas as it is subjected to change of pressure, temperature, volume, addition of heat and removal of heat.

5. Fuel trapped:-

1. Nowadays, there is an increasing demand for improving engine performance in order to fulfil customer expectation meet more restrictive environment regulation and release fewer emission.
2. To improve the engine performance, its influential parameter should be recognized.
3. One of its is the amount of residual gas remained in the cylinder from the previous cycle.
4. This is because of wall collision and absorption of gas particle on wall of combustion chamber.
5. The maximum amount fuel mass trapped in the cycle is about 1.564e-5 kg

6. Liquid Spray:-

1. Liquid spray drop represent number of active Lagrangian parcel in the domain. These are formal due to vapourization and after the combustion take place, end of the show that amount of drop which are left over that in the unbrust hydrocarabon.
2. Here, the amount of drop left is almost zero which increase overall efficiency of the engine.

1. What is the compression ratio of this engine?

In a reciprocating engine, the static compression ratio is the ratio between the volume of the cylinder and the combustion chamber when the piston is at the bottom of its stroke and the volume of the combustion chamber when the piston is at the top of its stokes.

C.R. = maximum volume/minimum volume

C.R. = 0.000574216/ 5.7029438e-5

C.R. = 10.06:1

2. Why do we need a wall heat transfer model? Why can't we predict the wall temperature from the CFD simulation?

1. It is known that heat transfer in I. C. Engine affect engine efficiency and emission. An increase of heat transfer to the combustion chamber walls lower the in cylinder pressure and the average gas temperature and this reduce the work per cycle transferred to the piston.
2. Thus, the magnitude of engine heat transfer is strongly dependent on engine efficiency the change in the gas temperature due to heat loss through the combustion chamber also have an impact on the pollutant emission formation.
3. A higher in cylinder temperature promotes the NOx emission and the lower in cylinder temperature causes the particular during the exhaust. Since, the engine heat transfer is important, the accurate predicted engine heat transfer result are needed.
4. It takes a lot of time especially in I. C. Engine for computing the equation of fluid part along with the combustion and reaction process. In order to obtain accurate values of heat flux of a multi dimensional model for a core region, one dimensional model, conversion of mass, momentum and energy were generally used within the wall layer. Since the mechanism of wall model generally used within the wall layer.
5. Since the mechanism of wall layer are similar to the physics in the boundary layer, the predicted heat flux were solved by using thermal boundary. Wall heat transfer model are basically used for approximation in this case.
6. Wall heat transfer model are dedicated modelling to focus only on heat transfer among the core region. The internal combustion engine industry is moving toward simulating the entire system rather than independent component.
7. Converge after Conjugate Heat Transfer (CHT) the simulation prediction of heat transfer in both the fluid and solid portion of the domain is of critical importance in a full engine simulation. The accuracy of the predicted combustion in the cylinder is dependent on the temperature boundary condition in the cylinder. By considering heat transfer in the metal component in the simulation, the cylinder was no longer has a user specified temperature, but instead has temperature predicted a part of the system simulation.
8. This makes the overall simulation results more predictive by reducing the dependence on boundary condition.

3. Calculate the combustion efficiency of this engine

Combustion efficiency is defined as the ratio between the energy released by the burnt fuel and the theoretical energy content of the fuel mass during on complete engine cycle.

• From the above plot, total heat during the combustion that the Work output is 1241.15 J
• The fuel energy input is product of amount of fuel and Calorific value of fuel
• Amount of fuel used = 30 micron = 30e-6 kg
• Calorific value of Iso-Octave = 44.8 MJ/kg
• Therefore, Fuel input = 30e-6 * 44.8 = 1344 J
• Combustion efficiency = Work done/ Fuel Input = 1241.15/1344 = 0.9234 = 92.34%

4. Use the engine performance calculator, to determine the power and torque for this engine.

• Power = Work/Time
• Work done = 1241.15 J
• RPM = 3000, RPS = 3000/60 = 50, DPS = 50*360 =18000
• Therefore, Time per degree = 1/DPS = 1/18000 = 5.55e-5 sec/degree
• Time for moving 240.199 degree = 240.199 * 5.55e-5 = 0.013331 seconds
• Power = 1241.15/0.013331 = 35.15 kW
• Power = `frac{2piNT}{60}`
• 35.15 = (2*3.14*T*3000)/60
• T = (35.15 * 60)/(2*3.14*3000)
• T = 111.95 Nm
• Therefore, Torque is 111.95 Nm

5. What is the significance of CA10, CA50 and CA90?

The significance of CA10, CA50 and CA90 are as follows:-

1. CA10 refers to the time when 10% of charge mixture has combusted depending upon the crank angle. It value for this PFI engine is 6.83717 degree.
2. CA50 defines the crank angle when the half of charge mixture completed to burn in the combustion chamber. It value for this PFI engine is 18.4623 degree.
3. CA90 define as the time 90% of mixture has completed to combust. It value for this PFI engine is 31.701 degree

Animation:-