Combustion simulation of Port Fuel Injection SI engine

Aim: Port Fuel Injection SI Engine.

Objectives: In this part of the projects, the Full-Hydrodynamic case will be set-up and the processes of SI Engine with respect to crank angles will be simulated.

Multipoint fuel injection (MPI), also called port fuel injection (PFI), injects fuel into the intake ports just upstream of each cylinder's intake valve, rather than at a central point within an intake manifold. MPI systems can be sequential, in which injection is timed to coincide with each cylinder's intake stroke; batched, in which fuel is injected to the cylinders in groups, without precise synchronization to any particular cylinder's intake stroke; or simultaneous, in which fuel is injected at the same time to all the cylinders. The intake is only slightly wet, and typical fuel pressure runs between 40-60 psi.

Introduction: The internal combustion IC engine is a heat engine that converts the chemical energy of a fuel into mechanical energy, usually mechanical energy available on a rotating output shaft. The chemical energy of the fuel is first converted into thermal energy by means of combustion of fuel with air inside the engine. This thermal energy raises the pressure and temperature of the gases inside the engine, and the high-pressure gas then expands against the mechanical mechanism of the engine. This expansion of gases is converted by the mechanical linkage of the engine to the rotating crankshaft, which is the output of the engine.

Theory:

INTERNAL COMBUSTION ENGINE PARTS AND THEIR FUNCTION:

1. Cylinder Block:- It is a container fitted with piston, where the fuel is burnt and power is produced.
   Cylinder is the main body of IC engine. Cylinder is a part in which the intake of fuel, compression of fuel and burning of fuel take place. The main function of cylinder is to guide the piston.
   For cooling of cylinder a water jacket (for liquid cooling used in most of cars) or fin (for air cooling used in most of bikes) are situated at the outer side of cylinder.
   At the upper end of cylinder, cylinder head and at the bottom end crank case is bolted.
2. Cylinder Head/Cylinder Cover:- One end of the cylinder is closed by means of cylinder head. This consists of inlet valve for admitting air fuel mixture and exhaust valve for removing the products of combustion.
   The inlet valve, exhaust valve, spark plug, injector etc. are bolted on the cylinder head. The main function of cylinder head is to seal the cylinder block and not to permit entry and exit of gases on cover head valve engine.
3. Piston:- Piston is used to reciprocate inside the cylinder.
4. Piston Rings:- These are used to maintain a pressure tight seal between the piston and cylinder walls and also it transfer the heat from the piston head to cylinder walls.
   These rings are fitted in grooves which have been cut in the piston. They are split at one end so they can expand or slipped over the end of piston.
5. Connecting Rod:- One end of the connecting rod is connected to piston through piston pin while the other is connected to crank through crank pin.
   It transmits the reciprocatory motion of piston to rotary crank.
   There are two end of connecting rod one is known as big end and other as small end. Big end is connected to the crankshaft and the small end is connected to the piston by use of piston pin.
6. Crank:- It is a lever between connecting rod and crank shaft.
7. Crank Shaft:- The function of crank shaft is to transform reciprocating motion in to a rotary motion.
   The crankshaft of an internal combustion engine receives the efforts or thrust supplied by piston to the connecting rod and converts the reciprocating motion of piston into rotary motion of crankshaft.
   The crankshaft mounts in bearing so it can rotate freely.
   The shape and size of crankshaft depends on the number and arrangement of cylinders.
8. Fly wheel:- Fly wheel is a rotating mass used as an energy storing device.
   A flywheel is secured on the crankshaft. The main function of flywheel is to rotate the shaft during preparatory stroke. It also makes crankshaft rotation more uniform.
9. Crank Case:-
   It supports and covers the cylinder and the crank shaft. It is used to store the lubricating oil.
   The main body of the engine to which the cylinder are attached and which contains the crankshaft and crankshaft bearing is called crankcase. It serves as the lubricating system too and sometime it is called oil sump. All the oil for lubrication is placed in it.
10. Poppet Valves: A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways.

The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust.
Note that both valves are closed during compression and combustion so that the combustion chamber is sealed.

11. Spark Plug:

The main function of a sparkplug is to conduct the high potential from the ignition system into the combustion chamber.
It provides the proper gap across which spark is produced by applying high voltage , to ignite the mixture in the ignition chamber.

12. Fuel Atomizer or Injector
Fuel injection is a system for mixing fuel with air in an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburettors in the late 1980s.
The primary difference between carburettors and fuel injection is that fuel injection atomizes the fuel by forcibly pumping it through a small nozzle under high pressure, while a carburettor relies on low pressure created by intake air rushing through it to add the fuel to the airstream.
The fuel injector is only a nozzle and a valve: the power to inject the fuel comes from a pump or a pressure container farther back in the fuel supply.

13 Manifold
The main function of manifold is to supply the air fuel mixture and collects the exhaust gases equally form all cylinder. In an internal combustion engine two manifold are used, one for intake and other for exhaust.

Terminology used in IC engine:

1. Cylinder bore (D): The nominal inner diameter of the working cylinder.
2. Piston area (A): The area of circle of diameter equal to the cylinder bore.
3. Stroke (L): The nominal distance through which a working piston moves between two successive reversals of its direction of motion.
4. Dead centre: The position of the working piston and the moving parts which are mechanically connected to it at the moment when the direction of the piston motion is reversed (at either end point of the stroke).

(a) Bottom dead centre (BDC): Dead centre when the piston is nearest to the crankshaft.

(b) Top dead centre (TDC): Dead centre when the position is farthest from the crankshaft.

5. Displacement volume or swept volume (Vs): The nominal volume generated by the working piston when travelling from the one dead centre to next one and given as, Vs=A × L
6. Clearance volume (Vc): the nominal volume of the space on the combustion side of the piston at the top dead centre.
7. Cylinder volume (V): Total volume of the cylinder. V= Vs + Vc
8. Compression ratio (r): r=Swept volume(Vs)/ Clearance volume(Vc)

Simulation:

The following Simulation tools will be incorporated:

1.Converge studio:- To pre-process the data that needs to simulate the case. It plays an important role in generating important 3d input files only using GUI. It does not run simulation directly, however it generates inputs files which use to run the simulation.

2. Cygwin:- Cygwin is a collection of GNU and open-source tools that provide the functionality similar to Linux distribution on windows.
3. Converge msmpi 3.0:- To run the simulation using these input files in Cygwin in series or in parallel.
4. Post convert:- To convert all the output files which are processed by converge msmpi into the files which will be readable for post-processing in Paraview.
5. Paraview :- To post-processing to obtain the contour, plots, etc. It is an open-source, multi-platform data analysis and visualization software.

Geometry Setup:

Boundary Flagging

• To cleanup the model, we first need to flag the boundaries, so that we can hide the parts while cleaning up.

Flag Inflow.

• Create boundary fence to top and bottom of liner and flag it.

• Flag Cylinder head by creating a boundary fence across its boundaries.

Flag Exhaust and Outflow

• Flag the exhaust and inlet valves into three different parts as we want to create the disconnect triangles between the Valve and the port and also we want embedding in the Inlet and Exhaust valves angles.

• Now, we can see that, the valves and are intersecting with the Port. Hence we need to move the valves to avoid intersection error.

For that measure the position of the top valve.

Measure->Direction->Arc normal->select 3 top points of Inlet valve top->Apply. Copy Arc normal from the Message log and paste it.

Then translate the valve from, Transform->Translate->Selected boundary-> Select Inlet valve top, angle and bottom->Translate amount 0.001m

• Create the rim triangles to avoid the alignment error.

• Patch the Open edges to avoid Open edge error by deleting the intersecting triangles and stiching them.

• Remove normal error by changing the normal direction inwords.
• Flag Spark plug and Spark plug Terminal.

• Divide the Intake port into two different regions as our Injector will inject the Air+fuel mixture from the half portion of the port.

• There is a slight gap between the port and the valve in close position, hence we are creating disconnect triangles to restrict the flow of the mixture in the cylinder by assigning Events. The Converge studio looks for the nearby intersection points with them the disconnect triangles will be created.

Not desirable as the below figure shows the disconnect triangles restricting the flow completely even when the valve opens.

• Fixed Embedding near the Inlet and Exhaust valve angles

• When the valve is at close position, still there is very small gap of 0.2mm between the valve angle (valve seat) and port angle, is called as min lift. We want a cutcell in min lift such that it should not get paired with its main cell. That is the cut cell size should be 30% greater than the normal cell size. Otherwise the cell size in mean lift will be bigger than 0.2mm and our Mesh quality will be reduced.

Final Geometry:

Case Setup/Simulation Setup:

Click on IC engine. ->Assign cylinder dimensions, cylinder bore=0.086m, Stroke=0.09m, Connecting rod length=0.18m, Crank speed=3000rpm.

MATERIAL:

Gas Simulation:

• check Reaction Mechanism.
• Predifined mixture: air
• Enable species(not in mech.dat) as we want to assign the participating species of Air like O2 and N2
• Parcel Simulation: Predefined liquid IC8H18 (for Petrol/Gasoline Engine)

Gas Simulation:

• Import thermo.dat (contains thermodynamic properties of species)

Reaction mechanism:

• Import mech.dat(Types of species)

Global Transport Properties

• Turbulent Prandtl number: 0.9
• Turbulent Schmidt number: 0.78

Species:

• Add Parcel species IC8H18

SIMULATION PARAMETER:

Run Parameter:

• Solver: Density-based Transient
• Simulation Mode: Full hydro.
• Gas flow Solver: Compressible (as air is working medium)

Simulation Time Parameter:

• End time: -480 degree
• Start time: 240 degree
• Initial time step: 1e-07 s
• Minimum time step: 1e-08 s
• Maximum time step: 1 s

BOUNDARY:

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

By using the right amount of fuel the end products/species should be CO2, H20 and N2

1. Exhaust valve top temperature - 525K.

Boundary type-wall. Wall motion type-Translating. Surface movement- Moving. Import exhaust lift file. Min lift 2e-4m.

1. Exhaust valve angle temperature - 525K.

Boundary type-wall. Wall motion type-Translating. Surface movement- Moving. Import exhaust lift file. Min lift 2e-4m.

1. Exhaust valve bottom temeprature - 525K

Boundary type-wall. Wall motion type-Translating. Surface movement- Moving. Import exhaust lift file. Min lift 2e-4m.

1. Intake port - 1 temperature 425K
2. Intake port - 2 temperature 425K
3. Inflow pressure - 1 bar total pressure
4. Inflow temperature - 363K
5. Inflow species - Air
6. Intake valve top temperature - 480K. Same BC as EV top.
7. Intake valve angle temperature - 480K. Same BC as EV angle.
8. Intake valve bottom temeprature - 480K. Same BC as EV bottom.

REGION & INITIALIZATION:

• Click on Region and Initialization and add 4 Regions

• Intake port - 1 (closer to combustion chamber where MPI Injector will be use to provide Air+Fuel mixture)

• 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 and for exhaust region

• Pressure - 1.85731 bar
• Temperature - 1360K

Events (to open and close Inlet and Exhaust valve wrt crank angle):

• If there are ‘N’ numbers of Regions then the Events should be ‘N-1’

Cyclic Event(between valves and Cylinder regions which opens wrt Crank angles)

Permanent Event(between Intake port1 and Intake port 2, always open)

Physical Model

Spray Modelling

• General-> Parcel distribution->Distribute parcel evenly thought the cone->Turbulent dissipation:O’Rourke model-> Evaporation model-Use Evaporative model ->Evaporative source-2- Source all base parcel species. Maximum radius for ODE droplet heating-1000
• Collision/ Breakup/ Drag - Collision model-NTC collision. Collison outcomes-Post collision outcomes-> Use collision mesh. Drop drag model-> Dynamic
• Wall interaction: Spray wall interaction model->Wall film. Film splash model(The spray hit the wall and get splash)-> O’Rourke.
• Injector: Add injector->Edit-> Injector species(Ic8H18)/ Rate shape(Shows entire injection process profile)-> Add 4 injectors
• Models: Check Kelvin-Holtzman and Reyleigh Taylor model. Discharge coefficient-0.8. Set recommendation for –Gasoline PFI. Time/temp/Mass/size, Injection temporal size-Cyclic, Start of injection->-480 degree, Injection duration->191.2degree, Total injection mass->3e-5 kg/cycle. Injected liquid temp->330k..

Fuel Calculation: RPM-3000, RPS-50, Degree per sec(DPS)-18000. Time per 1 degree=5.55e-5s, Time for 720degree=0.04s, Fuel flow rate=7.5e-4 kg/s, Fuel flow for time of 720 deg/Fuel mass per cycle=7.5e-4*0.04=3e-05 kg/cycle.

• To position the nozzle position from cylinder head center to Intake port, Go to Spray modelling->Injector 0->edit->Models->Nozzle->Nozzle location and orientation-cartesian, Nozzle0 @injector0-edit, Nozzle diameter 250e-06m, circular injection radius-125e-06m, Spray cone angle->10 deg. Now copy nozzle 0 cordinated from nozzle position parameters at given input and paste in coordinates of nozzle(X,Y,Z), Copy Allign vector(spray axis) and paste it in Spray orientation vector. Add 3 more nozzles by same process.
• To see Injection pressure and velocity, Injectors-> Tools->Spray rate preview-> Spray rate calculator->calculate rate-> Injection pressure

To see whether all the nozzle inside the computational domain, Tools-> validate nozzle location.

COMBUSTION MODELLING:

• Model->SAGE->Use adaptive zone model(to speed up combustion calc), Sage parameter->Min cell temp-600k, Min HC species-1e-8, Temporal time- CYCLIC, Cycle period-720deg, Start time(The combustion starts just before the spark ignition which is -15deg)= -17deg, End time= 130 degree(Combustion ends when the EV opens. To see the opening degree/time of EV, go to->Boudary-> EV angle->open exhaust.lift file which gives data about exhaust valve movement->plot).

• General-> Fuel species name-IC8H18.

SPARK PLUG SETUP:

Physical Model:

• Enable source/sink modelling->Add 1 source->Shape->Shape type-sphere, Now copy spark location from input parameter and paste it into the center of sphere and copy-paste the radius. General-> Source unit->Energy->value-0.02 J->Mode-Cyclic->start time=-15degr, End time= -14.5deg (This 1^st Energy source provide energy for only 0.5deg Crank angle.. Copy that 1^st source End time=-5 deg(This 2^nd Energy source provide energy for 10 deg of CA)

Turbulence model:

• RNG k-epsilon

Base grid:

• dx=0.004m; dy=0.004m; dz=0.004m.
• Add Embedding to Inlet valve angle, Exhaust Valve angle and Cylinder/ Combustion chamber
• fig
  • To make sure that the diffusion should be minimum and to have a good combustion, we need to refine the spark plug. Fixed embedding->Add spherical embedding. Entity type-> Sphere, Start time->-16 degree(Embedding starting 1 deg before the spark which is -15deg), End time->7 deg (Embedding will end 2 deg after the spark), Copy The center of sphere and radius(0.001m) from Input parameters and paste it. Embed scale->5. Add larger sphere Embedding , Embed scale 3 and radius=0.003m
• 
  • Provide Embedding to the Injectors, Add Injector, Entity type-> INJECTOR, cyclic, Period 720 deg, Scale 4, Start time= -482deg, End time= -286deg (Start and End time can be seen from timing map), Radius1=0.002m, Radius 2=0.004, Length=0.02m
• 
  • Embedding is important because only when the cells size is smaller, then only we can have a curvature of temperature which helps AMR to sence this curvature of temp and enables AMR.

  Adaptive Mesh Refinement:

  • AMR will be only useful in Intake port 1 and 2, and Cylinder region / Combustion chamber and we are not interested to capture the physics in Exhaust region.
  • Enable velocity AMR. Max embed scale 3. Sub grid criteria 1(the Amr will active when there a velocity difference of 1m/s between 2 points). Max cells->2e6.
  • Enable Temperature AMR. Timing control type->CYLIC. Start time=-17deg, End time=-135deg(Combustion end time).
  • Right-click on setup, Timing map, which shows the Combustion simulation parameters time(crank angles).

What is the compression ratio of this engine?

Compression ratio(r): It is the ratio of volume when the piston is at Bottom Dead Center to the volume when the piston is at Top Dead Center.

R = (Vd+Vc)/Vc = (0.000573+5.7e-05)/5.7e-05=11.057

where:

Vd = displacement volume. This is the volume inside the cylinder displaced by the piston from TDC to BDC

Vc = clearance volume. When the piston is at TDC, the volume contained in the cylinder above the top of the piston is called the clearance volume.

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

Due to more Computational time and cost associated with Fluid and solid domain, and Direct simulation of conjugate heat transfer problem can be too difficult in the case of multi-layered structures with internal cavities, such as IC engine Simulation, we need a wall heat transfer model, which helps us to develop combustion systems for advanced high-efficiency, low emissions engines.

2. Calculate the combustion efficiency of this engine

Combustion Efficiency: Combustion efficiency is the calculation/measurement, in percentage, of how well your equipment is burning a specific fuel. Complete combustion efficiency (100%) would extract all the energy available in the fuel. However, 100% combustion efficiency is not realistically achievable. Various combustion processes produce combustion efficiencies from 0% to 95⁺%. Combustion efficiency calculations assume complete fuel combustion and are based on three factors:

1. The chemistry of the fuel.
2. The net temperature of the stack gases
3. The percentage of oxygen or CO₂by volume after combustion.

Combustion efficiency is defined as the ratio of total heat released/utilized by the burning of fuel to the theoretical heat supplied.

Combustion efficiency = Total Heat released/Heat supplied

Total Heat released = 1241.05 J (from Integrated HR plot)

Heat supplied = Amount of fuel added per cycle (kg/cycle) * calorific value of fuel(J/kg)

Amount of fuel added per cycle= 3e-5 kg/cycle

Calorific value of fuel(Ic8h18) = 47e6

Hence, Combustion efficiency = 1241.05 / (3e-5*47e6) = 88.01%

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

CA from(degree)- The Crank angle from which combustion starts

CA to (degree)- The crank angle at which combustion stops

Duration (degree) –The duration of combustion for a period of crank angle

Gross work(N*m)- Work done by the piston inside cylinder

IMEP (Gross Pa)-Indicated mean effective pressure

PFP(Mpa) – Peak firing pressure/ Maximum pressure

PFP CA(deg) –Peak firing pressure at crank angle

HRR peak(J/deg) – Peak heat release rate

HRR peak CA (deg) - Peak heat release rate at crank angle

Power is the amount of work done (by piston) per unit time. It is also described as the under the PV curve is power.

Power =Work done/ Time(in degree)

Where, Work done = 468.465 (from Engine performance calculator of Converge)

Time per degree = 60/(360*3000)= 5.55e-5 sec/degree

Time per cycle = 5.55e-5*240.2 deg(combustion time per cycle -in degree)=0.01334 sec/cycle

Power = 468.465/0.01334 = 35.13 Kwatts

Power(P) = (2*π*N*T)/60

Torque = (35.13e3*60)/2*3.14*3000=111.408 N-m

5. What is the significance of ca10, ca50 and ca90?

The Crank angle at which 10%, 50% and 90% fuel burns.

Post-variable selection:

Output files:

Export input files and Running the Simulation:

Now we have successfully setup the Case and need to export the input files to run the Simulation.

Run the Simulation in Cygwin using parallel processor.

Post Converting:

Now we need to convert all the output files which are processed by converge msmpi into the files which will be readable for post-processing in Paraview

Paraview:

We need to Post-process the output files to obtain the contour.

Plots:

The pressure of the Combustion Chamber

Here the maximum/ peak pressure inside the combustion chamber is 3.88 Mpa at 23 degrees Crank angle.

Temperature

The maximum temperature is 2481 k at 33 degrees of Crank angle.

Volume change of cylinder due to piston movement from TDC to BDC:

The minimum volume when the piston is at TDC (Clearance volume)=5.7e-5 m^3

The maximum volume when the piston is at BDC (Swept volume+ clearance volume)= 0.000573 m^3

Fuel Mass:

Density:

Specific Heat at constant pressure(Cp):

Maximum Cp=1.467kj/kg-k

Specific Heat at constant volume(Cv):

Maximum Cp=1.1kj/kg-k

Gamma(Adiabatic Index):

It is the ratio of Specific heat at constant pressure(Cp) to the specific heat at constant volume(Cv)

Gamma(Adiabatic index) is 1.336 at -181 degrees crank angle.

Heat release rate(HRR): The amount of energy released per crank angle. It is expressed in J/degree

The maximum amount of heat 59.34 J/degree is released at 18.71 degrees of CA

Integrated Heat released(J): The total amount of Heat generated during Combustion is 1241.05 J

Spray (Injection plots):

Liquid-spray-drops:

The maximum liquid spray drops are 44057 at -227 degree of CA.

Fuel species mass(IC8H18):

Emissions:

The maximum amount of emission produced by CO2 and Hc.

Animation:

(i) Suction stroke (suction valve open, exhaust valve closed)-charge consisting of fresh air mixed with the fuel is drawn into the cylinder due to the vacuum pressure created by the movement of the piston from TDC to BDC.

(ii) Compression stroke (both valves closed)-fresh charge is compressed into clearance volume by the return stroke of the piston and ignited by the spark for combustion. Hence pressure and temperature is increased due to the combustion of fuel

(iii) Expansion stroke (both valves closed)-high pressure of the burnt gases force the piston towards BDC and hence power is obtained at the crankshaft.

(iv) Exhaust stroke (exhaust valve open, suction valve closed)- burned gases expel out due to the movement of the piston from BDC to TDC.

Conclusion:

• The full hydrodynamic setup for Port Fuel Injection SI Engine has been Simulated.
• The compression ratio of this engine is calculated which is 11.057
• Combustion Efficiency has been calculated which is 88.01%.
• Power and Torque have been calculated which is 35 Kw and 111 N-m respectively.