Simulation of a SI Engine using CONVERGE Studio

SITUATION

          To study the PFI Engine performance characteristics by setting up the spray modeling & combustion modeling in the CONVERGE studio and post-process the results in the Paraview and CYGWIN was used to run the commands for the simulation.

TASK

  1. To find the compression ratio and calculate the combustion efficiency of this engine.
  2. Why do we need a wall heat transfer model? Why can't we predict the wall temperature from the CFD simulation?
  3. Use the engine performance calculator, to determine the power and torque for this engine.
  4. Explain the significance of ca10, ca50, and ca90.

IC Engine

An internal combustion engine is a heat engine where the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high- temperature and high- pressure gases produced by combustion applies direct force to some component of the engine. The force is applied typically to pistons, turbine blades, rotors or a nozzle. This force moves the component over a distance, transforming chemical energy into useful mechanical energy.

     

1)The 4 cycles of the engine are explained above in which as we observe that only one stroke is power stroke so to maintain a smooth power output a flywheel is used to store the energy and a part of this energy is used in suction and compression of the air-fuel mixture.

2) Basically an engine converts chemical energy from fuel to mechanical energy by using combustion which means the thermal efficiency of the engine is a very important parameter to be studied. Thermal efficiency is the percentage of energy taken from the combustion which is actually converted to mechanical work. In a typical low compression engine, the thermal efficiency is only about 26%. In a highly modified engine, such as a race engine, the thermal efficiency is about a 34% compression ratio of an SI engine is usually in the range of 7 to 11 while diesel is high from 16 to 20. Here we are simulating a 4 stroke SI Engine which is Port injected. Multipoint fuel injection (MPI), also called port fuel injection, injects fuel into the intake ports just upstream of each cylinder's intake valve, rather than at a central point within an intake manifold.

COMBUSTION IN SI ENGINES

The combustion process of SI engines can be divided into three broad regions:

1)Ignition and flame development, (2) flame propagation, and (3) flame termination      Flame development is generally considered the consumption of the first 5% of the air-fuel mixture (some sources use the first 10%).

During the flame development period, ignition occurs and the combustion process starts, but very little pressure rise is noticeable and little or no useful work is produced (Fig. 7-1). Just about all useful work produced in an engine cycle is the result of the flame propagation period of the combustion process. This is the period when the bulk of the fuel and air mass is burned (i.e., 80-90%, depending on how defined).

During this time, pressure in the expansion stroke. The final 5% (some sources use 10%) of the air-fuel mass which burns is classified as flame termination. During this time, the pressure quickly decreases and combustion stops. In an SI engine, combustion ideally consists of an exothermic subsonic flame progressing through a premixed homogeneous air-fuel mixture. The spread of the flame front is greatly increased by induced turbulence, swirl, and squish within the cylinder. The right combination of fuel and operating characteristics is such that knock is avoided or almost avoided.

               

ACTION

Workflow for a CONVERGE CFD Simulation

   1. Pre-processing(preparing the surface geometry and configuring the input and data files).

   2. Running the simulation.

   3. Post-processing(analyzing the *.out ASCII files in the Case Directory and using a visualization program to view the information in the post*.out).

Pre-processing 

File -- > Import -- > Import STL file, this option is used to import the ICE geometry file.

Model 

 

Run the diagnosis test to find surface errors in the model.

                     

The various errors in the model are listed above.

The region option is used to separate the model into different regions so that the error can be rectified easily. Boundary --> Fence option is used to create a fence in the model.

The regions are divided into 4 regions for the ease of the initial condition setup and then the boundary is formed and the regions are assigned to the different boundary.

The topmost ring triangle of the valve port is connected to the intake port, this is used to avoid the errors created by translating the valve.

In the first figure, the ring triangle is not connected Intake port and second figure, the ring triangle is connected intake port. The valve translates when the simulations occur so this causes error the boundary is not created properly.
The open edges are corrected using the patch option. Repair --> patch -->Free edge loop--> open edge is selected to correct it.

Select on the Normal toggle option and direction on the normal must be in the direction of the flow of the mixture. The CONVERGE is mainly developed for running the IC engine simulation so IC Engine is selected.

Case Setup

  1. IC Engine – i) Cylinder bore – 0.086 m.                                                                                       ii) Stroke (2* crank radius) – 0.09m.                                                                         iii) Conrod length – 0.18m.                                                                                       iv) Crank speed – 3000 rpm & select their corresponding reference ID. 

       

  1. Materials – Select the parcels simulation & species.                                                                   i)Gas Simulation – Import the thermo.dat file.

         

                       ii)Reaction mechanism – Import mech.dat file & validate them.   

                                                                                                                                                                                                                  iii)Parcel simulation – Select the predefined liquid as IC8H18.

           

                       iv) Species – All the gas species are available in mech.dat file but the parcel won't be available. Select parcels & choose IC8H18.

                                                                                                                       

  1. Simulation Parameter – i) Simulation mode – Full hydrodynamic solver.                                                          ii) Simulation time parameter.

  1. Regions – i) Region 1 – Intake port 1 – Temp – 390k                                                                                                           Pressure – 101325 Pa.                                                                                               Species – The value of the species is provided in its mass fraction. The consider a general flow equation across the engine is consider were flow occurs according to the stoichiometric value.

                         C8H18 + 12.5(O2 + 3.76 N2) --- > 8CO2 + 9H2O + (3.76*12.5) N2.

From this equation, the valve for the intake port 1, exhaust port is taken.

                       

                                   

                        ii) Region 2 – Exhaust port  – Temp – 1360k                                                                                                                  Pressure – 185735 Pa.                                                                                                      Species – The value of the species is provided in its mass fraction.       

                                   

                        iii)  Region 3 – Intake port 2 – Temp – 370k                                                                                                                    Pressure – 101325 Pa.                                                                                                       Species – The air is select as species.

                       iv) Region 4 – Cylinder –         Temp – 300k                                                                                                                    Pressure – 101325 Pa.                                                                                                      Species – The value of the species is provided in its mass fraction. The cylinder species are taken as exhaust species since there temperature & pressure of these species are higher when compared to the inlet species so these values are preferred.

                       ii) Events – a) Select cyclic and click on add.

Region A                       Region B                            Event                   Profile                 Cylinder                     Intake port-1                          Close                  Intake_lift

 Cylinder                     Exhaust port                           Open                  Exhaust_lift

Intake lift profile data:

Exhaust lift profile data:

  1. b) Select permanent and click on add.

   Region A                                      Region B                              Event                              Intake port-1                              Intake port-2                            Open       

    5. Physical models – Select RNG k-e model is chosen under the turbulence model.

                                  a) Spray modeling – i) General.                                                                                              i) Parcel distribution – Distribute parcel evenly throughout cone.                                             This is used when the spray ejects evenly through the nozzle.                                                                                                                                                                                 ii) Turbulent dispersion – O’ Rourke model. O’Rourke model in      Turbulent Dispersion is for Gasoline and it used to analyze how turbulence affects droplet characteristics.                                                                                                            Use evaporation model is enabled because to capture the rate at which the parcel radius is going to change.

                                     iii) Evaporation source – Source all base species. The species on evaporated gets converted into their base species provided. The other two options are converted to the composites available and converted to the species provided.                                                             

                                    iv) Max radius of ODE – 1000. Maximum radius for ODE droplet heating is given as 1000. Here outside the sphere it is hotter and inside it is less hot due to temperature distribution. So the sphere is discretized into cells and the 2D heat equation is applied to solve it. In case of a small sphere, the entire sphere has the same temperature and it is reasonable. But in case of a bigger sphere, there will be a temperature gradient. So, outside the radius ODE is solved and inside it is not solved.

                                   v) No of FV Cells –                                                                                                           vi) Thermal conductivity – Physical.                                                                                   vii) Urea – No urea mode. This model is used for the simulation where exhaust flow parameters are considered for the flow.

Penetration:

                                                     

The liquid fuel penetration is calculated from the volume where there are about 95% of the total liquid fuel. The bin size for vapor penetration is used where different vapor are grouped together and the fuel vapor mass fraction value for calculating vapor penetration.

                                                        ii) Collision/ breakup – Select use a collision mesh & all the parameters are the same. Select include breakup. The parameters for the breakup must be included otherwise the fuel won't break up and the whole simulation won't be set up to a wrong.

                                                       iii) Wall interaction

                                                 Spray wall interaction – Wall film.                                                                                       Film splash model – O’ Roukee.

                                                      iv) Injector – Select +injector & click on edit option & select IC8H18 & provide the mass fraction as 1. As only the isooctane is used as fuel the mass fraction is provided as 1. Rate shape values as                                                                                                                   1) 0                                                                                                                                 2) 1                                                                                                                                 3) 1                                                                                                                                 4) 0

                

                                 b) Models – Select kelvin Helmholtz model & Rayleigh Taylor model. These models generally used for both diesel & petrol engine & select discharge coefficient models & set the value to be 0.8. Select gasoline PFI under set recommendation for.

                                 c) Time/ Temp/ Mass size – Start of injection - -480.

                                                                          Injection duration – 191.2.

                                                                          Total inject mass – 3e-5.

                                                                          Total no of injected parcels – 500000.

                                                                           Injected liquid temp – 330k.

Fuel Calculation for total inject mass

RPM – 3000.                                                                                                                RPS – 50.                                                                                                                    Degree/ Cycle – 18000. (RPS*360 for conv revolution to degree)                                          Time/ degree – 5.56e-5. (1/ degree per cycle)                                                                Time/ 720 – 0.04 s. (time/degree * 720)                                                                            fuel flow rate – 7.5e-4 kg/s                                                                                          Fuel mass/ cycle – 3e-5kg. (fuel flow rate * time/720).

 

                                d) Nozzles –

                                    Nozzle diameter = 250 micro-meters.                                                                                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.

               

    After all the values are provided. Select tools under injector & then spray rate preview which shows the pressure value is calculated depending on the value is provided & select tools -- > validate nozzle location to check whether all nozzles within nozzles.

                                                                      

The pressure value for the nozzle is provided but by the values we provided there will be only one pressure for which the fuel is ejected in order to calculate it use the option tools              -- >  spray rate preview.

 

                        b) Combustion Modelling – Select SAGE                                                                                          Max cell temp – 600k.                                                                                                      Min HC species mole fraction – 1e-8.                                                                                  Temporal type – cyclic.                                                                                                      Cyclic period – 720.                                                                                                          Start time - -17.                                                                                                              End time – 130 & under general select species name to be IC8H18. 

Select Source/ sink modeling under physical models.

Add 2 sources & under shape select sphere & copy-paste the center & radius of that of the spark plug. Initially more amount of energy is provided by using two sources in order to conduct through the spark gap & then one source is cut off as little energy is required to keep the conduction going on.

Source 1                                                      Source 2                              

Set value – 0.02.                                      Set value - 0.02.                                           Mode – Cyclic.                                          Mode – Cyclic.                                                    Start time - -15.                                       Start time - -15.                                            End time - -14.5                                       End time - -5.                                                Period – 720.                                            Period – 720.

         

6. Grid control – i) Base Grid – value of grid is provided as 0.0014.
                        ii) Fixed Embedding – i) Intake value angle – Type – permanent
                                                                   Boundary ID – Intake valve angle.
                                                                   Mode – Permanent.
                                                                   Scale – 3.
                                                                   Embed layer – 1.

The converge creates disconnect triangles to create the channel for the fuel mixture so embed are created to capture this.                                                            

                                                       ii) Exhaust value angle – Type                                                                                                              Boundary ID –Exhaust valve angle.                                                                                     Mode – Permanent.                                                                                                          Scale – 3.                                                                                                                        Embed layer – 1.   

                                                       iii) Big cylinder embed – Type – Cylinder.
                                                                                           Mode – Permanent.
                                                                                           Scale – 1.
                                                                                    Centre of Cylinder – 0 0 0.5
                                                                                                                  0 0 -0.15.
                                                                                           Cylinder radius 1 – 0.05.
                                                                                           Cylinder radius 2 – 0.05.
                                                       iv) Small cylinder embed – Type – Cylinder.
                                                                                               Mode – Permanent.
                                                                                               Scale – 1.
                                                                                    Centre of Cylinder – 0 0 0.018
                                                                                                                  0 0 -0.15.
                                                                                              Cylinder radius 1 – 0.05.
                                                                                              Cylinder radius 2 – 0.05.
                                                    

                                                       v) Small spherical embed – Type – sphere.                                                                                                                  Mode – Cyclic.                                                                                                                Period – 720.                                                                                                                   Scale – 5.                                                                                                                        Start time - -16.                                                                                                               End time – 7.                                                                                                                   Embed layer – 1.                                                                                                               Radius – 0.001.

                                                       vi) Large spherical embed – Type – sphere.                                                                                                                  Mode – Cyclic.                                                                                                                 Period – 720.                                                                                                                   Scale – 3.                                                                                                                         Start time - -16.                                                                                                              End time – 7.                                                                                                                   Embed layer – 1.                                                                                                              Radius – 0.003.

                                                       

                                                      vii) Injector – Type – injector.                                                                                                                 Mode – Cyclic.                                                                                                                 Period – 720.                                                                                                                   Scale – 4.                                                                                                                         Start time - -482.                                                                                                             End time – -286.                                                                                                              Radius – 0.002.                                                                                                               Radius – 0.004.                                                                                                                Length – 0.02.

                               

                                   iii) Adaptive Mesh Refinement – Select the active regions as Cylinder, Intake port-1, Intake port-2 and the exhaust port is not selected since the emission characteristic of the fuel is not consider.

Velocity

Temperature

 

Right-click on the Grid control -- > Timing map.

6. Boundary - i) Piston – The snip of piston boundary is provided and the value which is to be varied in other boundary is provided. 

                   

                     ii) Liner – Type – Wall.

                                    Wall motion – Stationary.

                                    Temperature – 450k.

                    iii) Cylinder head – Type – Wall.

                                                 Wall motion – Stationary.

 


Projects by Aravind Subramanian

SITUATION

          To study the Emission characterization on a CAT3410 engine & combus Read more

1. Different types of Turbocharger 

  • Fixed Geometry turbocharger - The amount of exhaust gas into the turbocharger cannot be varied, the turbocharger is optimized for the particular operating condition & the turbine size and/or Read more

Challenge 8 : Literature review RANS derivation and analysis Project Report : https://drive.google.com/file/d/1dgVXxMZVQRmEwqHjO1bts9tmRtqT-K-3/view?usp=sharing Read more

AIM        The objective of the project is to compare the SI vs CI Engine parameters for the BSFC, Exhaust temperature and A/F ratio. Change the MFB 50 and observe the impact on performance. PROCEDURE          The GT Power Read more

SITUATION          The separation of two regions having high & low-pressure fluid by a diaphragm. The two-fluid gets mixed when the diaphragm breaks and flow simulation is done in the CONVERGE studio and post-processes the results in Para v Read more

AIM         The objective of the project is to calculate the various parameters of the engine at a particular rpm for a single-cylinder engine.         Increase the power output by 10% at 3600 rpm by varying different param Read more

SITUATION

        The flow of air through a solid pipe & it is heated through an external heat source in converge studio and post-processes the results in Para View and CYGWIN was used to run the Read more

First Assignment
Aravind Subramanian · 2019-09-03 12:37:51

INTRODUCTION The foundation of GT-SUITE is a versatile multi-physics platform for constructing models of general systems based on many underlying fundamental libraries: Flow library (any fluid, gas or liquid or mixture) Acoustics library (both non-linea Read more

SITUATION              To simulate a supersonic flow through a Duct channel having the sharp corners to observe the formation of shock waves in converge studio and post-processes the results in Para View and CYGWIN was used to run the Read more


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The End