SI8 -PFI Engine Simulation

Objective: To simulate the entire SI8 - Port fuel injection engine using CONVERGE and to visualize; determine various engine parameters from the simulation results.

Process: 

  • The CAD model of the SI8-PFI engine was imported 
  • Surface preparation was performed on the geometry 
  • Boundaries were flagged
  • The case was setup for no-hydro condition
  • After the no-hydro case setup ran successfully, full hydro simulation was performed.
  • Full hydro results were post processed and recorded.

Engine Geometric Parameters:

Bore =0.086 m

Stroke = 0.09 m

Connecting rod length = 0.18 m

RPM = 3000

Geometry:

The pre-modeled geometry was imported into Converge and the geometry was inspected for any surface errors or open edges. After fixing all the errors, the boundaries were flagged and the case was setup.

 

Initial Conditions and Regions:

Four regions i.e Cylinder Region, Intake Region 1, Intake Region 2 and Exhaust Region were defined. The reason behind dividing intake regions into region 1 and region 2 is to provide better initial and boundary conditions.

Initial conditions for different regions are as indicated below.

Events:

In order to control the flow between the four regions, three events were defined.

Boundary Conditions:

 

Geometry Mesh:

Base mesh size of 4 mm was provided in the x, y, z directions; two cylinders i.e large and small cylinder regions were created with a grid scaling factor of 1 and 2 respectively to provide a smooth grid transition from the ports to the cylinder. Grid scaling factor of 3 was provided at the intake and exhaust valve angles to capture the fluid flow accurately. In addition to this, a cyclic embedding of factor 4 was provided at the injector to capture the fuel sprays. Spherical embedding of factor 4 was defined between the crank angles -16 deg to -3 deg where the spark is ignited.

Along with mesh embedding, velocity and temperature adaptive mesh refinement was also enabled. 

Simulation Time Parameters:

Start time = -520 deg

End time = 120 deg

Physical Models:

Spray Model:

Parcel Species : IC8H18 (Iso - Octane)

Start of Injection: -480 deg

Injection Duration: 191.2 deg

Tatal Injection Mass : 3e-5 Kg

Fuel Temperature: 330 K

 

Combustion Model:

SAGE detailed chemistry solver (CVODES)

Start time: -17 deg

End time : 130

Turbulence Model: RNG K-`epsilon`

Source/Sink Model:

Source 1

Energy: 0.02 J 

Start Time: -15 deg

End Time: -5

Source 2

Energy: 0.02 J 

Start Time: -15 deg

End Time: -14.5 deg

No Hydro Simulation:

Before running the full hydro case setup where the governing equations are solved, a no hydro simulation was run to make sure that the intake and the exhaust valve movements have been setup correctly in accordance to the piston movement.

Once the no hydro simulation ran successful, full hydro simulation was performed and the results are as follows.

Results:

1.Combustion and Spray simulation inside the engine: 

 

2. Compression Ratio:

Compression ratio is defined as the ratio of the maximum volume to the minimum volume in the cylinder.

 

             `"Maximum Volume = "57xx10^-5 m^3`

             `"Minimum Volume (Clearance volume) = "5.7xx10^-5 "" m^3`

             `"Compression ratio" = "Maximum Volume"/"Minimum Volume"`

             `" Cr"= 57/5.7 =10:1`

3. Combustion Efficiency

Combustion efficiency is defined as the ratio of the total heat released due to the combustion to the total heat content of the fuel.

             `"Combustion Efficiency " underset(c)(eta) = "Total Heat Released"/"Total Energy Content of the Fuel "`

From the integrated heat released plot, the total heat release is found to be `1240.87` J.

 

              The total heat content of the fuel = Amount of fuel x Calorific Value

              Amount of fuel = `3 xx10^-5 " Kg per cycle"`

              Calorific value = `44 " MJ/K"`

              The total heat content of the fuel = `3xx10^-5xx 44 xx10^6 = 1320 " J"`

              `underset(c)(eta) = 1240/1320 xx100 = 93.93 %`

4. Power and Torque

Power is given work done per unit time.

              `"Power" = "Work"/"Time"`

From the Engine Performance Calculator:

              `"Work" = 468.646 " Nm"`

Time Calculation:

              `"RMP" = 3000` 

Time per degree  `= "60"/(360xx"RPM")`

                            `  = 60/(360xx 3000`

                            ` = 5.55556xx10^-5 "Sec/deg"`

Time per `240.199` degree = Time per degree x `240.199`

                                         = `5.55556xx10^-5 xx 240.199`

                                         = `0.01334 " Sec/ cycle"`

Therefore, 

               `"Power" = "468.646"/"0.01334"`

               `"Power" = 35.13 " KW"`

               

Also, 

                `"Power" = (2piNT)/60`

                `"Torque"= (60P)/(2pi N`  

                             `= (60xx35.13xx10^3)/(2xxpixx3000)`

                `"Torque"= 111.8 " Nm"`

 

6. Emissions

The below plot indicates the variation of different emission constituents at different crank angles; the constituents which remains at the end of the combustion would be the exhaust gases which would be subjected to different exhaust aftertreatment systems before letting it out to the atmosphere. From the graph, it can be seen that the carbon monoxide composition is much more that the other emission constituents.The reason is due to incomplete conversion of carbon in the fuel.

Other emission constituents like Nox, HC and Hiroy Soot are 1.28e-6, 2.9e-6, 2.55e-8 respectively after combustion; constant efforts have been invested by many companies to bring these constituents even lower to meet the emission norms. 

7.Pressure and Temperature

The pressure and temperature plots inside the cylinder for different crank angles are as show below.

A sudden surge in the pressure and temperature values can be observed inside the cylinder. This is due to the combustion of fuel inside the cylinder; generating an enormous amount of energy in a short period of time as indicated in the below heat release rate plot.

A maximum Pressure of 3.8 MPa and a maximum mean temperature of 2498K was recorded.

Conclusion:

The full hydro simulation of SI8- PFI engine has aided in determining and analysing various engine parameters without actually building an actual engine. Since the engine of our interest is an imaginary one, there are no experimental data to validate the results. But as the trends in the plots are in accordance with our understanding of SI engines, the aim to simulate the SI engine using CONVERGE can be said to have been met.


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