FULL HYDRO case set up of Port Fuel Injection engine
Aim: To run the full hydro simulation using Converge to get all the performance parameters and graphs.
Surface Preparation: While diagnosing the geometry file of the engine few errors were found. The major errors are found on the surface of the piston and exhaust valve these are open edge errors. These errors are solved using the patch option. The normal orientation errors found on the intake port were solved by reversing the direction of the normal on the intake surface.
The above figure shows that no errors are found after diagnosis. with this, the surface preparation of the model is completed.
Boundary Flagging: The boundary flagging is done to the model to identify and differentiate the parts according to the regions with respect to there working.
The above figure shows the different boundaries of the model with specified regions.
Intake port:
The intake port is divided into two boundaries because to maintain the initial conditions in that region. The intake port near the cylinder head consists of some fuel particles while the area at the other end of the intake port doesn\'t contain any of the fuel particles to differentiate these conditions the intake port is divided into two parts and each part is assigned to different regions.
Valves:
In the above figure, we can notice that the valve is divided into 3 boundaries there are mainly two reasons for it.
1) The bottom part of the valve is faced with the inside region of the cylinder(they see the combustion). If we define the entire valve in a single boundary then there would be a problem while assigning the initial conditions and grouping them into regions.
2) For the moment of valves, we are using the events so for forming the disconnect triangles the area should be as minimum as possible for minimizing the error. These disconnect triangles are only formed in between two regions so the valve angle should regioned with there respective ports so that the disconnect triangle can be formed between port and cylinder head regions.
Exhaust Port:
There are two boundaries shown in the above figure one is exhaust port and another one is the outflow.
Spark plug:
The spark plug is divided into two boundaries one is a spark plug and another is spark plug terminal this is mainly done for differentiating the temperatures in that particular region and for meshing purposes.
Liner and Piston:
The Liner is the cylinder wall and piston represents the piston of the engine
Cylinder Head:
As per the requirements, the total model is divided into four regions
Cylinder Region:
The boundaries that fall under this region are Piston, Liner, Cylinder head, Valve bottom, spark plug, spark plug terminal.
Intake port-1:
The boundaries that fall under this region are the Intake port-1, intake valve, intake valve angle, Inflow.
Intake port-2:
The only boundary in this region is intake port-2
Exhust port:
The boundaries that fall under this region are the Exhaust port-1, Exhaust valve, Exhaust valve angle, Outflow.
Spray modeling:
For gaseous spray converge uses the Eulerian solver to solve the species mass fraction and mass flow rate at the inflow boundary
For liquid spray converge uses the Lagrangian solver to model the discrete parcel that occurs during the vaporization of the liquid fuel.
PARCEL:
Converge introduces parcels into the domain from the injector. Each parcel represents a group of identical drops(same size and shape). This parcel statistically represents the entire spray field.
Converge uses a sub-grid model for the spray process that occur on length scales that are too small to be resolved.
The Distribute parcel evenly throughout the cone is selected in which the fuel parcels are evenly spread in the injector cone.
These are the models that are selected for solving the spray equations.
The fuel is injected into the intake port according to the plot as shown above and four injectors are used at the intake port.
The parameters like starting time, duration time, and mass of the fuel is specified as above.
The parcel data animation: https://youtu.be/p7uengo8hmE
Combustion Modeling:
The Sage combustion model is used with conserve NOx option is used.
The time duration for activating the combustion model is specified with the selected fuel.
The RNG K-epsilon turbulence model is used.
Grid Control:
The 0.004m base grid size is used.
The adaptive mesh refinement is done at intake ports and cylinder region with respect to the temperature and velocity.
The fixed embedding is done at the above-shown reasons for getting accurate values at any point in time.
This is the time map for embedding which gives a brief idea of grid control.
The mesh generation video:https://youtu.be/Gnsg1IDRbe8
Performance Parameters:
1)Maximum pressure: The maximum pressure 3.9Mpa is obtained at 19deg crank angle this is because of the expansion phase and then pressure is decreasing rapidly.
2)Mean Temperature: The mean temperature during the compression stage reaches the maximum possible value of 2500K as shown in the figure below.
The Temperature Contour animation: https://youtu.be/AtjrrPN7Q5o
3) The below graph shows fuel entering into the cylinder from the valves at the initial stage due to the immediate opening of the valve some amount of fuel enters and the amount of fuel entering into the cylinder decrease because of insufficient pressure and volume as the piston goes done it creates volume with the decrease in pressure here the maximum amount of fuel enters into the cylinder.
4) Emissions: The plot shows the comparison of HC, CO,NOx emissions from the engine.
1) Compression Ratio: It is defined as the ratio of maximum volume to the minimum volume inside the cylinder of an I.C engine.
It can be written as C.R = `V_(max)/V_(min)`
where `V_(max) = V_d + V_C`
`V_(min) = V_C`
`V_d =`Displacment Volume
`V_C=`Clearence volume
Compression ratio = `(V_d + V_C)/V_C`
For this I.C engine `V_(max) = 5.74214*10^-4 m^3`
`V_(min) = 5.74576*10^-5 m^3`
These values are obtained from the volume graph of the I.C engine.
Hence Compression Ratio is = `V_(max)/V_(min) = (5.74214*10^-4)/(5.74576*10^-5) = 9.99`
2. Why do we need a wall heat transfer model? Why can\'t we predict the wall temperature from the CFD simulation?
In the I.C engine, 3 types of Heat transfer takes place wall to wall, fluid to fluid, wall to a fluid. In general, the predominant mode of heat transfer in solids is conduction and in fluids it is convection. Converge solves fluid heat transfer using energy equation and in solid it uses Heat conduction equation. For solving the Interface boundary condition Three Dimensional Heat conduction equation should be used.
`C_p*rho*(delT)/(delt) = grad*(K*triangleT) + S_h`
`grad*(K*triangleT)` is Heat flux due to conduction
`S_h` is a volumetric heat source
This equation should be solved at the solid side for predicting the properties of the solid-fluid interface and boundary conditions are need to be specified. This is included in the wall-heat transfer model and this mainly used in I.C engine and C.H.T simulations.
The CFD simulation uses only Navier-strokes, Turbulent, and Scalar transport equations for predicting the properties of the flow and these are not accurate for solving solid-fluid interface this is the reason why we needed the Wall heat transfer model.
3) Combustion Efficiency: The 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 one complete engine cycle.
The energy content of the fuel mass during one cycle = mass of fuel per cycle * Calorific value of the fuel
= `3*10^-5 * 44.651*10^6`
= 1339.53 J
The energy released by the burned fuel = 1240 J
This value is taken from the Integrated Heat release rate plot
Combustion Efficiency = `1240/1339.53 = 92.56%`
4) Determining the power and torque for this engine:
Work Done (Engine performance Calculator): 468.646 (N*m per cycle)
Engine speed N = 3000rpm
Time taken per degree = `60/(3000*360) = 1/18000 sec`
Time taken for completion of 1 cycle(720 deg) = `720/18000 = 0.04 sec`
The power developed = Work done per cycle = 468.46/0.04 = 11.7kW
power `P = (2*pi *N*T)/60`
`11700 = 2*3.14*3000. T/60`
`T = (11700*60)/(2*3.14*3000) = 37.26 Nm`
The Power Developed = 11.7kW
The Torque = 37.26Nm
5) What is the significance of ca10, ca50, and ca90?
Ca10, Ca50, and Ca90 refer to the crank angle which tells the percentage heat release of 10% 50% and 90% of cumulative combustion heat release rate.
- ca10 defines the crank angle at which the start of the combustion occurs in the engine.
- As per the settings, ca90 defines the crank angle at which the end of the combustion takes place in the engine.