Port Fuel Injection Simulation

Objective

• To simulate the Port fuel injection engine using Converge to determine its performance & emissions

Port Fuel Injection:Port fuel-injection systems long ago replaced carburettors in cars because of their efficiency and lower maintenance requirements. With port fuel-injection, gasoline is sprayed into the intake manifold, where it mixes with air, and then is sucked down into the cylinders. Direct injection places an injector on each cylinder, spraying gasoline into the cylinder itself. Direct injection leads to more efficient engines, as the gasoline-air mixture burns more completely. The individual injectors also ensure that each cylinder gets the same amount of fuel, and the spray can be more precisely timed.

Case

Step1.Geometry

• Converge provides an utility call make engine sector surface using these utility we have extract the bowl profile from 3D piston surface
• After extracting,we have created the surface using piston bowl profile & below engine geometric Parameters with the help of make engine sector utility.

Engine Geometric Parameters:

Bore=0.13761

Connecting Rod=0.263m

Stroke=0.1651m

Sector angle=60

Step1.Geometry

The geometry has been imported in Converge and it has been diagnosis

From the above image,after diagnosing we can see that geometry has multiple error inorder to eliminate this error we will first flag the boundary & regions,so that it became ease to eliminate the error

Regions Flagging

From the below image the reason behind dividing intake port into two regions is to give better initial & boundary conditions

Boundary Flagging

Boundary Conditions

Now,after boundary & regions flagging all the errors have been eliminate using boundary fence & patch option which can seen in the below image.

Step2.Case Setup

• Application:Crank angle-based IC engine
• Analysis:Transient state
• Type:Pressure type
• Simualtion mode:Full hydrodynamic

Simulation time parameters:

• Start time:-480deg
• End time:240deg
• Initial time step:1e-7sec
• Minimum time step:1e-8sec
• Maximum time step:0.0001sec

Physical Model

• Spray Model:The kelvin-Helmholtz model & Rayleigh-Taylor model are used since are spray is solid cone spray.Also an injector is used with four nozzles to spray the fuel.
  • Parcel Species:IC8H18 (ISO_OCTANE)
  • Start of Injection:-480deg
  • Injection Duration:191.2deg
  • Total Injection:3E-5kg
  • Fuel Temperature:330k

• Combustion Model:We have use SAGE detail chemical solver for combustion modelling.Converge use multizone model which accelerate the chemistry calculation by grouping computational cell together & then solving chemistry solver in each group rather then in each cell
  • Start time: -17 deg
  • End time:130 deg

• Turbulence Model:
  • K_e,RNG

Grid Control:

• Element size:dx = 0.004m, dy = 0.004m,dz = 0.004m

Events:When 2 regions are in contact with each other with no boundary in-between them, it is necessary to use events. The events flag creates triangles in the place between the 2 regions called as disconnect triangles.Events can be cyclic, permanent or sequential.Based on how the event should occur, the type of event can be chosen from the options available.

Fixed Embedding

• Fixed embedding is a method which is used to refine the mesh at particular area.
• In our case,we are more concern the area were the combustion will take place which are Nozzle,Piston & cylinder head so,for this we need more refine mesh for this we will use fixed embedding method.
• We have use a sequential embedding of factor 1 at the piston & cylinder head between the crank angle -20deg to 180deg.
• And for nozzle we have use embedding factor of 2 at the injector to capture the fuel spray

Adaptive Mesh refinement

• Its essential to capture the data accurately were the shock occur,so for this we need more refine mesh or local mesh in that area while keeping the mesh size in the other area as same as base grid size so,in order to do this we are using Adaptive mesh refinement technique.
• In converge adaptive mesh refinement gives variety of based technique in our case we have used temperature & velocity based sub-grid-criterion of three embedding level in cylinder,intake port1 & inatke port2 region.Converge will monitors the temperature & velocity property provided in the AMR and refines the mesh when the property of temperature curvature & velocity between the consecutive grid is more than the defined SGS value.
• AMR use below formula to determine the refine grid size
• Refine grid size=`frac{Base grid}{2^(embedd-Level)}

Output Files:

• Time interval for writing 3D output data files:2 deg
• Time interval for writing text output:0.1 deg
• Time interval for writing restarting output:10deg
• Maximum number of restart file saved:3

Step4.Plots

Mesh

Animation

Pressure

Temperature

Heat Release

From the above plot a sudden rise in the pressure & temperature is because of combustion of Air-Fuel mixture which leads to produce huge energy in short time this can been in the heat release rate plot that maximum heat is release in the comustion process.

Emission

From the above plot it quit clear that concentration of Carbon monoxide is much more higher then the other emissions this because of incomplete conversion of carbon into fuel.

Velocity Animation

Flame Propagation

Now,

Q1. What is the compression ratio of this engine?

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

Maximum Volume=0.00096`m^3`

Minimum Volume=0.00043`m^3`

Compression Ratio=Maximum Volume/Minimum Volume

Compression Ratio=0.00096/0.00043

CR=2.23:1

Q2. Why do we need a wall heat transfer model? Why can\'t we predict the wall temperature from the CFD simulation?

No,we cannot predict the wall temperature from our CFD simulation since we have simulated only fluid domain we haven\'t simulate any solid part.So,it doesn\'t make any sense of predicting the temperature from our CFD simulatiom.Hence we need a wall heat transfer model in order to captured the wall temperature properly.

Q3. Calculate the combustion efficiency of this engine

Comustion efficiency is defined as a ratio of total Heat released during combustion to total heat content in the fuel.

Integrated Heat Release

From the above plot total heat release during combustion is 1240.75 J

Total Heat cintent in the fuel=mass of fuel `xx` Calofiric value

Mass of fuel=3 `xx` `10^-5` kg per cycle,Calofiric value=44MJ/K

Total Heat cintent in the fuel=`3 xx 10^-5` `xx` 44 `xx 10^6`

Total Heat content in the fuel=1320 J

Combustion efficiency=`frac{1240.75}{1320}`

Combustion efficiency=93.99%

Q4.Determine the power and torque for this engine?

Power

• Power is defined as ratio of work done per unit time
• Power=Work Done/Time

Time calculation:

• Time per degree=`frac{60}{360xxRPM}`
• Time per degree=`frac{60}(360xx3000}`
• Time per degree=5.55`xx 10^-5`sec/deg
• Time per 270.189 degree=Time per degree `xx`240.199

=5.55`xx 10^-5 `xx`240.199

=0.0133 sec/cycle

From engine performance calculator,we get

Work done=468.64Nm

`thereforePower=frac{468.64}{0.0133}`

Power=35.13KW

Q5. What is the significance of ca10, ca50 and ca90?

• CA10,CA50 & CA90 basically represents the crank angle at 10%,50% & 90% of the combustion completed.
• Duration between CA10 to CA90 represents the combustion stroke.
• CA50 consider as the midpoint of the combustion were the maximum heat release take place.

Conclusion

• Successfully did the Fully Hyrdo simulation of Port fuel injection engine.
• Sucessfully determined the Emissions & thermodynamic variables for the PFI engine.
• Since,our PFI engine is designed engine not a real engine so,we cannot validated our results with experimental one.