Week 10: Project 1 - FULL HYDRO case set up (PFI)

Objective:

1.To setup and simulate full hydrodynamic case using PFI engine(by using converge and paraview)

2.Calculate the compression ratio and its efficiency ,power and torque of the engine from the plots

Case setup:

Simulation Parameters:

Intial Conditions and events:

Region and intialisation:

Entire geometry is divided into the volumetric regions which converted into different boundaries

Intialization of different regions

Events:

opening and closure of intake and exhaust valve plays a key role in the IC engine.to simulate the valves events are used

Physical models

spary modeling:

In general

Parcel-distribution-select-Distribute parcels evenly throughout the cone-- it is experimentally found that spay of gasoline fue is distributed evenly throughout the cone

Turbulent dispersion:select-O'Rourke model-- this better describes the spary of gasoline fuel

Evaporation model-Tell rate at which parcel going to evaporate

In wall interaction

Select wall film-we want wall film to be formed.

In Injectors:

Parcel species-IC8H18

*Import injection rate shape prepared file

Select KH+RT models:

Injection mass:

Flow rate for fuel injected =7.5e-4kg/sec

so by calculating for 3000 rpm of egine and 720 deg

fuel mass injected per cycle=3e-5kg/cycle

Temperature of fuel injected kept=330K

Nozzle positions

• 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

For particular nozzle,set diameter,location and orientation provided

Combustion Modeling:

Set the start time for combustion just some degree before fuel injection is happening,so the solver would be ready till the time of injetion

Turbulence Modeling-RNG K-epsilon model

Source/sink modeling

As it is a PFI engine using iso-octane(whose properties resemble gasoline),it need a spark to ignite fuel-air compressed mixture

so an energy source is provided

For -15 to -14.5 crank angle total 40MJ of energy given to initiate combustion then from -15 to 15 degrees only 20MJ energy given to sustain combustion already initiated

Grid control:

Enable- 1) Adaptive mesh refinement

2) Fixed embedding

1)AMR

Fixed embedding

1.What is compression ratio of the engine ?

Compression ratio:

In a piston engine, the static compression ratio is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke, and the volume of the combustion chamber when the piston is at the top of its stroke.It is therefore calculated by the formula.

displacement volume. This is the volume inside the cylinder displaced by the piston from the beginning of the compression stroke to the end of the stroke

clearance volume. This is the volume of the space in the cylinder left at the end of the compression stroke.

it can estimated by cylinder formula which is = area of the cylinder *stroke length

where, Area of the cylinder = Pi*R^2 ,r is the radius of the cylinder bore,Stroke length=s

Because of the complex shape of Vc it is usually measured directly. This is often done by filling the cylinder with liquid and then measuring the volume of the used liquid.

Vc=5.75877e-05

vd=5.74212e-4

CR=(5.75877e-05+5.74212e-4)/(5.75877e-05);

CR=10.971

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

Heat losses should be minimized to get maximum power output In the combustion stroke to obtain maximum power output there should be no heat losses during this stroke but in reality there would be heat loss in the system which would be transfered to the the cylinder head so heat transfer model should be adopted to accomplish efficient power output

For this PFI engine simulation it takes lot of time to compute the case as it involves a complex geometry and process.If we want to capture the heat transfer-especially convection of heat from fluid to solid surface ,energy equations should be solved. This increases the time of simulation for rr radiation of heat from the solid surface to atmosphere,an external mesh is to be made to depict the external atmosphere and to solve the energy equation which increases the cell count.It makes the simulation to run forever.Hence we use conjugate heat transfer model where solid part is solved in a steady state using super-cycling option and the fluid part is solved in the transient case

For simulating complex geometries like IC engine it takes alot of time to compute the fluid part itself iin transient case along with the combustion and reaction processes.So it becomes difficult to predict the wall temperature from the CFD simulationWall heat transfer models are used to approximate this case.Basically all physical models used in CFD simulation uses some approximation to minimize computational time.Wall heat transfer models are used if are focused only on heat transfer giving less importance to fluid motion and reaction.For efficient operation of the engine the walls should be maintained at a certain temperature.This is achieved by pumping coolant to take away the excess heat from cylinder wall

3. Calculate the combustion efficiency of this engine

Efficiency=IHR/(m*CV)

Maximum value of IHR=1241Joules

Calorific value of iso-octane at standard condition=47.78e6(J/kg)

Total mass of fuel injected in 720 degrees of crank angle=3e-05kg

efficiency=1241/(47.78e6*3e-5)= 0.865773=86.577%

4.To determine the power and torque for this Engine

Gross work done by the engine for 240.199 Crank angle = W=468.646N-m

given Engine rpm=3000

Rotation per second =rps=50;

One rotation of crank=360 deg

Therefore,

Total degree turned by crank in 1 sec= 50*360=18000

Time (sec)=240.199/18000

=0.01334sec

Therefore,

Power=468.646/0.01334

Power=35130.8845KJ/W

Torque calculation:

Power P=(2*pi*N*T)/(60)

T=(P*60)/(2*pi*N);

T=(35120.35)*(60)/(2*pi*3000)

=111.8489Nm

5.Significance of CA10,CA50 and CA90 :

It is the crank angle at 10%,50% and 90% fuel combusted.From these value we can see that the actual change of crank angle with respect to fuel combustion

The physical significance of CA10 is that it is used to identify the start of the ignition, whereas the CA50 indicates the end of the premixed combustion and start of diffusion combustion of fuel used in engine,Ca10-90 determines comustion duration and at ca90 the burning of unburnt fuel is done by propogating flame.If Ca90 value is large ,the crank angles taken increases and the exhaust stroke tends to push the premature combustion products