FINAL TEST

1* Compression ratio: It is the ratio of the volume of the cylinder and its head space when the piston is at the bottom dead center of its stroke to the volume of the head space when the piston is at the top dead center. In the PFI SI engine simulation I adjust the compression ratio of the engine setup on 8.

As the maximum volume is = 0.0005738 and the minimum volume is = 0.00007172

And the compression ratio is Maximum Volume / Minimum Volume = 0.0005738 / 00007172 = 8

2*

By changing the clearance volume

Clearance volume can be changed by offsetting the crank pin

To get CR of 10.3

(Vc + Vs)/Vc = 10.3

We know that Vs = Max Volume - Min Volume = 0.0005738 - 5.7032e-5 = 5.1676e-4 m^3

Vc = Min Volume = 5.7032e-5 m^3

(Vc + Vs)/Vc = 10.3

Vc + Vs = 10.3Vc

Vc - 10.3 Vc = -Vs

Vs = 10.3Vc - Vc = ( 10.3 - 1 )* Vc = 9.3Vc

New Vc = Vs/9.3 = 5.1676e-4/9.3 = 5.556e-5 m^3

So, clearance volume needs to be changed from 5.7032e-5 m^3 to 5.556e-5 m^3 to increase the compression ratio from 10.06 to 10.3

3* Volumetric efficiency: It is defined as the ratio of the mass density of the air-fuel mixture drawn into the cylinder at atmospheric pressure during suction to the mass density of the same volume of air in the intake manifold. In the PFI SI engine simulation its about 96.7%.

According to our case setup

mass = 0.0005005 kg

Volume can be obtained from the volume plot of thermo_region0(cylinder region)

Volume = 0.000574219 m^3

Density of air inside the cylinder = 0.0005005 kg/0.000574219 m^3 = 0.8716 kg/m^3

But as we go for mean temp. it varries alot so we take avg. of that as 365K

PV = m R T

P = ρ R ⋅ T

where P is the Atmospheric Pressure = 101325 Pa ; R is the Gas Constant for air = 287 J/Kg K; T is the temperature of air inside the intake manifold.

Hence ρ = P / R T = 101325 / 287 * 365

= 0.967257 k g m 3

So Volumetric Efficiency is ρ(cylinder) / ρ (during suction)= 0.8716 / 0.9672 = 0.901157

= 90.1157%

4* Air mass flow rate of the engine is the amount of air flow through the volume of the engine cylinder per unit of time.

Hence: Total Mass entering the cylinder (air+fuel) in 720 degrees = 0.0005005 Kg

Mass of Fuel sprayed in 720 degrees = 3e-5 Kg

So, Mass of air sucked in cycle = Total Mass entering the cylinder - Mass of fuel injected

Mass of air in complete cycle = (0.0005005 - 3e-5) = 4.705e-4 Kg

Mass of air involved in one Rotation = (4.705e-4)/2 Kg = 2.353e-4 Kg

Engine RPM = 3000

Engine RPS = RPM/60 = 3000/60 = 50 Rotations per second

Mass Flow Rate of Air = 50*2.3525e-4 = 0.012 Kg/s

5* The trend of the cell count is such that the no. of cells active initially is very less related to the cell count after the spray injection in increases slightly but after the opening of the inlet valve the tempature and velocity and some other boundary embeddings are comes into the action that raise the cell count graph till peak and then as the exhaust valve is start opening the trend again goes down.

6* In a real engine, valves are in contact with the cylinder head but while running simulation, there is a small gap because if we connect the valve with the cylinder head it cause overlapping of the surface that counts under the errors in the converge software. Hence a little gap is necessary. Other then that dur to the gap between two region converge is able to create discontinous triangles that is responsible for creating events.

If the gap is large then the large discontinous triangles are created that manipulates the event openning and closeure flow process. This will enhance the margin of errors. With this the speed of simulation also increased on the other hand.

7* Combustion duration is 50 degree

Engine RPM = 3000

Engine RPS = 3000/60 = 50

Degrees per second = 50*360 = 18000 degrees/s

Duration of Combustion = combution duration in terms of crank angle/Degrees per second = 50/18000 = 0.0027777 seconds = 2.78 milliseconds

PART-2

1* The advantage of the sector modeling is that we ca do study the complete analysis of a spray over the cylinder under the perfect closed cylinder setup without the interference of additional factors. It is used for analysing and to simulate the effect of the piston profile on the engine performance and emissions. This will leads to the accuracy in the results with lesser cell counts.

2* Sector approch is not work in the case of contributing high swirl and turbulence in the charge distribution. Rather then this if we consider the valves (not complete closed cylinder system) then also its not possible to go with sector approch. In case of single nozzle also sector approch is not considered.

3* We only model the compression and power strokes in a closed cycle scenario. The Start Crank Angle (SCA) and End Crank Angle (ECA), respectively, can be used to indicate the beginning of compression and the conclusion of the power cycle. According to the assumption that the intake stroke begins at zero degrees, the compression stroke will begin at 180 degrees (SCA), and the power stroke will conclude at 540 degrees. (ECA).

4* No PFI Engine is not be convert the PFI case into a SECTOR case. This is because in the port fuel injection the spray is done in intake port only all mixed charged is entered in the chamber. So thats why it is not be possible.

Anubhav.