FINAL TEST
(1)Compression ratio is defined as a ratio of the maximum volume to the minimum volume of the combustion cylinder. in our case compression ratio is 5.74e−45.70e−5=10.07
(2)To change compression ratio without changing geometrical parameters is possible only by changing clearance or swept volume.
maximum volume is clearance volume plus displacement volume clearance volume is the minimum volume and equals to 5.70e−55.70e-5.
Vmax=Vc+VdVmax=Vc+Vd where - VcVc is the clearance volume and VdVd is the displacement volume.
The compression ratio should be 10.3 therefore ratio=Vd+VcVc=10.3ratio=Vd+VcVc=10.3therefore VcVc is replaced to be 5.55e−55.55e-5, Furthermore we can change VdVd which will be 5.336e−35.336e-3 to get the compression ratio of 10.3
(3) Volumetric efficiency η=η= volume of air-fuel mix sucked into the cylinder/displacement volume
displacement volume is the maximum volume of the cylinder substituted to clearance volume therefore in our case displacement volume Vd=5.17e−4m3Vd=5.17e-4m3
According to the ideal gas equation, we can determine the volume of the sucked air. According to the output files sucked mass is approximately 0.0005kg.
According to the ideal gas equation V=m⋅R⋅TPV=m⋅R⋅TP where - mm is mass, RR is the universal gas constant, TT is the temperature in Kelvins and PP is the ambient pressure
(4) Mass of air during the 360 degrees of the crank angle is 0.0005kg. RPM in our case is 3000, therefore RPS will be 3000/60=50.
50 revolution per second in other words equals 50*60=18000degrees per second.
mass per 18000degrees will be 18000*0.0005/360 = 0.025kg/s
η=4.149e−45.17e−4⋅100=80.26≈80%.
(5) during the combustion process or fuel injection process we have temperature and velocity second derivative curvatures therefore we need refined mesh within some specific areas to appropriately predict the flow structure or temperature development, therefore we use AMR for proper calculations.
(6)In real live valves are in contact with the cylinder head in order to seal the combustion cylinder to prevent excessive heat transfer and therefore thermal losses.
In the simulation, we have a gap because we are using the disconnect triangle concept which ensures sealing while we are using the "VALVE" option in the "EVENT" section in the "Converge CFD".
(7)
The engine is running power stroke through 240degrees, thus we should determine the time needed for 240degrees of the crank angle.
As we know engine covers 18000degrees within 1 second, therefore to cover 240degrees the time t=24018000=0.013sec
(1) Sector simulation is used while having closed geometry with the symmetrical 360degree geometry. Main benefit of using this method is dramatically reducing the computational time.
(2)The sector approach will not work if we don't have a symmetrical case or having port injection valve openings which we faced in the PFI case.
(3)The start angle should be when the volume is maximum and the end angle should be when the piston reaches TDC in other words the clearance volume.
(4)We can not convert the PFI case into a Sector case because PFI is opened cycle case, where we have intake and exhaust phases, fuel injection via the port therefore flow structure in the combustion cylinder will be severely unsymmetrical leading Sector case simulation to unrealistic results.