FINAL TEST

Q1. What is the Compression ratio for the engine?

The compression quantitative relation is that the quantitative relation between the degree of the cylinder and combustion chamber in an enclosed combustion engine at their most and minimum values.

in a very piston engine, the static compression quantitative relation(CR) is that the ratio between the degree of the cylinder and combustion chamber once the piston is at the lowest of its stroke, and also the volume of the combustion chamber once the piston is at the highest of its stroke.

CR=Vs+VcVc">CR=Vs+VcVcCR=Vs+VcVc

where,

Vs">Vs = swept 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.

Vc">Vc= clearance volume. This is the volume of the space in the cylinder left at the end of the compression stroke.

Vs = can be estimated by the cylinder volume formula

Vs=π4⋅d2⋅L

Where:

d = cylinder bore (diameter)

L = piston stroke length

Maximum volume = 0.00057m3">0.00057m30.00057m3

Minimum volume = 5.75⋅10-5m3">5.75⋅10−5m35.75⋅10-5m3

Compression Ratio (CR) = Maximum volume / Minimum volume

= 0.00057 / 5.75⋅10-5m3">5.75⋅10−5m35.75⋅10-5m3

CR = 10:1

2) Modify the compression ratio for this engine to 10.3 without changing geometrical parameters.

To modify the compression quantitative relation of the engine while not dynamical its geometrical parameters, either the clearance volume (or) sweptback volume ought to be modified.

METHOD 1: sweptback volume is constant and clearance volume is varied.



Hence, to urge the desired compression quantitative relation ten.3, the sweptback volume is modified to five.3475*10-4 M3 by dynamical the bore (or) stroke length of the engine by keeping the clearance volume as constant.

`C R = V s + V c V c 10.3 = 5.75 ⋅ 10 − 5 + V s 5.75 ⋅ 10 − 5 V s = 5.3475 ⋅ 10 − 4 m 3`

3) Calculate Volumetric Efficiency for this engine.

Volumetric potency (VE) in burning engine engineering is outlined because the quantitative relation of the mass density of the air-fuel mixture drawn into the cylinder at gas pressure (during the intake stroke) to the mass density of a similar volume of air within the manifold.

`Volumetric Efficiency = V a V s ⋅ 100 We know that swept volume V s = 5.125 ⋅ 10 − 4 m 3 Assume the air used is ideal in nature. Therefore using the ideal gas equation, P * Va = m * R * T Va = (m * R * T) / P where, P – Pressure of air at atmospheric condition (101325 N/m2) m – Mass of air R – Universal gas constant (287 J/Kg-K) T – Temperature of air at atmospheric condition (293 K)`

`Mass is taken from the above plot as m = 0.000534 kg Va = [(0.000534 * 287 * 293)] / 101325 Va = 4.4317 * 10-4 m3 Volumetric Efficiency = (4.4317 * 10-4) / (5.125*10-4) * 100 Volumetric Efficiency = 86.47 %`

Q4. Measure the air mass flow rate for this engine in kg/s.

`The mass of air (m) is taken as 0.000534 Kg. This mass is the mass flow rate of air into the cylinder per 360 degree. Speed of the engine (N) = 3000 rpm = 3000 / 60 = 50 rps. Angle covered in one second = 50 * 360 = 18000 degrees. Mass of air entering for 18000 degrees = 0.000858711 * 50 = 0.0267 Kg/s. ṁa = 0.0267 Kg/s`

Q5.Why is the cell count varying during the simulation?

The cell count is variable throughout the simulation due to the accommodative Mesh Refinement(AMR) and glued embedding accustomed capture the physics accurately in vital areas.

the speed and temperature AMR ar utilized in PFI engine.

for instance in rate AMR if we have a tendency to set SGS as 1m/s then on top of it cell can become finer by an element of two^n here n is plant level if it's 2 mesh becomes finer by 2^2 is four times.

Q6. In a real engine, valves are in contact with the cylinder head but while running simulation, there is a small gap.

• WHY?
• What happens if this gap is big?

WHY?

In real engines, the valves area unit in touch with the plate to avoid escaping of fuels and warmth from the combustion chamber. The movement of valves area unit controled by victimization cam and follower mechanism.

In our PFI simulation we've not designed any mechanism to drive the valves. therefore there's little gap between plate and valve. throughout the simulation, converge mechanically creates disconnect triangles between the gap.

What happens if this gap is big?

when this gap is huge, the warmth dissipation between plate and cylinder wall cannot turn up. This will increase the temperature within the cylinder which might cause issues like detonation (or) knock and it can even increase the emission like Nox, unwanted HC and soot which is able to decrease the potency and lifetime of the engine.

7. How many seconds does combustion last in this case?

From the above plot,

Duration of combustion is 240.199 degrees.

Engine speed (N) = 3000 rpm => 50 rps

Revolution in degrees = 360*50 => 18000degrees/sec

Hence for 240.199 degrees, t = 240.199/18000

t = 0.0133 seconds

So, combustion lasts for 0.0133 seconds.

1. What is an advantage of SECTOR Simulation?

Sector simulation may be a method of victimization solely the arena of model for CFD simulation. Since size of the engine is cut backd the time taken for the simulation also will reduce specified it saves machine time. As this can be a closed cycle analysis the boundary conditions and parameters needed to outline a case is additionally minimum.

2. When will the sector approach not work?

The sector modelling doesnot add case of open cycle engine analysis. In open cycle analysis, the position of walls varies with time that can't be captured once we use sector modelling. So, sector modelling can't be applied for open cycle analysis whereas it are often used for closed cycle analysis wherever the valves aren't thought-about.

3. How to choose Start Crank Angle (SCA) and End Crank Angle (ECA) for a sector simulation?

The sector simulation is good incase of closed cycle analysis. So, the start crank angle can be taken at the beginning of compression stroke and the end crank angle can be taken at the end of expansion stroke.

For example if we assume the fuel to be injected at 0 degrees then 180 degree can be taken as start crank angle (SCA) and 180+360 = 540 degree can be taken as end crank angle (ECA) for diesel engine.

4. Can we convert the PFI case into a SECTOR case? Explain your answer?

PFI case is an open cycle analysis type. As i said before sector modelling is suitable only for closed cycle analysis where a closed part of 360 degree chamber can be simulated for saving computational time.

As in case of PFI the valves are considered which makes it a open cycle analysis. So the PFI case cannot be converted into a sector case.