FINAL TEST

Questions based on PFI Engine:

Q1. What is the Compression ratio for the engine?

The compression ratio is defined as the ratio between the volume of the cylinder with the piston in the bottom position, V_bottom (largest volume), and in the top position, V_top (smallest volume). The higher this ratio, the greater will be the power output from a given engine. It is generally in the 6–10 range.

Where:

Vd= 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.

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

Vd can be estimated by the formula

Where:

= diameter

= length

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

The cell count is varying because of adaptive mesh refinement with sub grid scale velocity and temperature and fixed embedding at the spark ignition source and the spray nozzle and volume embedding at the cylinder region to capture the flow physics accurately.

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

• WHY?

Converge is designed to share an edge by two triangles and hence there is a small gap between the valves and cylinder head. if the edges are shared more than two triangles it would lead to interference problems and would lead to improper result.

• What happens if this gap is big?

If the gap is large the diconnected triangles cannot be created and which will cause the flow of air and fuel to move out of the domain and may lead to wrong results.

Q7. How many seconds does combustion last in this case?

Q1. What is an advantage of SECTOR Simulation?

for axisymmetric engines the sector geometry of a model can be used to reduce the time required for simulation and hence the computation time can be reduced by reducing the cell count using sector geometry.As a result, CONVERGE provides built in support for making engine sector surface to speed up the close cycle analysis work flow.

Q2. When will the sector approach not work?

The sector modelling is not used for open cycle analysis where the position of valves varies with time and hence need to be modelled.Sector modelling approach can be applied only for closed cycle analysis where the valves are not considered.

Q3.How to choose Start Crank Angle (SCA) and End Crank Angle (ECA) for a sector simulation?

The sector simulation is good for closed cycle analysis. 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.

Q4. Can we convert the PFI case into a SECTOR case? Explain your answer?

PFI Engine simulation was for open cycle analysis but the sector simulation will limit the scope of our simulation only till the closed cycle of the PFI engine. Apart from this, the modelling of the spark plug in a will pose a significant challenge. From these reasons we can conclude that PFI Engine cannot be converted into a SECTOR case.