Assignment 4

CI Engine Modelling:

Comparision between CI and SI Engine

CI Engine:

1.Self Ignition Engine.

2.Operates on High Compression ratio.

3.Helical Port is required

4.Diesel or Biodiesel is used

5.Fuel Efficient engine is novelty

6.Due to abnormal Combustion, Denotation occurs

7.Low engine speed range 1000-4000 rpm

8.Emissions : CO, HC, Nox , Soot

9.Doc, DPF,SCR are used for removing exhaust gases.

SI Engine:

1.Spark Plug is used for ignition.

2.Operates on low compression ratio.

3.Directed Port or Tumble port is required.

4.Petrol,LPG, CNG is used

5.NVH, Driving comfort is novelty.

6.Due to abnormal combustion, Knocking occurs

7.High engine speed range 1000-8000 rpm

8.Emissions: CO, HC, NOx

9.3 way catalytic converted is used for removing Exhaust gases.

1 Cylinder CI engine:

Modelling of CI engine:

CI Engine Model:

CI Engine Model is shown in the below figure:

Parameters:

This Case is analyzed for a speed of 3600 rpm having 100 mm bore and connecting rod length for a compression ratio of 16.5 as shown below:

Results:

BSFC:

BSFC refers to brake specific fuel consumption.BSFC for CI engine in this case is 238.2 g/kW-h while in case of SI engine BSFC is 239.2 g/kW-h, Hence it can be concluded that fuel consumption in CI engine is less than SI engine.

Exhaust Temperature:

The Exhaust temperature of the CI engine model is found to be 1039K which is slightly less than the exhaust temperature of SI engine i.e,1209K.This is obvious because in CI engine no external source of ignition is involve in the combustion process, this model follows the process of autoignition.

AF ratio:

A/F ratio of the CI engine is 20.78 which is greater than that in SI engine i.e.14.4.This means that the fuel mixture required in CI engine is on the leaner side.Because the most important factor to burn the diesel is air and it requires a great amount of air that's why the A/F ratio is high in this case.

Impact of MFB 50 on performance of CI engine:

Change the Main duration to 50 and then run the model to see the results previously the main duration was set to 35.

Results:

Brake Power & Volumetric Efficiency:

In earlier case for MFB 35 Brake power was 36.3kW but in this case after it is reported as 39 kW.Whereas there is negligible change in Volumetric efficiency. But its volumetric efficiecy decreased compare to first case.

A/F ratio, Torque:

A/F ratio in this case is 20.77 earlier it was 20.78 hence it can be seen as A/F ratio has decreased Whereas Brake torque has increased which is shown above.

NOx :

If we compare the after effect of MFB 50 then we can clearly see that engine performance is improved like brake power,brake torque,A/F ratio etc.But the efficiency of the engine decreases and also the NOx formation is increased.In earlier case it was 1109.78 ppm while in this case it is 1110.21 ppm.