Assignment 4

1.Compare SI vs CI and list down differences (assignment no 2-SI)

BELOW ARE THE SNAPSHOTS OF THE DI_1Cyl and SI_1cyl models.

Major Differences between the the two models are 

1- Injector Position

2- Compression Ratio ( Engine Cylinder Geometry )

3- Combustion Model

and obviously the fuel used.

Notice the Injector Positions in the folowing two images. In Diesel Engines Fuel Injection is inside the Cylinder whereas in SI Engine Fuel Injection is inside the intake port.

Notice the Compression Ratio in the Diesel Engine is 16.5 whereas 9.5 in the SI Engine.

The other major difference is the combustion model used in the models. Diesel engine ine this model uses a non predictive Di_Weibi Model of Combistion whereas SI Engine uses SI Weibi.

2.Comments on following parameters

• BSFC
• Exhaust Temperature
• A/F ratios

BSFC is rate of fuel supplied to the power produced.

Exhaust Temperature is the Temperature of the exhaust gases that have been recently burned in the engine cylinder and escape the cylinder at the exhaust stroke 

Stoichiometric A/F Ratio is Air to fuel ratio that burns all the fuel with no excess or less air. For Gasoline C8H18 it is 14.7 whereas for diesel C12H23 it is 14.5.

Actual A/F Ratio is the Mass of Air divided by the Mass of Fuel in the actual working of an engine. Gasoline its round about the same as stoichiometric A/F Ratio whereas Diesel Engines operate lean i.e. there Actual A/F ratio is greater than 18 or so.

3.Change MFB 50 and observe impact on performance

In the Di_ Weibi Combustion model MFB50 can be changed using either the ignition delay or  Injection timing. But more reliable model is by Injection timing and fixing the other combustion constants because in the other case one have to constantly alter the injection timing along with ignition delay .