Assignment 2

Objective: To explore GT Suite and simulate SI Engine

1.Run the case at 1800 rpm and list down important parameters

Case Setup:

Two cases are setup two show difference between the default case setup for 3600 rpm and the given case setup for 1800 rpm.

Keeping all the default parameters constant and only running the case for 1800 rpm,the values of the following parameters are obtained:

• air flow rate=24.6 kg/h

• BMEP

PMEP needs to be always subtracted irrespective of the sign. Since, the sign of PMEP here is negative it is added to IMEP.

BMEP=IMEP-FMEP+PMEP

=10.61-1.13+(-0.05)

=9.43 bar

• BSFC= 239.2 g/kWh

• In-cylinder pressure= 48.89 bar

2. Increase the power output at 3600 rpm by 10%

The power output of an engine is dependent on various factors. The various factors considered here to increase the power output may not be feasible in case of SI engines. However, the power output was seen to be increased by 10%.

The following parameters were considered for performance increase:

1. Air Fuel Ratio
2. Compression Ratio
3. Bore Diameter
4. Stroke Length

Going by the above aparamters one by one,

1. Air Fuel Ratio

In SI Engines , typically stoichiometric air fuel ratio (AF=14.5) is maintained during combustion. Increasing or decrease in Air-fuel ratio is typically obtained by regulating the air-flow inside the cylinder by applying increasing/decreasing the throttle.

At Air fuel ratio of 14.5, the Brake Power is 16.7 kW. For a 10% increase, the Power Output should be 18.3 kW. The Brake Power does not increase despite any increase / decrease in Air-fuel ratio.

2. Compression Ratio

Increasing the compression ratio allows for more air to be compressed inside the cylinder and hence increasing the power output.

From the above figure, it can be seen that at a compression ratio of 16, the power output is 18.4 kW which is ,

(18.4-16.7)*100/16.7= 10.17%

However, it needs to be noted that a compression ratio of 16 in SI engines can lead to knocking tendency given the type of fuel used is gasoline. Such higher compression ratios are usually achievable in Diesel engines.

3. Bore Diameter

Increasing the bore diameter increases the volume of cylinder and hence the piston diameter thus generating higher peak pressure inside the cylinder. Also, more fuel can be inducted inside the cylinder.

For bore diameter of 90 mm (original diameter=86 mm,original power output=16.7 kW)we can see that the power output is 18.3 kW. Hence, (18.4-16.7)*100/16.7= 9.58%. It can be concluded that for diameter greater than 90 mm, the power output will be more than 18.3 kW i.e. greater than 10%.

4. Stroke Length

Increase in stroke length results in increase in the size of the cylinder and hence the swept volume. More air-fuel mixture can then be inducted inside the cylinder and hence more output power is produced.In the above figure, it can be seen that for a stoke length of 96 mm, the power output is 18.6 kW. Hence, by increasing the stroke length by, 96 mm - 86.1mm= 9.9 mm which is almost 10 mm we can increase the power output by more than 10%.