Assignment 4

Objective:

Explore the model of a DI engine and compare it with SI engine. Also, list down differences and change mass fuel burn to 50% and observe its impact on the performance.

Case 1: Comparision of SI vs DI at 1800 RPM.

SI engine model:

DI engine model:

Engine speed is adjusted to 1800 RPM for both the SI as well as DI engine. Both the models were simulated and their results were compared.

Characteristics	SI	DI
Compression ratio	9.5	16.5
Brake power(kW)	8.3	19.5
Brake Torque(N-m)	44.2	103.6
Air flow rate(kg/hr)	28.8	82.8
BSFC(g/kW-hr)	238.2	221.3
A/F ratio	14.5	19.18
NOx in ppm	73.59	997.92
CO in ppm	258.38	2.89

In-cylinder pressure of SI engine:

In-cylinder pressure of DI engine:

Mass flow rate of SI engine:

Exhaust:

Intake:

Mass flow rate of DI engine:

Exhaust:

Intake:

BSFC:

BSFC of a DI engine is lower compared to a SI engine because even though the power output is high but the fuel consumption is also higher. Hence, the ratio is less than that of a diesel engine.

Exhaust temperature:

Exhaust temperature of DI engine is 1045K.

Air-fuel ratio:

The quantity of fuel present in 1kg of air is known as air-fuel ratio. In DI engines, lean mixture is used. Hence, a higher air-fuel ratio is used compared to SI engines.

Case 2:

Main duration of fuel combustion was increased to 50 and the model was run at 1800 RPM.

Characteristics	DI at 50%	DI
Brake power(kW)	17.3	19.5
Brake Torque(N-m)	91.8	103.6
Air flow rate(kg/hr)	82.8	82.8
BSFC(g/kW-hr)	249.6	221.3
A/F ratio	19.18	19.18
NOx in ppm	1100.4	997.92
CO in ppm	3.76	2.89

Conclusion:

Due to increase in combustion duration, every major performance parameter was reduced such as power and torque. Hence, BSFC is increased also the NOx and CO emmisions were increased.