Comparison of CI vs SI

AIM:

1.Compare SI vs CI and list down differences

2.Comments on following parameters

• BSFC
• Exhaust Temperature
• A/F ratios

3.Change MFB 50 and observe impact on performance

PROCEDURE:

• The SI and CI engine models are run at 1800rpm with the following cylinder geometry.

CI ENGINE SI ENGINE

RESULTS:

I. CI ENGINE SI ENGINE

II.

Parameter	CI	SI
BSFC(g/kW-h)	221.3	239.2
EXHAUST TEMPERATURE(K)	1045	1147
AIR FUEL RATIO	19.18	14.5

• BSFC is high for SI and low for CI as here CI engine uses 221.3g of fuel to produce 1KW of power and hence is fuel efficient than SI.
• Exhaust temperature for SI is greater than CI because as fuel consumption increases,exhaust temperature also increases.
• The stoichiometric mixture for a gasoline engine is the ideal ratio of air to fuel that burns all fuel with no excess air and hence A/F ratio for SI is 14.5. In CI engine to limit soot production, lean mixture is used and hence A/F ratio is 19.18

III.

MFB50 i.e.mass fraction of fuel burned to 50% is anchor angle and hence it is altered to see the performance of the engine. Here the anchor angle is changed to 20.

without change of anchor angle:

with change of anchor angle:

From the above comparison of results we see that as the anchor angle(MFB50) is changed then the performance of the engine i.e. brake power and brake torque decreases and similarly all other parameters are reduced.