Week-4 : Basic Calibration of Single cylinder CI-Engine

AIM:

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

To Comment on following parameters

• BSFC
• Exhaust Temperature
• A/F ratios

To Change MFB 50 and observe impact on performance

Theoritical Background:

Difference between SI and CI engine

Mass Fraction Burned:

Mass fraction burned (MFB) in each individual engine cycle is a normalized quantity with a scale of 0 to 1, describing the process of chemical energy release as a function of crank angle.
The determination of MBF is commonly based on burn rate analysis. The energy conversion during a combustion cycle can be described by the Mass Fraction Burned (MFB) at a specific crank angle degree (CAD) and the MFB, in turn, can be used by feedback control systems. In IC engine, the MFB depends on engine geometry, engine speed, A/F, ignition angle, residual mass etc. Measuring and controlling the result can compensate many variables that affect the combustion process compensated on an individual cylinder basis

1 Cylinder SI Engine Model

SI Wiebe Combustion Model

1 Cylinder Diesel Engine Model

DI Wiebe Combustion Model

Case Setup:

BSFC:

CI Engine tend to have higher Brake Specific Fuel Consumption(BSFC) than SI Engine, since CI engines have higher Thermal Efficiency and leaner Air Fuel ratio.

Air-Fuel ratio:

CI engine operates at leaner Air fuel ratio and Stichiometric air fuel ratio is maintained in case of SI engine in order to achieve higher combustion efficiency. In the case of CI engine fuel is directly injected in to the cylinder to form heterogenous mixture with air. Some of the fuel molecules will not be able to burn due to insufficient supply of oxygen and this results in formation of Soot.

Exhaust Temperature:

CI engines have higher thermal efficiency since they have high compression ratio. Due to higher expansion ratio during expansion stroke CI engines tend to have lesser exhaust temperature than SI engine.

Effect of Main Fuel Burn (MFB) on performance