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

1. Compare SI vs CI and list down differences

SI Engine	CI Engine
SI Engine needs spark plug to start the ignition	CI Engine is compression ignition and the fuel self ignites under high pressure
Works on Otto Cycle	Works on Diesel cycle
In SI engine, mixture of air and fuel is injected into the combustion chamber (except in case of GDI engine where air is injected first and fuel is direclty injected into the chamber) and the mixture is compressed.	In CI engine, always air is taken into the combustion chamber and compressed. Fuel is introduced at the end of compression.
SI engine has a low compression ratio	CI engine has high compression ratio
Works at higher RPM	Works at lower RPM
Has lower thermal efficiency	Has higher thermal efficiency
Knocking is an issue in SI engine	Detonation is an issue in CI engine
Uses tumble motion in combustion chamber	Uses swirl motion in combustion chamber
Only 3 way Catalytic convertor is required for exhaust after treatment	DOC, DPF, SCR required for exhaust after treatment
Commonly used fuels are Petrol, CNG, LPG	Only diesel fuel is used
Produce lower torque	Produce higher torque
Major pollutants are CO & HC	Major pollutants are CO, NOx, Soot, HC

2. Comments on following parameters:

BSFC:

BSFC stands for Brake Specific Fuel Consumption. It is a parameter that reflects the efficiency of a combustion engine which burns fuel and produces rotational power. The formula for calculating brake specific fuel consumption is fuel consumption divided by power.

BSFC = Fuel consumption in unit time / Brake power.

The BSFC value indicates how efficiently the fuel supplied is turned into useful power.

Exhaust Temperature:

The temperature at exhaust manifold is normally called as exhaust temperature. Exhaust temperature plays an important role in the exhaust after treatment systems. The temperature of the exhaust gases is crucial in the efficient working of DOC, SCR etc in a CI engine as well as the working of 3way Catalytic convertor in a SI engine.

A/F ratios:

Air fuel ratio is the ratio of mass of air to mass of fuel used while running the engine. Air-Fuel ratio is critical in defining the proper combustion of fuel in an IC engine. SI engines work with a rich mixture (i.e. more fuel than air) whereas CI engines work with a lean mixture (more air than fuel) due to the very nature of the combustion process. The ratio of air to fuel such that complete fuel burns without leaving any residue fuel or air is called the Stoichiometric A/F ratio.

3. Change MFB 50 and observe impact on performance

SI Engine

CI Engine

Setting Up MFB50

• The mass fraction burned (MFB) shows how the in-cylinder combustion progresses as a function of the crank angle. The rate of combustion inside an engine cylinder is a very important parameter affecting the engine's thermal efficiency, peak cycle temperature and pressure, and exhaust emissions. This combustion rate is usually quantified by calculation of the burn crank angles at which the MFB reaches a specified value
• Combustion Control has always been an important role in the Modern Internal Combustion Engine system and being more crucial nowadays to improve driveability and reduce pollutant emissions.

From the above images, we can observe that the Brake power is reduced when we increased the Main duration of the moment of the piston, and also the Torque Power is also reduced and increases in the BSFC when we increase the main duration time.

• The CO2 emissions from the engine increase when we increase the Main duration, the CO emissions are up and downs when we changed the values of the main duration.

Graphical Results:

Graphical results of the MFB50 can be shown below with 35,40,45,50 crank angles with the Speed of 3600 RPM

Pressure Plot:

The crank angle 35 has a high inside cylinder pressure

Pressure- Velocity plot

Temperature Plot

Burned Fuel vs Crank Angle

The graphs show that due to the increased burn duration, burn rate has decreased. Also since the fuel is not burning violantly, the peak temperature and pressure has reduced. Torque and power has reduced and BSFC increased due to the increased burn duration.