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

 Aim:

• Compare SI vs CI and list down differences
• Comments on following parameters-BSFC,Exhaust Temperature,A/F ratios
• Change MFB 50 and observe impact on performance

Compairision between SI and CI Engin

S. No	SI Engine	CI Engine
1.	Spark is used to burn the fuel	Compressed air is used to burn the fuel
2.	Works on Otto Cycle	Works on Diesel cycle
3.	Draws mixture of fuel and air	Draws air only in suction
4.	Carburettor is used to mix and and petrol	In the cylinder itself mixing happens
5.	Injector is connected to carburettor	Injector is connected directly to Cylinder
6.	Compression ratio is on lower side around 6 to 10	Compression ratio is on higher side around 15 to 25
7.	It is cheaper and lighter due to low compression ratio	It is costlier and heavier due to high compression ratio
8.	Maximum Pressure attained is around 10 bar	Maximum pressure attained is around 35 bar
9.	Thermal efficiency is lower due to low compression ratio i.e, around 26%	Thermal efficiency is higher due to high compression ratio i.e, around 40%
10.	Generallly used in light duty vehicles such as scooter , cars, bike etc.	Generally used in heavy duty vehicles such as Trucks, Buses etc.
11.	Initial temperature and Pressure is lower.	Initial Temperature and Pressure is higher
10.	Weibe exponent is constant	Weibe exponent is fucntion of many parameters

Layout

CI Engine

SI Engine

BSFC: Brake specific fuel consumption abbreviated BSFC and also known by the term power-specific fuel consumption or simply specific fuel consumption, is a type of comparison ratio which looks at an engine's fuel efficiency in terms of how much fuel the car uses versus how much power it produces. The formula for calculating brake specific fuel consumption is fuel consumption divided by power, and often the results are expressed in kilowatts per hour.

Exhaust temperature: In modern internal combustion engines, the knowledge of the exhaust gas temperature is necessary for the management and diagnosis of the exhaust gas aftertreatment system, as well as for the protection of components that may be sensitive to thermal overloads.

In the diesel engine, aftertreatment components that are often actively managed based on exhaust gas temperature include diesel particulate filters (DPF) and NOx reduction catalysts such as SCR catalysts and NOx adsorber catalysts. In stoichiometric petrol engines, the engine management strategy depends on the temperature of the three-way catalyst (TWC).

A/F ratios: Thermal engines use fuel and oxygen (from air) to produce energy through combustion. To guarantee the combustion process, certain quantities of fuel and air need to be supplied in the combustion chamber. A complete combustion takes place when all the fuel is burned, in the exhaust gas there will be no quantities of unburned fuel. Air-fuel ratio (A/F) is the ratio between the mass of air and mass fuel used by the engine when running.

The ideal (theoretical) air-fuel ratio, for a complete combustion, is called stoichiometric air-fuel ratio. When the air-fuel ratio is higher than the stoichiometric ratio, the air-fuel mixture is called lean. When the air-fuel ratio is lower than the stoichiometric ratio, the air-fuel mixture is called rich. For a gasoline engine, the stoichiometric air-fuel ratio is around 14.7:1 and for diesel engine it is 14.5:1.

Mass fraction burned(MFB):  In each individual engine cycle is a normalized quantity with a scale of 0 to or in percentage, describing the process of chemical energy release as a function of crank angle.

We will change the parameter called as main duration, which is the duration of crank angle in degrees, where fuel is going to burn by main diffusion or where controlled combustion is happening. Default value of main duration is 35, we will change it to 50 means we are increasing the duration of main diffusion combustion. Mainly, drop in burn rate is expected, because burn duration has increased.

Case Setup:

Output Table

Pressure Contour

Temperature contour

Burned Fuel

Conclusion: It can be concluded that-

• The burned fuel rate decreases with increase in MBF
• With increase in MBF, the temperature decreases before power stroke and increases after power stroke
• There is pressure decreases in net with increase in MBF
• Brake power, brake torque and brake efficiency decrease and BSFC increases