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

1.Compare SI vs CI and list down differences

SI engine vs CI engine

S.No./Engine type	SI engine	CI engine
	It is an engine in which the spark plug is used to burn the fuel.	It is an engine in which heat of compressed air is used to burn the fuel.
	SI engine works on Otto cycle	CI engine works on Diesel Cycle
	It draws a mixture of fuel and air.	It draws only air during suction stroke.
	The carburettor is employed to mix air and petrol.	The injector is responsible to inject fuel.
	SI engine has compression ratio 6 to 10.	CI engine has compression ratio 15 to 25.
	These are high speed engines.	These are relatively low speed engine.
	SI engine are lighter and cheaper, due to low compression ratio and maintenance cost is low.	CI engine are heavier and costlier, due to high compression ratio and maintenance cost is high.
	The pressure at the end of compression is 10bar.	The pressure at the end of compression is 35bar.
	The thermal efficiency is up to 26%.	The thermal efficiency is around 40%.
	The SI engine are generally employed in light duty vehicles such as scooters, cars, motorcycles etc.	The CI engines are generally employed in heavy duty vehicles like trucks, buses, earth movers etc.

2.Comments on following parameters

• BSFC
• Exhaust Temperature
• A/F ratios

BSFC - Braking Specific Fuel Consumption, BSFC for short and also known as energy specific fuel consumption or simply specific fuel consumption, is a type of ratio that deals with the fuel efficiency of an engine in terms of how much fuel the car uses and how much fuel. the energy 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 gas temperature - In modern internal combustion engines, knowledge of the exhaust gas temperature is essential for controlling and diagnosing the exhaust gas aftertreatment system, as well as protecting components that may be sensitive to thermal overload.

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

A/F Ratios – Heat engines use fuel and oxygen (from air) to produce energy through combustion. In order to ensure the combustion process, a certain amount of fuel and air must be supplied to the combustion chamber. Complete combustion occurs when all the fuel is burned, there will be no amount of unburned fuel in the exhaust. The air-fuel ratio (A/F) is the ratio between the mass of air and the mass of fuel consumed by the engine while it is running.

The ideal (theoretical) air-fuel ratio for complete combustion is called the stoichiometric air-fuel ratio. When the air-fuel ratio is greater than the stoichiometric ratio, the air-fuel mixture is called lean. When the air-fuel ratio is less 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 a diesel engine, it is 14.5:1.

Mass Burned (MFB) in each individual engine cycle is a normalized quantity with a scale of 0 to 1 or in percentages, describing the process of chemical energy release as a function of crank angle.

We will change a parameter called main duration, which is the duration of the crank angle in degrees where the fuel will burn by main diffusion or controlled combustion. The default value of the main time is 35, we change it to 50, which means that we increase the duration of the main diffusion combustion. In particular, the burning rate is expected to decrease because the burning time has increased.

Case setup –

Simulation model:

Open GT power console>> select engine performance>> select 1cyclDI engine

Boundary conditions:

Injection duration

Combustion duration

Case set up as a function of rpm, injection duration and combustion duration

GT Post:

Inline cylinder pressure:

PV diagram:

Temperature variation:

Nox variation:

Engine performance :

From the engine performance data we obtain

BSFC at MFB 50= 276 g/kw-hr

BSFC at MFB 40=249.3g/kw-hr

BSFC at MFB 60=308.8 g/kw-hr

A/F ratio at MFB 50=20.78

A/F ratio at MFB 40=20.78

A/F ratio at MFB 60=20.79

BP at MFB 50=31.3kw

BP at MFB 40=34.7kw

BP at MFB 60=28kw

It can be seen from the engine performance that as the combustion time increases, the engine BP decreases and vice versa. Brake efficiency increases with burn time, but for ppm NOx it is lower with longer burn time.

Conclusions:

• CI engine is successfully designed with different combustion timing and same injection timing.
• Post-simulation calibration is performed to compare the impact on efficiency and other parameters.