(SEM V) THEORY EXAMINATION 2020-21 I C ENGINES FUELS AND LUBRICATIONS

SECTION A (Any 2 Questions Explained Briefly)
 

Compare SI and CI engines.
Spark Ignition (SI) engines use petrol as fuel and a spark plug to initiate combustion, whereas Compression Ignition (CI) engines use diesel fuel and combustion starts due to high temperature produced by compression. SI engines operate at lower compression ratios and have smoother operation, while CI engines operate at higher compression ratios and are more fuel efficient.
 

What do you mean by turbocharging?
Turbocharging is a method of increasing engine power by forcing more air into the engine cylinder using a turbine driven by exhaust gases. By supplying additional air, more fuel can be burned, resulting in higher power output without increasing engine size.
 

SECTION B (Any 2 Questions Explained)
 

Explain the working principle of a carburetor and its limitations.
A carburetor is a device that supplies the correct air–fuel mixture to an SI engine. It works on the principle of pressure difference created due to airflow through a venturi. As air velocity increases, pressure decreases and fuel is drawn into the air stream. However, a simple carburetor has limitations such as poor fuel distribution at varying speeds, difficulty in cold starting, and less precise air–fuel control.
 

Explain the wet sump lubrication system.
In a wet sump lubrication system, lubricating oil is stored in an oil pan at the bottom of the engine crankcase. The oil pump draws oil from the sump and supplies it to various engine parts such as bearings, pistons, and camshaft. After lubrication, the oil flows back to the sump by gravity. This system is simple, economical, and commonly used in passenger vehicles.
 

SECTION C (Any 2 Questions Explained)
 

Explain the stages of combustion in a CI engine.
Combustion in a CI engine occurs in four stages: ignition delay period, rapid pressure rise period, controlled combustion period, and after-burning period. During ignition delay, fuel is injected but combustion does not start immediately. Rapid combustion follows ignition, producing a sharp rise in pressure. Controlled combustion occurs as fuel continues to burn gradually, and after-burning completes combustion of remaining fuel.
 

What is swirl in a CI engine and why is it important?
Swirl is the circular motion of air inside the cylinder of a CI engine. It is generated by intake port design or combustion chamber shape. Swirl helps in better mixing of air and fuel, improves combustion efficiency, reduces ignition delay, and lowers exhaust emissions.
 

Most Questions in This PDF Are Related To
 

Most questions in the I.C. Engines, Fuels and Lubrications (KME-054) paper are related to SI and CI engine fundamentals, combustion process, ignition systems, fuel injection systems, engine testing, lubrication methods, supercharging and turbocharging, engine emissions, catalytic converters, alternative fuels, and performance parameters. The paper focuses on engine operation, efficiency improvement, and emission control concepts.