D. Arumuga PerumalAsst. Professor (senior) / SMBSVellore Institute of TechnologyVellore

Coverage / Objective

• Types of internal combustion engines• Thermodynamic principles involved• Components and purposes of each• Operation of systems

– Four stroke engines– Two stroke engines

Classification of Heat Engines

Heat Engines

External Combustion Engines Internal Combustion Engines

Rotary Engines Reciprocating Engines

Reciprocating Engines

2 – Stroke Engines 4 – Stroke Engines

S.I Engine C.I Engine S.I Engine C.I Engine

S.I & C.I engines

• In 1867, Nikolaus August Otto, a German engineer, developed the four-stroke "Otto" cycle.

• Spark Ignited (SI) engine works on Otto Cycle. S.I engines use Gasoline, LPG and Alcohol based fuels. For initiating ignition these engines use Spark Plug

• The Diesel Engine came about in 1892 by another German engineer,Rudolph Diesel. The Diesel engine is designed heavier and more powerful than gasoline engines and utilizes oil as fuel. Diesel engines are a commonly used in heavy machinery, locomotives, ships, and automobiles

• Compression Ignition (CI) or Diesel Engines engine works on Diesel cycle. CI engines uses Diesel , Bio-diesel and Bio based oils

4-Stroke Engines

Main parts of the 4 - stroke engine

Can be classified into

1. Structural Components2. Moving components

Four Strokes – 1. Suction Stroke 2. Compression Stroke

3. Expansion stroke 4. Exhaust stroke

• These four strokes require two revolutions of the crankshaft

Engine Stroke

• Engine stroke– A stroke is a single traverse of the cylinder by the piston (from TDC to BDC)– 1 revolution of crankshaft = 2 strokes of piston

Otto Cycle (4- Stroke SI Engines)

4-Stroke SI Engine

• The Intake Valve opens at a precise time to allow the air/fuel mixture to enter the cylinder

• The Spark Plug ignites the air/fuel mixture in the cylinder, which creates an explosion

• The Exhaust Valve opens at a precise time to allow the burned gases to leave the cylinder

• The force of the explosion is transferred to the Piston

• The force from the piston is then transferred to the Crankshaft through the connecting rod

• The piston travels up and down in a Reciprocation Motion

• The crankshaft converts the reciprocating motion of the piston, to the Rotating Motion

Diesel Cycle (4-StrokeCI Engines)

• The Diesel engine differs from the gasoline engine in that the intake stroke only pulls in air, not air and fuel. The fuel is injected into the cylinder at the end of the compression stroke. The fuel burns immediately (without the use of a spark plug) because of the high temperature of air in the cylinder.

2- Stroke Engines Main PartsSpark Plug

Crank Case

Transfer Port

Inlet PortPiston

Exhaust Port

Intake. The fuel/air mixture is first drawn into the crankcase by the vacuum created during the upward stroke of the piston. The illustrated engine features a poppet intake valve, however many engines use a rotary value incorporated into the crankshaft

Compression. The upward stroke of the piston compresses the fuel mixture. (At the same time, intake stroke is happening beneath the piston).

Power. At the top of the stroke the spark plug ignites the fuel mixture. The burning fuel expands, driving the piston downward, to complete the cycle

During the downward stroke the poppet valve is forced closed by the increased crankcase pressure. The fuel mixture is then compressed in the crankcase during the remainder of the stroke.

Transfer/Exhaust. Towards the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder. Unfortunately, some of the fresh fuel mixture is usually expelled as well.

Four stroke engines2 revolutions of crankshaft

Turning moment is not uniform – heavier flywheel

Less power for same size

Lesser cooling & lubrication requirements

More volumetric efficiency

Higher thermal efficiency

Higher initial cost

Two stroke enginesOne revolution of crankshaft

Uniform turning moment -lighter flywheel

More power for same size

Greater cooling & lubrication requirements

Less

Low

Low

SI ENGINESOtto cycle

Gasoline/ or petrol

Introduction of fuel – air mixture at suction stroke

Spark ignition

Compression ratio (6 to 11)

High speed

Low thermal efficiency

Lighter

CI ENGINESDiesel cycle

Diesel oil

Fuel introduction – at compression stroke

Self ignition

12 to 22

Low speed

High thermal efficiency

Heavier

injector

injector

injector

injector

injector