Title:- Combustion Cycle

Carnot cycle :-• Carnot devised an ideal cycle of operation for a heat

engine and know as carnot cycle Carnot heat engine:• A heat engine which works on the reversible carnot

cycle.• Nicolas Léonard Sadi Carnot was the first person

who developed the basic modle for this engine in 1824 .

• The carnot’s diagram is shown :

• Idealized thermodynamic cycle consisting of four reversible processes

• 1-Reversible isothermal expansion• 2-Reversible adiabatic expansion• 3-Reversible isothermal compression• 4-Reversible adiabatic compression

• Source:- A reservoir at high temperature is called a source or high temp. Reservoir (HTR) or boiler.

• Sink:- A reservoir at low temperature is called a sink or low temp. reservoir (LTR) or condenser

STEP-1Isothermal Expansion• The gas is allowed to expand iso-Thermally at temperature T1 by absorbingHeat Q from the hot reservoir. This stepIs shown by curve AB in Fig

STEP-2 Adiabatic Expansion The gas is allowed to expand adiabatically.No heat enter or leaves the system (Q=0)And temperature of the gas is deceased formT1 to T2. This step is shown by curve BC in The Fig

STEP-3Isothermal compression : The gas is compressed isothermally by increasing the pressure on gas at temperature T2. The heat Q is rejected to low temperature reservoir.This step is shown by curve CD in Fig

STEP-4.Adiabatic compression :The gas is allowed to compress adiabatically . No heat enter or leave the system (Q=0) and temperature of the gas is increased from T2 to T1.This step is shown y the path DA in the Fig

Applications :*All types of vehicles that we use cars, motorcycles, trucks, ships, aero planes, and many other types work on the basis of second law of thermodynamics and carnot cycle.* All the refrigerators, deep freezers, industrial refrigerator system, heat pumps etc work on the basis of the carnot cycle

Efficiency of Carnot cycle :

• Efficiency of Carnot cycle=work done/heat supplied

• Efficiency of Carnot cycle depends upon the temperature range

=1-(T2/T1)

• Efficiency increase with decrease in temperature

Combustion Cycle :

• A cycle in which the process of combustion of fuel takes place is known as Combustion cycle.

• Combustion of fuel may occur inside the engine cylinder( in ICE) or outside the engine cylinder (in ECE).

• Combustion cycle may be take place in four stroke or in two stroke engines .

• In a combustion cycle the combustion of fuel takes place with an oxidizer in a combustion chamber.

• An oxidizer is used for the process of combustion

History :• The first internal combustion engine was created by

Etienne Lenoir in 1859.

• It was the first internal combustion engine which was used commercially .

• Seigfried Marcus was the first person who invented the first modren combustion engine in 1864.

• Ideal P-V diagram of four stroke

Combustion process :• There are two type of combustion process• 1-Internal combustion process• 2-External combustion process

• Working principle :• An internal combustion engine works on the

temperature difference. Simply works on the Carnot heat engine.

• Internal combustion engine:-• In which process of combustion of fuel take place

inside the engine cylinder a chemical energy obtained from the combustion is converted into the mechanical energy further converted into mechanical work

• E.g petrol engine ,gas engine ,diesel engine

• Four stroke combustion engine:-• An internal combustion engine in which piston completes

the four separate stroke while turning the crankshaft

• Stroke:• A stroke is that refers to full travel of the piston along the

cylinder, in either directions.• The four separate strokes are given below:• Intake stroke.• Compression stroke. • Combustion stroke /working stroke.• Exhaust stroke.

• Intake stroke: This stroke of the piston begins at top dead center (T.D.C.) and

ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing vacuum pressure into the cylinder through its downward motion.

• Compression stroke: This stroke begins at B.D.C, or just at the end of the suction

stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.

• Combustion stroke: This is the start of the second revolution of the four stroke

cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. (the end of the compression stroke) the compressed air-fuel mixture is ignited by a spark plug (in a gasoline engine) or by heat generated by high compression (diesel engines), forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.

• Exhaust stroke: During the exhaust stroke, the piston once again returns from

B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust valve

Diagram :

Animation :

• Two stroke combustion engine:-• It's called a two-stroke engine because there is

a compression stroke and then a combustion stroke. • In a four-stroke engine, there are separate intake,

compression, combustion and exhaust strokes. • 2 Stroke cycle engine• Mix special two-stroke oil in with the gasoline• Mix oil in with the gas to lubricate the crankshaft,

connecting rod and cylinder walls

• Note: If you forget to mix in the oil, the engine isn't going to last very long!

Intake :The fuel/air mixture is first drawn into the crankcase by the vacuum that is created during the upward stroke of the piston.• Many engines use a rotary value incorporated into the crankshaft.• But in this case we use poppet intake valve.

Compression :The piston then rises, driven by flywheel momentum,

and compresses the fuel mixture. (At the same time, another intake stroke is happening beneath the piston)

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 remainder of the stroke.

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. (At the same time, another crankcase compression stroke is happening beneath the piston.)

Exhaust :Toward 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

Compression Stroke :• Now the momentum in the crankshaft starts

driving the piston back toward the spark plug for the compression stroke. As the air/fuel mixture in the piston is compressed, a vacuum is created in the crankcase. This vacuum opens the reed valve and sucks air/fuel/oil in from the carburetor.

• Reed valves are a type of check valve which restrict the flow of fluids to a single direction, opening and closing under changing pressure on each face

Piston functions : • On one side of the piston is the combustion chamber,

where the piston is compressing the air/fuel mixture and capturing the energy released by the ignition of the fuel.

• On the other side of the piston is the crankcase, where the piston is creating a vacuum to suck in air/fuel from the carburetor through the reed valve and then pressurizing the crankcase so that air/fuel is forced into the combustion chamber.

• Meanwhile, the sides of the piston are acting like valves, covering and uncovering the intake and exhaust ports drilled into the side of the cylinder wall

Diagram :

Difference b/w four and two stroke engine• Four stroke• It has one power stroke for every two

revolutions of the crankshaft.• Engine is heavy• Engine requires more space• Less fuel consumption and complete

burning of fuel.• Less noise is created by engine.• Engine design is complicated due to

valve mechanism.• Heavy flywheel is required and

engine runs unbalanced because turning moment on the crankshaft is not even due to one power stroke for every two revolutions of the crankshaft

• Used in cars, buses, trucks etc.

• Two stroke• It has one power stroke for each

revolution of the crankshaft.• Engine is light• Engine requires less space• More fuel consumption and fresh

charge is mixed with exhaust gases• More noise is created by engine• Engine design is simple due to absence

of valve mechanism• Lighter flywheel is required and engine

runs balanced because turning moment is more even due to one power stroke for each revolution of the crankshaft.

• Used in mopeds, scooters, motorcyclesetc

• External combustion engine:-• In which combustion of the fuel take place outside

the engine a chemical energy obtained from the combustion is converted into mechanical energy further converted into the mechanical work

• E.g• Steam engine

Difference b/w ICE and ECE engine• Internal combustion engine :• In an internal combustion engine,

the working fluid consists of a combustible fluid placed inside a cylinder.

• It can work at high temperature and pressure.

• It takes less place for installation.• It is more reliable and useful.

• External combustion engine :• In external combustion engines,

combustion occurs outside the cylinder. The heat needs to be transferred into the working fluid separately.

• It cannot work at high temperature and pressure

• It takes more place for installation.• It is not very reliable and useful.

Slides are over.Thanks.