engine sixth time

Heat Engines

A machine or device which derives heat from

the combustion of fuel and converts part of this

energy into mechanical work is called a heat

engine.

Gun Shoot

Rocket Launch

Heat Engines

Heat engines may be classified into two main classes asfollows:

1. External combustion engines2. Internal combustion engines.

What are they and give examples of both.

2 and 4 stroke engines we will discuss are internal combustion 2 and 4 stroke engines we will discuss are internal combustion (IC) engines

Construction details of 2 stroke engine

Co

nstru

ction

de

tails

of 4

strok

e e

ng

ine

1. Spark Plug or fuel nozzel

2. Valve Spring

3. Exhaust

4. Exhaust Valve

5. Combustion space

6. Piston Ring

7. Cylinder15. Piston

16. Fins

16. Inlet

Valve

17. Inlet

Co

nstru

ction

de

tails

of 4

strok

e e

ng

ine

7. Cylinder

8. Gudgeon Pin

9. Connecting Rod

10. Crank pin

11. Crank

12. Crankshaft13. Balance

Weight

14. Crank

Case

15. Piston

4 stroke engineIntake Valve Exhaust Valve

Top Dead

center (TDC)

Clearance

VolumeSpark Plug

Connecting

Rod

Cylinder

Crank

Crank Shaft

4 stroke engineIntake Valve Exhaust Valve

Top Dead

center (TDC)

Clearance

VolumeSpark Plug

Connecting

Rod

Stroke:

(Movement of

piston from TDC

to BDC)

or Bottom Dead

center (BDC)

Volume

Swept

or

(Movement of

piston from BDC

to TDC)

Pr

e

s

s

u

r

e

(

P

a

)

TDC BDC

PMax

(c)

(d)

(e)

P

r

e

s

s

u

r

e

(

P

a

)

Volume

Clearance

volumeSwept

volume

Patm(a)

(b)

(e)

(f)(g)

Pr

e

s

s

u

r

e

(

P

a

)

TDCBDC

PMax(c)(d)

(e)

P

r

e

s

s

u

r

e

(

P

a

)

Volume

Clearance

volumeSwept

volume

Patm(a)

(b)

(e)

(f)(g)

Construction details of 2 stroke engine

Working of 2 stroke engine

4 stroke Petrol

(otto) cycle

Real 4 stroke

Petrol cycle

4 stroke

Diesel cycle

Real 4 stroke

Diesel cycle

Air standard modeling of 4

stroke Petrol (otto) cycle with Q

and WQ (Heat is going in )

Q (Heat is going out )

Define what is air

standard otto cyclePetrol (otto) cycle

Air

Fig. p-V and T-s diagrams of a four stroke Otto cycle engine

Constant Volume or otto cycle efficiency

The above efficiency is called as efficiency or

thermal efficiency. Volumetric efficiency = actual

volume intake/swept volume

Constant Volume or otto cycle efficiency

Compression

ratio

= adiabatic

exponent or ratio

of specific heats

Pr

e

s

s

u

r

e

(

P

a

)

TDCBDC

PMax(c)(d)

(e)

P

r

e

s

s

u

r

e

(

P

a

)

Volume

Clearance

volumeSwept

volume

Patm(a)

(b)

(e)

(f)(g)

Air standard

modeling of 4

stroke Diesel cycle

with Q and W

Q (Heat is going in )

W (work is going out)

Q (Heat is going out )

Define what is air

standard Diesel cycleDiesel cycle

Air

Fig. p-V and T-s diagrams of a four stroke Diesel cycle engine

(a) (b)

Dual Cycle

Fig. p-V and T-s diagrams of a four stroke Dual cycle engine

Comparison Between 2 stroke and 4 stroke engines2 stroke 4 stroke

Number of

revolutions required

for one power stroke

1 2

Weight of engine for

same power

lighter heavier

Initial cost Lesser higher

Simplicity of More simpler Less simplerSimplicity of

mechanism and

construction

More simpler Less simpler

Ease of starting Easier to start Less easier to start

Over all Efficiency Lesser More

Operating

temperature

More less

Wear and tear More Less

Comparison Between 2 stroke and 4

stroke engines

2 stroke 4 stroke

Number of power

strokes in 2 cycles

2 1

Cooling requirement More Less

Consumption of More LessConsumption of

lubricant oil

More Less

Noise created by

exhaust gases

More Less

Simplicity of

mechanism

More simpler Less simpler

Space requirement Less more

Over all Efficiency Lesser More

Comparison Between petrol and diesel engines

Petrol Diesel

What is sucked in

during suction stroke

Air-petrol Mixture Air

Spark plug or fuel

injector

Spark plug Fuel Injector

Spark ignition or

compression ignition

Spark ignition Compression ignition

compression ignition

Thermal Efficiency Upto 25% Upto 40%

Running cost More Less

Motor cycles or truck Motor cycle Truck

Space Less More

Volatility More less

Weight Light Heavy

Carburetor Yes No

Classification of IC engines

Classification I.C. Engines (1)

According to:

1) Number

of cylinders

a) Single a) Single

cylinder

Engine

b) Multi-

cylinder

Engine


According to:

2) Method

of cooling

the cylinder

Hot sunny

Summer

b) the cylinder a) Air cooled

engine

b) Water

cooled

engine

a)

b)


According to:

3) Method

of Ignition

a) Spark a) Spark

Ignition

b) Compression

ignition


According to:

4) Type of

fuel used

a) Gasa) Gas

b) Petrol

c) Diesel


According to:

5) Number

of strokes

a) 2 Stroke a) 2 Stroke

b) 4 stroke

According to:

6) Cycle of

operation

a) Otto cycle


a) Otto cycle

b) Diesel cycle

c) Dual Cycle

According to the speed of the engine

a) Slow speed engines,

b) Medium speed engines, and

c) High speed engines.c) High speed engines.

Classification of I.C. Engines (contd..)

8. According to the method of fuel injection

a) Carburettor engines, and b) Air injection engines.

9. According to the arrangement of cylinders

a) Vertical engines, b) Horizontal engines, c) Radial engines,a) Vertical engines, b) Horizontal engines, c) Radial engines,

d) In-line multi-cylinder engines, e) V-type multi-cylinder

engines,

f) Opposite-cylinder engines, and g) Opposite-piston engines.

10. According to the valve mechanism

a) Overhead valve engines, and b) Side valve engines.

Heat EnginesA machine or device which derives heat from the combustion of fuel andconverts part of this energy into mechanical work is called a heat engine.

Heat engines may be classified into two main classes as follows:

1. External combustion engines

2. Internal combustion engines.

External Combustion Engines

In this case, combustion of fuel takes place outside the cylinderas in the case of steam engines where the heat of combustion isemployed to generate steam which is used to move a piston in acylinder. Other examples of external combustion engines arehot air engines, steam turbine and closed cycle gas turbine.

Dual Cycle

MPFI Multi point fuel injection systemMPFI Multi point fuel injection systemFuel injection is a system for admitting fuel into an internal

combustion engine. It has become the primary fuel delivery

system used in automotive engines, having replaced

carburetors during the 1980s and 1990s. A variety of

injection systems have existed since the earliest usage of the

internal combustion engine.

The primary difference between carburetors and fuelThe primary difference between carburetors and fuel

injection is that fuel injection atomizes the fuel by forcibly

pumping it through a small nozzle under high pressure, while

a carburetor relies on suction created by intake air

accelerated through a Venturi tube to draw the fuel into the

airstream.

Fuel injector is more precisely controlled than carburetor

hence is more efficient but is more expensive

Carburetor

Air and vaporized fuel mixture to the engine

Venturi

(accelerates air,

causing a pressure

drop, which pulls fuel

Connected to

throttle control

drop, which pulls fuel

through the nozzle)

Fuel Nozzle

Outside air enters here

Carburetor Fuel

Supply

Fuel Injector System

Fuel Flow Divider

Fuel Injectors:One Injector per cylinder

Fuel Pump

Air to Engine

Fuel Pump

Outside air enters here

Fuel / Air

Control Unit

engine sixth time

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