The document describes the four stroke cycle of a petrol engine: suction, compression, expansion, and exhaust. During suction, a fuel-air mixture is drawn into the cylinder when the piston moves down. In compression, the cylinder volume is compressed. In expansion, the fuel-air mixture is ignited by a spark plug in a petrol engine. During exhaust, the exhaust gases are expelled when the piston moves up. It then describes the same four strokes for a diesel engine, where fuel is injected and ignites spontaneously under high pressure during the expansion stroke.

1. Dr. V. Mathivanan
Associate Professor of
Physics
E.mail: mr.mathivanan@rediffmail.com

4.  Suction (charge exchange stroke)
When the piston moves down, fuel/air mixture is drawn
through the intake valve.
 Compression (power stroke)
The cylinder volume is compressed.
 Expansion (power stroke)
In the petrol engine, the fuel/air mixture is ignited by a
spark plug.
 Exhaust (charge exchange stroke)
The exhaust gas is expelled when the piston moves up.

6. Suction (charge exchange stroke)
When the piston moves down, air is drawn
through the intake valve.
Compression (power stroke)
The cylinder volume is compressed.
Expansion (power stroke)
In the diesel engine fuel is injected under high
pressure and the mixture ignites
spontaneously.
Exhaust (charge exchange stroke)
The exhaust gas is expelled when the piston
moves up.

8. Refregirator

9. Coefficient of performance
Coefficient of performance (COP) is defined
as the ratio of quantity of heat Q2 removed per
cycle from the contents of the refrigerator to
the energy spent per cycle W to remove this
heat.

12.  Freon liquid absorbs the heat energy from the food materials
 Due to absorption of heat, the liquid freon becomes low pressure
freon gas molecules
 The freon gas moleucules enters through the compressor and gets
compressed – becomes high pressure freon gas molecules
 The high pressure freon gas molecules loses their heat energy to the
coil to beocme freon liquid
 This a cyclic process which continues and to keep the things in the
refrigerator cool

13. How an air conditioner works

14. 1 Warm air from the room is sucked in through a grille at the
base of the machine
2 The air flows over some chiller pipes through which a
coolant fluid is circulating. This part of the machine works
just like the chiller cabinet in a refrigerator. It cools down
the incoming air and a dehumidifier removes any excess
moisture.
3 The air then flows over a heating element (similar to the
one in a fan heater). On a hot day, this part of the unit may
be turned right up so the HVAC works as a heater.
4 A fan at the top blasts the air back through another grille
into the room. If the heating element is turned down, the
air re-entering the room is much cooler, so the room
gradually cools down.

15. 5 Meanwhile, coolant (a volatile liquid that evaporates easily)
flows through the chiller pipes. As it does so, it picks up heat
from the air blowing past the pipes and evaporates, turning
from a cool liquid into a hotter gas. It carries this heat from
inside the room to the outside of the building, where it gives
up its heat to the outside air. How? Just like in a refrigerator,
the coolant flows through a compressor unit and some
condensing pipes, which turn it back into a cool liquid
ready to cycle round the loop again.What happens to the heat?
6 In the unit outside the building, there are lots of metal plates
that dissipate the heat to the atmosphere. An electric fan blows
air past them to accelerate the process.
7 Over time, the heat inside the building gradually pumps away
into the outside air.

16. Uses of air conditioners:
 Air Conditioning of Residential and Official Buildings
 Industrial Air Conditioning
 Spot Cooling
 Spot Heating
 Printing
 Textiles
 Precision Parts and Clean Rooms
 Photographic Products
 Computer Rooms
 Air Conditioning of Vehicles
 Food Storage and Distribution

17. NUMERICAL PROBLEM 1

19. NUMERICAL PROBLEM 2

20. 20