WELL-DEFINED DESCRIPTION OF 4 STROKE ENGINE WITH DIAGRAMS

1. FOUR STROKE ENGINE
AN IDEALIZED THERMODYNAMIC CYCLE

2.  ENGINE
INTRODUCTION TO ENGINES
 FUEL/PETROL ENGINE
 TWO STROKE ENGINE
 FOUR STROKE ENGINE

3. FOUR STROKE ENGINE
 A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in
which the piston completes four separate strokes while turning the crankshaft. A
stroke refers to the full travel of the piston along the cylinder, in either direction.
 It uses two types of valves.
 Inlet Valve
 Exhaust Valve
 Four stroke petrol engine works at the four types of stroke.
 Intake stroke
 Compression stroke
 Power stroke or expansion stroke
 Exhaust stroke

4. OTTO CYCLE
 In 1862 a German engineer Nikolaus Augustus Otto
began experimenting with different kinds of
engines.
 His first experiment was conducted on a 4-stroke
engine. 10 years later he introduced to the world
the Otto engine.
 The 4-stroke engine consists of a 4-stroke cycle
better known as the Otto cycle.

5. OTTO CYCLE PROCESS
 Each movement of the cylinder up or down the cylinders
one stroke of the four stroke combustion cycle or Otto
cycle.
 The four stroke cycle consists of
 induction stroke
 compression stroke
 ignition/power stroke
 exhaust stroke
 A single cycle requires two revolutions of the crankshaft
to complete.
Four Stroke Engine
Working

6. INTAKE OR SUCTION STROKE
 Intake valve opens.
 Piston moves down, ½ turn of crankshaft.
 Avacuum is created in the cylinder.
 Atmospheric pressure pushes the air/fuel
mixture into the cylinder.

7. COMPRESSION STROKE
 Valves close.
 Piston moves up, ½ turn of crankshaft.
 Air/fuel mixture is compressed.
 Fuel starts to vaporize and heat
begins to build.

8. POWER STROKE
 Valves remain closed.
 Spark plug fires igniting fuel mixture.
 Piston moves down, ½ turn of crankshaft.
 Heat is converted to mechanical energy.

9. EXHAUST STROKE
 Exhaust valve opens.
 Piston move up, crankshaft
makes ½ turn.
 Exhaust gases are pushed out
polluting the atmosphere.

10. FOUR STROKE ENGINE ANIMATION

11. FOUR STROKE DIESEL ENGINE

12. THERMODYNAMIC PROCESS ANALYSIS

13. PROCESSES
 Process 0–1 a mass of air is drawn into piston/cylinder arrangement at constant pressure.
 Process 1–2 is an adiabatic (isentropic) compression of the charge as the piston moves from
bottom dead center to top dead center.
 Process 2–3 is a constant-volume heat transfer to the working gas from an external source while the
piston is at top dead center. This process is intended to represent the ignition of the fuel-air mixture
and the subsequent rapid burning.
 Process 3–4 is an adiabatic (isentropic) expansion (power stroke).
 Process 4–1 completes the cycle by a constant-volume process in which heat is rejected from the air
while the piston is at bottom dead center.
 Process 1–0 the mass of air is released to the atmosphere in a constant pressure process

14. ADVANTAGES
 Less fuel consumption.
 Thermal efficiency is more.
 More volumetric efficiency.
 Less wear and tear.

15. DISADVANTAGES
 More components.
 Separate valve mechanism is required.
 More cost.
 More complicated design.

16. APPLICATIONS
The four stroke petrol engines are the most commonly used engines in today’s
automobile sector and vehicles, both in cases of single cylinder and multi
cylinder applications.
Four stroke petrol engine commonly used in
petrol cars
motorbikes
scooters
small propeller aircrafts
formula one
small motor powered boats
auto-rickshaw
water spray systems

17. 2018-ME-407 • SAAD
2018-ME-416 • MUNEEB-UR-REHMAN
DEPARTMENT OF MECHANICAL ENGINEERING
RACHNA COLLEGE OF ENGINEERING AND TECHNOLOGY, GUJRANWALA
A COSTITUENT COLLEGE OF UET, LAHORE
THANK YOU 