3. FOUR STROKE, TWO STROKE,
DIESEL,PRESENTATION OUTLINE
1.0 Four Stroke Engine Theory
• Internal combustion principles
• Valve operation
• Four cycles
• Variation
2.0 Two Stroke Engine Theory
• Two cycle operation
• Lubrication
• Variations
• Advantages/ limitations
12. FUEL MIX:-
• Uses a premix of gas and oil
• Oil injectors used in some
• Normal mixes range from 16:1 to 50:1
• Typical “hot” engines 16:1
• Typical “cool engine” 50:1
• CHECK OWNERS MANUAL !!!
13. ADVANTAGE OF TWO STROKES:-
• Runs in any position
• More horsepower for size
• Fewer moving parts
• Lighter
14. LIMITATIONS OF TWO STROKES:-
• Uses more fuel than four strokes
• Fuel and oil must be mixed
• Plugs foul easily
• Poor emissions
18. •This is a simplified model of a single cylinder Diesel
engine to show the principal parts, their relationships
to each other and how the engine works.
•Is not based on any real engine, but is generally
representative of real engines. Most real engines are
made up of several of this unit sharing a single
flywheel and cam shaft drive e.g. Three, four and six
cylinder engines.
•Many minor details and some components are left
out for clarity, for example the bearings, exhaust
pipe silencer, air intake filter and the fuel injection
pump.
FOUR STROKE DIESEL ENGINE:-
19. Cam Shaft Drive.The cam-shaft drive arrangement is simplyrepresented by a box. In
realitythere wouldbe a chaindrive or a gear trainbetween the crank-shaft andthe cam-
shafts.
Inside the solid body of
the Engine are a number of
fast moving parts
Moving parts
20. The Names of the Main Moving parts:-
Piston
Connecting
Rod
Gudgeon
Pin
Crank-Shaft
Cam-
Shafts
Valves
Fly-
Wheel
Piston
Ring
Valve Spring
Bolts and
fixings omitted
for clarity
21. Some stationary parts:-
Engine block
Cylinder
Head
Fuel
InjectorCylinder
Head Cover
Timing
Case
Sump
(holds lubricating oil)
Bolts and fixings
are omitted for
clarity
22. The Piston Rings fit
in grooves on the
Piston. They seal
the Piston to be
‘gas tight’ in the
Cylinder of the
Block
Cylinder, a
large round
hole bored
straight and
parallel
through the
Block
Block, a large strong
lump of metal that is
the main structural
member of the
engine
Piston, a cylindrical part made
to be a close, but free running,
fit in the Cylinder of the Block.
Cylinder Head, Cylinder and Piston:-
The Cylinder Head sits on the top of
the Block to close off the top of the
Cylinder. It also carries the Valves,
Fuel Injector and the Inlet and Exhaust
passages
Bolts and fixings
are omitted for
23. • The Connecting Rod is inserted into a large recess in
the bottom of the Piston
•The Piston is attached to swivel on the ‘little end’ of
the Connecting Rod by the Gudgeon Pin through the
side of the Piston.
•The ‘Big end’ of Connecting Rod fits onto the ‘throw’
of the Crank Shaft. (this end is usually split in half and
bolted together for assembly purposes)
•The Connecting Rod connects the linear ‘up and
down’ motion of the Piston within the Cylinder with
the circular rotary motion of the Crank Shaft.
•The Fly-Wheel is attached to the end of the Crank-
Shaft and serves to store the pulses of energy from the
Power Strokes, delivering energy to the other 3 strokes,
and power to whatever the engine is driving.
Piston
Gudgeon pin
Crank Shaft
Connecting
Rod
‘Little End’
‘Big End’
‘Throw’
PISTON, CRANK SHAFT & FLY-WHEEL:-
Fly-
Wheel
24. One set of a Cam and a Valve controls the Inlet flow of fresh air into the Cylinder.
The other set controls the burnt Exhaust Gases out of the Cylinder. Both these
Valves are spring loaded to shut and seal the Cylinder during the Compression
and Power strokes. They open into the Cylinder, so that they are held closed by
the high pressures during the Compression and Power strokes.
Spring
Inlet
Passage
Exhaust
Passage
Inlet Cam
& Valve
Exhaust
Cam & Valve
VALVES:-
Bump, or lobe, on the Cam pushes the Valve
open during part of the rotation of the Cam
25. •The Diesel Engine 4 Stroke cycle consists of four
distinct stages carried out whilst the engine Crank
Shaft does two complete turns (or as we say, two
revolutions).
•The Cams rotate once every two turns of the Crank
Shaft, i.e. once per complete 4 stroke cycle.
•A ‘stroke’ is a movement of the Piston from one end
of the Cylinder to the other end.
The four Stroke combustion cycle:-
26. 1st Stroke – INDUCTION:- Fresh air is drawn into
the Cylinder through the open Inlet Valve by the
Piston descending. The Inlet Valve closes when the
Piston reaches bottom of Cylinder, trapping the fresh
air in the Cylinder.
2nd Stroke – COMPRESSION:- The Air is squeezed
as the Piston rises, reaching about 40 bar pressure.
The air gets very hot (about 700° C) because of the
work done to it by the Piston. Diesel fuel is started to
be Injected into the Cylinder as the Piston gets near
to the top.
27. 3rd Stroke - POWER. Fuel is injected into the Cylinder
for a short while as the Piston is near the top. The fuel
spray ignites and burns in the hot air, creating even
higher pressures and temperatures in the cylinder. The
pressure of the hot gases push the Piston down,
delivering power to the crank-shaft and fly wheel.
4th Stroke - EXHAUST. The Exhaust Valve opens and the
rising Piston pushes the burnt gases out of the Cylinder.
When the Piston gets near the top the Exhaust Valve
closes and the Inlet Valve opens, ready to draw fresh air
in again.
28. COMPRESSION RATIOS
• “Squeeze” on air/fuel mixture before combustion
• Efficiency increases with higher CR
• About 9:1 on gas autos
• 17:1 to 24:1 for diesel engines
• About 24:1 CR max:
• too high compression for starting
• limiting strength of materials
• power loss- leakage around valves
29. ADVANTAGES OF THE DIESEL ENGINE
• High reliability
• Low fuel cost
• High power / lb. of engine
• Low fuel consumption
• Low fire hazard
• High torque at low RPM
• Greater heat efficiency- 30% (25% gas)
• Longer service intervals
30. DISADVANTAGES OF DIESEL POWER
• Expensive to repair
• Hard starting in cold weather
• Higher initial cost
