2. How Engine Use Fuel
Petrol and diesel engines requires fuel with
certain qualities. This is because of the
difference in the way the fuel is ignited in
each type.
3. Petrol Engine
Fuel and air mixed outside the cylinder, in the
carburetor and manifold
The mixture is forced in due to the partial
vacuum of the piston intake stroke
Uses electric spark to ignite the air fuel mixture
Function : The system supplies a combustible
mixture of fuel air to power the engine.
4. 3 basic parts
1) Fuel Tank – stores fuel for the engine
2) Fuel pump
Moves fuel from tank to carburetor
Is needed only with force feed supply system
When tank is above the engine, gravity moves fuel to
the carburetor
5. 3) Carburetor
Function :
– Atomizes fuel for the engine
– Provides proper fuel-air ratio
• Carburetor is basically an air tube which
operates by a change in air pressure
6. Operation of Carburetor
a) Fuel pump draws fuel through a line from the tank and
forces it to the float chamber of the carburetor
b) Filtered air flows in at one end and fuel air mixture is
drawn out at the other end
c) The pressure change is created when air flows through the
narrow neck or venturi. This lowers the air pressure beyond
the restriction
d) As low-pressure air rushes by the nozzle which projects
into the venturi, small drops of fuel are drawn out and
mixed with air
7. f) At the same time, the engines intake stroke creates a
partial vacuum which draws the air-fuel mixture into
the combustion chamber of cylinder
g) The fuel-air mixture passes the throttle valve which
opens or closes to let the right volume of fuel-air into
the engine. This is controlled as the operator sets the
engine speed
h) The choke valve also control the supply of fuel to the
engine. When starting the engine in cold weather, it can
be partly closed, forming a greater vacuum. This
vacuum causes more fuel and less air to be drawn into
the combustion chamber. The richer mixture burns
easier
8.
9. Importance of Service
Too rich mixture - Fuel consumption increased
- Cause carbon deposits to
accumulate in combustion
chamber
Too lean mixture - Reduces power
- Valve burning from extra hot
slow burning gases
Moisture in fuel cause rust and poor engine operation
10. Maintenance for Carburetor
Carburetor adjustment is part of the maintenance:
1. Always service the carburetor at these times:
a) After engine valve grinding or major
engine overhaul
b) Every year or at beginning of each season,
clean the carburetor, repack the shaft, check
the bearings and replace the seals & gaskets
11. 2. Always adjust the carburetor at the
following times:
a) During engine tune up
b) After major overhaul of the engine
c) Whenever the carburetor has been removed
for service
12. d) Anytime engines idle badly or requires speed
adjustment
e) Clean all parts thoroughly when repairing the
carburetor. Use a carburetor cleaning solution for
removing varnish-like deposits from all metal parts
and rinse them in solvent
f) Never use small wires or drills to clean out jets or
orifices
g) Never use a compressed air to clean a completely
assembled carburetor. This may cause the metal flat
to collapse
13. h)Always drain the carburetor before any long storage
period. Many carburetors have a drain plug in the fuel
bowl
i) Never turn adjusting needles too tightly against their
seats as damage may occurred
j) Be sure to tighten the screws which hold the throttle
disk in place. If loose, suction from the engine may
draw screws into combustion chamber
k) Always check the height of the float when assembling
the carburetor. See the technical manual for the correct
height. If the float is badly bent or warped, replace it
14. Diesel Fuel System
No premixing of air an fuel outside the cylinders
Air is drawn through the intake manifold and
compressed in the cylinders
Fuel is sprayed into the cylinder and mixed with air as
the piston nears the top of its compression stroke
Diesels use the heat of the compressed air for ignition
15.
16. Function
To inject a precise amount of atomized and
pressurized fuel into each engine cylinder
at a proper time
combustion occurs when this charge of fuel
is mixed with hot compressed air
No electrical spark is used
17. 5 Basic Parts
1) Fuel tank - store fuel
2) Fuel transfer pump
- pushes fuel through filters to injection pump
3) Fuel filters - clean the fuel
4) Injection pump
- times, measures and delivers fuel under pressure to cylinders
5) Injection nozzles
- atomize and spray fuel into cylinders
18. Operation
a) Fuel flows by gravity pressure from fuel
tank to fuel pump
b) Fuel pump pushes fuel through the filters,
where it is cleaned
c) Fuel is then pushed on to the injection pump
where it is put under high pressure and
delivered to each injection nozzle as the
exact time needed
19. d) The injection nozzles atomized the fuel and spray it
into the combustion chamber of each cylinder
Most diesel fuel system have a fuel return line which
returns excess fuel from the injection pump to fuel tank
e) Filters varies from one filter to 3 filters. If one filter, it
must be service regularly and carefully because there
are no other filters to help clean the fuel
f) Additional filters such as second stage and third stage
filters are often used to assure that water and dirt
particles will be removed from fuel.
20. Importance of Service
The injection pumps and nozzles are precision parts which can be
damaged by dirt particles or other contaminants
Dirt will caused wear and poor fuel delivery to injection pump
Dirt will also caused clog injector and make them inoperable
Water will rust the precision parts
Good maintenance will removed dirt and moisture from the
injection pump or the injectors
