FUEL SYSTEM

How Engine Use Fuel

Petrol and diesel engines requires fuel withcertain qualities. This is because of thedifference in the way the fuel is ignited ineach type.

Petrol EngineFuel 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.

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

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

Operation of Carburetora) 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

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

Importance of ServiceToo 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

Maintenance for CarburetorCarburetor 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

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

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

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

Diesel Fuel SystemNo 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

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

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

Operationa) 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

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.

Importance of ServiceThe 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

Maintenance

Parts that easily serviceable are I. Fuel filtersII. Fuel sediment bowlIII. Fuel tanks

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