How Engine Use FuelPetrol 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 thecarburetor and manifoldThe mixture is forced in due to the partialvacuum of the piston intake strokeUses electric spark to ignite the air fuel mixtureFunction : The system supplies a combustiblemixture of fuel air to power the engine.
3 basic parts1) Fuel Tank – stores fuel for the engine2) 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) CarburetorFunction : – 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 carburetorb) Filtered air flows in at one end and fuel air mixture is drawn out at the other endc) The pressure change is created when air flows through the narrow neck or venturi. This lowers the air pressure beyond the restrictiond) 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 cylinderg) 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 speedh) 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 chamberToo lean mixture - Reduces power - Valve burning from extra hot slow burning gasesMoisture 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 adjustmente) 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 solventf) Never use small wires or drills to clean out jets or orificesg) 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 bowli) Never turn adjusting needles too tightly against their seats as damage may occurredj) Be sure to tighten the screws which hold the throttle disk in place. If loose, suction from the engine may draw screws into combustion chamberk) 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 cylindersAir is drawn through the intake manifold andcompressed in the cylindersFuel is sprayed into the cylinder and mixed with air asthe piston nears the top of its compression strokeDiesels use the heat of the compressed air for ignition
FunctionTo inject a precise amount of atomized andpressurized fuel into each engine cylinderat a proper timecombustion occurs when this charge of fuelis mixed with hot compressed airNo electrical spark is used
5 Basic Parts1) Fuel tank - store fuel2) Fuel transfer pump- pushes fuel through filters to injection pump3) Fuel filters - clean the fuel4) Injection pump- times, measures and delivers fuel under pressure to cylinders5) Injection nozzles- atomize and spray fuel into cylinders
Operationa) Fuel flows by gravity pressure from fuel tank to fuel pumpb) Fuel pump pushes fuel through the filters, where it is cleanedc) 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 tanke) 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 fuelf) 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 bedamaged by dirt particles or other contaminantsDirt will caused wear and poor fuel delivery to injection pumpDirt will also caused clog injector and make them inoperableWater will rust the precision partsGood maintenance will removed dirt and moisture from theinjection pump or the injectors
MaintenanceParts that easily serviceable are I. Fuel filters II. Fuel sediment bowl III. Fuel tanks