fuel-supply-systems-part-1.pptx

I.C Engine
Mechanical Engineering Department http://hjdmech.weebly.com Prepaired By: Prof. Kunalsinh Kathia
Topic: Fuel supply systems
Part-1
By: Prof.Kunalsinh Kathia
Fuel Supply Systems (Part-1) I.C Engine

Essential parts of carburetor
• Fuel strainer
• Float chamber
• Metering and idiling system
• Choke and throttle

Fuel Supply Systems (Part-1)
I.C Engine

Fuel strainer
• As gasoline has to pass through narrow nozzle exit there is every possibility that the
nozzle may get clogged during prolonged operation of the engine.
• To prevent possible blockage of the nozzle by dust particles, the gasoline is filterd by
installing fuel strainer.
• The strainer contains fine wire mesh
• Its of cone shaped or cylindrical shaped.
• Its usually removable for cleaning purpose.
• It is retained in its seat by strainer plug or a compression spring.

The float chamber
• The supply of the fuel to the nozzle at a constant pressure head.
• This is possible by maintaining a constant level of fuel in the float bowl..
• Its designed to control the fuel level in float chamber.
• This fuel level must be maintained slightly below the discharge nozzle outlet holes in
order to provide the correct amount of fuel flow.
• As float rises with fuel incoming, the supply valve closes.

The main metering and Idling System
• This system control carburetor fuel flow during crusing and full throttle
operations.
• It consist of three principal units.
• i) the fuel metering orifice through which fuel is drawn from float chamber.
• ii) the main discharge nozzle
• iii) the passage leading to the idling system.

The choke and throttle
• When vehicle is kept at stationary for long period during cool winter seasons, may
overnights, starting becomes more difficult.
• At very low cranking speed and intake temperatures a very rich as 9:1 mixture is
required.
• Main reason is very larg fraction of fuel remains in cylinder.
• It may be noted that at very low temperature vapour fraction of fuel is alsovery
small and this forms combustible mixture to initiate combustion.
• The most popular method to provide this mixture is choke.
• Choke valve partially opend causes large depression at throat and large depression
causes large amount of fuel from nozzle.

Additional systems in Modern carburetors

Additional systems in Modern carburetors
• Anti-dieseling system
• RicherCoastingSystem
• Acceleration Pump system
• Economizer or Power Enrichment system

Anti dieseling system
• SI engine somtime continuous runs even after ignition stopped.This causes
misfire condition.
• This phenomena called Dieseling (after running or run on.)
• How they are solving this?
• Ans:A solenoid valve.

Richer Coasting System
• In modern cars when car is running at maximum acceleration and
accelerator pedal is suddenly released.
• The wheel will run engine at higher rpm, but Consequently the vaccum at
inlet and outlet chamber increases too much and this causes incomplete
combustion.
• How they solve this?
• By addingChamber at inlet valve (RicherCoastingSystem)

Acceleration Pump system
• In order to accelerate the vehicle quickly here mixture required is rich.
• This richness depends upon the vacuum created in throttle.
• In order to increase mixture richness the fuel has to be obtained very quickly.
• This everything has to be done very rapidly and quickly.
• If throttle is sudden opend ,it increases the air flow. But due to inertia of gasoline
fluid it comes out in certain amount only from fuel chamber.this causes lean
mixture and engine to misfire.
• How they solved this?
• Ans:Acceleration pump system.

Economizer or power Enrichment system
• At the maximum power range of 80% to 90% load, the air fuel ratio has to be
about 12:1 to 14:1.
• But air fuel ration 12:1 is expected always during maximum power.
• How they do this?
• Ans:Using economizer valve.

Types of Carburetors

Types of Carburetors
• There are mainly three types of carburators
• Up Draught
• Down Draught
• Cross Draught

Constant choke carburetor
• Air and fuel flow area are always maintained constant.
• But the depression or difference which causes the flow of fuel and air to be
maintained as per demand.
• The solex andZenith carburetors belong to these class.

Constant vacuum carburetor
• Its called variable choke carburetor.
• Air and fuel flow areas are varied as per demand, vacuum is constant always
same.
• The S.U andCarter carburetors belong to this class.

Multiple venture carburator
• The boost venture is located concentrically within the main venture.
• The discharge edge of the boost venture is located at the throat of the main venture.
• Only fraction of air passes through boost venture.
• This result following:
• High depression is created at the region of nozzle.
• At boost venture throat velocity of air is as high as 200 m/s
• Excellent low speed full throttle operation is possible.
• More efficient mixing of the air and fuel is obtained without incurring an avveptable
reduction in volumetric efficiency.

Multijet Carburetors
• A single barrel carburetor has only one barrel, whereas a dual carburetor has
two barrels.
• Each of these two barrels has different fuel jet,choke,throttle,ideling system
etc.
• Passenger cars with six or more cylinders are provided with dual carburators.
• Each venture supplies the air-fuel mixture to half of cylinders.

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