essential parts of carburetor - the most popular method to provide this mixture is choke....

I.C EngineTopic: Fuel supply systems

Part-1By: Prof.Kunalsinh Kathia

Fuel Supply Systems (Part-2) I.C Engine

Mechanical Engineering Department http://hjdmech.weebly.com Prepaired By: Prof. Kunalsinh Kathia

Essential parts of carburetor

• Fuel strainer

• Float chamber

• Metering and idiling system

• Choke and throttle



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 alsoverysmall 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

• Richer Coasting System

• 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 adding Chamber at inlet valve (Richer Coasting System)



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 and Zenith 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 and Carter 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 avveptablereduction 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.



Different modern carburators

• There are mainly two type of carburators

• Open choke

• Vacuum type.

• S.V carburetor are constant venture type.

• Zenith, solex,carter and Stromberg carburetors are constant venture type.



Types of different modern carburators

• Zenith Carburetor

• Solex Carburetor

• Carter Carburator



Zenith Carburator

• This is the oldest type of carburator.

• It was used in all automobile engines before 25 years.

• It consist of all components which basic carburator have.

• A. Starting jet

• B. Main Jet

• C. Compensating Jet

• D. Float chamber

• E. Choke and throttle valve.



2. Solex Carburator

• This is most comman type of carburator used in Fiat and Standard cars.

• It is famous for good and easy starting

• Performance and reliability.

• Its also runs on starting jet for starting purpose.

• In addition it contains starting jet, compensating jet and accelerating jet.

• How solex carburator works lets see in details.



Solex carburator (working procedure)

• Here are 5 basic actions which acts behind solex carburator to run.

• Starting

• Compensating jet

• Main Jet

• Idling Jet

• Accelerating Jet




• Starting:

• It has provision for bi starter.

• Starter valve is a disk in the foam of a different size

• Its connected with petrol jet.

• The starting air also supplied as shown in figure

• The quantity of the fuel supplied is depends upen hole size connected to the disk.

• As disk is connected by pedal or a flexible cable provided in the dash board.

• At starting the bigger holes are used for rich mixture and as engine speed increases, the smaller holes starts providing fuel.

• As engine gains speed the starting lever is brought to off Position.




• Compensating Jet:

• A double well type compensating jet is provided to maintain proper air fuel ratio.

• It is not shown in figure.




• Main Jet:

• Another addition of this carburetor in addition to buster venture.

• The fuel from main jet is supplied into buster venture.

• Here the entering air mixes up with small droplets of fuel at high speed (Supersonic speed)

• At this speed of air divides fuel into fine particles and this mixture enters into main venture.

• In main venture again mixture speed increases .

• This helps better vaporization of fuel.

• With arrangement of main venture and buster venture its assured that air fuel entering into engine is fine and vaporized well.



Solex carburator (working procedure)• Idling Jet:

• As we know a Rich mixture is required for idling jet, there is idling jet separately provided.

• A fuel connection from the main line leading to main jet is taken and opend to down side of the throttle valve through air screw .

• The rich mixture is provided down to the throttle valve.

• The volume control screw controls fuel flow.

• To ensure the smooth transfer from idle circuit to main jet circuit without occurrence of flat spot, a bypass orifice towards venture side near the idle jet is provided. As the throttle is wide open, the suction near idle jet decreases but suction is applied at bypass orifice which affects loss of the suction at the idle port.




• Accelerating Jet:

• A separate accelerating jet is provided .

• Whenever is accelerating pedal is pressed , an extra fuel is provided through accelerating jet.

• This provides rich mixture and brings engine into the power mode.

• As pedal is released , it taken up by spring provided into the pedal in accelerating well.

• This causes vacuum into accelerating chamber and fills up petrol again from main chamber.



essential parts of carburetor - the most popular method to provide this mixture is choke....

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