When engines are run for automotive purpose,a simple carburettor can't supply the correct air-fuel mixture for all conditions of speeds and loads at which engine required to run.To correct mixture strength according to demand of engine,some compensation methods are used in carburettor for providing additional fuel or reducing the fuel.
Following are the compensation methods adopted in simple carburettor.
01)Extra Air Valve Compensation:-
As throttle valve is opened more and more,an extra air valve,which is mounted on carburettor,opens against the force of a spring and supplies extra air to mixture.Thus throughout the economy range,the strength of mixture kept reasonably constant.
02)Restricted Air Bleed Compensation:-
A jet tube,which has opening at its periphery,is provided with carburettor in this type of compensation.A restricted air bleed opening connects main air passage to the outer enclosure of the jet tube.At starting time and at slow speed of engine,there is small pressure due to the effect of viscosity and surface tension of the fuel,the more quantity fuel flows into the venturi gives a rich mixture when throttle valve opens more at high speed.The effect of viscosity considerably diminishes and there is a higher pressure drop in the venturi due to which more fuel is to be drawn and sprayed by the nozzle but at this stage the air bubbles starts bleeding through the jet tube opening,making a lean mixture.
03)Compensating Jet Compensation:-
This method consists of main jet and compensating jet.The main jet is directly connected to the float chamber while compensating jet is connected to the float chamber through a tube,which top end is open to atmosphere.Both the jet supply fuel in venturi when throttle valve is slightly opened .As the throttle valve is gradually opened the fuel supply from the main jet increases but that from compensating jet decreases due to falling level of fuel in the tube,as atmospheric pressure acts on the tube.Some air is drawn in,through this tube,thus the richness of the mixture decreases.This method is also called as "Unrestricted air bleed compensation".
04)Economiser Needle In Metering Jet:-
The flow of fuel is restricted by changing the area of the metering nozzle supplying the fuel from the float chamber to the main jet.The area is changed by means of a needle operated with linkage from accelerator pedal.
Day by day,technology is changing and modifications are done frequently for proper functioning of the device,there by increasing the overall results of the automobile engines.
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