SIMPLE AND AUTOMOBILE CARBURETOR

140050119028Kanani Manthan

Faculty,Subhasis Sarkar

CONTENTS Simple Carburators Automobile Carburators

Simple Carburetor

A simple carburetor as described suffers from the fact that it provides the required air-fuel ratio only at one throttle position.

At all other throttle positions, the mixture is either leaner or richer depending on whether the throttle is opened less or more.

A simple carburetor is capable to supply a correct air-fuel mixture to the engine only at a particular load and speed.

In order to meet the engine demand at various operating conditions, the following additional systems are added to the simple carburetor.

idling system auxiliary port system power enrichment by economizer system accelerating pump system choke

Complete Carburetor

Idling System

During starting or idling, engine runs without load.

The throttle valve remains in closed position.

Engine produces power only to overcome friction between the parts.

A rich mixture is to be fed to the engine to sustain combustion.

IDEAL SYSTEM

(1) A single jet carburetor can not provide a very rich mixture as required at the time of starting the engine

(2) It can not provide very rich mixture required for sudden acceleration of the engine.

(3) For gradually increasing pressure differences over the jet (at higher speed of the engine), the weight of the petrol discharged from a single jet increases at a greater rate than does the air supply. Hence, a single jet carburetor gives a progressively richer mixture as the air speed increases when set to give a correct mixture at low air speeds.

(4) It can not reduce the quantity of air flow during starting as required in cold weather conditions.

(5) The automation control of air and fuel according to the required conditions is not possible.

LIMITATIONS OF SIMPLE CARBURETTOR

In the SI engine a combustible fuel-air mixture is prepared outside the engine cylinder. The process of preparing this mixture is called carburetion.

The carburetor, a device which atomises the fuel and mixes it with air. The pipe that carries the prepared mixture to the engine cylinders is called the intake manifold.

AUTOMOBILE CARBURATORS

AUTOMOBILE CARBURATORSA carburetor’s

primary purpose is to produce a mixture of air and fuel for different engine operating conditions.

StoreDeliverFilterMix air and fuelControl air and fuel mixture

PURPOSE OF CARBURETION

CARBURATION AIR FUEL REQUIREMENT

Ratio of air to fuel.

Example 14.7 lbs of air to 1 lb of fuel

Fuel ratiosRich / lean

ColdLow speedMid speed AccelerationHigh speed

CARBURETOR OPERATING CONDITIONS

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