Carburador – Diagrama, funcionamento, peças, tipos

Carburetor – Diagram, operation, parts, types

Carburization:
The process of preparing a fuel-air mixture outside the engine cylinder in the SI engine is known as carburization.

Important factors that affect the carburization process are presented below;
-time available for preparation of the mixture, i.e. atomization, mixing and vaporization
-Temperature of the incoming air
-quality of fuel supply
-design of the combustion chamber and induction system

-provide air-fuel mixture for all operating conditions
– Carburetor depression is the pressure differential in the float chamber and engine throat, which causes fuel to discharge into the air stream
-flow is controlled by small fuel passage hole
– throat pressure at wide open throttle condition is between 4 and 5 cm Hg and rarely exceeds 8 cm Hg
-gasoline engine is regulated by quantity
-The disadvantage of the simple carburetor is that it provides a very rich and very lean mixture due to the vacuum created in the throat being very high and very small, which is undesirable

simple carburetor simple carburetor

Complete carburetor:

Additional systems used with simple carburetor can help the engine to operate in all conditions, which are given below,

(i) Main measurement system:
-provide constant fuel-air ratio over wide range of speeds and loads.
-based mainly on best economy at full throttle (A/F ratio of about 15.6:1)

The different measurement systems are,

Compensation jet device: –

In addition to the main jet, a compensating jet is provided to provide the lean effect

Emulsion tube or air bleed device:
– the mixture is corrected only by bleeding air
– in this arrangement the main measuring jet is installed about 25 mm below the gasoline level, which is called a submerged jet

Back suction control or pressure reduction method:
– in this arrangement, a large vent line connects the carburetor inlet to the top of the float chamber and another small orifice line is connected to the top of the float chambers with the throat of the venture
-creates pressure differences according to engine operating conditions

Carburetor auxiliary valve :
-The auxiliary valve spring lifts the valve during increased engine load, which increases the vacuum in the venture
-Allows more additional air intake and the mixture is not too rich

Auxiliary Port Carburetor:
-the butterfly opening allows more air inductance, which reduces the amount of fuel consumed
-used in aircraft carburetors

(ii) Idle system:
-Idle jet is added for idling and low load operation, which requires a rich mixture with 12:1 A/F ratio
-consists of a small fuel line from the float chamber to a point on the throttle side
-gradual opening of the throttle can stop the jet at idle

(iii) Enrichment or energy saving system:
-This system provides the richest mixture for maximum operating power range
-Has large orifice metering rod economizer that opens into the main jet as the throttle is opened beyond a certain point
-the shank is tapered or stepped

(iv) Acceleration pump system:
-Engine acceleration condition or rapid increase in engine speed may open the throttle quickly, which will not be able to provide a rich mixture
– spring-loaded plunger acceleration pump is used for fuel supply.

(v) Suffocation:
-Rich mixture is required during the cold starting period, at low starting speed and before the engine is warmed up
-butterfly or choke valve is used between carburetor inlet and venture throat to meet the requirement
– Spring-loaded bypass choke is used at higher speeds

Carburetor types:

(i) Open choke: Zenith, solex and carter
Constant vacuum type: SU carburetor
(ii) type of updraft
Horizontal or descending: the mixture is assisted by gravity in its passage to the engine induction

(a) Solex Carburetor:
-provide ease of starting, good performance and reliability
-Used in Fiat and standard cars and Willey jeep
-Bi-starter is used for cold starting
– the emulsion system well is used for idle and idle conditions
-diaphragm type acceleration pump is used to increase speed

(b) Crankcase carburetor:
– downdraft carburetor used in jeeps
-has a triple diffuser type choke, in which the smallest is above the level fluctuation chamber, the other two are below the gasoline level, one below the other.
– multiple venturis result in better mixture formation at very low speeds, causing stable and smooth operation at very low and high engine speeds
-mechanical measurement method is used
-throttle valve is provided in the air circuit for cold starting
-plunger type acceleration pump is used

(c) SU Carburetor:
-constant air-fuel ratio is maintained due to vacuum depression
-has only one jet
-without separate idle jet or accelerator pump
-Constant high speed air through the jet can avoid using the jet at idle
-Jet lever arrangement provides rich mixture on cold start
-used in many British cars and the Hindustan ambassador's car

Disadvantages of the modern carburetor:
– inadequate mixture ratio in multi-cylinder engine
-Loss of volumetric efficiency due to obstruction of the mixing flow of the choke tubes, jets, butterfly valve, etc.
-wear of carburetor parts
– Low temperature freezing
-surge when the carburetor is tilted or during aircraft aerobatics
-explosion in the fuel line

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