carburetor and types based on design

CARBURETOR AND TYPES BASED ON DESIGN OF CARBURETOR :

CONTENTS :

1.1 DEFINITION
1.2 FUNCTIONS OF CARBURETION SYSTEM 

1.3 HISTORY OF CARBURETOR

      1.3.1 SURFACE CARBURETOR

      1.3.2 SPRAY CARBURETOR

1.4 WHAT DOES CABURETOR MEAN ?
1.5 COMPONENTS OF A CARBURETOR
1.6 HOW DOES A CARBURETOR WORKS
1.7 BASIC PRINCIPLES OF CARBURETOR OPERATION
1.8 CARBURETOR FAILURE
       1.8.1 CARBURETOR REBULIDING

1.1 DEFINITION :

          A carburetor is a mechanical device that mixes air and fuel for internal combustion engines in the proper ratio for combustion.The carburetor has two swiveling valves above and below the venturi.At the top there is a valve called the choke that regulates how much air can flow in.If the choke is closed,less air flows down through the pipe and the venturi  sucks in more fuel,so the engine gets a fuel-rich mixture.

Figure : basic carburetor

1.2 FUNCTIONS OF CARBURETION SYSTEM :

          The carburetion system are used to mix the fuel with the proper proportion of air,to vaporize the fuel and to deliver the correct amount of the air-fuel mixture to the cylinder combustion chamber.A  carburetor may be defined as device for automatically mixing fuel in the proper proportion with air to produce a combustible gas mixture.

The idle air to fuel mixture is 16:1 by weight.

A rich mixture might approach 17:1 and a lean mixture of 11.5:1

Additionally engine parts are closely allied to the carburetor include the fuel tank,fuel lines ,air cleaner,choke, speed control devices(governors).since these parts and their functions are closely allied to the carburetor.

1.3 HISTORY OF CARBURETOR :

          Early carburetors achieved this by simply allowing air to pass over the surface of the fuel (i.e. gasoline), but most later dispensed a metered amount of fuel into the air stream.

          Carburetion was the dominant method of mixing fuel and air for internal combustion engines until the 1980s, when emissions regulations and concerns about fuel efficiency resulted in fuel injection taking over. Although carbs were used in the United States, Europe, and other developed nations through the middle of the 1990s, they made use of increasingly complex control systems to meet emissions requirements.

          Different types of carburetors were developed by a number of automotive pioneers, including German engineer Karl Benz, Austrian inventor Siegfried Marcus, English polymath Frederick W. Lanchester, and others. Since so many different methods of mixing air and fuel were used in the early days of the automobile, and earlier, stationary gasoline engines also used carburetors, it’s somewhat difficult to pinpoint who “invented” the device. These early carbs also differed in their basic method of operation from the “modern” carbs that were dominant throughout much of the 20th century.

        Historic carb designs can be broken into two main types with an endless cavalcade of variations:

v  surface carburetor

v  spray carburetor

1.3.1 SURFACE CARBURETOR :

          All early carburetor designs were “surface” carbs, although there was a lot of variety in this category. For instance, Siegfried Marcus debuted something called a “rotating brush carburetor” in 1888, and Frederick Lanchester unveiled his wick-type carburetor in 1897. The former used rotating brushes to expose gasoline to air from the intake, and the latter relied on one or more wicks to suck up gasoline.

                   The first carburetor to use a float was developed in 1885 by Wilhelm Maybach and Gottlieb Daimler, and Karl Benz also patented a float-style carb around the same time. However, these early designs were “surface carburetors” that relied on passing air over the surface of the fuel in order to mix the two.

          Most surface carbs relied on simple evaporation, but others forced the issue. These were known as bubbling or filtering carburetors, and they operated by forcing up through the bottom of a volume of fuel. This resulted in a mixture of air and fuel above the main volume of fuel, which was then sucked into the intake.

1.3.2 SPRAY CARBURETORS :

          Although various surface carburetors were dominant during the very early days of the automobile, spray carbs started to take over right around the turn of the 20th century. Rather than relying on evaporation, these carburetors actually sprayed a metered amount of fuel into the air, where it was sucked into the intake. These carburetors used a float like Maybach and Benz’s earlier designs, but they operated based on the Bernoulli principle and also relied on the Venturi effect, just like modern designs.

          One notable subtype of the “spray carburetor” is the so-called “pressure carburetor,” which first appeared in the 1940s. Although pressure carbs resemble spray carbs superficially, they were actually early examples of fuel injection. Rather than relying on the Venturi effect to suck fuel out of a bowl, pressure carbs sprayed pressurized fuel out of valves in a manner that was very similar to a modern fuel injector.

Carburators became increasingly complex during the 1980s and 1990s

1.4What Does Carburetor Mean?

               Carburetor is an English word that is derived from the term “carbure,” which is French for “carbide.” In French, “carburer” simply means “(to) combine (something) with carbon.” Similarly, the English word “carburetor” technically means “(to) increase the carbon content (specifically of a fluid.)

Since air is a fluid, and gasoline is a hydrocarbon, a carburator is literally a device that adds gasoline (a hydrocarbon) to air (a fluid.)

1.5 Components of a Carburetor :

                 Different types of carburetors have different types of components, but modern spray type carbs all share a number of common characteristics, including:

v  An air passage (venturi)

v  A throttle valve

v  Throttle linkage

v  A power valve or metering/step-up rod

v  An accelerator pump

v  A choke

v  A bowl

v  A float

v  Adjustment screws

etc……….

1.6 How does a Carburetor works :

             Different types of carburetors work via different mechanisms. For instance, wick-type carbs work by forcing air to pass over the surface of gas-soaked wicks, which causes gasoline to evaporate into the air. However, wick-type carburetors (and other types of surface carbs) were more or less obsolete more than a century ago. Most carburetors that are used by vehicles that are still in service today use a spray mechanism, and they all operate in more or less the same way.

modern carburetor rely on the venturi effect to suck fuel from the bowl

1.7 Basic Principles of Carburetor Operation :

            Spray carbs work based on Bernoulli’s principle, which states that air pressure changes in a predictable way depending on how fast the air is moving. This is important because the air passage through a carburetor contains a narrow, constricted section called a venturi that causes air to speed up as it passes through. This is the section where the fuel inlets or “jets” are located, and the increased speed of the air causes fuel to be sucked into venturi.

The flow of air (rather than the flow of gas) through a carburetor is controlled by the accelerator pedal, which is linked to a throttle valve inside the carb. This valve closes off the venturi when the accelerator pedal isn’t in use, and it opens up when that pedal is depressed. That allows additional air to pass through the venturi, which sucks more fuel from the bowl, and subsequently provides more air and fuel to the engine for combustion.

         Although that describes the basic operation of a spray carburetor, there’s a lot more going on in practice. Most carburetors include an additional valve above the venturi called a choke, which acts as a secondary throttle valve. The choke remains partially closed when an engine is cold, which reduces the amount of air that can pass into the carb. That results in a richer air/fuel mixture, so the choke has to open (either automatically or manually) once the engine has warmed up and no longer needs a rich mixture.

       Other carburetor components are also designed to affect the air/fuel mixture during different types of operating conditions. For instance, a power valve or metering rod can increase the amount of fuel under open throttle, either by responding to low manifold vacuum or the physical position of the throttle valve.

1.8 carburetor failure :

 some carburetor problems can be solved by adjusting the choke,mixture , or idle, and others require a rebuild.

          Spray carbs work based on Bernoulli’s principle, which states that air pressure changes in a predictable way depending on how fast the air is moving. This is important because the air passage through a carburetor contains a narrow, constricted section called a venturi that causes air to speed up as it passes through. This is the section where the fuel inlets or “jets” are located, and the increased speed of the air causes fuel to be sucked into venturi.

The flow of air (rather than the flow of gas) through a carburetor is controlled by the accelerator pedal, which is linked to a throttle valve inside the carb. This valve closes off the venturi when the accelerator pedal isn’t in use, and it opens up when that pedal is depressed. That allows additional air to pass through the venturi, which sucks more fuel from the bowl, and subsequently provides more air and fuel to the engine for combustion.

             Although that describes the basic operation of a spray carburetor, there’s a lot more going on in practice. Most carburetors include an additional valve above the venturi called a choke, which acts as a secondary throttle valve. The choke remains partially closed when an engine is cold, which reduces the amount of air that can pass into the carb. That results in a richer air/fuel mixture, so the choke has to open (either automatically or manually) once the engine has warmed up and no longer needs a rich mixture.

           Other carburetor components are also designed to affect the air/fuel mixture during different types of operating conditions. For instance, a power valve or metering rod can increase the amount of fuel under open throttle, either by responding to low manifold vacuum or the physical position of the throttle valve.

1.8.1 Carburetor Rebuilding :

                Many carburetor problems can be solved by making adjustments or performing other fixes while the carb is still on the car, but other issues can only be dealt with by removing the unit and rebuilding it. A carburetor rebuild operation typically involves removing the unit, taking it apart, and cleaning it with a solvent that is designed specifically for that purpose. A number of internal components, seals, and other parts are then replaced before the unit is reassembled and installed.