In this article, you will learn about fuel injection systems. The carburetor is the very first mechanism that made it possible to combine gasoline with air in the right proportion to prepare the air-fuel mixture and supply it to the engine's combustion chambers. These devices are actively used to this day - on motorcycles, chainsaws, lawn mowers, and so on. That's just from the automotive industry, they have long been supplanted by injection injection systems, more advanced and perfect.
What is a carburetor?
A carburetor is a device that mixes fuel and air, delivers the resulting mixture to the intake manifold of an internal combustion engine. Early carburetors worked by simply allowing air to pass over the surface of the fuel (in this particular case, gasoline). But most of them later dispensed a measured amount of fuel into the air stream. This air passes through the jets. For a carburetor, the condition of these parts is extremely important.
The carburetor was the main tool for mixing fuel and air in internal combustion engines until the 1980s, when doubts arose about its effectiveness. When fuel is burned, a lot of harmful emissions are produced. Although carburetors were used in the United States, Europe, and other developed countries until the mid-1990s, they worked alongside more sophisticated control systems to meet carbon emissions requirements.
History of development
Various types of carburetors were developed by a number of automotive pioneers, including the German engineer Karl Benz, the Austrian inventor Siegfried Markus, the English polymath Frederick W. Lanchester, and others. Since so many different methods of mixing air and fuel were used in the early years of the existence and development of cars (and the original stationary gasoline engines also used carburetors), it is rather difficult to pinpoint who is the inventor of this complex device.
Types of carburetors
Early designs differed among themselves in the basic method of operation. They also differ from the more modern ones that dominated for most of the twentieth century. A modern carburetor for a spray-type chainsaw, similar ones are used on modern cars. The very first, historical, so to speak, constructions can be divided into two main types:
- Surface type carburetors.
- Spray carburetors.
Surface carburetors
All early carburetor designs were superficial, although there was a great deal of variety in this category as well. For example, Siegfried Markus introduced something called a "revolving carburetor brush" in 1888. And Frederick Lanchester developed his carburetor-type wick in 1897.
The first carburetor float was developed in 1885 and also patented the float type carburetor around the same time. However, these early designs were surface carburetors that worked by passing air over the surface of the fuel in order to mix them. But why does an engine need a carburetor? And without it, it was impossible to supply the fuel mixture to the combustion chambers (the injector was not yet known in the nineteenth century).
Most surface devices functioned on the basis of simple evaporation. But there were other carburetors, they were known as devices that work due to "bubble" (they are also called filter carburetors). They work by forcing air up through the bottom of the fuel chamber. As a result, a mixture of air and fuel is formed above the main volume of gasoline. And this mixture is subsequently sucked into the intake manifold.
Spray carburetors
Although various surface carburetors were dominant throughout the first decades of the automobile's existence, spray carburetors began to fill a significant niche around the turn of the 19th and 20th centuries. Instead of relying on evaporation, these carburetors actually sprayed a measured amount of fuel into the air that was sucked in by the intake. These carburetors use a float (like the Maybach and earlier Benz designs). But they operated on the basis of the Bernoulli principle, as well as the Venturi effect, like modern devices, such as the K-68 carburetor.
One subtype of aerosol carburetors is the so-called pressure carburetor. It first appeared in the 1940s. Although pressure carburetors only resemble aerosol carburetors in appearance, they were actually the earliest examples of forced fuel injection devices (injectors). Instead of relying on the Venturi effect to suck fuel out of the chamber, pressure carburetors sprayed fuel out of the valves in much the same way as modern injectors. Carburettors became increasingly complex during the 1980s and 1990s.
What does "carburetor" mean?
"Carburetor" is an English word that is derived from the term carbure, translated from French - "carbide". In French, carburer simply means "combine (something) with carbon". Similarly, the English word "carburetor" technically means "increase in carbon content".
The K-68 carburetor works similarly, which was used on scooters of the Tula type (later Ant), Ural and Dnepr motorcycles.
Components
All types of carburetors have different components. But modern appliances share a number of common characteristics, including:
How does a carburetor work?
All types of carburetors work with different mechanisms. For example, wick-type carburetors work by forcing air over the surface of the gas-soaked wicks. This causes the gasoline to evaporate into the air. However, wick-type devices (and other surface devices) have become obsolete over a hundred years ago.
Most carburetors that are used in vehicles today use a spray mechanism. They all work in the same way. Modern carburetors function by the Venturi effect to draw fuel out of the chamber.
Basic principles of operation of carburetors
Carburettors based on the Bernoulli principle have some peculiarities. Changes in air pressure are predictable and directly related to how fast it is moving. This is important because the air passage through the carburetor contains a narrow, compressed venturi. It is needed to accelerate the air as it passes through it.
Air flow (not mixture flow) through the carburetor is controlled by the accelerator pedal. It is connected to the throttle valve located in the carburetor with a cable. This valve closes the venturi when the accelerator pedal is not in use and opens when the accelerator pedal is depressed. This allows air to pass through the venturi. Consequently, more fuel is drawn from the mixing chamber. The operation of the carburetor is based on such principles.
Most carburetors have an additional valve above the venturi (called a throttle that acts as a secondary throttle). The throttle remains partially closed when the engine is cold, which reduces the amount of air that can pass into the carburetor. This results in more air/fuel, so the throttle should open (automatically or manually) as soon as the engine is warm and no longer needs a rich mixture.
Other components of carburetor systems are also designed to affect the air/fuel mixture during various operating conditions. For example, a power valve or metering rod may increase the amount of fuel at open throttle, or it may be in response to low vacuum system pressure (or actual throttle position). A carburetor is a complex element, and the physical basis for its operation is quite complex.
Problems
Some carburetor problems can be solved by adjusting the choke, mixture, or idle, while others require repair or replacement. Often the carburetor membrane wears out, stops pumping gasoline into the chambers.
When the carburetor fails, the engine will perform poorly under certain conditions. Some problems of carburetor systems lead to engine breakdown, it cannot normally idle without outside help (for example, pulling the choke or constant gasping). The most common problems occur during the cold season, when the engine is most difficult to work. And a carburetor that performs poorly on a cold engine may function normally when warm (this is due to problems with coking channels).
It is worth noting that the carburetor for a walk-behind tractor is the same in composition as an automobile one. The difference is in the number of elements and their sizes. In some cases, carburetor problems can be resolved by manually adjusting the mixture or idle speed. To this end, the mixture is usually adjusted by turning one or more screws. They have needle valves. These screws allow you to physically change the position of the needle valves, which means that the amount of fuel can be reduced or increased (rich mixture occurs) depending on the specific situation.
Carburetor repair
Many carburetor system problems can be solved by making changes or other fixes without removing the device from the engine. To adjust the carburetor for a walk-behind tractor, there is no need to remove it. But some problems can only be solved by removing the device and restoring it completely or partially. Rebuilding a carburetor typically involves removing the block, taking it apart, and cleaning it with a solvent designed specifically for this purpose.
A number of internal components, seals and other parts then must be replaced before installation. Only after careful processing is it necessary to assemble the carburetor and install it in place. To carry out quality service, you will need a carburetor repair kit. It includes all the most important design elements.
So, we found out that a carburetor is literally a device that adds gasoline (fuel) to the air and feeds this mixture into the engine's combustion chambers.
At first glance, a carburetor may seem like a very complex device. However, a small amount of theoretical knowledge will help to fully understand its principle of operation. Which, in turn, will allow you to independently clean and. To perform these operations at the proper level, basic information is sufficient.
How does a carburetor work
Regardless of the model, the principle of operation of the carburetor is similar. Structurally, any carburetor is made according to the following scheme: a channel for creating an air-fuel mixture, in which there is a special calibration hole for air inlet, a float chamber and an outlet for the finished mixture.
When the engine is running, a reduced pressure is created in (the element connecting the power unit and the fuel system) in relation to atmospheric pressure. This creates a vacuum in the carburetor. Due to this, air is drawn into the carburetor through a special narrowing channel and gasoline is captured from the fuel chamber. In the process, these ingredients are mixed, which leads to the creation of an air-fuel mixture, which ignites in the CC (combustion chamber) and causes the pistons to move. The amount of fuel in the finished mixture depends on the pressure created in the mixing chamber. Due to the fact that the chamber is connected to the atmosphere, due to the pressure difference, gasoline rises, mixing with air. The mixture then enters the combustion chamber. The narrowing of the passage accelerates the movement of air, which leads to its even greater discharge.
Air fuel supply
The fuel and air supply is controlled by the gas pedal, it is connected to and the element that blocks the float chamber (PC). When the pedal is free, the motor is idling (XX). The damper almost completely closes the calibrated air supply channel, and the needle opens the opening in the fuel chamber. The detail for closing the float chamber is made in the form of a needle divided into several parts, each of which has its own thickness. Thus, the higher it rises, the more fuel is supplied. The air damper works on the same principle, the wider the opening, the greater the flow.
What is carburetor idle - XX
Idling can be compared to standby. It is necessary for stable, when the car is not driving, so that the engine does not stall. In this case, the air mixture is saturated with the minimum amount of fuel necessary to maintain stable operation of the system. When the gas pedal is released, the spool needle maximally blocks the main gasoline supply channel. The air damper remains slightly open. The passage through which gasoline is supplied is located behind the air damper. The combustible mixture begins to flow through this channel only when there is an increased vacuum in the carburetor, which occurs when the air damper is strongly opened. To create an air-fuel mixture at the XX, the design provides an additional oxygen supply channel. It has a special element for adjusting the quality of the combustible mixture. The tighter the screw is tightened, the more the mixture is saturated with gasoline. The idle speed increases, and vice versa - unscrewing the screw reduces them. Thus, by adjusting this screw, you can achieve optimal options, increase efficiency.
For the correct dosage of the ingredients of the combustible mixture, jets are installed at the intake points. They are a special element with a certain diameter of the passage, which does not allow the consumption of fuel or air above the established norm. Also, the jet can act as an adjusting screw.
What is the purpose of a float chamber in a carburetor?
1
- float axis holder;
2
- float tongue;
3
- float
PC is one of the main elements of the carburetor, which contains fuel. The liquid level in the chamber is regulated and controlled by a special float. It has a needle attached to it. It closes the channel for supplying the combustible mixture from the gas tank. When the fuel level decreases, the float begins to fall, and the needle rises. When filling the chamber, the float rises and the level stabilizes.
The carburetor provides a mechanism for additional suction control DZ. This element is intended for manual enrichment of the mixture. An additional channel is provided for this function, it is smaller than the main one. The suction mechanism is controlled by a special lever on the dashboard. First, you need to pull the element completely towards you, thereby opening the damper as much as possible, as the engine warms up, the lever must be gradually returned to its original position.
Carburetor adjustment
Carburetor adjustment can only be carried out on. Regardless of the design, the principle of element calibration is identical.
- float chamber . Adjustment and control of the liquid level in the tank is carried out using a float connected by a wire to a needle. The level of required fuel in the chamber is indicated in the owner's manual for a specific car model. Check the current indicators, measure the height of the mirror with a caliper. If the level is above normal, carefully take the float in your hand and bend it down by mechanical action on the wire. If the fuel level is below normal, raise it.
- Setting XX . The optimal number of revolutions at the twentieth is 800-900 units. Tighten the mixture quality screw until it stops and unscrew it 4-5 turns back. Tighten the quantity screw until it stops and unscrew it 3 times. Turn on the engine, gradually start to tighten the first screw, in the process the speed should rise and the unstable operation of the motor will begin. When the instability phase begins, begin to tighten the adjusting element until the engine starts to run stably again. Finally, adjust the quantity screw.
- jet adjustment . With the help of suction, you need to close the air damper. The link shank must be at the end of the carburetor PU rod groove. In case of deviation, it should be eliminated by bending the rod. Then you need to remove the cover, and then measure the gap from the edge of the chamber wall to the air intake. The required indicators are indicated in the instruction manual. Adjustment is carried out using the PU adjusting screw.
Reading 5 min.
Knowing the device of the carburetor, the driver can clearly and correctly control his vehicle. In addition, in the event of a breakdown, this knowledge will help to quickly eliminate it.
Each new day brings its own changes to the engineering industry. In the same way, carbureted engines have been replaced by injection engines, which are considered more advanced, and by the way, they are. But on our roads for a long time old cars will drive, in which carburetors are just installed. For this and a host of other reasons, it is necessary to know the structure of the carburetor, and what functions it performs at the time of engine operation.
Purpose of the carburetor
The principle of operation of the carburetor is to enrich the fuel with air, then this fuel enters the engine cylinders and the car moves.
But not everything is so simple, there is an erroneous opinion that the engine itself sucks in fuel, of course, this is not so. The operation of supplying fuel occurs just thanks to the carburetor, in which there is a mechanism called a carburetor diffuser. It is designed to narrow the air throat of the carburetor. Those. at the moment of passage of air through this constriction, a rarefaction (pressure drop) occurs. Next, a small hole for supplying fuel, installed in this place, comes into action. Through it, under high pressure, fuel is squeezed out of the float chamber into the carburetor neck, from where enriched gasoline enters the exhaust manifold and further into the engine cylinders.
Also, the operation of the carburetor involves the recognition of different modes, such as:
- Engine idling (neutral gear);
- Average turns;
- The operation of the car after complete cooling (for example, being in the cold for a whole night).
All these modes differ in that when starting the engine, the carburetor must react differently. Enrich the fuel with oxygen in different ways, dose the amount of injected fuel, etc. To do this, each part of the mechanism must work properly and be clearly calibrated.
The internal structure of the carburetor
Let's start with such an element as a float chamber. It works as follows. At the moment of fuel consumption, the chamber is gradually emptied, and the float begins to go down, opening the needle valve. Then, with the help of a gasoline pump, fuel begins to flow back into the float chamber, and the needle valve closes. Thus, a constant volume of air-fuel mixture is maintained in the chamber. You can also put an electric fuel pump on the carburetor, this will significantly increase engine power and allow you to quickly gain a large number of revolutions.
Now it’s worth giving attention to such a part as the carburetor air damper. It allows you to start the engine after complete cooling, this happens due to the enrichment of the air-fuel mixture. Those. The damper blocks the air flow entering the carburetor and allows more enriched fuel to be injected from the float chamber into the engine cylinders. Thus, the cooled car receives more fuel and starts easier. If, in addition, you install autostart on the carburetor, then you do not have to sit in a cold car every morning and warm up the engine “manually”. It is also worth mentioning that when installing autostart, it would be useful to put an autochoke on the carburetor, then all warm-up actions will be performed fully automatically.
After the engine warms up, it would be logical to say about the idle system, it is needed to supply fuel at low speeds. Indeed, at low speeds, less fuel is required, and the main metering system does not function in this mode. The operation of the carburetor is regulated, in this mode it is very simple, you need to tighten or loosen the adjusting screws, then either the air supply or the fuel supply will be reduced, respectively, it will be more enriched.
Next, let's talk about the accelerator pump, this element of the system is necessary for a sharp increase in engine loads and so that the car does not stall. At the moment of its activation, the throttle valve opens and there is a sharp injection of fuel. This phenomenon is mandatory, both if you have a single-chamber carburetor and a two-chamber one.
There is also a transitional system, this element is necessary for the transition from idle mode to the inclusion of the main dosing system at increased loads.
Main dosing system
This system allows you to clearly separate and dose the amount of fuel entering the engine while driving at medium speed. It includes elements such as:
- Fuel jets;
- Main distributor;
- Diffuser.
In this case, the main fuel jet is located in a specially drilled channel between the float chamber and the main air atomizer, which consists of a small tube with holes for air supply. The main jet is responsible for what ratio the fuel will have when mixed with air.
At the same time, the device of the carburetor is such that for its calibration it is possible to install jets with different sections when setting up various modes of operation of the carburetor.
Economizer
It is also an extremely necessary part of the carburetor, and both a single-chamber carburetor and a two-chamber carburetor are inconceivable without it. The task of the economizer is to provide the engine with even more oxygen-rich fuel. Such a need arises with increasing loads, for example, to develop speeds above 110 km / h. At the moment of a sharp pickup of such speed, the throttle valves open as much as possible, and the supply of the air-fuel mixture increases as much as possible. To speed up this process and give the engine the necessary acceleration, professionals resort to the help of such a device as a carburetor accelerator pump. It allows you to bring the procedure to the maximum performance, as a result of which the engine will receive enriched fuel in a matter of milliseconds.
conclusions
By learning the principles of how a carburetor works, every car owner will be able to understand a few fundamental engine and vehicle handling.
Namely: the mechanism for providing fuel with oxygen, the moment when you need to change gears, how to properly warm up the engine in winter, which serves as the main force when accelerating the car, etc. Knowing all these things, your level of driving and the feeling of your "steel horse" will only increase.
And in the event of some accompanying breakdown, you will be able to determine what is out of order and take appropriate measures.
To diagnose malfunctions and effectively repair your car, you need to know the device, purpose, principle of operation of its main parts and mechanisms. Consider what a car carburetor is and why it is needed.
What is a car carburetor?
A carburetor is a device for preparing and dispensing a fuel mixture (gasoline + air) on which an automobile engine runs. The carburetor, along with the fuel pump, fuel tank, fuel lines and other elements, is included in the engine power system.
What is a carburetor for?
To understand what a car carburetor is for, you need to know that for each engine operating mode (idling, acceleration, average loads, power, etc.), it is necessary to prepare a fuel mixture of a certain composition. The optimal composition is 14.5-15 / 1 (15 parts of air to one part of gasoline). This is the so-called stoichiometric composition of the fuel mixture, at which its most complete combustion occurs with the release of maximum energy. In power modes, a richer fuel mixture is needed (for example, 1 to 13), at low loads it is poorer (for example, 17/1). That is, the more the driver presses the gas pedal, the more the fuel mixture entering the engine should be enriched.
The preparation of a fuel mixture of a certain composition for each mode of engine operation is precisely what the carburetor is engaged in. For this he is needed. Plus dosing, that is, the supply of the required volume. Structurally, the carburetor combines several systems and mechanisms that allow such work to be done.
For example, the starting system - prepares a rich fuel mixture to start the engine, the main metering systems - supply fuel to the engine in all modes except idling and forced idling, the accelerator pump - allows you to instantly enrich the mixture and accelerate when you sharply press the gas, the economizer - enriches mixture at increased engine loads, etc.
What makes a carburetor work?
An automobile carburetor works due to the rarefaction that occurs in the intake manifold when the engine pistons move. Under the influence of this rarefaction (low pressure area), the fuel is literally “sucked out” from the carburetor channels. The faster the pistons move, the higher the vacuum. The carburetor can itself regulate the amount of vacuum by opening and closing the throttle and air dampers.
How does a carburetor work?
When a cold engine is cranked by a starter in the start mode, a vacuum is created in the intake manifold, due to which a certain amount of fuel is drawn from the channels of the start-up system, which is necessary to start the engine.
After warming up, with the air damper fully open, it is the turn of the idle mode (XX), in which fuel is supplied to the engine through the channels of the idle system.
When you press the gas pedal, the accelerator pump is activated, injecting an additional dose of fuel and increasing engine speed.
Start of movement - the transition system of the first chamber works to prevent failure.
Power mode - the second chamber of the carburetor and its GDS come into operation.
What is better carburetor or injector?
Neither is the other, as each system has its pros and cons. The carburetor is simpler and cheaper to maintain, but the mixture it prepares is not stable and cannot be accurately dosed, it depends on extraneous factors that affect the consumption and operation of the engine. The injector doses the fuel mixture accurately, which allows you to reduce consumption and optimize its composition in each of the modes, but servicing the injection system is expensive and requires certain skills and knowledge.
But, the future belongs to the injector, since the environmental requirements for the exhaust of a car engine are constantly growing, and in terms of exhaust toxicity, the injector is superior to the carburetor.
Notes and additions
In the list of all systems and mechanisms of a modern carburetor.
- Starting device
- Main dosing system of the first chamber of the carburetor
- Main dosing system of the second chamber of the carburetor
- idle system
- Transition system of the first chamber of the carburetor
- Transition system of the second chamber of the carburetor
- Accelerator pump
— Economizer power modes
More articles on the design and purpose of car systems and mechanisms
What is a fuel pump and how does it work?
What is a car distributor and how does it work?
Internal combustion engine carburetor
The standard carburetor has an air diffuser, which is made in the form of a tapering carburetor neck. Air passing through this constriction creates a reduced pressure. A hole with a small diameter through which gasoline is supplied is specially placed in this place. Ambient air pressure forces gasoline out of the float chamber into this hole in the air inlet, then the fuel is sent to the intake manifold and then to the working area of the cylinders.
Since the engine operates in a wide range of speeds, it needs a mixture of different compositions, also in winter, when warming up, idling, in the medium speed range and under high load. Carburettors are equipped with various systems that help it do its job in all sorts of conditions. In addition to the components that will be discussed below, there are some components, including solenoids to stop fuel injection and pressure drop dampers used in special cases. These parts are placed for various reasons and their removal can significantly affect the normal functioning of the engine.
Simple carburetor device
A simple carburetor is made up of a float chamber and a mixing chamber. The process of mixing the combustible mixture lasts all the way through the movement of gasoline and air through the intake tract and up to the very cylinders, although it begins with the injection of gasoline into the mixing chamber of the carburetor.
float chamber
One of the criteria for the correct operation of the carburetor is the precise adjustment of the fuel level in the float chamber. Fuel is supplied through the fuel line channel to the float chamber. The fuel level in the float chamber is maintained by a float device with a needle valve. After filling the chamber, the float raises the needle and stops the supply of gasoline, while the displaced air is discharged through the hole intended for this. The atomizer and the float chamber are communicating vessels. The fuel level in the float chamber should be slightly below the nozzle cutoff.
mixing chamber
A tube-shaped atomizer installed in the mixing chamber is responsible for spraying fuel into the carburetor cavity. An air damper designed to adjust the composition of the mixture is placed in the mixing chamber above the diffuser. As it lowers, the ratio of fuel in the mixture will increase. Excessive obstruction of the air gap leads to the re-enrichment of the mixture and the termination of the combustion cycle of the fuel in the engine. To control the air-fuel mixture, a throttle valve is installed in the lower part of the mixing chamber on the engine side.
Diffuser
Diffuser - represents the section of the narrowing of the mixing chamber. The air entering the engine increases its speed in the diffuser, as a result, a vacuum is formed at the atomizer. Under the influence of this difference, the fuel is supplied from the atomizer and actively mixed with the air flow. Gasoline from the float chamber through the channel enters the atomizer. A jet is screwed into the channel - a screw with a through hole of strictly calculated diameter and shape. The jet is responsible for the rate of transfer of gasoline to the atomizer.
Suction. Carburetor starter control knob
The presence of a suction (or, more correctly, a carburetor starter control knob) simplifies starting the engine on a cold one in the near-winter season, when a negative temperature leads to active condensation of the working mixture on the walls of the cylinders and the carburetor mixing chamber. The purpose of the suction is to enrich the mixture, resulting in a much more fuel-rich mixture compared to conventional fuel/air ratios.
Later, many manufacturers introduced a system for automatically switching to starting mode and back, and carburetors with automatic suction arose. At the same time, the principle of operation of the manual control system of the starting damper has been preserved for more than 70 years. Covering the air at the carburetor inlet, it provides a more active outflow of fuel from the jets and, in the end, the same enriched engine operation mode.
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