We continue the series of articles on carburetor injection. The car engine operates in different modes while driving. For individual operating modes, a fuel-air mixture with a different composition is required. Most often, constant and sharp changes occur in such regimes, related to the amount of fuel vapors.
The main task of the carburetor is to prepare such a mixture, which will be optimal for any mode of operation of the motor. Carburetor device, which has a constant cross-section atomizer, includes various dosing devices. Each of these elements is gradually included in the work of the carburetor or is gradually turned off, and simultaneous work is also possible. It will depend on the load modes, revolutions of the power unit, throttle valve opening angle, etc. Dosing systems of carburetor injection are responsible for the optimal composition of the working fuel-air mixture in all modes and at the same time are designed to provide maximum power and the best indicator of economy.
We recommend that you additionally read the article about the carburetor device. From this article, you will be able to learn about the main design elements and principles of operation of this device.
The main fuel metering system
The specified main dosing system is such an element, which is found in the design of almost any carburetor. Current versions received a pneumatic system to compensate for the composition of the fuel-air working mixture. The system is based on 1 main fuel jet and 1 main air jet. These jets go into the well, which is called emulsion.
The emulsion well is located vertically or at an angle depending on the model and modification of the carburetor. The air stream passes through the air supply nozzle and enters the emulsion tube. The tube has rows of holes, located vertically. A fuel-air emulsion of the primary type is created between the emulsion tube and the walls of the emulsion well. The further route of the emulsion becomes the mixer chamber, where it moves along the channel and enters the sprayer. The main fuel nozzle is located in the lower part. For this reason, the fuel level tends to rise as the emulsion is consumed from the atomizer. This happens due to the inflow of fuel from the float chamber. The amount of fuel is limited by the fuel nozzle.
A decrease in the fuel level in the emulsion well means, that more air enters the emulsion, which passes through the holes in the emulsion tube. The result is an increase in the proportion of air in the working mixture, which determines a large degree of compensation. There are also systems, when gasoline and air immediately enter the tube. Early designs had a dosing system with parallel jets and diffusers, located in series. In such devices, the idling system was almost entirely responsible for compensation. Emphasis was also placed on the elasticity of the plates, which opened access for air flow in a larger diffuser. A compensating parallel jet provided fuel supply.
Structurally simple car carburetors with a small working volume of the motor had a main dosing system, which consisted of a compensating well and a compensating limiting jet. Such a decision was not able to make a significant compensation and ensure the supply of the proper amount of fuel in all cases. Such carburetors were not suitable for flexible operation in all internal combustion engine modes.
More advanced developments of the carburetor injection dosing system are able to provide such flexibility of the working fuel-air mixture, which is on the mark from 1/14 to 1/17, where the first number indicates the weight part of gasoline, and the second is air. The main operating modes of the motor become economical thanks to the dosing system. The system realizes the preparation of depleted compositions of approx 1/16 or 1 / 16,5.
horizontal carburetor
A separate place is occupied by the design, which is used in the device of the main dosing system of a horizontal carburetor with needle-type adjustment. Such a system provides a simultaneous mechanical change in the amount of air, which passed the diffuser thanks to the lift of the shutter, and regulating the amount enters the fuel diffuser, which is dosed using a needle with a variable profile.
The needle passes through the nozzle and mechanically changes the cross-section. In such carburetors, the ratio is clearly defined as the cross section of the diffuser, and the jet. These intersections directly depend on that height, on which the shutter rises. Carburetors, which have constant rarefaction, at the moment of time demonstrate the change of this characteristic according to the automatic principle. The task is implemented using a damping system, which has a spool at its base, and also relies on rarefaction in the area of the throttle valve. The system functions thanks to the load on the power unit and accounting for the angle of rotation of the throttle valve.
Transient system in the secondary chamber
If we talk about the transitional system with chokes, which are opened sequentially in the 2nd chamber, then this solution resembles an idle system, but with a number of features.
The main dosing system, located in the 2nd chamber of the carburetor, originally designed for that, to provide a "rich" mixture for power. Due to this, the chamber does not require the possibility of serious mixture compensation compared to the primary chamber. The result is that, that the transition system is connected in parallel, and her fuel jet is connected to the emulsion well of the main dosing system, and with a float chamber.
It turns out, that enters the work as a transitional one, so is the main system in the secondary chamber. Both systems are turned on at the same time, which allows you to enrich the working mixture to the desired degree.
Carburetor operation at low vacuum
System, which is responsible for idling, as well as the transitional system and the crankcase ventilation system are responsible for ensuring the stable operation of the motor in such modes, when rarefaction is minimal. This vacuum turns out not to be enough, to engage the main dosing system, so that in such modes of operation, these systems implement the correction of the composition of the fuel-air mixture.
When the engine is idling, there is no such vacuum above the throttle, which is required to activate the main dosing system. Obviously, that another system was required for low vacuum operation and slightly open throttle. This system is responsible for the process of formation of the working mixture with a small air flow, which flows under such conditions in the mixer chamber.
Idle system
A parallel system is extremely rare, more often presented ??serial or autonomous. According to the type of spray, throttle spray and spray in the space behind the throttle are distinguished. The system is arranged like this, which has channels for air at the base, fuel and emulsion. There are also dosing elements, which means jets for idling. idle jet, which is responsible for fuel supply, takes the emulsion in the lower part of the corresponding well of the main dosing system.
It turns out, that this nozzle is an element in the fuel channel of the dosing system. Jikler, which is responsible for air supply at idle speed, connects to the space in the mixer chamber. It is about the upper part of the camera, and such a device is able to realize a change in the amount of air, that is served, which enters the idling system at various loads and operating modes of the power unit.
Due to the specified characteristics, the idling system is an important participant in the chain of elements, which participate in the process of correcting the composition of the working mixture for the main dosing system.
This is often the case, that air enters the idling device through several channels (there are two or three channels). This implementation ensures the process of emulsion formation in two or three stages, which contributes to obtaining a more homogeneous working mixture and at the same time improves the uniformity of its composition for each individual cylinder of the internal combustion engine.
The idle system has an outlet in relation to the space of the mixer chamber. There is sufficient vacuum in the space behind the throttle valve at idle speed, which is enough for the operation of the idling system. Transition holes are opened in the channel of the system. These holes are located in the area of the slightly open edge of the throttle valve.
Models To 88, DAAZ 2108 and some others received a single vertical hole, looks like a slit. One part is below the edge of the throttle valve and is responsible for operation at idle speed. If you start to open the throttle, then the gap increases, contributing to the operation of the motor during transient modes.
At idle, the throttle valve is almost completely closed. The necessary vacuum in the carburetor is immediately behind the valve. This rarefaction allows fuel to be obtained from the main dosing system through the idle hole. This fuel goes through the idle fuel nozzle and mixes with the air, which enters through the idle air nozzle and other channels for its supply. The resulting fuel-air working mixture becomes enriched, which is what the engine needs to work at idle speed. The proportion of gasoline and air in this mixture is presented ??within the framework of 1/12 to 1 / 14,5.
The transition mode should be understood as the operation of the internal combustion engine with a small opening angle of the throttle valve. In the specified mode, a rich mixture from the channels of the idling system is detected in the area of the flap edge, passes through a single hole or a structural group of transition holes, mixes with the incoming air and becomes depleted within certain limits (1/15 or 1 / 16,5).
As already mentioned, certain models of carburetors may have only one hole in the area of the edge of the throttle valve, looks like a slit. This hole is located vertically. Structurally, this solution is able to provide effective compensation and quite smoothly change the composition of the fuel-air working mixture during the transition mode. If you take into account, that the shape of the gap can be specified, then it is appropriate to talk about an excellent transition characteristic. When the engine operates in other modes, the idling system compensates for the composition of the working mixture, which is formed by the main dosing system. It turns out, that the idle system plays an important role in the overall device of the entire carburetor injection and ensures its correct operation.
Such cases are not rare, when after an unprofessional adjustment of the idle speed and at the same time the revolutions normally set for this mode, the carburetor still showed low efficiency or even inoperability.
Autonomous idling
In some designs, the system is made autonomous, equipping with additional devices for the formation of a working fuel-air mixture. In other words, a kind of additional carburetor is obtained, operating inside the main carburetor and adapted for efficient operation in low air flow conditions. An example can be an autonomous idling system of the "Cascade" type. Such a system is needed for that, so that the composition of the working mixture remains uniform when distributed among the cylinders of the power plant, as well as to stabilize a number of characteristics and the mixture formation process itself, consistency with the moment of ignition, etc.
This system constructively received the main channel. The inlet of the channel is located in the area of the edge of the throttle valve, which descends. The channel basin itself has an exit to the area under the throttle. This arrangement is able to provide the ability to immediately stop the movement of air and fuel in the channel at that moment, when the throttle is opened. This channel becomes the main path for the emulsion, which was formed in the idle mode system.
The best spray quality is achieved by mixing this emulsion with air using special atomizers. Atomizers are able to provide the working fuel-air mixture with the highest movement speed in the mode of low air flow and emulsion, bordering on the speed of sound.
Such a feature of autonomous idling solutions allows to ensure the highest quality atomization of the mixture, which is impossible when used in carburetor injection of other systems. Advanced carburetors may have an autonomous idle system, which is characterized by emulsification from two times to four times.
Such autonomous systems can be arranged completely apart from each other. The simplest scheme of the device is demonstrated by the carburetor of the DAAZ model 2140. This carburetor has a design, in which the air flow passes through a small gap. Another slot from the channel is additionally opened in this slot in the upper part, through which the emulsion arrives. Due to the ratio of the intersections of these slits, the emulsion and air gain speed, close to the speed of sound.
The autonomous idle of the "Cascade" type received the type of atomizer, which resembles a ring in shape and has holes, located in a circle. Coming out of these holes, the emulsion meets the air flow. The entire autonomous idle system of this design strongly resembles the principles of operation of the mixing chamber of the carburetor. The atomizer in the center is equipped with a special adjusting screw with a special profile. This screw adjusts the amount of mixture in the autonomous system.
There are idle systems, which have atomizers-nozzles in the emulsion movement channel, directed to the central zone of the common channel. The air flow in such a design is supplied through the adjusting screw, also equipped with an air channel.
Forced idling
In this mode, the system connects the economizer. This device is a valve, which is able to cut off the fuel supply. An additional element is the economizer control system, which can be electro-pneumatic or only electronic.
When the internal combustion engine goes into forced idle mode, a control signal is applied to the operating valve. At motors, which received control with the help of a microprocessor, the signal is created by this control system. The executive valve can be located in the outlet of the automatic idling system and close the channel for supplying the fuel-air working mixture.
The second option is the design of the valve with a needle, which interrupts the fuel supply through the nozzle. This design leads to an increase in the inertia of the entire system. The peculiarity is a short period of time, when at the moment of leaving the forced idling mode, the general idling system is activated, but the fuel does not yet enter the main channel through the jet. Cheapness and simplicity of design are noted among the main advantages, as well as less susceptibility to potential malfunctions during active operation.
A system with a valve in the channel is a constructive solution in DAAZ models 2104, 2105, 2107. The mode change happens instantly, but a number of complications in the process of maintenance and operation often led to that, that the owners of cars with a similar system device had to deactivate forced idling.
A peculiar system of forced idling is implemented in the K90 model. The device has the following idle channels in two chambers, which in the end received solid cavities. The plates of the electromagnetic valves are located in the indicated cavities. When voltage is applied to them, then the supply of the working fuel-air mixture is stopped. These features allow the carburetor to work in regular mode then, when the economizer broke.
If a carbureted car has additional equipment, which takes away the power of the motor (automatic transmission, climatic installation, generator of increased power, etc.) then in the design you can find a controlled stop of the throttle valve. The task of such a solution is stabilization of idling speed when additional devices are turned on and the load on the motor increases. The throttle valve rises a little in such modes.
Econostat and economizer
These devices are used for that, to ensure the flow of fuel into the mixing chamber and provide a "rich" fuel-air working mixture at high dilution. This means peak loads on the motor, in which the depleted and economical mixture is not able to provide proper return from the power unit.
The economizer can be operated forcibly, as a pneumatic method, and mechanically. Econostat is a device in the form of a tube with a different cross-section, which can additionally have emulsion channels. These channels go into the upper space of the mixing chamber above the diffuser. It is in this area that rarefaction occurs during peak loads on the internal combustion engine.
Early models of carburetors, which had no emulsification, received an economizer with a jet, which opened forcibly and worked in parallel with the fuel jet of the main dosing system. Carburetors with emulsification did not receive this design. Cheap carburetor models, which always prepare a relatively "rich" mixture in almost all modes, devoid of economizer and econostat.
Crankcase ventilation and exhaust gas recirculation system
Crankcase ventilation allows the engine to recycle harmful crankcase gases. The crankcase ventilation has basically two channels. One larger channel, the other is smaller. The first channel is a tube. This tube contains the following elements, as a fire extinguisher and oil separator. Crankcase gases pass through these elements and enter the filter. The filter can be an inertial oil before the oil bath or a cardboard air filter, located next to the entrance to the primary chamber of the carburetor. Then the gases go through the process of mixing with air and are sent to the engine cylinders.
Idle speed and transition mode are distinguished by a weak vacuum above the chamber. To solve this problem, there is a second tube-channel for ventilation. This tube has a smaller diameter and connects the large tube to the space behind the throttle valve, where there is a suitable vacuum for the system. Different models of carburetors have a spool in a small tube for that, to block the message with a big pipe at that moment, when the throttle valve opens. The solution prevents air from entering the throttle at the same time as its fence into the carburetor mixing chamber.
Exhaust gas recirculation makes it possible to replace part of the air with exhaust. It happens on those modes, when engine braking is performed. The system allows to reduce the degree of content of toxic substances in the exhaust of the car. This system is not found on all types of engines.
Cold start device
The specified starting device is a damper, which has a control system and is located above the mixing chamber. If this flap is closed, then the rarefaction in the mixer chamber increases noticeably. The result is an immediate enrichment of the fuel-air mixture, which is ideal for starting a cold internal combustion engine. The damper does not completely block the air supply. This is due to both location, and so on, that structurally it is focused on the spring.
Another option is to install a valve, which lets in small amounts of air. To start the engine and bring it to operating temperature, you need to close the air damper and slightly open the throttle. The air damper can be equipped with a fully mechanical one, semi-automatic or automatic drive.
The mechanical drive is started by the driver from the cabin. This is done with a pen, which is called a knob. Among the people, the device received a more familiar name "suction". The semi-automatic drive has become more widespread due to its simplicity and reliability. The driver closes the flap himself, and opening happens automatically. The diaphragm is responsible for opening, which reacts to the appearance of a vacuum in the intake. This implementation does not allow the mixture to become highly enriched and prevents it, so that the engine stalls immediately after a cold start.
Although automatic cold start on domestic cars is not very common, this cannot be said about European and Japanese cars. The disadvantages of the automatic solution include its fragility, small resource and problematic use in conditions of temperature changes.
This type of drive turned out to be the most complex in terms of design and is more suitable for countries with a temperate climate. The machine is arranged like this, that the valve is covered with a special thermocouple. The element was heated by liquid from the cooling system, and could also be warmed by a separate electric heater. The stronger the engine warmed up, moreover, the thermocouple opened the damper and allowed air to pass through. Automatic systems with electronic thermocouple heaters had a drive, which was equipped with a temperature sensor.
booster pump
Such a device ensures the supply of additional fuel at moments of sharp throttling. In the conditions of instantaneous opening of the valve, there is a disturbance in the process of mixture formation in the intake, and the result is an insufficient amount of fuel supplied by carburetor injection into the engine cylinders at the initial stage of intensive acceleration.
The pump neutralizes the "failure" and is responsible for the correct composition of the working mixture in a similar mode. There are two types of booster pump: piston pump and diaphragm pump. The first type of accelerator is inferior to the second in terms of stability of a number of parameters. The main disadvantage is its inability to influence the injection and the intensity of the feed depending on the angle, to which the throttle is turned. Models of carburetors with adjustment of the needle type or with constant rarefaction are able to prepare the optimal composition of the working mixture for all modes of operation of the power plant. These carburetors do not require the installation of an accelerator pump.