A simple carburetor is composed of three parts, the upper part of the air inlet and float chamber, the middle part of the throat, orifice and nozzle, the lower part of the valve and so on.The float chamber is a rectangular container that stores gasoline from the gasoline pump. Inside the container, a float controls the amount of oil that comes in using the height of the float (oil surface).The middle nozzle inlet is connected with the measuring hole of the float chamber, and the oil outlet is at the throat of the throat tube.
The laryngeal tube is a bee waist shaped, large at both ends and small in the middle, among which the throat has the smallest cross-sectional area.
When the engine is started, the piston produces suction downward, and the suction airflow passes through the throat at the maximum speed, but the static pressure is the lowest, so the throat pressure is less than the atmospheric pressure, that is to say, there is a pressure difference between the throat and the float chamber, which is often called "vacuum degree", and the greater the pressure difference, the greater the vacuum degree.Gasoline under the action of vacuum from the nozzle out of the oil mouth, because the flow of air at the throat of the throat is 25 times the flow of gasoline, so the nozzle out of the oil flow is dispersed by high-speed air flow, the formation of different sizes of fog particles, that is, "atomization".The initial atomized oil particles are mixed with the air to form a "mixture" that passes through the throttle, intake pipe (4) and intake valve (5) into the combustion chamber of the cylinder.Here, the valve opening size and engine speed determine the vacuum degree at the throat, and the throttle opening changes directly affect the mixture proportion, which are important reasons affecting the engine operation.
Here involves a "air-fuel ratio" concept, the air-fuel ratio is the ratio of air and fuel quality, scientists believe that the 1 kg of gasoline combustion takes about 14.7 kg air, namely the air-fuel ratio was 14.7:1, the air-fuel ratio of mixture called standard mixture, because this value is hard to realize in practice, so also known as the "theory of mixture".Air - fuel ratio greater than the standard mixture is called thin mixture, less than the standard mixture is called thick mixture.
Because the change of mixture concentration is closely related to the change of engine load under various operating conditions, the simple carburetor is far from meeting the requirement of changing at any time, so new devices are constantly added to the simple carburetor to adjust the working state of the carburetor.Today, carburetors have been developed with various auxiliary devices, mainly idle, enrichment, acceleration and starting devices.At present, the common carburetor of 4-cylinder engine is the double-cavity split moving carburetor, which has two pipes and works separately or simultaneously according to different working conditions of the engine.The common carburetor for 6-cylinder engines is the double-chamber parallel carburetor, which is actually two single-chamber carburetors together, each chamber responsible for half the number of cylinder mixture gas supply.There are also multi-chamber carburetors, which are usually fitted to more powerful engines.
Among the various functional devices of the carburetor, the main fuel supply device is the basic fuel supply structure of the carburetor, which is required by all other working conditions except idle speed.Idle gear is a device that provides a small but thick mixture of air during idle operation to maintain a stable minimum engine RPM.The thickening device is an extra fuel supply device when the engine is under heavy load to make up for the shortage of the main fuel supply.Acceleration device is an extra fuel supply device when the valve opening suddenly increases when the car accelerates, so that the engine speed and power can increase rapidly.The starter is a device that provides a very thick mixture of air when the engine is started cold, usually by installing a choke in front of the throat to control the intake volume.
Idle is a special mention here.
Idling is the most commonly used engine condition, which is used in the process of engine thermal start and non-stop stop.It is of great significance to the vehicle driving performance, especially in the city, idling speed often determines the fuel consumption and pollution level of the vehicle driving.
Engine idling speed is usually only 600-800 RPM and the throttle is close to closing. The vacuum created by this speed is not able to pull gasoline out of the float chamber, but the vacuum behind the throttle is very high.Therefore, only on the basis of the simple carburetor, another idle oil channel, its jet hole is set in the throttle, the problem will be solved.
Because the idle speed needs less and thick mixture, it is sensitive to the engine running condition, so it is necessary to adjust the fuel quantity control and the throttle minimum opening to achieve the idle speed state of both stability and minimum speed.The current carburetor idle device has two adjusting screws that adjust the fuel volume and throttle opening respectively.At the same time, in order to prevent the car to close the ignition switch and the engine is still running phenomenon, in the carburetor idle oil channel is also equipped with idle solenoid valve, specially responsible for opening and cut-off idle oil channel, to ensure that the engine can quickly flameout.
