It is the primary source of torque and all subsequent processes of mechanical and electronic type in the vehicle. Its functioning is provided by a whole range of devices. This is the power system. gasoline engine.
How it works, what kind of breakdowns there are, should be considered by every owner of vehicles with a gasoline engine. This will help to properly operate and maintain the system.
general characteristics
The device of the power supply system of a gasoline engine allows you to ensure the normal functioning of the vehicle. For this, a mixture of fuel and air is prepared inside the fuel unit. The fuel system of a gasoline engine also stores and supplies components for fuel preparation. The mixture is distributed throughout the engine cylinders.
In this case, the power supply system of the internal combustion engine operates in different modes. The engine should start and warm up first. Then a period passes idle move. The engine is affected partial loads. There are also transition modes. The engine must function correctly under full load, which can occur under adverse conditions.
In order for the motor to work as correctly as possible, two basic conditions must be met. The fuel must burn quickly and completely. This produces exhaust gases. Their toxicity should not exceed the established norms.
To ensure normal conditions for the functioning of components and mechanisms, the fuel supply system of a gasoline engine must perform a number of functions. It provides not only the supply of fuel, but also stores and cleans it. Also, the power system cleans the air that is supplied to the fuel mixture. Another function is to mix the fuel components in the correct proportion. After that, the fuel mixture is transferred to the engine cylinders.
Regardless of the type of gasoline ICE, the power system includes a number of structural elements. It includes a fuel tank that provides storage for a certain amount of gasoline. The system also includes a pump. It provides fuel supply, its movement along the fuel line. The latter consists of metal pipes, as well as special rubber hoses. They carry fuel from the tank to the engine. Excess fuel is also returned through the tubes.
The gasoline supply system necessarily includes filters. They purify fuel and air. Another mandatory element are devices that prepare the fuel mixture.
Petrol
The purpose of the gasoline engine power system is to supply, clean and store special kind fuel that has a certain level of volatility and knock resistance. The operation of the engine largely depends on its quality.
The volatility index indicates the ability of gasoline to change its state of aggregation from liquid to vapor. This indicator significantly affects the characteristics of education. fuel mixture and her burning. In progress ICE operation only the gaseous part of the fuel is involved. If gasoline is in liquid form, it adversely affects the operation of the engine.
Liquid fuel flows down the cylinders. At the same time, oil is washed off their walls. Such a situation entails rapid wear metal surfaces. Also, liquid gasoline prevents proper combustion of fuel. Slow combustion of the mixture leads to a pressure drop. In this case, the motor will not be able to develop the required power. The toxicity of exhaust gases increases.
Also, another unfavorable phenomenon in the presence of liquid gasoline in the engine is the appearance of soot. This leads to the rapid destruction of the motor. In order to maintain the volatility index in the norm, it is necessary to purchase fuel in accordance with weather conditions. There is summer and winter gasoline.
Considering the purpose of the power supply system of a gasoline engine, one more characteristic of the fuel should be considered. This is knock resistance. This indicator is estimated using the octane number. To determine the knock resistance new gasoline compared with the indicators of reference types of fuel, the octane number of which is known in advance.
Gasoline contains heptane and isooctane. Their characteristics are opposite. Isooctane has no ability to detonate. Therefore, its octane number is 100 units. Heptane, on the contrary, is a strong detonator. Its octane number is 0 units. If the test mixture is 92% isooctane and 8% heptane, the octane number is 92.
Fuel mixture preparation method
The operation of the power supply system of a gasoline engine, depending on the features of its design, can vary significantly. However, regardless of how it is arranged, a number of requirements are put forward to the nodes and mechanisms.
Must be sealed. Otherwise, failures appear in its various parts. This will lead to improper operation of the motor, its rapid destruction. Also, the system must produce an accurate dosage of fuel. It must be reliable, provide normal conditions for the operation of the engine in any conditions.
Another important requirement that is put forward today to the fuel mixture preparation system is ease of maintenance. For this, the design has a certain configuration. This allows the owner of the vehicle to independently carry out maintenance if necessary.
Today, the power system of a gasoline engine differs in the way the fuel mixture is prepared. It can be of two types. In the first case, when preparing the mixture, a carburetor is used. It mixes a certain amount of air with gasoline. The second way to prepare fuel is forced injection into intake manifold gasoline. This process takes place through injectors. These are special injectors. This type of engine is called injection.
Both systems presented provide the correct proportion of gasoline and air. Fuel at the correct dosage burns out completely and very quickly. This indicator is largely influenced by the amount of both ingredients. A ratio in which there is 1 kg of gasoline and 14.8 kg of air is considered normal. If deviations occur, we can talk about poor or In this case, the conditions for the correct operation of the motor worsen. It is important that the system ensures the normal quality of the fuel supplied to the internal combustion engine.
The procedure takes place in 4 cycles. There are also two-stroke gasoline engines, but for automotive technology they do not apply.
Carburetor
The power supply system of a gasoline carburetor engine is based on the action of a complex unit. It mixes gasoline and air in a certain proportion. Most often it has a float configuration. The design includes a chamber with a float. Also in the system there is a diffuser and atomizer. Fuel is prepared in the mixing chamber. Also, the design has a throttle and air dampers, channels for supplying the ingredients of the mixture with jets.
The ingredients in the carburetor are mixed passively. When the piston moves, a reduced pressure is created in the cylinder. Air rushes into this rarefied space. It first passes through the filter. Fuel is formed in the mixing chamber of the carburetor. Gasoline that escapes from the distributor is crushed in the diffuser by an air stream. Then these two substances are mixed.
The carburetor type of design includes various metering devices that are sequentially switched on during operation. Sometimes several of these elements work at the same time. Depends on them right job unit.
The power supply system of a carburetor-type gasoline engine is also called mechanical. Today, it is practically not used to create engines for modern cars. It cannot meet existing energy and environmental requirements.
Injector
The injection engine is modern design ICE. It significantly exceeds in all respects carburetor systems gasoline engine power supply. The injector is a device that injects fuel into the engine. This design allows for high power engine. At the same time, the toxicity of exhaust gases is significantly reduced.
Injection engines are stable. When accelerating, the car demonstrates improved dynamics. At the same time, the amount of gasoline that a vehicle needs to move will be significantly lower than that of a carburetor power system.
Fuel in the presence of an injection system burns more efficiently and fully. At the same time, the process control system is fully automated. You do not need to manually configure the unit. The injector and carburetor differ significantly in design and principle of operation.
injection system power supply of a gasoline engine incorporates special nozzles. They inject gasoline under pressure. Then it mixes with air. Such a system allows you to save fuel consumption, increase engine power. It increases to 15% when compared with carburetor types of internal combustion engines.
Pump injection motor is not mechanical, as it was in carburetor designs, but electrical. It provides the required pressure during gasoline injection. The system supplies fuel to desired cylinder at the certain time. The whole process is controlled on-board computer. Using sensors, it evaluates the amount and temperature of air, engine and other indicators. After analyzing the collected information, the computer makes a decision on fuel injection.
Features of the injection system
The fuel injection system of a gasoline engine can have a different configuration. Depending on the design features, there are several types of devices of the presented class.
The first group includes engines with single-point fuel injection. This is the earliest development in the field of injection engines. It includes only one nozzle. It is located in the intake manifold. This injection nozzle distributes gasoline to all engine cylinders. This design has a number of disadvantages. Now it is practically not used in the manufacture of gasoline engines of vehicles.
A more modern variety has become a distributive type of injection design. For example, such a configuration of the power supply system for the Hyundai X 35 gasoline engine.
This design has a manifold and several separate nozzles. They are mounted above the intake valve for each cylinder separately. This is one of the most modern varieties fuel injection systems. Each injector delivers fuel to a separate cylinder. From here, the fuel enters the combustion chamber.
Distribution injection system can be of several types. The first group includes devices for simultaneous fuel injection. In this case, all injectors simultaneously inject fuel into the combustion chamber. The second group includes pairwise-parallel systems. Their nozzles open in two. They are set in motion at a certain moment. The first injector opens before the injection stroke, and the second before the exhaust. The third group includes phased distribution injection systems. The injectors open before the injection stroke. They inject fuel under pressure directly into the cylinder.
Injector device
The power supply system of a gasoline engine with fuel injection has a specific device. To carry out maintenance of such a motor yourself, you need to understand the principle of its operation and design.
The injection system incorporates several mandatory elements (the diagram is presented below).
It includes the electronic unit control (on-board computer) (2), electric pump (3), injectors (7). Also available fuel rail(6) and pressure regulator (8). The system is necessarily monitored by temperature sensors (5). All of these components interact with each other according to a certain scheme. Also in the system there is a gas tank (1) and a gasoline filter (4).
To understand the principle of operation of the presented power system, you need to consider the interaction of the presented elements using an example. New vehicles are often equipped with a multipoint injection system. When the engine starts, fuel flows to the fuel pump. It is in the fuel tank in the fuel. Further, fuel under a certain pressure enters the line.
Injectors are installed in the ramp. It supplies gasoline. There is a sensor in the rail that regulates the fuel pressure. It determines the air pressure in the injectors and at the intake. The sensors of the system transmit information to the on-board computer about the state of the system. It synchronizes the process of supplying the mixture components, adjusting their quantity for each cylinder.
Knowing how the injection process works, you can do it yourself Maintenance gasoline engine power systems.
Maintenance of the carburetor system
Do-it-yourself maintenance and repair of gasoline engine power system devices. To do this, you need to perform a number of manipulations. They come down to checking the fastenings of the fuel lines, the tightness of all components. The condition of the exhaust system, throttle actuators, carburetor air damper is also assessed. In addition, it is necessary to monitor the state of the limiter crankshaft.
If necessary, it is necessary to clean the pipelines, replace the seals. A feature of carburetor maintenance is the need to tune it in spring and autumn.
In some cases, the cause of performance degradation carburetor engine there may be malfunctions in other nodes. Before maintenance of the fuel supply system, other components of the mechanisms must be checked.
Malfunctions in the power supply system of a carburetor-type gasoline engine can be checked with the engine running and off.
If the engine is turned off, you can evaluate the amount of gasoline in the tank, as well as the condition sealing gum under the neck stopper. The fastening of the gas tank, fuel line and all its elements is also evaluated. Other elements of the system should also be checked for the strength of the fasteners.
Then you need to start the engine. Check for leaks at the joints. You should also evaluate the condition of the filters fine cleaning and a sump. The carburetor must be properly adjusted. In accordance with the manufacturer's recommendations, the ratio of air and gasoline is selected.
Frequent malfunctions of the injector
Repair of the power supply system of an injection-type gasoline engine is somewhat different. There is a list frequent malfunctions similar systems. Knowing them, establish the cause incorrect operation motor will be easier. Over time, sensors that monitor various indicators of the state of the system fail. Periodically, they need to be checked for performance. Otherwise, the on-board computer will not be able to select an adequate dosage and the optimal fuel injection mode.
Also, over time, filters or even the injector nozzles themselves become dirty in the system. This is possible when using gasoline of insufficient quality. The filter needs to be changed periodically. You also need to pay attention to the mesh cleaner of the fuel pump. In some cases, it can be cleaned. Once every few years you need to wash the gas tank. At this point, it is also advisable to change all the filters in the system.
If they get clogged over time injector nozzles the motor will lose power. Gasoline consumption will also increase. If this malfunction is not eliminated in time, the system will overheat, the valves will burn out. In some cases, the nozzles may not close tightly enough. This is fraught with an excess of fuel in the combustion chamber. Gasoline will mix with oil. To prevent adverse effects, the nozzles must be cleaned periodically.
The power supply system of an injection-type gasoline engine may require flushing of the injectors. This procedure can be done in two ways. In the first case, the injection nozzles are not dismantled from the car. A special liquid is passed through them. The fuel line must be disconnected from the ramp. With a special compressor flushing liquid enters the injectors. This allows you to effectively clean them from contaminants. The second cleaning option involves removing the nozzles. Then they are processed in a special ultrasonic bath or on a washing stand.
Experts recommend taking into account that the power supply system of a gasoline engine in operating conditions on Russian roads subjected to increased stress. Therefore, maintenance must be carried out frequently. you need to change every 12-15 thousand kilometers, clean the nozzles every 30 thousand km.
It is important to pay attention to the quality of fuel. The higher it is, the more durable the engine and the entire system will be. Therefore, it is important to purchase gasoline at proven points of sale.
Having considered the features and structure of the power supply system of a gasoline engine, one can understand the principle of its operation. If necessary, maintenance and repairs can be done with your own hands.
The main elements, which are nozzles.
The power supply system of a carburetor engine includes: fuel tank, sediment filter, fuel lines, fuel pump, fuel fine filter, air cleaner, inlet pipeline, exhaust pipeline, exhaust pipes, muffler, fuel level control devices.
Work power system
When the engine is running the fuel pump sucks fuel from the fuel tank and delivers it through filters to the carburetor float chamber. During the intake stroke, a vacuum is created in the engine cylinder and air, having passed through the air cleaner, enters the carburetor, where it mixes with fuel vapors and is fed into the cylinder in the form of a combustible mixture, and there, mixing with the rest of the exhaust gases, a working mixture is formed. After the stroke is completed, the exhaust gases are pushed out by the piston into the exhaust pipeline and through the exhaust pipes through the muffler into the environment.
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High pressure fuel pump device YaMZ |
Power supply and exhaust gas systems of a car engine:
1 - air supply channel to the air filter; 2 - air filter; 3 - carburetor; 4 - handle for manual control of the air damper; 5 - handle for manual control of throttle valves; 6 - throttle control pedal; 7 - fuel wires; 8 - filter-sump; 9 - silencer; 10 - receiving pipes; 11 - exhaust pipeline; 12 - fuel fine filter; 13 - fuel pump; 14 - fuel gauge; 15 - fuel gauge sensor; 16 - fuel tank; 17 - neck cover fuel tank; 18 - crane; 19 - muffler exhaust pipe.
Fuel. as a fuel in carbureted engines usually use gasoline, which is obtained as a result of oil refining.
Automobile gasolines, depending on the number of easily evaporating fractions, are divided into summer and winter.
For automobile carburetor engines, gasoline A-76, AI-92, AI-98, etc. are produced. The letter “A” indicates that gasoline is automobile, the number is the lowest octane number that characterizes the detonation resistance of gasoline. Isooctane has the highest detonation resistance (its resistance is taken as 100), the smallest is n-heptane (its resistance is 0). The octane number characterizing the knock resistance of gasoline is the percentage of isooctane in such a mixture with n-heptane, which is equivalent in knock resistance to the tested fuel. For example, the test fuel detonates in the same way as a mixture of 76% iso-octane and 24% n-heptane. The octane number of this fuel is 76. The octane number is determined by two methods: motor and research. When determining the octane number by the second method, the letter “I” is added to the marking of gasoline. The octane number determines the allowable compression ratio.
Fuel tank. The car is equipped with one or more fuel tanks. The volume of the fuel tank should provide 400-600 km of car run without refueling. The fuel tank consists of two welded halves made of stamped leaded steel. Inside the tank there are baffles that give rigidity to the structure and prevent the formation of waves in the fuel. In the upper part of the tank, a filler neck is welded, which is closed with a stopper. Sometimes, for the convenience of refueling the tank with fuel, a retractable neck with a strainer is used. A fuel gauge sensor and a fuel intake tube with a strainer are mounted on the upper wall of the tank. At the bottom of the tank there is a threaded hole for draining sludge and removing mechanical impurities, which is closed with a stopper. The filler neck of the tank is tightly closed with a stopper, in the body of which there are two valves - steam and air. The steam valve opens when the pressure in the tank rises and releases the steam into the environment. Air valve opens when there is fuel consumption and a vacuum is created.
Fuel filters. Coarse and fine filters are used to clean the fuel from mechanical impurities. The coarse filter-sump separates the fuel from water and large mechanical impurities. The filter-sump consists of a housing, a sump and a filter element, which is assembled from plates 0.14 mm thick. The plates have holes and protrusions 0.05 mm high. The plate package is mounted on a rod and is pressed against the body by a spring. In the assembled state, there are slots between the plates through which fuel passes. Large mechanical impurities and water are collected at the bottom of the sump and are periodically removed through a plug hole in the bottom.
Fuel tank (a) and operation of the exhaust (b) and intake (c) valves: 1—filter-sump; 2 - tank mounting bracket; 3 — a collar of fastening of a tank; 4 - sensor of the fuel level indicator in the tank; 5 - fuel tank; 6 - crane; 7 - tank cap; 8 - neck; 9 - cork lining; 10 - rubber gasket; P - cork body; 12 - exhaust valve; 13 - spring exhaust valve; 14 - inlet valve; 15 - tank plug lever; 16 - intake valve spring.
Settling filter: 1 - fuel wire to the fuel pump; 2 - body gasket; 3 - body-cover; 4 - fuel wire from the fuel tank; 5 - filter element gasket; 6 - filter element; 7— stand; 8 - sump; 9- drain plug; 10 - filter element rod; 11 - spring; 12 - filter element plate; 13 - hole in the plate for the passage of purified fuel; 14 - protrusions on the plate; 15 - hole in the plate for racks; 16 - plug; 17 — a bolt of fastening of the case cover.
Fine fuel filters with filter elements: a - mesh; b - ceramic; 1 - body; 2 - inlet; 3— gasket; 4— filter element; 5 - removable glass-sump; 6 - spring; 7— screw fastening the glass; 8— channel for fuel removal.
Fine filter.
To purify fuel from small mechanical impurities, fine filters are used, which consist of a housing, a settling glass and a filter mesh or ceramic element. The ceramic filter element is a porous material that provides labyrinthine fuel movement. The filter is held in place by a bracket and screw.
Fuel wires connect fuel system devices and are made of copper, brass and steel tubes.
Fuel pump supply system
The fuel pump is used to supply fuel through the filters from the tank to the carburetor float chamber. Eccentric-driven diaphragm pumps are used camshaft. The pump consists of a housing in which the drive is mounted - a two-arm lever with a spring, a head where inlet and discharge valves with springs are located, and covers. The edges of the diaphragm are clamped between the body and the head. The diaphragm rod is pivotally attached to the drive lever, which allows the diaphragm to work with a variable stroke.
When the two-arm lever (rocker) lowers the diaphragm down, a vacuum is created in the cavity above the diaphragm, due to which the inlet valve opens and the supra-diaphragmatic cavity is filled with fuel. When the lever (pusher) escapes from the eccentric, the diaphragm rises under the action of a return spring. Above the diaphragm, the fuel pressure rises, the intake valve closes, the discharge valve opens and the fuel enters through the fine filter into the carburetor float chamber. When changing filters, the float chamber is filled with fuel using a manual pumping device. In the event of a diaphragm failure (crack, break, etc.), fuel enters the lower part of the housing and flows out through the control hole.
Air filter serves to clean the air entering the carburetor from dust. Dust contains the smallest crystals of quartz, which, settling on the lubricated surfaces of parts, causes wear.
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Filter requirements:
. efficiency of air purification from dust;
. low hydraulic resistance;
. sufficient dust capacity:
. reliability;
. ease of maintenance;
. design manufacturability.
According to the method of air purification, filters are divided into inertial oil and dry.
Inertial oil filter consists of an oil bath housing, a cover, an air intake and a filter element made of synthetic material.
When the engine is running, air passing through the annular slot inside the housing and, in contact with the oil surface, sharply changes the direction of movement. As a result, large dust particles in the air adhere to the surface of the oil. Then the air passes through the filter element, is cleaned of small dust particles and enters the carburetor. Thus, the air undergoes a two-stage purification. When clogged, the filter is washed.
Dry Type Air Filter consists of a body, a cover, an air intake and a filter element made of porous cardboard. Change the filter element if necessary.
Power supply systems for gasoline and diesel engines differ significantly, so we will consider them separately. So, what is a car power system?
Gasoline engine power system
There are two types of power systems for gasoline engines - carburetor and injection (injection). Because on modern cars the carburetor system is no longer used; below, we will consider only the basic principles of its operation. If necessary, you can easily find Additional information on it in numerous special editions.
Gasoline engine power system, regardless of engine type internal combustion, designed to store fuel, clean fuel and air from impurities, as well as supply air and fuel to the engine cylinders.
The fuel tank is used to store fuel in the vehicle. Modern cars use metal or plastic fuel tanks, which in most cases are located under the bottom of the body at the rear.
The power supply system of a gasoline engine can be divided into two subsystems - air supply and fuel supply. Whatever happens, in any situation, our field assistance specialists on the roads of Moscow will come and provide the necessary assistance.
The power supply system of a carburetor-type gasoline engine
In a carburetor engine, the fuel supply system works as follows.
The fuel pump (petrol pump) supplies fuel from the tank to the float chamber of the carburetor. The fuel pump, usually a diaphragm pump, is located directly on the engine. The pump is driven by an eccentric on the camshaft using a pusher rod.
Purification of fuel from contaminants is carried out in several stages. The most rough cleaning occurs with a mesh on the intake in the fuel tank. Then the fuel is filtered by a mesh at the inlet to the fuel pump. Also, a strainer-sump is installed on the carburetor inlet pipe.
In the carburetor, purified air from air filter and gasoline from the tank are mixed and fed into the engine intake pipe.
The carburetor is designed in such a way as to ensure the optimal ratio of air and gasoline in the mixture. This ratio (by mass) is approximately 15 to 1. An air-fuel mixture with this ratio of air to gasoline is called normal.
A normal mixture is necessary for the engine to operate in steady state. In other modes, the engine may require air-fuel mixtures with a different ratio of components.
A lean mixture (15-16.5 parts of air to one part of gasoline) has a lower combustion rate compared to an enriched one, but it does complete combustion fuel. The lean mixture is used at medium loads and provides high efficiency, as well as a minimum emission of harmful substances.
A lean mixture (more than 16.5 parts air to one part gasoline) burns very slowly. On lean mixture engine interruptions may occur.
A rich mixture (13-15 parts of air to one part of gasoline) has top speed combustion and is used with a sharp increase in load.
A rich mixture (less than 13 parts air to one part gasoline) burns slowly. A rich mixture is needed when starting a cold engine and then idling.
To create a mixture other than normal, the carburetor is equipped with special devices - an economizer, an accelerator pump (enriched mixture), air damper(rich mixture).
in carburetors different systems these devices are implemented in different ways, so we won't cover them in more detail here. The point is simply that carburetor type gasoline engine power supply system contains such constructs.
To change the quantity air-fuel mixture and, therefore, the engine speed serves as a throttle valve. It is she who controls the driver, pressing or releasing the gas pedal.
Injection type gasoline engine power supply system
On a vehicle with a fuel injection system, the driver also controls the engine via throttle valve, but on this analogy with the carburetor gasoline engine power system ends.
The fuel pump is located directly in the tank and has an electric drive.
The electric fuel pump is usually combined with a fuel level sensor and a strainer into a unit called the fuel module.
On most injection vehicles, the fuel from the fuel tank is pressurized into the replaceable fuel filter.
The fuel filter can be installed under the bottom of the body or in the engine compartment.
Fuel pipelines are connected to the filter with threaded or quick-detachable connections. The connections are sealed with petrol-resistant rubber rings or metal washers.
Recently, many automakers have begun to abandon the use of such filters. Fuel cleaning is carried out only by a filter installed in the fuel module.
The replacement of such a filter is not covered by the maintenance plan.
There are two main types of fuel injection systems - central fuel injection (single injection) and distributed injection, or, as it is also called, multipoint.
For automakers, central injection has become a transitional stage from a carburetor to a distributed injection and is not used on modern cars. This is due to the fact that the system central injection fuel does not allow meeting the requirements of modern environmental standards.
The central injection unit is similar to a carburetor, but instead of a mixing chamber and jets, an electromagnetic nozzle is installed inside, which opens at the command of an electronic engine control unit. Fuel injection occurs at the inlet of the intake manifold.
In system multipoint injection the number of injectors is equal to the number of cylinders.
The injectors are installed between the intake manifold and the fuel rail. The fuel rail is maintained at a constant pressure, which is usually about three bar (1 bar equals about 1 atm). To limit the pressure in the fuel rail, a regulator is used, which bleeds excess fuel back into the tank.
Previously, the pressure regulator was mounted directly on the fuel rail, and a reverse connection was used to connect the regulator to the fuel tank. fuel line. IN modern systems the power supply of the gasoline engine, the regulator is located in the fuel module and the need for a return line is eliminated.
The fuel injectors open at the command of the electronic control unit, and fuel is injected from the rail into the intake pipe, where the fuel mixes with air and enters the cylinder as a mixture.
Injector opening commands are calculated based on signals from sensors electronic system engine control. This ensures the synchronization of the fuel supply system and the ignition system.
Injection type gasoline engine power supply system provides greater performance and the ability to meet higher environmental standards than carburetor.
in a carbureted engine gasoline is used as fuel. Gasoline is a flammable liquid that is obtained from petroleum by direct distillation, or cracking. Gasoline is one of the main components of the combustible mixture. At normal conditions combustion working mixture there is a gradual increase in pressure in the engine cylinders. When using fuel over Low quality than required technical specifications car engine, the speed of combustion of the working mixture can increase by 100 times and be 2000 m / s, such a rapid combustion of the mixture is called detonation. The propensity of gasoline to detonation is conditionally characterized by an octane number, the higher the octane number of gasoline, the less prone it is to detonation. Gasoline with a higher octane rating is used in automobile engines with a higher compression ratio. To reduce detonation, ethyl liquid is added to gasoline.
In the cylinders of an automobile engine, the working process proceeds quite quickly. For example, if crankshaft rotates at a speed of 2000 rpm, then each cycle takes 0.015 s. To do this, it is necessary that the speed of combustion of the fuel is 25-30 m/s. However, the combustion of fuel in the combustion chamber is slower. In order to increase the rate of combustion, the fuel is crushed into tiny particles and mixed with air. It has been established that for normal combustion of 1 kg of fuel, 15 kg of air is needed, a mixture with such a ratio (1:15) is called normal. However, at this ratio, complete combustion of the fuel does not occur. For complete combustion of fuel, more air is needed and the ratio of fuel to air should be 1:18. Such a mixture is called lean. With an increase in the ratio, the combustion rate decreases sharply, and at a ratio of 1:20, ignition does not occur at all. But the highest engine power is achieved at a ratio of 1:13, in which case the combustion rate is close to optimal. Such a mixture is called enriched. With this composition of the mixture, complete combustion of the fuel does not occur, therefore, with an increase in power, fuel consumption increases.
When the engine is running, the following modes are distinguished:
1) cold engine start;
2) operation at a low crankshaft speed (idling);
3) work at partial (average) loads;
4) work at full loads;
5) work with a sharp increase in load or crankshaft speed (acceleration).
In each individual mode, the composition of the combustible mixture must be different.
The engine power system is designed to prepare and supply a combustible mixture to the combustion chambers, in addition, the power system regulates the amount and composition of the working mixture.
Carburetor engine power system includes the following elements:
1) fuel tank;
2) fuel lines;
3) fuel filters;
4) fuel pump;
5) carburetor;
6) air filter;
7) exhaust manifold:
8) intake manifold;
9) exhaust silencer.
On modern cars, instead of carburetor power systems, they are increasingly using fuel injection systems. On engines cars a distributor fuel injection system or a centralized fuel injection system can be installed single point injection fuel.
Fuel injection systems have a number of advantages over carburetor power systems:
1) the absence of additional resistance to air flow in the form of a carburetor diffuser, which contributes to better filling of the combustion chambers of the cylinders and obtaining higher power;
2) improving the scavenging of cylinders by using the possibility of more long period overlapping valves (with simultaneously open inlet and outlet valves);
3) improving the quality of the preparation of the working mixture by purging the combustion chambers with clean air without the admixture of fuel vapors;
4) more accurate distribution of fuel over the cylinders, which makes it possible to use gasoline with a lower octane number;
5) more accurate selection of the composition of the working mixture at all stages of engine operation, taking into account its technical condition.
In addition to the advantages, the injection system has one significant disadvantage. The fuel injection system has more a high degree the complexity of manufacturing parts, and also this system includes many electronic components, which leads to an increase in the cost of the car and the complexity of its maintenance.
Distributor fuel injection system is the most modern and perfect. The main functional element of this system is the electronic control unit (ECU). The ECU is essentially the on-board computer of the car. The ECU provides optimal control of the mechanisms and systems of the engine, provides the most economical and efficient work engine with maximum protection environment in all modes.
The fuel injection system consists of:
1) air supply subsystems with throttle;
2) fuel supply subsystems with injectors, one for each cylinder;
3) afterburning systems for modified gases;
4) systems for capturing and liquefying gasoline vapors.
In addition to the control functions, the ECU has self-learning functions, diagnostic and self-diagnosis functions, and it also stores in memory the previous parameters and characteristics of the engine, changing its technical condition.
Central single point fuel injection system differs from the distributor injection system in that it does not have a separate (distributive) gasoline injection for each cylinder. The fuel supply in this system is carried out using a central injection module with one electromagnetic nozzle. The air-fuel mixture is controlled by a throttle valve. The distribution of the working mixture over the cylinders is carried out, as in the carburetor power system. The remaining elements and functions of this power supply system are the same as in the distribution injection system.
Gasoline engine fuel supply system⭐ is designed for placing and cleaning fuel, as well as preparing a combustible mixture of a certain composition and supplying it to cylinders in required quantity in accordance with the operating mode of the engine (with the exception of engines with direct injection, the power system of which ensures that gasoline enters the combustion chamber in the required amount and under sufficient pressure).
Petrol, like diesel fuel, is a product of the distillation of petroleum and consists of various hydrocarbons. The number of carbon atoms in gasoline molecules is 5 - 12. Unlike diesel engines in gasoline engines, fuel should not be intensively oxidized during compression, as this can lead to detonation (explosion), which will adversely affect performance, efficiency and power engine. The knock resistance of gasoline is measured by the octane number. The larger it is, the higher the knock resistance of the fuel and the allowable compression ratio. At modern gasolines the octane number is 72-98. In addition to anti-knock resistance, gasoline must also have low corrosivity, low toxicity and stability.
The search (based on environmental considerations) for alternatives to gasoline as the main fuel for internal combustion engines has led to the creation of ethanol fuel, consisting mainly of ethyl alcohol, which can be obtained from plant biomass. Distinguish pure ethanol (international designation - E100), containing only ethyl alcohol; and a mixture of ethanol with gasoline (most often 85% ethanol with 15% gasoline; designation - E85). In terms of its properties, ethanol fuel approaches high-octane gasoline and even surpasses it in terms of properties. octane number(more than 100) and calorific value. That's why this species fuel can be successfully used instead of gasoline. The only disadvantage of pure ethanol is its high corrosivity, requiring additional protection from corrosion of fuel equipment.
High requirements are imposed on the units and components of the fuel supply system of a gasoline engine, the main of which are:
- tightness
- fuel dosing accuracy
- reliability
- serviceability
Currently, there are two main methods for preparing a combustible mixture. The first one is related to the use special device- a carburetor in which air is mixed with gasoline in a certain proportion. The second method is based on the forced injection of gasoline into the engine intake manifold through special nozzles (injectors). Such engines are often referred to as injection engines.
Regardless of the method of preparing a combustible mixture, its main indicator is the ratio between the mass of fuel and air. The mixture, when ignited, should burn very quickly and completely. This can be achieved only with good mixing in a certain proportion of air and gasoline vapors. The quality of the combustible mixture is characterized by the excess air coefficient a, which is the ratio of the actual mass of air per 1 kg of fuel in this mixture to the theoretically necessary one, which ensures complete combustion of 1 kg of fuel. If 14.8 kg of air falls on 1 kg of fuel, then such a mixture is called normal (a \u003d 1). If there is a little more air (up to 17.0 kg), the mixture is lean, and a = 1.10 ... 1.15. When there is more than 18 kg of air and a > 1.2, the mixture is called lean. Reducing the proportion of air in the mixture (or increasing the proportion of fuel) is called its enrichment. At a = 0.85 ... 0.90 the mixture is enriched, and at a< 0,85 - богатая.
When a mixture of normal composition enters the engine cylinders, it works stably with average power and economy. When running on a lean mixture, engine power is slightly reduced, but its efficiency is noticeably increased. On a lean mixture, the engine is unstable, its power drops, and specific consumption fuel increases, so excessive lean mixture is undesirable. When an enriched mixture enters the cylinders, the engine develops highest power but fuel consumption also increases. When working on rich mixture gasoline burns incompletely, which leads to a decrease in engine power, an increase in fuel consumption and the appearance of soot in the exhaust tract.
Carburetor power systems
Let us first consider carburetor power systems, which until recently were widespread. They are simpler and cheaper than injector ones, do not require highly qualified maintenance during operation, and in some cases are more reliable.
Carburetor engine fuel supply system includes fuel tank 1, coarse 2 and fine 4 fuel filters, fuel priming pump 3, carburetor 5, inlet pipeline 7 and fuel lines. When the engine is running, fuel from tank 1 is supplied by pump 3 through filters 2 and 4 to the carburetor. There it is mixed in a certain proportion with the air coming from the atmosphere through the air cleaner 6. Formed in the carburetor combustible mixture through the intake manifold 7 enters the engine cylinders.
fuel tanks V power plants with carburetor engines are similar to the tanks of diesel fuel systems. The difference between the tanks for gasoline is only their better tightness, which does not allow gasoline to leak out even if the vehicle rolls over. To communicate with the atmosphere, two valves are usually installed in the tank filler cap - inlet and outlet. The first of them provides air to the tank as the fuel is consumed, and the second, loaded with a stronger spring, is designed to communicate the tank with the atmosphere when the pressure in it is higher than atmospheric (for example, at high ambient temperature).
Filters for carbureted engines similar to filters used in diesel fuel systems. Lamellar-slit and mesh filters are installed on trucks. For fine cleaning, cardboard and porous ceramic elements are used. In addition to special filters, individual units of the system have additional filter screens.
Fuel pump serves to force the supply of gasoline from the tank to the float chamber of the carburetor. On carbureted engines, a diaphragm-type pump is usually used, driven by a camshaft eccentric.
Depending on the engine operating mode, the carburetor allows you to prepare a mixture of normal composition (a \u003d 1), as well as a lean and enriched mixture. At low and medium loads, when it is not required to develop maximum power, should be cooked in a carburetor and fed into the cylinders lean mixture. At heavy loads(the duration of their action is usually short) it is necessary to prepare an enriched mixture.
Rice. Scheme of the fuel supply system of the carburetor engine:
1 - fuel tank; 2 - filter by fuel cleaning pipe; 3 - fuel priming pump; 4 - fine filter; 5 - carburetor; 6 - air cleaner; 7 - intake manifold
IN general case the carburetor includes the main metering and starting device, idling and forced idling systems, an economizer, an accelerator pump, balancing device and limiter of the maximum frequency of rotation of the crankshaft (for trucks). The carburetor may also contain an econostat and a high-altitude corrector.
Main dosing device functions in all main modes of engine operation in the presence of vacuum in the diffuser of the mixing chamber. Main constituent parts The devices are a mixing chamber with a diffuser, a throttle valve, a float chamber, a fuel jet and atomizer tubes.
Launcher devices o is designed to ensure the start of a cold engine, when the speed of the crankshaft rotated by the starter is low and the vacuum in the diffuser is small. In this case, for a reliable start, it is necessary to supply a highly enriched mixture to the cylinders. The most common starting device is an air damper installed in the intake pipe of the carburetor.
Idle system serves to ensure the operation of the engine without load with a low crankshaft speed.
Forced idle system allows you to save fuel while driving in engine braking mode, i.e. when the driver releases the accelerator pedal associated with the carburetor throttle while in gear.
Economizer designed for automatic enrichment of the mixture when the engine is running at full load. In some types of carburetors, in addition to the economizer, an econostat is used to enrich the mixture. This device supplies an additional amount of fuel from the float chamber to the mixing chamber only with a significant vacuum in the upper part of the diffuser, which is possible only when the throttle is fully opened.
accelerator pump provides forced injection into the mixing chamber of additional portions of fuel with a sharp opening of the throttle. This improves the throttle response of the engine and, accordingly, the vehicle. If there were no accelerator pump in the carburetor, then with a sharp opening of the damper, when the air flow increases rapidly, due to the inertia of the fuel, the mixture would be very lean at first.
Balancing device serves to ensure the stability of the carburetor. It is a tube connecting the intake pipe of the carburetor with the air cavity of a sealed (not communicating with the atmosphere) float chamber.
Engine speed limiter mounted on truck carburetors. The most widely used restrictor is the pneumatic centrifugal type.
Fuel injection systems
Injection fuel systems At present, they are used much more often than carburetor ones, especially on gasoline engines of cars. Injection of gasoline into the intake manifold injection engine is carried out using special electromagnetic injectors (injectors) installed in the cylinder head and controlled by a signal from the electronic unit. This eliminates the need for a carburetor, since the combustible mixture is formed directly in the intake manifold.
There are single and multi-point injection systems. In the first case, only one nozzle is used to supply fuel (with its help, a working mixture is prepared for all engine cylinders). In the second case, the number of nozzles corresponds to the number of engine cylinders. Injectors are installed in close proximity to intake valves. Fuel is injected in a finely atomized form onto the outer surfaces of the valve heads. atmospheric air, entrained in the cylinders due to vacuum in them during intake, washes fuel particles from the valve heads and contributes to their evaporation. Thus, the air-fuel mixture is prepared directly at each cylinder.
In an engine with multipoint injection when power is supplied to the electric fuel pump 7 through the ignition lock 6, gasoline from the fuel tank 8 through the filter 5 is supplied to the fuel rail 1 (injector rail), common to all electromagnetic injectors. The pressure in this rail is regulated by the regulator 3, which, depending on the vacuum in the inlet pipe 4 of the engine, sends part of the fuel from the rail back to the tank. It is clear that all injectors are under the same pressure, equal to the pressure of the fuel in the rail.
When it is required to supply (inject) fuel, an electric current is supplied to the solenoid coil of the injector 2 from the electronic unit of the injection system for a strictly defined period of time. The core of the electromagnet, connected to the nozzle needle, is retracted, opening the way for fuel into the intake manifold. Submission duration electric current, i.e. the duration of fuel injection, is regulated by the electronic unit. The program of the electronic unit in each mode of engine operation ensures optimal fuel supply to the cylinders.
Rice. Scheme of the fuel supply system of a gasoline engine with multipoint injection:
1 - fuel rail; 2 - nozzles; 3 - pressure regulator; 4 - inlet pipe of the engine; 5 - filter; 6 - ignition switch; 7 - fuel pump; 8 - fuel tank
In order to identify the engine operating mode and, in accordance with it, calculate the injection duration, signals from various sensors are fed into the electronic unit. They measure and convert the values of the following engine operation parameters into electrical impulses:
- throttle angle
- degree of vacuum in the intake manifold
- crankshaft speed
- intake air and coolant temperature
- exhaust oxygen concentration
- Atmosphere pressure
- battery voltage
- and etc.
Engines with gasoline injection into the intake manifold have a number of undeniable advantages over carbureted engines:
- fuel is distributed more evenly over the cylinders, which increases the efficiency of the engine and reduces its vibration, due to the absence of a carburetor, resistance is reduced intake system and improved cylinder filling
- it becomes possible to slightly increase the compression ratio of the working mixture, since its composition in the cylinders is more homogeneous
- the optimal correction of the composition of the mixture is achieved when switching from one mode to another
- provides better engine response
- exhaust gases contain less harmful substances
At the same time, power systems with gasoline injection into the intake manifold have a number of disadvantages. They are complex and therefore relatively expensive. Maintenance of such systems requires special diagnostic tools and devices.
Most promising system fuel supply for gasoline engines is currently considered to be a rather complex system with direct injection of gasoline into the combustion chamber, which allows the engine to operate for a long time on a very lean mixture, which increases its efficiency and environmental performance. At the same time, due to the existence of a number of problems in the system direct injection have not yet been widely adopted.
