Organizational part (15 min.).

Lesson 6. Fuel supply system of the Rotax 912 engine

TOPIC 4. Fuel supply system of the power plant Rotax 912.

Astana 2012

EDUCATIONAL AND EDUCATIONAL OBJECTIVES

POWER PLANT CONSTRUCTION

TOPIC 4. Fuel supply system of the Rotax 912 engine

1. To acquaint cadets with the structure of the fuel supply system of an internal combustion engine, with the general purpose of its units and systems.

2. Remind the students of some physics data.

3. To acquaint cadets with the basic technical data of the Rotax 912 engine fuel supply system.

4. To instill in cadets the ability to act competently in case of possible failures of the fuel supply system of the Rotax 912 engine.

TIME:3 hours

METHOD:lecture

A PLACE:classroom

DESIGNED BY: N.N.

Issues under study:

6.1. Organizational part (15 min.).

6.2. Purpose and design of the fuel supply system for internal combustion engines. (50 min.).

6.3. Composition, general diagram and operation of the fuel supply system for the Rotax 912 engine. (45 min.).

6.4. Basic data of the power supply system of the Rotax 912 engine (20 min.).

6.5. The final part (5 min.).

Poll on topic # 3.

The order of studying topic number 4.

Supply system fuelm of the internal combustion engine of the engine is intended for storing, cleaning and supplying fuel, cleaning air, preparing a combustible mixture and feeding it into the engine cylinders. At different operating modes of the engine, the quantity and quality of the combustible mixture must be different, and this is also provided by the fuel supply system. Since we are considering the operation of a carburetor gasoline engine, in the future, fuel will mean exactly gasoline.

Ri.s 6.1. The layout of the power system elements
1 - filler neck with plug; 2 - fuel tank; 3 - fuel level indicator sensor with a float; 4 - fuel intake with filter; 5 - fuel lines; 6 - fine fuel filter; 7 - fuel pumps; 8 - carburetor float chamber with a float; 9 - air filter; 10 - carburetor mixing chamber; 11 - inlet valve; 12 - inlet pipeline; 13 - combustion chamber

The power supply system (see figure 6.1.) Consists of:

fuel tank;

fuel filters;

fuel pump,

air filter,

carburetor;

fuel lines,

The fuel tank is a container for storing fuel. It is usually located in the safer part of the aircraft (fuselage, wing). Gasoline flows from the fuel tank to the carburetor through fuel lines. For a prudent driver, the first stage of gasoline purification occurs when it is poured into the fuel tank. To do this, install a mesh or some other filter in the filler neck of the tank. The second stage of fuel cleaning is a grid on the fuel intake inside the tank. It does not allow the remaining impurities and water to get into the engine power system. The presence and amount of gasoline in the tank is monitored according to the fuel level indicator. When there is a minimum remaining fuel on the instrument panel, the corresponding red light comes on - a reserve lamp. Fuel consumption is controlled according to the readings of the flow meter displayed on the engine parameters control device.

Fuel filter - the next, third stage of fuel purification. The filter is located in the engine compartment and is designed for fine cleaning of gasoline supplied to the fuel pump (it is possible to install a filter after the pump).

Fuel pump - designed for forced supply of fuel from the tank to the carburetor. The pump consists of (see fig. 6.2.):

body, diaphragm with spring and drive mechanism, intake and discharge (exhaust) valves. It also contains a mesh filter for the next - fourth stage of gasoline purification. The fuel pump is driven from the engine camshaft. When the shaft rotates, the eccentric on them runs onto the fuel pump drive rod. The stem begins to press on the lever, which, in turn, forces the diaphragm to go down. Above it, a vacuum is created and the inlet valve, overcoming the force of the spring, opens. A portion of the fuel from the tank is sucked into the space above the diaphragm. When the eccentric escapes from the rod, the diaphragm is released from the action of the lever and, due to the rigidity of the spring, rises up. The resulting pressure closes the inlet valve and opens the delivery valve. Gasoline above the diaphragm is sent to the carburetor. With the next run of the eccentric on the rod, gasoline is sucked in and the process is repeated. Please note that the supply of gasoline to the carburetor is only due to the force of the spring, which raises the diaphragm. This means that when the carburetor's float chamber is full and the needle valve (see Fig. 6.1.) Blocks the path of gasoline, the diaphragm of the fuel pump will remain in the lower position. And until the engine has consumed part of the fuel from the carburetor, the spring will not be able to "push" the next portion of gasoline from the pump.

Figure: 6.2. The scheme of the fuel pump a) fuel suction, b) fuel injection

1 - discharge pipe; 2 - coupling bolt; 3 - cover; 4 - suction pipe; 5 - inlet valve with spring; 6 - body; 7 - pump diaphragm; 8 - manual pumping lever; 9 - thrust; 10 - mechanical pumping lever; 11 - spring; 12 - stock; 13 - eccentric; 14 - pressure valve with a spring; 15 - fuel filter

Since the fuel tank is located below the carburetor, there is a need for a forced supply of gasoline. In this case, an electric pump is used to pump fuel.

Air filter (Fig. 6.3.) is designed to clean the air entering the engine cylinders. The filter is installed on top of the carburetor air intake. When the filter becomes dirty, the resistance to air movement increases, which can lead to increased fuel consumption, as the fuel mixture will be too rich in gasoline.

Figure: 6.3. Air filter

The carburetor is designed for preparing a combustible mixture and feeding it into the engine cylinders. Depending on the operating modes of the engine, the carburetor changes the quality (ratio of gasoline and air) and the amount of this mixture. The carburetor is one of the most complex devices in a car. It consists of many parts and has several systems that take part in the preparation of the combustible mixture, ensuring the smooth operation of the engine. Let's look at the device and the principle of operation of the carburetor in a somewhat simplified diagram (Figure 6.4.).

Figure: 6.4. The scheme of the simplest carburetor

1 - fuel pipe; 2 - float with a needle valve; 3 - fuel jet; 4 - sprayer; 5 - carburetor body; 6 - air damper; 7 - diffuser; 8 - throttle valve

The simplest carburetor consists of: a float chamber, a float with a needle shut-off valve, an atomizer, a mixing chamber, a diffuser, air and throttle valves, fuel and air channels with jets.

How is the combustible mixture prepared? When the piston moves in the cylinder from top dead center to bottom dead center (intake stroke), a vacuum is created above it. The air flow through the air filter and carburetor rushes into the vacated volume of the cylinder. When air passes through the carburetor, fuel is sucked out of the float chamber through the sprayer, which is located at the narrowest point of the mixing chamber - the diffuser. This is due to the pressure difference in the carburetor's float chamber, which is connected to the atmosphere, and in the diffuser, where a significant vacuum is created. The air stream crushes the fuel flowing out of the atomizer and mixes with it. At the outlet of the diffuser, the final mixing of gasoline with air takes place, and then the ready-made combustible mixture enters the cylinders.

From the operation diagram of a simple carburetor (see Fig. 6.4.), It can be understood that the engine will not work normally if the fuel level in the float chamber is higher than normal, since in this case more gasoline will pour out than necessary. If the level of gasoline is less than the norm, then its content in the mixture will be less, which will again disrupt the correct operation of the engine. Based on this, the amount of gasoline in the chamber should be unchanged. The fuel level in the carburetor's float chamber is regulated by a special float, which, dropping together with the needle shut-off valve, allows gasoline to enter the chamber. When the float chamber begins to fill, the float floats up and closes the gas passage with its valve.

Throttle valve, by means of levers or a cable, connected to the engine control handle. In the initial position, the damper is closed. when the throttle valve is opened, the air flow through the carburetor increases. In this case, the more the throttle valve opens, the more fuel is sucked out, since the volume and speed of the air flow passing through the diffuser increases and the “sucking” vacuum increases. When the throttle valve is closed, the air flow decreases and less and less combustible mixture enters the cylinders. The engine "loses speed", the engine torque decreases. When the throttle valve is fully closed, the engine is idling, the carburetor has its own channels through which air can still get under the throttle valve, mixing with gasoline along the way (see Figure 6.5.).

Figure: 6.5. Idling system operation diagram

1 - fuel channel of the idling system; 2 - fuel jet of the idling system; 3 - needle valve of the carburetor float chamber; 4 - fuel jet; 5 - throttle valve; 6 - screw "quality" of the idling system; 7 - air jet of the idle system; 8 - air damper

With the throttle valve closed, the air has no other way but to pass through the idle channel into the cylinders. And on the way, it sucks gasoline from the fuel channel and, mixing with it, again turns into a combustible mixture. The mixture, almost ready for "use", enters the throttle space, where it is finally mixed and then enters the engine cylinders.

When starting a cold engine, the throttle grip (choke knob) is used to control the air damper carburetor. If you close this flap (pull the "suction" handle towards you), then the vacuum in the mixing chamber of the carburetor will increase. As a result, the fuel from the float chamber begins to be sucked out more intensively and the combustible mixture is enriched, which is necessary to start a cold engine.

The combustible mixture is called normal, if one part of gasoline accounts for 15 parts of air (1:15). This ratio may vary depending on various factors, and will change accordingly mix quality. If there is more air, then the mixture is called impoverished or poor. If there is less air - enriched or rich.The lean and lean mixture is hungry food for the engine, it contains less fuel than normal. Rich and rich mixtures are too high-calorie food, as they have more fuel than necessary.

The main the purpose of the vehicle fuel system are the supply of fuel from the tank, filtration, the formation of a combustible mixture and its supply to the cylinders. There are several types of fuel systems for. The most common in the 20th century was carburetor system fuel mixture supply. The next step was the development of fuel injection using a single nozzle, the so-called mono injection. The use of this system has reduced fuel consumption. Currently, the third fuel supply system is used - injection. In this system, pressurized fuel is supplied directly to the intake manifold. The number of injectors is equal to the number of cylinders.

injection andcarburetor option

Fuel system device

All engine power systems are similardiffer only in the methods of mixture formation. The fuel system includes the following elements:

1. The fuel tank is designed for storing fuel and is a compact container with a fuel intake device (pump) and, in some cases, coarse filtration elements.
2. Fuel lines are a set of fuel pipes, hoses and are designed to transport fuel to the mixing device.
3. Mixing devices ( carburetor, mono injection, injector) Is a mechanism in which fuel and air (emulsion) are combined for further supply to the cylinders at (intake stroke).
4. The control unit for the operation of the mixture formation device (injection power systems) is a complex electronic device for controlling the operation of fuel injectors, cut-off valves, control sensors.
5. A fuel pump, usually a submersible pump, is designed to pump fuel into the fuel line. It is an electric motor connected to a liquid pump in a sealed case. Lubricated directly with fuel and long-term operation with a minimum amount of fuel, leads to engine failure... In some engines, the fuel pump was attached directly to the engine and was driven by rotating the intermediate shaft, or camshaft.
6. Additional coarse and fine filters... Installed filter elements in the fuel supply chain.

How the fuel system works

Let's consider the operation of the entire system as a whole. The fuel from the tank is sucked in by the pump and is fed through the fuel line through the cleaning filters to the mixture formation device. In the carburetor, the fuel enters the float chamber, where it is then fed through the calibrated jets to the mixture formation chamber. Mixed with air, the mixture enters the intake manifold through the throttle valve. After opening the intake valve, it is fed into the cylinder. AT mono injection system fuel is supplied to the injector, which is controlled by the electronic unit. At the right time, the nozzle opens and the fuel enters the mixture formation chamber, where, as in the carburetor system, it mixes with air. Further, the process is the same as in the carburetor.

AT injection system fuel is supplied to the injectors, which are opened by control signals from the control unit. The injectors are connected to each other by a fuel line, which always contains fuel. All fuel systems have a fuel return line, through which excess fuel is drained into the tank.

The power supply system of a diesel engine is similar to a gasoline one. True, fuel is injected directly into the combustion chamber of the cylinder, under high pressure. Mixing takes place in the cylinder. A high pressure pump (high pressure fuel pump) is used to supply fuel under high pressure.

All modern cars with gasoline engines use the fuel injection system, since it is more advanced than the carburetor one, despite the fact that it is structurally more complex.

The injection engine is not new, but it became widespread only after the development of electronic technology. This is because it was very difficult to mechanically organize the control of a system with high precision. But with the advent of microprocessors, this has become quite possible.

The injection system is distinguished by the fact that gasoline is supplied in strictly predetermined portions forcibly to the manifold (cylinder).

The main advantage possessed by the injector power supply system is the observance of the optimal proportions of the components of the combustible mixture in different operating modes of the power plant. This results in better power output and economical consumption of gasoline.

System design

The fuel injection system consists of electronic and mechanical components. The first monitors the operating parameters of the power unit and, on their basis, gives signals for the actuation of the executive (mechanical) part.

The electronic component includes a microcontroller (electronic control unit) and a large number of tracking sensors:

• crankshaft position;
• mass air flow;
• throttle position;
• detonation;
• coolant temperature;
• air pressure in the intake manifold.

Injector system sensors

Some cars may have a few more additional sensors. They all have one task - to determine the operating parameters of the power unit and transfer them to the ECU

As for the mechanical part, it includes the following elements:

• electric fuel pump;
• fuel lines;
• filter;
• pressure regulator;
• fuel rail;
• nozzles.

Simple fuel injection system

How it works

Now we will consider the principle of operation of the injection engine separately for each component. With the electronic part, in general, everything is simple. The sensors collect information about the speed of rotation of the crankshaft, air (supplied to the cylinders, as well as its residual part in the exhaust gases), the position of the throttle (associated with the accelerator pedal), and coolant temperature. These data are constantly transmitted by the sensors to the electronic unit, due to which a high accuracy of gasoline dosage is achieved.

The ECU compares the information received from the sensors with the data entered in the cards, and on the basis of this comparison and a number of calculations, it controls the executive part. some gasoline, others - so much).

1973 Toyota's first injection engine

To make it clearer, let us consider in more detail the algorithm of the electronic unit, but according to a simplified scheme, since in reality a very large amount of data is used in the calculation. In general, all this is aimed at calculating the time length of the electrical impulse that is supplied to the injectors.

Since the scheme is simplified, we will assume that the electronic unit calculates only a few parameters, namely the basic time pulse length and two coefficients - the coolant temperature and the oxygen level in the exhaust gases. To obtain the result, the ECU uses a formula in which all the available data is multiplied.

To obtain the basic pulse length, the microcontroller takes two parameters - the crankshaft rotation speed and the load, which can be calculated from the manifold pressure.

For example, the engine speed is 3000, and the load is 4. The microcontroller takes this data and compares it with the table entered in the map. In this case, we get a base time pulse length of 12 milliseconds.

But for the calculations, you also need to take into account the coefficients, for which readings are taken from the coolant temperature sensors and the lambda probe. For example, the temperature is 100 degrees, and the oxygen level in the exhaust gases is 3. The ECU takes this data and compares it with several more tables. Suppose the temperature coefficient is 0.8 and the oxygen coefficient is 1.0.

Having received all the necessary data, the electronic unit calculates. In our case, 12 is multiplied by 0.8 and 1.0. As a result, we get that the pulse should be 9.6 milliseconds.

The described algorithm is very simplified, in fact, more than a dozen parameters and indicators can be taken into account in the calculations.

Since the data is constantly fed to the electronic unit, the system almost instantly reacts to changes in the engine operating parameters and adjusts to them, providing optimal mixture formation.

It is worth noting that the electronic unit controls not only the fuel supply, its task also includes adjusting the ignition angle to ensure optimal engine operation.

Now about the mechanical part. Everything is very simple here: a pump installed in the tank pumps gasoline into the system, moreover, under pressure to ensure a forced supply. The pressure must be certain, so a regulator is included in the circuit.

Gasoline is fed through the highways to the ramp, which connects all the injectors. An electrical impulse supplied from the ECU leads to the opening of the injectors, and since gasoline is under pressure, it is simply injected through the opened channel.

Types and types of injectors

There are two types of injectors:

1. With single point injection. Such a system is outdated and no longer used on cars. Its essence is that there is only one injector installed in the intake manifold. This design did not provide an even distribution of fuel over the cylinders, so its operation was similar to the carburetor system.
2. Multipoint injection. This type is used on modern cars. Here, a separate nozzle is provided for each cylinder, therefore such a system is distinguished by high dosing accuracy. The injectors can be installed both in the intake manifold and in the cylinder itself (injection).

On a multi-point fuel injection system, several types of injection can be used:

1. Simultaneous. In this type, a pulse from the ECU goes to all the injectors at once, and they open together. Now this injection is not used.
2. Paired, it is also paralleled. In this type, the nozzles work in pairs. Interestingly, only one of them supplies fuel directly in the intake stroke, while the second does not match. But since the engine is a 4-stroke, with a valve timing system, the timing mismatch does not affect the engine's performance.
3. Phased. In this type, the ECU sends signals to open for each injector separately, so the injection occurs with the same stroke.

It is noteworthy that a modern fuel injection system can use several types of injection. So, in the normal mode, phased injection is used, but in the event of a transition to emergency operation (for example, one of the sensors has failed), the injection engine switches to twin injection.

Sensor feedback

One of the main sensors, on the readings of which the ECU regulates the opening time of the injectors, is the lambda probe installed in the exhaust system. This sensor detects the residual (unburned) amount of air in the gases.

Evolution of the lambda probe from Bosch

This sensor provides the so-called "feedback". Its essence is as follows: the ECU carried out all the calculations and gave an impulse to the injectors. Fuel entered, mixed with air and burned out. The resulting exhaust gases with unburned particles of the mixture are discharged from the cylinders through the exhaust gas system, in which the lambda probe is installed. Based on its readings, the ECU determines whether all the calculations were carried out correctly and, if necessary, makes adjustments to obtain the optimal composition. That is, on the basis of the already carried out stage of fuel supply and combustion, the microcontroller makes calculations for the following.

It is worth noting that during the operation of the power plant, there are certain modes in which the readings of the oxygen sensor will be incorrect, which may disrupt the operation of the motor or a mixture with a certain composition is required. In such modes, the ECU ignores the information from the lambda probe, and it sends signals to supply gasoline based on the information stored in the cards.

In different modes, the feedback works like this:

• Starting the motor. For the engine to start, a rich fuel mixture with an increased percentage of fuel is needed. And the electronic unit provides this, and for this it uses the given data, and it does not use the information from the oxygen sensor;
• Warming up. In order for the injection engine to reach the operating temperature faster, the ECU sets increased engine speed. At the same time, he constantly monitors its temperature, and as it warms up, he adjusts the composition of the combustible mixture, gradually depleting it until its composition becomes optimal. In this mode, the electronic unit continues to use the data specified in the cards, still not using the readings of the lambda probe;
• Idling. In this mode, the engine is already fully warmed up, and the exhaust gas temperature is high, therefore, the conditions for the correct operation of the lambda probe are met. The ECU is already starting to use the readings of the oxygen sensor, which makes it possible to establish the stoichiometric composition of the mixture. With this composition, the greatest power output of the power plant is provided;
• Movement with a smooth change in engine speed. To achieve economical fuel consumption at maximum power output, a mixture with a stoichiometric composition is needed, therefore, in this mode, the ECU regulates the supply of gasoline based on the readings of the lambda probe;
• A sharp increase in revs. In order for the injection engine to react normally to such an action, a somewhat enriched mixture is needed. To provide it, the ECU uses map data, and not the readings of the lambda probe;
• Braking by the motor. Since this mode does not require power output from the motor, it is enough that the mixture simply does not allow the power plant to stop, and a lean mixture is suitable for this. For its manifestation, the readings of the lambda probe are not needed, therefore the ECU does not use them.

As you can see, although the lambda probe is very important for the operation of the system, the information from it is not always used.

Finally, we note that, although the injector is a structurally complex system and includes many elements, the breakdown of which immediately affects the functioning of the power plant, but it provides more rational gasoline consumption, and also increases the environmental friendliness of the car. Therefore, there is no alternative to this power system yet.

Autoleek

In a carburetor 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. Under normal conditions of combustion of the working mixture, a gradual increase in pressure in the engine cylinders occurs. When using fuel of a lower quality than required by the technical parameters of an automobile engine, the combustion rate 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 detonate is conventionally characterized by its octane number, the higher the octane number of gasoline, the less prone to detonation it is. Gasoline with a higher octane number 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 work process proceeds quite quickly. For example, if the crankshaft rotates at 2000 rpm, then each stroke is completed in 0.015 seconds. For this, it is necessary that the fuel combustion rate is 25-30 m / s. However, the combustion of fuel in the combustion chamber is slower. In order to increase the combustion rate, 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 this ratio (1:15) is called normal. However, with such a ratio, complete combustion of the fuel does not occur. More air is needed for complete combustion of fuel and the ratio of fuel to air should be 1:18. This mixture is called lean. With an increase in the ratio, the combustion rate drops sharply, and at a ratio of 1:20, no ignition occurs at all. But the greatest engine power is achieved at a ratio of 1:13, in which case the combustion rate is close to optimal. This mixture is called enriched. With this mixture composition, complete combustion of fuel does not occur, therefore, with an increase in power, fuel consumption increases.

When the engine is running, the following modes are distinguished:
1) starting a cold engine;
2) work at low speed of the crankshaft (idle mode);
3) work at partial (medium) loads;
4) work at full loads;
5) work with a sharp increase in load or speed of the crankshaft (acceleration).

For 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) muffler of noise of exhaust gases.

On modern cars, instead of carburetor power systems, they are increasingly used fuel injection systems ... Passenger car engines can be equipped with a multi-point fuel injection system or a central single-point fuel injection system.

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 a higher power;
2) improvement of cylinder purging by using the possibility of a longer valve overlap period (with simultaneously open intake and exhaust valves);
3) improving the quality of preparation of the working mixture by blowing the combustion chambers with clean air without admixture of fuel vapors;
4) more accurate distribution of fuel among 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 drawback. The fuel injection system has a higher degree of complexity in the manufacture of parts, and this system also includes many electronic components, which leads to an increase in the cost of the car and to the complexity of its maintenance.

Distribution 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 performs optimal control of the mechanisms and systems of the engine, provides the most economical and efficient engine operation with maximum environmental protection in all modes.

The distribution fuel injection system consists of:
1) air supply subsystem with a throttle valve;
2) fuel supply subsystems with nozzles, 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-diagnostic functions, and it also stores the previous parameters and characteristics of the engine's operation, changes in its technical state in memory.

Central single point fuel injection system differs from the distribution injection system in that it does not have a separate (distribution) gasoline injection for each cylinder. Fuel supply in this system is carried out using a central injection module with one electromagnetic injector. The air-fuel mixture supply is controlled by the throttle valve. The distribution of the working mixture over the cylinders is carried out as in the carburetor power system. The rest of the elements and functions of this power supply system are the same as in the distribution injection system.

The power supply system is an integral part of any internal combustion engine. It is designed to solve the following tasks.

□ Fuel storage.

□ Fuel cleaning and feeding it to the engine.

□ Purification of the air used for the preparation of a combustible mixture.

□ Preparation of a combustible mixture.

□ Supply of a combustible mixture to the engine cylinders.

□ Discharge of exhaust (exhaust) gases into the atmosphere.

The power supply system of a passenger car includes the following elements: a fuel tank, fuel hoses, a fuel filter (there may be several of them), a fuel pump, an air filter, a carburetor (an injector or other device used to prepare a combustible mixture). Note that carburetors are rarely used in modern cars.

The fuel tank is located at the bottom or at the rear of the vehicle: these are the safest places. The fuel tank is connected to the device, which creates a combustible mixture, through fuel hoses that run through almost the entire vehicle (usually along the underbody).

However, any fuel must undergo preliminary purification, which can include several stages. If you are filling fuel from a canister, use a funnel with a strainer. Remember that gasoline is more fluid than water, so very fine mesh can be used to filter it, in which the cells are almost invisible. If your gasoline contains an admixture of water, then after filtration through a fine mesh, water will remain on it, and gasoline will leak out.

Cleaning fuel when filling it into the fuel tank is called pre-cleaning or the first stage of cleaning - because on the way of fuel to the engine it will go through a similar procedure more than once.

The second stage of cleaning is carried out using a special mesh located on the fuel intake inside the fuel tank. Even if some impurities remain in the fuel at the first stage of cleaning, they will be removed at the second stage.

For the highest quality (fine) cleaning of the fuel entering the fuel pump, a fuel filter (Fig. 2.9) located in the engine compartment is used. By the way, in some cases the filter is installed both before and after the fuel pump - in order to improve the quality of cleaning the fuel entering the engine.

Important.

The fuel filter should be changed every 15,000 - 25,000 km (depending on the specific make and model of the vehicle).

A fuel pump is used to supply fuel to the engine. It usually includes the following parts: body, diaphragm with actuator and spring, inlet and outlet (discharge) valves. There is also another mesh filter in the pump: it provides the last, fourth stage of fuel purification before feeding it to the engine. Among other parts of the fuel pump, we note the rod, delivery and suction pipes, manual fuel pump lever, etc.

The fuel pump can be driven by the oil pump drive shaft or by the engine camshaft. When any of these shafts rotate, the eccentric on them exerts pressure on the fuel pump drive rod. The stem, in turn, presses on the lever, and the lever on the diaphragm, causing it to go down. After that, a vacuum is formed above the diaphragm, under the influence of which the inlet valve overcomes the spring force and opens. As a result, a certain amount of fuel is sucked from the fuel tank into the space above the diaphragm.

When the eccentric then “releases” the fuel pump rod, the lever stops pressing on the diaphragm, as a result of which, due to the rigidity of the spring, it rises up. In this case, pressure is formed, under the action of which the inlet valve closes tightly, and the discharge valve opens. Fuel above the diaphragm is directed to the carburetor (or other device used to prepare a combustible mixture - for example, an injector). When the eccentric once again starts to press on the rod, the fuel is sucked in and the process is repeated again.

However, it is not only the fuel that should be cleaned, but also the air used to prepare the combustible mixture. For this, a special device is used - an air filter. It is installed in a special case after the air intake and closed with a cover (Fig. 2.10).

The air passing through the filter leaves on it all the contained debris, dust, impurities, etc., and is used in a purified form to prepare a combustible mixture.

Remember this.

The air filter is a consumable item that should be replaced after a certain gap (usually 10,000 - 15,000 km). A clogged filter makes it difficult for air to pass through. This becomes the reason for excessive consumption of fuel, since the combustible mixture will contain a lot of fuel and little air.

The purified components of the combustible mixture (gasoline and air), each on their own way, enter the carburetor or other device specially designed to create a combustible mixture from gasoline and air vapors. The finished mixture is fed into the engine cylinders.

Note.

The carburetor automatically regulates the composition of the combustible mixture (the ratio of gasoline vapor to air), as well as its amount supplied to the cylinders, depending on the engine operating mode (idle, measured driving, acceleration, etc.). As we noted earlier, carburetors are rarely used on modern cars (everything is controlled by electronics, the most famous such device is the injector), but Soviet and Russian cars (VAZ, AZLK, GAZ, ZAZ) were produced with a carburetor. Since half of Russia still drives such cars today, we will further consider in detail the principle of operation and the structure of the carburetor.

The carburetor (Fig. 2.11) consists of a large number of different parts and includes a number of systems necessary for stable engine operation.

The key elements of a typical carburetor are: a float chamber, a float with a needle valve, a mixing chamber, an atomizer, an air damper, a throttle valve, a diffuser, fuel and air passages with jets.

In general, the principle of producing a combustible mixture in a carburetor looks like this.

When the piston, when the fuel mixture is injected into the cylinder, begins to move from TDC to BDC, a vacuum is formed above it in accordance with the laws of physics. Accordingly, the air stream, after preliminary cleaning with an air filter and passing through the carburetor, enters this zone (in other words, it is sucked there).

When the purified air passes through the carburetor, fuel is sucked in from the float chamber through the atomizer. This sprayer is located at the narrowest point of the mixing chamber, called the "diffuser". By the incoming stream of purified air, gasoline flowing out of the sprayer is "crushed", after which it is mixed with air, and the so-called initial mixing takes place. The final mixing of gasoline with air is carried out at the outlet of the diffuser, and then the combustible mixture enters the engine cylinders.

In other words, the carburetor uses the principle of a conventional spray gun to produce a combustible mixture.

However, the engine will operate stably and reliably only when the gasoline level in the carburetor's float chamber is constant. If it rises above the set limit, there will be too much fuel in the mixture. If the level of gasoline in the float chamber is below the set limit, the combustible mixture will be too lean. To solve this problem, a special float is designed in the float chamber, as well as a needle shut-off valve. When there is too little gasoline in the float chamber, the float is lowered along with the needle shut-off valve, thereby allowing gasoline to flow into the chamber unhindered. When there is enough fuel, the float floats up and the valve blocks the path of gasoline flow. To see this principle in action, take a look at how a simple toilet cistern works.

The harder the driver presses the gas pedal, the more the throttle valve opens (in the initial position it is closed). This allows more gas and air to flow into the carburetor. The more the driver releases the accelerator pedal, the more the throttle valve closes and the less gas and air flow into the carburetor. The motor works less intensively (rpm drop), so the torque transmitted to the wheels of the car decreases, respectively - the car slows down.

But even when you fully release the gas pedal (and close the throttle), the engine will not stall. This is because a different principle applies when the engine is idling. Its essence lies in the fact that the carburetor is equipped with channels specially designed so that air can penetrate under the throttle valve, mixing with gasoline along the way. With the throttle valve closed (at idle speed), air is forced into the cylinders through these channels. At the same time, it "sucks" gasoline from the fuel channel, mixes with it, and this mixture enters the throttle space. In this space, the mixture finally assumes the required state and enters the engine cylinders.

Note.

For most engines, when idling, the optimum crankshaft speed is 600-900 rpm.

Depending on the current operating mode of the engine, the carburetor prepares a fuel mixture of the required quality. In particular, when starting a cooled engine, the combustible mixture should contain more fuel than when a warm engine is running. It should be noted that the most economical operating mode of the engine is smooth driving in the highest gear at a speed of about 60-90 km / h. When driving in this mode, the carburetor creates a lean mixture.

Note.

Car carburettors come in a variety of models and designs. Here we will not give a description of various modifications of carburetors, since it is enough for us to have at least a general idea of \u200b\u200bthe operation of the carburetor. Detailed information on how the carburetor functions in a particular car can be found in the owner's manual for that car.

As we noted above, exhaust gases are generated during the operation of an internal combustion engine. They are a product of combustion of the working mixture in the engine cylinders.

It is the exhaust gases that are removed from the cylinder during the last, fourth stroke of its working cycle, which is called the release. Then they are released into the atmosphere. For this, each car has an exhaust gas release mechanism, which is part of the power system. Moreover, its task is not only to remove them from the cylinders and release them into the atmosphere, which of course, but also to reduce the noise that accompanies this process.

The fact is that the release of exhaust gases from the engine cylinder is accompanied by a very loud noise. It is so strong that without a muffler (a special device that absorbs noise, Fig. 2.12), the operation of cars would be impossible: it would be impossible to stay near a running car because of the noise it produces.

The exhaust mechanism of a standard vehicle includes the following components:

□ outlet valve;

□ outlet channel;

□ front exhaust pipe (in the driver's slang - "pants");

□ additional muffler (resonator);

□ main muffler;

□ connecting clamps with which the parts of the muffler are connected to each other.

In addition to the listed elements, many modern cars also use a special catalyst for neutralizing exhaust gases. The name of the device speaks for itself: it is designed to reduce the amount of harmful substances contained in the exhaust gases of a car.

The exhaust mechanism works quite simply. From the engine cylinders, they enter the exhaust pipe of the muffler, which is connected to an additional muffler, and that, in turn, to the main muffler (the end of which is the exhaust pipe protruding from the rear of the car). The resonator and the main silencer inside have a rather complex structure: there are numerous holes, as well as small chambers, which are staggered, resulting in a complex intricate maze. As the exhaust fumes pass through this labyrinth, they slow down significantly and exit the tailpipe with virtually no noise.

Note that the exhaust gases of a car contain many harmful substances: carbon monoxide (the so-called carbon monoxide), nitric oxide, hydrocarbon compounds, etc. Therefore, never warm up the car indoors - this is deadly: there are a lot of cases when people died in own garages from carbon monoxide.

OPERATING MODES OF THE POWER SYSTEM

Depending on the goals and road conditions, the driver can apply different driving modes. They also correspond to certain operating modes of the power system, each of which has a fuel-air mixture of a special quality.

1. The mixture will be rich when starting a cold engine. At the same time, air consumption is minimal. In this mode, the possibility of movement is categorically excluded. Otherwise, this will lead to increased fuel consumption and wear of parts of the power unit.
2. The composition of the mixture will be enriched when using the "idle" mode, which is used when "coasting" or when the engine is running in a warm state.
3. The mixture will be lean when driving at partial loads (for example, on a flat road at medium speed in high gear).
4. The mixture will be enriched at full load while driving at high speed.
5. The composition of the mixture will be rich, close to rich, when driving under conditions of sharp acceleration (for example, when overtaking).

The choice of operating conditions for the power supply system, therefore, must be justified by the need for movement in a certain mode.

FAULTS AND SERVICE

During the operation of the vehicle, the fuel system of the vehicle is under stress, leading to its unstable operation or failure. The following faults are considered the most common.

INSUFFICIENT SUPPLY (OR LACK OF SUPPLY) OF FUEL INTO ENGINE CYLINDERS

Poor-quality fuel, long service life, environmental impact lead to contamination and clogging of fuel lines, tank, filters (air and fuel) and technological openings of the combustible mixture preparation device, as well as damage to the fuel pump. The system will require repair, which will consist in the timely replacement of the filter elements, periodic (every two to three years) cleaning the fuel tank, carburetor or injector nozzles and replacing or repairing the pump.

LOSS OF ICE POWER

A malfunction of the fuel system in this case is determined by a violation of the regulation of the quality and amount of the combustible mixture entering the cylinders. Elimination of the malfunction is associated with the need to diagnose the device for preparing a combustible mixture.

FUEL LEAK

Fuel leakage is a very dangerous and categorically unacceptable phenomenon. This malfunction is included in the "List of malfunctions ...", with which the movement of the car is prohibited. The causes of the problems lie in the loss of tightness by the components and assemblies of the fuel system. Elimination of the malfunction consists either in replacing damaged system elements, or in tightening the fasteners of the fuel lines.

Thus, the power supply system is an important element of the internal combustion engine of a modern car and is responsible for the timely and uninterrupted supply of fuel to the power unit.