How does a diesel engine work? How a car diesel engine works What does diesel mean

Diesel technology has developed rapidly over the past ten years. Most of the modern cars that are produced in Europe are produced with diesel engines. Of course, the principle of operation of this device has not changed. However, a modern diesel engine is much quieter. It has become more environmentally friendly. In the distant past, strong rattling, thick black smoke and an unpleasant smell during operation of the device remained. So, what is the working principle of a diesel engine?

How does a diesel engine work?

The principle of operation of a diesel engine is as follows: in the cylinder

clean air is sucked in when the piston moves down. And when you move the valve up, it heats up. It should be noted that the temperature during operation of a diesel engine can be from 700 to 900 °. This is achieved with strong compression. When the piston moves to top dead center, diesel fuel is injected into the combustion chamber at a sufficiently high pressure. When in contact with hot air, the fuel ignites. As a result, the pressure in the cylinder increases as the self-igniting fuel expands. This is what causes a lot of noise during operation of the unit.

Advantages and disadvantages

This principle of operation of a diesel engine allows the use of a lean mixture. Fuel for such devices is relatively inexpensive. This makes diesel engines unpretentious and economical. It is worth noting that, unlike gasoline units, such units have a large torque, and the efficiency is 10% higher. By cons

a diesel engine should include an increased noise level, vibration, low power per unit volume, and the difficulty of a cold start. More modern models are practically devoid of such shortcomings.

The device and features of some nodes

Given the principle of operation of a diesel engine, parts for such units are significantly strengthened, as they must withstand high loads. Among the main parts of the unit, it is worth highlighting the piston. The shape of its bottom depends on the type of combustion chamber that can be built into the bottom of the valve. In a piston for a diesel engine, the bottom usually extends beyond the top of the cylinder block. There is no conventional ignition system in units of this type. Although they also use candles.

Turbine

The power that the engine is able to develop depends on the amount of fuel and air that enters it. To increase the capabilities of the unit, it is necessary to increase the content of the listed components. In order for more fuel to enter the combustion chamber, the air level must be raised, which

enters the cylinder. For this, additional equipment is used. The principle of operation of a diesel engine turbine is quite simple. The part allows you to pump more air. This increases the volume of fuel burned, which significantly increases the amount of energy released.

combustion chambers

Several types of combustion chambers can be used in diesel engines: divided and undivided. The first type was used in the passenger car industry, but recently it has been replaced by a simpler one. Indeed, when using divided compartments, fuel was injected into the combustion chamber, which was located in the cylinder head, and not into the piston cavity. Similar parts were also made in different ways and it depended on the processes of mixture formation: vortex-chamber or pre-chamber.

In the latter case, the fuel is injected into the preliminary compartment, which

communicates with small valves or holes with a cylinder. In this case, the fuel mixes with air, hitting the walls. Self-igniting fuel enters the main chamber, where it burns completely. As for the vortex chamber combustion process, it, as in the first case, begins in a separate compartment, which is a hollow sphere. Through the connecting channels, air enters the chamber during the compression stroke. It twists in it and forms a vortex. As a result, the combustible mixture injected into the compartment is well mixed with air. This structure of the combustion chambers has several disadvantages. Firstly, more fuel is consumed, as there are large losses due to the volume of the compartments. Secondly, significant losses during the flow into the additional chamber from the air cylinder, as well as to the reverse process: the movement of fuel into the cylinder. It is worth noting that a similar principle of operation of a diesel engine is rarely used, since the starting characteristics of the unit deteriorate.

Undivided combustion chambers

In a direct injection engine, the combustion chamber has a certain shape and is a cavity. Such a combustion chamber is built directly into the bottom

piston. In this case, fuel is injected directly into the cylinder. Despite the simplicity of the design, such a system also has disadvantages. Diesel engines of this kind are almost impossible to use if the car has a small displacement. When picking up speed in such a vehicle, an increase in noise level is observed, and vibration also increases.

New developments

Today, electronic systems are more often used that control the amount of fuel entering the combustion chamber. This made it possible to reduce the noise level, as well as the vibration of the unit during operation. Today, completely new diesel engines are being developed, in the designs of which direct injection of a combustible mixture is used.

As you know, diesel engines are more expensive to maintain and even more so to repair, due to the fact that their components and parts (high pressure fuel pump or high pressure fuel pump, injector pump, turbocharger, injector) are made with the highest possible accuracy. At the same time, they, as a rule, are more economical than gasoline ones and have a higher efficiency (efficiency) - by 10-14 percent. In addition, modern diesel engines have great power and excellent throttle response. And to further increase the power and traction characteristics, diesel engines are equipped with turbocharging and an intercooler.

The principle of operation of a diesel engine and its difference from a gasoline counterpart.

The principles of operation of diesel and gasoline engines, as noted above, are completely different.

In gasoline internal combustion engines (carburetor, injection), the preparation of the mixture, as a rule, occurs in the intake tract: a ready-made mixture is fed into the cylinder, which lights up there with a spark plug at the moment of compression.

In diesel engines, everything is different, and mixture formation occurs directly in the cylinder. The igniter is air, which, when compressed, heats up and ignites the diesel fuel. This fuel itself is fed into the combustion chamber by an injector and a high-pressure fuel pump (injector pump) at high pressure.

Now let's get acquainted with this process in more detail, step by step. By the way, the number of the latter in diesel and gasoline engines is (four). Let's take a look at each of the steps.

The first stroke of a diesel engine is the intake stroke.

During the first cycle, the piston moves from top dead center (TDC) to bottom dead center (BDC). At this stage, the intake valve is open, while the exhaust valve is naturally closed. When the piston moves in Nmt, a vacuum is created and the motor cylinder is filled with air, which, before entering the cylinder, is cleaned of mechanical impurities in the air filter.

The second stroke will be the compression stroke.

At this point in time, the valves (inlet and inlet) are closed and the piston moves from BDC to TDC. And since the valves are closed, the air has nowhere to go, so it compresses, creating high pressure, and heats up - up to 800 degrees Celsius.

The third cycle is the expansion cycle (work stroke).

While the piston is moving to TDC, diesel fuel is supplied to the cylinder under high pressure (from 150 to 300 bar) by means of a nozzle and sprayed there. In the process of fuel atomization, it is mixed with hot air and, consequently, its subsequent ignition. When the mixture burns, the temperature in the cylinder rises rapidly - up to 1750 -1800 degrees Celsius. At the same time, the pressure also increases, which reaches 10-12 MPa. Gases are formed that push the piston from top to bottom. Moving down, the piston performs the work assigned to it. In Nmt, pressure decreases with temperature.

The fourth cycle is the final one, it is also the release cycle.

The piston moves up. The exhaust valve opens and gases tend to leave the combustion chamber through channels in the cylinder head (cylinder head) into the exhaust manifold. Further, the gases enter the muffler, where they are cleaned (soot filters are installed in modern diesel engines) and into the environment. At this time, the temperature in the cylinder decreases to 450-540 degrees, and the pressure drops to 10-20 Bar.

Video.

The principle of operation of which is based on the self-ignition of fuel when exposed to hot compressed air.

The design of a diesel engine as a whole is not much different from a gasoline engine, except that the diesel engine does not have an ignition system as such, since the fuel is ignited according to a different principle. Not from a spark, as in a gasoline engine, but from high pressure, which compresses air, causing it to become very hot. High pressure in the combustion chamber imposes special requirements for the manufacture of valve parts that are designed to withstand more serious loads (from 20 to 24 units).

Diesel engines are used not only in trucks, but also in many models of cars. Diesels can run on various types of fuel - on rapeseed and palm oil, on fractional substances and on pure oil.

The principle of operation of a diesel engine

The principle of operation of a diesel engine is based on the compression ignition of fuel that enters the combustion chamber and mixes with a hot air mass. The working process of a diesel engine depends solely on the heterogeneity of the fuel assemblies (fuel-air mixture). The supply of fuel assemblies in this type of engine occurs separately.

First, air is supplied, which during the compression process is heated to high temperatures (about 800 degrees Celsius), then fuel is supplied to the combustion chamber under high pressure (10-30 MPa), after which it self-ignites.

The process of fuel ignition itself is always accompanied by a high level of vibration and noise, so diesel-type engines are noisier than gasoline counterparts.

A similar principle of operation of a diesel engine allows the use of more affordable and cheaper (until recently :)) types of fuel, reducing the cost of its maintenance and refueling.

Diesels can have both 2 and 4 working strokes (intake, compression, stroke and exhaust). Most cars are equipped with 4-stroke diesel engines.

Types of diesel engines

According to the design features of the combustion chambers, diesel engines can be divided into three types:

With split combustion chamber. In such devices, fuel is supplied not to the main, but to the additional, the so-called. a swirl chamber, which is located in the head of the cylinder block and is connected to the cylinder by a channel. When it enters the vortex chamber, the air mass is compressed as much as possible, thereby improving the process of fuel ignition. The self-ignition process begins in the vortex chamber, then passes into the main combustion chamber.
With undivided combustion chamber. In such diesel engines, the chamber is located in the piston, and fuel is supplied to the space above the piston. On the one hand, inseparable combustion chambers allow saving fuel consumption, on the other hand, they increase the noise level during engine operation.
Prechamber engines. Such diesel engines are equipped with a plug-in prechamber, which is connected to the cylinder by thin channels. The shape and size of the channels determine the speed of movement of gases during the combustion of fuel, reducing the level of noise and toxicity, increasing the life of the engine.

Fuel system in a diesel engine

The basis of any diesel engine is its fuel system. The main task of the fuel system is the timely supply of the required amount of the fuel mixture under a given operating pressure.

Important elements of the fuel system in a diesel engine are:

high pressure fuel pump (TNVD);
fuel filter;
nozzles

Fuel pump

The pump is responsible for supplying fuel to the injectors according to the set parameters (depending on the speed, the operating position of the control lever and the turbo boost pressure). In modern diesel engines, two types of fuel pumps can be used - in-line (plunger) and distribution.

Fuel filter

The filter is an important part of a diesel engine. The fuel filter is selected strictly in accordance with the type of engine. The filter is designed to isolate and remove water from the fuel, and excess air from the fuel system.

nozzles

Nozzles are equally important elements of the fuel system in a diesel engine. Timely supply of the fuel mixture to the combustion chamber is possible only with the interaction of the fuel pump and injectors. In diesel engines, two types of nozzles are used - with a multi-hole and font distributor. The nozzle distributor determines the shape of the flame, providing a more efficient self-ignition process.

Cold start and turbocharged diesel engine

Cold start is responsible for the preheating mechanism. This is ensured by electric heating elements - glow plugs, which are equipped with a combustion chamber. When starting the engine, glow plugs reach a temperature of 900 degrees, heating the air mass that enters the combustion chamber. The glow plug is de-energized 15 seconds after the engine starts. Heating systems before starting the engine ensure its safe start even at low atmospheric temperatures.

Turbocharging is responsible for increasing the power and efficiency of a diesel engine. It provides the supply of more air for a more efficient process of combustion of the fuel mixture and increase the working power of the engine. A special turbocharger is used to ensure the required boost pressure of the air mixture in all operating modes of the engine.

It only remains to say that the debate over what is better for an ordinary motorist to choose as a power plant in his car, gasoline or diesel, has not subsided so far. Both types of engine have advantages and disadvantages and it is necessary to choose based on the specific operating conditions of the car.

Slightly different from gasoline counterparts. The main difference can be considered the ignition of the fuel-air mixture, which does not come from an external source (ignition spark), but from strong compression and heating.

In other words, self-ignition of fuel occurs in a diesel engine. In this case, the fuel must be supplied under extremely high pressure, since it is necessary to spray the fuel as efficiently as possible in the cylinders of a diesel engine. In this article, we will talk about which diesel injection systems are actively used today, and also consider their design and principle of operation.

Read in this article

How does the diesel fuel system work?

As mentioned above, in a diesel engine, self-ignition of the working mixture of fuel and air occurs. In this case, at first only air is supplied to the cylinder, then this air is strongly compressed and heated from compression. To ignite, you need to apply closer to the end of the compression stroke.

Given that air is highly compressible, the fuel also needs to be injected at high pressure and atomized efficiently. Injection pressure can differ in different diesel engines, starting, on average, from 100 atmospheres and ending with an impressive figure of more than 2 thousand atmospheres.

For the most efficient fuel supply and ensuring optimal conditions for self-ignition of the charge, followed by complete combustion of the mixture, fuel injection is implemented through a diesel injector.

It turns out, no matter what type of power system is used, there are always two main elements in diesel engines:

a device for creating high fuel pressure;

In other words, on many diesel engines, pressure is created (high-pressure fuel pump), and diesel fuel is supplied to the cylinders through nozzles. As for the differences, in different fuel supply systems the pump may have one or another design, and the diesel injectors themselves also differ in their design.

Also, power systems may differ in the location of certain components, have different control schemes, etc. Let's look at diesel injection systems in more detail.

Diesel engine power systems: an overview

If we divide the power systems of diesel engines, which are most widespread, we can distinguish the following solutions:

Power supply system based on in-line injection pump (in-line injection pump);
A fuel supply system that has a fuel injection pump of a distribution type;
Solutions with pump nozzles;
Common rail fuel injection (high pressure accumulator in the common rail).

These systems also have a large number of subspecies, and in each case one or another type is the main one.

So, let's start with the simplest scheme, which assumes the presence of an in-line fuel pump. The in-line injection pump is a well-known and proven solution that has been used on diesel engines for decades. Such a pump is actively used on special equipment, trucks, buses, etc. Compared to other systems, the pump is quite large in size and weight.

In a nutshell, in-line injection pumps are based on. Their number is equal to the number of engine cylinders. The plunger pair is a cylinder that moves in a "glass" (sleeve). When moving up, the fuel is compressed. Then, when the pressure reaches the required value, a special valve opens.

As a result, pre-compressed fuel enters the nozzle, after which injection occurs. After the plunger starts moving back down, the fuel inlet channel opens. Through the channel, fuel fills the space above the plunger, then the cycle repeats. In order for diesel fuel to enter the plunger pairs, the system additionally has a separate booster pump.

The plungers themselves work due to the fact that the pump device has a camshaft. This shaft works similarly where the cams "push" the valves. The pump shaft itself is driven by the engine, since the injection pump is connected to the motor using an injection advance clutch. The specified clutch allows you to adjust the operation and adjust the injection pump during engine operation.

The power supply system with a distribution pump does not differ much from the scheme with an in-line injection pump. The distribution injection pump is similar to the in-line one in design, while the number of plunger pairs is reduced in it.

In other words, if in an in-line pump, pairs are needed for each cylinder, then in a distribution pump, 1 or 2 plunger pairs are sufficient. The fact is that in this case one pair is enough to supply fuel to 2, 3 or even 6 cylinders.

This became possible due to the fact that the plunger was able not only to move up (compression) and down (inlet), but also to rotate around the axis. Such rotation made it possible to implement the alternate opening of the outlets through which diesel fuel is supplied under high pressure to the nozzles.

Further development of this scheme led to the emergence of a more modern rotary injection pump. In such a pump, a rotor is used, in which plungers are installed. These plungers move towards each other, and the rotor rotates. This is how diesel fuel is compressed and distributed over the engine cylinders.

The main advantage of the distribution pump and its varieties is reduced weight and compactness. At the same time, it is more difficult to configure this device. For this reason, electronic control and regulation circuits are additionally used.

The power supply system of the "pump-injector" type is a scheme where initially there is no separate high-pressure fuel pump. To be more precise, the nozzle and the pump section were combined in one housing. It is based on the already familiar plunger pair.

The solution has a number of advantages compared to systems that use high-pressure fuel pumps. First of all, the fuel supply to individual cylinders can be easily adjusted. Also, if one nozzle fails, the rest will work.

Also, the use of pump nozzles allows you to get rid of a separate injection pump drive. The plungers in the pump nozzle are driven by the timing camshaft, which is installed in. Such features have allowed diesel engines with pump injectors to become widespread not only on trucks, but also on large cars (for example, diesel SUVs).

The Common Rail system is one of the most modern solutions in the field of fuel injection. Also, this power scheme allows you to achieve maximum efficiency at the same time as high. In parallel, the toxicity of exhaust gases is also reduced.

The system was developed by the German company Bosch in the 90s. Given the obvious advantages in a short time, the vast majority of diesel ICEs in cars and trucks began to be equipped exclusively with Common Rail.

The general scheme of the device is based on the so-called high pressure accumulator. Simply put, the fuel is under constant pressure, after which it is supplied to the nozzles. As for the pressure accumulator, this accumulator is actually a fuel line, where fuel is injected using a separate injection pump.

The Common Rail system partially resembles a gasoline injection engine, which has a fuel rail with injectors. Gasoline is pumped into the rail (fuel rail) under slight pressure by the fuel pump from the tank. In a diesel engine, the pressure is much higher, the fuel is pumped by the injection pump.

Due to the fact that the pressure in the accumulator is constant, it has become possible to implement fast and “multi-layered” fuel injection through the injectors. Modern systems in Common Rail engines allow injectors to make up to 9 metered injections.

As a result, a diesel engine with such a power supply system is economical, efficient, runs smoothly, quietly and elastically. Also, the use of a pressure accumulator made it possible to make the design of the injection pump on diesel engines simpler.

We add that high-precision injection on Common Rail engines is completely electronic, since a separate control unit monitors the operation of the system. The system uses a group of sensors that allow the controller to determine exactly how much diesel fuel needs to be supplied to the cylinders and at what point.

Summing up

As can be seen, each of the considered diesel engine power systems has its own advantages and disadvantages. If we talk about the simplest solutions with in-line injection pumps, their main advantage can be considered the possibility of repair and the availability of maintenance.

In schemes with unit injectors, it must be remembered that these elements are sensitive to the quality of the fuel and its purity. The ingress of even the smallest particles can damage the unit injector, resulting in an expensive element requiring replacement.

As for Common Rail systems, the main disadvantage is not only the high initial cost of such solutions, but also the complexity and high cost of subsequent repairs and maintenance. For this reason, the quality of the fuel and the condition of the fuel filters must be constantly monitored, as well as scheduled maintenance should be carried out in a timely manner.

The evolution of the diesel engine

As you know, at the initial stage, power units of this type could not adequately compete with gasoline counterparts. The fact is that the diesel engine remained a high-torque and economical engine for a long time, but it was slow-moving.

In practice, this means that such an internal combustion engine confidently pulled from the very bottom, but there was no talk of high revs and, accordingly, high speeds. At the same time, the main advantage remained low consumption and high at low speeds. For commercial vehicles, this solution was optimal, but not suitable for passenger vehicles.

If we add noise and increased vibrations to this, then it becomes clear why diesel engines were not in demand in passenger cars. However, over the past 30 years, the situation has changed radically. Taking into account the reduction of oil reserves, the tightening of environmental standards and the constant increase in fuel prices, fuel consumption has come to the fore.

Automakers began to actively introduce the latest developments, the diesel engine received an upgraded fuel injection system and. As a result, it was possible to almost completely get rid of noise and vibration, as well as bring diesel engines closer to gasoline engines in a number of performance indicators.

Advantages of a diesel engine

So let's start with the obvious benefits. Diesel fuel consumption is usually 30-35% less than that of gasoline engines.
Also, the diesel engine has a high torque at low revs, which allows you to achieve excellent acceleration dynamics from a standstill and confident traction.
The diesel unit is more environmentally friendly, as it burns the fuel charge more fully and efficiently. As a result, the toxicity of the exhaust of modern diesel internal combustion engines is significantly reduced.
more than gasoline engines. In practice, such a power unit, subject to proper maintenance, is able to cover about 350-400 thousand km, while a gasoline engine may need overhaul by 200 thousand km.
The absence of a diesel engine in the design eliminates a number of problems that are inherent in gasoline power units (, weak, breakdown, etc.). There is no need to change spark plugs, ignition coils, high voltage wires and other elements.
The design features and the method of igniting the fuel in the cylinders from compression provide the diesel engine with a higher . In other words, as a result of burning fuel, more energy is converted into useful work. This means that the power of such an engine is greater.

Disadvantages of a diesel engine

It would seem that a modern diesel engine is not only not inferior to gasoline, but also surpasses it in a number of important indicators. However, in practice, diesel internal combustion engines also have several significant drawbacks. For this reason, especially in the CIS, many drivers still choose gasoline cars. Let's figure it out.

First of all, you need to start with the cost. A diesel car, on average, initially costs 25-35% more than its gasoline counterparts (depending on the type and class of car).

It is also worth understanding that when selling a used diesel car older than 5-7 years, the price in the secondary market drops significantly. In other words, selling a used diesel in a few years for the same 25-30% more expensive compared to a similar model on gasoline is quite difficult.

Even taking into account the fact that diesel internal combustion engines have become more resourceful, cars with such an engine are still less fast. It should also be added that a diesel engine is heavier than a gasoline engine, which affects the weight distribution of the car, its dynamic characteristics and handling.

On diesels with "mechanics" you need to change gears more often. If an automatic or robotic gearbox is installed on a diesel car, the box resource may be less than on exactly the same gasoline model. The reason is that the gearbox must withstand significant torque.

. The reason is that the diesel efficiency is higher, that is, less energy from the combustion of diesel fuel is spent on heat. As a result, the motor is more efficient, but less heat generation also means that such a unit is “cold” at the same time.

In practice, this manifests itself in a way that is useless. This motor needs to be warmed up in motion, that is, under load. It turns out that if a car with such an internal combustion engine is operated for short trips around the city, the motor simply will not have time to reach. As a result, the resource of the unit is reduced.

As for comfort, many owners of diesel cars without special additional interior heating note a slow warming up of the interior space in the winter.

The problem of difficult operation in the winter period largely concerns diesel engines. First of all, diesel fuel tends to freeze and wax in the cold. To prevent this from happening, with the onset of cold weather, special additives are separately added to the fuel. In other words, .

The owner must take this feature into account and fill in diesel fuel that is suitable for the season. Taking into account the fact that the quality of fuel at filling stations in the CIS is not the highest, the risks are obvious. Also in regions where the temperature drops significantly, a diesel vehicle must be equipped with separate preheating systems. We add that the owners of diesel cars need to monitor the condition and regularly change the glow plugs that warm up the combustion chamber before starting the internal combustion engine.

Diesel engines are more expensive to maintain and repair. Such motors usually require more oil, it is necessary to change the lubricant and filters more often. As a rule, taking into account the quality of fuel in the CIS and a number of other features of operation, the service interval for a diesel engine is reduced by 40-50%.

Even taking into account the fact that a diesel engine has a longer service life before overhaul, the repair itself is much more expensive compared to gasoline units.

All modern diesel engines are also equipped with sophisticated high-tech fuel injection systems. For this reason, increased requirements are put forward for the quality of lubricant and fuel, as well as for the general condition of the internal combustion engine. It is important to understand that expensive fuel is of poor quality or the wrong type of fuel.

In fairness, we note that for residents of large cities the issue of fuel is not so acute. However, this cannot be said about those motorists who live in rural areas or regularly refuel a diesel car at small gas stations along highways during trips. The problem of finding high-quality diesel fuel in this case remains quite relevant.

The reliability of a diesel turbine and individual elements of the power system (for example, or a pump injector) is far from the same as that of the engine itself. Repair or replacement of these parts is quite a costly undertaking.

It should also be added that the diagnostics and repair of modern diesel engines require expensive equipment and specialized specialists. As a rule, not every service station has qualified diesel masters, and the cost of any manipulations with such a motor and its systems will definitely be higher.

Increased noise, as well as a higher level of vibration, can still be noted even on the most modern diesel engine when compared with gasoline counterparts. Although the difference is not so critical, it is still present.

Summing up

As you can see, the advantages of a diesel engine in a passenger car in practical operation on domestic roads can largely overlap with the above disadvantages.

It is important to understand that purchasing a car with a diesel engine allows you to save on fuel, but the benefit can be partially or completely offset by the higher maintenance and repair costs of this type of unit. In other words, before buying, you need to consider not only the advantages, but also the disadvantages of a diesel engine.

Finally, I would like to add that if the diesel car is commercial and is purchased new, then such a decision is fully justified. If the owner plans to purchase a passenger car with a diesel engine, especially a used one, then you need to be prepared for higher costs, expensive breakdowns and stringent requirements regarding the operation of such a vehicle.

How does a diesel engine work? How a car diesel engine works What does diesel mean