Very common in cars. Many models have at least one option in the engine range. And this is without taking into account trucks, buses and construction equipment, where they are used everywhere. Next, we consider what a diesel engine is, design, principle of operation, features.

Definition

This unit is the operation of which is based on the self-ignition of atomized fuel from heating or compression.

Design features

A gasoline engine has the same structural elements as a diesel engine. The scheme of functioning as a whole is also similar. The difference lies in the processes of formation of the air-fuel mixture and its combustion. In addition, diesel engines are more durable parts. This is due to about twice the compression ratio of gasoline engines (19-24 versus 9-11).

Classification

According to the design of the combustion chamber, diesel engines are divided into options with a separate combustion chamber and with direct injection.

In the first case, the combustion chamber is separated from the cylinder and connected to it by a channel. When compressed, the air entering the vortex-type chamber is twisted, which improves mixture formation and self-ignition, which begins there and continues in the main chamber. Diesel engines of this type were previously common in passenger cars due to the fact that they were distinguished by a reduced noise level and a large speed range from the options discussed below.

In direct injection, the combustion chamber is located in the piston, and the fuel is supplied to the over-piston space. This design was originally used on low-speed high-volume engines. They were distinguished by a high level of noise and vibration and low fuel consumption. Later, with the advent of electronic control and optimization of the combustion process, the designers achieved stable operation at a range of up to 4500 rpm. In addition, increased efficiency, decreased noise and vibration levels. Among the measures to reduce the rigidity of the work is a multi-stage pre-injection. Due to this, engines of this type have become widespread in the last two decades.

According to the principle of operation, diesel engines are divided into four-stroke and two-stroke, as well as gasoline engines. Their features are discussed below.

Operating principle

To understand what a diesel engine is and what determines its functional features, it is necessary to consider the principle of operation. The above classification of piston internal combustion engines is based on the number of strokes included in the working cycle, which are distinguished by the magnitude of the angle of rotation of the crankshaft.

Therefore, it includes 4 phases.

• Inlet. Occurs when the crankshaft rotates from 0 to 180°. In this case, the air passes into the cylinder through the inlet valve open at 345-355 °. At the same time, during the rotation of the crankshaft by 10-15 °, the exhaust valve is opened, which is called overlap.
• Compression. The piston, moving up at 180-360°, compresses the air by 16-25 times (compression ratio), and the intake valve closes at the beginning of the cycle (at 190-210°).
• Workflow, extension. Occurs at 360-540°. At the start of the stroke, until the piston reaches top dead center, fuel is injected into the hot air and ignited. This is a feature of diesel engines that distinguishes them from gasoline engines, where ignition advance occurs. The resulting combustion products push the piston down. In this case, the fuel combustion time is equal to the time of its supply by the nozzle and lasts no longer than the duration of the working stroke. That is, during the working process, the gas pressure is constant, as a result of which diesel engines develop more torque. Also an important feature of such motors is the need to provide excess air in the cylinder, since the flame occupies a small part of the combustion chamber. That is, the proportion of the air-fuel mixture is different.
• Release. At 540-720 ° of crankshaft rotation, the open exhaust valve, the piston, moving up, displaces the exhaust gases.

The two-stroke cycle is distinguished by shortened phases and a single process of gas exchange in the cylinder (purge) occurring between the end of the stroke and the start of compression. When the piston moves down, the products of combustion are removed through the exhaust valves or windows (in the cylinder wall). Later, the inlet windows are opened to let in fresh air. As the piston rises, all windows close and compression begins. A little before TDC is reached, fuel is injected and ignited, and expansion begins.

Due to the difficulty of purging the swirl chamber, two-stroke engines are only available with direct injection.

The performance of such engines is 1.6-1.7 times higher than the characteristics of a four-stroke diesel engine. Its growth is provided by twice as frequent implementation of working strokes, but is partially reduced due to their smaller size and blowing. Due to the double number of working strokes, the two-stroke cycle is especially relevant if it is impossible to increase the speed.

The main problem with such engines is the scavenging due to its short duration, which cannot be compensated without reducing efficiency by shortening the stroke. In addition, it is impossible to separate the exhaust and fresh air, due to which part of the latter is removed with the exhaust gases. This problem can be solved by providing advance exhaust windows. In this case, the gases begin to be removed before the purge, and after the outlet is closed, the cylinder is supplemented with fresh air.

In addition, when using one cylinder, difficulties arise with the synchronism of opening / closing windows, so there are engines (PDP) in which each cylinder has two pistons moving in the same plane. One of them controls the intake, the other controls the exhaust.

According to the mechanism of implementation, the purge is divided into slotted (window) and valve-slotted. In the first case, the windows serve as both inlet and outlet openings. The second option involves using them as intake ports, and a valve in the cylinder head is used for exhaust.

Typically, two-stroke diesel engines are used on heavy vehicles such as ships, diesel locomotives, tanks.

Fuel system

The fuel equipment of diesel engines is much more complicated than that of gasoline engines. This is due to the high requirements for the accuracy of fuel supply in terms of time, quantity and pressure. The main components of the fuel system - injection pump, nozzles, filter.

A computer-controlled fuel supply system (Common-Rail) is widely used. She squirts it in two shots. The first of them is small, serving to increase the temperature in the combustion chamber (pre-injection), which reduces noise and vibration. In addition, this system increases torque at low speeds by 25%, reduces fuel consumption by 20% and soot content in exhaust gases.

Turbocharging

Turbines are widely used in diesel engines. This is due to the higher (1.5-2) times the pressure of the exhaust gases that spin the turbine, which makes it possible to avoid turbo lag by providing boost from lower revs.

Cold start

You can find many reviews that at low temperatures The difficulty of starting such motors in cold conditions is due to the fact that this requires more energy. To facilitate the process, they are equipped with a preheater. This device is represented by glow plugs placed in the combustion chambers, which, when the ignition is turned on, heat the air in them and work for another 15-25 seconds after starting to ensure the stability of the cold engine. Thanks to this, diesel engines are started at temperatures of -30 ... -25 ° С.

Service features

To ensure durability during operation, it is necessary to know what a diesel engine is and how to maintain it. The relatively low prevalence of the engines under consideration in comparison with gasoline engines is explained, among other things, by more complex maintenance.

First of all, this concerns the fuel system of high complexity. Because of this, diesel engines are extremely sensitive to the content of water and mechanical particles in the fuel, and its repair is more expensive, as well as the engine as a whole, compared to gasoline of the same level.

In the case of a turbine, the requirements for the quality of engine oil are also high. Its resource is usually 150 thousand km, and the cost is high.

In any case, diesel engines should be changed oil more often than gasoline engines (2 times according to European standards).

As noted, these engines have cold start problems when at low temperatures. In some cases, this is caused by the use of unsuitable fuel (depending on the season, different grades are used on such engines, since summer fuel freezes at low temperatures).

Performance

In addition, many do not like such qualities of diesel engines as lower power and operating speed range, higher noise and vibration levels.

A gasoline engine is indeed usually superior in performance, including liter power, to a similar diesel. The motor of the type in question at the same time has a higher and even torque curve. A higher compression ratio, which provides more torque, forces the use of stronger parts. Since they are heavier, power is reduced. In addition, this affects the mass of the engine, and consequently, the car.

A small range of operating speeds is due to a longer ignition of the fuel, as a result of which it does not have time to burn out at high speeds.

An increased level of noise and vibration causes a sharp increase in pressure in the cylinder during ignition.

The main advantages of diesel engines are considered higher traction, efficiency and environmental friendliness.

Tyagovity, that is, high torque at low speeds, is explained by the combustion of fuel as it is injected. This provides greater responsiveness and facilitates efficient use of power.

The cost-effectiveness is due to both low consumption and the fact that diesel fuel is cheaper. In addition, it is possible to use low-grade heavy oils as it due to the absence of strict requirements for volatility. And the heavier the fuel, the higher the efficiency of the engine. Finally, diesel engines run on lean mixtures compared to gasoline engines and at a high compression ratio. The latter provides less heat loss with exhaust gases, that is, greater efficiency. All these measures reduce fuel consumption. Diesel, thanks to this, spends it 30-40% less.

The environmental friendliness of diesel engines is explained by the fact that their exhaust gases have a lower content of carbon monoxide. This is achieved by the use of complex cleaning systems, thanks to which the gasoline engine now meets the same environmental standards as a diesel engine. A motor of this type was previously significantly inferior to gasoline in this regard.

Application

As is clear from what a diesel engine is and what its characteristics are, such motors are most suitable for those cases where high traction at low revs is needed. Therefore, they are equipped with almost all buses, trucks and construction equipment. As for private vehicles, among them such parameters are most important for SUVs. Due to the high efficiency, urban models are also equipped with these motors. In addition, they are more convenient to manage in such conditions. Diesel test drives testify to this.

Good day. I think a lot of people will be interested in this topic. Advantages and disadvantages ... All below.
In 1890, Rudolf Diesel developed the theory of the "economical thermal engine", which, due to the strong compression in the cylinders, greatly improves its efficiency. He received a patent for his engine on February 23, 1893. The first functioning example was built by Diesel by the beginning of 1897, and on January 28 of the same year it was successfully tested.
It is interesting that Diesel in his book, instead of the diesel fuel familiar to us, described coal dust as an ideal fuel. Experiments also showed the impossibility of using coal dust as a fuel - primarily because of the high abrasive properties.

But Ackroyd Stewart also considered the theory of the diesel engine. He did not consider the benefits of high compression, he simply experimented with the possibility of eliminating spark plugs from the engine, that is, he did not pay attention to the biggest advantage - fuel efficiency. Perhaps this was the reason why the term "Diesel engine", "diesel engine" or simply "diesel" is currently used, since the theory of Rudolf Diesel became the basis for the creation of modern compression ignition engines. In the future, for about 20-30 years, such engines were widely used in stationary mechanisms and power plants of marine vessels, however, the fuel injection systems that existed at that time did not allow the use of diesel engines in high-speed units. The low speed of rotation, the significant weight of the air compressor necessary for the operation of the fuel injection system made it impossible to use the first diesel engines in vehicles.
In the 1920s, the German engineer Robert Bosch improved the built-in high-pressure fuel pump, a device that is still widely used today. The use of a hydraulic system for pumping and fuel injection eliminated the need for a separate air compressor and made it possible to further increase the rotational speed. The high-speed diesel demanded in this form has become increasingly popular as a power unit for auxiliary and public transport, however, the arguments in favor of electric ignition engines (the traditional principle of operation, ease and low cost of production) allowed them to be in great demand for installation on passenger and small In the 1950s and 1960s, diesel was installed in large quantities in trucks and vans, and in the 1970s, after a sharp rise in fuel prices, it was given serious attention by world manufacturers of low-cost small passenger cars.

Work principles:
Four stroke cycle.
At first bar(intake stroke, piston down) Fresh air is drawn into the cylinder through the open intake valve.
At second measure(compression stroke, piston going up) the intake and exhaust valves are closed the air is compressed in volume by about 17 times (from 14:1 to 24:1), i.e. the volume becomes 17 times smaller than the total volume of the cylinder, and the air becomes very hot.
Right before the start third bar(stroke stroke, piston goes down) fuel is injected into the combustion chamber through the injector nozzle. During injection, the fuel is atomized into fine particles, which are evenly mixed with compressed air to create a self-igniting mixture. Energy is released during combustion when the piston begins its movement in the stroke of the power stroke.
The exhaust valve opens when fourth measure(exhaust stroke, the piston goes up) and the exhaust gases pass through the exhaust valve.

Duplex cycle.
The piston is at bottom dead center and the cylinder is filled with air. During the upward stroke of the piston, the air is compressed; near the top dead center, fuel is injected, which spontaneously ignites. Then there is a working stroke - the combustion products expand and transfer energy to the piston, which moves down. Near the bottom dead center, a purge occurs - the combustion products are replaced by fresh air. The cycle ends.
To carry out purge, purge windows are arranged in the lower part of the cylinder. When the piston is down, the windows are open. When the piston rises, it closes the windows.

Since the strokes are twice as frequent in a two-stroke cycle, you can expect a twofold increase in power compared to a four-stroke cycle. In practice, this cannot be realized, and a two-stroke diesel engine is more powerful than a four-stroke diesel of the same volume by a maximum of 1.6 - 1.7 times.
Currently, two-stroke diesel engines are widely used only on large marine vessels with a direct (gearless) propeller drive. When it is impossible to increase the speed of rotation, the two-stroke cycle is beneficial; such low-speed diesel engines have a power of up to 100,000 hp.

Advantages and disadvantages.
A gasoline engine is rather inefficient and is only capable of converting about 20-30% of the fuel's energy into useful work. A standard diesel engine, however, typically has an efficiency of 30-40%, turbocharged and intercooled diesels in excess of 50% (e.g. MAN S80ME-C7 consumes only 155g per kW, achieving an efficiency of 54.4%). The diesel engine, due to the use of high pressure injection, does not impose requirements on the volatility of the fuel, which allows the use of low-grade heavy oils in it.
A diesel engine cannot develop high speeds - the mixture does not have time to burn out in the cylinders. This leads to a decrease in the specific power of the engine per 1 liter of volume, and hence to a decrease in the specific power per 1 kg of engine weight.
The diesel engine does not have a throttle valve, power control is carried out by regulating the amount of fuel injected. This results in no reduction in pressure in the cylinders at low speeds. This is why a diesel produces high torque at low revs, which makes a car with a diesel engine more responsive in motion than the same car with a gasoline engine. For this reason, most trucks are now equipped with diesel engines.
The obvious disadvantages of diesel engines are the need to use a high-power starter, turbidity and solidification of summer diesel fuel at low temperatures, the difficulty in repairing fuel equipment, since high-pressure pumps are devices made with high precision. Also, diesel engines are extremely sensitive to fuel contamination with mechanical particles and water. Such contaminants very quickly disable the fuel equipment. Repair of diesel engines, as a rule, is much more expensive than the repair of gasoline engines of a similar class. The liter output of diesel engines is also generally inferior to those of gasoline engines, although diesel engines have more even torque in their operating range. The environmental performance of diesel engines was significantly inferior to gasoline engines until recently. On classic diesel engines with mechanically controlled injection, it is only possible to install oxidative exhaust gas converters (“catalyst” in common parlance), operating at exhaust gas temperatures above 300 ° C, which oxidize only CO and CH to carbon dioxide (CO2) harmless to humans and water. Also, these converters used to fail due to poisoning with sulfur compounds (the amount of sulfur compounds in the exhaust gases directly depends on the amount of sulfur in diesel fuel) and the deposition of soot particles on the catalyst surface. The situation began to change only in recent years in connection with the introduction of diesel engines of the so-called "Common-rail" system. In this type of diesel engines, fuel injection is carried out by electrically controlled nozzles. The supply of a control electrical impulse is carried out by an electronic control unit that receives signals from a set of sensors. The sensors monitor various engine parameters that affect the duration and timing of the fuel pulse. So, in terms of complexity, a modern - and as environmentally friendly as a gasoline - diesel engine is in no way inferior to its gasoline counterpart, and in a number of complexity parameters it significantly surpasses it. So, for example, if the fuel pressure in the injectors of a conventional diesel engine with mechanical injection is from 100 to 400 bar, then in the latest Common-rail systems it is in the range from 1000 to 2500 bar, which entails considerable problems. Also, the catalytic system of modern transport diesel engines is much more complicated than gasoline engines, since the catalyst must be able to work in conditions of an unstable exhaust gas composition, and in some cases, the introduction of a so-called "particulate filter" is required. A "particulate filter" is a conventional catalytic converter-like structure installed between a diesel exhaust manifold and a catalyst in the exhaust stream. A high temperature develops in the particulate filter, at which soot particles can be oxidized by residual oxygen contained in the exhaust gases. However, part of the soot is not always oxidized and remains in the "particulate filter", so the control unit program periodically switches the engine to the "particulate filter" cleaning mode by the so-called "post-injection", that is, the injection of additional fuel into the cylinders at the end of the combustion phase in order to raise the temperature of the gases, and, accordingly, clean the filter by burning the accumulated soot. The de facto standard in the design of transport diesel engines has become the presence of a turbocharger, and in recent years, the so-called "intercooler" - that is, a device that cools the air compressed by a turbocharger. The supercharger made it possible to raise the specific power characteristics of mass diesel engines, as it allows more air to pass through the cylinders during the working cycle.

And finally, the most interesting. MYTHS about diesel engines.

Diesel engine is too slow.
Modern turbocharged diesel engines are much more efficient than their predecessors, and sometimes outperform their naturally aspirated (non-turbocharged) gasoline counterparts with the same engine size. This is evidenced by the diesel prototype Audi R10, which won the 24-hour race at Le Mans, and the new BMW engines, which are not inferior in power to naturally aspirated (non-turbo) gasoline and at the same time have huge torque.

The diesel engine is too loud.
A properly tuned diesel engine is only slightly “louder” than a gasoline one, which is noticeable only at idle. There is practically no difference in operating modes. A loud running engine indicates improper operation and possible malfunctions. In fact, the old diesels with mechanical injection really have a very tough job. Only with the advent of high-pressure common-rail fuel systems for diesel engines was it possible to significantly reduce noise, primarily by dividing one injection pulse into several (typically from 2 to 5 pulses).

The diesel engine is much more economical.
The times when diesel fuel was three times cheaper than gasoline are long gone. Now the difference is only about 10-30% in terms of fuel prices. Despite the fact that the specific heat of combustion of diesel fuel (42.7 MJ/kg) is less than that of gasoline (44-47 MJ/kg), the main efficiency is due to the higher efficiency of the diesel engine. On average, a modern diesel consumes up to 30% less fuel. The service life of a diesel engine is indeed much longer than a gasoline engine and can reach 400-600 thousand kilometers. [source not specified 211 days] Spare parts for diesel engines are also somewhat more expensive, as is the cost of repairs. Despite all of the above reasons, the cost of operating a diesel engine, if properly maintained, will not be much less than that of a gasoline engine. [source not specified 211 days]

The diesel engine does not start well in cold weather.
With proper operation and preparation for winter, there will be no problems with the engine. For example, the VW-Audi 1.9 TDI diesel engine (77 kW / 105 hp) is equipped with a quick start system: glow plugs are heated to 1000 degrees in 2 seconds. The system allows you to start the engine in any climatic conditions without preheating.

A diesel engine cannot be converted to use cheaper gas as fuel.
The first examples of diesel engines running on cheaper fuel - gas, were pleased back in 2005 by Italian tuning companies that used methane as fuel. At present, options for the use of propane gas diesel engines have successfully proven themselves, as well as cardinal solutions for converting a diesel engine into a gas engine, which has an advantage over a similar engine converted from gasoline due to an initially higher compression ratio.

What about a diesel engine?

Authors: Vladimir Egorov, Andrey Dalimaev
Source: website

What is a diesel car?

Diesel vehicles use an engine that has a different combustion cycle than a gasoline engine.

In a gasoline engine, fuel mixes with air, enters the cylinder and is ignited by a spark plug. In a diesel engine, air is forced into the cylinder and compressed first without fuel. This compression heats the air to such a high temperature that when the fuel is then injected into the cylinder, it ignites.

By using higher compression levels and higher combustion temperatures, diesels are more energy efficient. As a result of this, diesel powered vehicles perform better than their petrol counterparts. In addition, a liter of diesel fuel contains about 10% more energy than a liter of gasoline. These two factors help modern diesels achieve about 50% better fuel economy than their gasoline counterparts. Diesel vehicles now account for nearly half of all new car sales in Europe, and a small but growing market share in the US. In Russia, in 2009, the market share of new cars occupied by diesel was only 5.6%, according to the Avtostat agency.

Diesel advantages

• Better fuel efficiency (20-40% more than gasoline vehicles).
• Diesel engines last longer and earn a higher resale value.
• Diesel engines can use biodiesel as fuel.
• Diesel provides more torque; great for fast acceleration and towing.
• More range per tank.

Diesel Disadvantages

• In Russia, diesel fuel is of very low quality.
• The range of models with a diesel engine is small.
• Diesel fuel is not available at all petrol stations.
• Diesel vehicles tend to be more expensive.
• Exhaust emissions of nitrogen oxides and particulate matter are generally higher.
• Considering the advantages and disadvantages of a diesel engine, we can conclude that the latter are not significant and can be overcome.

Dreams of a diesel hybrid

Toyota, Ford, Volkswagen, Peugot and Citroën produce concept vehicles that combine a diesel engine with a hybrid system. The "Citroën C-Metisse" diesel hybrid introduced at the 2006 Paris Motor Show is pictured below. Combining two fuel-saving technologies in one vehicle can be phenomenal.

Unfortunately, the extra cost of combining a diesel engine with a hybrid system comes at a cost. Most analysts predict that the diesel hybrid will be a specialty item.

The same year it was successfully tested. Diesel actively engaged in the sale of licenses for the new engine. Despite the high efficiency and ease of operation compared to a steam engine, the practical use of such an engine was limited: it was inferior to the steam engines of that time in terms of size and weight.

The first Diesel engines ran on vegetable oils or light petroleum products. Interestingly, he initially proposed coal dust as an ideal fuel. Experiments also showed the impossibility of using coal dust as a fuel - primarily because of the high abrasive properties of both the dust itself and the ash resulting from combustion; there were also big problems with the supply of dust to the cylinders.

Principle of operation

Four stroke cycle

• 1st measure. Inlet. Corresponds to 0° - 180° crankshaft rotation. Through the open ~345-355° inlet valve, air enters the cylinder, at 190-210° the valve closes. At least up to 10-15 ° of rotation of the crankshaft, the exhaust valve is simultaneously open, the time of joint opening of the valves is called valve overlap .
• 2nd beat. Compression. Corresponds to 180° - 360° crankshaft rotation. The piston, moving to the TDC (top dead center), compresses the air 16 (in low-speed) -25 (in high-speed) times.
• 3rd beat. Working stroke, extension. Corresponds to 360° - 540° crankshaft rotation. When fuel is sprayed into hot air, fuel combustion is initiated, that is, its partial evaporation, the formation of free radicals in the surface layers of drops and in vapors, and finally, it flares up and burns out as it comes from the nozzle, combustion products, expanding, move the piston down. The injection and, accordingly, the ignition of the fuel occurs a little earlier than the moment the piston reaches the dead center due to some inertia of the combustion process. The difference from the ignition advance in gasoline engines is that the delay is necessary only because of the presence of the initiation time, which in each particular diesel engine is a constant value and cannot be changed during operation. Combustion of fuel in a diesel engine thus occurs for a long time, as long as the supply of a portion of fuel from the nozzle lasts. As a result, the working process proceeds at a relatively constant gas pressure, due to which the engine develops a large torque. Two important conclusions follow from this.
  • 1. The combustion process in a diesel engine lasts exactly as long as it takes to inject a given portion of fuel, but not longer than the working stroke.
  • 2. The fuel/air ratio in the diesel cylinder can differ significantly from the stoichiometric one, and it is very important to provide an excess of air, since the flame of the torch occupies a small part of the volume of the combustion chamber and the atmosphere in the chamber must provide the required oxygen content to the last. If this does not happen, there is a massive release of unburned hydrocarbons with soot - "the diesel locomotive" gives "bear".).
• 4th beat. Release. Corresponds to 540° - 720° crankshaft rotation. The piston goes up, through the exhaust valve open at 520-530 °, the piston pushes the exhaust gases out of the cylinder.

Depending on the design of the combustion chamber, there are several types of diesel engines:

• Diesel with undivided chamber: the combustion chamber is made in the piston, and the fuel is injected into the space above the piston. The main advantage is the minimum fuel consumption. The disadvantage is increased noise ("hard work"), especially at idle. Currently, intensive work is underway to eliminate this shortcoming. For example, a Common Rail system uses (often multi-stage) pre-injection to reduce harshness.
• Split chamber diesel: fuel is supplied to the additional chamber. In most diesel engines, such a chamber (it is called a vortex or prechamber) is connected to the cylinder by a special channel so that when compressed, the air entering this chamber swirls intensively. This contributes to good mixing of the injected fuel with air and more complete combustion of the fuel. Such a scheme has long been considered optimal for light diesel engines and has been widely used in passenger cars. However, due to the worse efficiency, the last two decades have been actively replacing such diesel engines with single-chamber engines and Common Rail fuel supply systems.

push cycle

Purge of a two-stroke diesel engine: at the bottom - purge windows, the exhaust valve at the top is open

In addition to the four-stroke cycle described above, a two-stroke cycle can be used in a diesel engine.

During the working stroke, the piston goes down, opening the outlet windows in the cylinder wall, exhaust gases exit through them, the inlet windows open at the same time or somewhat later, the cylinder is blown with fresh air from the blower - carried out purge combining the intake and exhaust strokes. When the piston rises, all windows close. From the moment the inlet windows close, compression begins. Just before reaching TDC, fuel is sprayed from the nozzle and lights up. An expansion occurs - the piston goes down and opens all the windows again, etc.

Scavenging is an inherent weak link in the two-stroke cycle. The purge time, in comparison with other cycles, is small and cannot be increased, otherwise the efficiency of the stroke will decrease due to its shortening. In a four-stroke cycle, half of the cycle is allotted for the same processes. It is also impossible to completely separate the exhaust and fresh air charge, so some of the air is lost, going straight into the exhaust pipe. If the change of cycles is provided by the same piston, there is a problem associated with the symmetry of opening and closing windows. For better gas exchange, it is more advantageous to have an advance opening and closing of the exhaust windows. Then the exhaust, starting earlier, will provide a decrease in the pressure of the residual gases in the cylinder by the beginning of the purge. With the exhaust windows closed earlier and the inlet windows still open, the cylinder is recharged with air, and if the blower provides excess pressure, it becomes possible to pressurize.

Windows can be used both for exhaust gases and for fresh air intake; such a purge is called slot or window. If the exhaust gases are vented through a valve in the cylinder head and the windows are only used to let in fresh air, the purge is called valve-slot. There are engines where in each cylinder there are two counter-moving pistons; each piston controls its windows - one inlet, the other outlet (Fairbanks-Morse - Junkers - Koreyvo system: diesel engines of this system of the D100 family were used on diesel locomotives TE3, TE10, tank engines 4TPD, 5TD (F) (T-64), 6TD (T -80UD), 6TD-2 (T-84), in aviation - on Junkers bombers (Jumo 204, Jumo 205).

In a two-stroke engine, the working strokes occur twice as often as in a four-stroke one, but due to the presence of a purge, a two-stroke diesel engine is more powerful than a four-stroke one of the same volume by a maximum of 1.6-1.7 times.

At present, low-speed two-stroke diesel engines are widely used on large marine vessels with a direct (gearless) propeller drive. Due to the doubling of the number of strokes at the same speed, the two-stroke cycle is beneficial when it is impossible to increase the speed, in addition, a two-stroke diesel engine is technically easier to reverse; such low-speed diesel engines have a power of up to 100,000 hp.

Due to the fact that it is difficult to organize a purge of the vortex chamber (or prechamber) in a two-stroke cycle, two-stroke diesel engines are built only with undivided combustion chambers.

Design options

For medium and heavy two-stroke diesel engines, the use of composite pistons is typical, which uses a steel head and an duralumin skirt. The main purpose of this complication of the design is to reduce the total mass of the piston while maintaining the maximum possible heat resistance of the bottom. Oil-cooled liquid-cooled designs are very often used.

Four-stroke engines containing crossheads in the design are allocated to a separate group. In crosshead engines, the connecting rod is connected to the crosshead - a slider connected to the piston by a rod (rolling pin). The crosshead works along its guide - the crosshead, without exposure to elevated temperatures, completely eliminating the effect of lateral forces on the piston. This design is typical for large long-stroke marine engines, often double-acting, the piston stroke in them can reach 3 meters; trunk pistons of such dimensions would be overweight, trunks with such a friction area would significantly reduce the mechanical efficiency of a diesel engine.

Reversible motors

The combustion of the fuel injected into the diesel cylinder occurs as it is injected. This is why a diesel produces high torque at low revs, which makes a diesel-powered vehicle more responsive in motion than the same gasoline-powered vehicle. For this reason, and due to the higher efficiency, most trucks are currently equipped with diesel engines.. For example, in Russia in 2007, almost all trucks and buses were equipped with diesel engines (the final transition of this vehicle segment from gasoline engines to diesel engines was planned to be completed by 2009). This is also an advantage in marine engines, as high torque at low rpm makes it easier to use the engine's power efficiently, and higher theoretical efficiency (see Carnot cycle) gives higher fuel efficiency.

Compared to gasoline engines, diesel engine exhaust typically has less carbon monoxide (CO), but now, with the introduction of catalytic converters on gasoline engines, this benefit is less noticeable. The main toxic gases that are present in the exhaust in appreciable quantities are hydrocarbons (HC or CH), oxides (oxides) of nitrogen (NO x) and soot (or its derivatives) in the form of black smoke. The most polluting vehicles in Russia are truck and bus diesels, which are often old and unregulated.

Another important safety aspect is that diesel fuel is non-volatile (i.e. does not evaporate easily) and thus diesel engines are much less likely to catch fire, especially since they do not use an ignition system. Together with high fuel efficiency, this led to the widespread use of diesel engines in tanks, since in everyday non-combat operation the risk of a fire in the engine compartment due to fuel leaks was reduced. The lower fire hazard of a diesel engine in combat conditions is a myth, since when penetrating armor, a projectile or its fragments have a temperature that is much higher than the flash point of diesel fuel vapors and can also quite easily set fire to the leaked fuel. The detonation of a mixture of diesel fuel vapors with air in a pierced fuel tank is comparable in its consequences to an explosion of ammunition, in particular, in T-34 tanks, it led to rupture of welds and knocking out of the upper frontal part of the armored hull. On the other hand, a diesel engine in tank building is inferior to a carburetor in terms of specific power, and therefore in some cases (high power with a small engine compartment) it may be more advantageous to use a carburetor power unit (although this is typical for too light combat units).

Of course, there are also disadvantages, among which is the characteristic knock of a diesel engine during its operation. However, they are noticed mainly by owners of cars with diesel engines, and are almost invisible to an outsider.

The obvious disadvantages of diesel engines are the need to use a high-power starter, turbidity and solidification (waxing) of summer diesel fuel at low temperatures, the complexity and higher cost of repairing fuel equipment, since high-pressure pumps are precision devices. Also, diesel engines are extremely sensitive to fuel contamination with mechanical particles and water. Repair of diesel engines, as a rule, is much more expensive than the repair of gasoline engines of a similar class. The liter capacity of diesel engines is also usually inferior to that of gasoline engines, although diesel engines have a more even and higher torque in their displacement. The environmental performance of diesel engines was significantly inferior to gasoline engines until recently. On classic diesel engines with mechanically controlled injection, it is only possible to install oxidizing exhaust gas converters operating at exhaust gas temperatures above 300 ° C, which oxidize only CO and CH to carbon dioxide (CO 2) and water that are harmless to humans. Also, these converters used to fail due to poisoning with sulfur compounds (the amount of sulfur compounds in the exhaust gases directly depends on the amount of sulfur in diesel fuel) and the deposition of soot particles on the catalyst surface. The situation began to change only in recent years in connection with the introduction of diesel engines of the so-called Common rail system. In this type of diesel engines, fuel injection is carried out by electronically controlled nozzles. The supply of a control electrical impulse is carried out by an electronic control unit that receives signals from a set of sensors. The sensors monitor various engine parameters that affect the duration and timing of the fuel pulse. So, in terms of complexity, a modern - and as environmentally friendly as a gasoline - diesel engine is in no way inferior to its gasoline counterpart, and in a number of parameters (complexity) it significantly surpasses it. So, for example, if the fuel pressure in the injectors of a conventional diesel engine with mechanical injection is from 100 to 400 bar (approximately equivalent to "atmospheres"), then in the latest Common-rail systems it is in the range from 1000 to 2500 bar, which entails presents a lot of problems. Also, the catalytic system of modern transport diesel engines is much more complicated than gasoline engines, since the catalyst must be able to work under conditions of unstable exhaust gas composition, and in some cases, the introduction of the so-called "particulate filter" (DPF - particulate filter) is required. A "particulate filter" is a conventional catalytic converter-like structure installed between a diesel exhaust manifold and a catalyst in the exhaust stream. A high temperature develops in the particulate filter, at which soot particles can be oxidized by residual oxygen contained in the exhaust gases. However, part of the soot is not always oxidized and remains in the "particulate filter", so the control unit program periodically switches the engine to the "particulate filter cleaning" mode by the so-called "post-injection", that is, injection of additional fuel into the cylinders at the end of the combustion phase in order to raise the temperature of the gases, and, accordingly, clean the filter by burning the accumulated soot. The de facto standard in the design of transport diesel engines has become the presence of a turbocharger, and in recent years - and " intercooler" - a device that cools the air after turbocharger compression - so that after cooling to get a large mass air (oxygen) in the combustion chamber at the same capacity of the collectors, and The supercharger made it possible to raise the specific power characteristics of mass diesel engines, as it allows more air to pass through the cylinders during the working cycle.

Basically, the design of a diesel engine is similar to that of a gasoline engine. However, similar parts of a diesel engine are heavier and more resistant to high compression pressures that occur in a diesel engine, in particular, the hone on the surface of the cylinder mirror is rougher, but the hardness of the cylinder block walls is higher. Piston heads, however, are specially designed for the combustion characteristics of diesel engines and are almost always designed for higher compression ratios. In addition, the piston heads in a diesel engine are located above (for an automobile diesel engine) the upper plane of the cylinder block. In some cases - in older diesel engines - the piston heads contain a combustion chamber ("direct injection").

Applications

Diesel engines are used to drive stationary power plants, on rail (diesel locomotives, diesel locomotives, diesel trains, railcars) and trackless (cars, buses, trucks) vehicles, self-propelled machines and mechanisms (tractors, asphalt rollers, scrapers, etc.). ), as well as in shipbuilding as main and auxiliary engines.

Myths about diesel engines

Turbocharged diesel engine

• Diesel engine is too slow.

Modern turbocharged diesel engines are much more efficient than their predecessors, and sometimes outperform their naturally aspirated (non-turbocharged) gasoline counterparts of the same displacement. This is evidenced by the Audi R10 diesel prototype, which won the 24-hour race at Le Mans, and the new BMW engines, which are not inferior in power to naturally aspirated (non-turbocharged) gasoline engines and at the same time have huge torque.

• The diesel engine is too loud.

Loud engine operation indicates improper operation and possible malfunctions. In fact, some older direct-injection diesels do work quite hard. With the advent of common-rail high-pressure fuel systems (“Common-rail”), diesel engines have been able to significantly reduce noise, primarily due to the division of one injection pulse into several (typically from 2 to 5 pulses).

• The diesel engine is much more economical.

The main economy is due to the higher efficiency of the diesel engine. On average, a modern diesel consumes up to 30% less fuel. The service life of a diesel engine is longer than a gasoline engine and can reach 400-600 thousand kilometers. Spare parts for diesel engines are somewhat more expensive, the cost of repairs is also higher, especially for fuel equipment. For the above reasons, the cost of operating a diesel engine is somewhat less than that of a gasoline engine. Savings compared to gasoline engines increase in proportion to power, which determines the popularity of using diesel engines in commercial vehicles and heavy vehicles.

• A diesel engine cannot be converted to use cheaper gas as fuel.

From the first moments of the construction of diesel engines, a huge number of them were built and are being built, designed to work on gas of different composition. There are basically two ways to convert diesel engines to gas. The first method is that a lean gas-air mixture is supplied to the cylinders, compressed and ignited by a small pilot jet of diesel fuel. An engine operating in this way is called a gas-diesel engine. The second way is to convert a diesel engine with a reduction in the compression ratio, install an ignition system and, in fact, build a gas engine instead of a diesel engine based on it.

record holders

Largest/Most Powerful Diesel Engine

Configuration - 14 cylinders in line

Working volume - 25 480 liters

Cylinder diameter - 960 mm

Piston stroke - 2500 mm

Average effective pressure - 1.96 MPa (19.2 kgf / cm²)

Power - 108,920 hp at 102 rpm. (recoil per liter 4.3 hp)

Torque - 7 571 221 Nm

Fuel consumption - 13,724 liters per hour

Dry weight - 2300 tons

Dimensions - length 27 meters, height 13 meters

The largest diesel engine for a truck

MTU 20V400 designed for installation on a BelAZ-7561 mining dump truck.

Power - 3807 hp at 1800 rpm. (Specific fuel consumption at rated power 198 g/kW*h)

Torque - 15728 Nm

The largest / most powerful serial diesel engine for a serial passenger car

Audi 6.0 V12 TDI since 2008 it has been installed on the Audi Q7.

Configuration - 12 cylinders V-shaped, camber angle 60 degrees.

Working volume - 5934 cm³

Cylinder diameter - 83 mm

Stroke - 91.4 mm

Compression ratio - 16

Power - 500 hp at 3750 rpm. (return per liter - 84.3 hp)

Torque - 1000 Nm in the range of 1750-3250 rpm.

The principle of operation of a diesel engine looks like self-ignition of the supplied atomized fuel when interacting with air heated by compression. In a nutshell, it is not entirely clear what is at stake, so we will devote this article entirely to a diesel engine.

Diesel engine device - main parts

Such engines have both a number of advantages and a number of disadvantages. The first include: the principle of its operation is ideal for heavy trucks; it is more economical compared to a gasoline power unit. Disadvantages: the process of fuel combustion itself is tantamount to an explosion, which in itself cannot be a virtue; fuel equipment has a rather complicated design, so if it fails, you will have to tinker well; the developed speed will be less than when working on gasoline engines.

The diesel engine device is presented as follows. It all starts with the intake valve, through which air can enter the working cylinders. The piston creates the necessary pressure so that the incoming air is heated to the required temperature, and the crankshaft perceives the force from the piston and converts it into torque. This is what a diesel engine looks like in a nutshell.

The principle of operation of a diesel engine - choose the type of combustion chamber

There are two types of fuel ignition areas, depending on the type of fuel itself. The undivided combustion chamber is located in the piston, while the fuel in this case is injected into the over-piston space. In this case, you can count on efficiency, since the consumption of the combustible mixture will be minimal, but increased noise will serve as a negative point, especially during idling.

In divided combustion chambers, fuel is supplied to a separate chamber, which is connected to the cylinder through a special channel. Excellent mixing of fuel with air is provided, only after that it is already fed into the working space, which contributes to better combustion of the mixture. This increases the cleanliness of emissions, engine durability and car power.

How a diesel engine works - engine cycle

The scheme of operation of a diesel engine is two-stroke and four-stroke. In the first case, the work occurs as follows: during the working stroke, the piston moves down, while the outlet holes in the cylinder open and exhaust gases exit from it. At the same time (sometimes a little later), the inlet windows are opened, and air is blown through. Then the piston starts moving upwards, all windows are closed, and the process of air compression takes place. Before the piston reaches TDC (highest dead center), fuel is sprayed from the injector, an explosion occurs, and the whole process is repeated anew.

It is important to know how a diesel engine works and the four-stroke circuit. In the first stroke, air is admitted, at the same time, the exhaust valve is open. The second stroke corresponds to compressing the air so that it reaches the required temperature. On the third stroke, a combustible mixture is injected into the combustion chamber, and as a result of interaction with heated air, an explosion occurs. During the fourth stroke, exhaust gases are removed from the cylinder body.

A four-stroke engine, other things being equal, has less power than a two-stroke one, but it has greater efficiency and a more efficient degree of fuel combustion.

How a diesel engine works - modern realities

The device of a modern diesel engine is equipped with a computer controlled fuel supply. This system allows the injection of a combustible mixture into the cylinders in metered portions. This moment is very important for diesel power units, since with such a supply, the pressure that occurs in the combustion chamber increases smoothly without the occurrence of various kinds of “jerks”, and this is the best way to contribute to the soft and silent operation of the power unit.