Engine combustion chamber- this is a closed space, a cavity for burning gaseous or liquid fuels in engines internal combustion. The combustion chamber prepares and burns the air-fuel mixture.

Along with ensuring optimal mixture formation, ⭐ combustion chambers should contribute to obtaining high economic performance and good starting qualities of engines. Depending on the design and the method of mixture formation used, the combustion chambers of diesel engines are divided into two groups:

• undivided
• separated

Undivided combustion chambers are a single volume and usually have a simple shape, which is generally consistent with the direction, size and number of fuel jets at injection. These chambers are compact, have a relatively small cooling surface, which reduces heat loss. Engines with such combustion chambers have decent economic indicators and good starting qualities.

Undivided combustion chambers are distinguished by a wide variety of shapes. Most often they are performed in the bottom of the pistons, sometimes partly in the bottom of the piston and partly in the cylinder head, less often in the head.

The figure shows some designs of undivided combustion chambers.

Rice. Combustion chambers of undivided diesel engines: a - toroidal in the piston; b - hemispherical in the piston and cylinder head; c - hemispherical in the piston; g - cylindrical in the piston; d - cylindrical in the piston with lateral placement; e - oval in the piston: g - ball in the piston; h - toroidal in a piston with a neck; and - cylindrical, formed by the bottoms of the pistons and the walls of the cylinder; k - vortex in the piston; l - trapezoidal in the piston; m - cylindrical in the head under the exhaust valve

In the combustion chambers shown in the figure, a-d quality Mixing is achieved solely by atomizing the fuel and matching the shape of the chambers with the shape of the fuel injection jets. These chambers most often use multi-hole nozzles and use high injection pressures. Such chambers have minimal cooling surfaces. They have a low compression ratio.

The combustion chambers shown in fig. f-h, they have a more developed heat transfer surface, which somewhat worsens the starting properties of the engine. However, by displacing air from the over-piston space into the volume of the chamber during compression, it is possible to create intense vortex charge flows that contribute to good mixing of fuel with air. This provides high quality mixture formation.

The combustion chambers shown in the figure, to-m, are used in multi-fuel engines. They are characterized by the presence of strictly directed charge flows, which ensure the evaporation of fuel and its introduction into the combustion zone in a certain sequence. To improve the working process in a cylindrical combustion chamber in the head under the exhaust valve (fig. m), the high temperature of the exhaust valve, which is one of the walls of the chamber, is used.

Separated combustion chambers

Separated combustion chambers consist of two separate volumes interconnected by one or more channels. The cooling surface of such chambers is much larger than that of undivided chambers. Therefore, due to large heat losses, engines with divided combustion chambers usually have worse economic and starting qualities and, as a rule, higher compression ratios.

However, with separate combustion chambers, due to the use of the kinetic energy of gases flowing from one cavity to another, it is possible to ensure high-quality preparation of the fuel-air mixture, due to which a fairly complete combustion of the fuel is achieved and exhaust smoke is eliminated.

Rice. Combustion chambers of diesel engines of a divided type: a - prechamber; b - vortex chamber in the head; c - vortex chamber in the block

In addition, the throttling effect of the connecting channels of the divided chambers can significantly reduce the "rigidity" of the engine and reduce the maximum load on the parts of the crank mechanism. Some reduction in the "rigidity" of engines with separated combustion chambers can also be achieved by increasing the temperature of individual parts of the combustion chambers.

Intermittent engine combustion chamber

Engine combustion chamber- the volume formed by a combination of engine parts in which the combustible mixture is burned. The design of the combustion chamber is determined by the operating conditions and the purpose of the mechanism; as a rule, heat-resistant materials are used. Depending on the temperature developed in the continuous combustion chamber, the following materials are used as structural materials for their manufacture:

• up to 500 ° C - chromium-nickel steels;
• up to 900 ° C - chromium-nickel steels with the addition of titanium;
• above 950 °C - special materials.

The combustion chamber- this is a closed space, a cavity for burning gaseous or liquid fuels in internal combustion engines.
Combustion chamber of a gas turbine engine- a device in which, as a result of the combustion of fuel, the temperature of the air (gas) entering it rises.

classification

According to the principle of action

• continuous action(for gas turbine engines (GTE), turbojet engines (TRD), air-jet engines (WFD), liquid rocket engines(LPRE)).
• periodic action(for piston internal combustion engines (ICE));

Continuous combustion chambers, in turn, are classified:
By appointment

• Basic;
• Reserve;
• intermediate heating;

In the direction of air flow and combustion products

• straight-through;
• countercurrent combustion chambers (the latter are rarely used because of the high hydraulic resistance).

By layout

• built-in;
• Remote;

According to the design features of the body and the flame tube

• Ring;
• Tubular-ring;
• tubular;

Intermittent combustion chambers, in turn, are classified:
By fuel used

• Petrol;

By design gasoline combustion chambers share:

• • Lateral
  • Central
  • Semi-wedge
  • Wedge
• Diesel.

By design diesel combustion chambers share:

• • Undivided (they have only one compartment, in which both mixture formation and fuel combustion occur)
  • Separated (divided into two parts: main and additional, interconnected by a neck. At the same time, fuel is injected into an additional chamber)

According to the method of mixing

• • Volumetric (for undivided combustion chambers);
  • Film;
  • Combined.

Continuous combustion chamber

The continuous combustion chamber is one of the most important components of aviation and space propulsion systems, special and transport gas turbine plants, which are widely used in the energy sector, chemical industry, on the railroad transport, sea and river vessels.

Principle of operation

The combustion chamber is a unit of a gas turbine engine (GTE), in which the air-fuel mixture is prepared and burned. To prepare the air-fuel mixture, fuel is supplied to the combustion chamber through nozzles and air is supplied from the compressor. In the process of starting the engine, the air-fuel mixture is ignited by an electric spark (or starting device), and during further operation, the combustion process is maintained continuously due to the contact of the resulting air-fuel mixture with hot combustion products. The gas formed in the combustion chamber is sent to the compressor turbine.

The stability and perfection of the processes in the combustion chamber largely ensure the reliable and economical operation of a gas turbine engine.

Requirements for a continuous combustion chamber

• Stability of the combustion process under all possible modes and flight conditions. It is necessary that the combustion of the fuel be continuous and that there is no flameout or pulsating combustion, which can cause the engine to self-shutdown. In the process of changing the engine operating mode and flight conditions, the ratio of fuel and air entering the combustion chamber changes, i.e. the quality of the mixture changes.
• Ensuring a uniform gas temperature field in front of the turbine. Usually the combustion chambers have several nozzles for supplying fuel, therefore, there is a tendency to obtain zones of different temperatures at the outlet of the gases from the combustion chamber. A significant non-uniformity of the gas temperature field can lead to the destruction of turbine blades.
• Minimum flame length, i.e. the combustion process must end within the combustion chamber. Otherwise, the flame reaches the blades of the nozzle apparatus, which can lead to their burnout.
• Reliable operation, long service life, easy control and Maintenance. Ensuring long-term and reliable operation of the combustion chamber is achieved both by a number of design measures and by strict observance of flight and flight rules. technical operation. For maximum fulfillment of the listed requirements, each type of engine is selected with the appropriate type of combustion chamber.

Batch combustion chamber

Gasoline powered combustion chamber

Gasoline engine with wedge combustion chamber

Hemispherical combustion chamber

The designs of the combustion chambers of automobile engines are different. Engines with overhead valves use central chambers, as well as chambers of semi-wedge and wedge types. With the lower location of the valves, the main volume of the combustion chamber is shifted away from the axis of the cylinder (L-shaped); This design of the chamber enhances the swirl of the combustible mixture and improves mixture formation. Combustion chambers of semi-wedge and wedge types are widely used on modern engines.

Wedge combustion chamber- Derived from flat oval sloping valves to obtain a better shape of the gas channels. The spark plug in this case is shifted towards the exhaust valve, the movement of the charge in the chamber is directed towards the candle. In a wedge-shaped combustion chamber, most of its volume is concentrated near the candle, due to which the largest amount of charge must burn first, and in the zone of the combustion chamber farthest from the candle, where there is a danger of detonation, there should be relatively little a large number of supercooled mixture in the displacer gap. Such a chamber provides soft combustion and low heat losses. The rigidity of the engine is estimated by the rate of pressure increase, i.e., by increasing the pressure in the cylinder when the crankshaft is turned, the turning section corresponding to the interval between the formation of a spark discharge (ignition of the mixture) and TDC is of decisive importance. The combustion process is considered to be soft, in which the rate of pressure increase lies within 0.2 - 0.6 MPa per 1 ° angle of rotation of the crankshaft. The noise level during engine operation also depends on the clearances between the piston and cylinder and between the shaft and its bearings.

Widely used in the past semi-wedge combustion chamber is currently undergoing changes. A chamber of this shape is used in engines of sports, racing cars to achieve high power density. With the use of two camshafts in the cylinder head and a large camber angle, large diameter valves can be placed in the cylinder head. In this case, the surface of the combustion chamber in relation to its volume is quite small. A good inflow of charge through the valves into the cylinder is also ensured, since it is not obstructed by the walls of the cylinder or the combustion chamber. The inlet and outlet channels have a small length and a small surface. Engines with such a combustion chamber have a fairly high efficiency.

Diesel combustion chamber

A- Hemispherical undivided combustion chamber for volumetric mixing
b– toroidal undivided combustion chamber for volumetric mixing
G- Undivided combustion chambers for film mixing
d- undivided combustion chambers for combined mixture formation

In diesel engines, the requirements for the shape of the combustion chamber are determined by the mixture formation process. A very short time is allotted to create a working mixture in them, since almost immediately after the start of fuel injection, combustion begins, and the remainder of the fuel is already fed into the burning medium. Each drop of fuel must come into contact with the air as quickly as possible so that heat release occurs at the beginning of the expansion stroke.

Film mixing is used in a number of designs of combustion chambers, when almost all the fuel is directed to the near-wall zone. Approximately 5–10% of the fuel injected by the injector enters the central part of the combustion chamber. The rest of the fuel is distributed on the walls of the combustion chamber in the form of a thin film (10–15 µm). Initially, part of the fuel ignites in the central part of the combustion chamber, where there is usually no charge movement and the highest temperature is set. Later, as it evaporates and mixes with air, combustion spreads to the main part of the fuel directed to the near-wall layer. Film mixing requires less fine atomization of the fuel. Single nozzle nozzles are used. The fuel injection pressure does not exceed 17–20 MPa.

Film mixing in comparison with volumetric mixing provides better economic performance of the engine, simplifies the design of fuel equipment.

The main disadvantage is the low starting properties of the engine at low temperatures due to the small amount of fuel involved in the initial combustion. This disadvantage is eliminated by heating the intake air or by increasing the amount of fuel involved in the formation of the initial combustion chamber.

Combined mixing is obtained with smaller diameters of the combustion chamber, when part of the fuel reaches its wall and is concentrated in the near-wall layer. Another part of the fuel droplets is located in the internal volume of the charge. Approximately 50% of the fuel settles on the surface of the chamber. When inlet in the chamber, no rotational movement of the charge is created. The charge is set in motion when it is forced out of the over-piston space into the combustion chamber, and a vortex is created. The speed of charge movement reaches 40–45 m/s.

Distinctive feature From the film mixture formation is the oncoming movement of the jets of fuel and charge displaced from the over-piston space, which contributes to an increase in the amount of fuel suspended in the volume of the combustion chamber, and brings the process closer to volumetric mixture formation. Nozzles are used with sprayers having 3-5 nozzle holes

Volumetric combustion chambers. In diesel engines with such chambers, fuel is injected directly into the combustion chamber by a nozzle with an operating pressure of 15–30 MPa, which has multi-hole atomizers (5–7 holes) with a small diameter of nozzle channels (0.15–0.32 mm). Such high injection pressures are used due to the fact that in this case the atomization of the fuel and its mixing with air is achieved mainly due to the kinetic energy imparted to the fuel during injection. For uniform distribution of fuel in the chamber, the nozzles of such engines are often made with several holes.

Requirements for all engine combustion chambers

The basic requirements for all continuous combustion chambers are:

• stability of the combustion process
• high heat stress
• maximum combustion efficiency
• minimal heat loss
• reliable operation during the established engine life.

See also

Literature

• Ionin A.A. main and afterburner combustion chambers of a turbojet engine / Nenishev A.S., Lebedev V.M.. - Omsk: OmGTU, 2005. - 92 p.

Combustion chambers of diesel engines

For good mixing at the same time, it is extremely important to correctly combine fuel atomization and air movement in the combustion chamber. This will improve the distribution of fuel in the chamber and carry out the combustion process with the least amount of air.

The shape of the combustion chamber must:

• correspond to the direction and range of the jet of injected fuel;
• ensure organized movement of air flow, intensive mixing of fuel and air, complete combustion of fuel in a short period with the least amount of air;
• smooth pressure build-up in the cylinder, moderate maximum combustion pressure and minimal heat loss;
• create conditions for easy starting of the engine.

By design, diesel engines are divided into two main categories: with undivided and divided combustion chambers. Undivided chambers have only one compartment, in which both mixture formation and fuel combustion take place. Divided chambers are divided into two parts: main and additional, connected by a neck. In this case, fuel is injected into an additional chamber.

According to the method, volumetric, film and combined mixture formation is distinguished.

With volumetric mixture formation, the fuel is sprayed in the volume of the combustion chamber and only a small part of it enters the near-wall layer. Volumetric mixture formation is carried out in undivided combustion chambers.

Film mixing is used in a number of designs of combustion chambers, when almost all fuel is directed to the near-wall zone. Approximately 5–10% of the fuel injected by the injector enters the central part of the combustion chamber. The rest of the fuel is distributed on the walls of the combustion chamber in the form of a thin film (10–15 µm). Initially, part of the fuel ignites in the central part of the combustion chamber, where there is usually no charge movement and the highest temperature is set. Later, as it evaporates and mixes with air, combustion spreads to the main part of the fuel directed to the near-wall layer. Film mixing requires less fine atomization of the fuel. Single nozzle nozzles are used. The fuel injection pressure does not exceed 17–20 MPa. Film mixing compared to volumetric mixing provides better economic performance of the engine, simplifies the design of fuel equipment. The main disadvantage is the low starting properties of the engine at low temperatures due to the small amount of fuel involved in the initial combustion. This disadvantage is eliminated by heating the intake air or by increasing the amount of fuel involved in the formation of the initial combustion chamber.

Combined mixture formation is obtained with smaller diameters of the combustion chamber, when part of the fuel reaches its wall and is concentrated in the near-wall layer. Another part of the fuel droplets is located in the internal volume of the charge. Approximately 50% of the fuel is deposited on the surface of the chamber. When inlet in the chamber, no rotational movement of the charge is created. The charge is set in motion when it is forced out of the over-piston space into the combustion chamber, and a vortex is created. The speed of charge movement reaches 40–45 m/s. A distinctive feature of the film mixture formation is the oncoming movement of the jets of fuel and charge displaced from the over-piston space, which contributes to an increase in the amount of fuel suspended in the volume of the combustion chamber, and brings the process closer to volumetric mixture formation. Nozzles are used with sprayers having 3-5 nozzle holes.

Combustion chambers with direct injection. In diesel engines with such chambers, fuel is injected directly into the combustion chamber by a nozzle with an operating pressure of 15–30 MPa, which has multi-hole atomizers (5–7 holes) with a small diameter of nozzle channels (0.15–0.32 mm). Such high injection pressures are used due to the fact that in this case the atomization of the fuel and its mixing with air is achieved mainly due to the kinetic energy imparted to the fuel during injection. For even distribution of fuel in the chamber, the nozzles of such engines are often made with several holes.

On fig. 6.4 shows the combustion chambers of engines with direct injection, providing volumetric mixing.

Rice. 6.4. Undivided combustion chambers for volumetric mixing:

a - hemispherical, b - toroidal

Rice. 6.6. Undivided combustion chambers for film mixing:

a - MAN diesel type, b - Hesselmann type

In addition to the above, with film mixing, the combustion chamber is made plate-shaped (Fig. 6.6b). The jet of fuel from the nozzle, due to the short distance, reaches the bottom of the chamber and settles in the form of a film.

The jets of fuel hit the wall at an acute angle and travel a relatively short distance. Approximately 50% of the fuel is deposited on the conical surface of the chamber.

The main advantage of direct injection combustion chambers in comparison with other types of chambers is as follows.

1. The simple and compact shape of the combustion chamber ensures less heat loss during the combustion process and higher effective efficiency.

2. Less intense air cooling during the compression period (compactness of the chamber and relatively small vortex air movement) creates conditions for easier start-up. The time for starting an engine with direct injection is 1.8–3.6 times shorter than for starting engines with other combustion chambers.

3. The structure of the cylinder head is simplified.

The disadvantages of combustion chambers with direct injection are as follows.

1. Mixing occurs at high injection pressures (up to 30 MPa). This increases the requirements for fuel supply equipment.

2. The combustion process is characterized by significant pressures. The pressure rise rate is high. Due to the increase in the load on the crank mechanism, it is necessary to increase the margin of safety of the engine components.

3. Small nozzle holes of the injector atomizer (0.1–0.25 mm) require precise execution and can become clogged if the fuel is not sufficiently purified. For this reason, the fuel must be cleaned with great care. Minor deviations in fuel quality from the norm impair engine performance.

Prechambers. Pre-chamber diesel engines have a combustion chamber divided into two parts (Fig. 6.8). The main chamber is located directly above the piston. Its volume is 0.75–0.60 of the entire volume of the combustion chamber. The prechamber is made in the cylinder head. It occupies 0.25–0.40 of the total chamber volume. The prechamber is connected to the main chamber by one or more channels.

In this case, from 20 to 30% of the injected fuel burns, which corresponds to the amount of oxygen in the air contained in the prechamber.

When part of the fuel is burned, the temperature and pressure in the prechamber increase. Burning gases and unburned fuel rush from the pre-chamber to the main chamber. Here, the combustion of the fuel continues and ends in the expansion process.

In pre-chamber engines, intensive mixture formation is achieved mainly due to the energy of the fuel partially burned in the pre-chamber. This energy causes a pressure drop between the prechamber and the main chamber (usually 1.5 MPa), which creates conditions for intensive mixing and finer atomization of the fuel previously sprayed in the prechamber.

Mixture formation is facilitated by the formation of vortex movements of air when it moves during compression from the main chamber to the prechamber. The nozzle of such engines is usually made with one hole.

Vortex chambers. Engines with swirl chambers, like pre-chamber engines, have a chamber divided into two parts (Fig. 6.9). The main chamber is located directly above the piston and has a relatively small volume. The vortex chamber is made in the cylinder head, has a streamlined shape (ball or flattened ball) and is cooled by water. Its volume is from 50 to 75% of the total volume of the combustion chamber. Such a volume allows a large amount of air to be involved in the vortex motion. The vortex chamber communicates with the main chamber through the neck.

During the combustion period, the pressure rises sharply in the vortex chamber. In this case, the products of combustion and the unburned part of the fuel rush into the main chamber. Here the combustion process continues, ending with expansion.

In engines with swirl chambers for mixture formation, mainly vortex air flows created during the compression process in a swirl chamber are used. The pressure difference between the chambers is relatively small (usually 0.6 MPa). Nozzles for such engines are usually used with one hole. The feed start pressure is 8–10 MPa.

Diesel engines with split combustion chambers achieve smoke-free operation at low excess air ratios. The requirements for the quality of fuel atomization are significantly reduced, and closed-type nozzles with one large-diameter nozzle hole (1–2 mm) are used. The fuel injection pressure is 12–15 MPa, and is provided soft work engine. These diesel engines are the fastest of all diesels.

The main disadvantages of separate combustion chambers:

Combustion chambers of diesel engines - concept and types. Classification and features of the category "Combustion chambers of diesel engines" 2017, 2018.

As is clear, combustion chambers must provide not only
not bad mixture formation, and getting better characteristics
efficiency and starting properties of the motor. There are two constructive
groups of combustion chambers of diesel engines that are separated from each other not only
design, and the principle of formation of the fuel consistency in the chamber. This
broken and undivided combustion chambers.

Broken combustion chambers

Such chambers have two channels independent of volume connected to each other:

• antechamber;
• vortex chamber.

The vortex chamber can be placed both in the block head
cylinders, and in the block itself. The cooling surface of broken chambers is very
high. In this regard, the engine is prone to significant thermal losses,
which leads to a decrease in starting properties and a bad effect on the factor
economy. Usually, diesel engines with broken combustion chambers
provide a sufficiently high degree of compression.

The main advantage of broken combustion chambers is
production of a virtually ideal fuel consistency. Through the use
kinetic energy of gases due to the flow between the cavities of the chamber,
fuel combustion is greatly increased and exhaust smoke is minimized
systems.

In addition, the interaction of channels in broken chambers
assigns stability to the engine during its operation. The main
loads on such fundamental parts as connecting rods, crankshaft, piston pins.
Reduce in some way the so-called roughness of the diesel engine with
broken combustion chambers can also be due to an increase in temperature
modes of certain areas of the cameras.

Undivided combustion chambers

Undivided combustion chambers, unlike broken ones, have
only volume and the simplest form, consistent with direction, number and
the size of the fuel streams of the injected fuel. These cameras are very
small dimensions, as it should, have a small cooling surface.
In this way, the loss of thermal energy in engines with undivided chambers
combustion is significantly less than in engines with broken chambers. Such
diesel has good starting and economic characteristics.

The shapes of the undivided combustion chambers are distinguished by their
variety. More often they are designed in the bottoms of the pistons. But meets
placement of chambers in the cylinder head, also partly in the piston crowns
and partly in the head.

It is possible to break the undivided combustion chambers of diesel
engines according to their fundamental constructive arrangement with subsequent
way:

1. Toroidal in the piston.
2. Hemispherical in piston and block head
   cylinders.
3. Hemispherical in the piston.
4. Cylindrical piston.
5. Cylindrical in the piston with lateral placement.
6. Rounded in the piston.
7. Ball in the piston.
8. Toroidal with a neck in the piston.
9. Cylindrical, formed with a piston crown and
   cylinder wall.
10. Vortex in the piston.
11. Trapezoidal in the piston.
12. Cylindrical under head
    outlet valve.

In combustion chambers type 1, 2, 3,
4, 5 very high degree of fuel consistency property comes out
thanks to fuel atomization and matching the forms of its fuel flows with
camera shapes. In such combustion chambers, nozzles are more often installed,
having multi-hole atomizers that allow you to control the forms of fuel
flows, also use the highest injection pressure satisfied. These cameras
have very small cooling surfaces. For diesel engines with
the listed types of combustion chambers are characterized by low characteristics of the degree
compression.

For combustion chambers type 6, 7, 8,
9 features wider cooling surfaces. It is, though inconsequential,
but still affects the starting qualities of the motor. But in the process
displacement of air above the piston into the combustion chamber at the time of compression
vortex-type flows are created, which contributes to good air mixing
with fuel, forming a fairly benign fuel mixture.

Combustion chambers type 10, 11, 12
are used not only in diesel engines, but also in engines with
the possibility of using various kinds fuel. A relevant feature of such cameras
is a serious direction of eddy currents, which promotes evaporation
fuel and delivering it in a certain sequence to the required place
combustion. To improve performance in cylindrical chambers in the head
cylinder block under the exhaust valve use the highest exhaust temperatures
valve, which is immediately the wall of the combustion chamber.

Types of combustion chambers
There are various designs of diesel engine combustion chambers, each designed in such a way as to obtain the most efficient vortex flow. These structures can be divided into two main classes:
* Direct injection combustion chamber
* Combustion chamber with indirect injection.
In the first design, the fuel is injected directly at the closed end of the cylinder, while in the second design, the fuel is injected into a separate additional combustion chamber, which is connected to the cylinder through a small channel.
direct injection
On fig. 30.2 shows an open-type combustion chamber. For many years, direct injection combustion chambers have been used in heavy vehicles and, in a slightly modified form, they are now common in vehicles with a 2 liter engine.
The deep recess in the piston contains air when the piston is at TDC very close to the flat cylinder head. In order to obtain the required compression ratio, overhead valves are required. Shallow recesses in the piston head provide the clearances needed for the cylinder heads.

Incorrect valve adjustment will cause the valves to hit the piston. The multi-hole injector delivers finely atomized fuel at high pressure (175 bar) into the fast-moving air stream and immediately enters the piston recess (combustion chamber).
The vortex is formed in two planes, vertical and horizontal. When the piston is lifted, air enters directly into the recess and moves approximately as shown in the figure. When the piston reaches TDC, this movement is accelerated by the swirl of the piston between the piston and the head. A horizontal or rotating swirl can be obtained by tilting the intake port tangentially to the cylinder, or by using a swirler on the intake valve. On fig. 30.2a shows the most common design. The combination of the two vortexes creates a whirlpool of air in the recess and provides a good supply of oxygen to the combustion area.
indirect injection
Until about the mid-1980s, indirect injection (IDI - InDirect Injection) engines were the most common engines installed in small cars. Compared with traditional heavy duty direct injection engines, the indirect injection engine can run more evenly; in such an engine, lower injection pressure can be used, in addition, this engine provides a greater range of revolutions.
Most of the combustion chambers of engines with indirect injection have a design proposed by Ricardo Comet, shown in fig. 30.3. This design has a vortex chamber, which is connected to the main chamber through a channel, which allows you to work at a temperature higher than the temperature of the surrounding metal.
Air is forced through the hot channel into the swirl chamber during compression, so that at the end of this cycle, very hot air is in the chamber at a high degree of swirl. The fuel is injected into this fast moving mass of air and quickly atomized into very fine particles. This atomization is quite effective even when the fuel is injected in the form of a "soft" jet using a pin nozzle or a set of nozzles at a relatively low pressure (about 100 bar).
After initiation of combustion in the vortex chamber, the burning fuel, together with unburned or partially burned fuel, is fed into the main combustion chamber made in the piston crown. If the injection time is increased to provide more engine power, most of the fuel injected at the end of the injection period does not ignite until it mixes with the air in the main chamber. This ensures that the combustion period can continue for a relatively long time until eventually a stage is reached where the fuel does not have enough oxygen to burn. Starting from this point, black smog begins and the appearance of this smog indicates the maximum amount of fuel that can be injected without sacrificing economy, as well as the maximum power that can be obtained from the engine.

Rice. 30.3
Dual cavity combustion chamber of a compression ignition engine - indirect fuel injection
In an indirect injection engine, the combination of hot air and very fine atomization results in a short ignition delay. Compared with a straight-range engine, the intensity of the "hard" operation of the engine is less, the engine runs more evenly; in such engines, fuel with a lower cetane number can be used. All compression ignition engines require special cold start aids. To start a cold engine with compression ignition, more fuel is usually injected and more flammable fractions are present in the injected portion, however, large heat losses in indirect injection engines require additional cold start aids. Compared to direct injection engines, which use a compression ratio of 16, indirect injection engines use a compression ratio of about 22, in some cases up to 30.
In addition to providing cold starts, a high compression ratio is also necessary to increase thermal efficiency, i.e. economy, as in a direct injection engine. This compensates for the large heat losses that occur due to the larger surface area of ​​the combustion chamber of an indirect injection engine.
One or more of the following additional tools are used to provide a cold start for an indirect injection engine:
1 Glow plug - an electrically heated device installed in the vortex chamber. The air in the chamber is heated electrically a few seconds before starting a cold engine. At present, such glow plugs are usually controlled automatically.
2 Header heaters - electrical devices designed to electrically heat the air passing through the intake manifold to the cylinders.
3 Pintox nozzle - a pin nozzle with an additional hole for direct fuel supply through a special channel into the combustion chamber while cranking the engine crankshaft with a starter.
Modern engines designed for installation on cars
The use of small compression ignition engines in automobiles is very attractive, since such small engines have fuel consumption up to 40 percent less than spark ignition engines of similar power. This advantage is even more attractive if the vehicle is used intensively enough that the fuel savings can then outweigh the higher initial cost of a more expensive engine.
This advantage, combined with the general rise in demand for these types of engines, has led many car manufacturers to turn their attention to small diesel engines.
In the past, compression ignition engines were very noisy and could not compete with spark ignition engines, but in Lately great improvements have been made in this area. Improving the shape of the combustion chamber and the use of silencers ensured a reduction in noise levels, and by installing a slightly larger engine displacement, the power gap with spark ignition engines was reduced.