Internal mixing. Mixing in diesel engines (internal mixing)

Petrol engines -
one of the types of ICE
(engines of internal
combustion) in which ignited
mixtures of air and fuel,
carried out in
cylinders, through
sparks from spark plugs.
The role of the power regulator
performs throttle
valve that regulates
flow of incoming
air.

According to the way the working cycle is carried out, engines are divided into
two-stroke and four-stroke.
Two-stroke engines have more power per unit
volume, but lose in efficiency. So they found their way
where compactness is important, not efficiency (motorcycles, motor
boats, chainsaws and other motorized tools).
Four-stroke engines dominate the rest
movement.

Fuel-air system
The main task of the fuel-air system is uninterrupted
delivery of a mixture of fuel and air to the engine. Fuel supply system
also called fuel system or fuel supply system.
Such a system is designed to power the engine, store and clean
fuel.
Structural structure
fuel tank
fuel pump
fuel filter
injection system
fuel lines

The principle of operation of the fuel-air system

The whole scheme of the fuel supply system is as follows
way:
The driver turns on the ignition;
The fuel pump pumps fuel into the system and creates a working
pressure;
Fuel enters the injection system;
Atomization and the formation of fuel-air
mixtures;

mixture formation

Under the mixture formation in engines with spark ignition is meant
a complex of interrelated processes accompanying dosing
fuel and air, atomization and evaporation of fuel and its mixing
with air. High-quality mixing is a prerequisite
obtaining high power, economic and environmental
engine performance.

Mixture formation of injection internal combustion engine

Provides storage
fuel needed
to power the engine
cars. Specified
tank in cars
often located in
back and fixed
on the bottom of the body.
Responsible for cleaning
fuel.
Responsible for supplying fuel to the injection system and
maintains the required working pressure in
fuel system.

The principle of operation of the injector is that the ECU
(electronic control unit) supplies it with
electrical impulse. Under the impulse
the injector opens and injects gasoline into
intake manifold. Received air fuel
the mixture is sucked in through the intake valves by the piston
on the intake stroke. Point in time and duration
injection for the injector is determined by the ECU.

The mixture formation of a carburetor internal combustion engine

The formation of a mixture of gasoline with
air takes place in
carburetor where gasoline
mixed with suction
air into the engine
the right amount,
sprayed and partially
evaporates. Further
evaporation and mixing
take place in the intake
pipeline and in themselves
engine cylinders.

10.

The method of forming a combustible mixture in the simplest
carburetor (Fig. 71)
Fuel from the tank under pressure enters through the channel,
closed by needle valve 4, into the float chamber
2. Float 3 measures the fuel level in the float
chamber, and consequently, the pressure of the fuel is maintained
almost constant so that this level is somewhat
below the nozzle hole 7; thus, at
When the engine is not running, there is no fuel leakage. At
suction stroke of the piston 10, i.e. when moving it down
air passes through the pipe 8 diffuser 6, in which it
the speed increases significantly, and consequently, the pressure
goes down. Due to rarefaction, the fuel from the float
chamber through a calibrated through hole 1,
called a jet, and nozzle 7 gushing into
diffuser, breaking up into small droplets,
evaporating in the air stream. The amount of mixture
sucked in through the inlet valve 9, is regulated by the throttle valve 5.

Mixture formation in diesel engines occurs inside the cylinder and coincides in time with the introduction of fuel into the cylinder and partially with the combustion process.

The time allotted for the processes of mixture formation and fuel combustion is very limited and amounts to 0.05-0.005 sec. In this regard, the requirements for the mixture formation process are primarily reduced to ensuring complete combustion of the fuel (smokeless).

The mixture formation process in marine diesel engines is especially difficult, since the diesel operation mode for the propeller with the highest number of revolutions, i.e., the mode with the shortest time interval in the mixture formation process, corresponds to the smallest excess air ratio in the working mixture (full engine load).

The quality of the mixture formation process in a diesel engine is determined by the fineness of the atomization of the fuel supplied to the cylinder and the distribution of fuel droplets there over the combustion space.

Therefore, let us first consider the process of fuel atomization. The jet of fuel flowing from the injector nozzle into the compression space in the cylinder is under the influence of: external forces of aerodynamic resistance of compressed air, surface tension and fuel cohesion forces, as well as disturbances that occur during fuel outflow.

The forces of aerodynamic resistance impede the movement of the jet, and under their influence the jet breaks into separate drops. With an increase in the velocity of the outflow and the density of the medium into which the outflow occurs, the aerodynamic forces increase. The greater these forces, the earlier the jet loses its shape, breaking up into separate drops. The forces of surface tension and the forces of cohesion of the fuel, on the contrary, by their action tend to preserve the shape of the jet, i.e., to lengthen the continuous part of the jet.

The initial perturbations of the jet arise due to: the turbulent movement of fuel inside the nozzle of the nozzle, the influence of the edges of the nozzle hole, the roughness of its walls, the compressibility of the fuel, etc. The initial perturbations accelerate the decay of the jet.

Experiments show that the jet at a certain distance from the nozzle breaks up into separate drops, and the length of the continuous part of the jet (Fig. 32) can be different. In this case, the following forms of jet breakup are observed: jet breakup without the action of aerodynamic air resistance forces (Fig. 32, a) occurs at low outflow velocities under the action of surface tension forces and initial disturbances; disintegration of the jet in the presence of some influence of the forces of aerodynamic air resistance (Fig. 32, b); disintegration of the jet, which occurs with a further increase in the velocity of the outflow and the appearance of initial transverse perturbations (Fig. 32, c)] disintegration of the jet into separate drops immediately after the jet leaves the nozzle hole of the nozzle.

The last form of jet disintegration should be in order to obtain a high-quality mixture formation process. The disintegration of the jet is mainly affected by the speed of the outflow of fuel and the density of the medium where the outflow occurs; less affected by the turbulence of the fuel jet.

The scheme of jet decay is shown in fig. 33. The jet at the exit of the nozzle breaks up into separate threads, which in turn break up into separate drops. The jet cross section is conditionally divided into four annular sections; the outflow velocities in these annular sections are expressed by the ordinates 1;2;3 and 4. The outer annular section, due to the greatest air resistance, will have the lowest speed, and the inner (core) will have the highest outflow speed.

Due to the difference in velocities in the jet cross section, movement occurs from the core to the outer surface of the jet. As a result of the disintegration of the fuel jet, drops of various diameters are formed, the size of which varies from a few microns to 60-65 microns. According to experimental data, the average drop diameter for low-speed diesels is 20-25 microns, and for high-speed diesels it is about 6 microns. The fineness of the spray is mainly affected by the rate of fuel flow from the injector nozzle, which is approximately determined as follows:

To obtain a spray of fuel that meets the requirements of mixture formation, the flow velocity must be in the range of 250-400 m/s. The outflow coefficient φ depends on the condition of the nozzle surface; for cylindrical smooth nozzle holes with rounded input edges (r? 0.1.-0.2 mm) is 0.7-0.8.

To assess the perfection of fuel atomization, atomization characteristics are used, which take into account the fineness and uniformity of atomization.

On fig. 34 shows spray characteristics. The y-axis shows the percentage of drops of a given diameter from the total number of drops located in a certain area, and the abscissa shows the droplet diameters in microns. The closer the top of the characteristic curve to the y-axis, the greater the fineness of the atomization, and the uniformity of the atomization will be the greater, the steeper the rise and fall of the curve. On fig. 34, characteristic a has the finest and most uniform atomization, characteristic b has the coarsest, but homogeneous, and characteristic 6 has medium fineness, but inhomogeneous atomization.

The droplet sizes are determined empirically, as the most reliable, since the theoretical path presents significant difficulties. The method for determining the number and size of droplets can be different. The most widely used technique is based on trapping on a plate covered with some liquid (glycerin, liquid glass, a mixture of water with tanning extract), drops of a sprayed jet of fuel. A microphotograph taken from the plate makes it possible to measure the diameter of drops and count their number.

The required value of the injection pressure, with an increase in which the fuel outflow rate increases, is finally set during the adjustment test of the engine. Usually, for low-speed diesel engines, it is about 500 kg / cm 2, for high-speed 600-1000 kg / cm 2. When using a pump-injector, the injection pressure reaches 2000 kg/cm 2 .

Of the structural elements of the fuel supply system, the nozzle fineness has the greatest influence on the fineness of the spray.

With a decrease in the diameter of the nozzle hole, the fineness and uniformity of spraying increase. In high-speed engines with single-chamber mixture formation, the diameter of the nozzle holes is usually 0.15-0.3 mm,2 in low-speed engines it reaches 0.8 mm, depending on the cylinder power of the engine.

The ratio of the length of the nozzle hole to the diameter, within the limits used in engines, has almost no effect on the quality of fuel atomization. A smooth cylindrical nozzle opening of the nozzle provides the least resistance to the outflow of fuel, and therefore the outflow from such a nozzle occurs at a higher speed than from nozzles of a different shape. Therefore, a smooth cylindrical nozzle provides a finer atomization. Thus, for example, a helical fluted nozzle has an exhaust ratio of about 0.37, while a smooth cylindrical nozzle has an exhaust ratio of 0.7-0.8.

An increase in the number of revolutions of the engine shaft, and, accordingly, the number of revolutions of the fuel pump shaft, increases the speed of the fuel pump plunger and, consequently, increases the discharge pressure and the speed of the outflow of fuel.

Consideration of the decay process of the outflowing fuel jet allows us to conclude that the viscosity of the fuel also affects the fineness of the spray. The higher the viscosity of the fuel, the less perfect the atomization process will be. Experimental data show that the greater the viscosity of the fuel, the larger the droplets of atomized fuel.

The jet of fuel at the exit from the injector nozzle, as described earlier, is broken into separate threads, which in turn break up into separate drops. The entire mass of droplets forms the so-called fuel plume. The fuel jet expands as it moves away from the nozzle, and, consequently, its density decreases. The density of the torch within the same section is also not the same.

The shape of the fuel jet is shown in fig. 35, which shows the core of the torch 1 (more dense) and shell 2 (less dense). Curve 3 shows the quantitative distribution of drops, and curve 4 shows the distribution of their velocities. The core of the torch has the highest density and speed. This distribution of drops can be explained as follows. The first drops that enter the space of compressed air quickly lose their kinetic energy, but create more favorable conditions for the movement of subsequent drops. As a result, the rear drops catch up with the front ones and push them to the sides, continuing to move forward themselves until they are pushed back by moving drops, and. etc. Such a process of pushing some drops out by others goes on continuously until there is an equilibrium between the energy of the jet in the exit section of the nozzle and the energy expended on overcoming friction between fuel particles, on pushing forward droplets of the fuel jet, on overcoming jet friction about the air, on the entrainment of air and on the creation of vortex movements of air in the cylinder.

The depth of penetration of the fuel jet, or its range, plays a very significant role in the process of mixture formation. Under the penetration depth of the fuel flame understand the depth of penetration of the top of the flame for a certain period of time. The penetration depth of the flame must correspond to the shape and dimensions of the combustion space in the engine cylinder. With a short range of the torch, the air located near the cylinder walls will not be involved in the combustion process, and thus the conditions for fuel combustion will worsen. With a long range, fuel particles, falling on the walls of the cylinder or piston, form carbon deposits due to incomplete combustion. Thus, the correct determination of the flare range is of decisive importance in the formation of the mixture formation process.

Unfortunately, the solution of this problem theoretically encounters enormous difficulties, which consist in taking into account the influence on the range of the effect of facilitating the movement of some drops by others and the movement of air in the direction of the jet.

All obtained formulas for determining the range of the torch L f do not take into account these factors and are essentially valid for individual drops. Below is a formula for determining bf, which is obtained from an empirical pattern:

Here? - fuel jet speed;

0 - speed of movement in the injector nozzle channel;

k is a coefficient that depends on the injection pressure, on the back pressure, on the nozzle diameter, on the type of fuel, etc.;

T - range time.

When deriving formula (26), it was assumed that k = const, and therefore it does not reflect reality and, moreover, does not take into account the influence of the previously indicated factors. This formula is rather valid for determining the flight of an individual drop, rather than for the jet as a whole.

More reliable are the results of experiments to determine the range. On fig. 36 shows the results of experiments to determine the range L f, the maximum width of the torch B f and the speed of movement of the top of the torch? depending on the angle of rotation of the fuel pump roller? at various counterpressures in the bomb p b.

Nozzle diameter 0.6 mm. Injection pressure pf = 150 kg/cm2 ; amount of injected fuel? V = 75 mm 3 for a move. Pump shaft rotation speed 1000 rpm. Torch range at p b \u003d 26 kg / cm 2 reaches L f \u003d 120 cm, and the speed is about 125 m / s and quickly drops to 25 m / s.

Curves? = f(?) and Lf = f(?) show that with an increase in counterpressure, the range and the speed of the flame outflow decrease. The flame width Vf changes from 12 cm at 5° to 25 cm at 25° of rotation of the pump shaft.

Reducing the period of fuel supply, increasing the velocity of the expiration contribute to an increase in the initial velocity of the flame front and the depth of its penetration. However, due to the finer spray pattern, the spray velocity drops faster. With an increase in the diameter of the nozzle, while maintaining a constant flow rate, the range of the torch increases. This happens due to an increase in the density of the core of the torch.

With a decrease in the diameter of the nozzle, with a constant total area of ​​​​the nozzles, the angle of the cone of the torch increases, and therefore the frontal resistance also increases, while the range of the torch decreases. With an increase in the total area of ​​the nozzle openings of the injector, the atomization pressure decreases, the outflow rate decreases, and the range of the fuel jet decreases.

The experiments of VF Ermakov show that the preheating of the fuel before it is injected into the cylinder significantly affects the dimensions of the torch and the fineness of the spray.

On fig. 37 shows the dependence of the flame length L f on the temperature of the injected fuel.

The dependence of the flame length on the fuel temperature after 0.008 sec from the start of injection is shown in Fig. 38. At the same time, it was found that with increasing temperature, the width of the torch increases, and the length decreases.

The indicated change in the shape of the flame with an increase in the temperature of the fuel indicates a finer and more uniform spray of the fuel. With an increase in fuel temperature from 50 to 200°C, the flame length decreased by 22%. The average droplet diameter decreased from 44.5 microns at a fuel temperature of 35°C to 22.6 microns at a fuel temperature of 200°C. The indicated experimental results allow us to conclude that heating the fuel before injecting it into the cylinder significantly improves the mixture formation process in a diesel engine.

Numerous studies show that the process of self-ignition of fuel is preceded by its evaporation. In this case, the amount of evaporating fuel until the moment of self-ignition depends on the size of the droplets, on the pressure and temperature of the air in the cylinder, and on the physicochemical properties of the fuel itself. An increase in the volatility of the fuel improves the quality of the mixture formation process. The method for calculating the process of volatility of the fuel flame, developed by prof. D. N. Vyrubov, makes it possible to assess the influence of various factors on the course of this process, and the quantitative assessment of the concentration fields of fuel vapors in a mixture with air is especially important.

Assuming that the medium surrounding the drop at a sufficient distance from it has the same temperature and pressure everywhere, with concentration.

When deriving formula (27), it was assumed that the drop has a spherical shape and is immobile with respect to the environment. vapors equal to zero (at the same time, the medium directly at the surface of the drop is saturated with vapors, the partial pressure of which corresponds to the temperature of the drop), a formula can be obtained that determines the time of complete evaporation of the drop:

The air temperature in the cylinder has the greatest influence on the rate of fuel evaporation. With an increase in the degree of compression, the rate of droplet evaporation increases due to an increase in air temperature. An increase in pressure somewhat slows down the rate of evaporation.

The uniform distribution of fuel particles in the combustion space is mainly determined by the shape of the combustion chamber. In marine diesel engines, undivided chambers (mixture formation in this case is called single-chamber) and divided chambers (with pre-chamber, vortex-chamber and air-chamber mixture formation) have been used. Single-chamber mixture formation has the greatest application.

Single-chamber mixing is characterized by the fact that the volume of the compression space is limited by the bottom of the cylinder head, the walls of the cylinder and the bottom of the piston. The fuel is injected directly into this space, and therefore the spray jet, if possible, should ensure the uniform distribution of fuel particles over the combustion space. This is achieved by coordinating the shapes of the combustion chamber and the fuel spray jet, while observing the requirements for the range and fineness of the fuel jet spray.

On fig. 39 shows diagrams of various undivided combustion chambers. All of these combustion chambers have a simple configuration, do not require complicated design of the cylinder cover and have a small relative cooling surface Fcool / V c . However, they have serious disadvantages, which include: uneven distribution of fuel over the space of the combustion chamber, as a result of which, for complete combustion of the fuel, it is necessary to have a significant excess air coefficient (α = 1.8–2.1); The required fineness of atomization is achieved by a high fuel discharge pressure, in connection with which the requirements for fuel equipment increase and the mixture formation process will be sensitive to the type of fuel and to changes in the engine operating mode.

Combustion chambers can be divided into the following groups: chambers in the piston (schemes 1-5); chambers in the cylinder cover (schemes 6-8); between the piston and the cover (schemes 11-15); between two pistons in engines with PDP (schemes 9-10).

Of the chambers in the piston in medium-speed and high-speed diesel engines, the chamber of shape 2, in which the depressions in the piston reproduce the shape of the spray jets, is most widely used, and thereby an increase in the uniformity of the distribution of fuel particles is achieved. In order to improve mixture formation in undivided chambers, the air charge of the cylinder is given a vortex motion.

In four-stroke diesel engines, the vortex motion is achieved by placing screens on the intake valves or by the corresponding direction of the intake channels in the cylinder cover (Fig. 40). The presence of screens on the inlet valve reduces the flow area of ​​the valve, as a result of which hydraulic resistance increases, and therefore it is more expedient to use the curvature of the inlet channels to form a vortex air movement. In two-stroke diesel engines, air swirling is achieved by a tangential arrangement of purge windows. A very uniform mixture formation is achieved in the chambers, most of which are located in the piston (see Fig. 39, diagrams 4 and 5). In them, when air flows from the under-piston space (during the compression stroke) into the chamber in the piston, radially directed vortices are created that contribute to better mixture formation. Chambers of this type are also called "semi-split".

Chambers located in the cylinder cover (see Fig. 39, diagram 6-8) are used in two-stroke engines. The chambers between the piston and the cylinder cover (Fig. 39, diagrams 11-15) are obtained in the most advantageous form without large recesses in the piston or in the cylinder cover. Such chambers are mainly used in two-stroke diesel engines.

In combustion chambers between two pistons (see Fig. 39, diagrams 9 and 10), the nozzle axis is directed perpendicular to the cylinder axis, with nozzle holes located in the same plane. In this case, the injectors have a diametrically opposite arrangement, which achieves a uniform distribution of fuel particles over the space of the combustion chamber.

In carburetor engines, the combustible mixture is prepared in a special device called carburetor.

A diagram of an elementary carburetor with a falling flow is shown in fig. 16.9.

in the float chamber 2 using a float 4 and needle valve 3 maintains a constant fuel level.

When the engine is running due to the suction action of the piston in the diffuser 6 a vacuum is created. Fuel from the float chamber 2 through a calibrated hole 1, called e jet, is sucked to the atomizer 5, which sprays it.

To prevent leakage of fuel from the atomizer 5 when the engine is not running, its upper edge is located 2-3 mm above the fuel level in the float chamber 2. The latter happens balanced And unbalanced. In the first case, the float chamber communicates with at-

Rice. 16.9.

1 - jet; 2 - float chamber; 3 - needle valve; 4 - float; 5 - atomizer; 6 - diffuser; 7 - throttle valve; 8 - pipeline with atmospheric air through an air cleaner, in the second - directly with atmospheric air, as shown in fig. 16.9.

The advantages of balanced float chambers include the fact that in them, regardless of the resistance of the air filter, the flow of air and gasoline is better balanced and the chamber is less polluted.

Formed in a diffuser 6 combustible mixture in the intake manifold 8 through the intake valves is directed to the engine cylinders. Fuel evaporation and mixture formation begin in the diffuser 6 of the carburetor, continue when the combustible mixture moves through the suction pipe 8 and end when it is compressed in the cylinder. In four-stroke engines, this process occurs over two piston strokes, which corresponds to 330-340° of crankshaft rotation. During suction and compression, turbulence is formed, as a result of which the evaporated fuel mixes well with air.

For better fuel evaporation during mixture formation, the combustible mixture is sometimes heated in the suction pipe, which ensures economical fuel combustion at low excess air ratios and high crankshaft speed.

The amount of combustible mixture entering the engine, and therefore its power, is regulated by the throttle 7. With a larger opening, the air velocity in the diffuser increases 6, the rarefaction and intensity of the outflow of fuel from the atomizer 5 increase, as well as the amount of the combustible mixture entering the cylinder.

Depending on the design of the engine and its load, the air velocity in the diffuser ranges from 50 to 150 m/s. The composition of the combustible mixture prepared in the carburetor is characterized by the coefficient of excess air a. The combustible mixture at a = 1 is called normal, at a = 1-=-1.15 - depleted, when a > 1.15 - poor. Engine operation from medium to full load on a lean mixture provides the lowest specific fuel consumption. When a > 1.3, the combustible mixture does not ignite due to lack of fuel. A combustible mixture with an excess amount of fuel at a = 1.00-ID 5 is called enriched, while at a rich. When a

When operating on an enriched mixture, the greatest engine power is provided due to an increase in the heat of combustion of the charge and a higher flame propagation speed. However, when operating on this mixture, the fuel does not burn completely, which leads to its increased specific consumption.

The engine should run on a rich mixture during start-up, idling and at maximum power.

When the engine is running with an elementary carburetor during the start-up period, due to a small vacuum in the diffuser and the location of the fuel level in the atomizer 2-3 mm below its mouth, there is no outflow of fuel from the atomizer, and clean air enters the engine (a -? ° °) . Thus, starting an engine with an elementary carburetor is impossible.

An elementary carburetor cannot provide engine start and stable idling, as well as the required mixture composition when switching from one operating mode to another. Therefore, it is equipped with devices that provide the most advantageous mixture composition for various engine operating modes. Such devices include compensation jets, economizers, accelerator pumps, etc.

mixture formation is the preparation of a working mixture of fuel and air for combustion in the engine cylinders. The mixture formation process occurs almost instantly: from 0.03 to 0.06 s in low-speed internal combustion engines and from 0.003 to 0.006 s in high-speed ones. To achieve complete combustion of fuel in the cylinders, it is necessary to ensure that the working mixture of the required composition and quality is obtained. With unsatisfactory mixture formation (due to poor mixing of fuel with air), with a lack of oxygen in the working mixture, incomplete combustion occurs, which leads to a decrease in the efficiency of the internal combustion engine. The economical operation of the engine is achieved primarily by ensuring the most complete and rapid combustion of fuel in the cylinders near c. m. t. In this case, atomization of the fuel into the smallest possible homogeneous particles and their uniform distribution throughout the entire volume of the combustion chamber is very important.
Currently, in marine internal combustion engines, mainly single-chamber, pre-chamber and vortex-chamber mixing methods are used.
At single-chamber mixing fuel in a finely dispersed state under high pressure is injected directly into the combustion chamber formed by the piston crowns, caps and cylinder walls. With direct injection, the fuel pump creates a pressure of 20-50 MPa, and in some types of engines 100-150 MPa. The quality of mixture formation depends mainly on matching the configuration of the combustion chamber with the shape and distribution of the fuel combustion torches. For this nozzle nozzles have; 5-10 holes with a diameter of 0.15-1 mm. The fuel during injection, passing through small holes in the nozzle, acquires a speed of more than 200 m/s, which ensures its deep penetration into the air compressed in the combustion chamber.
Hesselmann type combustion chamber:

The quality of mixing of fuel particles with air depends primarily on the shape of the combustion chamber. Very good mixture formation is achieved in the chamber shown in the figure above and first proposed by Hesselmann. It is widely used in four- and two-stroke internal combustion engines. Borders 1 at the edges of the piston prevent fuel particles from getting on the walls of the sleeve 2 cylinder at a relatively low temperature.
High power internal combustion engines often have pistons with a concave bottom. The combustion chamber formed by the cylinder cover and the piston of this design allows you to achieve good mixture formation.
In mixture formation with direct injection of fuel into an undivided chamber, the latter can have a simple shape with a relatively small cooling surface. Therefore, internal combustion engines with a single-chamber mixture formation method are simple in design and most economical.
The disadvantages of the single-chamber mixing method are as follows: the need for increased excess air ratios to ensure high-quality fuel combustion; sensitivity to a change in speed mode (due to a deterioration in the quality of atomization with a decrease in the engine speed); very high pressure of injected fuel, which complicates and increases the cost of fuel equipment. In addition, due to the small openings of the injector nozzles, carefully refined fuel must be used. For the same reason, it is very difficult to carry out single-chamber mixing in high-speed low-power internal combustion engines, since at low fuel consumption, the diameters of the injector nozzle openings must be significantly reduced. It is very difficult to manufacture multi-hole nozzles with a very small diameter of nozzle holes, moreover, such holes quickly become clogged during operation and the nozzle fails. Therefore, in high-speed low-power internal combustion engines, mixing with separate combustion chambers (pre-chamber and vortex-chamber), carried out with a single-hole nozzle, is more efficient.

The figure shows an internal combustion engine cylinder with pre-chamber mixing. The combustion chamber consists of a prechamber 2 located in the lid and the main chamber 1 in the over-piston space, interconnected. The volume of the prechamber is 25-40% of the total volume of the combustion chamber. When compressed, the air in the cylinder enters at high speed through the connecting channels 4 into the prechamber, creating an intense vortex formation in it. Fuel under a pressure of 8–12 MPa is injected into the prechamber by a single-hole nozzle 3 , mixes well with air, ignites, but burns out only partially due to lack of air. The remaining (unburned) part of the fuel, together with the products of combustion under a pressure of 5-6 MPa, is thrown into the main combustion chamber. In this case, the fuel is intensively sprayed, mixed with air and burned. The advantages of premixed internal combustion engines include the fact that they do not require fuel equipment operating under very high pressure and do not require high-purity fuel.
The main disadvantages of these internal combustion engines are: a more complex design of cylinder covers, which creates the risk of cracking due to thermal stresses; difficulty starting a cold engine; increased fuel consumption due to imperfect mixing. The relatively large surface of the walls of the pre-chamber causes a strong cooling of the air when it is compressed during engine start, which makes it difficult to obtain the temperature necessary for self-ignition of the fuel. Therefore, in engines with a pre-chamber method of mixture formation, higher compression is allowed (the compression ratio reaches 17-18), and electric glow plugs and heating of the intake air during the start-up period are also used.

Vortex chamber mixing method also used in low-power high-speed internal combustion engines. In these engines, the combustion chamber is also divided into two parts. The swirl chamber, having a spherical or cylindrical shape, is placed in the cylinder head or cylinder block and communicates with the main combustion chamber by a connecting channel directed tangentially to the wall of the swirl chamber. Due to this, the compressed air flowing into the vortex chamber through the connecting channel 1 , receives a rotational movement in it, which contributes to good mixing of fuel with air. The volume of the vortex chamber is 50-80% of the total volume of the combustion chamber. Fuel is supplied to the vortex chamber by a single-hole nozzle 2 under pressure of 10-12 MPa. The nozzle hole diameter is 1-4 mm.
The use of the vortex-chamber method of fuel atomization ensures sufficiently complete combustion of fuel in high-speed internal combustion engines. The disadvantages of such engines are increased fuel consumption and the difficulty of starting it. An electric glow plug is used to facilitate starting the internal combustion engine. 3 located next to the nozzle.
Specific fuel consumption for engines with pre-chamber and vortex-chamber mixture formation is 10–15% higher than for engines with single-chamber mixture formation.

Combustion of fuel can proceed only in the presence of an oxidizing agent, which is used as oxygen in the air. Therefore, for the complete combustion of a certain amount of fuel, it is necessary to have a certain amount of air, the ratio of which in the mixture is estimated by the excess air coefficient.

Since air is a gas, and petroleum fuels are liquid, for complete oxidation, liquid fuel must be turned into a gas, i.e., evaporated. Therefore, in addition to the four processes considered, corresponding to the names of the cycles of the engine, there is always one more - the process of mixture formation.

mixture formation- this is the process of preparing a mixture of fuel with air for burning it in the engine cylinders.

According to the method of mixture formation, internal combustion engines are divided into:

• engines with external mixture formation
• engines with internal mixture formation

In engines with external mixing, the preparation of a mixture of air and fuel begins outside the cylinder in a special device - a carburetor. Such internal combustion engines are called carburetor. In engines with internal mixture formation, the mixture is prepared directly in the cylinder. These ICEs include diesel engines.