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.
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 followsway:
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 meanta 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 storagefuel needed
to power the engine
cars. Specified
tank in cars
often located in
back and secured
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 withair 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 simplestcarburetor (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.
1. The process of mixture formation in engines with spark ignition.
The complex of interrelated processes of dosing fuel and air, atomizing and evaporating fuel, as well as mixing fuel with air is called mixture formation. The efficiency of the combustion process depends on the composition and quality of the air-fuel mixture obtained during mixture formation.
In four-stroke engines, usually organize external mixing, which begins with the dosing of fuel and air in the nozzle, carburetor or in the mixer (gas engine), continues in the intake tract and ends in the engine cylinder.
There are two types fuel injection: central - injection of fuel into the intake manifold and distributed - injection into the intake channels of the cylinder head.
Fuel spray with central injection and in carburetors, it begins at a time when the fuel jet, after it exits the nozzle or atomizer hole, under the influence of aerodynamic resistance forces and due to the high kinetic energy of air, breaks up into films and drops of various diameters. As the drops move, they break up into smaller ones. With an increase in the fineness of the atomization, the total surface of the droplets increases, which leads to a more rapid conversion of the fuel into steam.
With an increase in air velocity, the fineness and uniformity of atomization improve, and with high viscosity and surface tension of the fuel, they deteriorate. So, when starting a carburetor engine, there is practically no atomization of fuel.
When injecting gasoline, the quality of atomization depends on the injection pressure, the shape of the nozzle atomizing holes and the speed of the fuel flow in them.
In injection systems, electromagnetic nozzles are most widely used, to which fuel is supplied under a pressure of 0.15 ... 0.4 MPa to obtain droplets of the required size.
The spraying of the film and drops of fuel continues when the air-fuel mixture moves through the sections between the intake valve and its seat, and at partial loads - in the gap formed by the covered throttle valve.
The formation and movement of a film of fuel occurs in the channels and pipelines of the intake system. When the fuel moves, due to interaction with the air flow and gravity, it partially settles on the walls of the intake pipe and forms a fuel film. Due to the action of surface tension forces, adhesion to the wall, gravity and other forces, the speed of the fuel film is several tens of times less than the speed of the mixture flow. Droplets of fuel can be blown off the film by air flow (secondary atomization).
When gasoline is injected, usually 60 ... 80% of the fuel gets into the film. Its amount depends on the location of the nozzle, the jet range, the fineness of the spray, and in the case of distributed injection into each cylinder, on the moment it starts.
In carburetor engines at full load and low speed, up to 25% of the total fuel consumption falls into the film at the outlet of the intake manifold. This is due to the low air flow rate and the insufficient fineness of the fuel atomization. When the throttle valve is closed, the amount of film in the intake manifold is less due to the secondary atomization of fuel near the valve.
Fuel evaporation necessary to obtain a homogeneous mixture of fuel with air and to organize an efficient combustion process. In the intake duct, before entering the cylinder, the mixture is two-phase. The fuel in the mixture is in the gas and liquid phases.
With central injection and carburation, the intake pipe is specially heated with liquid from the cooling system or exhaust gases to evaporate the film. Depending on the design of the intake tract and the mode of operation at the outlet of the intake pipeline, 60 ... 95% of the fuel in the combustible mixture is in the form of vapors.
The process of fuel evaporation continues in the cylinder during the intake and compression strokes, and by the beginning of combustion, the fuel evaporates almost completely.
With distributed fuel injection on the inlet valve plate and engine operation at full load, 30 ... 50% of the cycle dose of fuel evaporates before entering the cylinder. When fuel is injected onto the walls of the inlet channel, the proportion of evaporated fuel increases to 50...70% due to an increase in the time for its evaporation. Heating of the inlet pipeline is not required in this case.
The conditions for the evaporation of gasoline in cold start modes worsen, and the proportion of evaporated fuel before entering the cylinder is only 5 ... 10%.
Uneven composition of the mixture, entering different cylinders of the engine, with central injection and carburation is determined by the different geometry and length of the channels (unequal resistance of the branches of the intake tract), the difference in the speeds of air and vapors, drops and, mainly, the fuel film.
With an unsuccessful design of the intake tract, the degree of uniformity of the mixture composition can reach ± 20%, which significantly reduces the efficiency and power of the engine.
The uneven composition of the mixture also depends on the mode of operation of the engine. With central injection and in a carburetor engine, with increasing speed, atomization and evaporation of the fuel are improved, so the uneven composition of the mixture is reduced. The mixture formation improves as the engine load decreases.
With distributed injection, the uneven composition of the mixture over the cylinders depends on the identity of the operation of the injectors. The greatest non-uniformity is possible in the idle mode at low cyclic doses.
The organization of external mixture formation of gas automobile engines is similar to carburetor engines. The fuel is introduced into the air stream in the gaseous state. The quality of the air-fuel mixture with external mixture formation depends on the boiling point and the diffusion coefficient of the gas. This ensures the formation of an almost homogeneous mixture, and its distribution over the cylinders is more uniform than in carburetor engines.
The fuel used in spark ignition engines is more volatile than diesel, and it takes longer to mix with air before it enters the combustion chamber than diesel. As a result, spark ignition engines run on more homogeneous mixtures, which, moreover, are very close to stoichiometric (λ = 1). Diesel engines always run on lean mixtures (λ > 1). If the excess air ratio of the fuel-air mixture is not large enough (λ< 1), это приводит к повышенным выбросам сажи, CO и CH.
Mixture formation of a homogeneous fuel mixture
For high-quality mixture formation of a homogeneous fuel-air mixture, the fuel must completely evaporate at the moment of ignition, since only a high-quality gas or gas-vapor mixture can achieve a state of uniformity.
If there are factors that prevent the complete evaporation of the fuel and lead to a deterioration in the quality of the mixture (for example, low temperature during a cold start of the engine), then an additional portion of fuel should be added to enrich the air-fuel mixture and thus make it highly flammable (enrichment of the mixture at cold start). engine start).
The mixture formation system, in addition to ensuring the homogeneity of the mixture, is also responsible for regulating the engine load (throttle control) and minimizing the deviation of the air / fuel ratio in different cylinders of the engine.
Mixture formation of a heterogeneous fuel mixture
The purpose of mixing a non-uniform fuel-air mixture is to ensure the operation of the engine in all its modes without throttle power control. Internal cooling is a side effect of using direct fuel injection and engines of this type can operate at higher compression ratios. The combination of these two factors (lack of throttling and higher compression ratios) results in higher efficiency than with homogeneous fuel mixtures. The engine load is controlled by changing the amount of fuel injected.
The development of mixture formation systems gives new impetus to the development of a "hybrid" mixture formation method or a "layered charge distribution by composition" method, the possibilities of which have been intensively studied since the 1970s. A certain breakthrough in this matter occurred with the development of high-speed fuel systems with electromagnetic injectors, which made it possible to provide flexibility in regulating the moment of injection of the fuel mixture and the required high pressures of this injection.
GDI – gasoline direct injection– has become a generic term used to identify mixing systems being developed around the world. The mixture formation is mainly influenced by the location of the spark plug and fuel injector, and the nature of the circulation of this mixture in the combustion chamber is a concomitant factor. The vortex motion of the mixture (produced by helical and tangential channels) is basically rotation about an axis parallel to the axis of the engine cylinder.
The exact placement of the spark plug relative to the jet of fuel supplied by the injector is the defining moment for a direct fuel injection system.
The spark plug is under heavy load as it is directly exposed to the injected fuel. With the mixture formation method, when fuel is injected into a recess on the piston bottom or into a swirling air flow and directed to the spark plug due to the rotational movement of the charge, the requirements for the accuracy of the location of the spark plug and nozzle in this case are not so high.
Methods for mixing a heterogeneous mixture work with excess air (control without using a throttle) and therefore it is necessary to develop catalytic converters that reduce the emission of nitrogen oxides in the exhaust gases of engines operating on lean mixtures.
BLUE FORMATION- (in internal combustion engines) the formation of a combustible mixture. External mixture formation (outside the cylinder) is carried out by a carburetor (in carburetor engines) or a mixer (in gas engines), internal mixture formation by a nozzle ... ... Big Encyclopedic Dictionary
mixture formation- I; cf. The process of formation of mixtures. Accelerated s. C. in internal combustion engines (mixing fuel with air or other oxidizer for the most complete and rapid combustion of fuel). * * * mixture formation (in engines of internal ... ... encyclopedic Dictionary
mixture formation- (in internal combustion engines), the formation of a combustible mixture. External mixture formation (outside the cylinder) is carried out by a carburetor (in carburetor engines) or a mixer (in gas engines), internal mixture formation by a nozzle ... ... Automobile dictionary
BLUE FORMATION- the process of obtaining a working (combustible) mixture in internal engines. combustion. There are 2 main type C.: external and internal. With external S., the process of obtaining a working mixture is carried out by Ch. arr. outside the working cylinder of the engine. With internal S., ... ... Big encyclopedic polytechnic dictionary
Building VSH.
Effective Torque:
with pre-chamber 
vortex 
diesel 
.
Hourly fuel consumption: 
5. Piston acceleration.
,
supercharged, non-aspirated
by number of cylinders
by ignition system
according to the power system
piston speed.
,
8 Piston movement
m, and at = m
9 Supercharging. 
,
That 
10. Release process
11. cooling system
14 .Calculation of oil pumps.
combustion process.
The main process of the engine operating cycle, during which heat is used to increase the internal energy of the working fluid and to perform mechanical work.
According to the first law of thermodynamics, we can write the equation:
For diesels:
For gasoline:
The coefficient expresses the number of fractions of the net calorific value used to increase internal energy and to perform work. For injection engines: 
, carburetor: 
, diesels: 
.
The utilization factor depends on the operating mode of the engine, on the design, on the speed, on the cooling system, on the method of mixture formation.
The heat balance in the area can be written in a shorter form: 
Calculation equations of combustion: - for gasoline engines: T z - temperature of the end of combustion, when heat is supplied at isochore (V=const), follows:
For diesels: with V=const and p= const:
Where - 
degree of pressure increase.
Average molar heat capacity of combustion products:
After substituting all known parameters and subsequent transformations, the second-order equation is solved:
Where: 
Combustion pressure for gasoline engines: 
Pressure increase ratio:
Combustion pressure for diesels: 
Pre-Expansion Degree: 
compression process.
During the compression process, the temperature and pressure of the working fluid increase in the engine cylinder, which ensures reliable ignition and efficient combustion of the fuel.
The calculation of the compression process is reduced to determining the average index of the compression polytrope , the parameters of the end of compression 
and heat capacity of the working fluid at the end of compression 
.
For gasoline engines: pressure 
and temperature 
at the end of compression.
Average molar heat capacity of the working mixture:
ICE classification.
Internal combustion engines are divided into: carburetor, diesel, injection.
By the method of implementation. gas exchange: two-stroke, four-stroke, naturally aspirated
According to the method of ignition: with compression ignition, with forced ignition.
According to the method of mixture formation: with external (carburetor and gas), with internal (diesel and gasoline with fuel injection into the cylinder).
By type of application: light, heavy, gaseous, mixed.
According to the cooling system: liquid, air.
ICE diesel: supercharged, naturally aspirated.
According to the location of the cylinders: single-row, double-row, V-shaped, opposed, in-line.
Oil cooler, calculation.
The oil cooler is a heat exchanger for cooling the oil circulating in the engine system.
The amount of heat removed by water from the radiator:
Heat transfer coefficient from oil to water, W \ m 2 * K
Cooling surface of a water-oil radiator, m 2;
Average oil temperature in the radiator, K;
Average water temperature in the radiator, K.
Heat transfer coefficient from oil to water, (W \ (m 2 * K))
α1-heat transfer coefficient from oil to radiator walls, W / m 2 * K
δ-thickness of the radiator wall, m;
λthermal coefficient of thermal conductivity of the wall, W/(m*K).
α2-heat transfer coefficient from the radiator walls to water, W / m 2 * K
The amount of heat (J \ s) removed by the oil from the engine:
Average heat capacity of oil, kJ/(kg*K),
Oil density, kg / m 3,
Circulation oil consumption, m 3 / s
And - the temperature of the oil at the inlet to the radiator and at the outlet from it, K.
The cooling surface of the oil cooler, washed by water:
Nozzle, calculation.
Nozzle serves for atomization and uniform distribution of fuel throughout the volume of the diesel combustion chamber and are open or closed. In closed nozzles, the atomizing orifice communicates with the high pressure pipeline only during the period of fuel transfer. In open nozzles, this connection is constant. Calculation of the nozzle - def. Nozzle hole diameter.
The volume of fuel (mm3/cycle) injected by the injector in one stroke of a four-stroke diesel engine (cycle supply):
Fuel Expiration Time (s):
Angle of rotation of the crankshaft, hail
Average speed of fuel outflow (m/s) through the nozzle openings of the atomizer:
Average fuel injection pressure, Pa;
- average gas pressure in the cylinder during the injection period, Pa;
Pressure at the end of compression and combustion,
The total area of the nozzle holes:
- fuel consumption coefficient, 0.65-0.85
Nozzle hole diameter:
12. In gasoline engines, they are most widely used:
1. Offset (L-shaped) (Fig. 1);
2. Hemispherical (Fig. 2);
3. Semi-wedge (Fig. 3) combustion chambers
In diesel engines, the shape and placement of the combustion chamber determine the method of mixture formation.
Two types of combustion chambers are used: undivided and divided.
Undivided combustion chambers (Fig. 4) are formed
Building VSH.
Effective Torque:
The effective power of the gasoline engine:
Effective power of a diesel (with an undivided combustion chamber) engine:
with pre-chamber
vortex
Specific effective fuel consumption: gasoline
diesel .
Hourly fuel consumption:
5. Piston acceleration.
,
Engines of external and internal mixture formation.
by type: carburetor, injection, diesel
by mixture formation: external, internal
fuel: gasoline, diesel, gaseous
cooling system: air, water
supercharged, non-aspirated
by number of cylinders
according to the location of the cylinders: V, W, X - figurative
by ignition system
according to the power system
by design features
piston speed.
,
8 Piston movement depending on the angle of rotation of the crank for an engine with a central crank mechanism
For calculations, it is more convenient to use an expression in which the piston displacement is a function of one angle, only the first two terms are used, due to the small value of c above the second order, it follows from the equation that when m, and at = m
Fill in the table, and build a curve. When the crank is rotated from top dead center to bottom dead center, the movement of the piston occurs under the influence of the movement of the connecting rod along the axis of the cylinder and its deviation from this axis. As a result of the coincidence of the directions of movement of the connecting rod when the crank moves along the first quarter of the circle (0-90) the piston travels more than half of its path. When passing the second quarter (90-180) passes less distance than the first. When constructing a graph, this regularity is taken into account by introducing the Brix correction
Piston movement in an offset crank mechanism
9 Supercharging. Analysis of the engine effective power formula, shows that if we take the working volume of the cylinders and the composition of the mixture unchanged, then the value of Ne at n=const will be determined by the ratio 𝝶е/α, the value 𝝶v and the parameters of the air entering the engine. Because the mass charge of air Gv (kg) remaining in the engine cylinders ,
That it follows from the equations that with an increase in the density of the air (boost) supplied to the engine, the effective power Ne increases significantly.
A) the most common scheme with a mechanical drive of the supercharger, from the crankshaft. Centrifugal, piston or rotary gear superchargers.
B) the combination of a gas turbine and a compressor is most common in cars and tractors
C) combined boost-1 stage compressor is not mechanically connected to the engine, the second stage of the compressor is driven by the crankshaft.
D) the turbocharger shaft is connected to the crankshaft - this arrangement allows, with an excess of gas turbine power, to give it to the crankshaft, and in case of a shortage, take it away from the engine.
10. Release process. During the exhaust period, exhaust gases are removed from the engine cylinder. Opening the exhaust valve before the piston arrives at n.m.t., reducing the useful work of expansion (area b "bb'' b"), contributes to the high-quality cleaning of the cylinder from combustion products and reduces the work required to expel the exhaust gases. In modern engines, the intake valve opens at 40 - 80 BC (point b ') and from that moment the exhaust gases begin to flow at a critical speed of 600
700 m/s. During this period, ending near n.m.t. in naturally aspirated engines and a little later with supercharging, 60-70% of the exhaust gases are removed. With further movement of the piston to V.M.T. the outflow of gases occurs at a speed of 200 - 250 m / s and by the end of the swusch does not exceed 60 - 100 m / s. The average speed of the outflow of gases for the period of release in the nominal mode is in the range of 60 - 150 m / s.
The exhaust valve closes in 10-50 after TDC, which improves the quality of cylinder cleaning due to the ejection properties of the gas flow leaving the cylinder at high speed.
Reducing toxicity during operation: 1. Increased requirements for the quality of adjustment of fuel supply equipment, systems and devices for mixture formation and combustion; 2. wider use of gas fuels, the combustion products of which are less toxic, as well as the transfer of gasoline engines to gaseous fuels. When designing: 1 installation of additional equipment (catalysts, afterburners, neutralizers); 2 development of fundamentally new engines (electric, inertial, battery)
11. cooling system. Engine cooling is used to force the removal of heat from heated parts to ensure the optimal thermal state of the engine and its normal operation. Most of the heat removed is perceived by the cooling system, the smaller part - by the lubrication system and directly by the environment. Depending on the type of coolant used in automobile and tractor engines, a liquid or air cooling system is used. As a liquid coolant
substances Use water and some other high-boiling liquids, and in an air cooling system - air.
The advantages of liquid cooling include:
A) more efficient heat removal from heated engine parts under any thermal load;
b) fast and uniform heating of the engine at start-up; c) the admissibility of the use of block structures of engine cylinders; d) less prone to detonation in gasoline engines; e) a more stable thermal state of the engine when changing its operating mode; f) lower power consumption for cooling and the possibility of using thermal energy removed to the cooling system.
Disadvantages of the liquid cooling system: a) high maintenance and repair costs in operation; b) reduced reliability of engine operation at negative ambient temperatures and greater sensitivity to its change.
The calculation of the main structural elements of the cooling system is based on the amount of heat removed from the engine per unit time.
Liquid cooled heat dissipation (J/s)
where ( is the amount of fluid circulating in the system, kg/s;
4187 - heat capacity of the liquid, J/(kg K); - the temperature of the liquid leaving the engine and entering it, K. the calculation of the system is reduced to determining the dimensions of the liquid pump, the surface of the radiator, and the selection of the fan.
14 .Calculation of oil pumps. One of the main elements of the lubrication system is the oil pump, which serves to supply oil to the rubbing surfaces of the moving parts of the engine. By design, oil pumps are gear and screw. Gear pumps are simple, compact, reliable in operation and are the most common in automobile and tractor engines. The calculation of the oil pump is to determine the size of its gears. This calculation is preceded by the determination of the circulating oil flow in the system.
The circulating oil flow depends on the amount of heat it removes from the engine. In accordance with the heat balance data, the value of ‚ (kJ/s) for modern automobile and tractor engines is 1.5 - 3.0% of the total amount of heat introduced into the engine with fuel: Qm = (0.015 0.030)Q0
The amount of heat released by the fuel during 1 s: Q0= НuGt/3b00, where Нu is expressed in kJ/kg; GT - in kg/h.
Circulation oil flow (m3/s) at a given value ‚ Vd=Qm/(rmsm) (19.2)
