Many of us always have a fear of the exhaust system. We all know that everything heats up because of hot exhaust gases coming from the engine, as a result of which many people received burns from it. This is especially known to the owners of motorcycles in which the exhaust pipes are located in close proximity to the legs. But how hot does it really get? exhaust system? Are all elements of the system heated evenly? Watch a detailed video about this on the example of the S2000 car, which was filmed using a special thermal imager.

This . The author of these videos this time made a video about the operation of the exhaust system of a car. The video was taken from the start of the engine. Then the author, after a good gas run, showed us how all the components of the exhaust system heat up.

An excellent video that shows us in detail the system for removing hot gases from the engine combustion chamber.

Please note that the data of various components of the exhaust system is superimposed on the video (upper left corner). As you can see, for example, the muffler, contrary to fears, does not actually heat up very much. Although the individual components of the exhaust system are indeed very hot.

True, it is worth noting that the video was filmed when the car is standing still at idle. And what will the exhaust system look like through the eyes of a thermal camera while the car is moving? It would also be interesting to see. We hope that the author of the video will answer this question soon.

For those who have not seen other videos shot with a thermal comer, here is a list.

CHEMICAL PRODUCTION

This year, the car muffler will celebrate its 113th anniversary. In 1894, a Panhard-Levassor car was first equipped with such a detail as an exhaust silencer.

And it was, of course, very progressive from a technical point of view, and from a philosophical point of view - in the highest degree humane step. Following the firm "Panar-Levassor" and other manufacturers of "horseless gasoline carriages" hastened to complete their products with the appropriate device. But who today remembers the name of the Panhard-Levassor car brand? Units, but meanwhile the first petrol car that crossed the border Russian Empire all in the same 1894, the car of the Panard-Levassor company became, and to the question "What is a car muffler?" Any student will give you the answer. Today, depending on the model of a particular car, their exhaust systems can differ significantly from each other. But schematically, a modern car muffler can be represented as follows: exhaust manifold, exhaust pipe, catalyst, resonator, muffler, inlet and outlet pipes.

The exhaust manifold, the most heat-loaded part in the vehicle exhaust system, is made of heat-resistant cast iron, as a rule, damage to the intake manifold is caused by mechanical influence on it (for example, rolled studs). The operating temperature of the exhaust manifold can reach +1300°C.

The exhaust pipe is attached to the exhaust manifold and also operates at high temperatures, the value of which at times reaches +1100°C.

Behind the front exhaust pipe is a catalytic converter. During the operation of the catalyst, its honeycombs can heat up to +1050°C.

The range of internal operating temperatures of the resonator installed after the catalyst can vary from +700° to +1000°C.

The rear muffler is the least heat-loaded part in the exhaust system; the operating temperature inside it does not exceed +350 °C.

At the same time, the temperature on the surface of various parts of the exhaust system is somewhat lower, the readings of which largely depend on design features each individual exhaust tract.

For the manufacture of parts of exhaust systems, ordinary or aluminized steel is used, less often stainless steel. Due to their longest service life, stainless steel exhaust systems are the choice of most vehicle manufacturers. However, stainless steel is also susceptible to corrosion, namely stress corrosion cracking. The tendency to corrosion cracking is also determined by the composition of the corrosive medium. For stainless steels, the onset of the cracking process is caused by the presence of chlorides and alkalis in the corrosive environment. At the same time, we recall that the most common means of combating icing today are the compositions of sodium chloride and calcium chloride. Yet even under these conditions, stainless steel exhaust systems can have a minimum service life of five years, and sometimes even more.

Next in life expectancy are exhaust systems made from aluminized steel. The minimum service life of such systems is 3–4 years.

Exhaust systems welded from ordinary (unalloyed) steel rarely cross the one and a half to two year milestone of guaranteed operation.

Accordingly, the price of such systems increases in proportion to the declared service life.

The reasons for the destruction of the elements of the exhaust system can be very different, including the design features of a particular exhaust system (susceptibility of its individual components to mechanical impact, deformation, stone impact, abrasion, vibration, etc.), unfavorable climatic conditions(for example, maritime climate), intensity of vehicle operation.

However, according to the conclusion of experts, they name the internal corrosion of metals as the main reason for the gradual destruction of parts of the exhaust system, while the chemical and electrochemical processes of its development are implied.

The chemical type of corrosion is characterized by the entry of the metal into direct chemical interaction with the components environment. Chemical corrosion occurs in gas environments at high temperatures, for the exhaust tract car engine the gas form of development of chemical corrosion is characteristic. Compounds of sulfur, chlorine, nitrogen, as well as oxygen and its compounds serve as aggressive components of the gaseous medium.

The active process of corrosion is facilitated by a decrease in the protective properties of films that are formed from corrosion products and, in turn, prevent direct contact of aggressive components with the metal. The decrease in the protective properties of such films leads to an increase in temperature, as well as getting into intake tract chemically active compounds that are formed during the combustion of liquid fuels. An increase in pressure and velocity of the gaseous medium also leads to an acceleration of the course of the corrosion process.

And yet, even under the most favorable circumstances for its development, the rate of chemical corrosion will always be inferior to the rate of the electrochemical corrosion process. The bodies of the main mufflers located at the very end of the exhaust system are most susceptible to this form of corrosion.

A necessary condition for the occurrence of electrochemical corrosion of a metal is the presence of an electrolyte on its surface ( aqueous solution salts, acids, alkalis), capable of conducting electricity. When the electrolyte comes into contact with the surface of an inherently heterogeneous metal (the only exception to this rule is absolutely pure iron, which contains no more than a tenth of a percent of various impurities), a lot of microgalvanic pairs are immediately formed on the metal surface, the work of which leads to the destruction of the metal.

When operating a car in a modern city, frequent short trips to a car that is usually not warmed up to the end or many hours of languishing in “traffic jams” lead to the fact that rear end the muffler is not able to heat up and dry properly, and as a result, more and more water gradually accumulates in its body. Additionally, the corrosion process of the main muffler is spurred on by the accumulation in its atmosphere a large number residues of not completely burned fuel, entering into an oxidative reaction with moisture accumulated in the muffler body, it turns the latter into a powerful electrolyte. Therefore, unlike fish, the exhaust system begins to rot from the “tail”. To some extent, special drainage holes made in the lower part of the main muffler body help to correct this situation, through which water that has entered the muffler body is drained.

WITH outside the exhaust tract is literally "in its own skin" is able to feel all the "charms" of those roads, "... that we get." Here he is met by dust, and sand, and fine gravel, and a cold shower during the rain, and from time to time there are also hard meetings of some of its parts with a curb stone. At the same time, one should not forget about such corrosion-prone areas of the exhaust tract as its welds. According to the characteristic type of damage - such corrosion, as if with a knife, cuts the metal along the weld - it is called "knife". Also, the corrosion protection of the exhaust system is not in the best way affected by the presence on its parts of rolled and rolling joints, protrusions, amplifiers, etc., those places where it becomes possible to accumulate dirt and moisture - a kind of avant-garde of corrosion.

Muffler repair may be accompanied by the replacement of a burned-out / rusted part of the muffler with a new one, welding and restoration work. Or you can use special repair compounds that are offered in special stores in the form of various bandages, patches, putties, etc., which allow you to produce self repair small damage to the exhaust system, taking into account the thermal loads characteristic of each of its sections.

Over the past few years, the number of offers of such "repair kits" in our market has increased significantly. At the same time, it must be assumed that the quality of such repair compounds has also improved, based on the fact that today it is produced, among other things, by those companies in high quality products of which we have already been able to verify ourselves more than once.

CONSUMER ANALYSIS The composition of the adhesive is used to seal small holes and cracks in automotive exhaust systems. The preparation includes in its composition: inorganic binders, glass fiber, a complex of special additives and water, does not contain asbestos and solvents. With the engine idling, the adhesive hardens within the first 10 minutes. After the final hardening, the adhesive copes well with all sorts of thermal and mechanical stresses.

CRC "Installation Paste"

CONSUMER ANALYSIS Mounting paste is used in the assembly of hose and flange connections in automotive and industrial exhaust (exhaust) connections, has good sealing and lubricating properties, which greatly facilitates the installation / dismantling of exhaust (exhaust) connections. The composition of the heat-resistant mounting paste water-based stable inorganic fillers and binders are included. The preparation does not contain asbestos and solvents. When heated, the composition of the paste swells and quickly hardens. After hardening, the mounting paste becomes resistant to thermal and mechanical stress.

CONSUMER ANALYSIS The kit is intended for sealing holes and cracks of various sizes in the exhaust system of a car. Bandage tape consists of fiberglass impregnated with epoxy composition. The bandage is used to eliminate through holes and cracks formed on the surface of the elements automotive system exhaust gases. The preparation does not contain asbestos in its composition, withstands thermal loads up to +400°C. The repair kit includes: a bandage tape (1.5 m), a piece of wire to fix the bandage tape in the desired position until it hardens, and a heat-resistant foil plate that helps to cover large areas of damage if necessary.

CONSUMER ANALYSIS The repair kit includes a bandage tape impregnated with a solution of liquid sodium silicate, and a metal wire that serves to temporarily fix the bandage tape in the desired position until it hardens. The repair kit is designed for repairing catalytic converter housings and exhaust pipes of the muffler; the bandage tape withstands temperature loads up to +1093 °С. Does not contain asbestos, after the final hardening the repair coating becomes resistant to various mechanical loads

CONSUMER ANALYSIS A high temperature sodium silicate formulation designed to repair minor damage to exhaust system components such as the muffler/catalyst resonator housing and to seal mating points. The composition of the cement is gas-tight and withstands thermal loads up to +1093°C. In the mode of normal operation of the car, the cement composition hardens within the next 24 hours after application.

CONSUMER ANALYSIS The bandage is designed for sealing small holes and cracks in the automotive exhaust system, easy to use, withstands temperature loads up to +426 °C, gas tight. The bandage tape itself is made of fiberglass impregnated with an epoxy composition. "Silencer bandage" is intended for repair of car exhaust system pipes and muffler/resonator housings. The final hardening of the bandage tape occurs when heated to the operating temperature of the automotive exhaust system.

CONSUMER ANALYSIS Turret repair paste is designed to repair parts made of cast iron, steel and other metals. The composition of the paste is well suited for sealing holes / cracks in the intake / exhaust manifold housing, the intake of the muffler. The paste is based on a water-based binder with ceramic and stainless steel fillers. The final solidification of the composition occurs when the repaired part is heated to operating temperature.

CONSUMER ANALYSIS High temperature ceramic tape for muffler repair (and pipes of any material). DONE DEAL DD6789 repair bandage is made of fiberglass impregnated with a solution of liquid sodium silicate, mixed with a complex of additives constituting the know-how of the company, and is designed to repair exhaust pipes, burnt mufflers, etc., operating at temperatures up to +650 °С and pressure up to 20 atm. At a temperature of +25 °C, after 30-40 minutes, the repaired section of the pipe is covered with a durable ceramic jacket. After the final hardening, the repaired area can be sanded and painted with heat-resistant paints.

CONSUMER ANALYSIS Repair kit VERSACHEM is designed for sealing holes, cracks and seals welds on car mufflers. The repair kit includes a bandage tape and a tube with a liquid activator. If it is necessary to cover a large area of ​​damage, you can use the material from which the tube body is made, with an activator. When carrying out repair work, the optimum temperature of the exhaust system is approximately + 15-20 ° C. It is possible to start the engine only after thirty minutes after the end of repair and restoration work. The final hardening of the repair bandage occurs within ten minutes when the engine is idling.

CONSUMER ANALYSIS Repair kit VERSACHEM "Muffler cast exhaust bandage" is designed to eliminate cracks in the catalyst housing, as well as repair small holes on the surface of the resonator and exhaust pipes. The repair kit is based on a bandage tape made of a material impregnated with a special heat-resistant compound, due to which its consumer qualities have noticeably improved compared to similar compounds with a fiberglass base. When carrying out repairs, the optimum temperature of the exhaust system is approximately + 15-20 ° C. At the end of the repair work, the bandage needs 10-12 hours to dry, in order to speed up the process of drying / hardening of the bandage tape, you can start the engine and let it idle for 10 minutes.

CONSUMER ANALYSIS VERSACHEM "Muffler-cast" bandage tape is designed to repair small holes and rust damaged areas on the surface of catalysts, resonators, intake and exhaust pipes. The tape is made of a special refractory material, due to which, in terms of its consumer properties, it surpasses similar products made on the basis of fiberglass, incl. well resists the process of chemical corrosion. Upon completion of the repair work, the bandage dries within 10-12 hours, to speed up the process of drying / hardening of the bandage tape, you can start the engine and let it idle for 10 minutes.

CONSUMER ANALYSIS VERSACHEM "Muffler weld" muffler cold weld compound is designed to repair minor damage to automotive exhaust system parts such as the resonator, main muffler, and exhaust pipes. "Cold welding" has excellent adhesion to various metal surfaces, including surfaces with traces of rust, its composition withstands the aggressive environment of hot exhaust gases well. When carrying out repairs, the optimum temperature of the exhaust system is approximately +15-20 ° C, finally, the agent dries up 10-12 hours after application.

CONSUMER ANALYSIS High-temperature, gas-tight paste designed for exhaust system seals. Prevents gas breakthroughs at the joints of the individual silencer components and the welding of the latter to each other. When conducting installation work the surfaces of the parts must be clean from rust and various types of contaminants. After applying the composition of the LIAUI MOLY Auspuff-montage paste on the parts, for better tightness of the connection, it is necessary to slightly “grind” their surfaces relative to each other. To improve the elasticity of the paste, wetting of the joints with water is allowed. The final hardening of the mounting paste comes from the heating of the exhaust system when the engine is idling.

CONSUMER ANALYSIS The LIQUI MOLY Auspuff-bandage gebreuchfertig kit is designed to seal large damages and cracks in the car exhaust system, absolutely gas-tight. The kit consists of 100 cm of fiberglass reinforcing tape and a pair of gloves. When carrying out repair and restoration work, the bandage tape is tightly applied around the damaged area with the aluminum side out. When the exhaust system is heated, the inner layer applied to the band hardens and seals the hole.

CONSUMER ANALYSIS Synthetic, high-temperature, metal-free LIQUI MOLY KERAMIK-PASTE paste prevents burning, sticking, rusting of threads, slots, pins, bolts, spindles and others, incl. non-metallic materials operating at high temperatures and corrosive environments (exhaust system, vehicle brake system). It is used as a lubricant for the treatment of highly loaded sliding surfaces operating at low sliding speeds and oscillatory movements. Temperature range of application from -30 °C to +1400 °C, the composition of LIQUI MOLY KERAMIK-PASTE paste is resistant to hot and cold water, as well as to acids and alkalis.

MOTIP Heat Resistant Paint

CONSUMER ANALYSIS Special heat resistant acrylic MOTIP paint, designed for surface treatment of parts exposed to high temperatures, such as elements of an automobile engine, exhaust systems, heating radiators, etc. Permanent heat resistance up to 650 °C, short-term - up to 800 °C. Red paint and heat-resistant colorless varnish have permanent heat resistance up to 300 °C. Colour: anthracite/dark anthracite, black, silver, white, beige, grey, red.

It is not known for certain who was the first to award a muffler to a car, but it is generally accepted that it was still the Panard-Levassor company. These guys were the first to lose their nerve and they decided to adapt their car to society. In order to prevent conservative citizens from interfering with the development of the car, several attempts were made to reduce the level of noise emitted by the engine. As a result, instead of cutting the pipe, a whole system was screwed to the motor, which was called an acoustic filter. It was in 1893. So society won the first victory over the car, and the car received another system - an acoustic filter, or silencer.

The car muffler is an integral part of the car.

Breakthroughs, burnouts and punctures

For too long, a car muffler could not remain in an embryonic state. It grew and developed along with the car, and the first more or less human muffler appeared already in 1917, at least the patent for its invention dates back to the year of the revolution. Along with technical improvement, the exhaust system also received new problems - the pipes burned through like paper, because the steel did not meet the working conditions and simply burned out in a short time.

Consequences of burning a car filter.

Manufacturers have not gone far since then, and the muffler has all the same problems as a hundred years ago. Only problems with catalysts, lambda probes and other new devices were added to them. Structurally, the muffler is quite simple - exhaust manifold, front pipe, corrugation, catalytic converter, resonator and muffler directly. And a couple of pipes of the estimated diameter. That's the whole structure. But it works in inhuman conditions, which primarily affect the service life of the system. Even the most sophisticated and expensive cars premium class silencers with stainless steel and aluminized steel silencers last no more than 10 years.
Mufflers that are supplied for replacement, the aftermarket position, last two to three years, and suspiciously cheap mufflers for expensive cars last a year or two at most. Depressurization, breakdowns, burnouts, chemical corrosion, huge operating temperatures and incorrect installation are the main technological punctures in the exhaust system.

Photo of a car filter structure.

Exhaust system operating conditions

Most of all goes to the exhaust manifold. The main thermal load in the exhaust system falls on it. The manifold is smelted from heat-resistant cast iron, since this is the only material available that can withstand operating temperatures up to 1300 ° C. The downpipe receives a temperature of up to 1100 degrees, the catalyst operates at a temperature of about 1000. Further along the system, the operating temperature drops, but the chemical and mechanical loads increase. But the resonator and its piping operate at temperatures up to 900°C, and the muffler is the coldest in the system. From the inside, it warms up to 300 degrees.

Exhaust manifold ZAZ Sens.

Temperature is not the exhaust system's only enemy. Almost a great danger for each of the elements is chemistry, which is abundantly scattered on city roads. The main ingredient in road de-icing products, sodium chloride, is even detrimental to stainless steel. It undergoes cracking after 5 years of active winter operation. Aluminized steels die much earlier, and low-alloyed ordinary steel is destroyed in a few winter seasons. If we add vibration load and mechanical damage to this set, then you will not envy the operating conditions of the exhaust system.

Repair or replacement

Even a bad replacement is better good repair, but not everyone can afford to change the exhaust system every year. It is possible to replace individual system components with low-cost low-carbon steel parts, but in this case, you need to balance the cost of the part and the cost of the repair. In addition, not all manufacturers can guarantee full compliance of the replacement element with the original one in terms of configuration and attachment points. Pipe bending angles, distortions in different planes, flange and diametrical seating dimensions can easily differ, so you should check them before buying.

Video tutorial on replacing the muffler outer shell:

When deciding to replace, it is better to look for products from trusted brands that produce kits not only for foreign cars, but also for VAZs - Walker, Bosal, Rosi, Tesh. Also, high-quality Turkish and Polish spare parts began to appear. The price of the finished part is affected not only by the brand, but also by the material - a running meter of a system made of ordinary steel will cost about 350 rubles, and stainless steel can cost twice as much. For example, a new muffler for an old IGL Passat will cost 1,460 rubles.

Images of the silencer for the Passat B3.

Silencer sealant and other auto chemicals

If you face the truth, then there is no worthy alternative to replacing a burned-out or bursting part. There are a number of temporary measures that will extend the life of the resonator or muffler. Even the highest quality welding and the most accurate seam placed on a dilapidated pipe will not lead to anything. Replacement is inevitable, like a demobilization from a conscript. We will not consider welding today, the topic is too voluminous and broad, but we will touch on the role automotive chemistry and we will try to determine how expedient it is to invest money in the foreign chemical industry.

Heat-resistant sealants allow you to repair only external problems in the car muffler.

All car chemicals intended for the repair and maintenance of the muffler are divided into three groups - assembly sealants for pipes, putties that can withstand high temperatures and bandage tapes to eliminate through damage to pipes and mufflers. To begin with, any chemotherapy only works on external surfaces. Damage to the internal organs of resonators and silencers cannot be treated. Only when fully unpacked. Previously, such operations were carried out regularly, but now there is no shortage of resonators and silencers, so few people will spend a lot of time repacking a damaged silencer.

Bandage tapes are used in case of through burning or rotting of elements of the round section exhaust system. They can eliminate burnout, but such a patch will last a year at most. Many tapes have a high-temperature adhesive layer, which makes them easy to install. Some of them can be planted on the muffler sealant. There are many types of such bandage tapes, for example, DONE DEAL tape DD6789. It is made of fiberglass and impregnated with a solution of liquid sodium silicate. The composition of the impregnation also includes some modifiers that harden at the temperatures of the exhaust system. The stripped section of the exhaust pipe is simply wrapped with such a tape when normal temperature, and after 40 minutes after wrapping, the ceramic jacket hardens completely. The ceramic bandage can be used at a working temperature of about 700°C, after hardening it is polished and can be painted with heat-resistant paint. Reviews say that the thing is quite convenient, but it stinks terribly for a long time.

Photo of a bandage tape for the exhaust system.

A heat-resistant sealant is a more functional thing and is used not only and not so much for filling holes, but for sealing thermally loaded mates in the exhaust system. It can help well in cases where it is not possible to disassemble the connection if the assembly was put on sealant during assembly. Pipes and clamps do not stick to each other, and good sealants make it possible to create fairly reliable and tight connections. The price of sealants does not exceed 300-400 rubles per 200-gram tube. To seal all the connections of the system, it will be enough to buy one tube of Abro sealant, there will also be repair work. As the instructions say, it is applied simply to the cleaned surface. After application, the engine is started for 10-15 minutes, after which the composition hardens.

Before use, it is necessary to withstand a few more hours for complete solidification. Of course, sealants and bandages are not suitable for a complete repair of the muffler, but they can save the situation for a year and a half, depending on the state of the exhaust system.

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Any failure of any engine of any vehicle causes a lot of thrills, because it occurs (in most cases) at the very moment when you demand the maximum output from it: takeoff, climb, go-around ... You might think that if in the moment of overtaking (this is about cars) the engine sneezes with a power failure, then everyone will be wildly delighted ...

So which is better? Wear pink ones - “yes, it’s a foreign car, what will it be ...” or, having read the “Operating Manual” from “A” to “Z”, be prepared for a sudden refusal? My opinion is that the second option is preferable, and the best option- to prevent failure….. And what is needed for this? - Proper operation timely service along with monitoring and diagnostics.

Failures crank mechanism and the cylinder-piston group are the most dangerous because of the "suddenness" and severity of the consequences. The bulk of such failures is associated with violations of the combustion process. There is a need to control and understand this process.

Normal combustion of the air-fuel mixture

The air-fuel mixture is compressed during the upward stroke of the piston and at a certain moment, called the “ignition point”, is ignited by an electrical spark. There is also the term "ignition advance" - a value measured in degrees of rotation of the crankshaft (PKV) or in millimeters of piston movement and showing the advance of the ignition moment of the time the piston reaches top dead points (TDC).

The combustion process begins at the end of the compression stroke, when the piston, compressing the fuel-air mixture, approaches TDC. At the moment of ignition (A), the spark discharge causes instantaneous (about 10-5 s or one hundredth of a microsecond) heating of the mixture to a temperature of more than 1000 ° C in a very small volume between the spark plug electrodes, leading to thermal decomposition, ionization of fuel and oxygen molecules and ignition of the mixture . A combustion center appears, saturated with combustion products, and an interface between it and the unburned mixture (flame front). If the volume of the hearth is sufficient to warm up and ignite the mixture layers in contact with it (this depends mainly on the power of the spark discharge, the temperature and pressure of the mixture at the end of the compression stroke), then the combustion process begins to spread through the volume of the combustion chamber from the spark plug to the side not yet burnt mixture at a speed of less than 1 m/s. The turbulent flows that occur when filling and compressing the mixture distort and destroy the clear boundaries of the flame front: the volumes of burning components are introduced into the non-combustible mixture. The surface area of ​​the front increases sharply, and with it the speed of the front propagation increases - up to 50-80 m / s (point (B) on the indicator diagram).

The accelerating motion of the front causes more and more rapid ignition and combustion of new portions of the mixture. As a result, the temperature and pressure in the combustion chamber increase dramatically. Point C, corresponding to the maximum pressure (5...6 MPa), approximately coincides with the moment when the flame front reaches the cylinder walls. A decrease in the amount of the mixture and heat removal from gases to the cylinder walls lead to a decrease in the combustion rate. The temperature of the combustion products, having reached a maximum (more than 2000°C) somewhat later than the pressure, begins to fall along with the beginning of the downward movement of the piston. The combustion process, which took 30 - 400 PKV, ended. The expansion process begins - the cycle of the working stroke.

The normal combustion process is characterized by the following parameters:

Flame propagation speed - 50-80 m/s.
magnitude and moment of maximum pressure - 5-6 MPa, 12 ... 150 after TDC
the value and moment of the maximum temperature - 2100-2300°C, 25 ... 300 after TDC.

These parameters are significantly influenced by many factors:

1. Design and dimensions of the combustion chamber;
2. Compression ratio;
3. The amount of residual gases;
4. Ignition advance;
5. Spark power;
6. Speed ​​of rotation of the crankshaft;
7. The temperature of the walls of the combustion chamber;
8.Temperature air-fuel mixture;
9. Air-fuel mixture pressure;
10. Air-fuel mixture quality;
11. Fuel properties;
12. Engine condition.

Only a part of these parameters can be controlled by the operator and an even smaller part must be controlled. If the requirements for installation, operation and maintenance of the engine are met, all parameters will be normal, and the manufacturer guarantees a normal combustion process, i.e. normal work engine.

This is ideal, but in real operating conditions it is not difficult to obtain an anomalous combustion process, given the peculiarities of national aeronautics and gasoline production.
There is a need to control the combustion process itself. Most affordable way- temperature control: cylinder head (THC) and exhaust gases (TEG).

THC is a complex parameter. The CHC value is influenced by the combustion temperature and the efficiency of the cooling system. The inertia of the parameter depends on the thermal conductivity of the head material.

TVG is a parameter that indirectly characterizes the process of fuel combustion. The measurement is practically inertia-free. A significant disadvantage given parameter is the ambiguity and complexity of the analysis. For the full use of the EGT indicator as an operational and diagnostic control tool, it is necessary, at a minimum, to know the normal values ​​​​of the EGG and the effect on them of various changes in operating conditions and deviations in the combustion process. Figure 2. A typical graph of the dependence of the TVG on the crankshaft speed is shown.

II. Combustion Disturbances

The most common causes of combustion failure are:
Malfunction fuel system
Ignition system malfunction
Shots (claps)
glow ignition
Dieseling
detonation combustion
Gasoline low octane rating or counterfeit gasoline

Fuel system malfunction

This malfunction refers to any violation or failure that causes a lean or rich air-fuel mixture.

The amount of air (or oxygen) necessary and sufficient for the complete oxidation of the fuel (in CO2 and H2O) is called theoretically necessary quantity air (or oxygen). On average, 14.8 kg of air is needed to burn 1 kg of fuel. In fact, this value strongly depends on the composition of gasoline (method of production) and can range from 13.8 to 15.2.

The amount of air at which fuel combustion occurs may differ from the theoretically required. In this case, combustion occurs with an excess or lack of air. To assess the ratio between fuel and air, the excess air coefficient alpha is used - the ratio of the amount of air available for combustion to the theoretically required one.

At alpha 1.0 (excess air), the mixture is called lean. A multi-cylinder engine can operate stably in the alpha range from 0.5 to 1.15.

The influence of the excess air coefficient on the combustion process and the thermal state of the engine are given in fig. 3 and 4.
For carburetor aircraft engines excess air coefficient is within 0.70…1.10. Most often, engines run on rich mixture with lack of air. This is explained by the fact that the engine develops the most power with a rich mixture of 0.85 ... 0.90. In takeoff mode, the mixture is enriched to 0.75 ... 0.80 to reduce the operating temperatures of the cylinder heads and exhaust valves. With a decrease in load (throttling), the thermal state of the engine becomes less stressed, which makes it possible to switch to leaner mixtures. Work on lean mixture(1.05 ... 1.10) is accompanied by a drop in power (by 4 ... 6%) and an increase in efficiency (by 10 ... 15%) compared with operation on a mixture composition corresponding to maximum power engine. At multi-cylinder engines, usually suffering from uneven distribution of fuel over the cylinders, it is necessary to set the composition of the mixture according to the poorest working cylinders. In this case, it is rarely possible to ensure stable operation at alpha values ​​> 1.05 (for the entire engine). Work on lean mixtures is possible only with throttling, at powers of the order of 0.6 ... 0.9 of the rated power. In idle mode, the mixture must be enriched to 0.65 ... 0.70 to ensure stable operation and improve throttle response. For a reliable start of a cold engine, an even greater enrichment of the mixture to 0.45 ... 0.55 is required.

The optimal composition of the fuel-air mixture in all engine operating modes should be provided by the carburetor. Six carburetor systems:

float chamber,
launch system,
system idle move,
intermediate system,
partial load system
full load system

responsible for preparing the air-fuel mixture for various modes engine operation.

Given the characteristics of the carburetor, the following conclusions can be drawn:
1. A slight enrichment of the fuel-air mixture is accompanied by a decrease in the temperature of the cylinder head and exhaust gases.
2. A slight lean air-fuel mixture is accompanied by a significant increase in the temperature of the cylinder head and exhaust gases. The most dangerous is the depletion of the mixture in the modes of 4500 ... 5000 rpm and 6000 ... 6800 rpm.
3. Severe lean or rich mixture causes a significant drop in the temperature of the cylinder head and exhaust gases. Because the combustion rate drops, the maximum pressure is reached at a later moment, which causes the engine to work hard.
4. A strong lean mixture (reducing the fuel supply) causes a decrease in power, a spontaneous drop in speed occurs, usually up to 4500 rpm (the smallest specific consumption fuel).
5. Strong depletion or enrichment of the mixture in one of the cylinders is accompanied by increased vibrations, a drop in the temperature of this cylinder, misfiring and complete shutdown cylinder.

The main reasons for enriching the mixture:
pollution air filter,

high blood pressure fuel,
"heavy" propeller.
The main reasons for the lean mixture:
air leakage into the fuel system or inlet pipe,
violation of the carburetor adjustment (one or more systems),
decrease in pump performance,
clogging of fuel system components,
incorrect installation cruising mode (when the throttle is moving from high speed to low).
"light" propeller.

During the operation of a car engine, combustion products are formed that differ high temperature and toxicity. For their cooling and removal from the cylinders, as well as to reduce the level of environmental pollution, the design provides for an exhaust system. Another function of this system is to reduce engine noise. The exhaust (exhaust) system consists of a sequential chain of elements, each of which performs a specific function.

Exhaust system design

Exhaust system

The main task of the exhaust system is the efficient removal of exhaust gases from the engine cylinders, reducing their toxicity and noise level. Knowing what the exhaust system in a car consists of will help you better understand how it works and why. possible problems. The design of a standard exhaust system depends on the type of fuel used, as well as on the applied environmental standards. The exhaust system may consist of the following elements:

• Exhaust manifold - performs the function of removing gases and cooling (purging) the engine cylinders. It is made of heat-resistant materials, since the temperature of the exhaust gases varies on average from 700°C to 1000°C.
• Downpipe - is a complex-shaped pipe with flanges for mounting to a manifold or turbocharger.
• (installed in gasoline engines of the Euro-2 and higher environmental standard) - removes the most harmful components CH, NOx, CO from the exhaust gases, converting them into water vapor, carbon dioxide and nitrogen.
• Flame arrester - installed in car exhaust systems instead of a catalyst or a particulate filter (as a budget replacement). It is designed to reduce the energy and temperature of the flow of gases leaving the exhaust manifold. Unlike a catalyst, it does not reduce the amount of toxic components in exhaust gases, but only reduces the load on mufflers.
• - serves to control the level of oxygen in the composition of the exhaust gases. There may be one or two oxygen sensors in the system. On modern engines(in-line) with a catalyst, 2 sensors are installed.
• (mandatory part of the exhaust system diesel engine) - removes soot from exhaust gases. It can combine the functions of a catalyst.
• Resonator (pre-silencer) and main silencer - reduce exhaust noise.
• Pipelines - connect individual elements automotive exhaust system into a single system.

The principle of operation of the exhaust system

Exhaust system location

In the classic version for gasoline engines, the exhaust system of a car works as follows:

• The exhaust valves of the engine open, and the exhaust gases with the remnants of unburned fuel are ejected from the cylinders.
• The gases from each cylinder enter the exhaust manifold, where they are combined into one stream.
• Through the exhaust pipe, the exhaust gases from the exhaust manifold pass through the first lambda probe ( oxygen sensor), which measures the amount of oxygen in the exhaust. Based on these data the electronic unit control adjusts the fuel supply and the composition of the air-fuel mixture.
• Further, the gases enter the catalyst, where they enter into a chemical reaction with oxidizing metals (platinum, palladium) and a reducing metal (rhodium). The operating temperature of the gases must not be below 300°C.
• At the outlet of the catalyst, the gases pass through the second lambda probe, with the help of which the correct operation of the catalytic converter is assessed.
• Further, the purified exhaust gases enter the resonator, and then the muffler, where the exhaust flows are converted (narrowed, expanded, redirected, absorbed), which reduces the noise level.
• From the main muffler, exhaust gases are already released into the atmosphere.

The diesel engine exhaust system has some features:

• As the exhaust gases leave the cylinders, they enter the exhaust manifold. The temperature of the exhaust gases of a diesel engine varies in the range of 500-700 °C.
• Then they enter the turbocharger, which performs supercharging.
• After that, the exhaust passes through the oxygen sensor and enters the particulate filter, which removes harmful components.
• Finally, the exhaust passes through the car muffler and exits to the atmosphere.

The evolution of the exhaust system is inextricably linked with the tightening of environmental standards for vehicle operation. For example, starting from the Euro-3 category, the installation of a catalyst and a particulate filter for gasoline and diesel engines mandatory, and replacing them with a flame arrester is considered a violation of the law.