The engine of a modern car is reliable and durable enough that, with proper operation and timely maintenance, it can "walk" 300-400 thousand km and even more. But no matter how hard designers and manufacturers try, the processes of aging and wear in the engine are inevitable. As well as the formation of various deposits.
The service life of a modern car is quite long and is at least 10-15 years. Of course, during this time, breakdowns and failures of individual parts and assemblies are very likely; abrupt, abrupt changes in the state of the engine. But still this happens relatively rarely, since it is probabilistic in nature. But the processes of changing the dimensions, physical and chemical properties of parts and components occur slowly, but continuously.
As long as such changes have not gone beyond the tolerances laid down by the designers, the consumer qualities of the engine remain stable. But one or more parameters are out of range.
In the operation of the engine immediately there are violations. No, there is no talk of failures or breakdowns yet. But there is a violation of the operation of a separate component, which has not yet led to the loss of its and, accordingly, the engine performance.
Unlike failures and breakdowns related to probabilistic phenomena, the described processes occur, albeit to varying degrees, but with absolutely all engines. Moreover, it is often much more difficult to determine where and in what place deviations occurred than to establish the fact and cause of an obvious breakdown.
Wear or... deposits?
Let's start with the most inevitable - wear and tear. You have to put up with him, because you can’t stop him completely. Although it is possible to slow down - the achievements of recent years in materials and engine production technology, in the development of engine oils and filters, combined with strict adherence to the rules for operating and maintaining the engine, give numerous examples of delaying the overhaul period far beyond 300 thousand kilometers.
It turns out that for the time being, you can not even remember about wear and tear. Therefore, at least during 100-200 thousand kilometers, other factors come to the fore, reducing the actual life of the engine. And first of all, this is the formation of various kinds of deposits.
We have already written about the danger of deposits in the lubrication system and engine crankcase associated with low quality, inconsistency of the oil grade or its untimely replacement (see "ABS-auto" 3/2000). At the same time, deposits that accumulate in the fuel system and intake manifold, combustion chamber, exhaust system are not always given importance, considering them to be something of secondary importance. However, practice shows that their influence on the engine is very significant, and in some cases dangerous. This is exactly what will be discussed.
Let's take a look at the points and components in the engine design that are most prone to deposit accumulation over the life of the engine. Some of them have little or no effect on the operation of the engine. Others, on the contrary, cause noticeable deviations in work even with relatively small deposits. These critical components from the point of view of the impact on the engine include the throttle body, intake valve plates and, of course, the nozzles.
Where do deposits come from?
The processes of deposit formation and their chemical composition are very different in different systems and devices. For example, the formation of deposits in the atomizing part of the injectors occurs mainly during the first 10-20 minutes after stopping a hot engine, when the injectors are under residual fuel pressure. The essence of the process is as follows: the fuel film, which inevitably remains in the zone of the atomizer seat, begins to evaporate under the influence of high temperature. Light fractions of gasoline evaporate, and heavier ones form a layer of solid deposits. Their main component is carbon.
Deposits on the intake valve plates have a more complex composition. So, low-quality fuel is the cause of tarry deposits. Oil penetrating through worn valve stem seals and the gap between the valve stem and sleeve leads to coke deposits: it is formed as a result of high-temperature oxidation of the oil that enters the hot plate. By the way, the process of valve coking is most intensive at idle, driving with a low load and during engine braking, when the maximum vacuum is created in the intake manifold.
Engine oil also contributes to contamination of the throttle and idle speed control channels, since the products of oxidation and oil contamination are carried into the intake manifold through the crankcase ventilation system.
Another component of deposits is soot. The reason for its formation is the combustion of an excessively rich air-fuel mixture in cold start, warm-up and acceleration modes. Soot entering the exhaust system can gradually lead to clogging of the channels of the exhaust gas recirculation system.
For engines that have been operated in Russia for a long time, certain types of deposits prevail. This is due to the use of low quality fuel and oil. That is why the engine, which is able to work perfectly "there" for many years, "here" relatively quickly begins to "act up".
Immunity to... deposits?
It cannot be said that engine designers forgot about deposits and simply "washed their hands", shifting these problems to the consumer. On the contrary, in recent years a lot has been done to develop engines of a kind of "immunity" to deposits. In other words, many components and systems in the latest engine models have become insensitive to deposits, i.e. the consequences of the accumulation of deposits are minimized.
For example, fuel dosing systems have long been adaptive; allow you to adapt (albeit within certain limits) to external conditions. And what are these external conditions? First of all - the accumulation of deposits in the spray part of the nozzles. The same approach is now used in most idle subsystems. Special design components have also appeared - deposit-resistant nozzles and Teflon-coated throttle valves.
The "immunity" to deposits provided by such difficult and very expensive measures is needed today more than ever. The fact is that the continuously tightening requirements for exhaust toxicity, efficiency and power density directly lead to the need for very “fine” tuning of the engine and all its systems. And it turns out that the more modern the engine, the more painfully it reacts even to a small amount of deposits.
Why are deposits dangerous?
All deposits, without exception, have one thing in common - they negatively affect the operation of the engine. Unsatisfactory starting performance, unstable idling, mixture misfires, acceleration dips, increased fuel consumption and exhaust emissions - this is not a complete list of obvious symptoms caused by the appearance of "unfriendly" formations in the engine intake tract. But worst of all, these deposits can accelerate the wear of the engine many times over and even lead to failures and breakdowns of its parts and components.
Indeed, what could be the connection between the coking of nozzles and the wear of parts, for example, a crank mechanism or a cylinder-piston group? The most direct: in cold weather, the engine does not start the first time, and the lower the temperature, the more you have to make attempts to start. Well, each such attempt is the work of mating parts in the semi-dry or even dry friction mode, equivalent in terms of wear to 20-40, and sometimes 100 km of real mileage.
How to clean parts from deposits?
We think that this example is quite enough to realize the seriousness of the problem. How can it be solved? The first thing that comes to mind is to simply remove the contaminated components and clean them chemically or mechanically. Indeed, this method gives the best results, but it takes too much time. Especially when it comes to complex engines, including multi-cylinder ones. In addition, the disassembly and subsequent assembly of components and systems on modern vehicles often requires the replacement of a mass of gaskets and sealing elements that are not always at hand.
The CIP engine cleaning technology is more attractive. It is based on special chemical compounds - solvents, which act specifically on specific types of deposits. And in order to remove deposits at a given point, a certain cleaning technique and special equipment are also required. About what solvents, cleaning methods and equipment to use in one case or another, we will tell in our next materials.
The main places of accumulation of deposits in engines:
1 - throttle body and idle speed controller;
2 - intake manifold;
3 - fuel rail;
4 - upper part of the nozzle;
5 - spray part of the nozzle;
6 - inlet valve plate;
7 - combustion chamber;
8 - piston bottom;
9 - oxygen sensor;
10 - catalyst;
11 - channels of the exhaust gas recirculation system.
Changing the properties of the oil in a running engine
The main changes in properties in a running engine occur for the following reasons:
- high temperature and oxidizing effects;
- mechanochemical transformations of oil components;
- permanent accumulation:
- conversion products of oil and its components;
- fuel combustion products;
- water;
- wear products
- contaminants in the form of dust, sand and dirt.
Oxidation
In a running engine, hot oil constantly circulates and comes into contact with air, products of complete and incomplete combustion of fuel. Air oxygen accelerates oil oxidation. This process is faster in oils prone to foaming. The metal surfaces of the parts act as catalysts for the oil oxidation process. The oil heats up in contact with heated parts (primarily cylinders, pistons and valves), which greatly speeds up the process of oil oxidation. The result can be solid oxidation products (deposits).
The nature of the oil change in a running engine is influenced not only by the chemical transformations of the oil molecules, but also by the products of complete and incomplete combustion of the fuel, both in the cylinder itself and breaking through into the crankcase.
Effect of temperature on engine oil oxidation.
There are two types of engine temperature conditions:
- operation of a fully warmed-up engine (main mode).
- operation of an unheated engine (frequent car stops).
In the first case, there is high temperature mode of changing the properties of the oil in the engine, in the second - low temperature. There are many intermediate working conditions. When determining the level of oil quality, motor tests are carried out both in high and low temperatures.
Oxidation products and changes in engine oil characteristics.
acids(acides). The most significant products of oil oxidation are acids. They cause corrosion of metals, and alkaline additives are consumed to neutralize the resulting acids, as a result of which the dispersing and detergent properties deteriorate and the service life of the oil is reduced. An increase in the total acid number, TAN (total acid number) is the main indicator of the formation of acids.
Carbon deposits in the engine(carbon deposits). A variety of carbon deposits form on the hot surfaces of engine parts, the composition and structure of which depend on the temperature of the metal and oil surfaces. There are three types of deposits:
- soot,
- sludge.
It must be emphasized that the formation and accumulation of deposits on the surface of engine parts is the result of not only insufficient oxidative and thermal stability of the oil, but also its insufficient detergency. Therefore, engine wear and reduced oil life is a complex indicator of oil quality.
Nagar(varnish, carbon deposits) are products of thermal destruction and polymerization (cracking and polymerization) of oil and fuel residues. It is formed on strongly heated surfaces (450° - 950°C). Nagar has a characteristic black color, although it can sometimes be white, brown or other colors. The thickness of the deposit layer periodically changes - when there are a lot of deposits, heat removal worsens, the temperature of the upper layer of deposits rises and they burn out. Less deposits form in a warm engine running under load. According to the structure, deposits are monolithic, dense or loose.
Nagar has a negative effect on the operation and condition of the engine. Deposits in the piston grooves around the rings prevent their movement and pressing against the cylinder walls (jamming, sticking, ring sticking). increases the breakthrough of gases into the crankcase and oil consumption Pressing the rings with deposits to the cylinder walls leads to excessive wear of the cylinders (excessive wear).
Cylinder wall polishing(bore polishing) - deposits on the top of the pistons (piston top land) polish the inner walls of the cylinders. Polishing prevents the oil film from retaining and retaining on the walls and significantly accelerates the wear rate.
varnish(lacquer). A thin layer of brown to black, hard or sticky carbonaceous substance that forms on moderately heated surfaces due to the polymerization of a thin layer of oil in the presence of oxygen. The skirt and the inner surface of the piston, connecting rods and piston pins, valve stems and the lower parts of the cylinders are varnished. The varnish significantly impairs heat removal (especially of the piston), reduces the strength and persistence of the oil film on the cylinder walls.
Deposits in the combustion chamber(combustion chamber deposits) are formed from particles of carbon (coke), as a result of incomplete combustion of fuel and metal salts included in the composition of additives as a result of thermal decomposition of oil residues entering the chamber. These deposits heat up and cause premature ignition of the working mixture (before a spark appears). This kind of ignition is called preignition or preignition. This creates additional stresses in the engine (detonation), which leads to accelerated wear of the bearings and the crankshaft. In addition, individual parts of the engine overheat, power decreases, and fuel consumption increases.
Clogged spark plugs(spark plug fouling). Deposits accumulated around the spark plug electrode close the spark gap, the spark becomes weak, and the ignition becomes irregular. As a result, engine power is reduced and fuel consumption is increased.
Tars, sludge, resinous deposits(sludge) (resins, sludge, sludge deposits) in the engine, sludge is formed as a result of:
- oxidation and other transformations of oil and its components;
- accumulation in the oil of fuel or decomposition products and incomplete combustion;
- water.
Resinous substances are formed in oil as a result of its oxidative transformations (crosslinking of oxidized molecules) and polymerization of oxidation products and incomplete combustion of fuel. The formation of resins increases when the engine is not warm enough. Products of incomplete combustion of fuel break into the crankcase during prolonged idling or in stop-start mode. At high temperatures and intensive engine operation, the fuel burns more completely. To reduce tar formation and engine oils, dispersant additives are introduced that prevent coagulation and precipitation of resins. Resins, carbon particles, water vapor, heavy fuel fractions, acids and other compounds condense, coagulate into larger particles and form sludge in the oil, the so-called. black sludge.
Sludge(sludge) is a suspension and emulsion in oil of insoluble solids and resinous substances from brown to black. Composition of crankcase sludge:
- oil 50-70%
- water 5-15%
- products of oil oxidation and incomplete combustion of fuel, solid particles - the rest.
Depending on the temperature of the engine and oil, the processes of sludge formation are somewhat different. Distinguish between low temperature and high temperature
Low temperature sludge(low temperature sludge). It is formed when breakthrough gases containing fuel and water residues interact with oil in the crankcase. In a cold engine, water and fuel evaporate more slowly, which contributes to the formation of an emulsion, which subsequently turns into sludge. The formation of sludge in the crankcase (sludge in the sump) is the cause of:
- increase in viscosity (thickening) of the oil (viscosity increase);
- clogging of channels of the lubrication system (blocking of oil ways);
- oil supply disturbance (oil starvation).
The formation of sludge in the rocker box is the cause of insufficient ventilation of this box (foul air venting). The resulting sludge is soft, friable, but when heated (during a long trip) becomes hard and brittle.
high temperature sludge(high temperature sludge). It is formed as a result of the combination of oxidized oil molecules under the influence of high temperature. An increase in the molecular weight of the oil leads to an increase in viscosity.
In a diesel engine, sludge formation and an increase in oil viscosity are caused by the accumulation of soot. Soot formation is facilitated by engine overload and an increase in the fat content of the working mixture.
additive consumption. Consumption, the operation of additives is the determining process of reducing the oil resource. The most important engine oil additives - detergents, dispersants and neutralizers - are used to neutralize acidic compounds, are retained in filters (along with oxidation products) and decompose at high temperatures. The consumption of additives can be indirectly judged by a decrease in the total base number TBN. The acidity of the oil increases due to the formation of acid oxidation products of the oil itself and sulfur-containing products of fuel combustion. They react with additives, the alkalinity of the oil gradually decreases, which leads to a deterioration in the detergent and dispersant properties of the oil.
The effect of increasing power and forcing the engine. The antioxidant and detergent properties of the oil are especially important when boosting engines. Gasoline engines are boosted by increasing the compression ratio and crankshaft speed, and diesel engines by increasing effective pressure (mainly with turbocharging) and crankshaft speed. With an increase in the crankshaft speed by 100 rpm or with an increase in effective pressure by 0.03 MPa, the piston temperature increases by 3°C. When forcing engines, their mass is usually reduced, which leads to an increase in mechanical and thermal loads on parts.
Motor oils "Automobile lubricants and special liquids" NPIKTS, St. Petersburg. Baltenas, Safonov, Ushakov, Shergalis.
The main changes in properties in a running engine occur for the following reasons:
high temperature and oxidizing effects;
mechanochemical transformations of oil components;
permanent accumulation:
conversion products of oil and its components;
fuel combustion products;
water;
wear products
contaminants in the form of dust, sand and dirt.
Oxidation.
In a running engine, hot oil constantly circulates and comes into contact with air, products of complete and incomplete combustion of fuel. Air oxygen accelerates oil oxidation. This process is faster in oils prone to foaming. The metal surfaces of the parts act as catalysts for the oil oxidation process. The oil heats up in contact with heated parts (primarily cylinders, pistons and valves), which greatly speeds up the process of oil oxidation. The result can be solid oxidation products (deposits).
The nature of the oil change in a running engine is influenced not only by the chemical transformations of the oil molecules, but also by the products of complete and incomplete combustion of the fuel, both in the cylinder itself and breaking through into the crankcase.
Effect of temperature on engine oil oxidation.
There are two types of engine temperature conditions:
operation of a fully warmed-up engine (main mode).
operation of an unheated engine (frequent car stops).
In the first case, there is high temperature mode of changing the properties of the oil in the engine, in the second - low temperature. There are many intermediate working conditions. When determining the level of oil quality, motor tests are carried out both in high and low temperatures.
Oxidation products and changes in engine oil characteristics.
acids (acides). The most significant products of oil oxidation are acids. They cause corrosion of metals, and alkaline additives are consumed to neutralize the resulting acids, as a result of which the dispersing and detergent properties deteriorate and the service life of the oil is reduced. An increase in the total acid number, TAN (totalacidnumber) is the main indicator of the formation of acids.
Carbon deposits in the engine (carbon deposits). A variety of carbon deposits form on the hot surfaces of engine parts, the composition and structure of which depend on the temperature of the metal and oil surfaces. There are three types of deposits:
soot,
varnish,
sludge.
It must be emphasized that the formation and accumulation of deposits on the surface of engine parts is the result of not only insufficient oxidative and thermal stability of the oil, but also its insufficient detergency. Therefore, engine wear and reduced oil life is a complex indicator of oil quality.
Nagar (varnish, carbondeposits) are products of thermal degradation and polymerization (crackingandpolymerization) of oil and fuel residues. It forms on very hot surfaces (450° - 950°C). Nagar has a characteristic black color, although it can sometimes be white, brown or other colors. The thickness of the deposit layer periodically changes - when there are a lot of deposits, heat removal worsens, the temperature of the upper layer of deposits rises and they burn out. Less deposits form in a warm engine running under load. According to the structure, deposits are monolithic, dense or loose.
Nagar has a negative effect on the operation and condition of the engine. Deposits in the piston grooves, around the rings, prevent their movement and pressing against the cylinder walls (jamming, sticking, ring sticking). As a result of jamming and difficulty in the movement of the rings, they do not press against the walls and do not provide compression in the cylinders, the engine power drops, gas breakthrough into the crankcase and oil consumption increase. Pressing the rings with deposits against the cylinder walls leads to excessive cylinder wear (excessive wear).
Cylinder wall polishing (borepolishing) - deposits on the top of the pistons (pistontopland) polish the inner walls of the cylinders. Polishing prevents the oil film from retaining and retaining on the walls and significantly accelerates the wear rate.
varnish (lacquer). A thin layer of brown to black, hard or sticky carbonaceous substance that forms on moderately heated surfaces due to the polymerization of a thin layer of oil in the presence of oxygen. The skirt and the inner surface of the piston, connecting rods and piston pins, valve stems and the lower parts of the cylinders are varnished. The varnish significantly impairs heat removal (especially of the piston), reduces the strength and persistence of the oil film on the cylinder walls.
Deposits in the combustion chamber (combustionchamberdeposits) are formed from carbon particles (coke), as a result of incomplete combustion of fuel and metal salts included in the composition of additives as a result of thermal decomposition of oil residues entering the chamber. These deposits heat up and cause premature ignition of the working mixture (before a spark appears). This kind of ignition is called preignition or preignition. This creates additional stresses in the engine (detonation), which leads to accelerated wear of the bearings and the crankshaft. In addition, individual parts of the engine overheat, power decreases, and fuel consumption increases.
Clogged spark plugs (sparkplugfouling). Deposits accumulated around the spark plug electrode close the spark gap, the spark becomes weak, and the ignition becomes irregular. As a result, engine power is reduced and fuel consumption is increased.
Tars, sludge, resinous deposits (sludge) (resins, sludge, sludge deposits) in the engine, sludge is formed as a result of:
oxidation and other transformations of oil and its components;
accumulation in the oil of fuel or decomposition products and incomplete combustion;
water.
Resinous substances are formed in oil as a result of its oxidative transformations (crosslinking of oxidized molecules) and polymerization of oxidation products and incomplete combustion of fuel. The formation of resins increases when the engine is not warm enough. Products of incomplete combustion of fuel break into the crankcase during prolonged idling or in stop-start mode. At high temperatures and intensive engine operation, the fuel burns more completely. To reduce tar formation and engine oils, dispersant additives are introduced that prevent coagulation and precipitation of resins. Resins, carbon particles, water vapor, heavy fuel fractions, acids and other compounds condense, coagulate into larger particles and form sludge in the oil, the so-called. black sludge.
Sludge (sludge) is a suspension and emulsion in oil of insoluble solids and resinous substances from brown to black. Composition of crankcase sludge:
oil 50-70%
water 5-15%
products of oil oxidation and incomplete combustion of fuel, solid particles - the rest.
Depending on the temperature of the engine and oil, the processes of sludge formation are somewhat different. Distinguish between low temperature and high temperature
Low temperature sludge (low temperature sludge). It is formed when breakthrough gases containing fuel and water residues interact with oil in the crankcase. In a cold engine, water and fuel evaporate more slowly, which contributes to the formation of an emulsion, which subsequently turns into sludge. The formation of sludge in the crankcase (sludgeinthesump) is the cause of:
increase in viscosity (thickening) of the oil (viscosityincrease);
clogging of the channels of the lubrication system (blockingofoilways);
violation of the oil supply (oilstarvation).
The formation of sludge in the rocker box is the cause of insufficient ventilation of this box (foulairventing). The resulting sludge is soft, friable, but when heated (during a long trip) becomes hard and brittle.
high temperature sludge (high temperature sludge). It is formed as a result of the combination of oxidized oil molecules under the influence of high temperature. An increase in the molecular weight of the oil leads to an increase in viscosity.
In a diesel engine, sludge formation and an increase in oil viscosity are caused by the accumulation of soot. Soot formation is facilitated by engine overload and an increase in the fat content of the working mixture.
additive consumption. Consumption, the operation of additives is the determining process of reducing the oil resource. The most important engine oil additives - detergents, dispersants and neutralizers - are used to neutralize acidic compounds, are retained in filters (together with oxidation products) and decompose at high temperatures. The consumption of additives can be indirectly judged by a decrease in the total base number TBN. The acidity of the oil increases due to the formation of acid oxidation products of the oil itself and sulfur-containing products of fuel combustion. They react with additives, the alkalinity of the oil gradually decreases, which leads to a deterioration in the detergent and dispersant properties of the oil.
The effect of increasing power and forcing the engine. The antioxidant and detergent properties of the oil are especially important when boosting engines. Gasoline engines are boosted by increasing the compression ratio and crankshaft speed, while diesel engines are boosted by increasing effective pressure (mainly with turbocharging) and crankshaft speed. With an increase in the crankshaft speed by 100 rpm or with an increase in effective pressure by 0.03 MPa, the piston temperature increases by 3°C. When forcing engines, their mass is usually reduced, which leads to an increase in mechanical and thermal loads on parts.
FLUSHING THE ENGINE.
During the operation of the car, even when using high-quality motor oils, harmful carbon deposits inevitably form on the internal surfaces of the engine and the channels of the lubrication system. When changing oil, some old used engine oil also inevitably remains in the internal cavities of the engine. Therefore, if fresh engine oil is poured immediately after draining the engine used without prior flushing, the detergent additives of the newly filled oil will immediately begin to actively dissolve all these deposits and contaminants remaining in the engine, which in turn can lead to a number of extremely negative consequences: in particular , to partial clogging of the oil filter and, accordingly, to a decrease in the efficiency of its operation, as well as to premature operation of the additive package and the loss of cleaning properties of fresh engine oil. All this has the most detrimental effect on the engine resource and its power characteristics. Today, the need to flush the lubrication system when changing engine oil is quite obvious, no one doubts and does not need any additional justification. In the combustion chamber of a gasoline engine, where the fuel-air mixture enters, it ignites, completely or partially combusts, resulting in carbon deposits. In addition, the products of incomplete combustion of fuel are the cause of the formation of varnish deposits on the internal surfaces of the engine. Further, most of the combustion products leave through the exhaust system, however, a small part of the gases breaks into the crankcase and, accordingly, comes into contact with the engine oil. In this case, the oil is oxidized and diluted, hardly soluble oxidation products are formed, which, in turn, additionally contribute to the formation of sludge and other deposits. In diesel engines, in addition, sulfur enters the combustion chamber with the fuel. As a result of oxidative reactions of sulfur, during the combustion of the fuel-air mixture, harmful deposits are formed, which result in corrosion and engine wear. Carbon deposits formed on the internal surfaces, channels of the lubrication system and engine parts lead not only to a deterioration in heat removal, but also to a noticeable decrease in the adhesion of oil to friction surfaces, which, accordingly, worsens the retention of the oil film on engine parts in friction units.
Reasons for the formation of deposits and soot in the engine
The use of high-quality oils does not eliminate the problem of coking, since deposits and deposits can form in the engine for reasons not related to the quality of fuels and lubricants:
1. Engine overheating . As a result of regular overheating, the oil ages faster, loses viscosity and forms polymer deposits in the grooves under the piston rings, on the walls of the combustion chamber, lubrication system and other parts.
2. Operation at low temperatures . The water vapor formed during the combustion of fuel reacts with cold oil, which leads to the formation of sludge in the crankcase.
3. Urban mode of operation . Short trips and traffic jams. With such operation, the engine does not reach normal operation, and as a result, carbonization of the cylinder-piston group begins.
4. Untimely oil change leads to a sharp increase in deposits arising as a result of its aging processes.
5. Turbocharger wear , as a result of which hot exhaust gases begin to enter the oil, and the properties of the oil change.
6. Antifreeze getting into the crankcase when the cooling system is depressurized, which changes the properties of the oil and initiates the processes of its polymerization.
7. Poor quality fuel . With incomplete combustion of fuel, part of it enters the crankcase through the rings and accelerates the aging process of the oil.
8. The formation of excess soot due to weak compression or late fuel injection in diesel engines.
When distilling oil with a low content of sulfur compounds, diesel fuels with high chemical stability are obtained. Such fuels retain their qualities for a long time (more than 5 years of storage).
After the use of such fuel in a diesel engine, carbon deposits and tarry deposits appear. The reason for this is incomplete evaporation and poor atomization of diesel fuel inside the cylinders due to the high viscosity of the fuel with a heavy fractional composition. In addition, the presence of mechanical impurities in diesel fuel is the cause of carbon formation.
Consequently, the presence of sulfur, actual tars, ash (non-combustible impurities) in the fuel and the tendency of such fuel to carbon formation determine the dynamics of carbon deposits accumulation, which is characterized by coke number, i.e. the ability of the fuel to form a carbonaceous residue during high-temperature (more than 800 ... 900? C) decomposition of the fuel without air access.
The carbonaceous residue or mineral residue is ash, i.e. non-combustible impurity that increases carbon formation. In addition, ash entering the engine oil causes accelerated wear of internal combustion engine parts. Therefore, the amount of ash is limited to a norm of not more than 0.01%. Thus, the following factors are the cause of the formation of carbonaceous residue:
1) insufficient depth of fuel purification from tar-asphalten compounds;
2) increased viscosity of diesel fuel;
3) heavy fractional composition of the fuel.
Also, the tendency of diesel fuel to soot is characterized by the content of actual resins in it, i.e. impurities remaining after cleaning the basic distillers. The actual resins cause gumming of the fuel, due to the presence of unsaturated hydrocarbons in the fuel, the amount of which is judged by the iodine number.
The iodine number is an indicator of unsaturated hydrocarbons (olefins) in diesel fuel, numerically equal to the number of grams of iodine added to unsaturated hydrocarbons contained in 100 g of fuel.
Usually, unsaturated hydrocarbons (olefins) react with iodine. That is, the more unsaturated hydrocarbons in the fuel, the more iodine reacts. Normal is such an amount of unsaturated hydrocarbons that react with iodine not exceeding 6 g of iodine per 100 g of winter or summer diesel fuel.
The more actual resins in diesel fuel, the higher its tendency to carbon formation. Therefore, the content of actual resins should not exceed:
for winter diesel fuel - 30 mg per 100 ml;
For summer DT - 60 mg per 100 ml.
The tendency of diesel fuel to varnish formation is estimated by the content of varnish in mg per 100 ml of fuel. To do this, the fuel is evaporated in a special lacquer at a temperature of 250?
Conclusions:
1) When a diesel engine runs on sour fuel, hard deposits and varnish deposits are formed that are difficult to remove, which causes wear on engine parts when it runs at low temperatures.
2) The carbonization of the fuel also leads to the formation of carbon deposits and varnish formation, as a result of which piston ring jamming can occur.
3) Due to the presence of mercapt sulfur particles in the fuel, during the oxidation of the fuel, resins are formed, which, in combination with resins formed from olefins and even the actual resins that are in diesel fuel, varnish films are deposited on the nozzle needles, which eventually causes the needles to freeze inside the nozzles.
4) Multifunctional additives and their influence on the properties of diesel fuels.
Improving the properties of diesel fuel is achieved by introducing multifunctional additives into their composition, such as:
Depressor;
· Increasing cetane number;
· Antioxidant;
· Detergent-dispersing;
Reducing the smoke of exhaust gases, etc.
Anti-smoke additives grades MST-15, ADP-2056, EFAP-6 at a concentration of 0.2…0.3 make it possible to reduce exhaust smoke by 40…50% and reduce soot content.
Zinc naphthenate grade anti-corrosion additive at a concentration of 0.25 ... 0.3%, added to engine oil, effectively neutralizes the destructive effect of acids.
To increase the cetane number of diesel fuel, improve its starting properties, additives are used: thionitrates RNSO; isopropyl nitrates; peroxide RCH 2 ONO at a concentration of 0.2 ... 0.25%.
Depressant additives - copolymers of ethylene and vinyl acetate with a concentration of 0.001 ... 2.0% are used to lower the pour point. They cover with a monomolecular layer of microcrystals of hardening paraffins, prevent their enlargement and precipitation.
Antioxidant additives at a concentration of 0.001 ... 0.1% increase the thermal-oxidative resistance of fuels.
Anti-corrosion additives at a concentration of 0.0008 ... 0.005% reduce the corrosive aggressiveness of diesel fuels.
Biocidal additives at a concentration of 0.005 ... 0.5%, which suppress the reproduction of microorganisms in the fuel.
Multifunctional additives, consisting of depressant, detergent and anti-smoke components, which not only expand the low-temperature properties of fuels, but also reduce the toxicity of exhaust gases. For example, the introduction of ADDP additive into diesel fuel in the amount of 0.05...0.3% reduces the pour point of the fuel by 20...25%, while the filterability temperature decreases by 10...12? C, smoke - by 20...55? C, and carbon formation - by 50 ... 60%.
Thus, the introduction of various additives and additives into diesel fuel significantly improves its performance properties.
Deposits in the engine
As the viscosity of the oil increases, the amount of precipitation in the engine decreases. Deposits in the engine are gray-brown to black sticky, greasy substances that are deposited during operation in the engine, in the crankcase, in the valve cover, in the oil system and in filters. Basically, it is an emulsion of water in oil, contaminated with various impurities. The ingress of water into the oil is one of the main causes of deposits. The composition of deposits is not constant and depends on the conditions under which it is formed.
The ratio of substances included in the composition of sediments can change dramatically, but their content varies within the following limits (in wt.%):
- Oil............................50-85,
- Water.................................5-35,
- Fuel............................1-7,
- Hydroxy acids..............2-15,
- Asphaltenes..................... 0.1-1.5,
- Carbenes, carboids .......... 2-10,
- Ash.................................1-7.
The presence of deposits in the engine is a great danger. They can clog the oil passages, oil receiver and filter. If the oil pump receiver and oil lines are clogged with sediment, the normal oil supply will be disrupted, resulting in melting of the bearing shells, crankshaft journal scuffing, and even engine failure. If the oil filter is clogged with sediment, then untreated contaminated oil enters the rubbing parts, as a result of which the wear of parts increases sharply, there is a risk of burning piston rings, etc. If there is sediment in the engine, the quality of the new filled oil deteriorates sharply. In addition, deposits can thicken and harden over time so that it is difficult to clean parts from them even mechanically. Therefore, the more often used oil is changed, the less sedimentation in the engine. Also, the amount of precipitation in the engine is affected by crankcase ventilation, as ventilation from the crankcase helps to remove water vapor and gas escaping from the combustion chamber. With poor ventilation, even the use of the best grades of gasoline and oil does not save from the formation of deposits.
It is necessary to take into account temperature factors: the effect of air temperature at the inlet manifold (carburetor) - with an increase in T? air inlet, sedimentation in the engine is reduced; influence of coolant temperature: at high coolant temperature, the possibility of water vapor condensation in the crankcase is less, so the formation of deposits in the engine is less. Among other factors, the fractional composition of the fuel is influenced: the heavier the fractional composition of the fuel, the more of it penetrates into the crankcase and leads to the growth of deposits. When the engine is running on leaded gasoline, lead gets into oil together with gasoline, the compounds of which sharply accelerate sedimentation, and this is also facilitated by poor mixture formation and combustion of fuel. Therefore, any measures that improve mixture formation and combustion of fuel reduce the intensity of sedimentation. An increase in the temperature of the working mixture leads to the same effect. As a very significant factor influencing the appearance of precipitation, the engine operation mode should be indicated: operation in light modes is the most dangerous, since this creates the most favorable conditions for precipitation formation. Operation of the machine at low speed, with low loads, frequent and long stops, engine idling leads to lower operating temperatures in the engine, more severe contamination of crankcase oil by products of incomplete combustion of fuel, dilution of oil by fuel.
Deposits can be conditionally divided into the following types:
1. Violating oil circulation due to clogging of the grid of oil receivers and oil supply channels, which leads to insufficient lubrication of the main friction units.
2. Contributing to the premature failure of individual parts:
a) deposits on the valves, which can lead to burning and / or burnout of the valves;
b) deposits in the area of the piston rings, causing their coking;
c) deposits of soot in the combustion chamber, which lead to loss of power, uncontrolled (glow) combustion and the occurrence of detonation;
d) the formation of solid deposits in the crankcases, which, getting to the rubbing surfaces, cause their rapid wear.
Depending on the temperature conditions of the parts, all types of deposits can be divided into 3 main groups:
1. High-temperature, the main reason for the formation of which is the lack of stability and low detergent properties of oils.
2. Medium temperature.
3. Low-temperature, the formation of which is closely related to the ingress of water, soot and unburned fuel into the oil.
The mechanism for the formation of high-temperature deposits was discussed above (Coking of piston rings. The work of oil in the friction unit). Low-temperature deposits are no less dangerous for the machine. The most intense low-temperature deposits are formed during short trips with frequent starts and stops (urban cycle), with an increase in the length of the car's run, the disturbances associated with the formation of precipitation (especially low-temperature ones) almost completely disappear. Heavy duty detergent oils are now widely used. These oils keep sediments and pollution products in a finely dispersed state and reduce the risk of their falling out, keep engine parts clean during their operation.
The mechanism of formation of low-temperature deposits can be represented as follows:
1. Significant oil pollution by fuel combustion products is mainly observed when the engine is idling and decreases sharply when the engine is loaded. It can be assumed that the main reason for such intense oil contamination is an excessively rich air-fuel mixture.
2. The operation of the engine in low-temperature mode contributes to the ingress of water vapor and fuel into the engine crankcase.
3. To reduce the intensity of oil contamination, the temperature in the cooling jacket and oil in the crankcase must be maintained equal to at least 70°C.
4. Insufficient crankcase ventilation contributes to oil contamination and prevents the removal of aggressive products.
5. Low-temperature sludge is a liquid, ointment-like mass that falls out of the oil after its "carrying capacity" is exceeded. Higher loads and rotational speeds and, accordingly, higher temperatures contribute to the transformation of liquid sludge into more solid or sticky deposits.
6. Engine operation in alternating mode leads to the formation of both low-temperature deposits and high-temperature deposits in the piston ring area.
Pollution and Precipitation Prevention
Intensive formation of deposits can cause malfunctions and failures in the engine, chassis and other elements of the car. When oils with low performance properties are used in forced installations, the processes of formation of both low-temperature and high-temperature deposits proceed at a higher rate.
In this regard, it is useful to know some recommendations to reduce sedimentation and thereby extend the life of oils and the car as a whole:
1. It is important that after starting the engine, the temperature in the cooling system be raised to 60-70°C as soon as possible. It is necessary to ensure that the thermostat works flawlessly under appropriate temperature conditions.
2. At low temperatures, it is necessary to install curtains near the radiator to reduce liquid cooling. It should be possible to change the radiator insulation depending on the air temperature.
3. To facilitate fuel evaporation, removal of fuel and water from the crankcase, the oil temperature must be at least 70°C.
4. The oil pans cool very quickly, so it is necessary to insulate it or install a special shield that protects the oil pan from the flow of cold air. It is also useful to insulate the valve box.
5. Carefully monitor the operation of the carburetor and adjust it. On rich mixtures, precipitation is formed more intensively.
6. Should:
a) regularly check the operation of the ignition system, as interruptions and misalignment of its operation contribute to oil pollution;
b) do not forget to control the condition of the candles, clean and adjust the contacts between the electrodes.
7. Check the condition and adjustment of the high-pressure fuel pump and diesel injectors, monitor the condition of the fuel filter elements.
8. Avoid running the engine for a long time at idle or warming it up in cold weather. It is necessary to move off immediately, as soon as the oil pressure is established (Warm up or do not warm up the engine). When idling, many engines fail to warm up sufficiently.
9. Control the crankcase ventilation system, periodically clean it, otherwise increased oil contamination is observed.
10.Check the operation of air filters; air cleaner contamination leads to an enrichment of the air-fuel mixture and a decrease in combustion efficiency.
11. When changing the oil, drain it immediately after stopping the engine, while the oil and engine are still hot.
12. The oil should be changed at such a time that it does not accumulate pollution products in an amount dangerous from the point of view of sedimentation. When using low quality oils, it is necessary to change the oil more often to remove contamination products before they form in dangerous quantities.
13. Together with the replacement of engine oil, change the filter element.
14. It is necessary to periodically open the engine crankcase to clean the crankcase pan and the oil receiver grid, preventing a decrease in the oil supply to the friction units (periodic, but not late, flushing the engine with flushing oils or liquids prevents this). When the internal combustion engine is running on oils of low quality groups, it is desirable to perform this operation more often.
15. If water droplets or whitish (foamy) deposits appear on the inner surface of the oil filler cap or on the oil dipstick, check the condition of the block head gasket and, if necessary, replace it to prevent water (coolant) from entering the oil system. It should be borne in mind that during frequent short trips in winter, when a hot engine cools, condensation forms on the inside of the valve cover, forming an emulsion on it. Over time, dissolving in the total volume of oil in the engine, it leads to more rapid aging of the oil.
16. Avoid mixing/topping up motor oils of different brands, as compatibility cannot be unambiguously guaranteed. It is impossible to predict the compatibility of the additive packages that make up the oils (the total content can reach more than 20%), since the base oils are mostly compatible. The chemicals that make up the additive package may be incompatible with each other. Incompatibility can be expressed in different ways: a sharp change in transparency or darkening of the oil after mixing, foaming; delamination or precipitation; sharp oxidation of the mixture - the formation of greasy deposits in the engine.
