ANALYSIS OF OIL CONSUMPTION IN DIESEL ENGINES

ABSTRACT

This article provides information about the corrosion of engine parts, the service life of oil depends on the physico-chemical properties of the oil, the speed of their changes during oil wear, and the fact that the temperature of the oil on the friction surface is above the critical level, which sharply increases the corrosion rate.  The analysis of oil consumption in diesel engines is covered.

АННОТАЦИЯ

В данной статье приведены сведения о коррозии деталей двигателя, срок службы масла зависит от физико-химических свойств масла, скорости их изменения при износе масла, а также о том, что температура масла на трении поверхности выше критического уровня, что резко увеличивает скорость коррозии.  Приведен анализ расхода масла в дизельных двигателях.

Keywords: Oil consumption, oil consumption, carbon layer, thermal shock, tars, asphaltenes, carbenes, carbides.

Ключевые слова: Расход нефти, расход нефти, углеродистый слой, термоудар, гудроны, асфальтены, карбены, карбиды.

Oxidation of hydrocarbons in engine oils can proceed in two main directions [8-9], for which oxidation products are different.  Oxidation products along the first direction are acidic and form precipitates at low temperatures.  Oxidation products in the second direction are neutral and form varnishes and compounds.

The most rapid wear of oil occurs in the region of the piston rings of the engine, where the thin oil film has a high temperature and a concentration of fuel combustion products, especially sulfur.  Alkalinity of oil decreases as a result of neutralization of acidic compounds of sulfur fuel products.  Sulfur oxides in the presence of water form sulfur and sulfuric acid, which in turn interact with oil hydrocarbons and their oxidation products and form sulfonic acids.

Another place where engine oil wears out the fastest is the turbo compressor.  The gas temperature at the entrance to the turbine stage reaches 700-1000 ºС [2], which causes overheating of the turbocompressor body, including the bearing networks.  After stopping the engine, the rotor shaft of the turbocharger continues to rotate for 20-30 seconds without oil in the bearing network.

As a result of "thermal shock", the oil in the bearings heats up to 200-220 ºС, and for modern oils, the critical temperature at which coking occurs is 150-160 ºС.  With such a heat load, the oil very quickly forms coke and varnish in the bearing networks, and thus the turbocompressor stops working.

When the oil is overheated, oxyacids and asphaltenes, which are insoluble and sticky in the oil, are particularly dangerous oxidation products.  They are filled with ring ditches, causing the piston rings to stick and the turbocharger rotor shaft to seize.  The neutralizing effect of additives is based on the interaction of additive metal with acidic products of fuel combustion or oil oxidation.

When the engine is running with a constant oil content G in the oil system (adding oil equal to its burn), the amount of alkaline additive c is equal to the initial amount Co, the total amount of alkaline additive that corresponds to the unit fraction of the system oil  It depends on the speed of ac consumption, oxidation products, combustion speed Qu for neutralization and additional oil injection Qd [1, 3-5].

The amount of alkaline additive is reduced to a unit volume of oil or Gdc to a whole volume of dc in the distance traveled by Dl.  Such a decrease occurs as a result of the consumption of an alkaline additive to neutralize oxidation products during operation, ascdl, the elimination of the alkaline additive with the burnt oil Qucdl, and the consumption of the alkaline additive when adding QuCodl oil;  because:

Q_у = Q_д = Q₀. Gdc cdl cQdl c

To neutralize oxidation products, the unit of the working supplement is obtained in proportion to the intensity of  the distance unit walking,  the amount of sulfur in the hungry fraction fuel, and the cost of fuel. After unraveling mathematical conversions and the equation, the  dependence of alkali on the diaphragm is first derived from l:

For neutralization of oxidation products, the working additive is taken in proportion to the speed of the unit of distance traveled, the ac fraction, the amount of sulfur in the fuel, and the fuel consumption.  After mathematical transformations and solving the equation, the dependence of the alkalinity on the range with respect to λ is first obtained:

ac=c’G/l,

where c' is the percentage of the alkaline unit of oil used to neutralize oxidation products.

As the alkalinity decreases from the value of Cn, corrosion corrosion increases due to the complete neutralization of acids.  Therefore, if the initial alkalinity level Co is large and ac>cn with the mileage, then the oil change period is determined by the accumulation of contaminants.

The speed of the exponential decrease in the concentration of the alkaline additive during operation depends on the thermal regulation of engine compounds, oil contamination and fuel quality.  Therefore, when diesel engines accelerate, the requirements for the composition of additives and the periodicity of oil changes increase.

Currently, chemistry does not have a unified approach to restore the properties of engine oil or replace it according to its actual condition, or a single indicator that describes its quality.  There are many methods for evaluating the quality of working engine oil, which include the use of various combinations of one or another physicochemical parameters as criteria for evaluating its performance [6].  However, the results of these studies and the developed methods are mainly aimed at solving the problems of timely replacement of oils that have consumed their resources.

Alkaline and acid numbers, both new and working oil, are the most important indicator of the composition and effect of additives in the oil.  Thus, in a number of technologies known to extend the service life of motor oils and replace them according to their actual condition, the main number is taken as a defective indicator [7].

In order to express the operational characteristics of running engine oils, it is proposed to use a quality indicator that reflects both the dynamic state of oil properties and the quality of cleaning from old products [6].  Using this technique allows you to avoid the usual inefficient oil change and extend its service life.  The CKrmm indicator was adopted as a sum of quality indicators in the research work [9], which describes the interdependence and interdependence of the oil condition and the parameters of the technological process of cleaning working engine oils from obsolete products.  It is expressed as a sum of one approximate indicators.  The use of this indicator increases the adequacy of the assessment of the properties of oils in the conditions of real operation of agricultural machinery.

Thus, the proposed combined indicator characterizes the quality of cleaning of working engine oil by the number of oil combustion products and alkalis as a reserve of insoluble pollutants (tars, asphaltenes, carbenes, carbides) of oil wear products.  This makes it possible to optimize the technological process of cleaning working motor oils from obsolete products by determining the optimal parameters of cleaning agents without draining the oils from the crankcase of internal combustion engines [6].

In connection with the strengthening of engines, the problem of coatings on parts is becoming more and more relevant, and they are divided into three main types - carbon layers, varnishes and coatings [3-5,8-11]:

• bodies are solid carbonaceous substances on the surfaces of the combustion chamber, their residues cause poor combustion of the fuel mixture depending on the temperature;
• varnishes are products of oxidation of thin oil films on the surface of cylinder-piston group details under the influence of high temperature.  The most dangerous is the formation of varnish in the joints of rings and pistons, as well as in the region of the turbocompressor's compression rings, which causes them to coke (lose mobility), which also disrupts heat transfer to the piston and heat removal from it;
•  sediments (sludge) are often formed in parts due to frequent starting and stopping when the engine is running in winter, their amount mainly depends on the quality of engine oil.

 Oil aging is based on the processes of oxidation, polymerization and decomposition of hydrocarbons, which are observed along with contamination.  There are the following types of oil oxidation in engines [8-11]: in a thick layer - in the crankcase;  in a thin layer - on the surface of heated details;  in the case of fog (drip) - in cylinder-piston and valve groups.  In a thick layer, oxidation forms a sediment in the form of turbidity, in a thin layer - in the form of varnish..

 Varnish formation on the surfaces of engine pistons increases with increasing temperature.  At the same time, the growth rate of varnish formation on external surfaces decreases due to friction of varnish.

Figure 1. The composition of mechanical mixtures depends on the time the oil is processed in the ZMZ-402.10 engine [9]

Figure 2. The dependence of the composition of mechanical compounds on the operating time of the oil in the ZMZ-402.10 engine [9]

The regular growth of varnish layers on the inner (non-working) surface of the pistons leads to a decrease in heat transfer to the oil with an increase in the working time.  This operating time causes the engine temperature to gradually increase as the vehicle approaches the next TO-2 oil change. Due to the decrease in the water content of the crankcase oil, the formation of deposits on the surfaces of the crankcase and valve cover decreases with the increase in surface temperature.

Figure 3. The dependence of the thickness of deposits on the crankcase surface of the ZMZ-5234.10 engine on its temperature [9]

Figure 4. Dependence of the thickness of sediment layers on the surface of the valve cover of the ZMZ-5234.10 engine on its temperature [9]

Additional factors affecting the composition and properties of engine oil during operation are its consumption and the amount of new oil filled.  In addition to working conditions, oil consumption is also affected by the technical condition of engines and the quality of their service.  According to oil experts, 50% of engine wear occurs in the last 20% of the oil's service life [12].  Thus, the main task of ensuring the performance of the engine is to determine the torque that has developed 80% of its resource, in order to ensure timely draining of oil and simultaneous replacement of the oil filter.

 In this regard, the methods of assessing the condition of working oil and determining its limiting condition, as well as the periodicity of oil replacement, are of great interest.

Table 1.

Motor oil change intervals of different companies [12

Table 2.

Limit values of engine oil state indicators [12]

The information given varies significantly due to the fact that it is based on different detection methods.  Therefore, it is appropriate to analyze the methods and criteria for determining the periodicity of oil change.

Based on the above material and its analysis, the following conclusions can be drawn on the section:

Modern car diesel engines are characterized by an increase in total power due to the use of a turbocharger, which allows to increase the power by two to three times and reduce the specific fuel consumption due to the mechanical and thermal stress of the parts.  Reliable operation of such reinforced engines is ensured by significantly improving the quality of used engine oils and their additives, as well as by changing the design of engines, increasing the efficiency of crankcase ventilation, oil cooling and oil cleaning, etc.  During operation, the process of oil wear occurs.  Therefore, in the operation of cars, it is necessary to take into account the laws of oil wear and its effect on performance characteristics.  The rate of decrease in the number of alkalis during operation depends on the engine's thermal regime, oil contamination, and fuel quality.  Therefore, when boosting car diesel engines, the requirements for additives and the periodicity of oil changes are increased.

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