Analysis of factors affecting the quality of lubricant blending
In recent years, lubricants in various types of automobiles, machinery and equipment to reduce friction, protection of machinery and processed parts of the liquid or semi-solid lubricants are more and more widely used, mainly lubrication, cooling, rust, cleaning, sealing and buffering, etc., by the user’s favor, and the consumer is more concerned about the quality of the lubricant and the quality of lubricant blending, then the quality of the lubricant blending by the impact of what factors?
1, the precise measurement of the formula components feeding
For the blending process, the control of the formula to join the proportion that is accurate measurement is very important. It can effectively guarantee the accurate implementation of the formula. For the control of the formula feeding ratio, need to achieve a reasonable formula calculation, accurate data operation, measuring instruments / equipment calibration is effective, accurate measurement; the use of each component of the material balance, such as raw material tanks in and out of the balance of the amount of raw materials, raw materials out of the components of the amount of the sum of the total amount of the balance of the total amount of material in the tank and the blending and so on, to verify that the feeding ratio of the various components of the formula is in line with the requirements.
2, the production process of material temperature
In the process of lubricating oil blending, choose the appropriate blending temperature, the effect of mixing and oil quality has a great impact, the temperature is too high may cause oxidation or thermal deterioration of the oil and additives, the temperature is too low to make the components of the liquidity of the deterioration of the effect.
3、Mixing uniformity of the production process
For different viscosity levels of refined oil, the viscosity of raw oil is different, the proportion of light and heavy raw materials is different, the mixing form, mixing equipment power is different, the blending temperature is different, the mixing time is different, and the uniformity of the mixing effect is also different. Need to determine the mixing time according to the specific circumstances.
4, air in the oil
For the phenomenon of air mixed in the oil, but the presence of air is also very unfavorable to the mixing. The presence of air may not only promote the decomposition of additives and oil oxidation, but also due to the presence of air bubbles lead to inaccurate measurement of components, affecting the correct proportion of components.
5、Dilution and dissolution of additives
Part of the solid additives, very viscous additives, additives with low solubility, should be melted, diluted, modulated into a suitable concentration of additives before use of the mother liquor, otherwise it may affect the degree of uniformity of the blend, but also may affect the accuracy of measurement. However, the additive mother liquor should not add too much diluent, so as not to affect the quality of lubricant products.
6, impurity pollution
Reconciliation system exists within the solid impurities and non-concordant components of the base oil and additives, etc., are the pollution of the system, may result in the quality of the product and the quality of the product is unqualified, so the lubricant blending system to keep clean. Lubricating oil contains mechanical impurities can not only make the viscosity of the oil increase, and will accelerate the mechanical parts of the abrasion, pulling and scratches and other wear. Increased mechanical impurities in the engine lubricant will aggravate engine wear, increase the generation of carbon deposits, clogging the oil circuit nozzle and filter, resulting in lubrication failure. It can also reduce the antioxidant stability of the oil. Transformer oil with mechanical impurities will reduce its insulating properties. Therefore, the lubricant blending process needs to avoid mixing impurities and components outside the formula. In actual production, on the one hand, try to clean up the pollutants, on the other hand, should be arranged in a system of similar quality, variety of oil blending, in order to ensure the quality of blended products.
What are some common viscosity index improvers?
In order to improve the viscosity index and viscosity-temperature characteristics of lubricating oils, and to improve the low-temperature starting performance and high-temperature viscosity retention performance of lubricating oils, viscosity index improvers (referred to as viscosity index improvers) are usually added to lubricating oils in order to obtain multigrade lubricating oils with excellent high and low-temperature performance, and with a wider range of applicable temperatures and regions.
Viscosity index improver is a kind of oil-soluble chain polymer, its mechanism of action is to improve the viscosity index at low temperatures when the molecular chain of the viscosity index improver curl shrinkage, hydrodynamic volume and surface area becomes smaller, the lubricating oil to reduce the impact of internal friction, and accordingly to the lubricating oil of the thickening ability to be reduced; at high temperatures when the viscosity index improver molecular chain expansion, the hydrodynamic volume and surface area increases, the lubricating oil of the impact of internal friction At high temperature, the molecular chain of viscosity index improver expands, the hydrodynamic volume and surface area increase, the effect on the internal friction of the lubricating oil increases, and the thickening ability of the lubricating oil increases accordingly. Therefore, the viscosity index improver can improve the viscosity index of the lubricating oil greatly, i.e., the lubricating oil with the addition of the viscosity index improver has a lower viscosity at the low temperature and higher viscosity at the high temperature, and it is suitable for a wider range of temperature.
The main types of viscosity index improvers available in the market today are polyisobutylene (PIB), polymethacrylate (PMA), ethylene propylene copolymer (OCP), and hydrogenated styrene diene copolymer (HSD).
The performance of viscosity index improvers is mainly measured by four indicators: thickening ability, low temperature performance, shear stability and thermo-oxidative stability. The better the indexes of these four aspects, the better the comprehensive performance of the viscosity index improver, but it is difficult to balance these properties, especially the pair of contradictions between the thickening ability and shear stability is difficult to balance.
So far, the viscosity index improver with excellent performance in all aspects has yet to be developed, relatively speaking, the performance of HSD type viscosity index improver is more comprehensive and balanced.
2.1 Thickening ability
The thickening ability of viscosity index improver (expressed as D value) is the contribution of viscosity index improver to the viscosity of oil, the larger the D value, the stronger the thickening ability of viscosity index improver. Add 1.0% of the viscosity index improver into 150SN base oil, measure the 100 ℃ kinematic viscosity after dissolution, and subtract the 100 ℃ kinematic viscosity of the base oil to get the increased value, which is the thickening ability of the viscosity index improver.
Specific viscosity (expressed as ηsp) can also be used to measure the thickening ability of the viscosity index improver, see equation (1):
ηsp = (η-η0 )/η0 (1)
In equation (1), η0 is the viscosity of the base oil, and η is the viscosity of the base oil containing the viscosity index improver. the larger the ηsp, the stronger the thickening ability of the viscosity index improver. ηsp is related to the temperature, the content of the viscosity index improver, and the viscosity of the base oil, and is not an intrinsic constant of the viscosity index improver, so it is necessary to use the same benchmark when comparing the ηsp of different viscosity index improvers. Therefore, the same benchmark must be used when comparing ηsp of different viscosity index improvers.
2.2 Low Temperature Performance
The influence of viscosity index improver on the low temperature performance of lubricating oil is mainly characterized by low temperature dynamic viscosity (CCS) and low temperature pumping viscosity (MRV), CCS mainly reflects the low temperature starting performance of lubricating oil, the smaller the value of CCS is, the easier the lubricating oil is to start at low temperature; MRV mainly reflects the low temperature pumping performance of lubricating oil, the smaller the value of MRV is, the easier the lubricating oil is to pump to the lubricating part at low temperature. The smaller the MRV value, the easier it is to pump the lubricant to the lubricating part. The smaller the MRV value, the easier it is for the lubricant to pump to the lubrication site at low temperatures. Viscosity index improvers with good low-temperature performance have less negative impact on the CCS and MRV of the lubricant.
2.3 Shear Stability
Viscosity index improvers, as polymers, are subjected to shear stresses that cause the molecular chains to break, resulting in a loss of thickening ability. During the use of multigrade lubricants with poor shear stability viscosity index improvers, the viscosity of the lubricant will drop significantly due to the shear action of the oil pump, piston and other mechanical parts, resulting in abnormal wear, oil consumption and fuel dilution will also increase.
Shear stability is one of the important indexes to measure the performance of viscosity index improver, mainly using diesel nozzle method, ultrasonic method or L-38 single-cylinder method to evaluate the shear stability of viscosity index improver, shear stability index (SSI) to characterize the viscosity index improver of the shear stability of the advantages and disadvantages of the viscosity index improver, the smaller the value of SSI, the better the viscosity index improver of the shear stability, see the equation ( (2)
SSI = (V1 -V2) / (V1 -V0) (2)
In equation (2), V1 is the kinematic viscosity at 100 ℃ before shear, V2 is the kinematic viscosity at 100 ℃ after shear, and V0 is the kinematic viscosity at 100 ℃ of the base oil.
2.4 Thermo-oxidative stability
Viscosity index improver belongs to polymer, generally at about 100 ℃ will begin to occur thermal oxidative degradation, degradation produces a large number of low molecular compounds, at the same time part of the low molecular compounds will also be condensation reaction, resulting in higher molecular mass of polymer compounds. The free radicals generated by the thermo-oxidative degradation of the viscosity index improver will also accelerate the oxidation of the base oil, causing the viscosity of the multigrade lubricant to first decrease and then increase dramatically.
The main methods for evaluating the thermo-oxidative stability of viscosity index improvers are crankcase simulation test method, rotary oxygen bomb method and L-38 single cylinder method.
Properties and Applications of Different Viscosity Index Improvers
A comparison of the thickening ability, low temperature performance, shear stability and thermo-oxidative stability of commonly used viscosity index improvers, such as polyisobutylene (PIB), polymethylmethacrylate (PMA), ethylene propylene copolymer (OCP), and hydrogenated styrene dienophthalate (HSD), is shown in Table 1.
From the comparison in Table 1, it can be seen that polyisobutylene (PIB) viscosity index improver has good shear stability and thermo-oxidative stability, but its thickening ability and low-temperature performance are poor, and it is not suitable for blending multigrade internal combustion engine oils with a large span and low viscosity level, and it is generally used for the blending of multigrade gear oils, hydraulic oils, insulating oils, and metalworking oils, and the low-molecular-mass PIB is mostly used in the blending of 2-stroke Low molecular mass PIB is mostly used to blend two-stroke engine oils.
Polymethacrylate (PMA) viscosity index improvers have excellent low-temperature performance and thermo-oxidative stability, and good shear stability (especially the new comb-shaped PMA viscosity index improvers can reach an excellent level of SSI of less than 5%), but their thickening ability is poor, and they need to be added in larger quantities to achieve the same viscosity level, which leads to a greater impact on the cleanliness of the lubricant. The cost of polymethacrylate (PMA) viscosity index improver is higher, so it is mostly used in the formulation of high-grade lubricants, such as low-viscosity multi-grade gasoline engine oil, automatic transmission oil, ultra-low-temperature hydraulic oil, etc., and it is not suitable to be used alone in the formulation of multi-grade diesel engine oils which have very high requirements for cleanliness.
Ethylene propylene copolymer (OCP) viscosity index improver has good comprehensive performance, and its raw materials are abundant and easy to obtain, the production process is simple, so the price also has a great advantage. Good overall performance and outstanding cost-effective ethylene propylene copolymer (OCP) viscosity index improver has become the most used viscosity index improver, and its sales volume accounts for more than 60% of all viscosity index improvers. OCP viscosity index improvers are mainly used in multigrade engine oils, especially suitable for blending diesel engine oils. However, because of its general low temperature performance, it needs to be used in combination with ester-type depressants when blending low viscosity grade multigrade oils.
Hydrogenated styrene diene copolymer (HSD) viscosity index improver has special star structure or block structure and narrow molecular mass distribution, so the thickening ability and shear stability are more balanced, and it has high thickening ability and excellent shear stability at the same time. Hydrogenated styrene diene copolymer (HSD) viscosity index improvers also have outstanding low-temperature performance, and are particularly suitable for blending high-end multigrade gasoline engine oils, and can also be used for blending multigrade diesel engine oils.
Currently, the mainstream polyisobutylene (PIB), polymethacrylate (PMA), ethylene propylene copolymer (OCP) and hydrogenated styrene diene copolymer (HSD) viscosity index improvers each have unique performance characteristics, and are accordingly suitable for different multigrade lubricants. With the continuous progress of engine technology, environmental emissions and fuel economy regulations are becoming increasingly stringent, with which the multigrade engine oils are constantly upgraded and replaced, the performance of multigrade engine oil additives has also put forward higher requirements. As a very important additive, the viscosity index improver is moving towards the development of new viscosity index improver with excellent overall performance and the application of molecular design technology to synthesize multifunctional viscosity index improver based on the existing viscosity index improver.
What is the effect of viscosity index improvers on gasoline engine oil fuel economy?
In order to reduce fuel consumption and improve fuel economy, in addition to improving engine design, improving the lubrication state between engine friction parts is also an effective way. Generally speaking, during engine operation, the bearing parts are mainly in the state of elastic fluid lubrication, while the valve system, piston and cylinder liner parts are mainly in the state of boundary lubrication and mixed lubrication. For the fluid lubrication state, the choice of low viscosity gasoline engine oil can reduce friction loss; for the boundary lubrication state, to reduce friction loss, add friction improver in the engine oil is a more effective method. For the mixed lubrication condition, it is necessary to consider the optimization of the viscosity characteristics and friction characteristics of gasoline engine oil.
In order to improve the fuel economy of passenger cars, it is necessary to study the effect of gasoline engine oil components on fuel economy. As an additive that can improve the viscosity-temperature properties of lubricating oils, viscosity index improvers have been widely used in engine oils.
Commonly used viscosity index improvers are hydrogenated styrene diene copolymer (HSD), olefin copolymer (OCP), polymethacrylate (PMA), hydrogenated styrene-isoprene copolymer (SDC), and polyisobutylene (PIB), etc. The comprehensive performance of OCP and HSD is better, but HSD has a better shear-resistant property than OCP, which is more commonly used in high-grade gasoline engine oil. PMA is also widely used in high-performance gasoline engine oils because it has the characteristics of improving the low-temperature performance and viscosity index of gasoline engine oil. It has been reported that the gasoline engine oil formulated with PMA viscosity index improver can help to form a boundary oil film on the metal surface at high temperature and low speed, which can significantly reduce the friction and improve the fuel economy of gasoline engine oil.
One HSD viscosity index improver and three PMA viscosity index improvers (denoted as PMA1 viscosity index improver, PMA2 viscosity index improver and PMA3 viscosity index improver, respectively) were selected to formulate four 0W-20 viscosity grades of gasoline engine oil. With the help of High Frequency Reciprocating Rig (HFRR) and engine stand, the effects of these four viscosity index improvers on the fuel economy of gasoline engine were examined comparatively.
1 Test Equipment
1.1 High Frequency Reciprocating Rig
The HFRR is a microprocessor-controlled reciprocating wear test system for testing the friction and wear characteristics of gasoline engine oils.The HFRR can simulate the friction of the reciprocating motion of the engine cylinder liner – piston (ring) and other components, and examine the lubrication effect of gasoline engine oils by comparing the test parameters (friction factor, wear spot diameter).
1.2 Engine Rack
A 1.2 L turbocharged direct-injection engine produced by a car company is connected to a dynamometer through a torque flange, and the friction torque value under different working conditions is tested by back-dragging the engine with an electric motor in a non-ignition state. The engine stand is shown in Fig. 1
2 Test Sample
One HSD viscosity index improver and three PMA viscosity index improvers (denoted as PMA1 viscosity index improver, PMA2 viscosity index improver and PMA3 viscosity index improver) were selected as test samples, and some of the typical physical and chemical properties of these four viscosity index improvers are shown in Table 1.
Four gasoline engine oil samples were obtained by using the same base oil (API Ⅲ base oil of the same batch) and main agent under the condition of unchanged proportioning. In these four gasoline engine oil samples, HSD viscosity index improver, PMA1 viscosity index improver, PMA2 viscosity index improver and PMA3 viscosity index improver were added to obtain HSD gasoline engine oil, PMA1 gasoline engine oil, PMA2 gasoline engine oil and PMA3 gasoline engine oil in turn. The viscosity index improvers should be added in amounts as close as possible to the high-temperature, high-shear viscosity (150°C, 106 s-1 ) of the gasoline engine oil, which is close to the 0W-20 viscosity grade of 2.60 mPa – s, in order to obtain a better fuel economy.Typical physicochemical data of the HSD gasoline engine oils, the PMA1 gasoline engine oils, the PMA2 gasoline engine oils, and the PMA3 gasoline engine oils are shown in Table 2.
3 Results and Discussion
3.1 High Frequency Reciprocation Simulation Test
The simulation test conditions of the high frequency reciprocating tester (HFRR) are as follows: stroke 1 mm, frequency 40 Hz, load 3.92 N, temperatures 80 ℃ and 110 ℃, and 15 min at each temperature point; the material of the HFRR friction ball is AISI E-52100 steel, Rockwell hardness 58-66, and the material of the friction disk is AISI E-52100 steel. The friction factor and spot diameter of HSD gasoline engine oil, PMA1 gasoline engine oil, PMA2 gasoline engine oil and PMA3 gasoline engine oil were examined by HFRR simulation test and the results are shown in Table 3.
The results are shown in Table 3. From the examination of Table 3, it can be seen that PMA1 gasoline engine oil performs better in reducing the friction factor, which indicates that PMA1 gasoline engine oil has better friction reduction and lubrication performance. This is because the shear stability index (SSI) of PMA1 is smaller (see Table 1), the shear stability is better and the 100 ℃ kinematic viscosity is relatively low (see Table 2). This indicates that gasoline engine oils with good shear stability and low kinematic viscosity at 100 ℃ are more conducive to reducing the friction factor. From the aspect of wear spot diameter, the wear of PMA2 gasoline engine oil is slight, and the wear of PMA3 gasoline engine oil is serious, indicating that the greater the 100 ℃ kinematic viscosity of gasoline engine oil (see Table 2), the more it helps to reduce the wear of the friction parts.
3.2 Engine backward drag test
The friction torque of HSD gasoline engine oil, PMA1 gasoline engine oil, PMA2 gasoline engine oil and PMA3 gasoline engine oil was examined on the engine energy-saving stand in a backward drag test to test the actual fuel economy of gasoline engine oils formulated with different viscosity index improvers.
During the test, the friction torque of the reference oil (referred to as pre-friction torque) was measured at a certain temperature and speed, and then the test oils (i.e., HSD, PMA1, PMA2, and PMA3) were flushed and the friction torque of the test oils was measured at the same conditions, and then the friction torque of the reference oils was tested (referred to as post-friction torque). The friction torque of the reference oil is compared with the friction torque of the test oil by taking the average of the friction torque of the reference oil and the friction torque of the test oil to calculate the torque difference between the two (Torque Difference = Average Friction Torque of the Reference Oil – Friction Torque of the Test Oil), and then finally, the fuel consumption of the oil blended with different viscosity index modifiers is calculated by using the NEDC (New European Driving Cycle) simulation cycle test software. Finally, the fuel economy of HSD, PMA1, PMA2 and PMA3 gasoline engine oils formulated with different viscosity index improvers was calculated using the NEDC (New European Driving Cycle) simulation cycle test fuel consumption software.
Based on the approximate power density distribution of the NEDC cycle test, the operating conditions of the NEDC cycle test were determined, i.e., oil temperatures of 35 °C, 50 °C, 80 °C and 110 °C, engine speeds of 1100 r/min, 1450 r/min, 2000 r/min, 2500 r/min, 3000 r/min, 3500 r/min, 4000 r/min and 4500 r/min, and fuel economy of PMA3 gasoline engine oil. The engine speeds were 1100 r/min, 1450 r/min, 2000 r/min, 2500 r/min, 3000 r/min, 3500 r/min, 4000 r/min and 4500 r/min respectively, and the reference oil was gasoline engine oil of 0W-30 viscosity grade.
The torque of HSD gasoline engine oil, PMA1 gasoline engine oil, PMA2 gasoline engine oil and PMA3 gasoline engine oil was tested and the torque difference between the reference oil and the test oil was calculated at different temperatures and engine speeds, as shown in Fig. 2 – Fig. 5.