Diesel oil is extracted from petroleum. According to different distillation process, it can be divided into two categories: light diesel oil and heavy diesel oil. Due to the high speed of construction machinery diesel engine, light diesel oil is used. The color of light diesel oil is light yellow. To the deep yellow, some are slightly green, not easy to evaporate, the hand feels a little sticky.
A. Requirements for the use of light diesel.
1 Ignition should be moderate. The ignitability of diesel is the ability of diesel and air to form a combustible mixture to ignite and burn. It is usually expressed by “hexadecene valueâ€.
As for the cetane number, it is not a unit, but a comparison value. It means that the combustion performance of diesel is equivalent to the volume percentage of hexadecane in the mixture of cetane and a-methylnaphthalene. The combustion and starting properties of hexadecane are much better than that of a-methylnaphthalene. Suppose that the combustion performance of hexadecane is 100 units, and the a-methylnaphthalene is 0 units. The two substances with different combustion properties are different. According to different volume ratios, a variety of standard diesel oils with cetane numbers from 0 to 100 can be obtained. For example, light diesel oil No. 0 has a cetane number of not less than 50, indicating its combustion performance. It is equivalent to a mixture of 50% hexadecane and 50% a-methylnaphthalene. The higher the cetane number, the better the combustion performance. The light diesel oil used in engineering machinery diesel engines, the cetane number is generally 45-60. Good. The cetane number is too low, which will cause the diesel engine to work rough and difficult to start in winter. The cetane number is too high, the diesel fuel injected into the combustion chamber is too late to mix with the air, and the fire is incomplete, resulting in diesel exhaust. Black smoke, reduced power and increased fuel consumption.
2 Good low-temperature fluidity The low-temperature fluidity of diesel fuel is expressed by the freezing point. The freezing point refers to the temperature at which the diesel engine used in diesel engine cools to the loss of fluidity and is one of the important indicators of diesel.
3 It is necessary to have a certain viscosity to ensure that the plunger of the fuel injection pump is well lubricated under the premise of good spray and complete combustion.
4 The evaporability of suitable evaporative diesel oil is expressed by the temperature of distillation of 50%, 90%, and 95% fractions. It reflects the performance of diesel fuel from liquid to gas. The lower the temperature, the better the evaporability. Too good, the diesel fuel in the combustion chamber will evaporate too fast, which will cause the diesel to burn too fast, make the cylinder pressure increase rate too large and work rough. The evaporation is too low, it will be difficult due to diesel evaporation, it is difficult Mixed with air, can not form a good combustible mixture, resulting in incomplete combustion, increased carbon deposits, black smoke and fuel consumption, and difficult to start.
B. Selection method of domestic light diesel oil The grades and specifications of domestic light diesel oil are divided into three grades of superior grade, first grade and qualified by quality, and are divided into 10, O, -10, -20, -35 according to the freezing point. , -50 and other six brands.
The main difference between the quality index, the first grade product and the qualified product of light diesel oil is the sulfur content. Considering the current situation of diesel engine lubricating oil in China, the engineering machinery diesel engine should use sulfur content at 0.20/0~0.50/0. Light diesel oil. This is because when the sulfur content of diesel is too large, sulfur trioxide will be formed after combustion, and the corrosive sulfuric acid will form a strong corrosive sulfuric acid, which will seriously corrode the cylinder.
In order to ensure the normal operation of the diesel engine, if the temperature is allowed, the high-condensation point diesel oil can be selected as much as possible. The purpose is to improve the economic benefit. For this reason, the diesel condensation point is usually lower than the local minimum temperature by about 5 °C. For example, when the ambient temperature is above 4~7°C, the purchase of diesel with O size can guarantee the normal use of diesel engine. Similarly, light diesel-10 is suitable for use in areas with a minimum temperature above -5 °C.
Different grades of light diesel oil, because their performance indicators are basically the same except for the freezing point. Therefore, the oil unit can be mixed and used in the case of insufficient container, which does not affect its quality. However, the highest concentration point must be obtained at this time. Diesel, as a basis for use. Otherwise, the diesel engine will not work properly because it is not suitable for the local ambient temperature.
Natural Graphite , as its name implies, is naturally formed by natural Graphite , which is generally found in graphite schist, graphite-gneiss, graphite-bearing schist and metamorphic shale.
Features
The chemical composition of graphite is carbon (C). Naturally produced graphite is rarely pure and often contains impurities, including SiO2, Al2O3, MgO, CaO, P2O5, CuO, V2O5, H2O, S, FeO and H, N, CO2, CH4, NH3, etc. Natural graphite minerals are black, steel gray, striated black; Metallic luster, crypto, dull, opaque; The hardness is isotropic, the vertical cleavage surface is 3 ~ 5, the parallel cleavage surface is 1 ~ 2; Qualitative soft, density is 2.09 ~ 2.23 g/cm3, have the feeling of greasy, easy to contaminate finger. Mineral chip under the transmitted light is generally not transparent, extremely thin can pervious to light, the light green gray, refractive index of 1.93 ~ 2.07, under the reflected light is light gray, reflective pleochroism, Ro gray with brown, Re dark blue gray, reflectivity Ro23 (red), Re5.5 (red), the reflected color, double reflection were significantly, strong heterogeneity, polarization color for straw yellow.
Graphite is a complex six-party double cone, assumes the six-party tabular crystal, common simplex are parallel double, six-party double cone, hexagonal prism, but in good condition with rare crystal forms, the generally show scaly or platy, aggregate density lump, earthy or globular.
Type
The process performance and usage of graphite is mainly depends on the degree of crystallization, in accordance with its natural Graphite Crystal morphology can be divided into crystalline graphite, Flake Graphite ) and aphanitic graphite (earthy graphite) two types of industry.
Crystalline graphite
In the crystalline (scale) graphite ore, the diameter of graphite crystals is greater than 1 mu m. Ore grade is low, but optional; The mineral associated with graphite is usually mica, feldspar, quartz, diopathic stone, diabase, garnet and a small amount of pyrite, calcite, etc., some of which have some useful components, such as rutile and vanadium. The ore is scales, grainy scales or granulocyte structures, flaky, flaky, or blocky structures.
The high purity graphite (fixed carbon content is greater than or equal to 99.9%) is mainly used for flexible graphite sealing material, nuclear graphite, instead of platinum crucible for chemical reagent melting and lubricant base material, etc.
High carbon graphite (fixed carbon content 94.0% ~ 99.9%) is mainly used for refractory materials, lubricant substrate, brush raw materials, carbon products, battery raw materials, pencil materials, filling materials and coatings, etc.
Carbon graphite (80% ~ 94% fixed carbon content) is mainly used for crucible, refractories, casting materials, foundry coatings, pencil raw materials, battery materials and dyes, etc.
Low carbon graphite (fixed carbon content 50.0% ~ 80.0%) is mainly used for foundry coatings.
Cryptocrystalline graphite
Cryptocrystalline graphite is also called soil graphite or amorphous graphite. In cryptocrystalline graphite ore, graphite crystals are less than 1 mu m in diameter, which are microcrystalline and can only be seen in the electron microscope. High grade of ore, but poor selectable; The mineral associated with graphite is often quartz and calcite; The ore is microscaly - cryptocrystalline structure, block or soil structure.
Cryptocrystalline graphite ore is mainly distributed in contact metamorphic deposits. Actually the diameter graphite flake graphite ore is uneven, the so-called crystalline graphite ore, may also contain the aphanitic graphite, are too many content is often referred to as the mixed type graphite ore, may also contain a small amount of aphanitic graphite quality mineral crystalline flake graphite piece diameter slightly larger than 1 microns.
Cryptocrystalline graphite ore is mainly used in pencil, battery, electrode, graphite emulsion, graphite bearing ingredients and the raw materials of battery carbon rod. The non-ferrous graphite is mainly used for casting materials, refractory materials, dyes and electrode paste.
