Knowledge of the use of vehicle fuel

carIt is an important means of transportation and transportation indispensable in modern production and life. When you have the opportunity to drive a car, I believe you will care and care for your beloved car.
Maybe you care about the ignition circuit,Spark plug, To see if they affect the output power of the engine; or consider what fuel-saving device to install will save some expenses; or go to various places to select catalytic devices to cope with the random inspection of exhaust emissions. But, have you ever thought of what role the most common fuel plays in it?
Composition and characteristics of vehicle fuel
The cars we usually use are powered by internal combustion engines, which are divided into gasoline engines and diesel engines according to their working methods. Both gasoline and diesel are refined from petroleum. The remains of animals and plants in ancient times were pressed deep in the stratum due to the movement of the earth's crust. Under the conditions of high temperature, high pressure, and lack of oxygen, petroleum was gradually formed through complex chemical changes. The chemical composition of petroleum is more complicated. It is not composed of a single element, but a mixture of various hydrocarbons. The main component of gasoline is alkanes, which are stable in nature, have a large calorific value and are not easy to oxidize; the aromatic hydrocarbons in gasoline have strong anti-knock properties, which is good for gasoline, but it will burn diesel in diesel The performance deteriorates, which is not good for diesel. In addition, a small amount of nitrides, oxides, and sulfides contained in petroleum are undesirable components in the oil and should be removed as much as possible during the refining process.
Crude oil extracted from underground undergoes a very complicated refining process in the refinery, and finally fuels such as gasoline, diesel and kerosene are refined. In general, gasoline and diesel that have been processed to a certain quality standard are in the form of a light yellow transparent liquid, and have a lower density than water. The smell of gasoline and diesel is different, and the touch feel is different. Dip a little gasoline with your hand, and your hands will feel cold and astringent. After the gasoline evaporates, your skin will turn white: Dip diesel with your hand will feel slippery and oily.
The correct choice of gasoline
The correct choice of fuel can make the engine play its due efficiency. If the fuel is improperly selected, not only will the engine not be able to produce the power it should have, but on the contrary it will also cause damage to the engine and reduce its performance and service life.
Gasoline is a very volatile fuel, even at a low temperature of -30°C, it can produce gas that can be ignited. The better the volatility of gasoline, the easier it is to vaporize. In the low temperature environment in winter, cold cars can start and work normally. However, excessively volatile gasoline is likely to cause air resistance in the gasoline pump, the tortuous part of the fuel pipe, or the hot part of the fuel pipe. If the volatility of gasoline is not enough, it will be difficult to fully vaporize, not only the engine is not easy to start in a low temperature environment, but also cannot fully burn in the engine, which makes the engine work unstable, increases fuel consumption, and produces a large amount of carbon deposits. Therefore, the volatility of gasoline can neither be too strong nor too bad, which is controlled during the refining process of gasoline.
Motor gasoline is distinguished by labels according to its octane number. The octane number is an indicator of the anti-knock resistance of gasoline, and it is one of the important quality indicators of gasoline. At present, there are two most commonly used methods for determining octane number:motorMethod and research method, the values ​​measured by the two methods are different. At present, the label of motor gasoline in my country is determined by the research method. No. 93 gasoline indicates that its octane number is not less than 93, and so on. The engine should choose gasoline of different labels according to the different compression ratio, which will be marked in the user manual of each car. If an engine with a high compression ratio uses unsuitable low-grade gasoline, knocking will occur.
Because the engine with a high compression ratio has good economy, it has high efficiency and low fuel consumption, so the engine compression ratio of modern cars is generally designed to be higher. Engines with high compression ratios also have a greater tendency to knock, which requires the use of gasoline with good knock resistance, that is, high octane number. There are two main ways to increase the octane number of gasoline: one is to add antiknock agents to the gasoline, and the other is to use a gasoline refining process that contains high-octane hydrocarbons. Among the many kinds of antiknock agents, people have found that the antiknock effect of tetraethyl lead is particularly significant. Only a small amount of tetraethyl lead can greatly increase the octane number of gasoline. Therefore, since 1921, tetraethyl lead has been used as an effective Also economical gasoline antiknock agents are widely used.
Tetraethyl lead is a highly toxic oily liquid with a fruity scent. It can enter the human body through the respiratory tract, esophagus and unwound skin, and is difficult to excrete. When the lead in the human body accumulates to a certain amount, it will cause poisoning. Mild poisoning will cause symptoms such as dizziness, headache, loss of appetite, fatigue, fatigue, insomnia, and drop in blood pressure; severe poisoning will cause abdominal cramps and nerves The system is messed up and even died. Therefore, leaded gasoline causes great harm to the environment and humans. Due to the increasing number of cars in modern society, in order to protect the environment and control pollution, many countries have strictly banned the use of leaded gasoline, and have formulated increasingly stringent automobile exhaust emission control standards and environmental protection regulations. my country has taken the lead in Beijing Unleaded gasoline will be used uniformly, and unleaded gasoline will be used nationwide in 2000. However, the use of unleaded gasoline also has some new problems.
The right choice of diesel
The combustion performance of diesel is mainly expressed by the cetane number. The higher the cetane number, the better the combustion performance of diesel, but its freezing point is also higher. The freezing point indicates the low-temperature fluidity of diesel, which refers to the highest temperature at which the oil starts to solidify and lose fluidity when cold, and is one of the important indicators of diesel. The mark of the diesel we use indicates its freezing point. There is no direct correspondence between the freezing point and the low temperature performance of diesel. Because the paraffin crystals are precipitated before the diesel is solidified, the shapes and sizes of these crystals are different for the diesel obtained from different crude oils and different refining methods. They often block the filter screen of the diesel engine and cause the oil supply to be interrupted. Therefore, cars using diesel engines should pay attention to selecting the appropriate label of oil according to the ambient temperature of the place of use.
Diesel fuel should be fully precipitated and filtered before use to remove impurities, and generally should not be less than 48 hours. This is because the high-pressure fuel pump and fuel injection nozzles of high-speed diesel engines are very precise parts, and a little mechanical impurities will be severely worn. In addition, when diesel is used under low temperature conditions, it should be preheated. Different grades of diesel oil, because its quality indicators are basically the same except for the freezing point, it can be mixed with the oil in the season.
Unleaded gasoline and the problem
We know that although lead is an economical and efficient anti-knock additive, it is inevitable that it will eventually be eliminated due to its greater toxicity to the human body and serious pollution to the environment. The use of unleaded gasoline will undoubtedly control the harmfulness of lead to human beings, but at the same time, in order to maintain high knock resistance of gasoline, some other solutions and means must be adopted to replace the role of lead.
Generally speaking, there are three ways for factories to increase gasoline octane number:
One is to select good raw materials and improve processing techniques, such as using secondary processing techniques such as catalytic cracking and reforming.
The second is to add high-octane components with excellent knock resistance to the product, such as isooctane, cumene, and alkylbenzene.
The third is to add antiknock agents. In actual work, one or several methods can be used according to specific conditions to obtain high-octane gasoline.
In practice, people realize that adding a small amount of high-efficiency antiknock agent to gasoline can greatly improve the antiknock resistance of low-octane gasoline, and it is also the most economical way to obtain high-octane gasoline, especially when purely processing and When the blending method is difficult to achieve the desired effect, adding antiknock agents has become an effective way to adjust the gasoline octane number.
The technology and manufacturing materials of modern automobile engines are very different from the past.EFI replacedCarburetor, Light alloys are widely used in cylinder heads, cylinder walls,piston,Piston ring, Connecting rod and platoonValveThe manufacture of other parts to reduce the inertia of moving parts and the mass of the engine. But whether it is EFI or alloy materials, there is a big defect: the resistance to corrosion is very weak. When using leaded gasoline, the surface of the valve, piston top, cylinder wall, nozzle and other parts will be covered with a layer of lead film, which naturally plays a protective role and reduces the effects of oxides and sulfides in gasoline components on the engine. Corrosion of parts. However, the use of unleaded gasoline will lose this effect, and the alloy parts will directly contact the corrosive components in the gasoline, which will be easily corroded and affect the service life of the engine.
Antiknock agent in unleaded gasoline
Since the chemical composition of additives is similar to that of petroleum products, and they have indeed played an irreplaceable role in improving the quality of oil products, the use of additives to obtain high-quality oil products has become one of the most important methods in the world, especially in Adding antiknock agents to gasoline has become the most effective and commonly used method to increase the octane number. Nowadays, a certain amount of antiknock agent is generally added to gasoline produced in various countries in the world.
Over the years, among the many metal and non-metal antiknock agents that people have tested, manganese-based organic compounds are one of the best quality antiknock agents, referred to as MMT. MMT can effectively increase the octane number in unleaded gasoline, and it also has the effect of reducing engine wear. But its biggest disadvantage is its high cost, which is about four times that of lead antiknock agent, and it has the effect of destroying the purification of automobile exhaust, making it controversial in its use.
Although metal organic antiknock agents have good effects, metal oxides are solid and are not easy to discharge from the cylinder. Even if the lead-out agent is used, long-term use will inevitably cause the problems of spark plug failure, shortened exhaust valve life, and increase in combustion chamber carbon caused by metal accumulation. So people are studying the use of pure organic compounds as antiknock agents. For example, an antiknock agent called MMA, which has been produced and used in some European countries, has quite good antiknock properties, but its cost is relatively high and its use is also restricted. An organic antiknock agent, referred to as MTBE, is widely used in our country. This antiknock agent is widely used in the world. The addition of MTBE to gasoline has little effect on the physical and chemical properties and density of gasoline, and has good anti-knock properties. Its disadvantage is that it makes gasoline easier to absorb water and should be controlled during use, storage and transportation. The amount of MTBE added to gasoline varies from country to country. The United States stipulates 11% and the European Community allows 15%. At present, it is unrealistic to find an additive that fully meets all the conditions and requirements. This requires the addition of different types of additives to balance and achieve different goals.