Is it more economical to refuel in the morning? Check out the common misconceptions about refueling in life

Is it more economical to refuel in the morning than at noon? Is the oil grade proportional to the oil quality? If the amount of water discharged from the car's exhaust pipe increases, is it because the oil is not good? ... Take stock of the misunderstandings about "refueling" in life.

Written by reporter Zhao Tianyu Edited by Liu Zhao

New Media Editor/Lv Bingxin

Interview experts

Guo Qun (Professor-level Senior Engineer, Science and Technology Development Department, Sinopec)

Is it more economical to refuel in the morning than at noon? Is the oil grade proportional to the oil quality? Is the amount of water discharged from the car exhaust pipe increasing? Is it because the oil is not good? Are all private gas stations selling shoddy oil? ...

Every winter, the problems of short battery life and false mileage of electric vehicles give many new energy vehicle owners a headache. Traditional fuel vehicles have shown great advantages in terms of battery life. The most closely related to the battery life of fuel vehicles is refueling with gasoline. After all, without fuel, it cannot drive. However, many common sense about refueling are actually rumors, and even many experienced drivers have fallen for them.

Rumor: Is it cheaper to refuel in the morning?

The truth: There is not much difference between morning, noon and evening

There is a saying among experienced drivers: "It is most cost-effective to go to refuel in the morning or evening, especially in the morning, when you can get more gas for the same money."

This statement is not groundless. According to the principle of thermal expansion and contraction in physics: the lower the temperature of the liquid, the higher the density; the higher the temperature, the lower the density of the liquid. The amount of gasoline is charged based on volume rather than weight. Under the same volume, the higher the density, the greater the mass, and at the same price, the more gasoline is added.

Because of the scientific principle "endorsement", many car owners believed it to be true, and some even went to refuel early in the morning. But the final result is not hard to imagine, and the purpose of saving money was not achieved. Does the scientific principle no longer apply? In fact, this is not the case.

Guo Qun, a professor-level senior engineer at the Science and Technology Development Department of Sinopec, explained that gas stations currently all have underground oil storage depots, and all have a certain degree of protection layer. Gasoline is stored at a constant temperature all year round and is not affected by the external temperature. The idea that refueling in the morning and evening saves money is naturally not true.

"Even if the technology level in the early years did not meet the current standards and could not achieve underground constant temperature oil storage, the density of gasoline did not change much under different temperature conditions, and the resulting price difference was very small."

In fact, if the saying that refueling in the morning is more economical is true, refueling in winter should be more economical than in summer, then the oil price should change all year round, otherwise the gas station will lose money. Therefore, the real way to save fuel is to develop good driving habits. In our daily use of cars, fuel consumption is often greater due to queuing, idling or violent driving.

Rumor: The higher the oil grade, the better the quality?

The truth: There is no direct relationship between oil grade and quality

The main components of gasoline are C5-C12 aliphatic hydrocarbons and cycloalkanes, as well as a certain amount of aromatic hydrocarbons. As a kind of petroleum refining product, gasoline has a higher octane number, that is, anti-knock combustion performance.

According to the current laws and regulations in my country, gasoline is produced and sold by brand, which is divided by octane number. There are three national (IV) gasoline brands, namely 90, 93, and 97. National (V) gasoline brands are 89, 92, 95, and 98. The higher the brand, the better the anti-knock performance.

Since the price of No. 95 gasoline is higher than No. 92 gasoline, and the relatively high-priced mid-range family cars are generally filled with No. 95 gasoline, many car owners therefore think that the higher the gasoline grade, the better the quality. Some people even deliberately fill high-grade gasoline to improve combustion quality.

In this regard, Guo Qun said that the gasoline grade is related to anti-knock ability, but has no direct relationship with quality. This is because most civilian gasoline engines use the four states of "intake-compression-combustion-exhaust" to work repeatedly, and the specific type of oil to be filled mainly depends on the parameter of "compression ratio".

The compression ratio refers to the ratio of the cylinder volume when the piston is at the bottom dead center and the top dead center of the stroke. Cars with high engine compression ratios have better power and higher thermal efficiency, and the vehicle acceleration and maximum speed will also be improved accordingly. Therefore, many mid-range cars use engines with high compression ratios and need to be filled with high-grade gasoline. Compact cars and small cars use engines with low compression ratios and fill with low-grade gasoline, which is a more fuel-efficient approach.

Guo Qun suggested that consumers do not need to deliberately fill up with high-grade gasoline, but should refuel according to the grade given by the manufacturer, or judge based on the engine compression ratio. For example, if the compression ratio is around 8.0-8.5, you can choose 92-95 gasoline, if the compression ratio is around 8.5-9.0, you can choose 95 gasoline, if the compression ratio is around 9.5-10.0, you can choose 95-98 gasoline, and if the compression ratio is higher than 10.0, it is recommended that 98 is better.

Rumor: Adding “Fuel Treasure” can reduce fuel consumption?

The truth: The real effect is exaggerated, regular maintenance is more important

"Your engine is full of carbon deposits. How about adding a bottle of fuel saver?" In recent years, when many car owners go to gas stations to refuel, they are always enthusiastically promoted by the staff a fuel additive that can improve combustion efficiency and remove carbon deposits - fuel saver.

Although it is small, it is not cheap. Generally, a set of 6 bottles costs about 200 yuan, or even higher. Some car owners feel that the effect is not obvious after adding it, and they directly say that they have paid an IQ tax.

Guo Qun said that there are currently two types of fuel savers on the market. One type claims to be able to adjust the octane number, increase the thermal efficiency of the engine, and enhance the driving experience. This type of fuel saver does not have a significant effect after use on general family cars except for some old models.

Another type of fuel saver is a cleaner for engine carbon deposits. It removes carbon deposits inside the engine and discharges them after high-temperature combustion, playing a certain role in dissolving and removing carbon deposits.

"It is worth noting that how much carbon deposits this additive can remove, the scientific community currently does not have an accurate evaluation value, and therefore cannot evaluate the true effect." Guo Qun said that on the other hand, the fuel saver is mixed in the gasoline, and can only produce a cleaning effect at places that the gasoline can reach. Theoretically, there is no possibility of cleaning at places that the gasoline cannot reach, such as the throttle body and the back of the intake valve of a direct injection engine, where there will be carbon deposits.

Therefore, the real effect of the fuel saver has been exaggerated, and it is not as "magical" as advertised or claimed by gas station attendants.

Consumers should be more cautious when choosing products. The most effective way to remove carbon deposits is to go to a 4S shop or a regular auto repair shop for vehicle maintenance on time. The maintenance workers will use professional equipment to clean for users, which is safe, efficient and more targeted.

Rumor: Is the increase in exhaust pipe discharge due to poor oil quality?

The truth: After gasoline burns, water vapor turns into water when it cools down

With the coming of winter, the temperature continues to drop, and many car owners have observed this phenomenon, that is, the exhaust pipe of the car will drip out, or even "flow" continuously. This makes many car owners terrified, thinking that it is caused by adding low-quality gasoline.

After gasoline is completely burned, water and carbon dioxide are generated. Water becomes water vapor at high temperatures, but when the temperature is below 100°C, water vapor will condense into water. If the condensed water droplets accumulate, they become liquid water, and when they reach a certain amount, they are discharged through the exhaust pipe. So the water we see in the exhaust pipe is actually the result of water vapor generated by gasoline combustion, which condenses in the exhaust pipe and muffler.

It is worth mentioning that automobile exhaust pipes generally have a small hole for drainage. The lower the temperature, the more obvious the water flow phenomenon. Guo Qun said that in Northeast my country, when vehicles are waiting for red lights in winter, you can often see a group of vehicles collectively "draining water". This phenomenon does not mean that there is a problem with the fuel quality or the fuel system. Instead, it means that the engine is fully burning and in good working condition.

However, it should be noted that if the liquid in the exhaust pipe is black and very sticky, accompanied by blue smoke, the engine oil is consumed quickly, and the engine power is obviously insufficient, this situation indicates that the gap between the engine's piston, cylinder liner, and piston ring is too large and it can no longer work normally. Professional inspection and maintenance should be carried out immediately.

Rumor: Are all private gas stations selling “black oil”?

The truth: The source of oil products is guaranteed, but "big factories" are more trustworthy

Gas stations in my country are composed of three parts: state-owned, private, and joint ventures. As of the end of 2020, among the 112,000 gas stations in the country, 50% were operated by state-owned enterprises, 48.1% were operated by private enterprises, and 1.9% were operated by foreign-funded enterprises.

Among private gas stations, in addition to well-known oil companies such as Sinochem Petroleum and Yanchang Petroleum, there are also many "private gas stations" named after towns or randomly named. Compared with state-owned gas stations, private gas stations have lower prices. There has always been a saying among the people that "the quality of oil products at private gas stations is poor" and "small rural gas stations all sell black-hearted oil."

"my country's 'Technical Specifications for the Management of Finished Petroleum Retail Enterprises' clearly stipulates that finished petroleum retail enterprises should have stable and legal finished petroleum supply channels and should purchase finished petroleum from enterprises that are qualified to engage in finished petroleum wholesale operations." Guo Qun said that from a legal perspective, the source of oil products for both private and state-owned gas stations is guaranteed, and in theory there is no such thing as "black heart oil."

However, Guo Qun also reminded consumers that some unreliable small gas stations or private gas stations in remote areas may use inferior oil due to insufficient supervision. The so-called "black gas stations" have not disappeared. If it is not a particularly urgent situation, it is still recommended to give priority to state-owned gas stations such as Sinopec and PetroChina, or well-known private gas stations. After all, "big companies" are more trustworthy.

Produced by: Science Central Kitchen

Produced by: Beijing Science and Technology News | Beijing Science and Technology Media

Welcome to share to your circle of friends