12 key questions about gasoline

What is the durability of gasoline? Is it dangerous to drive with stale fuel? Why is the octane number one in Europe and another in America? Is gasoline more expensive today than it was under socialism? Does it matter what color it is? In this article, we decided to answer many of the questions people ask about car fuel.

Why did the A-86 and A-93 disappear?

In late socialism, three gasolines were offered - A-86, A-93 and A-96. Today they have been replaced by the A-95, A-98 and A-100. Previously, there were gasolines with an octane rating of 76, 66 and even 56.

There are two reasons for their disappearance. One of them is ecological: low-octane gasolines do not meet modern requirements for sulfur, benzene, and so on.

The second is related to the evolution of engines. Low-octane gasolines do not allow high compression ratios - for example, A-66 has an upper compression limit of 6,5, A-76 has a compression ratio of up to 7,0. However, environmental standards and downsizing have led to the massive introduction of turbocharged engines with much higher compression ratios.

What is an octane number?

This conventional unit of measurement indicates the resistance of gasoline to detonation, that is, the probability that it ignites spontaneously in the combustion chamber before the spark plugs generate a spark (which, of course, is not very good for the engine). Higher octane gasolines can handle higher compression ratios and therefore generate more energy.

The octane number is given for comparison with two standards - n-heptane, which has a knock tendency of 0, and isooctane, which has a knock tendency of 100.

Why are octane numbers different?

People who have traveled a lot around the world may have noticed a difference in the readings of gas stations. While in European countries it is mostly fueled with RON 95 gasoline, in countries like the United States, Canada or Australia, most motorists fill 90.

In fact, the difference is not in the octane number, but in the way it is measured.

RON, MON and AKI

The most common method is the so-called research octane number (RON), adopted in Bulgaria, the EU, Russia and Australia. In this case, the fuel mixture is run through a test engine with a variable compression ratio at 600 rpm and the results are compared with those for n-heptane and isooctane.

However, there is also MON (engine octane number). With it, the test is carried out at an increased speed - 900, with a preheated fuel mixture and adjustable ignition. Here the load is greater and the tendency to detonation appears earlier.

The arithmetic mean of these two methods, called AKI - Anti-Knox Index, is recorded at gas stations in the US. For example, a standard German A95 with 10% ethanol has an RON of 95 and a MON of 85. Both results in an AKI of 90. That is, a European 95 in America is 90, but actually has the same octane number.

What is the sensitivity to gasoline?

Gasolines have another parameter called "sensitivity". This is practically the difference between RON and MON. The smaller it is, the more stable the fuel under any conditions. And vice versa - if the sensitivity is high, this means that the tendency to knock changes significantly with changes in temperature, pressure, etc.

How long can gasoline be stored?

Drivers who use cars less often or hibernate should remember that gasoline is far from eternal. Shelf life - 6 months, but when stored closed, without contact with atmospheric air and at a temperature not higher than room temperature. If the temperature reaches 30 degrees, gasoline can lose its properties in just 3 months.

In countries with colder climates, such as Russia and Iceland, the official shelf life of gasoline is one year. But then in the USSR there was a delimitation by area - in the north, the shelf life was 24 months, and in the south - only 6 months.

The shelf life of gasoline actually decreased after the lead compounds were eliminated.

Is stale gasoline dangerous?

If the fuel has lost quality (cyclic hydrocarbons in it have become polycyclic), you may have problems with ignition or maintaining speed. Adding fresh gasoline usually solves this problem. However, if gasoline has been exposed to air and oxidized, deposits can form in the gasoline and damage the engine. Therefore, for a longer stay of the car, it is recommended to drain the old fuel and replace it with a new one before starting the engine.

When does gasoline boil?

Most people are genuinely surprised to learn that standard gasoline has a boiling point of 37,8 degrees Celsius for its lightest fractions and up to 100 degrees for the heavier ones. In diesel fuel, the boiling point is at the earliest 180 degrees.

Therefore, on old cars with carburetors, it was quite possible to turn off the engine in hot weather and it will not want to start again until it cools down a little.

Can different octane be mixed?

Many people find that mixing different octane fuels in a tank is dangerous because they have different densities and will stratify. It is not true. There is no negative effect of adding 98 to the tank with 95. Of course, it doesn't make much sense to mix them, but if necessary, it is not a problem.

Does the color of the gasoline matter?

The natural color of gasoline is yellowish or clear. However, refineries may add various dyes. Previously, this color was standardized - for example, A-93 was bluish. But today there is no current regulation, and each manufacturer uses the color they want. The main goal is to distinguish the fuel from fuels from other manufacturers so that, if necessary, its origin can be traced. For the end user, this color does not matter.