Aviation gasoline: characteristics

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Aviation gasoline is a flammable liquid that enters the engine of an aircraft, mixing with air to obtain thermal energy as a result of the process of oxygen oxidation of the incoming air into the combustion chamber. Reciprocating engines run on this fuel.

The following indicators are valued in aviation gasoline:

• Knock resistance.
• Chemical stability.
• Faction composition.

Measuring the knock resistance parameter of aviation gasoline is necessary to decide on the suitability of using such fuel in units where there is a high degree of compression of the mixture coming from the gas tank. For the normal operation of the aircraft engine, it is important to avoid detonation ignition.

Fractional composition must be known to determine the volatility of gasoline. During the measurement, it is found out whether it forms a fuel-air mixture.

Chemical stability is the resistance to changes in the composition of a combustible liquid during transportation, storage and operation.

Types of gasoline used in aviation

There are 2 types of base gasoline - straight-run and actyl-gasoline. The first type of fuel gained popularity in the middle of the 20th century; it was mined by direct distillation. A straight-run combustible mixture is obtained by distillation and subsequent selection of oil fractions, which evaporate at a certain heating. If the fractions evaporate at temperatures up to 100 degrees Celsius, gasoline is classified as first grade, if the heating temperature for evaporation is up to 110 degrees, then gasoline is called special. If oil fractions evaporate in gasoline at temperatures up to 130 degrees, then the fuel has a 2nd quality grade.

Different grades of distilled gasoline have a single factor that unites them - low octane. Using the straight-run method, it is possible to obtain a gasoline mixture with an OC above 65 only from oil produced in Azerbaijan, the Krasnodar Territory, Sakhalin and Central Asia. In other places where “black gold” is mined, the combustible mixture is obtained with a low SP due to the presence of paraffinic hydrocarbons.

Dignity of straight-run gasoline

The positive qualities of straight-run gasolines are:

• stability;
• anti-corrosion properties;
• excellent evaporation;
• high thermal conductivity (about 10,500 bcal/kg);
• resistance to low temperatures (up to 100 degrees Celsius);
• low hygroscopicity.

Because this fuel has too high knock resistance, it is used only together with impurities, inresulting in an increase in octane.

What is octane?

The octane number characterizes the resistance to detonation of a combustible material, i.e. the ability of a liquid to ignite spontaneously during compression in an internal combustion engine. The octane number is equal to the content of isooctane in the combustible mixture together with the substance n-heptane. The mixture must be equivalent in resistance and detonation to the test fuel sample under normal conditions. The substance isooctane is poorly oxidized, therefore its resistance to detonation was taken as 100 units, and the substance n-heptane detonates even at the slightest compression, therefore its resistance to detonation is taken as zero. To determine the resistance to detonation of gasoline, whose octane exceeds 100 units, a special scale was created. It uses isooctane with the addition of tetraethyl lead in varying amounts.

Varieties of SP

Octane numbers are divided into two types: OCHM and OCHI. The ROI (research octane number) shows how gasoline reacts at light to medium engine loads. To determine the ROI, a setup is used that simulates a single-cylinder engine. The design is capable of compressing fluid with varying force. The crankshaft speed is 600 rpm at a temperature of 50 degrees Celsius.

MOND (engine octane number) demonstrates the behavior of a flammable liquid during heavy loads. The determination method is similar to the previous one, however, the crankshaft speed of the installation simulating the engine is 900 rpm, and the air temperature during the tests reaches150 degrees Celsius.

Increased SP with additives

Modern engines used in aviation require fuel with a minimum octane rating of at least 95 units. Refined gasolines after direct distillation are obtained with a low octane number, they are not suitable for use in modern aircraft engines. An increase in anti-knock properties can be achieved with the help of additives. Previously, only ethyl liquid was used for these purposes. Nowadays, whole complexes have been developed to increase the RP, which contain oxygen-containing components, esters, stabilizers, dyes, anti-corrosion agents and much more.

The difference between gasoline B 91 115 and Avgas 100 ll

Aviation gasoline B 91 115 is a mixture of fuel obtained by direct distillation using catalytic reforming. The composition of such fuel includes alkylbenzenes, toluene and various additives (ethyl, antioxidant, dye). Aviation gasoline Avgas 100 ll consists of a mixture of similar high-octane and base components. To obtain this brand of fuel, ethyl, dye and additives are added to prevent the formation of corrosion and static electricity.

The differences between the two brands of combustibles lies in the grade, additives used, components and different content of tetraethyl lead. In the first grade of fuel, the amount of tetraethyl lead should not exceed 2.5 g/kg, in the second - 0.56 g/l. The letter code ll in the name means low lead content in the fuel. Howless lead in aviation gasoline, the better its environmental performance. Cleaner gasoline will not only protect nature from destruction, but also reduce the toxic effect of fuel on workers who are constantly forced to contact with it. It should be noted that the legislation of the Russian Federation does not regulate the addition of additives against corrosion, crystallization and statics to aviation fuel.

Fuel grade

The grade of the mixture affects its resistance to explosion during the operation of the internal combustion engine at the maximum possible power. For example, in the grade of fuel under No. 115, an increase in power during the operation of the internal combustion engine is 15 percent more than on isooctane. The grade of aviation gasoline Avgas 100 ll, according to the documentation, must be at least 130 units. Aviation gasoline 91,115 has at least 115 units, based on GOST 1012 for aviation gasoline. Fuel Avgas 100 ll gives an increase in power, but only if the internal combustion engine runs on an enriched mixture. The power in this case is increased by 15 percent compared to grade B fuel 91 115.

Aviation gasoline production

The production of aviation gasoline is a complex process that consists of the following technological operations:

• Production of various components (stable catalyst, toluene, etc.).
• Filtration process of additives and other components.
• Mixing additives and components.

In our country aviation gasoline is not produced. The reason lies in the ban on the production of ethyl in the Russian Federation. Even if the missing component is purchased abroad, the production of combustible material is economically unprofitable due to the small volumes of its consumption. Finished fuel for aircraft is purchased abroad. The current situation puts the aviation industry in Russia at a disadvantage, because the production of domestic aircraft depends on the purchase prices for fuel from abroad, as well as the volume of purchases.

Why is tetraethyl lead needed in aviation gasoline?

A substance called tetraethyl lead (TEP) is added to aviation gasoline without fail. This is beneficial from the point of view of economy, since, if it is present in the composition, the fuel has a greater detonation resistance during combustion in the engine. In addition, TES prevents wear of the moving parts of the aircraft engine. It should be added that TES in its pure form is not used, it is converted into ethyl liquid. The content of tetraethyl lead in such a liquid reaches 50 percent.

Gasoline requirements for aviation

Compared to automotive fuel, GOST requirements for aviation gasoline are much tougher. Its production is regulated by the number of technological processes. Combustible liquid for aircraft is being developed, taking into account all the design features of fuel systems and engines in aircraft.

Special requirements for aviation gasolines used in aviation:

• Increased evaporation. This parameter makes it easier to start the engine, improves the quality of the mixture.
• Explosion resistance under high loads.
• Slightly hygroscopic (moisture absorption).
• Resistant to low temperature.

Gasoline B-70

B-70 aviation gasoline is a flammable fuel with a pungent odor. If it gets on the skin, eyes or internal organs, it can lead to irreversible processes, since this substance is very toxic. All necessary work with such fuel is carried out with working ventilation, and rubber gloves are used to protect people.

Technical characteristics of aviation gasoline B-70:

• colorless and transparent substance;
• density at room temperature is no more than 0.7g/cm3;
• beginning of distillation - no higher than 80 degrees Celsius;
• the distillation process is carried out at a temperature not exceeding 100 degrees Celsius;
• aromatic carbohydrates in the composition take no more than 1.5 percent;
• share of sulfur - no more than 1.5%.