Aviation gasoline is a flammable liquid that enters the aircraft engine, mixed with air, to receive thermal energy as a result of the oxygen oxidation of the incoming air into the combustion chamber. Piston engines run on such fuel.
The following indicators are valued in aviation gasoline :
- Knock resistance.
- Chemical stability.
- Fractional composition.
The measurement of the knock resistance parameter of aviation gasoline is necessary to decide on the suitability of using such fuel in units where a high compression ratio of the mixture coming from the gas tank occurs. For normal operation of the aircraft engine, it is important to avoid detonation ignition.
The fractional composition must be known to determine the volatility of gasoline. During the measurement, it is determined whether the air-fuel mixture forms.
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 the method of rectification and subsequent selection of oil fractions that evaporate with 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, the fuel has a 2 grade quality.
Different types of gasoline obtained through distillation have a single factor that unites them - low octane number. Using the straight-run method, a gasoline mixture with an OCh above 65 can only be obtained from oil produced in Azerbaijan, the Krasnodar Territory, Sakhalin and the territory of Central Asia. In other places of extraction of "black gold" the combustible mixture due to the presence of paraffin hydrocarbons is obtained with low RH.
Advantages of straight-run gasoline
The positive qualities of straight-run gasolines are:
- stability;
- anticorrosive properties;
- excellent evaporation;
- high thermal conductivity (about 10,500 b.cal / kg);
- resistance to low temperatures (up to 100 degrees Celsius);
- low hygroscopicity.
Since such a fuel has too high detonation resistance, it is used only with impurities, as a result of which the octane number rises.
What is an octane number?
The octane number characterizes the resistance to detonation of a combustible material, i.e., the ability of a liquid to self-ignite 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 should 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, the resistance to detonation is taken as zero. To determine the resistance to detonation of gasoline, in which the OF exceeds 100 units, created a special scale. It uses isooctane with the addition of tetraethyl lead in different quantities.
Varieties of OCh
Octane numbers are divided into two types: OCHM and OCH. OCHI (research octane number) demonstrates how gasoline reacts at low and medium engine loads. A unit simulating a single-cylinder engine is used to determine OCHI. The design is capable of compressing fluid with varying strength. The crankshaft rotation frequency is 600 rpm at a temperature of 50 degrees Celsius.
OBM (motor octane number) demonstrates the behavior of a combustible liquid during heavy loads. The determination method is similar to the previous one, however, the rotational speed of the crankshaft of an engine simulating engine is 900 rpm and the test temperature reaches 150 degrees Celsius.
Increase in RP thanks to additives
Modern engines used in aviation need fuel with a minimum octane rating of at least 95 units. Refined gasolines after direct distillation are obtained with a low octane rating; they are not suitable for use in modern aircraft engines. Improving antiknock properties can be achieved using additives. Previously, only ethyl fluid was used for these purposes. Nowadays, whole complexes have been developed for increasing OR, which contain oxygen-containing components, esters, stabilizers, dyes, anti-corrosion substances and much more.
The difference between gasoline B 91 115 and Avgas 100 ll
B 91 115 aviation gasoline is a mixture of fuel obtained by direct distillation using catalytic reforming. The composition of such fuels includes alkylbenzenes, toluene and various additives (ethyl, antioxidant, dye). Avgas 100 ll aviation gasoline consists of a mixture of these high-octane and base components. To obtain this type of fuel , ethyl, dye and additives are added to prevent the formation of corrosion and static electricity.
The differences between the two brands of flammable substances is in grade, additives used, components and different contents of tetraethyl lead. In the first grade of fuel, the amount of tetraethyl lead should not be more than 2.5 g / kg, in the second - 0.56 g / l. The letter cipher ll in the name means low lead content in the fuel. The less lead in aviation gas, the better its environmental performance. Cleaner gasoline will not only protect nature from destruction, but also reduce the toxic effects of fuel on workers who are constantly forced to contact with it. It is worth noting that the legislation of the Russian Federation does not regulate the addition of anti-corrosion, crystallization and static additives 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 fuel grade No. 115, an increase in power during ICE operation is allowed by 15 percent more than on isooctane. The grade of Avgas 100 ll aviation gasoline, according to the documentation, must be at least 130 units. Aviation gasoline has 91,115 - at least 115 units, based on GOST 1012 for aviation gasolines. Fuel Avgas 100 ll gives an increase in power, but only if the internal combustion engine runs on an enriched mixture. Power in this case increases by 15 percent, compared with fuel grade B 91 115.
Gasoline Production
The production of aviation gasoline is a complex process, which consists in the following technological operations:
- Production of various components (stable catalyst, toluene, etc.).
- The process of filtering additives and other components.
- Mixing additives and components.
In our country, 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 disadvantageous due to the small volumes of its consumption. Ready-made 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 in aviation gasoline needed?
A substance called tetraethyl lead (TPP) is added to aviation gasolines 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, TPP prevents the wear of moving parts of the aircraft engine. It must be added that TPP 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.
Aviation gasoline requirements
Compared to automobile fuel, GOST requirements for aviation gasoline are much stricter. Its manufacture is regulated by the number of technological processes. Flammable liquid for aircraft is developed, taking into account all the design features of fuel systems and engines in aircraft.
Special requirements for aviation gasolines used in aviation:
- Increased volatility. This parameter facilitates starting the engine, improves the quality of the mixture.
- Resistance to explosion at high loads.
- Low hygroscopicity (moisture absorption).
- Resistance to low temperatures.
B-70 gasoline
Aviation gasoline B-70 is a flammable fuel that has a pungent odor. Contact with skin, eyes or internal organs can lead to irreversible processes, as this substance is very toxic. All necessary work with such fuel is carried out with working ventilation, and rubber gloves are used to protect a person.
Technical characteristics of aviation gasoline B-70:
- colorless and transparent substance;
- density at room temperature is not more than 0.7 g / cm 3 ;
- start of distillation - not higher than 80 degrees Celsius;
- the distillation process is carried out at a temperature not exceeding 100 degrees Celsius;
- aromatic carbohydrates in the composition occupy no more than 1.5 percent;
- sulfur content - not more than 1.5%.