The ratio of the mass of matter to its volume or massits unit volume is called the density. It is different for all substances and depends on their nature and composition. For example, for fresh water, it is about 1.003 g / cm3, and for the sea - 1.025 g / cm3. Also this physical quantity obeys the additivity rule. That is, the density of the multicomponent mixture (which is, for example, gasoline) will be equal to the sum of the products of this characteristic of each component by its mass fraction: ρ mixture = Σρi • ci. The calculation method can be used with a known composition, as well as in those cases where it is not required to determine the density of gasoline with high accuracy. Another drawback of the calculation method is the complexity and high cost of determining the mass fraction of each component. It requires expensive chromatographic equipment and highly qualified personnel, since each brand of petroleum products is characterized by a wide variability of sets from a large number of individual, mainly, organic substances (hydrocarbons).
Qualitative and quantitative composition,causing the density of gasoline, varies and depends on the initial raw material and the technological method of its processing. Various grades are obtained by direct distillation of oil, reforming, isomerization, alkylation, catalytic cracking. Gasoline mainly consists of a mixture of paraffins, naphthenes and olefins. At present, many countries have imposed restrictions on the content of aromatic hydrocarbons and olefins. This situation is caused by environmental requirements and the need to reduce carbon formation, which is due to the presence of benzene and ethylene compounds in the fuel, they often contain gasoline. The density of products, the octane number of which is increased by aromatics, is generally higher than that of a fuel with a lower content of benzene and its homologues.
In addition, the finished product may containspecial additives. They also affect the density of gasoline. For example, oxygen-containing compounds such as ethanol make it possible to increase the completeness of fuel combustion and to reduce the concentration of carbon monoxide in the exhaust gases. The regulatory document and the technological regulations of the enterprise determine those components that can be added to the fuel. Currently, several documents are in force in our country that normalize the quality of motor fuels for vehicles with gasoline engines.
Interstate Standard GOST 2184-77reissued in February 2003 with changes 1-6 of 1981, 1983, 1984, 1990, 1997 and 2002, as well as with two amendments from 2000 and 2001. It was recognized by 10 states - former Soviet republics. In the Russian Federation, its requirements apply only to the unleaded A-76 product. The density of gasoline at 20 oC according to this GOST is not regulated, but its definition is mandatory before shipment to the consumer. For this, the areometric and pycnometric test methods are used, which are described in GOST 3900-85.
State standard of our country GOST R51105-97 (published in 1999 and 2000 changes No. 1 and No. 2) is applied from 01.01.1999 and applies to unleaded automotive gasolines that, depending on the value of the octane number, are divided into the following brands: Super 98, Premium 95, Regular 92, Regular 91, Normal 80. The density of gasoline 92 and other products with octane number from 91 to 98 is normalized at 15 ° C and lies in the range from 725 to 780 kg / m3. For the product of Normal 80, it can vary from 700 to 750 kg / m3. Determine this characteristic using a hydrometer according to the test method in accordance with GOST R 51069-97.
Another state standard is GOST R51886-2002 - entered into force in the Russian Federation from 01.07.2002, and from 01.07.2008 it was amended No. 1. The document corresponds to the European norm EN 228-2004, it applies to unleaded gasoline of the brands Super Euro-98 and Premium Euro- 95. They are characterized by an octane number of 98 and 95, respectively. The density of gasoline of both grades at 15 ° C lies in the range 720-750 kg / m3 and is determined by GOST R 51069-97 by the hydrometric method.
Why is the need to determine the densitymotor fuel? First, this value indirectly characterizes the composition of the product and helps to identify it. For example, if the measured density is 0.980 kg / m3 or 0.650 kg / m3, then it is safe to say that this is not gasoline, but some other product. Also, the density of gasoline is widely used in practice: knowing the volume of the product in a large tank that can not be weighed, calculate its mass by multiplying the density by the volume. This method is called indirect, the requirements for it are GOST R 8.595-2004. Measure the temperature and product level in the tank and calculate its volume. Samples are selected in accordance with the requirements of GOST 2517-85, combine them and determine the density according to GOST 51069-97 or GOST 3900-85. The results of the measurements lead to standard conditions (temperature 15 or 20 оС), only after that these quantities are used to calculate the mass of the product in the tank.
