Each of the gas components has a certain boiling point, so the pressure of the LPG vapor phase depends on both the temperature and its component composition.
The component composition of liquefied petroleum gas is regulated by GOST 20448-90 "LIQUEFIED PETROLEUM FUEL gases FOR municipal consumption".
The standard provides for 3 brands of gas:
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PT (technical propane),
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SPBT (a mixture of technical propane and butane),
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BT (technical butane).
The content of propane, butane and other impurities in LPG affects many of its properties, because it significantly affects the octane number and the density of fuel vapor.
The octane number (OCH) is an indicator of the fuel's resistance to detonation:
it increases due to an increase in the content of saturated hydrocarbons (propane, n-butane, isobutane, etc.),
unsaturated hydrocarbons polymerize, which contributes to the formation of sludge in the tank, in the fuel system and the combustion chamber.
The vapor elasticity (the volatility of the mixture) is very important at low ambient temperatures. Keeping it at the appropriate level allows the CIS to exit the tank. Both components of the mixture are gaseous and low-boiling.