Gasoline (A-80, 92, 95)
The present day motor and aviation gasoline should meet the different requirements ensuring economic and reliable engine operation, and operating requirements:
– to have good evaporating capacity which allows to get homogeneous air-fuel mixture of tailored composition at any temperatures;
– to have hydrocarbon-type content ensuring the stable non-detonating combustion process at all modes of engine operation;
– not to change its composition and properties on long storage and not to have unfavorable effect on fuel system components, reservoirs, rubber technical goods;
– to have good antiknock properties, etc.
Ecological properties of fuel are significantly highlighted in recent years.
Evaporating Capacity
Clean fuel burning process in engine requires to transfer it from liquid state to vaporized state in short term and mix it with air at a certain ratio 1:14, i.e. to create air-fuel mixture. Physico-chemical parameters that influence the evaporating capacity of gasoline, include saturated vapor pressure, fractional composition, latent heat of evaporation, vapor diffusion coefficient, viscosity, surface tension, thermal capacity, density. The most important of the above listed indicators determining the evaporating capacity of gasoline are saturated vapor pressure and fractional composition.
Saturated Vapor Pressure
Saturated vapor pressure depends on temperature and ratio of vapor and liquid states and decreases due to decrease of temperature and increase of the ratio of vapor and liquid states. Saturated vapor pressure is determined at 37.8°С and ratio of vapor and liquid states (3.8-4.2):1 in “Reid Vapour Pressure Bomb” (GOST 1756-52) or mechanical dispersion machine such as “Vihr” (GOST 28781-90) in a laboratory environment.
Fractional Composition
Fractional composition of gasoline shall be determined on the special device, recording initial boiling point, evaporating temperature of 10, 50, 90 % and end boiling point, or evaporating volume at 70, 100 and 180°С. Requirements for fractional composition and saturated vapor pressure of gasolines are determined by the structure of motor engine and environmental operating conditions.
Anti-Knock Value
This indicator characterizes the capacity of motor gasolines to prevent self ignition under compression. High anti-knock value of fuels ensures their normal combustion at all modes of engine operation. Fuel combustion process in engine is of radical character. Under compression of air-fuel mixture, the temperature and pressure are raised and oxidation of hydrocarbons which is intensified after mixture ignition, is occurred. Intensive accumulation of peroxide compounds occurs if hydrocarbons of unburned part of fuel has insufficient resistance to oxidation, after that explosive disintegration is occurred. Thermal explosion which leads to self-ignition of fuel is occurred in the high concentration of peroxide compounds.
Performance Characteristics
Motor gasoline should be neutral and non-corrosive for metals and reservoirs, and its combustion products should be non-corrosive for engine parts. Corrosiveness of gasoline and its combustion products depend on content of total and mercaptan sulphur, acid capacity, content of water-soluble acids and alkali, presence of water. These indicators are described in technical standard documentation for gasoline. Gasoline should stand the copper strip test. The efficient method of corrosion protection is addition of special anti-corrosive or multi-purpose additives to gasoline.