The flash poin of oil products is the temperature at which the vapor sample, when heated, flashes when the ingnition source is introduced, and mixes with air. Flash poin can be measured using open-cup and closed-cup method. The value obtained by the first method is always higher by several degrees.
Determination of the flash point is important for reliable information about an oil product properties and evaluation of its quality. This parameter is also used to divide production facilities and equipment into fire hazard classes.
Methods of definition
GOST provides two key methods for determining the flash point:
- in a closed crucible,
- in an opened crucible.
Crucibles are chemical vessels intended for heating, melting, burning and other operations with experimental materials, including various fuels.
The study in an open crucible is less accurate, because the sample pairs freely mix with air and need more time to accumulate the required volume. In the quality passport of the oil product, the close-cup flash point indicated, as the most reliable.
To measure it, the vessel is filled with fuel to the indicated level and heated with continuous stirring. When you open the lid of the vessel above the surface of the mixture, an open fire automatically appears. The measurement is carried out through each degree of heating, and during the opening of the lid the stirring stops. The flash point is taken to be the value at which, when the ignition source is introduced, a bluish flame arises.
There are also special apparatus for determining the flash point. This device includes the following elements:
- electric heater with a capacity of 600 W,
- a standard vessel with an internal diameter of 50.8 mm and a capacity of about 70 ml,
- brass agitator,
- igniter (electric or gas),
- thermometers with a graduation of 1⁰С.
Flash point of various oil products
According to the flash point, liquid oil products are classified into flammable liquids (FL) and combustible liquids (CL). The flash point of flammable liquids is above 61° C for a closed crucible and above 65 ° C for an open crucible. Liquids flashing at a temperature below these values are considered flammable. The flammable liqids is divided into 3 categories:
- Especially dangerous (closed flash point from -18⁰С and below).
- Permanently dangerous (closed flash point from -18⁰С and below).
- Dangerous with increasing air temperature (closed flash point from 23 ° C to 61 ° C).
The flash point of diesel fuel is an important indicator of its quality. It directly depends on the type of fuel. For example, the modern diesel fuel EURO flashes when it reaches 55 ° C or more.
The flash point of fuel for locomotives and marine engines is higher than for diesel fuel of general use. Summer fuel, warming up, flashes 10-15 ° C earlier than the winter and arctic fuels.
Light oil fractions have low closed flash point, and vice versa. For example:
- flash point of engine oil (heavy oil fractions) – 130-325 ° C
- flash point of kerosene (medium kerosene and gas oil fractions) – 28-60 ° C,
- flash point of gasoline (light gasoline fractions) – up to -40 ° C, that is, gasoline flashes at minus temperatures.
The flash point of oil is determined by the fractional composition, but basically its values are negative (as for gasolines) and range from -35 ° C to 0 ° C. And the flash point of gases, as a rule,
is generally not determined. Instead, the values of the upper and lower limits of flammability, which depend on the content of gas vapor in the air, are used.