8.
Significance of Tests.
We will limit our discussion of specific tests to the ones you will most likely use on a routine basis. Additionally,
we will group these tests by the characteristic which they measure.
a. Volatility tests. Flash and fire points tests are performed on light distillate fuels such as diesel and
JP8, lubricating oils, hydraulic fluids, gear oils, and brake fluids. Aviation and motor gasolines, JP4 and other
naphtha-based fuels do not have flash or fire points tests performed on them. Naptha-based fuels have a
flash point below -50C. The flash point of a product is the temperature at which the product first gives off
sufficient flammable vapor to ignite with application of an outside heat source. The fire point is the temperature
at which the product vapors will continue to burn without the application of an outside heat source. The fire point
of any product ranges about 10 to 70ƒC higher than its flash point. These tests are performed to ensure that
products have not been contaminated with low flash point products and to ensure new products have been refined
properly. These tests ensure that the products flash and fire points are above the expected operating temperatures.
The flash point requirement is usually about 50ƒC above the expected operating temperature.
Off-specification products are disposed of or blended with suitable quantities of an on-specification product. Use
of off-specification products could cause engine or seal blow out, or start a fire. There are three principal methods
of determining flash and fire point:
(1) The Cleveland Open Cup -- determines the flash and fire points of oils.
(2) The Pensky-Martens Closed Cup -- determines flash points of distillate fuel oils such as diesel
and burner oils.
(3) Tag Closed Cup Method - determines flash points of jet turbine fuels such as JP8.
b. Distillation. This test is performed on light distillates such as jet turbine fuel, diesel fuel, gasolines,
and kerosene. This test evaluates vaporization characteristics of the fuel which aids in the prediction of
performance characteristics. Gasoline must be sufficiently volatile to permit easy starting but not so excessively
volatile that excessive evaporation loss occurs or that premature vaporization in carburetors or fuel lines takes
place. Incompatibility between fuel and engines due to vaporization characteristics could lead to equipment loss
or damage.
c. Vapor Pressure. All liquids tend to vaporize as a result of positive pressure exerted by the liquid. By
placing a liquid in a suitable container under controlled conditions, an accurate measure of this vapor pressure can
be determined. Vapor pressure is an important factor in all gasolines from a safety and performance point of
view. In internal combustion engines, the fuel must vaporize into the cylinder through the carburetor into the
manifold. If the vapor pressure is too high, the fuel will vaporize in the fuel pump and feed lines causing vapor
lock. If the vapor pressure is too low, the fuel will not vaporize readily enough, resulting in unevenness of
10-7
QM5200
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