Downloaded from https://www.everyspec.com FM 1-506 that are normally formed are insoluble in gasoline and JP fuels and may cause restrictions in fuel strainers and liners. Aviation fuel must also retain its original proper- ties during storage. Grades Turbine fuels are high-quality fuels covering the general heavy gasoline and kerosene boding range. They do not contain dyes or tetraethyl lead. Purity. Aviation fuel must be free from water, dirt, and sulfur. Small amounts of water will not usually cause any difficulty because water can be removed from the fuel system by draining. Large amounts of this impurity, how- ever, can cause complete engine failure.
It is very impor- tant that corrosive sulfur be eliminated from fuel. The sulfur content of fuel may form corrosive acids when brought in contact with the water vapor formed in the combustion process. One of the major differences between the wide- boiling and kerosene types is the fuel volatility. JP-4 fuels have a wider boding range with an initial boiling point considerably below that of kerosene. As a group these fuels have lower specific gravities than kerosene types. Wide-boil-range fuels have Reid vapor pres- sures of 2 to 3 pounds and flash points below room temperature.
Kerosene-type fuels have Reid vapor pres- sures of less than 0.5 pound and flash points higher than l00 o F (38 o C). Wide-boiig-range fuels generally have lower freezing points than kerosene fuels. Flush Point. The flash point is the lowest tempera- ture at which fuel will vaporize enough to forma combus- tible mixture of fuel vapor and air above the fuel. It is found by heating a quantity of fuel in a special container while passing aflame above the liquid to ignite the vapor. A distinct hash of flame occurs when the flash point temperature has been reached. The fuel authorized for Army aircraft gas turbine engines is JP-4.
The letters “JP" stand for jet propulsion; the number 4 indicates fuel grade. Military specification MIL-T-5624 covers JP-4, JP-5, and JP-8 fuels. Jet A, Jet Al, and Jet B are commercial fuels which conform to the American Society for Tinting Materials specification ASTM-D-1655. Fire Point. The fire point is the temperature which must be reached before enough vapors will rise to produce a continuous flame above the liquid fuel. It is obtained in much the same manner as the flash point. Reid Vapor Pnessure. Reid vapor pressure is the approximate vapor pressure exerted by a fuel when heated to 100% This is important because it is used to determine when a fuel will create a vapor lock.
Jet B is a JP-4 type fuel; its freezing point is -56°F (-49 o C) instead of -72 o F (-58 o C) for JP-4. JP-5, Jet 4 and Jet A-1 are kerosene-type fuels. ASTM Jet A and A-1 differ primarily in their fuel freezing points. Jet A is considered suitable down to fuel temperatures of -36 o F (-38 o C); Jet A-1, to -54 o F (48 o C). Specific Gravity. Specific gravity is the ratio of the density (weight) of a substance (fuel) compared to that of an equal amount of water at 60 o F. Specific gravity is expressed in terms of degrees API. Pure water has a specific gravity of 10. Liquids heavier than water have a number less than 10. Liquids lighter than water have a number greater than 10.
An example is JP-4, whose specific gravity in degrees API is 57. The American Petroleum Institute (API) has chosen pure water by which to measure the specific gravity of fuels. JP-4 is a fuel consisting of approximately 65 percent gasoline and 35 percent light petroleum distillate, with rigidly specified properties. JP-4 is currently the Army standard fuel for turbine engines. JP-5 is a specially refined kerosene having a mini- mum flash point of 140 o F and a freezing point of -51 o F (-46°C). JP-8 is a specially refined kerosene with a minimum flash point of 110 o F and a freezing point of -54°F (-48°C). This fuel is being classified as a total replacement fuel for all of NATO.
It will replace all fuels currently used in military equipment from generators to tanks to aircraft and even to trucks. This classification will ease logistics in combat. Having only one fuel for all equipment prevents accidentally mixing or using the wrong fuels. To date testing of JP-8 is proceeding well with the total single-fuel concept on its way to full fielding. NOTE: Both flash and fire points give a relative measure of the safety properties of fuel a high flash point denotes that a high temperature must be reached before dangerous handling conditions are en- countered. The minimum flash point per- mitted in a fuel is usually written into the specifications.
JP fuels vary from water white to light yellow; color coding, however, does not apply to these fuels. 1-3