(1)
The volatility of the fuel; that is, its ability to vaporize easily, especially at low temperatures.
(2)
The degree of atomization, which depends upon the viscosity of the fuel, the fuel pressure applied, and the design of the atomizer.
110.
The calorific value (fig. 10-21) of a fuel is an expression of the heat or energy content per pound or gallon that is released during combustion. This value, which is usually expressed in British thermal units, influences the range of an aircraft. Where the limiting factor is the capacity of the aircraft tanks, the calorific value per unit volume should be as high as possible, thus enabling more energy, and hence more aircraft range, to be obtained from a given volume of fuel. When the useful payload is the limiting factor, the calorific value per unit of weight should be as high as possible, because more energy can then be obtained from a minimum weight of fuel.
Other factors which affect the choice of heat per unit of volume or weight, must also be taken into consid-eration; these include the type of aircraft, the duration of flight, and the required balance between fuel weight and payload.
Fig. 10-21 Relationship between calorific图10-21 热值和比重的关系
value and specific gravity.
111.
Turbine fuels tend to corrode the components of the fuel and combustion systems mainly as a result of the sulphur and water content of the fuel. Sulphur, when burnt in air, forms sulphur dioxide; when mixed with water this forms sulphurous acid and is very corrosive, particularly on copper and lead. Because it is impracticable to completely remove the sulphur content, it is essential that the sulphur be kept to a controlled minimum. Although free water is removed prior to use, dissolved water, i.e. water in solution, cannot be effectively removed, as the fuel would re-absorb moisture from the atmosphere when stored in a vented aircraft or storage tank (para. 118).
112.
All gas turbine fuels are potentially dangerous and therefore handling and storage precautions should be strictly observed.
Vapour locking and boiling
113.
The main physical difference between kerosine and wide-cut fuels is their degree of volatility, the latter type of fuel having a higher volatility, thus increasing the problem of vapour locking and boiling. With kerosine-type fuels, the volatility is controlled by distil-lation and flash point, but with the wide-cut fuels it is controlled by distillation and the Reid Vapour Pressure (R.V.P.) test. In this test, the absolute pressure of the fuel is recorded by special apparatus with the fuel temperature at 37.8 deg. C. (100 deg. F.).
114.
Kerosine has a low vapour pressure and will boil only at extremely high altitudes or high tempera-
燃油比重
112．所有燃气涡轮发动机的燃油都是潜在危险品，因此在处理和储存时要严格遵守注意事项。
Fuel system
117. For sustained supersonic flight, some measure of tank insulation is necessary to reduce kinetic heating effects, even when lower volatility fuels are used.
Fuel contamination control
118. Fuel can be maintained in good condition by well planned storage and by making routine aircraft tank drain checks. The use of suitable filters, fuel/water separators and selected additives will restrict the contamination level, e.g. free water and solid matter, to a practical minimum. Keeping the fuel free of undissolved water will prevent serious icing problems, reduce the microbiological growth and minimize corrosion. Reducing the solid matter will prevent undue wear in the fuel pumps, reduce corrosion and lessen the possibility of blockage occurring within the fuel system. 115．飞行中的燃油温度取决于高度、爬升率、在高空中飞行的持续时间，及由于飞行速度产生的动力加热。当发生沸腾时，蒸发损失将非常高，特别是对于宽馏分燃油，这就会造成蒸气堵塞，随之发生发动机燃油系统和燃油计量设备的失灵。
116．为了避免或减少沸腾的危险，通常要对燃油箱增压。这就涉及到在任何特定的温度下，均要使燃油的绝对压力高于其蒸发压力。通过采用惰性气体或采用可控制的通风系统来保持燃油的蒸发压力就可以做到这一点。
117．对于持续的超音速飞行，需要采用某种油箱绝热的措施，以减小动力加热的影响，即使对于采用低挥发性燃油也应如此。
燃油污染控制
118．通过良好有计划的储存及从事常规的飞机油箱放油检查，就可使使燃油保持良好状况。采用适当的油滤、油／水分离器和有选择的添加剂将能把污染的水平，例如游离水、固态物限制到实际可能的最低限度。保持燃油没有不溶解水可以防止严重的结冰问题，及降低微生物的滋长和减低腐蚀。减少固态物质将防止燃油泵不应有的磨损，减步腐蚀和在燃油系统中发生堵塞的可能性。
tures, whereas a wide-cut fuel wilt boil at a much lower altitude.
115.
The fuel temperature during flight depends upon altitude, rate of climb, duration at altitude and kinetic heating due to forward speed. When boiling does occur, the vapour loss can be very high, especially with wide-cut fuels, and this may cause vapour locking with consequent malfunctions of the engine fuel system and fuel metering equipment.
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