(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圖10-21 熱值和比重的關系
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．所有燃氣渦輪發動機的燃油都是潛在危險品，因此在處理和儲存時要嚴格遵守注意事項。
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．飛行中的燃油溫度取決于高度、爬升率、在高空中飛行的持續時間，及由于飛行速度產生的動力加熱。當發生沸騰時，蒸發損失將非常高，特別是對于寬餾分燃油，這就會造成蒸氣堵塞，隨之發生發動機燃油系統和燃油計量設備的失靈。
116．為了避免或減少沸騰的危險，通常要對燃油箱增壓。這就涉及到在任何特定的溫度下，均要使燃油的絕對壓力高于其蒸發壓力。通過采用惰性氣體或采用可控制的通風系統來保持燃油的蒸發壓力就可以做到這一點。
117．對于持續的超音速飛行，需要采用某種油箱絕熱的措施，以減小動力加熱的影響，即使對于采用低揮發性燃油也應如此。
燃油污染控制
118．通過良好有計劃的儲存及從事常規的飛機油箱放油檢查，就可使使燃油保持良好狀況。采用適當的油濾、油／水分離器和有選擇的添加劑將能把污染的水平，例如游離水、固態物限制到實際可能的最低限度。保持燃油沒有不溶解水可以防止嚴重的結冰問題，及降低微生物的滋長和減低腐蝕。減少固態物質將防止燃油泵不應有的磨損，減步腐蝕和在燃油系統中發生堵塞的可能性。
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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