Jet FuelsRequirements for jet fuels are much less exacting than those for the spark-ignition engine. At the present time, the requirements for a jet fuel are still in a state of flux, because desirable fuel properties change with new developments in the gas turbines themselves. Kerosene, gasoline, and the lighter gas oils have all been used as fuels for jets and gas turbines. Because of nature of the constant-pressure combustion in the gas turbine, a high-octane fuel is not required. Neither is a highly volatile fuel necessary. For use in aircraft, a high-heating-value fuel with a low specific gravity is ideal, since this permits the greatest heat release for the least weight of fuel. Storage stability and cleanliness are as desirable in jet fuels as in gasolines. In addition, the freezing point for any fuel which is to be used at high altitudes and cold temperatures should be ratter low.
Exercise 16. Translate the sentences in the Present Continuous Tense. Put all types of questions to them. 1. We are reading the text "Aviation Fuels". 2. The student is writing the general formula for the olefins. 3. They are learning the formation of the Present Continuous Tense. 4. The man is watching the TV program. 5. The visitors are watching the sights of Kyiv. 6. I am waiting for you. 7. She is writing a letter.
Exercise 17. Put questions to the underlined words. 1. The students are watching the TV program. 2. Your friend is smoking in the corridor. 3. He is talking to a friend of mine. 4. She is taking the book off the table. 5. They are looking at the blackboard. 6. She is opening the exercise-book. I'm closing the door.
Exercise 18. Compare the sentences.
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