Jet Fuels

Requirements 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.

8. I'm closing the door.

Exercise 18. Compare the sentences.

Present Indefinite Tense Present Continuous Tense

He reads newspaper every day. She is reading a newspaper now.

I speak Spanish well. I am speaking English now.

We use tape recorders We are working now.

regularly at our lessons. You are using the recording machines now.

Exercise 19. Use the Present Indefinite or the Present Conti­nuous Tense.

1. The students (to go) to the Institute every day.

2. The students (to listen) to the explanation of this rule now.

3. She always (to study) well.

4. This man (to speak) English with his friend now.

5. Jane (to know) English grammar well.

6. I (to like) English classes.

7. The dictionary (to contain) mаnу words.

8. The teacher (to explain) English grammar to the students.

9. I (to hear) nice music.

10. They (to wait) for their airliners now.

Exercise 20. Translate the sentences.

1. Зараз ми вивчаємо тему “Авіаційні палива".

2. Літак підіймається у повітря.

3. Він перекладає статтю.

4. Вона пише на дошці хімічну формулу нафтенів.

5. Вона малює на дошці схему пяти груп вуглеводневих сполук.

6. Що ви робите? Я слухаю повідомлення про фізико-хімічні властивості авіаційних палив.

Exercise 21. Translate the following questions. Give short and full answers to them.

1. What is she doing?

2. Who is talking to your teacher now?

3. What are you reading?

4. Why are you taking the book off the table?

5. Who is opening the exercise-book?

6. Who is making a report on "Aviation Fuels"?

7. What text are you reading now?

8. What are you telling your friends about?