Английский язык: Сборник текстов и упражнений для студентов специальности "Эксплуатация судовых энергетических установок". Писарева Л.П. - 29 стр.

      VIII. Answer the questions to the text.
      1. What is a purpose of supercharging?
      2. What is a turbocharger?
      3. What’s the difference between normally aspirated engine and turbocharged engine?
      4. What does the rotation of the rotor depend on?
      5. What permits the combustion of a larger quantity of fuel?
      6. What is the result of this combustion?
      7. What is the disadvantage of the pulse turbocharging?




                                             Lesson 10
                                        Air Starting System

                                                Part I

       Although all small engines and some fairly large ones used in connection with electric drive
are started by electric motors? In connection with electric drive are started by electric motors, the
method almost used for starting engines of more than 200 h. p. is by admitting air at 250 to 400 lb.
pressure to the cylinders through timed valves. Air for this purpose is provided at any convenient
point in the engine room and connected to the starting valves in the cylinder heads.
       This compressor is of two-stage construction because of the lower pressure to be han-
dled. In some cases the compressor is built into the engine but driven by gears, chairs, or V-
belts, and in most installations, especially of large engines, it is independently operated, usually
by an electric motor but in some cases by a separate auxiliary engine. Since the maintenance of
an adequate supply starting air is vitally essential, the air compressors must be installed in dup-
licate. If an attached compressor is used, a small independent unit must be provided; if no at-
tached compressor is used, two and sometimes three units are installed.
       In order to eliminate the possibility of the compressor’s not being started in time during
extended periods maneuvering, automatic controls should be installed that will start and stop
the compressors in accordance with pressure changes in the air tanks.


                                                Part II

       Although every air starting system uses timed valves in the cylinder heads for admitting air
into the cylinders at the right point in the cycle, there are several different methods in use for oper-
ating these valves. In every case the air main leading from the tanks is connected to each starting
valve, but air is turned into these lines only during the times when the valves are in operation.
       In one arrangement the valves are operated by cams and levers, the levers being mounted on
eccentric fulcrum bearings. Normally the rollers are held up clear of the cams but, when the eccen-
tric bearings are rotated by the control gear, which at the same time operates to open the valve that
admits air to the lines leading to the cylinders, the rollers drop onto the cams and the valves open
and close in accordance with their timing under the influence of the cams and valve levers.
       In another arrangement the starting valves in the heads are simply spring-loaded valves
that open when air pressure in the valve body exceeds the spring pressure. Air is admitted to
the valves at the right times by cam – operated control valves in a control unit at the operating
station. In other designs the starting valve is operated by a piston in a cylinder incorporated in
the valve body. Air is admitted to this cylinder through a small pipe line leading to a timed pi-
lot valve in the control unit at the operating station. In every case the maneuvering gear is ar-
ranged so that air from the tanks is automatically turned on when starting controls are moved to
the start position, and cut off when they are moved to the run or stop position.
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