There are two main types of diesels: two-stroke and four- stroke engines.
In two-stroke diesels compression occurs during the first stroke, combustion and expansion occur during the second stroke; exhaust, scavenging and recharging with air occur at the end of the second stroke and at the beginning of the first stroke. The working cycle of a four-stroke diesel requires four separate strokes of the engine piston to complete the operation. These four strokes are called suction, compression, combustion-expansion and exhaust, but only the third stroke provides the power to drive the ship while the other three require power from the remaining cylinders to perform their various duties. So, what happens during these four cycles? First stroke: suction Inlet valve is open, exhaust valve is closed. Air is drawn into the cylinder. Second stroke: compression Both valves are closed. Piston compresses the air to high temperature. Third stroke: combustion- expansion Fuel injected burns. Temperature and pressure of combustion gases increase. Gas pressure forces the piston down (valves are closed). As the volume available for the gases increases, their pressure and temperature decrease. Piston displacement is used to produce power. Fourth stroke: exhaust Exhaust valve is open; inlet valve is closed. Burnt gases are forced out of the engine. The Diesel Engine is made up of stationary and moving parts. Stationary parts These are principally: bedplate, cylinders, cylinder covers and cylinder liners. Moving parts. These include: piston, connecting-rod, crankshaft, flywheel and valves. Vocabulary
20 21
The turbine is a heat engine consisting of a rotor carrying moving blades, a casing in which the rotor revolves, and stationary nozzles through which the steam is expanded or directed. Glands, bearings, throttle valve, governor and other devices are necessary for operation of the unit. There are two kinds of turbines: steam turbines and gas turbines. The steam turbine consists of two principal elements: 1) nozzles, a device for converting some of the thermal energy of the steam into kinetic energy, and 2) moving blades, an arrangement for converting the kinetic energy of the steam into shaftwork. Steam turbines may be classified as impulse turbines and reaction turbines. In the impulse turbine the steam expands only through stationary nozzles, dropping in pressure and increasing in velocity. The steam then impinges against the moving blades causing rotation and mechanical work. In the reaction turbine the stationary nozzles have the same appearance as the moving blades. The steam drops in pressure and at the same time expands while passing through both the stationary nozzles and the moving blades. Turbines are classed also as: 1) high, 2) intermediate and 3) low pressure. There may be single-cylinder and compound turbines. Single-cylinder indicates that the unit consists of one turbine contained in one casing. A compound unit consists of two or more individual turbines. Compound turbines are further classified as: 1) tandem-compound, and 2) cross-compound. In the tandem- compound unit all the individual turbines are mounted upon a common shaft. In the cross- compound unit each turbine has a separate shaft. According to the direction of steam flow the turbines are axial-flow and radial-flow. They may be condensing and non-condensing as well. The condensing turbine exhaust their steam to a condenser which maintains back pressure, while the non-condensing unit usually exhaust its steam to another device where it is used for heating. Gas turbines work on exactly the same thermodynamic cycle as an ordinary Diesel engine: they draw in air from the atmosphere, compress it, heat the compressed air by the direct burning of fuel in it and then make the air perform work. The units which make up a complete gas turbine power plant are: the compressor, combustion chamber, intercooler, reheater and gas turbine itself. Vocabulary
22 23 28. casing 29.to revolve 30.stationary nozzles 31. to expand 32. gland 33. bearing 34. shaft 35. throttle valve 36. governor 37. pressure drop 38. to impinge 39. to cause 40. rotation 41. to constitute 42. drive 43. to increase 44. to decrease 45.diaphragm 46.successive stage
47. cast iron 48. cast integral 49. plate steel 50. cast steel 51. to weld 52. nozzle 53. orifice 54. corrosion-resisting alloy 55. alloy 56. cross-section 57. solid section 58. partition 59. convergent 60. divergent 61. steel forging 62. solid forging 63. built-up rotor 64. journal 65. groove 66. gland strip корпус вращаться направляющие сопла расширяться уплотнение подшипник вал дроссельный клапан регулятор перепад давления ударяться вызывать вращение составлять привод увеличивать уменьшать перегородка последовательная ступень чугун цельнолитой толстолистовая сталь литая сталь сваривать сопло отверстие коррозийно-стойкий сплав сплав поперечное сечение сплошная секция перегородка суживающийся расширяющийся стальная поковка цельнокованый составной ротор шейка вала паз уплотнительное кольцо 24
комплект лопаток газотурбинная силовая установка компрессор камера сгорания промежуточный охладитель нагреватель аксиально-проточный или турбокомпрессор
Suggest English equivalents for the following and memorize them: тепловой двигатель, движущиеся лопатки, ротор, корпус, неподвижные сопла, подшипник, дроссельный клапан, уплотнение, регулятор, механизм, установка, активная турбина, реактивная турбина, паровая турбина, газовая турбина, преобразование тепловой энергии пара в кинетическую энергию, преобразование кинетической энергии пара в работу вала, расширяться, падение давления, увеличение скорости, ударяться о лопатки, вращение, однокорпусная турбина, составная турбина, одновальная и двухвальная турбина, осевая турбина, радиальная турбина, конденсатор, сжатый воздух, газотурбинная силовая установка, компрессор, камера сгорания, промежуточный охладитель, нагреватель. 25 ЧАСТЬ 4. ТЕКСТЫ ДЛЯ ВНЕАУДИТОРНОГО ЧТЕНИЯ
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