Text 1B OTHER TYPES OF POWER PLANTS

The internal-combustion-engine power plant. The fuel is burned directly in the cylinder of the engine or prime mover, and the high pressure thus generated drives the piston downward and rotates a crankshaft.

Air is supplied to the engine through a silencer and cleaner the function of which is to reduce noise and remove dust which would accelerate cylinder and piston wear if allowed to enter the cylinder.

A supercharger is installed in the air-intake system. The function of the supercharger is to increase the amount of air supplied to the cylinder by acting as an air pump. This in turn permits burning more fuel and obtaining more power from a given size of cylinder. An intake manifold is used to distribute the air equally from the supercharger to the various cylinders of multicylinder engine.

The exhaust system consists of an exhaust manifold for collecting the discharge gases from each of the cylinders into a common exhaust line, an exhaust silencer or muffler for reducing noise, and the exhaust stack for disposing of the exhaust gases to the atmosphere without creating a public

nuisance.

The cooling system includes a pump for circulating water through the cylinder jackets and heads of each cylinder and a heat exchanger to remove the energy absorbed in the engine by the cooling water. The heat exchanger may be air-cooled as in the automobile radiator, or it may be water-cooled. Seldom is raw water fit to circulate directly through the jackets of an internal-combustion engine.

The lubricating oil may be passed through a cooler, filter, and reservoir and is supplied to the engine under pressure by means of an oil pump, usually to a hollow crankshaft. The oil serves as a lubricant for the rubbing surfaces of the engine and also as a coolant.

The fuel system consists of a storage tank from which the fuel may be supplied to a small day tank or reservoir. The oil is filtered and pumped as needed to the fuel-injection sys­tem which is an integral part of the engine.

Since the fuel is burned directly in the cylinder of the prime mover, the internal-combustion-engine power plant is simpler and more compact than the steam power plant. It is seldom built in engine sizes of more than 4000 hp, whereas a 300,000-hp steam turbine is common. It is more efficient than a steam power plant of comparable size but not so efficient as large steam central-station plants, which moreover can burn a cheaper grade of fuel. Consequently, the internal-combustion engine is used primarily in the transportation field for driving automobiles, buses, trucks, tractors, locomotives, ships, and airplanes where a compact, light-weight, efficient power plant of relatively small size is necessary.

The gas−turbine power plant. Air is compressed in an axial flow compressor from atmos­pheric, pressure to a pressure which is usually between the limits of 75 and 120 psi. The compressed air may then flow through a regenerator or heat exchanger in which the hot exhaust gas from the turbine is utilized to increase the temperature of the air, thereby recovering energy that would otherwise be lost to the atmosphere. Fuel is sprayed into the combustor in which it combines chemically with the oxygen in the air to produce a hot gas leaving the combustor at some temperature between 1200° and 1700° F. The pressure of the air decreases slightly between the compressor discharge and turbine inlet because of friction, but the increase in temperature in the regenerator and combustor results in more than doubling the volume. The hot gas then expands in the turbine in which it does enough work to drive the compressor as well as an electric generator or some other suitable machine. The exhaust gases leaving the turbine are cooled in the re­generator before being discharged to the atmosphere.

Where space and weight limitations are critical or fuel is cheap, the regenerator may be omitted with a substantial decrease in efficiency. The turboprop engine as applied to the airplane operates without a regenerator and with a geared propeller as the load. In the turbojet engine as applied to the airplane, the turbine develops only enough to drive the compressor and exhausts into a nozzle at a back pressure considerably in excess of atmospheric pressure. The rearward expansion of the exhaust gases from the nozzle at high velocity creates the thrust which propels the airplane.

In the nuclear power plant energy is released in a reactor by nuclear fission. A coolant is pumped through the reactor to absorb and remove this energy and thereby prevent an excessive temperature in the reactor. In the more common types of nuclear power plants, the high-temperature coolant that leaves the reactor flows through a heat exchanger in which steam is generated.

Extensive provisions are made to protect the operating personnel and the general public from the hazards of radioactivity by the installation of radiation and containment shields which enclose all radioactive components of the system.

The heat exchanger serves as a steam boiler. The steam flows through a turbine and associated equipment that are identical in design and arrangement with similar equipment in a conventional steam power plant. In other words, the nuclear reactor, heat exchanger, and pump replace the fuel-burning equipment and the steam generator of the conventional steam power plant.

 









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