There are engines of various designs. They differ in the number of cylinders, their position, their operating cycle, valve mechanism, ignition and cooling system.
Most automobile engines have six or eight cylinders, although some four-, twelve-, and sixteen-cylinder engines, are used. The activities that take place in the engine cylinder can be divided into four stages which are called strokes. The four strokes are: intake, compression, power and exhaust. «Stroke» refers to the piston movement. The upper limit of piston movement is called top dead centre, TDC. The lower limit of piston movement is called bottom dead centre, BDC.A stroke constitutes piston movement from TDC to BDC or from BDC to TDC. In other words, the piston completes a stroke each time it changes the direction of motion.
Engine Operation
An automobile, powered by a petrol engine, begins to operate when the driver turns a flywheel connected to the engine crankshaft. As the crankshaft revolves, a mixture of fuel and air is drawn from a carburetor into the engine cylinders. The ignition system provides the electric sparks that ignite this mixture. The resultant explosions of the mixture turn the crankshaft, and the engine starts moving. By regulating the flow of the fuel and air with a throttle, the driver controls the rotational speed of the crankshaft.
Cooling, electrical ignition and lubrication systems are of great importance for the good performance of a car. The lights, radio and heater add to the flexibility, comfort and convenience of the car. The indicating devices keep the driver informed as to engine temperature, oil pressure, amount of fuel, and battery charging rate.
Brakes are of drum and disk types. The steering system consists of a manually operated steering wheel which is connected by a steering column to the steering gear from which linkages run to the front wheels. It is difficult to turn the steering wheel, and special hydraulic power mechanisms are used to lessen this effort. Suitable springings are used against shocks. These are leaf springs, coil springs, torsion bars and air suspensions.
Disel Engines
The oil engine (diesel engine)is also a form of internal combustion engine. It has the usual arrangement of cylinder, piston, connecting rod, crank, inlet and exhaust valves as we find in petrol engine. In place of carburetor and sparking plug it has an injection pump and a fuel injection valve (injector).Unlike spark-ignition engines it uses the heat of compression to fire the fuel and is, therefore, called compression-ignition engine.
It utilizes a fuel known as diesel oil, which is forced in the form of a fine spray through a suitable nozzle directly into the combustion space. No mixture of fuel and air is introduced into the cylinder, the compression-ignition (CI)engine draws in pure air only. This air is then compressed by the ascending piston to a high pressure. As a result of it the temperature of the air is raised considerably so that the fuel oil injected into the cylinder ignites rapidly. Thereafter the gaseous products expand providing the energy for the power stroke.
The high-output oil engines are nearly all of two-stroke type. The charge is filled into the cylinder by means of a blower which assists both the intake and exhaust processes. One cycle completed within one revolution, i.e. in two strokes-compression and expansion.
Air-cooled Engines
All vehicle engines are air-cooled to some degree. Even in water-cooled engines heat is transmitted first from cylinder to water and afterwards, in the radiator, from water to air. This method of cooling is not difficult to accomplish, because the heat taken off the hot cylinder walls by water can be distributed without difficulty upon the large cooling surface of the radiator, and so easy transmission of air is made possible.
Reciprocating engines used in aircraft are almost entirely air-cooled. Aircaft engines cooled by air are manufactured today in sizes ranging from 50 to 3500 hp and they superseded water-cooled engines. The principal advantages of air-cooled aircraft engines are low weight, and greater reliadilim reliability in operation. Modern motor-cycles are also designed almost exclusively with air-cooled engines.
New designs of air-cooled vehicle engines are notable for their easy maintenance, reliability and economical operation.
Power Engineering
Volta made his experimental cell in 1800,producing for the first time a steady reliable electric current. During the nineteenth century, the development of practical applications of electrical energy advanced rapidly. The first major uses of electricity were in the field of communications-first for the telegraph and the telephone. They used not only electric current but also electromagnetic effects.
Thomas Edison’s invention of the electric light bulb was perhaps the most momentous development of all, but not because it was such a unique invention. It was momentous because it led to the creation of an electric power system which has since reached into nearly every corner of the world. Actually, other people were working simultaneously on the same problem, and Edison’s claim to the invention was disputed. Perhaps Edison’s most important claim to fame is his pioneering work in engineering, which helped to provide for New York City in 1882.
The application of electricity has grown to the point where most of us lead electrified life, surrounded by a variety of devices that use electric energy. Less visible, but probably more important, are the thousands of ways industry has put electric energy to work. The direct-current machine is one of the most important ways.
Turbines
The turbine is a machine for generating mechanical power from the energy of the stream of fluid. Steam, hot air or gaseous products of combustion, and water are the most widely used working fluids.
A steam turbine may be defined as a form of heat engine in which the energy of the steam is transformed into kinectic energy. It consists of the following fundamental parts: a) a casing or shell containing stationary blades: c) a set of bearings; d) a governor and valve system for regulating the speed and power of the turbine. The main types of steam turbines are axialflow turbines and radial-stage turbines.
The reciprocating steam engine came into its own during the nineteenth century, when it found greatest use in mills, locomotives and pumping systems. The modern steam turbine, developed last century, is rapidly replacing the reciprocating engine for large installations. Gas is used as the working fluid in gas turbines. The basic theory underlying their design and their operating characteristics is identical with that for steam turbines. The energy of water is converted into mechanical energy of a rotating shaft in hydraulic turbines. Power may be developed from water by three fundamental processes: by action of its weight, of its pressure or of its velocity; or by a combination of any or all three.
Boilers
A boiler is a closed vessel in which water, under pressure, is transformed into steam by the application of heat. Open vessels and those generating steam at atmospheric pressure are not considered to be boilers. The furnace converts the chemical energy of the fuel into heat. The function of the boiler is to transfer this heat to the water in the efficient manner.
Progress in steam-boiler development has been rapid. The first boilers were very crude affairs, as contrasted with our present-day standards. The greatest number of contributions have been made in the last half century. The field of application is diversified. Boilers are used for heating, supplying steam for processes, furnishing steam to operate engines, etc.
Maintaining the correct boiler water level is the most important duty of the boiler operator. It is of the utmost importance that the manufacturer supply suitable and reliable devices for indicating the water level. Coal as well as liquid and gaseous fuels are used for boiler firing. The ideal boiler must be of correct design, sufficient steam and water space, and good water circulation.
Electric motors
There is a wide variety of d.c. motors. There are shunt motors, series motors, synchronous motors, induction motors, single-,two-,and three-phase motors. They are used to drive various machines.
Direct-current motors are of three principal kinds, and are named according to the manner in which their field coils are connected to the armature. They are named respectively: series, shunt, and compound.
In the series motors the field windings and armature are connected in series with each other. All the current which passes through the armature passes through the field coils. The field windings are therefore composed of a few turns of thick wire. Starting under heavy load, a series motor will take a large current to provide the huge torque required.
The field coils of shunt motors are connected direct across the brushes, hence they have the full voltage of the mains applied to them. The shunt motor may by called a constant speed motor, and is suitable for driving machine tools, lathes, wood-working machines and any machines requiring a steady speed.
A compound motor has both shunt and series field windings and therefore partakes of the nature of both types of motors.
A. C. Electric Motor
Motors for alternating-current circuits may by either single-phase or polyphase (two-or three-phase).They may again be divided into two kinds, named respectively:1.Synchronous;2.Non-or asynchronous, ordinarily called induction motors.
The most widely used a.c. motor is the induction motor. It has two main parts: a)the stationary winding or stator, which sets up a rotating magnetic field, and b)the rotating part of the motor, i.e. the rotor. The rotor of a commercial a.c. motor consists of an iron core with large copper bars placed in sets around the circumference and connected at both ends to copper rings. This is called a squirrel-cage rotor. When a rotor is placed in a rotating magnetic field, a large current is induced in it.
A.c. motors are exactly similar in construction to a.c. generators and may be called inverted alternators, since the same machine may be used as either a generator or motor.
Synchronous motors are very suitable for large powers, where the machine can be started up without load, and once started run for long periods.
For supplying direct-current power networks, the supply comes first from an alternating-current source and is converted to direct current by synchronous convertors or motor-generator sets.
New Energy from Old Sources
The resources of fossil fuel which made the industrial revolution possible and have added to the comfort and convenience of modern life were formed over a period of 600-million years. We will consume them in a few hundred years at current rates.
But energy is available to use in practically unlimited quantities from other sources. Large amounts of energy can be received from ocean tides and currents, from huge underground steam deposits, from the power of wind and from the heat of the Sun.
Most solar-heating systems coming on the market use a black surface to absorb the Sun’s heat. Engineers cover the surface with glass which lets in the rays, but holds heat. The heat is transferred to water that runs through small pipes. The hot water is then circulated through the house. It is estimated that 40 million new buildings will be heated by solar energy by the year 2000.
The solar cell is another way to produce power from the Sun. It converts sunlight directly into electricity. These cells are used with great success in the space program, but remain far too expensive for wide-spread application.
Putting the wind to work researchers are showing great interest in the age-old windmill. Several big companies are now studying windmills ranging from 100 to 2,000 kilowatts. The smallest would provide sufficient electricity to power several homes, the largest could provide electricity to a small village.
Japan Stores Sunlight in Crystals
Japan has managed to store the Sun’s energy for 61 days in an important development in the use of solar power. Scientists have produced a stable chemical compound to store the energy.
The new compound takes the form of a yellow crystal. It changes its molecular structure when exposed to sunshine. When a small catalyst of silver was applied to it the substance reverted to its original molecular structure, generating heat at any required moment.
If produced in liquid form, the compound would retain the energy for 61 days without a boost of sunshine.
The temperature of the compound does not rise when solar energy is stored. The energy takes the form of molecular change at normal temperatures. In this way energy is not lost through the dissipation of heat.
Initial tests showed that 2.2 lb of the substance would conserve 92,000 calories. The research team said a solar heater with a surface of a square metre could store 85 million calories of energy a year. The compound could also be transported while it stored energy.
If the compound was produced in solid form, it could store energy for indefinite periods if the silver catalyst was not applied. However, it would have to be produced in a more impure liquid for practical use.
The new compound could be used to store energy for heating, cooling and eventually the generation of electrical power. There was little wastage and no pollution.
Forms and Functions of Architecture
Architecture is the art and the science of building. Without consideration of structural principles, materials, and social and economic requirements a building cannot take form, but unless aesthetic quality also is inherent in its form the building cannot be considered as a work of architecture.
From the very beginnings of architecture many skills, systems, and theories have been evolved for the construction of the buildings that have housed nations and generations of men in all their essential activities, and writing on architecture is almost as old as writing itself. The oldest book we have that sets forth the principles upon which buildings should be designed and aims to guide the architect is the work of Marcus Virtruvius Pollio, [ ‘ma:k s vit’ruvi s p ‘liou] written in the first century B.C.
Architecture is an art, its contemporary expression must be creative and consequently new. The heritage of the past cannot be ignored, but it must be expressed in contemporary terminology.
From the History of Sewerage
The first engineer who made a comprehensive study of metropolitan sewerage needs thus described the conditions of London basements and cellars in 1847: «There are hundreds, I may say thousands of houses in this metropolis which have no drainage whatever and the greater part of them have stinking overflowing cesspools. And there are also hundreds of streets, courts and alleys that have no sewers». After two outbreaks of cholera a royal commission was appointed to inquire into sanitary improvements of London. In 1855 Parliament passed an act for the better local management of the metropolis which laid the basis for the sanitation of London.
In the continent a marked progress in sewerage began in 1842 when a severe fire destroyed the old part of the city of Hamburg. The portion ruined was the oldest and it was decided to rebuild it according to the modern ideas of convenience. As a result Hamburg was the first city which had a complete systematic sewerage system throughout built according to modern ideas.
Forestry
The main directions in the economic development of Russia in forestry are: to improve the reproduction and utilization of forest resources, to use forest lands more intensively, to pay more attention to planting belts, to increase control over the rational use of forest resources and protect forests against fires, pests and diseases.
Graduates from the department for forest engineering work as production engineers in the sphere of logging mechanization, wood felling operations and transportation of timber by land and water.
In order to be an educated and qualified engineer it is necessary to study about 40 subjects of general education and engineering.
Russian engineering supplies the timber industry with various machinery: gasoline-motor-powered saws, branch cutters, loaders of original design, heavy-duty motor trains, semiautomatic lines with automated sorting transport belts.
The Sibirian Cedar
The Sibirian cedar grows to the east of the Urals. It has soft wood with beautiful texture. The world does not know better material for pencils.
One hectare of cedar forest annually produces up to five tonnes of nuts which are four times as expensive as cedar wood.
Cedar oil is as good as the best varieties of olive oil. The Sibirian cedar occupies 50 million hectares - a territory twice as large as Britain.
Larch
In the world there are 10-12 species of larch (according to some other sources there are 20 species).
The European larch grows usually upon dry uplands. It ranges from the mountains of Southern Siberia.
The average height of the tree is from 30 to 35 m. The wood of the larch is hard and rich in resin. Its bark contains tannin.
Larch is a very valuable tree. According to some source, the larch piles on which part of old Venice rests to this day, were brought from Russian forests.