Two-Stroke and Diesel Engines




Two-Stroke Engines

By suitable design it is possible to operate a diesel as a two-stroke or two-cycle engine with a power stroke every other stroke of the piston instead of once every four strokes. The efficiency of such engines is less than that of four-stroke engines, and therefore the power of a two-stroke engine is always less then half that of a four-stroke engine of comparable size.

The general principle of the two-stroke engine is to shorten the periods in which fuel is introduced to the combustion chamber and in which the spent gases are exhausted to a small fraction of the duration of a stroke instead of allowing each of these operations to occupy a full stroke.

In the simplest type of two-stroke engine, the valves are the openings in the cylinder wall that are uncovered by the piston at the end of its outward travel. In the two-stroke cycle the fuel mixture or air is introduced through the intake port when the piston is fully withdrawn from the cylinder. The compression stroke follows and the charge is ignited when the piston reaches the end of this stroke. The piston then moves outward on the power stroke, uncovering the exhaust port and permitting the gases to escape from the combustion chamber.

 

 

Text 25 DIESEL ENGINE

The diesel engine was invented in 1890's by Rudolf Diesel, a German, and is named after its inventor. This is the most widely used engine in military vehicles of today.

Diesels get better mileage than gasoline engines and the fuel is usually cheaper. Diesel fuel is less volatile than gasoline and therefore safer to handle. Die­sels generally become competitive with gasoline engines above 30 hp. They are nor­mally chosen because of their operating economy and greater durability.

The diesels require fuel injection, which contributes lo their higher cost In general, a diesel costs about 2 % times as much as a gasoline engine, but on die aver­age a diesel serves about 2 '/i times longer. Besides being more costly than gasoline engine, diesels also tend to produce more noise and vibration. They are also heavier and much larger thin gasoline engines of the same power potential.


Mileage - пробег в милях

cheap - дешевый

volatile - летучий

safe - безопасный

to handle - обращаться

competitive - конкурирующий

to choose (chose, chosen) - выбирать

durability - прочность

fuel injection – впрыск топлива

to contribute - способствовать

cost - стоимость


Two-Stroke and Diesel Engines

Most diesels are also four-stroke engines. The first or suction stroke draws air, but no fuel, into the combustion chamber through an intake valve. On the second or com­pression stroke the air is compressed to a small fraction of its former volume and is heated to approximately 440°C by this compression. At the end of the compression stroke vaporized fuel is injected into the combustion chamber and burns instantly because of the high temperature of the air in the chamber. Some diesels have auxiliary electri­cal ignition systems to ignite the fuel when the engine starts and until it warms up. This combustion drives the piston back on the third or power stroke of the cycle. The fourth stroke is an exhaust stroke.

The efficiency of the diesel engine is greater than that of any petrol engine and in actual engines today is slightly over 40 per cent. Diesels are in general slow-speed engines with crankshaft speeds of 100 to 750 revo­lutions per minute (rpm) as compared to 2,500 to 5,000 rpm for typical petrol engines. Some types of diesel, how­ever, have speeds up to 2,000 rpm. Because diesels use compression ratios of 14 or more, they are generally more heavily built than petrol engines, but this disadvantage is counterbalanced by their greater efficiency and the fact that they can be operated on less expensive fuel.

 

Text 26 ROTARY ENGINES

There are two types of rotary engines: the gas turbine and the Wankel.

A gas turbine engine consists of two sections: the gasifier section, where the fuel is burned; and the power section, where the power from the burned fuel is pro­duced. The turbine can use gasoline, kerosene, or oil for fuel. So, this would be a major advantage if petroleum shortage develops.

Gas turbines have been used in a few buses and trucks. High cost is a major disadvantage of this type of engines. The turbine cars now operating are hand-built models that cost more than 1 million dollars each. Alloys of precious metals are still required for some turbine parts. The progress in ceramics may help make turbines practical alternative lo present day engines. Yet, some engineers believe that we shall never see gas turbine as a mass-produced engine.

The Wankel engine is new in the automotive industry. The engine concept was proposed by Wankel in the 1950's. The Wankel engine is called a rotary-combustion engine because the combustion chambers rotate. The engine uses a three-lobe rotor that rotates eccentrically in an oval housing. The four actions - intake, compression, power and exhaust - are going on at the same time around the rotor when the engine is running. In a way, a single-rotor Wankel engine is equivalent to a three-cylinder piston engine.

In terms of functional characteristics - weight, power output efficiency and speed – the Wankel resembles a 2-cycle gasoline engine.

 

Text 27 STIRLING ENGINE

Unlike the internal combustion engine, the Stirling engine is an external com­bustion engine that produces heal external to the engine's moving parts. It can bum a variety of fuels, from diesel oil and gasoline to kerosene without major modifications. The engine can even be adapted to use non-petroleum fuels such as coal or wood chips.

A Stirling engine can be divided into three main systems. Fuel is converted to heat in the external combustor (external heat system). Then the heat transfers to the working fluid in the seal-closed section of the engine (hot engine system) where it drives the pistons. In the third engine section (cold engine/ drive system) reciprocat­ing piston motion transfers to rotary motion through connecting rods and a crank­shaft.

Modern Stirling engines operate on a double-acting principle. The piston moves back and forth between the hot and cold regions while transmitting power to the drive shaft. Double-acting engines need a minimum of three pistons, but four or six are more efficient.

Because the Stirling engine doesn't produce power through explosion, it generates little vibration and noise. This eliminates the need for a muffler. Other unnecessary parts include a camshaft, spark plugs, and a carburetor. The reduction in moving parts means longer engine life and lower maintenance.

MTI has installed Stirling engine in cars ranging from AMC Concords and Spirits lo Chevrolet Celebrities and Opels, in the NASA/DOE program, an MTI Mod I Stirling engine was first installed in an Air Force van. A Mod II Stirling engine is to be tested in a US Postal Service van. It has fewer moving parts and is lighter than the 600-fb Mod I version. Al about 39 mpg, it also gets 30% better fuel economy. How­ever, work is needed to reduce engine weight, size and cost Experts believe that cost reductions can make the Stirling engine cost-competitive with diesel engines.

Unlike
non-petroleum fuels
to transfer
seal-closed
connecting rod
back and forth
drive shaft
to eliminate
muffler
reduction

 

в отличие от
Не нефтяные топлива
Передавать
Герметичный
Шатун
назад и вперед
Ведущий вал
Устранять, исключать
глушитель
сокращение

 

 
     
Text 28 Crank Gear Word-list:  
Crankshaft
immovable
crank case
piston ring
piston pin connecting rod flywheel to cast cast iron liner wear combustion chamber L-head overhead valve gasket seal plain compound alloy forged shell split journal bearing to link to fit

 

коленчатый вал
неподвижный
Картер
Поршневое кольцо
Поршневой палец Шатун Маховик отливать   чугун гильза износ камера сгорания с боковым расположение клапанов клапан верхнего расположения прокладка уплотнение простой составной сплав кованный вкладыш разъемный шейка подшипник соединять устанавливать

 

 
       

 

Crank gear serves for converting reciprocating motion of the piston into rotating motion of the crankshaft. Crank gear consists of immovable and mobile details, details are cylinder block, cylinder head and crankcase. The mobile with piston rings, piston pins, connecting rods, crankshaft and flywheel.

Basically, the modem multi-cylinder automotive engine consists of cylinders that are cast into a block. Most cylinder blocks arc made of cast iron, though some American car producers have been offering lightweight aluminum engines in some models since 1960s. Such cylinder blocks are fitted with cast-iron liners to provide wear resistance.

Bolted to the lop of the cylinder block, the cast-iron or aluminum cylinder head provides a separate combustion chamber above each piston. There are two typos of cylinder heads:

L-head, which contains no valves (intake and exhaust valves are arranged in the cylinder block): and overhead-valve, in which both intake and exhaust valves arc installed in the cylinder head. Practically all modem passenger car engines are of overhead-valve design. A gasket of asbestos or sheet steel provides a seal be­tween cylinder head and cylinder block.

The piston, together with its connecting rod, transmits the force of combus­tion chamber explosions to the engine crankshaft. To provide the piston-to-cylinder seal, piston rings are installed in the outer wall of the piston. The upper compression rings are plain, while the bottom oil control ring is compound. All pistons in Ameri­can-made cars are made of light-weight aluminum alloys.

An I-section connecting rod made of forged or cast steel, links the piston to the crankshaft. Its upper end is connected to the piston by a steel piston ring; its lower end is fitted with a shell split to permit its installation on the crankshaft.

The function of the engine crankshaft is to convert the reciprocating motion of the pistons into rotary motion. The crankshaft is supported by journal bearings at the-bottom of the cylinder block. Crankshafts may be forged of steel or made of special cast lion.

Because each cylinder is producing power during only one stroke of the 4-stroke cycle, a flywheel is bolted to the crankshaft rear flange. The flywheel serves to keep the crankshaft rotating during the other three strokes.

 

Text 29 TIMING GEAR

timing gear - распределительный механизм

manifold - коллектор

poppet valve - подъемный клапан

stem - стержень  
tappet - толкатель  
сam - кулачок  
Camshaft - распределительный вал  
rocker arm - плечо коромысла  
tappet rod - штанга толкателя  

correctly-timed sequence - правильно рассчитанная по времени последовательность

to ensure - обеспечивать

to admit - впускать

to seal off - изолировать

to return - возвращаться

to actuate - приводить в действие

 

The timing gear ensures the inlet of the fuel-air mixture into the cylinder and outlet of the burnt gases.

Each cylinder is provided with one intake and one exhaust valve. These valves have three functions: the intake valve admits an air-fuel mixture from the car­buretor and intake manifold; both intake and exhaust valves seal off the combustion space during the compression and power strokes; the exhaust valve opens to let out the exhaust gases from the cylinder.

The poppet valves, used in American automotive engines, consist of a circular head and stem in one piece. Valve seats arc provided in the cylinder block or cylinder head. The valves are opened to a correctly timed sequence by the revolving crank­shaft; they are returned to their scats by steel springs.

According to their valve arrangement engines are classified as L-head and overhead valve engines. In the L-head engine the valves ore arranged along one side of the cylinder block and actuated by valve tappets that rest directly on the cams of the camshaft. In the overhead-valve engine the valves are installed in the cylinder head and driven either by an overhead camshaft or by a rocker-arm, tappet-rod and valve-tappet arrangement.

 

 

Text 30 VALVE KNOCKING

When valve knocking is heard it is necessary to check, and if needed, to ad­just the clearance between the valves and rocker arms that must be within the limits of 0.25 to 0.30 mm both for intake and exhaust valves. The clearances in the timing gear must be adjusted on a cold engine by means of an adjusting screw with a lock nut. The adjusting screw is fitted in the short rocker aim. To adjust the clearance of the timing gear it is necessary to set the piston of the first cylinder in the top dead center.

A continuous operation with the incorrectly adjusted clearances may cause a premature Wear of the timing gear parts, burning of the valves, wear of the rocker arms, tappets and cams.

 

Text 31 LUBRICATING SYSTEM

 

уменьшать износ скользящий избыток поверхность требовать снабжение сетчатый плавающий подниматься
падать  
уровень  
подавать  
разветвленный канал разбрызгивать измерительный прибор  
 
 
измерять  
щуп  
вентиляционное устройство  
загрязнение  
вызывать  
пары  

 

to reduce

wear

sliding

excess

surface

to require

supply

screened

floating

to rise

to fall  
level  
to deliver  
branch passage  
to throw (throw, thrown)  
gauge  
to measure  
stick  
venting device  
pollution  
to cause  
vapors  

 

 

The engine lubricating system serves to reduce the metal-to-metal friction and wear between rotating and sliding parts and to carry excess heal away from the en­gine. The important surfaces requiring lubrication are the crankshaft journal bearings, connecting rod bearings, piston pins, cylinder walls, piston skirts and rings, camshaft hearings, valve mechanism, and timing gears.

An oil supply of 4 to 5 liters (depending on the engine size and7design) is contained in the crankcase. A screened floating oil intake is provided in the deepest part of the crankcase. The intake rises and falls with the oil level.

Oil is sucked by the oil pump and delivered to the main gallery at a pressure of about 3 kg/cm2. Branch passages then deliver oil to the valve mechanism, timing gears, camshaft bearings and crankshaft main bearings. Cylinder walls and piston skirts arc lubricated by oil thrown from the rotating parts. Excess oil is scraped from the cylinder walls by the oil control ring and delivered back to the crankcase.

A gauge or signal light on the instrument panel indicates the oil pressure. The oil level in the crankcase is measured by a graduated "stick" type of gauge.

Since 1962, American cars have been equipped with.internal venting devices by means of which the unburned gases are led back to the engine combustion cham­bers and burned. This ventilation system serves to reduce air pollution caused by crankcase vapors.

      Text 32
  COOLING SYSTEM
condition
to draw (drew, drawn)
tube
waste heat
flow
to pass
blade
belt
to pull
to maintain
to prevent
to freeze
to crack
damage
volume
fin
exterior
to improve
excellent
duct
damper
to blow (blew, blown)

 

 
условие(состояние)
всасывать
трубка
использованное тепло
поток
проходить
лопасть
ремень
тянуть
поддерживать
предотвращать
замерзать
треснуть
повреждение
объем
ребро, радиаторная пластина
внешность
улучшаться
превосходный, отличный
проход
заслонка
дуть

 

The cooling system serves to ensure normal temperature conditions of the en­gine operation.

Most American automobile engines are water-cooled. In this system water ii drawn from the bottom of the radiator and circulated by a small centrifugal pump through the jackets in the cylinder head and cylinder block. Then the water is re­turned lo the top of the radiator. As the water passes down through the tubes of the radiator, it transfers waste beat to the air flow passing through the radiator.

Mounted directly behind the radiator is the fan. A typical cooling fan has four to six blades and is driven by a V-belt from the crankshaft. Its function is to pull air through the radiator when the vehicle is moving slowly.

Optimum engine operating temperatures (72° - 82°C) are maintained by a thermostat. This device controls automatically the temperature of the coolant by pre­venting water circulation in a cold engine.

Water expands a3 it freezes; therefore an antifreeze solution must be added to the cooling system to prevent cracking cylinder block, head and other components at the temperatures below 0" C. Ethylene glycol or alcohol ensure good protection against damage from freezing.

In the air-cooled systems, waste heat is transferred to the atmosphere by cir­culating a large volume of air over the engine. Built-in cooling fin3 on the exterior surfaces of the cylinder block and head increase the surface area exposed to the cooling air. Heat transfer is improved by making the cylinder block and head of alu­minum, an excellent conductor of heat.

A fen, driven by a V-belt from the crankshaft, directs air to the engine through sheet-metal ducts. Engine temperature is controlled by a thermostat-operated damper regulates the volume of cooling air blown over the engine fins.

Lubrication

In the force-feed system, a pump forces the oil to the main crankshaft bearings and then through drilled holes in the crankpins. In the full-force system, oil is also forced to the connecting rod and then out to the walls of the cylinder at the piston pin.

Cooling

At the moment of explosion, the temperature within the cylinder is much higher than the melting point of cast iron. Since the explosions take place as often as 2,000 times per minute in each cylinder, the cylinder would soon become so hot that the piston, through ex­pansion, would «freeze» in the cylinder. The cylinders are therefore provided with jackets, through which water is rapidly circulated by a small pump driven by a gear on the crankshaft or camshaft. During cold weather, the water is generally mixed with a suitable antifreeze, such as alcohol, wood alcohol, or ethylene glycol.

To keep the water from boiling away, a radiator forms part of the engine-cooling system. Radiators vary in shape and style. They all have the same function, how­ever, of allowing the water to pass through tubing with a large area, the outer surface of which can be cooled by the atmosphere. In air cooling of engine cylinders, vari­ous means are used to give the heat an outlet and carry it off by a forced draught of air.

 

Text 33 THERMOSTAT

The thermostat serves to facilitate the warming of a cold engine and to protect the engine from supercooling.

When a cold engine is being warmed, the passage connecting the engine cooling jacket to the radiator is closed by the thermostat gate. When the temperature of the cooling liquid rises up to 79-80° C, ceresine contained in the thermostat melts. Expanding it moves the rod upward and opens the gate after which the cooling liquid starts circulating through the radiator. When the temperature of the cooling liquid drops, the volume of ceresine decreases and the gate is closed by a spring.

 

Text 34 FUEL SYSTEM

Word-list:  
Manifold
Float
float chamber
to actuate
sediment bowl
particle
Dirt
to meter
to atomize
hill climbing
lean mixture
to trap
Supercharge
available

 

Коллектор
поплавок поплавковая камера
приводить в действие
стакан-отстойник
Частица
Грязь
Измерять
Распылять
продление подъема
бедная смесь
улавливать
нагнетатель
Доступный

 

 

 

The fuel system consists of a fuel tank, fuel pump, carburetor, intake manifold and exhaust manifold.

The fuel tank, ranging in capacity from 14 to 20 gallons, generally is located under the body or at the rear of the automobile. A float within the tank operates an electric gauge on the instrument panel to indicate the fuel level.

The mechanical fuel pump is of diaphragm type. The pump is actuated by a special cam on the camshaft. It serves to maintain a constant level of gasoline in the carburetor float chamber at alt road speeds. A sediment bowl and filter serve to clean fuel of particles of dirt.

The carburetor serves to meter and atomize the fuel, to mix it with air and to deliver it to the engine cylinders by means of the intake manifold. Theoretically, the air-fuel ratio required to bum the fuel is 14.7: 1. However, die carburetor is capable of varying the mixture ratio automatically for different operating conditions. For ex­ample, a rich mixture is required for acceleration, hill climbing, and high speeds; for level driving, maximum economy is ensured by running the engine on a leaner mix­ture.

An air cleaner, connected to the carburetor intake,-keeps particles of dirt out of the engine by trapping them in the filtering element.

Superchargers, available as optional equipment on some American passenger car engines, improve engine performance by delivering more air into the cylinders.

Fuel injection was first offered by an American auto maker in 1957. Instead of carburetor this system uses high-pressure pump to deliver gasoline directly into the cylinder. Metered air is introduced into the cylinder through an intake manifold.

 

Text 35 CARBURETOR

The majority of spark-ignition engines have carburetors. Their primary func­tion is to measure out the precise quantities of petrol to be mixed up with the air in­take. A secondary function is to break up the petrol into fine particles so that the mixture will burn rapidly in the combustion chamber.

The principle of the carburetor is as follows:

Air is drawn through the intake into a venturi. Because the air flow is ob­structed in the narrow venruri, it is speeded up and its pressure is lowered. Hence, petrol will flow from the float chamber through the main jet into the venturi because of the depression. The petrol will be broken up by the air current and will mix with it.

The choke flap can shut off the air flow when the engine is cold.

venturi - диффузор

main jut - главный жиклер

choke flap – дроссельная заслонка

 

Carburation

Air is mixed with the vapour of the petrol in the car­burettor. To prevent the air and the carburettor from becoming too cold for successful evaporation of the fuel, the air for the carburettor is usually taken from a point close to a heated part of the engine. Modern carburet­tors are fitted with a so-called float-feed chamber and a mixing or spraying chamber. The first is a small cham­ber in which a small supply of petrol is maintained at a constant level. The petrol is pumped from the main tank to this chamber, the float rising as the petrol flows in until the desired level is reached, when the inlet closes. The carburettor is equipped with such devices as accel­erating pumps and economizer valves, which automati­cally control the mixture ratio for efficient operation under varying conditions. Level-road driving at constant speed requires a lower ratio of petrol to air than that needed for climbing hills, for acceleration, or for start­ing the engine in cold weather. When a mixture ex­tremely rich in petrol is necessary, a valve known as the choke cuts down the air intake, permitting large quanti­ties of unvaporized fuel to enter the cylinder.

 

Text 36 FUEL FEED SYSTEM MAINTENANCE

Word-list:  

assemble - собирать
blow through - продувать
cause - вызывать
check - проверять
clean - чистить
damage - повреждать
drain - сливать
drip eliminate - устранять empty - опорожнять fill - наполнять - капать

flush - промывать

remove - снимать

require - требовать

screw - привинчивать

tighten - затягивать

wash - промывать

wet - смачивать

 


 

Fuel Pump

In the process of operation check the pump for proper sealing and, if required, eliminate leakage of fuel. When dissembling the pump remove the screen filter and wash it in clean gasoline. Disassemble and assemble the pump carefully so as not to damage the diaphragm and gasket. When disassembling the diaphragm see that no particles of dust, metal chips, etc. get between the disks and the diaphragm, as it «uses rapid wear of the diaphragm.

 

Fuel Filter-Settler

Care of the fuel filter-settler consists in draining water and dirt through the drain plug as well as in disassembling and flushing the filtering element.

For flushing the filtering element unscrew the bolt on the filler cover and remove the bowl together with the filtering element. Having unscrewed and emptied the settler, wash it with clean gasoline. Having flushed the filtering element, reinstall it and tighten the bolt on the cover.

 

Fuel tanks

In the service period it is necessary to check and tighten periodically the at­tachments of the fuel tanks and brackets, to drain sediment from the tanks and wash them, to clean and wash the valves on the auxiliary tank and to blow through the pipes connecting the main and auxiliary tanks.

 

Air Cleaner

The air cleaner is periodically cleaned and refilled with oil. In the process of cleaning wash thoroughly all the parts of the air cleaner in gasoline or kerosene. After washing wet the filtering element with oil. Before reinstalling the filtering element let an excess of oil drip off. Lubricate the filtering element and fill the air cleaner bath with oil used for lubrication of the engine.

Never operate the engine without the air cleaner or with the air cleaner not filled with oil.

 



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