Fuel Injection

The function of the fuel injection mechanism is to put the correct amount of fuel into the cylinder of the engine at the proper time under the right pressure and to ensure good mixing the air and the fuel for complete burning.

At present there are three principal methods of mechanical injection:

1. Direct injection or open combustion chamber method.

2. Pre-combustion chamber method.

3. Air turbulence method.

1. During the direct injection method the fuel is injected directly into the combustion chamber through a spray nozzle and under sufficient pressure. It is done in order to carry the fuel particles into the mass of the compressed air, the injector being fitted into the cylinder head.

The loss of heat during the compression is a minimum, the delay combustion period being short. This method of fuel injection gives better starting from the cold.

2. With a pre-combustion chamber method the cylinder head has a smaller combustion chamber communicating with the cylinder head through a neck.

The compressed air circulates in this chamber, at a certain moment the fuel being injected into the chamber. The fuel immediately begins to ignite. The mixture of burning and unburnt fuel passes from the pre-combustion chamber into the cylinder through the communicating neck.

3. The air turbulence method is used in several types of engines.

This method provides efficient atomizing and mixing the fuel particles with the air at the end of the compression stroke. As the volume of the injected fuel is very small in comparison with the volume of compressed air, the holes in the nozzle must be very fine and numerous. The pressure required to obtain the necessary penetration of the fuel must be very high and the sprays must have a sufficient depth of penetration to reach all the compressed air in the cylinder head.

direct injection method метод прямого впрыска

pre-combustion chamber method метод предкамерного

смесеобразования

air turbulence method вихрекамерный метод

смесеобразования

sufficient, adj достаточный

particle, n частица

amount, n количество

loss, n потеря

delay combustion period период задержки

воспламенения

smooth, adj плавный

neck, n канал

mixture, n смесь

обеспечивать

provide, v

insure, v

atomizing распыление

in comparison with в сравнении с

numerous, adj многочисленный

penetration, n проникновение

depth, n глубина

pass, v проходить

Combustion

Combustion is a chemical reaction in which certain elements of the fuel combine with oxygen of the air increasing the temperature of the gases. The main combustible elements are carbon and hydrogen. There are two general methods of burning the fuel in an engine cylinder:

1. Combustion at constant volume and

2. Combustion at constant pressure.

Combustion at constant volume means that during combustion the volume doesn't change and that all the heat energy developed by the fuel goes into an increase of the gas temperature and pressure.

The rate of combustion is so high that the piston has no time to move during combustion. Such combustion is obtained when the |piston is at the top center.

The advantage of this method is a high thermal efficiency. Its disadvantage is a sudden increase of pressure and the resulting noisiness of the engine.

During combustion at constant pressure the temperature increases at such a rate that the pressure increase counteracts the volume increase and the pressure doesn't change. The heat energy generated by the fuel goes partly into an increase of the gas temperature and partly into producing outside work.

During combustion at constant pressure the fuel is burnt gradually. The pressure attained at the end of the compression stroke is maintained during the greater part of the combustion event. Its advantage is smooth running and a more even torque produced by an engine.

High-speed diesel engines operate on a cycle which is approximately a combination of the above two methods.

combustion, n горение, сжигание

combustible, adj горючий

during, prep во время

mean, v значить, означать

combine, v соединять/ся/

certain, adj определенный

oxygen, n кислород

carbon, n углерод

hydrogen, n водород

at constant volume при постоянном объеме

at constant pressure при постоянном давлении

rate, n зд. скорость

such, adj такой

obtain, v получать

advantage, n преимущество

disadvantage, n недостаток

thermal efficiency тепловой к.п.д.

sudden, adj внезапный, резкий

noisiness, n шум

counteract, v противодействовать,

уравновешивать

influence, n влияние

generate, v образовывать

attain, v достигать

maintain, v поддерживать,

обслуживать

torque, n крутящий момент

even, adj зд. плавный, равномерный

approximately, adv приблизительно

gradually, adv постепенно

smooth, adj плавный, гладкий

Lubrication

The aim of lubrication is to make the rubbing surfaces operate with as little friction as possible and so reduce wear to a minimum and obtain the maximum power out of the burnt fuel. Good lubrication is one of the main factors for satisfactory engine work.

Every moving part must be lubricated to ensure a lasting oil film which prevents metal-to-metal contact. There are three general methods of lubrication:

1. Mechanical force feed lubrication;

2. Circulating lubrication;

3. Splash lubrication.

During mechanical force feed lubrication oil is delivered to all points from one or more mechanical lubricator units. The number of individual
pumps in each unit is determined by the number of points to be lubricated. At each feed point there is a check valve preventing oil from draining or blowing back.

The second method of lubrication may be divided into lubrication by gravity and by pressure circulation. Gravity lubrication is seldom used in modern engines. At present all engines are lubricated by pressure circulation method. Pressure delivers oil to all bearings and gears or chain-drivers. From the main bearing the oil passes through holes in the crankshaft to the connecting rod bearings and through the connecting rod to the wrist pin or crosshead.

During the splash lubrication method the crankcase is filled with oil. The rotating cranks dip into the oil and spray it over bearings and cylinder walls. Valves and other parts are lubricated by hand oiling, but cylinders are sometimes oiled by mechanical lubrication.

prevent, v предотвращать

lubrication, n смазка

ensure, v обеспечивать

film, n пленка

lasting film прочная пленка

metal-to-metal contact сухое трение

mechanical force feed lubrication механическая смазка под

давлением

circuiting lubrication циркуляционная смазка

splash lubrication смазка разбрызгиванием

unit, n установка, агрегат

determine, v определять

blow back втягиваться

lubrication by gravity смазка самотеком

gear, n зубчатая передача

chain-driver, n цепная передача

wrist pin, n поршневой палец

crosshead, n крейцкопф

dip, v погружать

crankcase, n картер

Дата добавления: 2015-10-30