What a Supercharging Is

The more air and fuel we can burn in the cylinders, the more power we can get from the engine. Air is forced into the cylinder of an ordinary four-cycle engine by the atmospheric pressure.

Let’s look at the ordinary four-cycle engine. The piston descends on the inlet stroke. The inlet valve is opened. The air is sucked in. Why is air sucked in? The descending piston makes a partial vacuum, that is, it lowers the pressure inside the cylinder below that of the outside atmosphere. The outside pressure pushes air into the cylinder, filling it with air of to, or near the outside pressure.

To increase the engine’s power more air must be put into the cylinder. For this purpose a supercharger is used. A supercharger makes the outside pressure higher than atmospheric and thus forces more air into the cylinder.

A supercharger is simply a kind of air pump that takes air out of the surrounding atmosphere, compresses it to a higher pressure, and then feeds it to the engine’s inlet valves. It is called a "supercharger" because it charges the engine with air at a "super" pressure. Superchargers come in many forms. They are used for two important purposes. The first is to get more power out of a given engine by feeding it with more air (and more fuel also) than it would take directly from the atmosphere in normal operation. Thus, we get an engine of greater power for the same dimensions and almost the same weight. The second purpose is to restore some of the power which an engine loses when it is taken up to a high altitude above sea level. So there is less pressure to force air into the cylinder, and the engine becomes weaker for lack of air. An engine’s power at 8.000 feet above sea level is only 75 per cent of its power at sea level. It’s here where the supercharger comes in. It can increase the low atmospheric pressure to the sea-level pressure and thus restore most of the lost power. It can’t restore all the lost power because some of the regained power must be used to drive the supercharger.

Words

ordinary, adj обычный

descend, v опускать/ся/

lower, v снижать

charge, v заряжать

purpose, n цель

lose (lost, lost), v терять

altitude, n высота

above sea level над уровнем моря

previously, adv ранее

lack, n недостаток

regain, v получить обратно

drive, v приводить в действие

To be read after texts 6 and 7.

Fuel Injection and Combustion

The fuel is delivered into the cylinder either by highly compressed air at a pressure of about 1,000 lbs per sq.in. or by the pumps themselves working at from 4,000 to 20,000 lbs per sq.in. Before the fuel enters the cylinder it is atomized so that it ignites and burns upon coming into contact with the hot air.

The air necessary to bring about combustion in four-cycle engines is either drawn directly from the atmosphere during the intake stroke of the cycle, or supplied to the cylinder under pressure of about 4 lbs per square inch by pumps. The former are called atmospherically charged engines and the latter – supercharged engines. Combustion of the fuel is brought about by the highly compressed air. Approximately 14 pounds of air is required for the combustion of 1 pound of fuel oil. However, to ensure complete combustion of the fuel an excess amount of air is always supplied to the cylinders.

The ratio of the amount of air supplied to the quantity of fuel injected during each power stroke is called the air-fuel ratio and is very important in the operation of any internal combustion engine. When the engine is operating at light loads there is a very large excess of air, but even when the engine is overloaded there is an excess of air over the minimum required for complete combustion.

In order to accomplish complete combustion of the fuel each of the small fuel particles must be surrounded by sufficient air and the air in the cylinder must be in motion. This is called turbulence. In the air- injection engine the sprayed air creates the necessary turbulence in the cylinder. However, in mechanical injection engines some other means must be provided.

In two-stroke cycle engines the scavenging air may be admitted to the cylinder with a whirling motion in order to create the necessary turbulence. The following conditions are necessary for good combustion:

a) The fuel must enter the cylinder at the proper time. That is, the fuel-injection valve must be opened and closed in correct relation to the position of the piston.

b) The fuel must enter the cylinder in a fine mist or fog. The finer the atomization of the fuel and the higher the temperature, the sorter is the ignition delay period.

c) The fuel must be mixed intimately with the air which supports its combustion.

d) Sufficient air must be present to ensure complete combustion.

e) The temperature of compression must be sufficient to ignite the fuel.

Words

bring about осуществлять

draw in (drew, drawn) всасывать

the former первый /из двух/

the latter последний /из двух/

excess, n излишек

quantity, n количество

accomplish, v завершать

turbulence, n завихрение

means, n средство

whirling motion вращение, вихревое движение

lbs per sq.in фунты на квадратный дюйм

that is то есть

internal combustion engine двигатель внутреннего

сгорания

air-injection engine двигатель с воздушным

впрыском

mechanical injection engine двигатель с механическим

впрыском