Text 2. What a Diesel Engine Is

A diesel engine is a machine which produces power by burning oil in a body of air which has been squeezed to a high pressure by a moving piston. Since it is a machine that produces power, it is called an engine, and since the burning or combustion takes place within the engine itself, it is called an internal-combustion engine. A steam engine uses steam made by burning fuel outside the engine. That is external combustion.

To compress the air, put in the oil, and produce power, every diesel engine must have certain basic parts. It must have a round sleeve, or cylinder, in the bore of which a close-fitting plug or piston can slide in and out to make strokes. The piston must be connected to a mechanism which controls its sliding. For this purpose ordinary engines use a crank mechanism. This consists of, first, a round bar or shaft which can turn or revolve in circular guides called bearings and which has an offset or crank (which turns in a circle when the shaft revolves), and, second, a connecting rod which, as the name implies, connects the crank to the piston. The connecting rod is a straight rod with a bearing at each end. The crank mechanism (which is also used in many other kinds of machinery) is a device for converting the in-.and-out motion of the piston to rotating motion of the crankshaft. The power produced by the engine is taken off the crankshaft.

Other basic parts are necessary. Valves or ports are needed to let the air into the cylinder, and also to let out the burned оr spent gases after they have done their work. Also a spray nozzle, or fuel injector, is needed to deliver the oil for burning in the form of a finely divided spray. (It works something like the nozzle on a garden hose ) To do this the oil must be put under pressure. This is accomplished l»v a pump which is called a fuel-injection pump.

Notes

in squeeze – стискувати; проштовхувати

sleeve – муфта

bore – отвір

plug – втулка; пробка

crank – кривошип, коліно

shaft – вісь, держак

valve – клапан, вентиль

nozzle –сопло, форсунка

to accomplish – виконувати, здійснювати

Text 3. What Happens Inside the Engine

To begin learning how a diesel engine works, let's see what happens inside the engine, step by step.

Basic Actions.— First, air must be gotten into the cylinder because no fuel will burn without air.

Burning or combustion is the process of uniting a fuel or combustible with the oxygen in the air. The process is a chemical one, which means that the fuel and oxygen, in uniting, change into new substances.

Second, the air must be squeezed or compressed to a high pressure.

There are two reasons for compressing the air. One reason is that if the combustible mixture has been compressed to a high pressure before it starts to burn, it will produce more power than if it had not been compressed. The other reason is that when air (or any gas, for that matter) is compressed, its temperature goes up — the higher the pressure, the higher the temperature. In a diesel engine, the air is compressed so much that it becomes as hot as red-hot iron, in fact, so hot that it will ignite oil that is sprayed into it.

This is a fundamental difference between a diesel engine and a gasoline engine such as the one in an automobile. In a gasoline engine, a spark is used to ignite the combustible mixture, while in a diesel engine the fuel ignites by itself just from contact with air – air that is very hot because it has been highly compressed.

Third, the fuel must be squirted into the cylinder in the form of a fine spray. The oil squirted in after the air has been compressed and thus heated to a high temperature. It must be in the form of a fine spray so that a cloud of oil droplets will spread throughout all of the air. This produces a thorough or "homogeneous" mixture of oil and air, which is needed for quick and complete combustion. (It all must happen so fast in an engine that there's no time to waste.)

Fourth, combustion takes place immediately after the oil is sprayed into the cylinder; this generates a large amount of heat. The gaseous mixture gets hotter and tries to grow larger or expand. It pushes on the piston, which in turn transmits the force through the connecting rod to the crank on the crankshaft. This makes the crankshaft revolve and thus deliver power to whatever machine the engine is driving.

Fifth and last, when the piston has finished its preceding power stroke, and the gases in the cylinder have lost their pressure, the spent gases must be gotten rid of or exhausted.

Meaning of a "Cycle". — When the cylinder is rid of the spent gases, it is ready to receive a fresh charge of air and start the cycle all over again. A cycle, in other words, is a full series of the separate steps or events which follow each other.

This is a good place to learn what is meant by the common terms of' two-cycle engines and four-cycle engines. These terms are really abbreviations for two-stroke cycle and four-stroke cycle, which make more sense, but almost everyone now uses the shorter terms. In a two-cycle engine, it takes two strokes of the piston (that is, one up-stroke and one down-stroke) to go through one complete cycle of events. In a four-cycle engine, a complete cycle requires four strokes of the piston (one up, one down, one up and one down). These terms apply to all kinds of internal-combustion engines, not merely to diesels.

Notes

spark – іскра, спалах

to squirt – пускати струмінь

homogeneous – однорідний

to generate – породжувати; викликати

exhaust – випуск, вихлоп

merely – тільки, лише; просто