Lesson 5. Engine Air Systems and Cooling Systems

ENGINE AIR SYSTEMS

Parts and accessories, which supply the cylinders of an engine with air for combustion, and remove the waste gases after combustion, are called intake and exhaust systems.

In the intake systems of all modern 2-stroke cycle engines and some 4-stroke cycle engines, a device, usually a blower is installed to increase the flow of air into the cylinders. This is accomplished by the blower compressing the air and forcing it into an air box or manifold (reservoir) which surrounds or is attached to the cylinders of an engine. Clearing the cylinder of the gases of combustion is called scavenging.

An increase in air flow into the cylinders of an engine can be used to increase power output, in addition to being used for scavenging. Since the power of an engine is developed by the burning of fuel, an increase of power requires more fuel; the increased fuel, in turn, requires more air, since each pound of fuel requires a certain amount of air for combustion. Supplying more air to the combustion spaces is called supercharging. In some 2-stroke cycle diesel engines, the cylinders are supercharged during the air intake simply by increasing the amount and pressure of scavenge air. The same blower is used for supercharging and scavenging. Supercharging a 4-stroke cycle diesel engine requires the addition of a blower to the intake system.

The system, which functions to convey gases away from the cylinders of an engine, is called the exhaust system. In addition to this principal function, an exhaust system may be designed to perform one or more of the following functions: muffle exhaust noise, quench sparks, remove solid material from exhaust gases, and furnish energy to a turbine-driven supercharger.

I. Answer the questions

1. What systems are spoken about in the text?

2. What is scavenging?

3. What is supercharging and how is it provided?

4. How is the supercharger driven?

5. What are the functions of the exhaust system?

ENGINE COOLING SYSTEMS

A great amount of heat is generated within an engine during operation. Combustion produces the greater portion of this heat; however, compression of gases within the cylinders and friction between moving parts add to the total amount of heat developed within an engine.

Of the total heat supplied to the cylinder of an engine by the burning fuel, only one-third is transformed into useful work; an equal amount is lost to the exhaust gases, and approximately 30 to 35 percent of the heat of combustion must be removed in order to prevent damage to engine parts. The greater portion of the heat, which may produce harmful results, is transferred from the engine through the medium of water; lubricating oil, air, and fuel are also utilized to aid in the cooling of the engine. All methods of heat transfer are utilized in keeping engine

parts and fluids (air, water, fuel, and lubrication oil) at safe operating

temperatures.

The cooling system may be of the open or closed type. In the open system, the engine is cooled directly by salt water. In the closed system fresh water, (or an antifreeze solution) is circulated through the engine. The fresh water is then cooled by salt water. In marine installations the closed system is the type commonly used.

The cooling system of an engine may include such parts as pumps, coolers, engine passages, water manifolds, valves, expansion tank, piping, strainers, connections, and instruments. Design and location of parts may differ considerably from one engine to another.

I. Answer the questions.

1. What are the sources of the heat generated in an engine?

2. How much heat is transformed into useful work?

3. How many percent of the heat must be removed from the engine by means of cooling?

4. What fluids are utilized for cooling purposes in an engine?

5. What parts does the water cooling system of an engine include?

II. Translate into English.

1. При роботі дизеля його частини сильно нагріваються.

2. Висока температура пошкоджує деталі дизеля, тому їх слід охолоджувати.

3. Для охолодження деталей дизеля використовують масло, дизельне паливо і дистильовану воду.

4. Для охолодження дизеля оптимально використовувати воду температурою 90-95 ° С.

5. Ефективність охолодження деталей дизеля може знизитися через накип і корозію.

6. Структура системи охолодження залежить від розміру дизеля.

7. Найзручнішою охолоджуючою речовиною для морських дизелей є морська вода, бо не потрібні танки для зберігання і холодильники.

8. Але забортна вода рідко використовується в системі охолодження через ризик відкладення солі і корозії деталей двигуна.

9. Втулки циліндра можуть охолоджуватися морською абопрісною водою, в той час як поршні зазвичай охолоджуються маслом.

10. Повітря не використовується для охолодження двигунів великої потужності, тому що ефективність такого охолодження низька.

11. Ефективність охолоджуючої системи морською водою зменшується, як тільки на внутрішніх частинах двигуна утворюєся накип.

12. Необхідно примусове охолодження, для того, щоб підтримувати допустиму температуру головки (днища) поршня.