Ignition Type

Two methods for igniting fuel are used, spark ignition and compression ignition. Gasoline car engines use spark ignition whereas diesel engines use compression ignition. This method compresses the air to the point where the resulting rise in temperature causes ignition to occur when diesel fuel is added.

Strokes per Cycle

Strokes per cycle are the number of times the pistons travel up and down during one cycle. Modern engines have four strokes per cycle: intake, compression, power, and exhaust. Two-stroke engines are not used due to their poor power output at low rpm, they are less fuel efficient, generate an unacceptable amount of pollution, and require more maintenance.

Cooling System

Engines can be air-cooled or liquid-cooled. Air-cooled engines are used largely by motorcycles and piston powered aircraft. Liquid-cooled engines are the standard with most other vehicles. Air-cooled engines have large cooling fins surrounding the cylinder. Air moving across the fins carries away heat. Liquid-cooled engines have internal channels called water jackets in the cylinder block and cylinder head, through which coolant circulates, removing heat. In order to meet strict exhaust emissions standards, engine temperature must be maintained fairly constant. This is why most engines are liquid-cooled.

VI. Comprehension check.

Activity 1. Do the false / true activity:

1. Car engines are mainly electric engines.

2. Most of the engines are piston or internal and external combustion engines.

3. Engines can be classified only according to the type of ignition system used.

4. Gasoline car engines use compression ignition.

5. Alternate fuels such as liquefied petroleum gas (LP-gas), gasohol (90% gasoline, 10% alcohol), and pure alcohol are used in very limited situations.

6. There are two types of engine block geometry: V-type and slant.

7. A V-type allows the hood line to be lower.

8. A turbocharged, four-cylinder engine can produce more power than a normally aspirated six-cylinder engine.

9. The camshaft can be located only in the engine block.

10. Air-cooled engines are used largely by motorcycles and piston powered aircraft.

Activity 2. Look through the text 2A carefully. Then complete the following to make suitable sentences according to the meaning of the text:

1. Car engines are mainly _________________________________.

2. The heat engines are classified into ________________________.

3. Engines can be classified in several ways such as _____________.

4. Gasoline car engines use _____ ignition whereas diesel engines use _____ ignition.

5. There are four types of engine block geometry: _______________.

6. The number of cylinders is an indication of __________________.

7. There are two possible locations for the camshaft: _____________.

8. A dual overhead cam (DOHC) engine uses two camshafts ______.

9. The hemispherical combustion chamber, also called «hemi-head», is designed with _______________________________________.

10. Strokes per cycle are _______________________________.

11. Air-cooled engines have ____________________________.

12. Liquid-cooled engines have _________________________.