Chapter 6 Engine Types and Classifi cations 147 Copyright by Goodheart-Willcox Co., Inc. Figure 6-44. This is a horizontally opposed engine. It provides for a very low center of gravity and the lower main bearing friction of the boxer design. It is a 24-valve, 6-cylinder engine equipped with dual overhead cams and fuel injection. (Subaru) Cylinder numbers identify the cylinders, pistons, and connecting rods of the engine. Firing order refers to the sequence in which combustion occurs in the engine. There are several different ways to classify an engine crankshaft. Some classifications include inline or V-type, cast iron or forged steel, and externally or internally balanced. There are two types of systems providing cooling for the engine—liquid cooling and air cooling. Almost all vehicles now have a liquid-cooled engine. The two common types of fuel are gasoline and diesel. Fuel metering is achieved through fuel injection. Diesel engines are multiport fuel injected. A gasoline engine may be multiport or throttle body fuel injected. Gasoline engines have spark ignition. Diesel engines have compres- sion ignition. There are four basic combustion chamber shapes for gasoline engines. These are pancake, wedge, hemis pherical, and pent-roof. In addition, there are many different types of combustion chamber. The number of valves or spark plugs per chamber often define the type of combustion chamber Engines may also be classified by the location of the valves. In addition, the location and number of camshafts are important. There are three basic camshaft drive systems—belt, chain, and gears. Engine aspiration refers to how air enters the engine, or how the engine “breathes.” There are three types of engine aspiration. An engine can be classified as normally aspi- rated, turbocharged, or supercharged. An engine may be internally or externally balanced. An internally balanced engine uses the counterweights on the crankshaft to counteract the piston and rod weight. An externally balanced engine has extra weight added to the flywheel and balancer. There are several alternative engine designs in produc- tion or development. These include rotary and Miller cycle engines. Other alternative designs include hybrid and fuel cell vehicles. Review Questions—Chapter 6 Answer the following questions using the information provided in this chapter. 1. Explain the four common types of automotive engine cylinder arrangements. 2. Car and light truck engines normally have _____, _____, or _____ cylinders. 3. _____ identify the cylinders, pistons, and connecting rods of an engine. 4. How can you normally tell which cylinder is the number one cylinder in a V-type engine? 5. Define firing order. 6. The most common type of cooling system on automobiles is the _____ cooling system. 7. Describe the major differences between a gasoline engine and a diesel engine. 8. A diesel engine is a(n) _____ ignition engine. 9. Which of the following is not a common combustion chamber shape? (A) Wedge. (B) Symmetrical. (C) Hemispherical. (D) Pancake. 10. How does swirl help combustion efficiency? 11. Explain the advantages of a four-valve combustion chamber. 12. What is a stratified charge combustion chamber? 13. In a(n) _____ or _____ valve engine, both valves are located in the cylinder head. 14. A(n) _____ engine has one camshaft in each cylinder head and a(n) _____ engine has two camshafts per cylinder head. 15. Describe the operation of a rotary engine.