Chapter 4 Principles of Engine Operation 85 Copyright Goodheart-Willcox Co., Inc. to the crank also affects torque generation. Numerous short-duration power strokes will not generate as much torque as fewer longer-lasting power strokes. This is why torque levels decrease as engine speed levels (rpm) and horsepower increase. Torque is measured in foot-pounds (ft-lb) or inch- pounds (in-lb). The metric unit for torque is the newton- meter (N⋅m). The formula for determining torque in a diesel engine is: torque = 5252 × horsepower rpm To determine the metric equivalent in newton-meters, multiply your answer in ft-lbs by a conversion factor of 1.3558. Summary A diesel engine consists of a number of systems and subassemblies that work together to produce power. The cylinder block is the foundation of the engine. It supports all major engine components and has openings for cylin- ders and passages for coolant and lubricant. It houses the powertrain components, such as the crankshaft, pistons, and connecting rods. The camshaft is timed to the crankshaft using timing gears. It coordinates the operation of the intake valves, the exhaust valves, and in some systems, the fuel injectors with the action of the pistons. Lobes on the camshaft transfer the rotational motion of the shaft into an up-and- down motion that is transferred to the valves and, if appli- cable, the injectors. The cylinder head bolts to the top of the cylinder block and forms the top of the combustion chamber. It has passages for coolant circulation, intake air, and exhaust. It also contains openings for the fuel injectors. Valves are used to seal the air passages in the cyl- inder head. Cylinders can be equipped with either two, three, or four valves. Manifolds are used to deliver air to the engine and carry away the exhaust gases produced by combustion. Turbochargers and superchargers are air pumps that help deliver more combustion air to the engine. Charge air coolers cool the intake air so that it is denser and contains more oxygen. Four-stroke diesel engines operate using four sepa- rate piston strokes to complete one combustion cycle. Two-stroke diesel engines operate using only two piston strokes per combustion cycle. Ports in the cylinder wall take the place of intake valves on these engines and a blower is used to supply air to the cylinder and help clear exhaust gases. Diesel engines are commonly built in inline and V-type configurations. Double-acting piston engines are also produced. Most high-speed diesel engines use direct fuel injection. Indirect combustion chamber designs include the precombustion chamber, swirl chamber, and energy cell configurations. The fuel injection system must deliver the proper amount of fuel for combustion and provide the same amount of fuel to each cylinder to ensure smooth engine operation. Fuel injection systems in use today include indi- vidual pump systems multiple-plunger, inline pump sys- tems distributor pump systems pressure-time injection systems unit injector systems hydraulic electronic unit injector systems and common rail injection systems. Engines are often rated according to horsepower and torque. Horsepower is the ability to maintain load at a desirable or fixed speed. It is a measure of how fast work can be done. Torque is the measurement of rotational or twisting force around a fixed point. Review Questions—Chapter 4 Answer the following questions using the information provided in this chapter. 1. The _______ is a large casting that bolts to the top of the cylinder block and forms the top of the combustion chamber. (A) intake manifold (B) air box (C) cylinder head (D) piston head 2. List, in order, the four piston strokes of a four-cycle engine. 3. In a diesel engine, when do valves open and close? 4. Two-cycle engines use a series of _______ to control airflow into the cylinder. 5. The power stroke of a two-cycle engine is _______ than that of a four-cycle engine. 6. List three advantages of the vertical inline cylinder arrangement. 7. List three advantages of V-type cylinder configurations. 8. List the seven types of diesel injection systems described in this chapter. 9. Name two ways vibrations are decreased in a diesel engine. 10. Which engine component converts the rotational motion of a camshaft lobe into an up-and-down motion? (A) Rocker arms. (B) Push rods. (C) Cam followers, tappets, or lifters. (D) Crosshead or bridge.