SUBCOURSE EDITION OD0610 A PRINCIPLES OF AUTOMOTIVE ENGINES PRINCIPLES OF AUTOMOTIVE ENGINES Subcourse Number OD 0610 EDITION A United States Army Combined Arms Support Command Fort Lee, VA 23801-1809 3 Credit Hours Edition Date: November 1991 SUBCOURSE OVERVIEW This subcourse is designed to teach you the Principles of Automotive Engines. Contained within this subcourse is instruction on how to identify component functions, characteristics, and principles of operations of the two-stroke, four stroke spark, compression ignition, and turbine engines, to include a comparison of gasoline and diesel system components. There are no prerequisites for this subcourse. This subcourse reflects the doctrine which was current at the time the subcourse was prepared. Always refer to the most current publications in a working environment. The words "he", "his", and "men", when used in this publication, represent both the masculine and feminine genders, unless otherwise stated. PLEASE NOTE Proponency for this subcourse has changed From Armor (AR) to Ordnance (OD). i TERMINAL LEARNING OBJECTIVE TASK: Identify the internal functions of selected components of spark and compression ignition and turbine internal combustion engines. CONDITIONS: Given this subcourse containing information describing principles of automotive engines. STANDARD: You must identify component functions, characteristics, and principles of the two-stroke, four-stroke spark, compression ignition, and turbine engines, to include a comparison of gasoline and diesel system components. ii OD0610 TABLE OF CONTENTS SECTION PAGE Subcourse Overview ...................................... i Lesson: Principles of Automotive Engines ................ 1 Part A: Engine Construction. .................. 3 Classification of Engines .............. 8 Engine Operation ....................... 10 Four-Stroke and Two-Stroke Engines...... 13 Practice Exercise ...................... 17 Answer Key and Feedback ................ 18 Part B: Diesel Engines ......................... 19 Practice Exercise. .................... 41 Answer Key ad Feedback ................. 44 iii OD0610 LESSON PRINCIPLES OF AUTOMOTIVE ENGINES MQS Manual Task: None OVERVIEW TASK DESCRIPTION In this lesson, you will learn the characteristics and principles of operation of automotive engines. LEARNING OBJECTIVE TASK: Identify the internal functions of selected components of spark and compression ignition and turbine internal combustion engines. CONDITIONS: Given this subcourse containing information describing principles of automotive engines. STANDARDS: You must identify component functions, characteristics, and principles of the two-stroke, four-stroke spark, compression ignition, and turbine engines, to include a comparison of gasoline and diesel system components. REFERENCES: TM 9-8000. 1 OD0610 INTRODUCTION This subcourse is a guide for personnel charged with the responsibility of maintenance on any army vehicle. This subcourse will provide the motor officer with the information on different engines, their construction, characteristics, and operation. The rising cost of Army materiel and the need for a high state of equipment readiness on the part of Army units dictate the need for an efficient and responsive system of maintenance. Properly trained, well supervised operations and repairmen, supported by a high level of command emphasis for quality maintenance, are the most essential elements of a successful maintenance program. But, without the knowledge of engine components, the supervisor may not know what is causing the malfunctions and high costs of repairs. 2 OD0610 LESSON CONTENT Part A. 1. Engine Construction. Upon completion of Part A, you will be able to answer questions about the characteristics and principles of operation of two-stroke and four-stroke cycle spark ignition engines. a. Internal and external combustion engines. In the internal combustion engine, the combustion of fuel takes place inside the engine cylinder. This is in contrast to external combustion engine, such as a steam engine, where the combustion takes place outside. Figure 1-1 shows, in simplified form, an external combustion engine. The external combustion engine requires a boiler in which fuel is burned. This combustion causes water to boil to produce steam. The steam passes into the engine cylinder under pressure and forces the piston to move downward. With the internal combustion engine, the combustion takes place inside the cylinder and is directly responsible for forcing the piston to move downward. In both type engines, valves are arranged to permit better intake and exhaust. The most common used engine is the internal combustion engine. Figure 1-1. Comparison of Internal and External Combustion Engines. 3 OD0610 b. No matter how many cylinders an engine has, whether 1, 2, 4, 6, or 12, the same actions take place in each cylinder. Much can be learned about construction and operation by studying a single cylinder engine (Figure 1-2). This engine is a four-stroke cycle, internal combustion, gasoline engine; these terms are explained in subsequent paragraphs. Figure 1-2. Single-Cylinder, Four-Stroke, Internal Combustion Gasoline Engine (Cut-Away View). (1) Cylinder and piston. Each cylinder of a typical engine has a piston that reciprocates (moves up and down or back and forth) within the cylinder and is connected to the crankshaft by a link known as a connecting rod (Figure 1-3). Engine pistons transmit the force of the explosion to the crankshaft through the connecting rod, and act as a guide for the upper end of the connecting rod, and serve as a carrier for the piston rings used to seal the piston in the cylinder. The top of the piston may be flat, concave, convex, or a great variety of shapes to promote turbulence or help control combustion. 4 OD0610 (2) Connecting Rod and Crankshaft. The up-and-down movement of the piston is called reciprocating motion. This reciprocating motion must be changed to rotary motion to propel the vehicle. The change is accomplished by the crankshaft and a connecting rod which connects the piston (Figure 1-3) and the crankshaft. The connecting rod is attached to the piston by a piston pin or "wrist pin". The pin passes through the bearing and surfaces in the piston and connecting rod. The lower end of the connecting rod is attached to the crankpin on the crankshaft. As the piston moves up and down in the cylinder, the upper end of the connecting rod moves up and down with it. Figure 1-3. Piston, Connecting Rod, and Piston Pin. 5 OD0610 (3) Stroke. The lower end of the connecting rod also moves up and dawn but, because it is attached to the crankpin on the crankshaft (Figure 1-4), it also moves in a circle. Each movement of the piston from the top to the bottom or from bottom to top is called a stroke. The piston takes two strokes as the crankshaft makes one complete revolution, an upstroke and a downstroke. When the piston is at the top of a stroke, it is said to be at top dead center (TDC). When the piston is at the bottom of the stroke, it is said to be bottom dead center (BDC). These positions are called rock positions. Figure 1-4. Relationship of Piston, Connecting Rod, and Crank on Crankshaft as Crankshaft Turns One Revolution. 6 OD0610 (4) Valves. There are two valves (Figure 1-5) at the top of the cylinder. A valve is an accurately machined plug that fits into a machined opening at the top of the cylinder. When the valve is resting in this position, it is said to be seated. When a valve is so positioned, it is closed and the opening is sealed off. When the valve is pushed off its seat, it is opened. The valves in the cylinder are closed part of the time and opened part of the time. One of the valves, called the intake valve, opens to admit a mixture of fuel and air into the cylinder. The other valve, called the exhaust valve, opens to allow the escape of burned gases after the fuel and air mixture has burned. Valves are opened by the camshaft rotation and closed by a spring. Figure 1-5. Intake and Exhaust Valves. (5) Camshaft. The camshaft is designed to open the intake valve at the beginning of the intake stroke and hold it open long enough to obtain the most efficient filling of the cylinder. Likewise, the camshaft opens the exhaust valve at the beginning of the exhaust stroke and holds it open long enough to obtain the most efficient emptying of the cylinder. In most engines, the lobes on the camshaft are designed to open the valves smoothly and gradually. This avoids shock to the valves and allows quietness of operation. The final design is usually a compromise between efficiency and quiet operation. When the cam lobe rotates out of the way, the valve is closed and held closed by spring pressure. In four-stroke engines, each valve is opened every other revolution of the crankshaft, so the camshaft is geared to run at one-half the crankshaft speed. 7 OD0610 2. Classification of Engines. Automotive engines may be classified according to the type of fuel used, type of cooling system employed, or valve and cylinder arrangement. They all operate on the same basic principles, and are constructed to meet the needs of the system it will be used for. a. Fuel. (1) Gas. A hydrocation, obtained from petroleum, that is suitable as an internal combustion engine fuel. (2) Diesel. The substance that is burned to produce heat and create motion of the piston on the power stroke in an engine. b. Cooling. Engines are classified as to whether they are air- or liquid- cooled. All engines are cooled by air to some extent, but air-cooled engines are those in which air is the only external cooling medium. Lubricating oil and fuel help cool engine parts, but there must be an additional external means of dissipating the absorbed heat. (1) Air-Cooled. Air-cooled engines are used extensively in military vehicles as well as in aircraft. This type is used where there must be an economy of space and weight.