Week 3.2 LECTURE AMT 214 Piston Engine Construction PDF

AMT 214 PISTON ENGINE LECTURE 3.2 PISTON ENGINE CONSTRUCTION OBJECTIVES: To determine the important parts of a piston engine. To know the importance and uses of each part during the operation of the engine. PISTON ENGINE – ENGINE CONSTRUCTION The basic major...

AMT 214 PISTON ENGINE LECTURE 3.2 PISTON ENGINE CONSTRUCTION OBJECTIVES: To determine the important parts of a piston engine. To know the importance and uses of each part during the operation of the engine. PISTON ENGINE – ENGINE CONSTRUCTION The basic major components of a reciprocating engine are the : 1. Crankcase 2. Cylinders 3. Pistons 4. Connecting rods 5. Crankshaft 6. Valves 7. Valve operating mechanism CRANKCASE The foundation of an engine is the crankcase. It contains the bearings and bearing supports in which the crankshaft revolves. Cast or forged aluminum alloy is generally used for crankcase construction because it is light and strong.  In addition to the transverse webs that support the main bearings, a set of camshaft bosses are typically cast into a crankcase. These bosses support the camshaft which is part of the valve operating mechanism. ACCESSORY SECTION The accessory (rear) section usually is of cast construction and the material may be either aluminum alloy, which is used most widely, or magnesium, which has been used to some extent. RADIAL ENGINE CRANKCASE In general, a typical radial engine crankcase separates into four main sections: the nose section, the power section, the supercharger section, and the accessory section. RADIAL ENGINE THE FOUR BASIC POWER DELIVERING PARTS: Cylinder Piston Connecting Rod Crankshaft CYLINDERS The part of the engine in which power is being developed. Four major factors in the design and construction of the cylinder assembly : 1. Be strong enough to withstand the internal pressures. 2. Be constructed of a lightweight metal. 3. Have good heat-conducting properties. 4. Be comparatively easy and inexpensive to manufacture, inspect, and maintain. CYLINDER HEADS The purpose of the cylinder head is to provide a place for combustion of the fuel/air mixture and to give the cylinder more heat conductivity for adequate cooling. The cylinder head of an air-cooled engine is generally made of aluminum alloy because aluminum alloy is a good conductor of heat and its light weight reduces the overall engine weight. PISTONS The piston in a reciprocating engine is a cylindrical plunger that moves up and down, back and forth within a cylinder. Two Primary functions of a Piston : 1. It draws fuel and air into a cylinder, compress the gases, and purge burned exhaust gases from the cylinder. 2. they transmit the force produced by combustion to the crankshaft. Usually made of aluminum alloy AMS 4140 for forged pistons Alcoa 132 alloy for cast pistons. Piston temperature may exceed 4000°F and pressures may be as high as 500 psi or up. PARTS OF A PISTON Piston Head Piston Head - The piston's top surface is called the piston head and is directly exposed to the heat of combustion. Ring Land Ring Grooves - Is a cut into a piston's Ring outside surface to hold a set of piston Grooves rings. As many as six ring grooves may be machined around a piston. Piston pin Ring Land - The portion of the piston between the ring grooves. boss Piston Skirt Piston pin boss - Is an enlarged area inside the piston that provides additional bearing area for a piston pin to attach the piston to a connecting rod. Piston Skirt- Help align a piston in a cylinder, the piston base is extended to form the piston skirt. PISTON HEAD DESIGNS CAM-GROUND PISTON All pistons expand as they heat up and can cause a piston to take on an oblong, or oval shape, at normal engine operating temperatures, resulting in uneven piston and cylinder wear. A cam ground piston is machined with a slightly oval shape. That is, the diameter of the piston parallel to the piston boss is slightly less than the diameter perpendicular to the piston boss. PISTON ATTACHMENTS Piston rings - perform three functions in aircraft reciprocating engines 1. They prevent leakage 2. Reduce oil seepage 3. transfer heat from the piston to the cylinder walls. Piston pin - The piston pin joins the piston to the connecting rod and sometimes called a wristpin. Piston pin circlip - Is a small component that holds the piston pin in place when the piston pin is attached in the piston pin boss. PISTON RING JOINTS Butt Joint Step Joint Angle Joint TYPES OF PISTON RINGS: Compression rings Oil rings COMPRESSION RINGS Compression rings - Compression rings prevent gas from escaping past the piston during engine operation and are placed in the ring grooves immediately below the piston head. COMPRESSOR RING CROSS- SECTION DESIGNS Of the three different ring cross sections, the tapered face presents the narrowest bearing edge to the cylinder wall to help reduce friction and hasten ring seating. OIL RINGS Oil rings control the amount of oil that is applied to the cylinder walls as well as prevent oil from entering the combustion chamber. Types of Oil Rings: 1. Oil control rings 2. Oil scraper ring OIL CONTROL RINGS The primary purpose of oil control rings is to regulate the thickness of the oil film on the cylinder wall. To allow an oil control ring to remove excess oil and return it to the crankcase, small holes are drilled in the piston ring grooves, or ring lands. OIL SCRAPER RINGS This ring is used to regulate the amount of oil that passes between the piston skirt and the cylinder wall. Sometimes called an oil wiper ring, usually has a beveled face and is installed in a ring groove at the bottom of the piston skirt.