AMT 613 A/C Powerplant I (Reciprocating Engine) PDF

A/C POWERPLANT I (RECIPROCATING ENGINE) POWERPLANT - are sources of power. ▪ HYDRO-ELECTRIC POWERPLANT ▪ THERMAL POWERPLANT ▪ NUCLEAR POWERPLANT ▪ WINDMILL. ENGINE- are devices that convert one form of energy to other. An engine or motor is a machine designed to convert energy i...

A/C POWERPLANT I (RECIPROCATING ENGINE) POWERPLANT - are sources of power. ▪ HYDRO-ELECTRIC POWERPLANT ▪ THERMAL POWERPLANT ▪ NUCLEAR POWERPLANT ▪ WINDMILL. ENGINE- are devices that convert one form of energy to other. An engine or motor is a machine designed to convert energy into useful mechanical motion. ▪ Heat engines, including internal combustion engines and external combustion engines (such as steam engines) burn a fuel to create heat, which then creates force. ▪ Electric motors converts electrical energy into mechanical motion ▪ Pneumatic motors use compressed air. WHAT IS THE PURPOSE OF AIRCRAFT ENGINE?  TO PROVIDE THRUST -It is the force that propels an airplane forward through the air. BRIEF HISTORY IN AIRCRAFT POWERPLANT In the 1st century, Hero of Alexandria demonstrates a steam-powered spinning sphere called an Aeolipile. ▪ Pistons in cylinders first saw use in steam engines. Scotland's James Watt crafted the first good ones during the 1770s. ▪ A century later, the German inventors Nicolaus Otto and Gottlieb Daimler introduced gasoline as the fuel, burned directly within the cylinders. ▪ Such motors powered the earliest automobiles. They were lighter and more mobile than steam engines, more reliable, and easier to start. ▪ Some single-piston gasoline engines entered service, but for use with airplanes, most such engines had a number of pistons, each shuttling back and forth within its own cylinder. ▪ Each piston also had a connecting rod, which pushed on a crank that was part of a crankshaft. ▪ This crankshaft drove the propeller. ▪ In 1862, Nicolaus Otto was the first to build and sell the engine. ▪ He designed an indirect- acting free-piston compression less engine whose greater efficiency won the support of Eugen Langen and then most of the market, which at that time was mostly for small stationary engines fueled by lighting gas.  A 1920s era American Otto Engine for Stationary Use The Otto/Langen Atmospheric 1885 Daimler's Engine of 1867 Petroleum Reitwagen First Use in Transportation ▪ The Otto & Langen engine was a free piston atmospheric engine (the explosion of gas was used to create a vacuum and the power came from atmospheric pressure returning the piston). ▪ It is the engine (the Otto Silent Engine), and not the Otto & Langen engine, to which the Otto cycle refers. This was the first commercially successful engine to use in-cylinder compression (as patented by William Barnett in 1838). ▪ George Brayton, developed a two-stroke kerosene engine ▪ (it used two external pumping cylinders). However, it was considered the first safe and practical oil engine. ▪ Otto and his manager Gottlieb Daimler had a major disagreement on the future direction of the Otto engine. ▪ While Otto wanted to produce large engines for stationary applications Daimler wanted to produce engines small enough to be used in transportation. ▪ Gustav Otto, the son of inventor and industrialist Nicolaus August Otto, was a pioneer aviator in Bavaria. ▪ His company was one of the foundation of the Bayerische Flugzeugwerke (BFW) which will later be known as Bayerische Motoren Werke (BMW). ▪ The blue and white panels of the Bavarian national flag were placed at the center of the BMW logo. Not until the late 1920s was the logo lent a new interpretation as representing a rotating propeller. 1885 ▪ Karl Benz builds a three-wheel automobile powered by a gasoline engine. 1887 ▪ Henry Ford builds his first automobile in Michigan. 1887 ▪ Gottlieb Daimler uses his internal combustion engine to build a four-wheel vehicle, considered the first modern automobile. ▪ In 1892, Dr. Rudolf Diesel developed his Carnot heat engine type motor ▪ 1893 February 23rd , Rudolf Diesel received a patent for his compression ignition (diesel) engine. ▪ 1900, Rudolf Diesel demonstrated the diesel engine in the 1900 Exposition Universelle (Worlds Fair) using peanut oil fuel. ▪ The diesel engine has the benefit of running more fuel-efficiently than gasoline engines due to much higher compression ratios and longer duration of combustion, which means the temperature rises more slowly, allowing more heat to be converted to mechanical work. ▪ In 1903, the Wright Brothers flew, The Flyer, with a 12 horse power gas powered engine. ▪ From 1903, the year of the Wright Brothers first flight, to the late 1930s the gas powered reciprocating internal-combustion engine with a propeller was the sole means used to propel aircraft. Combustion engines are heat engines driven by the heat of a combustion process. "Combustion" refers to burning fuel with an oxidizer, to supply the heat. ▪ The Internal Combustion Engine is an engine in which the combustion of a fuel (generally, fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. ▪ In an internal combustion engine, the expansion of the high temperature and high pressure gases (which are produced by the combustion) directly applies force to components of the engine (such as the pistons or turbine blades or a nozzle) and by moving it over a distance, generates useful mechanical energy. ▪ Aircraft require thrust to produce enough speed for the wings to provide lift or enough thrust to overcome the weight of the aircraft for vertical takeoff. ▪ All aircraft engines must meet certain general requirements of efficiency, economy, and reliability. ▪ Aircraft engines can be classified by several methods. ▪ They can be classed by operating cycles, cylinder arrangement, or the method of thrust production. All are heat engines that convert fuel into heat energy that is converted to mechanical energy to produce thrust. ▪ Most of the current aircraft engines are of the internal combustion type because the combustion process takes place inside the engine. ▪ Aircraft engines come in many different types, such as gas turbine based, reciprocating piston, rotary, two or four cycle, spark ignition, diesel, and air or water cooled. ▪ An inline engine generally has an even number of cylinders, although some three-cylinder engines have been constructed. ▪ This engine may be either liquid cooled or air cooled and has only one crank shaft, which is located either above or below the cylinders. ▪ If the engine is designed to operate with the cylinders below the crankshaft, it is called an inverted engine. Walter LOM 210-hp engine installation in the STOL CH 801 (4/00) ▪ The opposed-type engine has two banks of cylinders directly opposite each other with a crankshaft in the center. ▪ The pistons of both cylinder banks are connected to the single crankshaft. ▪ Although the engine can be either liquid cooled or air cooled, the air-cooled version is used predominantly in aviation. ▪ It is generally mounted with the cylinders in a horizontal position. Continental Engines. Continental O-200-D O-320-H2AD, C172, ▪ In V-type engines, the cylinders are arranged in two in-line banks generally set 60° apart. ▪ Most of the engines have 12 cylinders, which are either liquid cooled or air cooled. ▪ This type of engine was used mostly during the second World War and its use is mostly limited to older aircraft. The Liberty L-12 V-12 ▪ The radial engine consists of a row, or rows, of cylinders arranged radially about a central crankcase. ▪ This type of engine has proven to be very rugged and dependable. ▪ The number of cylinders which make up a row may be three, five, seven, or nine. ▪ Radial engines are still used in some older cargo planes, war birds, and crop spray planes. Although many of these engines still exist, their use is limited. Radial Engine on a PT17 Stearman bi-plane  RECIPROCATING ENGINES ❑The basic major components of a reciprocating engine are the crankcase, cylinders, pistons, connecting rods, valves, valve-operating mechanism, and crankshaft. ❑In the head of each cylinder are the valves and spark plugs. ❑One of the valves is in a passage leading from the induction system; the other is in a passage leading to the exhaust system. ❑Inside each cylinder is a movable piston connected to a crankshaft by a connecting rod. ❑The foundation of an engine is the crankcase. ❑It contains the bearings and bearing supports in which the crankshaft revolves. ❑It also provides support for attachment of the cylinder assemblies, and the powerplant to the aircraft ▪ It is cast in one piece and provided with means for mounting the accessories, such as magnetos, carburetors, fuel, oil, vacuum pumps, starter, generator, tachometer drive, etc., in the various locations required to facilitate accessibility. ❑The crankshaft is the backbone of the reciprocating engine. ❑The crankshaft is carried in a position parallel to the longitudinal axis of the crankcase and is generally supported by a main bearing between each throw. ❑Its main purpose is to transform the reciprocating motion of the piston and connecting rod into rotary motion for rotation of the propeller. ▪ Crankshaft has three main parts journal, crankpin, and crank cheek. ▪ Counterweights and dampers, although not a true part of a crankshaft, are usually attached to it to reduce engine vibration. ▪ The journal is supported by, and rotates in, a main bearing. ▪ It serves as the center of rotation of the crankshaft. It is surface hardened to reduce wear. The crankpin is the section to which the connecting rod is attached. ▪ It is off-center from the main journals and is often called the throw. Two crank cheeks and a crankpin make a throw ▪ Excessive vibration in an engine not only results in fatigue failure of the metal structures, but also causes the moving parts to wear rapidly. ▪ In some instances, excessive vibration is caused by a crankshaft that is not balanced. ▪ A crankshaft is statically balanced when the weight of the entire assembly of crankpins, crank cheeks, and counterweights is balanced around the axis of rotation. ▪ When checked for static balance, it is placed on two knife edges. If the shaft tends to turn toward any one position during the test, it is out of static balance. ❑The connecting rod is the link that transmits forces between the piston and the crankshaft. ❑Connecting rods must be strong enough to remain rigid under load and yet be light enough to reduce the inertia forces that are produced when the rod and piston stop, change direction, and start again at the end of each stroke. ❑The piston of a reciprocating engine is a cylindrical member which moves back and forth within a steel cylinder. ❑The piston acts as a moving wall within the combustion chamber. ❑As the piston moves down in the cylinder, it draws in the fuel/air mixture. As it moves upward, it compresses the charge, ignition occurs, and the expanding gases force the piston downward. ❑This force is transmitted to the crankshaft through the connecting rod. ❑The piston pin joins the piston to the connecting rod. ❑The piston pin used in modern aircraft engines is the full- floating type, so called because the pin is free to rotate in both the piston and in the connecting rod piston-pin bearing. ❑The piston pin must be held in place to prevent the pin ends from scoring the cylinder walls ❑The piston rings prevent leakage of gas pressure from the combustion chamber and reduce to a minimum the seepage of oil into the combustion chamber. ❑The rings fit into the piston grooves but spring out to press against the cylinder walls; when properly lubricated, the rings form an effective gas seal. ❑The purpose of the compression rings is to prevent the escape of combustion gases past the piston during engine operation. ❑They are placed in the ring grooves immediately below the piston head. ❑Oil control rings are placed in the grooves immediately below the compression rings and above the piston pin bores. ❑There may be one or more oil control rings per piston; two rings may be installed in the same groove, or they may be installed in separate grooves. ❑If too much oil enters the combustion chamber, it burns and leaves a thick coating of carbon on the combustion chamber walls, the piston head, the spark plugs, and the valve heads. ❑The portion of the engine in which the power is developed is called the cylinder. ❑The cylinder provides a combustion chamber where the burning and expansion of gases take place, and it houses the piston and the connecting rod. ▪ This carbon can cause the valves and piston rings to stick if it enters the ring grooves or valve guides. In addition, the carbon can cause spark plug misfiring as well as detonation, preignition, or excessive oil consumption. ▪ There are four major factors that need to be considered in the design and construction of the cylinder assembly. It must: 1. Be strong enough to withstand the internal pressures developed during engine operation. 2. Be constructed of a lightweight metal to keep down engine weight. 3. Have good heat-conducting properties for efficient cooling. 4. Be comparatively easy and inexpensive to manufacture, inspect, and maintain.  ❑The cylinder used in the air cooled engine is the overhead valve type. ❑Each cylinder is an assembly of two major parts: cylinder head and cylinder barrel Cutaway view of the cylinder assembly. ❑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 fuel/air mixture is ignited by the spark in the combustion chamber and commences burning as the piston travels toward top dead center (top of its travel) on the compression stroke. ▪ The cylinder barrel in which the piston operates must be made of a high-strength material, usually steel. ▪ It must be as light as possible, yet have the proper characteristics for operating under high temperatures. ❑The firing order of an engine is the sequence in which the power event occurs in the different cylinders. ❑The firing order is designed to provide for balance and to eliminate vibration to the greatest extent possible. ❑For a reciprocating engine to operate properly, each valve must open at the proper time, stay open for the required length of time, and close at the proper time. ❑Intake valves are opened just before the piston reaches top dead center, and exhaust valves remain open after top dead center. ❑At a particular instant, therefore, both valves are open at the same time (end of the exhaust stroke and beginning of the intake stroke). ❑This valve overlap permits better volumetric efficiency and lowers the cylinder operating temperature. ❑This timing of the valves is controlled by the valve- operating mechanism and is referred to as the valve timing. Valve-operating mechanism (opposed engine). ❑The fuel/air mixture enters the cylinders through the intake valve ports, and burned gases are expelled through the exhaust valve ports. ❑The head of each valve opens and closes these cylinder ports. ❑The valves are also typed by their shape and are called either mushroom or tulip because of their resemblance to the shape of these plants Neck ❑The valve mechanism of an opposed engine is operated by a camshaft. ❑The camshaft is driven by a gear that mates with another gear attached to the crankshaft. ❑The camshaft always rotates at one- half the crankshaft speed. ❑As the camshaft revolves, the lobes cause the tappet assembly to rise in the tappet guide, transmitting the force through the push rod and rocker arm to open the valve. ▪ The function of the tappet assembly is to convert the rotational movement of the cam lobe into reciprocating motion and to transmit this motion to the push rod, rocker arm, and then to the valve tip, opening the valve at the proper time. The tappet assembly consists of: 1. A cylindrical tappet, which slides in and out in a tappet guide installed in one of the crankcase sections around the cam ring 2. A tappet roller, which follows the contour of the cam ring and lobes 3. A tappet ball socket or push rod socket 4. A tappet spring. ❑Solid lifters or cam followers generally require the valve clearance to be adjusted manually by adjusting a screw and lock nut. ❑Valve clearance is needed to assure that the valve has enough clearance in the valve train to close completely. ❑This adjustment or inspection was a continuous maintenance item until hydraulic lifters were used. ▪ Some aircraft engines incorporate hydraulic tappets that automatically keep the valve clearance at zero, eliminating the necessity for any valve clearance adjustment mechanism. ▪ When the engine valve is closed, the face of the tappet body (cam follower) is on the base circle or back of the cam. ▪ The light plunger spring lifts the hydraulic plunger so that its outer end contacts the push rod socket, exerting a light pressure against it, thus eliminating any clearance in the valve linkage. ▪ As the plunger moves outward, the ball check valve moves off its seat. Oil from the supply chamber, which is directly connected with the engine lubrication system, flows in and fills the pressure chamber. As the camshaft rotates, the cam pushes the tappet body and the hydraulic lifter cylinder outward. ❑The push rod, tubular in form, transmits the lifting force from the valve tappet to the rocker arm. A hardened-steel ball is pressed over or into each end of the tube. ❑One ball end fits into the socket of the rocker arm. ❑ In some instances, the balls are on the tappet and rocker arm, and the sockets are on the push rod. ❑It permits the engine lubricating oil under pressure to pass through the hollow rod and the drilled ball ends to lubricate the ball ends, rocker-arm bearing, and valve- stem guide. ❑The push rod is enclosed in a tubular housing that extends from the crankcase to the cylinder head, referred to as push rod tubes. ❑The rocker arms transmit the lifting force from the cams to the valves. ❑Rocker arm assemblies are supported by a plain, roller, or ball bearing, or a combination of these, which serves as a pivot. Generally, one end of the arm bears against the push rod and the other bears on the valve stem. ❑The arm may have an adjusting screw, for adjusting the clearance between the rocker arm and the valve stem tip. ❑Each valve is closed by two or three helical springs. If a single spring were used, it would vibrate or surge at certain speeds. ❑To eliminate this difficulty, two or more springs (one inside the other) are installed on each valve. ❑Each spring vibrates at a different engine speed and rapid damping out of all spring- surge vibrations during engine operation results. ❑Two or more springs also reduce danger of weakness and possible failure by breakage due to heat and metal fatigue. ❑A bearing is any surface which supports, or is supported by, another surface. ❑A good bearing must be composed of material that is strong enough to withstand the pressure imposed on it and should permit the other surface to move with a minimum of friction and wear. ❑Bearings are required to take radial loads, thrust loads, or a combination of the two. ❑The vast majority of certified aircraft reciprocating engines operate on the four-stroke cycle, sometimes called the Otto cycle after its originator, a German physicist ❑In this type of engine, four strokes are required to complete the required series of events or operating cycle of each cylinder. ❑During the intake stroke, the piston is pulled downward in the cylinder by the rotation of the crankshaft. ❑This reduces the pressure in the cylinder and causes air under atmospheric pressure to flow through the carburetor, which meters the correct amount of fuel. ❑The fuel/air mixture passes through the intake pipes and intake valves into the cylinders. ❑The quantity or weight of the fuel/air charge depends upon the degree of throttle opening. ❑After the intake valve is closed, the continued upward travel of the piston compresses the fuel/air mixture to obtain the desired burning and expansion characteristics. ❑The charge is fired by means of an electric spark as the piston approaches TDC. ❑The time of ignition varies from 20° to 35° before TDC, depending upon the requirements of the specific engine to ensure complete combustion of the charge by the time the piston is slightly past the TDC position. ❑As the piston moves through the TDC position at the end of the compression stroke and starts down on the power stroke ❑As the piston is forced downward during the power stroke by the pressure of the burning gases exerted upon it, the downward movement of the connecting rod is changed to rotary movement by the crankshaft. ❑Then, the rotary movement is transmitted to the propeller shaft to drive the propeller. ▪ As the piston travels through BDC at the completion of the power stroke and starts upward on the exhaust stroke, it begins to push the burned exhaust gases out the exhaust port.