AVIA-1065 Week 3 Study Guide 23F PDF

RECIPROCATING ENGINE Intro 1 Fuel-Injection Systems AVIA-1065 2  Fuel-Injection Systems have many advantages over a conventional carburetor system:...

RECIPROCATING ENGINE Intro 1 Fuel-Injection Systems AVIA-1065 2  Fuel-Injection Systems have many advantages over a conventional carburetor system: less danger of induction system icing since the drop in temperature due to fuel vaporization takes place in or near the cylinder improved acceleration-positive action of the injection system improved fuel distribution-this reduces the overheating of individual cylinders often caused by variation in mixture due to uneven distribution better fuel economy than a system in which the mixture to most cylinders must be richer than necessary so that the cylinder with the leanest mixture operates properly Fuel-Injection Systems 3 Bendix/Precision Fuel- AVIA-1065 Injection System 4 Bendix/Precision Fuel- consists of: – an injector Injection System – a flow divider – fuel discharge nozzles It is a continuous-flow system – measures engine air consumption – uses airflow forces to control fuel flow to the engine the fuel distribution system to the individual cylinders is obtained by the use of: – a fuel flow divider – air bleed nozzles 5 Bendix/Precision Fuel-Injection System Fuel Injector the assembly consists of: – an airflow section – a regulator section – a fuel metering section some are equipped with an automatic mixture control unit 6 Bendix/Precision Fuel- Injection System Airflow Section airflow consumption of the engine is measured by sensing: impact pressure venturi throat pressure in the throttle body – movement of the throttle valve causes a change in engine air consumption – this results in a change in the air velocity in the venturi – the pressure on the left of the diaphragm is lowered due to the drop in pressure at the venturi throat 7 Bendix/Precision Fuel- Injection System Airflow Section when airflow through the engine increases the diaphragm moves to the left opening the ball valve contributing to this force is the impact pressure that is picked up by the impact tubes [Figure 2-32] 8 Bendix/Precision Fuel- Injection System Airflow Section this pressure differential is referred to as the “air metering force” accomplished by channeling the impact and venturi suction pressures to opposite sides of a diaphragm 9  Regulator Section consists of: a fuel diaphragm opposes the air metering force fuel inlet pressure is applied to one side metered fuel pressure is applied to the other side the differential pressure across the fuel diaphragm is called the “fuel metering force” the fuel pressure shown on the ball side of the fuel diaphragm is the pressure after the fuel has passed through the fuel strainer and the manual mixture control rotary plate and is referred to as metered fuel pressure fuel inlet pressure is applied to the opposite side of the fuel diaphragm Bendix/Precision Fuel- Injection System 10 Bendix/Precision Fuel- Regulator Section Injection System a ball valve is attached to the fuel diaphragm controls the orifice opening and fuel flow through the forces placed on it [Figure 2-33] the distance it opens is determined by the difference between the pressures acting on the diaphragms this difference in pressure is proportional to the airflow through the injector 11 Bendix/Precision Fuel- Regulator Section Injection System the volume of airflow determines the rate of fuel flow the difference in pressure created by the venturi is insufficient to accomplish consistent regulation of the fuel under low power settings a constant-head idle spring is incorporated to provide a constant fuel differential pressure this allows an adequate fuel flow in the idle range 12 Bendix/Precision Fuel- Injection System Fuel Metering Section attached to the air metering section contains: an inlet fuel strainer a manual mixture control valve an idle valve is connected to the throttle valve by means of an external adjustable link the main metering jet [Figure 2-34] a power enrichment jet in some injector models 13 Bendix/Precision Fuel- Injection System Fuel Metering Section the manual mixture control valve produces full rich condition when the lever is against the rich stop progressively leaner mixture as the lever is moved toward idle cutoff may be adjusted externally to meet individual engine requirements 14 Bendix/Precision Fuel- Injection System Fuel Metering Section purpose: to meter and control 15 the fuel flow to the flow divider [Figure 2-35]  Flow Divider The metered fuel is delivered from the fuel control unit to a pressurized flow Bendix/Precision Fuel- divider. This unit keeps metered fuel under pressure, divides fuel to the various cylinders at all engine speeds, and shuts off the individual nozzle lines Injection System when the control is placed in idle cutoff. http://www.precisionairmotive.com/Publications/15-812_b.pdf 16 Bendix/Precision Fuel- Flow Divider Injection System Referring to the diagram in Figure 2-36, metered fuel pressure enters the flow divider through a channel that permits fuel to pass through the inside diameter of the flow divider needle. At idle speed, the fuel pressure from the regulator must build up to overcome the spring force applied to the diaphragm and valve assembly. This moves the valve upward until fuel can pass out through the annulus of the valve to the fuel nozzle 17 Bendix/Precision Fuel- Flow Divider [Figure 2-37] Since the regulator meters and delivers a Injection System fixed amount of fuel to the flow divider, the valve opens only as far as necessary to pass this amount to the nozzles. At idle, the opening required is very small; the fuel for the individual cylinders is divided at idle by the flow divider. As fuel flow through the regulator is increased above idle requirements, fuel pressure builds up in the nozzle lines. This pressure fully opens the flow divider valve, and fuel distribution to the engine 18 becomes a function of the discharge nozzles  Flow Divider A fuel pressure gauge, calibrated in pounds per hour fuel flow, can be used as Bendix/Precision Fuel- a fuel flow meter with the Bendix RSA injection system. This gauge is connected to the flow divider and senses the pressure being applied to the Injection System discharge nozzle This pressure is in direct proportion to the fuel flow and indicates the engine power output and fuel consumption 19 Bendix/Precision Fuel- Injection System Fuel Discharge Nozzles air bleed configuration 20 Bendix/Precision Fuel- Fuel Discharge Nozzles Injection System air bleed configuration one nozzle for each cylinder located in the cylinder head outlet is directed into the intake port incorporates a calibrated jet 21 jet size is determined by the available fuel inlet pressure and the maximum fuel flow required by the engine fuel is discharged through this jet into an ambient air pressure chamber within the nozzle assembly Bendix/Precision Fuel- Injection System Fuel Discharge Nozzles 22 Bendix/Precision Fuel- Injection System Fuel Discharge Nozzles before entering the individual intake valve chambers fuel is mixed with air to aid in atomizing the fuel fuel pressure, before the individual nozzles, is in direct proportion to fuel flow a simple pressure gauge can be calibrated in fuel flow in gallons per hour or lbs per hour and be employed as a flowmeter Engines modified with turbosuperchargers must use shrouded nozzles By the use of an air manifold, these nozzles are vented to the injector air inlet pressure. 23 Bendix/Precision Fuel-Injection System Continental/TCM Fuel- Injection System AVIA-1065 25 Continental/TCM Fuel-Injection System Continental/TCM Fuel-Injection System injects fuel into the intake valve port in each cylinder head [Figure 2-39] Continental/TCM Fuel-Injection System Continental/TCM Fuel-Injection System consists of: a fuel injector pump a control unit a fuel manifold a fuel discharge nozzle is a continuous-flow system controls fuel flow to match engine airflow permits the use of a rotary vane pump does not require timing to the engine  Fuel-Injection Pump a positive-displacement, rotary-vane type with a splined shaft for connection to the accessory drive system of the engine [Figure 2-40] Continental/TCM Fuel- Injection System 28  Fuel-Injection Pump a spring-loaded, diaphragm-type relief valve is provided the relief valve diaphragm chamber is vented to atmospheric pressure a check valve is also provided boost pump pressure to the system can bypass the engine- driven pump for starting this feature also suppresses vapor formation under high ambient temperatures of the fuel, and permits use of the auxiliary pump as a source of fuel pressure in the event of Continental/TCM Fuel- engine driven pump failure Injection System 29 Continental/TCM Fuel- Fuel-Injection Pump Injection System the use of an engine driven fuel pump means changes in engine speed affect total pump flow proportionally since the pump provides greater capacity than is required by the engine, a recirculation path is required by arranging a calibrated orifice and relief valve in this path, the pump delivery pressure is also maintained in proportion to engine speed these provisions assure proper pump pressure and fuel delivery for all engine operating speeds 30  Fuel-Injection Pump the process: fuel enters at the swirl well of the vapor separator vapor is separated by a swirling motion so that only liquid fuel is delivered to the pump the vapor is drawn from the top center of the swirl well by a small pressure jet of fuel it is then directed into the vapor return line this line carries the vapor Continental/TCM Fuel- back to the fuel tank Injection System 31 Continental/TCM Fuel- Fuel/Air Control Unit function: Injection System controls engine air intake to control and to set the metered fuel pressure for proper fuel/air ratio air throttle mounted at the manifold inlet and its butterfly valve positioned by the throttle control in the aircraft controls the flow of air to the engine [Figure 2- 42] 32 Continental/TCM Fuel- Fuel/Air Control Unit Injection System air throttle assembly: an aluminum casting which contains: the shaft the butterfly-valve assembly casting bore size tailored to the engine size no venturi or other restriction is used 33  Fuel Control Assembly Continental/TCM parts: – Body made of bronze for best bearing action with the stainless steel valves Fuel-Injection – central bore contains a metering valve at one end and a mixture control valve at the other System end – each stainless steel rotary valve includes a groove which forms a fuel chamber  Fuel Control Assembly Continental/TCM control lever Fuel-Injection mounted on the mixture control valve shaft connected to the cockpit mixture control System Fuel enters the control unit through a strainer  Fuel Control Assembly Continental/TCM passes to the metering valve [Figure 2-43] this rotary valve has a camshaped edge on the outer part of the end Fuel-Injection face the position of the cam at the fuel delivery port controls the fuel passed to the: System 1.manifold valve 2. nozzles 36  Fuel Control Assembly Continental/TCM returns through the fuel return port connects to the return passage of the center metering plug Fuel-Injection the alignment of the mixture control valve with this passage determines the amount of fuel returned to the fuel pump the fuel flow is properly proportioned to airflow for the correct System fuel/ air ratio by connecting the metering valve to the air throttle 37  Fuel Manifold Valve Continental/TCM Fuel- contains: a fuel inlet Injection System a diaphragm chamber diaphragm spring-loaded operates a valve in the central bore of the body moved by fuel-fuel pressure provides the force for moving the diaphragm enclosed by a cover that retains the diaphragm loading spring fine screen is installed in the diaphragm chamber that all incoming fuel must pass 38 through Continental/TCM Fuel- Fuel Manifold Valve a fuel-injection control valve Injection System – the fuel lines to the cylinders are closed off when the valve is down against the lapped seat in the body which is drilled for passage of fuel from the diaphragm chamber to its base – a ball valve is installed within the valve – fuel is delivered to the fuel manifold valve and provides a central point for dividing fuel flow to the individual cylinders 39 Continental/TCM Fuel- Injection System Fuel Manifold Valve outlet ports for the lines to the individual nozzles [Figure 2-44] a plunger valve raised or lowered by a diaphragm to open or close the individual cylinder fuel supply ports simultaneously 40 Continental/TCM Fuel- Injection System Fuel Discharge Nozzle located in the cylinder head outlet directed into the intake port contains a drilled central passage with a counterbore at each end. [Figure 2- 45] 41  Fuel Discharge Nozzle lower end is used as a chamber for fuel/air mixing before the spray leaves the nozzle upper bore contains a removable orifice for calibrating the nozzles Nozzles are calibrated in several ranges, and all nozzles furnished for one engine are of the same range and are identified by a letter stamped on the hex of the nozzle body Drilled radial holes connect the upper counterbore with the outside of the nozzle body Continental/TCM Fuel- Injection System 42  Fuel Discharge Nozzle These holes enter the counterbore above the orifice and draw air through a cylindrical screen fitted over the nozzle body. A shield is press-fitted on the nozzle body and extends over the greater part of the filter screen, leaving an opening near the bottom. This provides both mechanical protection and an abrupt change in the direction of airflow which keeps dirt and foreign material out of the nozzle Continental/TCM Fuel- interior. Injection System 43 Carburetor Maintenance AVIA-1065 44 Carburetor Maintenance Carburetor Removal The procedures are generally much the same make sure the fuel shutoff (or selector) valve is closed disconnect the throttle and mixture control linkages lockwire the throttle valve in the closed position 45 Carburetor Maintenance disconnect: the fuel inlet line all vapor return lines all gauge lines all primer lines DO NOT alter the rigging of the throttle and mixture controls if the same carburetor is to be reinstalled remove the air scoop or air scoop adapter remove the air screens and gaskets from the carburetor remove the nuts and washers securing the carburetor to the engine remove the carburetor https://www.youtube.com/watch?v=MiO- 3vplZis 46 Carburetor Maintenance use extreme care to ensure that nothing is dropped into the engine when removing a downdraft carburetor immediately install a protective cover on the carburetor mounting flange of the engine to prevent small parts or foreign material from falling into the engine plug open fuel lines using the proper cover fittings when there is danger of foreign material entering them during removal or installation of the carburetor 47  Rigging Carburetor Controls Connect and adjust Carburetor Maintenance carburetor or fuel metering equipment throttle controls so that full movement of the throttle is obtained from corresponding full movement of the control in the cockpit Check and adjust the throttle control linkages so that springback on the throttle quadrant in the aircraft is equal in both the full-open and the full-closed position Correct any excess play or looseness of control linkage or cables Springback 48 Carburetor Maintenance Controls should be checked so that they go stop-to-stop on the carburetor Check for complete and full travel of each control 49  50 Fuel System Inspection and Maintenance Check for the presence of: sediment water slime In the drain plugs or valves in the fuel system or the filter and sump The filters or screens must be clean and free from corrosion Fuel Tank Inspect the tanks for: corrosion on the external surfaces security of attachment correct adjustment of straps and slings check the fittings and connections for leaks or failures Fuel System Inspection and Main Line Strainers Maintenance Drain water and sediment from the main line strainer at each preflight inspection Remove and clean the screen at the periods specified in the airplane maintenance manual Examine the sediment removed from the housing Particles of rubber are often early warnings of hose deterioration Check for leaks and damaged gaskets 51 Reciprocating Engine Lubrication Systems AVIA-1065  Reciprocating Engine Lubrication Systems can be divided into two basic classifications: wet sump dry sump both systems use similar types of components the dry sump system is explained as an example system because the dry sump system contains all the components of the wet Reciprocating Engine sump system Lubrication Systems 53  Reciprocating Engine Lubrication Systems can be divided into two basic classifications: Reciprocating Engine wet sump Lubrication Systems stores oil in a reservoir inside the engine it is returned to this crankcase based reservoir after the oil is circulated through the engine 54  Reciprocating Engine Lubrication Systems can be divided into two basic classifications: dry sump pumps the oil from the engine’s crankcase to an external tank that stores the oil uses: 1. a scavenge pump 2. some external tubing 3. an external tank to Reciprocating Engine store the oil Lubrication Systems 55  Reciprocating Engine Lubrication Systems Combination Splash and Pressure Lubrication The lubricating oil is distributed to the various moving parts of a typical internal combustion engine by either: pressure splash a combination of pressure and splash 56  Reciprocating Engine Lubrication Systems Combination Splash and Pressure Lubrication pressure principal method of lubricating aircraft engines advantages: – positive introduction of oil to the bearings – cooling effect-caused by the large quantities of oil that can be pumped, or circulated, through a bearing – satisfactory lubrication in various attitudes of flight 57 Reciprocating Engine Lubrication Systems Combination Splash and Pressure Lubrication splash may be used in addition to pressure lubrication on aircraft engines never used by itself aircraft-engine lubrication systems are always either the pressure type or the combination pressure and splash type usually the latter a combination of pressure and splash 58 Reciprocating Engine 59 Lubrication Systems Lubrication System Requirements must be designed and constructed so that it functions properly within all flight attitudes and all atmospheric conditions that the aircraft is expected to operate in in wet sump engines, this requirement must be met when only half of the maximum lubricant supply is in the engine the crankcase must be vented to the atmosphere to prevent leakage of oil from excessive pressure Reciprocating Engine Lubrication Systems Dry Sump Oil Systems many reciprocating and turbine aircraft engines have pressure dry sump lubrication systems the oil supply in this type of system is carried in a tank a pressure pump circulates the oil through the engine scavenger pumps then return it to the tank as quickly as it accumulates in the engine sumps 60 Reciprocating Engine Lubrication Systems Dry Sump Oil Systems the need for a separate supply tank is apparent when considering the complications that would result if large quantities of oil were carried in the engine crankcase each engine is supplied with oil from its own complete and independent system the functions of all such systems are the same 61 Reciprocating Engine Dry Sump Oil Systems Lubrication Systems the principal units in a typical reciprocating engine dry sump oil system include [Figure 6-4]: an oil supply tank an engine-driven pressure oil pump a scavenge pump an oil cooler with an oil cooler control valve oil tank vent necessary tubing pressure and temperature indicators 62 Reciprocating Engine Lubrication Systems Oil Tanks generally associated with a dry sump lubrication system a wet sump system uses the crankcase of the engine to store the oil usually constructed of aluminum alloy must withstand any: vibration inertia fluid loads https://www.youtube.com/watch?v=cWDC XFwPLIs&t=10s 63 Reciprocating Engine Oil Tanks Lubrication Systems oil tank vent lines are provided to ensure proper tank ventilation in all attitudes of flight usually connected to the engine crankcase – to prevent the loss of oil through the vents indirectly vents the tanks to the atmosphere through the crankcase breather 64 Reciprocating Engine the return line in the top of the Lubrication Systems tank is generally positioned to discharge the returned oil against the wall of the tank in a swirling motion – this method considerably reduces foaming that occurs when oil mixes with air – baffles in the bottom of the oil tank break up this swirling action – to prevent air from being drawn into the inlet line of the oil pressure pump – foaming oil increases in volume and reduces its ability to provide proper lubrication 65 Reciprocating Engine Lubrication Systems Oil Pump Oil entering the engine is pressurized, filtered, and regulated by units within the engine. They are discussed along with the external oil system to provide a concept of the complete oil system. https://youtu.be/eFe43SnBl MI 66 Reciprocating Engine Lubrication Systems Oil Pump As oil enters the engine, it is pressurized by a gear- type pump [Figure 6-6] 67 Reciprocating Engine Oil Pump This pump is a positive displacement pump that consists Lubrication Systems of two meshed gears that revolve inside the housing The clearance between the teeth and housing is small The pump inlet is located on the left and the discharge port is connected to the engine’s system pressure line One gear is attached to a splined drive shaft that extends from the pump housing to an accessory drive shaft on the engine Seals are used to prevent leakage around the drive shaft As the lower gear is rotated 68 counterclockwise, the driven idler gear turns clockwise  Oil Pump As oil enters the gear chamber, it is picked up by the gear teeth, trapped between them and the sides of the gear chamber, is carried around the outside of the gears, and discharged from the pressure port into the oil screen passage The pressurized oil flows to the oil filter, where any solid particles suspended in the oil are separated from it, preventing possible damage to moving parts Reciprocating Engine of the engine Lubrication Systems 69 Reciprocating Engine Oil Pump Lubrication Systems Oil under pressure then opens the oil filter check valve mounted in the top of the filter. This valve is used mostly with dry sump radial engines and is closed by a light spring loading of 1 to 3 pounds per square inch (psi) when the engine is not operating to prevent gravity-fed oil from entering the engine and settling in the lower cylinders or sump area of the engine If oil were allowed to gradually seep by the rings of the piston and fill the combustion chamber, it could cause a liquid lock This could happen if the valves on the cylinder were both closed and the engine was cranked for start Damage could occur to the engine 70 Reciprocating Engine Oil Pump Lubrication Systems The oil filter bypass valve, located between the pressure side of the oil pump and the oil filter, permits unfiltered oil to bypass the filter and enter the engine if the oil filter is clogged or during cold weather if congealed oil is blocking the filter during engine start The spring loading on the bypass valve allows the valve to open before the oil pressure collapses the filter; in the case of cold, congealed oil, it provides a low- resistance path around the filter. Dirty oil in an engine is better than no lubrication 71 Reciprocating Engine Lubrication Systems Oil Filters The oil filter used on an aircraft engine is usually one of four types: – Screen – Canister – spin-on – Cuno 72 Reciprocating Engine Lubrication Systems Oil Filters A screen-type filter with its double-walled construction provides a large filtering area in a compact unit. [Figure 6-6] 73 Reciprocating Engine Oil Filters Lubrication Systems As oil passes through the fine-mesh screen, dirt, sediment, and other foreign matter are removed and settle to the bottom of the housing At regular intervals, the cover is removed and the screen and housing cleaned with a solvent Oil screen filters are used mostly as suction filters on the inlet of the oil pump 74 Reciprocating Engine Oil Filters A canister housing filter Lubrication has a replaceable filter element Systems that is replaced with rest of the components other than seals and gaskets being reused [Figure 6-7] 75 Reciprocating Engine Oil Filters Lubrication Systems The filter element is designed with a corrugated, strong steel center tube supporting each convoluted pleat of the filter media, resulting in a higher collapse pressure rating. The filter provides excellent filtration, because the oil flows through many layers of locked-in-fibers 76 Reciprocating Engine Lubrication Systems Oil Filters Full flow spin-on filters are the most widely used oil filters for reciprocating engines. [Figure 6-8] 77 Reciprocating Engine Lubrication Systems Oil Filters Full flow spin-on filters 78 Reciprocating Engine Oil Filters Lubrication Systems Full flow means all the oil is normally passed through the filter the filter is positioned between the oil pump and the engine bearings filters the oil of any contaminants before they pass through the engine bearing surfaces also contains an – anti-drain back valve – pressure relief valve – all sealed in a disposable housing 79 Reciprocating Engine Lubrication Systems Oil Filters The bypass valve is used in case the filter becomes clogged The bypass valve opens to allow the oil to bypass, preventing the engine components from oil starvation 80 Reciprocating Engine Lubrication Systems Oil Pressure Regulating Valve An oil pressure regulating valve limits oil pressure to a predetermined value, depending on the installation. [Figure 6-6] 81 Reciprocating Engine 82 Lubrication Systems Oil Pressure Regulating Valve This valve is sometimes referred to as a relief valve but its real function is to regulate the oil pressure at a preset pressure level The oil pressure must be sufficiently high to ensure adequate lubrication of the engine and its accessories at high speeds and powers This pressure helps ensure that the oil film between the crankshaft journal and bearing is maintained However, the pressure must not be too high, as leakage and damage to the oil system may result Reciprocating Engine Lubrication Systems Oil Pressure Regulating Valve The oil pressure is generally adjusted by loosening the locknut and turning the adjusting screw. [Figure 6-10] 83  Oil Pressure Regulating Valve On most aircraft engines, turning the screw clockwise increases the tension of the Reciprocating Engine spring that holds the relief valve on its seat and increases the oil pressure; turning the adjusting screw counterclockwise decreases the spring tension and lowers the pressure Lubrication Systems Some engines use washers under the spring that are either removed or added to adjust the regulating valve and pressure 84 Reciprocating Engine Lubrication Systems Oil Cooler The cooler consists of a core enclosed in a double- walled shell The core is built of copper or aluminum tubes with the tube ends formed to a hexagonal shape and joined together in the honeycomb effect. [Figure 6-11] 85 Reciprocating Engine Oil Cooler Lubrication Systems The ends of the copper tubes of the core are soldered, whereas aluminum tubes are brazed or mechanically joined The tubes touch only at the ends so that a space exists 86 between them along most of their lengths This allows oil to flow through the spaces between the tubes while the cooling air passes through the tubes. Oil Change-Cessna 172 Reciprocating Engine 87 Lubrication Systems Oil Cooler The space between the inner and outer shells is known as the annular or bypass jacket Two paths are open to the flow of oil through a cooler From the inlet, it can flow halfway around the bypass jacket, enter the core from the bottom, and then pass through the spaces between the tubes and out to the oil tank This is the path the oil follows when it is hot enough to require cooling As the oil flows through the core, it is guided by baffles that force the oil to travel back and forth several times before it reaches the core outlet.  Oil Cooler The oil can also pass from the inlet completely around the bypass jacket to the outlet without passing through the core Oil follows this bypass route when the oil is cold or when the core is blocked with thick, congealed oil. Reciprocating Engine Lubrication Systems 88 Principles of Engine Lubrication AVIA-1065 89 Principles of Engine Lubrication Principles of Engine Lubrication the primary purpose of a lubricant is to reduce friction between moving parts liquid lubricants or oils are used universally in aircraft engines because they can be circulated readily in theory, fluid lubrication is based on the actual separation of the surfaces so that no metal-to-metal contact occurs 90 Principles of Engine Lubrication Principles of Engine Lubrication metallic friction is replaced by the internal fluid friction of the lubricant as long as the oil film remains unbroken friction and wear are held to a minimum under ideal conditions 91 Principles of Engine 92 Lubrication Principles of Engine Lubrication oil is generally pumped throughout the engine to all areas that require lubrication overcoming the friction of the moving parts of the engine consumes energy and creates unwanted heat (Friction HP) the reduction of friction during engine operation increases the overall potential power output Principles of Engine Lubrication engines are subjected to several types of friction Types of Friction sliding friction rolling friction wiping friction 93 Principles of Engine Lubrication sliding friction occurs when one surface slides over another the surfaces are not completely flat or smooth and have microscopic defects these defects cause friction between the two moving surfaces [Figure 6-1] found in the use of plain bearings 94 Principles of Engine Lubrication rolling friction occurs when a roller or sphere rolls over another surface such as with ball or roller bearings also referred to as antifriction bearings the amount of friction created by rolling friction is less than that created by sliding friction 95 Principles of Engine Lubrication wiping friction occurs between gear teeth pressure can vary widely loads applied to the gears can be extreme the lubricant must be able to withstand the loads 96 Principles of Engine Lubrication Functions of Engine Oil reducing friction acting as a cushion between metal parts [Figure 6-2] 97 Principles of Engine 98 Lubrication Functions of Engine Oil this cushioning effect is particularly important for such parts as: reciprocating engine crankshafts connecting rods which are subject to shock loading as the piston is pushed down on the power stroke, it applies loads between the connecting rod bearing and the crankshaft journal the load-bearing qualities of the oil must prevent the oil film from being squeezed out, causing metal-to- metal contact in the bearing Principles of Engine Lubrication Functions of Engine Oil oil cooling oil circulates through the engine it absorbs heat from the pistons and cylinder walls these components are especially dependent on the oil for cooling in reciprocating engines can account for up to 50% of the total engine cooling is an excellent medium to transfer the heat from the engine to the oil cooler 99 Principles of Engine Lubrication Functions of Engine Oil prevents leakage – the oil aids in forming a seal between the piston and the cylinder wall to prevent leakage of the gases from the combustion chamber cleaning – oils clean the engine by reducing abrasive wear by picking up foreign particles and carrying them to a filter where they are removed – the dispersant, an additive to the oil, holds the particles in suspension and allows the filter to trap them as the oil passes through the filter 100 Principles of Engine Lubrication Functions of Engine Oil prevents corrosion on the interior of the engine by leaving a coating of oil on parts when the engine is shut down one of the reasons why the 101 engine should not be shut down for long periods of time is that the coating of oil preventing corrosion will not last on the parts, allowing them to rust or corrode  Requirements and Characteristics of AVIA-1065 Reciprocating Engine Lubricants 102 Requirements and Characteristics of Reciprocating Engine there are several Lubricants important properties that satisfactory reciprocating engine oil must possess its viscosity is most important in engine operation oil that flows slowly is viscous or has a high viscosity oil that flows freely has a low viscosity 103 Requirements and Characteristics the viscosity of oil is of Reciprocating Engine affected by temperature it was not uncommon for Lubricants earlier grades of oil to become practically solid in cold weather increasing drag making circulation almost impossible other oils may become so thin at high temperatures that the oil film is broken causing a low load carrying ability resulting in rapid wear of the moving parts https://www.youtube.com/watch?v=V5a4kP-5Jiw 104 Requirements and Characteristics of Reciprocating Engine the oil selected for aircraft Lubricants engine lubrication must be: light enough to circulate freely at cold temperatures heavy enough to provide the proper oil film at engine operating temperatures it is extremely important that only the approved grade or Society of Automotive Engineers (SAE) rating be used lubricants vary in properties no one oil is satisfactory for all engines and all operating conditions 105 Requirements and Characteristics several factors must be considered in determining of Reciprocating Engine the proper grade of oil to use in an engine Lubricants the most important of which are: operating load rotational speeds operating temperatures the grade of the lubricating oil to be used is determined by: the operating conditions to be met in 106 the various types of engines  the oil used in aircraft reciprocating engines has a relatively high viscosity required by: large engine operating clearances due to: the relatively large size of the moving parts the different materials used the different rates of expansion of the various materials high operating Requirements and Characteristics temperatures high bearing pressures of Reciprocating Engine Lubricants 107 Requirements and Characteristics of Reciprocating Engine Viscosity Lubricants commercial aviation oils are generally classified by a number an approximation of the viscosity as measured by a testing instrument called the Saybolt Universal Viscosimeter 108 Requirements and Characteristics of Reciprocating Engine Lubricants Viscosity letters the letter W-occasionally is included in the SAE number giving a designation such as SAE 20W indicates that the oil is satisfactory oil for winter use in cold climates in addition to meeting the viscosity requirements at 109 the testing temperature specifications EX: 20W50 (20SAE in winter, 50 SAE in Summer) Requirements and Characteristics of Reciprocating Engine Lubricants Viscosity When W is placed in front of either: the grade weight number indicates the oil is of the ashless dispersant type Ie W100 or W100 Plus 110 Viscosity 101 Requirements and Characteristics of Reciprocating Engine Lubricants 111 Viscosity Index a number that indicates the effect of temperature changes on the viscosity of the oil when oil has a low viscosity index, the oil becomes: thin at high temperatures thick at low temperatures when oil has a high viscosity index, it has small changes in viscosity over a wide temperature range (can handle a greater temperature range) Requirements and Characteristics of Reciprocating Engine Lubricants 112 Viscosity Index the best oil for most purposes is one that maintains a constant viscosity throughout temperature changes oil having a high viscosity index resists excessive thickening when the engine is subjected to cold temperatures this allows for: rapid cranking speeds during starting prompt oil circulation during initial startup resists excessive thinning when the engine is at operating temperature provides full lubrication and bearing load protection Requirements and Characteristics of Reciprocating Engine Lubricants 113 Flash Point and Fire Point determined by laboratory tests that show Flash Point-the temperature at which a liquid begins to give off ignitable vapors Fire Point-the temperature at which there are sufficient vapors to support a flame or fire established for engine oils to determine that they can withstand the high temperatures encountered in an engine Requirements and Characteristics Mineral Oils of Reciprocating Engine In the early years, the Lubricants performance of aircraft piston engines was such that they could be lubricated satisfactorily by means of straight mineral oils, blended from specially selected petroleum base stocks. Oil grades 65, 80, 100, and 120 are straight mineral oils blended from selected high-viscosity index base oils 114 Requirements and Characteristics of Reciprocating Engine Lubricants 115 Straight Weight Mineral Oils These oils do not contain any additives except for very small amounts of pour point depressant, which helps improve fluidity at very low temperatures, and an anti-oxidant. This type of oil is used during the break-in period of a new aviation piston engine or those recently overhauled Requirements and Characteristics of Reciprocating Engine Lubricants 116 Mineral Oils The first additives incorporated in straight mineral piston engine oils were based on the metallic salts of barium and calcium. In most engines, the performance of these oils with respect to oxidation and thermal stability was excellent, but the combustion chambers of the majority of engines could not tolerate the presence of the ash deposits derived from these metal-containing additives. Requirements Mineral Oils and To overcome the disadvantages of harmful Characteristics combustion chamber deposits, a nonmetallic of (i.e., non-ash forming, polymeric) additive Reciprocating was developed that was incorporated in blends of selected mineral oil base stocks Engine W oils are of the ashless type and are still in Lubricants use The ashless dispersant grades contain additives, one of which has a viscosity stabilizing effect that reduces the tendency of the oil to thin out at high oil temperatures 117 and thicken at low oil temperatures Requirements and Mineral Oils Characteristics The additives in these oils extend operating of temperature range and improve cold engine Reciprocating starting and lubrication of the engine during Engine the critical warm-up period permitting flight Lubricants through wider ranges of climatic changes without the necessity of changing oil. Semi-synthetic multigrade SAE W15 W50 oil for piston engines has been in use for some time. 118 Requirements and Characteristics of Reciprocating Engine Lubricants 119 Ashless Dispersant Oils Oils W80, W100, and W120 are ashless dispersant oils specifically developed for aviation piston engines. They combine nonmetallic additives with selected high viscosity index base oils to give exceptional stability, dispersancy, and antifoaming performance. Dispersancy is the ability of the oil to hold particles in suspension until they can either be trapped by the filter or drained at the next oil change Requirements and Characteristics of Reciprocating Engine Lubricants Ashless Dispersant Oils The dispersancy additive is not a detergent and does not clean previously formed deposits from the interior of the engine. 120 Requirements and Characteristics of Reciprocating Engine Lubricants Oils Some multigrade oil is a blend of synthetic and mineral based oil semisynthetic, plus a highly effective additive package, that is added due to concern that fully synthetic oil may not have the solvency to handle the lead deposits that result from the use of leaded fuel As multigrade oil, it offers the flexibility to lubricate 121 effectively over a wider range of temperatures than monograde oils Requirements and Characteristics Oils of Reciprocating Engine Compared to monograde Lubricants oil, multigrade oil provides better cold-start protection and a stronger lubricant film (higher viscosity) at typical operating temperatures. The combination of nonmetallic, antiwear additives and selected high viscosity index mineral and synthetic base oils give exceptional stability, dispersancy, and antifoaming performance. 122 Requirements and Characteristics of Reciprocating Engine Oils Lubricants Start up can contribute up to 80 percent of normal engine wear due to lack of lubrication during the start-up cycle The more easily the oil flows to the engine’s components at start up, the less wear occurs The ashless dispersant grades are recommended for aircraft engines subjected to wide variations of ambient temperature, particularly the turbocharged series engines that require oil to activate the various turbo controllers. 123 Requirements Oils and At temperatures below 20 °F, Characteristics (-6C) preheating of the engine and oil supply tank is of normally required regardless of the type of oil used. Reciprocating Premium, semisynthetic multigrade ashless dispersant Engine oil is a special blend of a high-quality mineral oil and Lubricants synthetic hydrocarbons with an advanced additive package that has been specifically formulated for multigrade applications. The ashless antiwear additive provides exceptional wear protection for wearing 124 surfaces. Requirements and Characteristics of Reciprocating Engine Lubricants 125 Oils Many aircraft manufacturers add approved preservative lubricating oil to protect new engines from rust and corrosion at the time the aircraft leaves the factory This preservative oil should be removed at the end of the first 25 hours of operation When adding oil during the period when preservative oil is in the engine, use only aviation grade straight mineral oil as required, of the correct viscosity Requirements and Characteristics of Reciprocating Engine Lubricants 126 Oils If ashless dispersant oil is used in a new engine, or a newly overhauled engine, high oil consumption could be experienced. The additives in some of these ashless dispersant oils may retard the break in of the piston rings and cylinder walls. This condition can be avoided by the use of mineral oil until normal oil consumption is obtained, then change to the ashless dispersant oil Requirements and Characteristics of Reciprocating Engine Lubricants 127 Oils Mineral oil should also be used following the replacement of one or more cylinders or until the oil consumption has stabilized. In all cases, refer to the manufacturers’ information when oil type or time in service is being considered. https://youtu.be/Q7yuDJUcJ74