Engine Components

OBJECTIVE 3-1b. Engine Components Without reference, identify basic facts and terms about engine component identification and engine oil servicing. A minimum of 11 out of 15 must be correct. INTRODUCTION Several different components mounted to the engine or incorporated inside the engine provide support systems for effective engine operation. The engine needs a method of starting, the moving surfaces must be lubricated, and the fuel control ensures the engines receive the necessary amount of fuel to operate in different environments. INFORMATION: Engine Components Starters Jet engine starters provide initial rotation of the gearbox and compressor, which provides air under pressure to support combustion and rotation of the engine to increase the rotor RPM until the engine reaches a self-sustaining speed. The starter is generally mounted on the main accessory section gearbox and consist of two different types, which are the pneumatic and mechanical types. The start and/or control switches or buttons are located at the pilot’s station console. Pneumatic type The air turbine starter (fig. 3-16) is pneumatically driven by low pressure high volume compressed air which is called bleed air and mechanically connected to the engine through a gearbox. The starter’s source of compressed bleed air derives from one of three possible sources: a piece of Aerospace Ground Equipment (AGE) containing an external gas turbine compressor, a small jet engine internally mounted in the aircraft called an auxiliary power unit (APU), or bleed air from another operating engine on the same aircraft. Fig. 3-16, Pneumatic Starting CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 93 Mechanical type A Jet Fuel Starter (JFS), (fig. 3-17) is used mostly on fighter aircraft. A JFS is a small internally mounted gas turbine engine (like an APU) used to start the engines mechanically. Mechanical rotational speed and torque created by the JFS turns the engine compressor for start sequence through the accessory section gearbox tower shaft geared to the engine. Ignition System Three things are necessary to cause a fire—a combustible material (such as aircraft fuel), oxygen, and heat. Ignition is necessary only during the start cycle to ignite the fuel-air mixture. Electronic ignition systems provide internal combustion for aircraft engines. All that is needed is a series of sparks with enough intensity to cause combustion. The ignition/exciter unit (fig. 3-18) is a dual-circuit and dual-output unit that supplies a high-voltage, high-energy electrical current for ignition. Therefore, the exciter (coil/distributor) develops voltage of sufficient amplitude to produce a spark as the voltage jumps across the gap at the end of the igniter plugs (spark plugs). The resultant spark across the gap is of high heat intensity, capable of igniting fuel mixtures. Fig. 3-18, Ignition/Exciter System Fig. 3-17, Jet Fuel Starter (JFS) CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 94 Engine Fuel System (fig. 3-19) The engine fuel system is used to provide regulated fuel flow to the combustion section of the engines (and augmenter sections of low-bypass engines) to meet engine demands. It schedules (meters) the correct amount of fuel to the combustion chambers. The fuel is then mixed with compressed air and ignited. The system relies on many sub-components such as pumps, control units, and manifolds working in unison to operate effectively. Engine-Driven Fuel Pump The engine-driven fuel pump (fig. 3-20) is turned by gears in the accessory section of the engine. The purpose of this pump is to deliver a continuous supply of fuel at the proper pressure to the fuel control unit during engine operation. Constant pressure is maintained by a spring-loaded pressure relief valve. Fig. 3-20, Engine-driven Fuel Pump Fig. 3-19, Engine Fuel System CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 95 Fuel Control Unit The fuel control unit (fig. 3-21) is the heart of the gas turbine engine fuel system. Depending upon the type of engine and the performance expected of it, fuel controls may vary in complexity. Modern fuel control units sense some or all of the following engine operating variables: • Pilot’s demand (throttle position) • Compressor inlet temperature • Compressor discharge pressure • Burner pressure • Compressor inlet pressure • RPM • Turbine temperature The fuel control consists of a fuel-metering system and a computing system. These two internal systems work together to regulate the amount of fuel being delivered to the fuel nozzles in the combustion section, via the fuel manifold. Fig. 3-21, Fuel Control Unit CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 96 Fuel Manifold The fuel delivered from the fuel control unit is carried from outside the engine by a manifold system. The fuel manifold supplies metered fuel as it leaves the fuel control and delivers it to the fuel nozzles located at the front of the combustion chambers (burners). As you can see in, (fig. 3-22) the fuel manifold is a series of tubing and pipes designed to carry (distribute) fuel to multiple locations. Fig. 3-22, Engine Fuel Manifold CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 97 Fuel Nozzles In jet engines, the function of the fuel spray nozzles (fig. 3-23) is to inject fuel into the combustion area in a highly atomized, precisely patterned spray (fig. 3-24). This allows the fuel to burn evenly and in the shortest possible space and time. It is very important that the fuel be evenly distributed by the spray to prevent the formation of any hot spots in the combustion chambers. It is of particular value for this reason that the spray be well centered in the flame area of the combustion chamber liners. Fuel nozzle types vary between engines; mostly fuel is sprayed into the combustion area under pressure through small orifices in the nozzles. Atomization of the fuel occurs as it exits the fuel nozzle to help form the correct spray pattern (that resembles the spray of an aerosol can) inside the combustion chambers for proper burning of the fuel mixture. Fuel Flow Indicator (fig. 3-25) Fuel flow indicating systems provide a continuous indication of the rate of fuel delivery to the engine. The rate of flow is in Pounds per Hour (PPH). Fuel flow transmitters are incorporated into the engine fuel system to monitor the amount of fuel flowing into an engine. The signal from the transmitter is sent to the fuel flow indicator inside the cockpit or flight deck. Fig. 3-23, Fuel Nozzle Operation Fig. 3-24, Duplex Spray Pattern Fig. 3-25, Fuel Flow Indicator CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 98 Engine Control System Throttles directly control the power output of the engines; more throttle, equals more power. In most engines (car, lawnmower, etc.) this also controls the RPMs of the engine. Push forward for higher RPMs, pull back for less. Aircraft use a throttle quadrant (fig. 1-24) to house all the engine’s throttle levers that are needed to operate the engine control systems through mechanical throttle linkage or electrical signals. The pilot moves the throttles to control the engine’s thrust. Therefore, the throttle linkage connects the throttle to the fuel control unit to determine how much power (thrust) the engine can develop by controlling the amount of fuel and air entering the engine. When full power is needed (pushed forward), the throttle allows the maximum amount of fuel and air to enter the system to produce maximum thrust. When idle power is warranted (pulled back) only a small amount of fuel and air can enter the system, and the engine produces minimum thrust. As you can see, the engine fuel control, one for each engine, responds to throttle positions and supplies the proper amount of fuel to the fuel manifolds. Fig. 3-26, Throttle System CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 99 Instrument System Aircraft instruments are essential to the pilot during flight, as well as to the mechanic when checking proper engine operation, troubleshooting, or performing maintenance on the engine. Instruments provide a means of monitoring critical engine operating conditions using separate indicators for each engine. Range Markings Operating limitations and ranges are illustrated by colored markings which appear on an instrument’s face (fig. 3-27). Red markings indicate the limit above or below which continued operation is likely to cause damage or shorten life. The green markings indicate the safe or normal range of operation. The yellow markings indicate the range when special attention should be given to the operation covered by the instrument. Operation in the yellow range is permissible but should be avoided. Therefore, color-coded range markings on the indicators reflect normal and abnormal operating ranges. In addition, the instruments may be analog or digital depending on the type of aircraft configuration. Types Engine instruments provide indications of exhaust temperature, oil and fuel pressure, engine RPM, oil temperature, and fuel flow rate. The pilot must always be aware of engine operations. If oil pressure falls below the normal operating limit or exhaust temperature becomes excessively high, the engine instruments provide these indications to the pilot. Tachometer The tachometer indicator (fig. 3-28) is an instrument that shows the speed of a gas turbine engine (jet) main rotor assembly. The dials of tachometer indicators used with jet engines are shown in percentage of RPM. Basically, the tachometer system monitors compressor RPMs based upon the rotational speed of the compressor section. For example, an engine designed to operate at a maximum RPM of 5800 but is only spinning at 4600 would indicate an output amount of 80% on the tachometer indicator. Fig. 3-27, Range Markings Fig. 3-28, Tachometer CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 100 Exhaust Gas Temperature/Turbine Inlet Temperature To properly monitor the operation of an aircraft engine, you must know various temperature indications. Temperature sensing devices, called thermocouples, mounted near the turbine section of an engine extend into the exhaust gas stream. The thermocouples convert the gas temperature into an electrical signal to be displayed by the indicator in degrees Celsius, referred to as Exhaust Gas Temperature (EGT). Some aircraft place the thermocouples into the exhaust stream to measure the EGT. Others place them in front of the turbine and measure the Turbine Inlet Temperature (TIT). Regardless of which indicating system is used, they both provide a visual temperature indication using gauges (fig. 3-29) in the cockpit of the engine’s gasses. The EGT or TIT indicator is on the pilot’s main instrument panel and the scale ranges from 0°C to 1,200°C. Oil Pressure Indicator Oil pressure indicators (fig. 3-30) show that oil is or is not circulating properly. Pressure sensors mounted in the system measure the oil pressure produced by the pumps and send the data to indicators in the flight deck or cockpit to display the pressure in pounds Per Square Inch (PSI). Oil Temperature Indicators As oil passes through the engine, it absorbs heat from the metal it contacts. Unlike oil pressure, changes in oil temperature occur more slowly. This is particularly noticeable after starting a cold engine, when it may take several minutes or longer for the gauge to show any increase in oil temperature. Sensors in the system measure the temperature and send a signal to the gauges (fig. 3-31) located on the pilot’s control panels. A green area shows the normal operating range and the red area indicates the minimum/maximum allowable temperatures. High oil temperature indications may signal a plugged oil line, a low oil quantity, a blocked oil cooler, or a defective temperature gauge. Low oil temperature indications may signal improper oil viscosity during cold weather operations. Fig. 3-29, Temperature Gauges Fig. 3-30, Oil Pressure Fig. 3-31, Oil Temperature CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 101 Thrust Reversers The extreme weight of modern cargo aircraft imparts a tremendous amount of stress on the landing gear and brakes during landing. A thrust reverser system (fig. 3-32) used on these aircraft relieves some of this stress by assisting with slowing the aircraft during landing roll or aborted take-off. Mechanical doors behind either the fan section or exhaust section redirect thrust forward to slow the aircraft. These doors are moved into the fan/exhaust air stream using actuators controlled by positioning the throttle. The doors, when activated, will redirect the exhaust air flow in a forward direction and assist in slowing the aircraft down without using breaks. Only high bypass engines have this system. If the engines are located under or behind the wings either the clamshell or bucket type is used. On most larger aircraft, with engines placed in front, the cold stream is utilized. NOTE: Some engine thrust reversers allow the aircrew to back up the aircraft on the ground. Fig. 3-32, Thrust Reverser Systems CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 102 Compressor Anti-stall System A compressor stall is caused when the airflow into an engine is disrupted. This causes turbulence and pressure fluctuations within the engine and can lead to engine failure. The compressor anti-stall system prevents compressor stalls and surges due to the disruption of the airflow into the compressor section during rapid acceleration or deceleration. The use of variable inlet guide vanes and/or variable stator vanes permits the angle of one or more rows of stator vanes in a compressor to be adjusted preventing airflow disruption. Variable Inlet Guide Vanes (fig. 3-33) An engine component in which the angle of the inlet guide vanes can be changed to meet the requirements of the engine-operating conditions (Turbo Fan only). These are normally in front of the first stage of an axial compressor and sometimes in the subsequent stages as well. Normally, they are closed during engine starting and low RPM, but they open progressively as the RPM is increased. At low RPM, the angle of attack of the low-pressure blades is kept moderate to avoid stalling. Variable Stator Vanes The Variable Stator Vane (VSV) system is positioned behind the compressor rotor blades. The function of the VSV system (fig. 3-34) changes the angle of the stator vane to optimize the airflow through the engine as the air passes from one stage to the next at all engine speeds. VSVs operate in the same manner as the IGV and are positioned aft of the rotor blades. Engine Anti-Ice System Whenever icing conditions are encountered, the performance characteristics of aircraft deteriorate. Routing a portion of the hot bleed air from the engine compressor section through ducts in the fan and inlet sections prevents the formation of ice (fig. 3-35). Left unattended, this ice will disturb the airflow into the engine and cause damage to the engine. Fig. 3-33, Variable Inlet Guide Vanes Fig. 3-34, Variable Stator Vanes Fig. 3-35, Anti-Ice System CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 103 Oil System Lubricating oils must perform three basic functions in a jet engine: • Lubrication • Cooling • Cleaning In most cases, a pressure pump system furnishes oil to the engine to be lubricated and cooled in either a dry sump (fig. 3-36) or a wet sump (fig. 3-37) lubrication system. A scavenging pump returns the oil to the tank for reuse. Most systems will include a heat exchanger (air or fuel version) to cool the oil. In general, the parts to be lubricated and cooled include the main bearings and gears sealed within the engine. Fig. 3-36, Dry Sump Oil System Fig. 3-37, Wet Sump Oil System CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 104 Reservoir The reservoir stores the system oil supply. The location of the reservoir determines if the oil system is a dry-sump or wet-sump design. The wet-sump style uses the accessory gearbox located at the bottom of the engine to store the oil. In the dry-sump style (fig. 3-38), oil is stored in an external tank mounted somewhere near the engine. Pumps The oil pressure pump (fig. 3-39) supplies oil under pressure to engine bearings and gears to cool and reduce friction between moving parts. Once the oil has served its purpose the scavenge pumps return the oil to the reservoir/tank. Filter assemblies Filter assemblies contain the filter elements used to keep oil clean. The filters are an important part of the lubrication system, since they remove most foreign particles in the oil. Without some type of filter in the oil system, dirt or metal particles suspended in the oil could damage bearings, clog passages, and cause engine failure. To allow for oil flow in the event of filter blockage (clogged), some versions of filter assemblies incorporate a bypass or relief valve as part of the filter or in the oil passages. When the pressure differential reaches a specified value (about 15 to 50 psi), the internal bypass relief valve opens to allow oil to bypass the filter (fig. 3-40). When this occurs, the filtering action is lost, allowing unfiltered oil to be pumped to the bearings. This is a dangerous situation; however, unfiltered oil is better than no oil. Some filters have a Differential Pressure Indicating Pin (Delta-P), located somewhere on the filter assembly, which pops (extends) to alert you when a filter has clogged to the point that it needs to be checked. Fig. 3-38, Dry-sump Reservoir Fig. 3-40, Bypass & Delta-P Indicator Fig. 3-39, Oil Pressure Pump CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 105 Oil Cooler Oil coolers reduce the temperature of the oil by passing it near streams of ram air (fig. 3-41) or fuel (fig. 3-42). The heat energy in the oil transfer to the cooling medium (air or fuel) and exit the cooler at a lower temperature. Since the fuel flowing through the cooler is greater than the oil flow, the fuel can absorb a considerable amount of heat. These coolers keep the temperature of the oil within the proper range. Pressure/Breather Vent Vapors created in the bearing cases is another issue that occurs when the oil heats up in the system. The vent system removes the oil vapors from the entire system by venting all the bearing compartments, oil tanks and accessory gearboxes. Oil System Servicing Oil is the lifeblood of the aircraft engine. If the oil supply to the bearings stops, the lubricating films break down and cause scoring, seizing, and burning between moving parts. Manufactures normally require turbine engine oil servicing within a short time after shutdown, primarily to prevent over servicing as oil may leak from storage tank to gearbox over time. In all cases the TOs should be followed for the specific aircraft not only for servicing procedures, but also for type and grade of oil used. Servicing Requirements Aircraft oil tanks (fig. 3-43) are normally checked after each flight and serviced as needed IAW applicable aircraft TOs. Aircraft oil tanks are serviced with either clean unopened oil cans or oil servicing carts and should never be filled to above maximum capacity or above the labeled full mark on the gauge or dipstick. This is because oil expands when it becomes hot, and at high altitude it bubbles and expands. When pouring oil into the tanks through the filler neck or servicing through the connection port, be sure rags or other foreign substances do not get into the tanks. Foreign material in the oil system restricts the flow of oil and can cause engine failure. Fig. 3-41, Ram Air-Oil Cooler Fig. 3-42, Fuel-Oil Cooler Fig. 3-43, Oil Tank CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY CUI//Rel To USA, AF, AR, BL, BR, CI, CO, EC, ET, ASFF (H5 and J3), FR, GB, HO, ID, IQ, JO, KU, MX, NK, NI, PE, PI, RO, SR, TU, TK AND UY Block III SG J3ATR2AX3X 048C 106 Precautions Before servicing, get your aircraft’s specific maintenance TO for the task to determine the proper Military (MIL) preference of oil, servicing equipment, procedures, and PPE (gloves and goggles) for use. The extremely high engine temperatures transferred to the engine oil present a serious burn hazard to you. The highly toxic nature of the engine oil contributes to negative health effects, including fetal hazards. Always consult the Safety Data Sheet (SDS) to determine the exact toxicity and hazards associated with oil system servicing (fig. 3-44). If oil contact occurs, you must wash any effected skin areas and seek medical attention if you ingest oil. SUMMARY The core of powered flight is the use of very powerful engines producing massive amounts of thrust. Everything in the engine must work in perfect unison to provide this power and propel aircraft into the sky. If one piece of the system malfunctions the results can be catastrophic. Abnormal range mark readings on the instruments provide early indication of problems and maintenance technicians must understand these readings. Your knowledge of these systems and the decisions about engine maintenance may be the difference between many successful sorties or aircraft never returning from a mission.