An additional power unit ( APU ) is a device on vehicles that provide energy for functions other than propulsion. They are usually found in large aircraft and ships as well as some large ground vehicles. APU aircraft generally produce alternating current of 115 V (AC) at 400 Hz (not 50/60 Hz in main supply), to run an aircraft electrical system; the other can produce a direct current of 28 V (DC). APU can provide power through a one or three phase system.
Video Auxiliary power unit
Transport plane
Function
The main purpose of an APU aircraft is to provide power to start the main engine. The turbine engine must be accelerated to a high speed of rotation to provide sufficient air compression for self-help. Smaller jet engines are usually started by an electric motor, while larger engines are usually started by an air turbine motor. Before the engine is turned on, the APU starts, generally by a battery or hydraulic accumulator. After the APU runs, it provides power (electric, pneumatic, or hydraulic, depending on the design) to start the main engine of the aircraft.
To begin, jet engines require pneumatic rotation from turbines, AC-electric fuel pumps, and AC-electric "flash" ignites fuel. When the turbine (behind the combustion chamber) is already rotating, the front inlet fan also rotates. After ignition, both fans and turbines accelerate their rotation. When the combustion is stable, the engine only needs fuel to run at idle. The engine that starts now can replace the APU when starting the machine further.
During flight, the APU and its generators are not needed because power is provided by the machine; in rare events when engine shutdown is complete, APU can be used to run important computer systems and flight controls, as seen on the US Airways Flight 1549 water landing. It also allows the cabins to be comfortable as passengers ride before the engine starts. Electrical power is also used to run the system for preflight checking. In addition, some APUs are connected to hydraulic pumps, allowing crews to operate hydraulic equipment (such as flight controls or flaps) before starting the engine. This function can also be used, on some planes, as in-flight backup in case of engine or hydraulic failure.
Aircraft with APU can also receive power and pneumatic power from ground equipment when APU has failed or not been used. Some airports reduce APU usage due to noise and pollution, and soil strength is used whenever possible.
APUs installed for twin-engine aircraft (ETOPS) are important security devices, as they provide backup power and compressed air instead of a dead machine or a failed primary engine generator. Although some APUs may not work on the flight, ETOPS-compliant APUs must be able to fly at altitudes up to the ceiling of aircraft services. The recent app has set a start up to 43,000 ft (13,000 m) of full cool-wading conditions such as the Hamilton Sundstrand APS5000 for the Boeing 787 Dreamliner. If the APU or electric generator is not available, the aircraft can not be removed for ETOPS flights and are forced to take longer non-ETOPS routes.
APUs that provide electricity at 400 Hz are smaller and lighter than their 50/60 Hz counterpart, but more expensive; The drawback is that such high frequency systems suffer from voltage drops.
History
During World War I, the British Coast-class balloon, one of several types of aircraft operated by the Royal Navy, carried the ABC 1.75 hp (1.30 kW) auxiliary engine. It's a powered generator for craft radio transmitters and, in an emergency, can light an extra air blower. One of the first permanent military wing aircraft to use the APU was Britain, World War 1, Supermarine Nighthawk, an anti-Zeppelin Night fighter.
During World War II, a large number of American military aircraft were fitted with APU. This is usually known as putt-putt , even in official training documents. The putt-putt on the B-29 Superfortress bomber is mounted on the unpacked section on the rear of the aircraft. Various models of four-stroke, Flat-twin or V-twin engines are used. The 7 horsepower (5.2 kW) engine drives a P2 , DC, generator rated at 28.5 Volts and 200 Amps (multiple generators P2 , driven by the main engine, is a DC B-29 resource in flight). Putt-putt provides the power to start the main engine and is used after take-off to a height of 10,000 feet (3,000 m). Putt-putt resumed when the B-29 descended to the mainland.
Some of the B-24 Exemptor models have putt-putts mounted on the front of the plane, inside the nose-wheel compartment. Some models of Douglas C-47 Skytrain carrying a putt-putt under the cockpit floor.
The first German jet engine built during the Second World War used the early mechanical APU system designed by German engineer Norbert Riedel. It consists of 10 horsepower (7.5 kW) flat two-step machines, which for the Junkers Jumo 004 design is hidden in the intake diverter, essentially serving as an example of a pioneer of additional power units to start the jet engine. The hole in the extreme nose of the diverter contains a manual-pull handle that initiates the piston engine, which in turn rotates the compressor. Two spark plug access ports are on the Jumo 004 intake switch to serve the cylinder of the Reidel in situ unit, for maintenance purposes. Two small "premix" tanks for Riedel fuel/gasoline are installed in the annular intake. This machine is regarded as an extreme short stroke (bore/stroke: 70 mm/35 mm = 2: 1) design so it can fit in a jet engine jumper intake like Jumo 004. For reduction it has an integrated planetary fixture. It was manufactured by Victoria in Nuremberg and served as an APU-style mechanical starter for all three German jet engine designs to make it at least prototype stage before May 1945: Junkers Jumo 004, BMW 003, and prototype (19 built) from Heinkel HeS 011 engine more forward, mounted just above the inlet on the nose sheet metal made by Heinkel.
Boeing 727 in 1963 was the first jet aircraft featuring APU gas turbines, allowing it to operate at smaller airports, independent of ground facilities. APU can be identified on many modern aircraft by the exhaust pipe in the tail of the aircraft.
Section
The typical gas turbine APU for commercial transport aircraft consists of three main parts:
Power section
The power section is the gas generator part of the engine and produces all the shaft power for the APU.
Load the compressor section
Load compressors are generally a piston-mounted compressor that provides pneumatic power for aircraft, although some APUs extract air from the electric compressor. There are two driven devices: an inlet propeller that regulates airflow to a load compressor and a spike control valve that maintains stable turbocharged or spike-free engine operation.
Gearbox section
The gearbox transfers power from the main engine shaft to an oil-cooled generator for electrical power. Inside the gearbox, power is also transferred to machine accessories such as fuel control unit, lubrication module, and cooling fan. In addition, there is also a starter motor connected through a dental gear to perform the initial function of the APU. Some APU designs use a starter/generator combination to start APUs and power plants to reduce complexity.
On a more-electric Boeing 787 aircraft, APU only delivers power to the aircraft. The absence of a pneumatic system simplifies the design, but high demand for electricity requires a heavier generator.
Onboard, the cellophane solid oxide fuel (SOFC) APU is being investigated.
Manufacturer
The two main companies compete in the aircraft APU market: United Technologies Corporation (through its subsidiaries Pratt & Whitney Canada and Pratt & Whitney AeroPower), and Honeywell International Inc.
Maps Auxiliary power unit
Military plane
Smaller military aircraft, such as fighter and attack aircraft, have additional power systems that are different from those used in transport aircraft. The engine function starts and provides electric and hydraulic power is shared between two units, jet fuel starter and emergency power unit .
Starters of jet fuel
The jet fuel starter (JFS) is a small turboshaft engine designed to drive jet engines into self-accelerating RPMs. Rather than supplying the air to the starter motor by way of APU, the JFS output shaft is mechanically connected to the engine. As soon as JFS starts spinning, the engine changes; unlike APUs, these starters are not designed to generate power when the machine is not running.
Jet fuel starters use free-power turbine parts, but the method of connecting them to the engine depends on the design of the aircraft. On single-engine aircraft like the A-7 Corsair II and F-16 Fighting Falcon, the JFS power section is always connected to the main engine through the machine accessory gearbox. Instead, the F-15 Eagle double engine has a single JFS, and the JFS power section is connected through a central gearbox that can be connected to one machine at a time. In the F-15, the jet fuel starter (JFS) is mated to a central gearbox (CGB). CGB has an extended longitudinal pawl axle to reach an aircraft-mounted accessory drive (AMAD) mounted in front of each machine. AMAD is connected to a jet engine by a power takeoff (PTO) shaft. As the engine accelerates to its initial speed, the PTO shaft becomes the method to drive AMAD during the flight. Once the aircraft engine starts and starts moving AMAD, the pawl shaft on the CGB returns to the pulled position and the JFS is turned off.
Emergency power unit
Hydraulic power and emergency power are provided by various types of gas turbine engines. Unlike most gas turbines, the emergency power unit does not have a gas compressor or ignitor, and uses a combination of hydrazine and water instead of jet fuel. When a mixture of hydrazine and water is released and through an iridium catalyst, it spontaneously lights up, creating a heat-infusing gas that drives the turbine. The created power is transmitted through the gearbox to drive the electric generator and the hydraulic pump.
Hydrazine is contained in a closed nitrogen-filled accumulator. When the system is armed, hydrazine is released whenever the engine-driven generator off-line, or if all engine-driven hydraulic pumps fail.
Airport equipment
Many airports have adopted the APU as a solution for high fuel consumption. Most equipment used for cleaning and cleaning runways will use an average of two or more gallons per hour of diesel when stopped. Adding APU will provide power, heating and cooling as well as hydraulic heating if needed and can result in significant fuel savings and maintenance.
Spacecraft
APU Space Shuttle provides hydraulic pressure. The shuttle has three redundant APUs, powered by hydrazine fuel. They are only supported for climbing, re-entry, and landing. During the ascent, APU provides hydraulic power for the gimballing of three Shuttle machines and controls their large valves, and for the movement of the control surfaces. During the landing, they move the control surface, lower the wheel, and power the brakes and steering wheel. The landing can be completed with only one functioning APU. In the early years of the Shuttle there was a problem with the reliability of the APU, with malfunctions on three of the first nine Shuttle missions.
Armor
APUs are installed on several tanks to provide power without high fuel consumption and large infrared signatures from the main engine. As far back as World War II, the American Sherman M4 is known to have a small piston-engined APU to charge the tank battery, its Soviet "partner" features produced for the diesel-engined Lend-Lease M4A2. Shermans the Red Army received a T-34 tank designed by Mikhail Koshkin, unknown to own it. Both the M1 Abrams and Leopard 2 variants such as the Spanish and Danish variants carry the APU on the right hull section. Successful versions of M1 (M1A2 SEPv1, etc.) have different APUs, ranging from previously stored on the turret rack, to the newer on the back, the left side of the hull replacing the fuel cell. The British Centurion Tank uses the Austin A-Series inline-4 as an additional power unit. The self-propelled howitzer Turkey T-155 F? Rt? Na uses a 2-step diesel engine located on the right hull rear to supply power to the computer's extinguishing control and hydraulic turret.
Towed artillery
Many modern pieces of artillery are equipped with internal combustion engines, mainly to provide hydraulic power to assist in the installation of weapons and for the flick film or other tools to load. This machine can also be used to provide limited battlefield mobility when no artillery tractor is available.
Commercial vehicles
A cooled or frozen semi-finished or coach car or carriage may be equipped with an APU and an independent fuel tank to keep the low temperatures on the way, without the need for a power source provided by external transport.
In the United States, federal Transportation Department regulations require a 10 hour break for every 11 hours of driving. When stopped, drivers often empty their engines to provide heat, light, and power. Idling inefficiently burns fuel and puts wear on the machine. Some trucks carry an APU designed to eliminate these long spots. APU can save up to 20 gallons of US (76Ã, L) (Cat 600 - 10 hour downtime @ 2 gallons per hour idling) fuel a day, and can extend the life of the main engine by about 100,000 miles (160,000 km)), by reducing processing time non-productive.
In some older diesels, an APU is used instead of an electric motor to start the main engine. It is mainly used in large construction equipment.
Diesel
The most common APU for commercial trucks is a small diesel engine with its own cooling system, heating system, generator or alternator system with or without an inverter, and an air-conditioning compressor, housed in a cage and mounted onto one of the semi-truck frame rails. Other designs fully integrate additional cooling, heating, and electrical components throughout the truck chassis. The APU generator engine is a fraction of the size of the main engine and uses a fraction of the fuel; some models can run for eight hours on 1 gallon US (3.8 liter) diesel. The generator also drives the main engine block and fuel system heater, so the main engine can start easily just before departure if the APU is allowed to run for the previous period. These units are used to provide climate control and electric power for the truck bed cabin and engine block heaters during the stop time on the road as mandated by statewide law for idle reduction.
Propane
Less common APUs available for commercial and sleeping diesel truck cabs include heating & amp; cooling system, 110 volt duplex electrical outlet inside and outside the cab. This is all supported by a single propane fueled generator. With this system in place, it no longer needs to use diesel fuel during rest and sleep periods to provide air/heater conditions and power tools for the driver.
Electricity
APU electricity has started getting acceptance. This electric APU uses a battery pack instead of a diesel engine on a traditional APU as a power source. The APU battery pack is charged when the truck is in motion. When the truck is idle, the energy stored in the battery is then used to turn on the air conditioner, heater, and other devices (television, microwave oven, etc.) in bed.
Fuel cell
In recent years, truck manufacturers and fuel cells have worked together to create, test and demonstrate APU fuel cells that eliminate almost all emissions and use more efficient diesel fuel. In 2008, a DOE-sponsored partnership between Delphi Electronics and Peterbilt showed that fuel cells can provide power for electronics and air conditioning from Peterbilt Model 386 under simulated "blackout" conditions for 10 hours. Delphi says that the 5kW system for Class 8 trucks will be released in 2012, at a price of $ 8000-9000 that will be competitive with other two-cylinder "midrange" two-cylinder APUs, in case they can meet the deadlines and cost estimates.
Other forms of transport
Where the elimination of exhaust or noise emissions is critical (such as yachts, van caravans), fuel cells and photovoltaic modules are used as APUs for power generation.
APUs are installed on some diesel locomotives, allowing prime mover to be switched off during an extended stopover. It provides power and heat to maintain air pressure, provides battery charging and prevents prime mover cooling from freezing.
See also
- Air start system
- Hydraulic auxiliary system
- Coffman machine starter - a similar system that uses explosive cartridges to supply gas pressure
- Ram air turbine
Note
References
External links
- "Space Shuttle Orbiter APU"
- "APU sound from inside Boeing 737 cabin"
- The Riedel Starter Motor In: Messerschmitt Me 262B in Detail; Airframe, engine, and canopy
Source of the article : Wikipedia
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