An air-start system is a power source used to provide the initial rotation to start large diesel engines and gas turbines.
Compared to a gasoline (petrol) engine, a diesel engine has a very high compression ratio, an essential design feature, as it is the heat of compression that ignites the fuel. An electric starter with sufficient power to turn a large diesel engine would itself be so large as to be impractical so there is a need for an alternative system.
An air start system has three main components along with various safety components, namely the air start injector, the distributor and the air receivers. When the system is initiated, starting air from the receivers is distributed by the distributor unit to each respective air start valve according to the firing order of the engine’s cylinders. Safety components include flame traps, to prevent air line explosions, a turning gear interlock which ensures that air-start cannot be initiated when the turning gear is engaged, relief valves and isolation valves, as well as drain valves at certain points along the system. Control components include the control valves and remote air-start valves. [1] A direct start system as used on a marine slow-speed diesel is required to have up to 12 starts on a non-reversing engine or 6 starts on a reversible, or geared, engine.
When starting the engine, compressed air is admitted to whichever cylinder has a piston just over top dead center, forcing it downward. [2] As the engine starts to turn, the air-start valve on the next cylinder in line opens to continue the rotation. After several rotations, fuel is injected into the cylinders, the engine starts running and the air is cut off.
To further complicate matters, a large engine is usually "blown over" first with zero fuel settings and the indicator cocks open, to prove that the engine is clear of any water build up and that everything is free to turn. After a successful blow ahead and a blow astern, the indicator cocks are closed on all the cylinders, and then the engine can be started on fuel. Significant complexity is added to the engine by using an air-start system, as the cylinder head must have an extra valve in each cylinder to admit the air in for starting, plus the required control systems. This added complexity and cost limits the use of air-starters to very large and expensive reciprocating engines.
Another method of air-starting an internal combustion engine is by using compressed air or gas to drive a fluid motor in place of an electric motor. [3] They can be used to start engines from 5 to 320 liters in size and if more starting power is necessary two or more motors can be used. Starters of this type are used in place of electric motors because of their lighter weight and higher reliability. They can also outlast an electric starter by a factor of three and are easier to rebuild. Engines operating in underground mining activities tend to operate on this type of starter system to reduce the risk of an electrical system igniting flammable material.
All vane type air starters should have a lubricator installed to insure long-life and maximum performance. [4] Lubricators give the moving parts a needed friction barrier, reduce metal corrosion and keep vanes sealed properly against the cylinder walls. Even the so-called lube-free air starters require lubrication to prolong trouble free life. Two basic lubricator devices are typically employed. One is an in-line or reservoir type that typically stores up to 2 quarts of lubricant, and is installed along the air supply line. The second style of lubricator is a small one shot device that dispenses a measured amount of lubricant every time the starter is engaged. Installed directly onto the air inlet of the starter, the in-line lubricators are self priming pneumatic pumps that require a 1/4″ lubrication line piped from as far away as 4 feet. Air Starter lubricators perform best using misting type, non-detergent oils such as diesel fuel or Marvel Mystery oil. If emissions are a concern, there are environmentally friendly type lubricants available on the market.
Not all air starters require lubrication. Turbine type air starters do not require air motor lubrication, although some turbine air starters do use an oil filled transmission that may require periodic inspections and maintenance.
Compressed air has been used to start gas turbine engines using air impingement starting (in which air is directed at the engine turbine blades through nozzles in the turbine casing, used on US Navy General Electric J79 engines). It is much more efficient to use an air turbine starter (ATS) which is usually mounted on an accessory gearbox. [5] An early axial compressor turbojet had an ATS located in the compressor nose cone (eg particular variants of the J79).
Air impingement starting was not used for US military aircraft after the F-4B, A-5A [6] and F-5 as the pneumatic energy requirement was several times greater than when using an air turbine starter. The gas turbine compressor required to start a J79 with impingement starting was sufficient to start two J79 engines simultaneously in a B-58 when using air turbine starters. [7]
An ATS has its own turbine and gears to change its low torque and high speed to low speed and high torque at the engine mounting pad. Further gears in the engine gearbox connect to the engine shaft (high pressure spool on multi-spool engines). Compressed air is sent to the ATS turbine from the aircraft auxiliary power unit ( bleed air from the gas generator or from a free-turbine load compressor, eg PW901 APU), from an already-running engine (bleed air) on a multi-engined aircraft or, for early jet aircraft, from an air compressor mounted on ground support equipment.
Compared with electric starters, air-starters have a higher power-to-weight ratio so are used on large engines as an electric starter would be too big and, with its cables, too heavy and expensive. However, for smaller engines, which don't need as much starter power, an electric starter is more suitable. It has a dual function as a generator (is known as a starter/generator) at speeds above which the engine no longer requires starter assistance. [8]
In an internal combustion engine, a turbocharger is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake air, forcing more air into the engine in order to produce more power for a given displacement.
An auxiliary power unit (APU), is a device on a vehicle that provides energy for functions other than propulsion. They are commonly found on large aircraft and naval ships as well as some large land vehicles. Aircraft APUs generally produce 115 V AC voltage at 400 Hz (rather than 50/60 Hz in mains supply), to run the electrical systems of the aircraft; others can produce 28 V DC voltage. APUs can provide power through single or three-phase systems. A jet fuel starter (JFS) is a similar device to an APU but directly linked to the main engine and started by an onboard compressed air bottle.
A starter is a device used to rotate (crank) an internal-combustion engine so as to initiate the engine's operation under its own power. Starters can be electric, pneumatic, or hydraulic. The starter can also be another internal-combustion engine in the case, for instance, of very large engines, or diesel engines in agricultural or excavation applications.
An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Aircraft using power components are referred to as powered flight. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many small UAVs have used electric motors.
A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:
An air compressor is a machine that takes ambient air from the surroundings and discharges it at a higher pressure. It is an application of a gas compressor and a pneumatic device that converts mechanical power into potential energy stored in compressed air, which has many uses. A common application is to compress air into a storage tank, for immediate or later use. When the delivery pressure reaches its set upper limit, the compressor is shut off, or the excess air is released through an overpressure valve. The compressed air is stored in the tank until it is needed. The pressure energy provided by the compressed air can be used for a variety of applications such as pneumatic tools as it is released. When tank pressure reaches its lower limit, the air compressor turns on again and re-pressurizes the tank. A compressor is different from a pump because it works on a gas, while pumps work on a liquid.
The Brayton cycle, also known as the Joule cycle, is a thermodynamic cycle that describes the operation of certain heat engines that have air or some other gas as their working fluid. It is characterized by isentropic compression and expansion, and isobaric heat addition and rejection, though practical engines have adiabatic rather than isentropic steps.
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Engine braking occurs when the retarding forces within an internal combustion engine are used to slow down a motor vehicle, as opposed to using additional external braking mechanisms such as friction brakes or magnetic brakes.
The General Electric J79 is an axial-flow turbojet engine built for use in a variety of fighter and bomber aircraft and a supersonic cruise missile. The J79 was produced by General Electric Aircraft Engines in the United States, and under license by several other companies worldwide. Among its major uses was the Lockheed F-104 Starfighter, Convair B-58 Hustler, McDonnell Douglas F-4 Phantom II, North American A-5 Vigilante and IAI Kfir.
The Coffman engine starter was a starting system used on many piston engines in aircraft and armored vehicles of the 1930s and 1940s. It used a cordite cartridge to move a piston, which cranked the engine. The Coffman system was one of the most common brands; another was the Breeze cartridge system, which was produced under Coffman patents. Most American military aircraft and tanks which used radial engines were equipped with this system. Some versions of the Rolls-Royce Merlin engine used in the British Supermarine Spitfire used the Coffman system as a starter. The Hawker Typhoon and Hawker Tempest also used the Coffman system to start their Napier Sabre engines.
The General Electric CJ805 is a jet engine which was developed by General Electric Aircraft Engines in the late 1950s. It was a civilian version of the J79 and differed only in detail. It was developed in two versions. The basic CJ805-3 was a turbojet and powered the Convair 880 airliner, and the CJ805-23 a turbofan derivative which powered the Convair 990 Coronado variant of the 880.
A rotary-screw compressor is a type of gas compressor, such as an air compressor, that uses a rotary-type positive-displacement mechanism. These compressors are common in industrial applications and replace more traditional piston compressors where larger volumes of compressed gas are needed, e.g. for large refrigeration cycles such as chillers, or for compressed air systems to operate air-driven tools such as jackhammers and impact wrenches. For smaller rotor sizes the inherent leakage in the rotors becomes much more significant, leading to this type of mechanism being less suitable for smaller compressors than piston compressors.
A free-piston engine is a linear, 'crankless' internal combustion engine, in which the piston motion is not controlled by a crankshaft but determined by the interaction of forces from the combustion chamber gases, a rebound device and a load device.
This article briefly describes the components and systems found in jet engines.
Internal combustion engines come in a wide variety of types, but have certain family resemblances, and thus share many common types of components.
The accessory drive is a gearbox that forms part of a gas turbine engine. Although not part of the engine's core, it drives the accessories – such as generators, pumps for fuel and lubrication oil, air compressors, hydraulic pumps and engine starters – that are otherwise essential for the operation of the engine or the aircraft on which it is mounted. Accessory drives on large engines handle between 400–500 hp.
Many variations of aircraft engine starting have been used since the Wright brothers made their first powered flight in 1903. The methods used have been designed for weight saving, simplicity of operation and reliability. Early piston engines were started by hand. Geared hand starting, electrical and cartridge-operated systems for larger engines were developed between the First and Second World Wars.
An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance. This process transforms chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.
The 4 VD 14,5/12-1 SRW is an inline four-cylinder diesel engine produced by the VEB IFA Motorenwerke Nordhausen from 1967 to 1990. The engine was one of the standard modular engines for agricultural and industrial use in the Comecon-countries. Approximately one million units were made.