Wastegate - AbsoluteAstronomy.com

A wastegate is a valve

Valve

A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...

that diverts exhaust gas

Exhaust gas

Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline/petrol, diesel fuel, fuel oil or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack or propelling nozzle.It often disperses...

es away from the turbine

Turbine

A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

wheel in a turbocharged engine system. Diversion of exhaust gases regulates the turbine

Turbine

speed, which in turn regulates the rotating speed of the compressor

Gas compressor

A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...

. The primary function of the wastegate is to regulate the maximum boost pressure in turbocharger systems, to protect the engine and the turbocharger. One advantage of installing a remote mount wastegate to a free-float (or non-WG) turbo includes allowance for a smaller A/R turbine housing, resulting in less lag time before the turbo begins to spool and create boost.

External

An external wastegate is a separate self-contained mechanism typically used with turbochargers that do not have internal wastegates. An external wastegate requires a specially constructed turbo manifold with a dedicated runner going to the wastegate. The external wastegate may be part of the exhaust housing itself. External wastegates are commonly used for regulating boost levels more precisely than internal wastegates in high power applications, where high boost levels can be achieved. External wastegates can be much larger since there is no constraint of integrating the valve or spring into the turbocharger and turbine housing. It is possible to use an external wastegate with an internally gated turbocharger. This can be achieved through a specially designed bracket that easily bolts on and restricts the movement of the actuator arm, keeping it from opening. Another route involves welding

Welding

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

the internal wastegate shut which permanently keeps it from opening, but failure of the weld can allow it to open again.

External wastegates generally use a valve similar to the poppet valve

Poppet valve

A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide...

found in the cylinder head

Cylinder head

In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...

. However they are controlled by pneumatics

Pneumatics

Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...

rather than a camshaft

Camshaft

A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...

and open in the opposite direction. External wastegates can also use a butterfly valve

Butterfly valve

A butterfly valve is a valve which can be used for isolating or regulating flow. The closing mechanism takes the form of a disk. Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because they are lower in cost to other valve...

, though that is far more rare.

Atmospheric/divorced wastegates

A "divorced" wastegate dumps the gases directly into the atmosphere, instead of returning them with the rest of an engine's exhaust. This is done to prevent turbulence to the exhaust flow and reduce total back pressure

Back pressure

Back pressure refers to the resistance to a moving fluid by obstructions or tight bends in the confinement vessel along which it is moving, such as piping or air vents, against its direction of flow....

in the exhaust system. Divorced wastegate dumper pipes are commonly referred to as "screamer pipes" due to the unmuffled waste exhaust gases and the associated loud noises they produce.

Manual

The simplest control for a wastegate is a mechanical linkage that allows the operator to directly control the wastegate valve position. This manual control is used in some turbo-charged light aircraft.

Pneumatic

The simplest closed-loop control for a wastegate is to supply boost pressure directly from the charge air side to the wastegate actuator. A small hose can connect from the turbocharger compressor outlet, charge pipes, or intake manifold to the nipple on the wastegate actuator. The wastegate will open further as the boost pressure pushes against the force of the spring

Spring (device)

A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...

in the wastegate actuator until equilibrium

Mechanical equilibrium

A standard definition of static equilibrium is:This is a strict definition, and often the term "static equilibrium" is used in a more relaxed manner interchangeably with "mechanical equilibrium", as defined next....

is obtained. More intelligent control can be added by integrating an electronic boost controller

Boost controller

A boost controller is a device to control the boost level produced in the intake manifold of a turbocharged or supercharged engine by affecting the air pressure delivered to the pneumatic and mechanical wastegate actuator...

.

Standard wastegates have one port for attaching the boost control line from the charge air supply line or boost control solenoid. This is the most common configuration and the only type of configuration found on internal wastegates.

A dual port wastegate adds a second port on the opposite side of the actuator. Air pressure allowed to enter this second port aids the spring to push harder in the direction of closing the wastegate. This is exactly the opposite of the first port. The ability to help the wastegate remain closed as boost pressure builds can be increased. This also adds further complexity to boost control, requiring more control ports on the solenoid or possibly a complete second boost control system with its own separate solenoid. Use of the second port is not necessary. Secondary ports, unlike primary ports, cannot be simply attached to a boost control line and require electronic or manual control to be useful. C02 can also be used to apply pressure to the second port, to control boost on a much finer level.

Electric

Some 1940s aircraft engines featured electrically operated wastegates, such as the Wright R-1820

Wright R-1820

|-See also:-References:* Bridgman, L, Jane's Fighting Aircraft of World War II. Crescent. ISBN 0-517-67964-7* Eden, Paul & Soph Moeng, The Complete Encyclopedia of World Aircraft. Amber Books Ltd. Bradley's Close, 74-77 White Lion Street, London, NI 9PF, 2002, ISBN 0-7607-3432-1), 1152...

on the B-17 Flying Fortress. General Electric

General Electric

General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...

was the biggest manufacturer of these systems. Being before the age of computers, they were entirely analog. Pilots had a cockpit control to select different boost levels. Electric wastegates soon fell out of favor due to design philosophies which mandated the separation of the engine controls from the electrical system.

Hydraulic

Most modern turbocharged aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

use a hydraulic wastegate control with engine oil as the fluid. Systems from Lycoming

Lycoming Engines

Lycoming Engines is a U.S. aircraft engine company, known primarily for its general aviation engines. For most of its history Lycoming has been part of the AVCO group as AVCO Lycoming. In 1987 AVCO was purchased by Textron to become Textron Lycoming...

and Continental operate on the same principles and use similar parts which differ only in name. Inside the wastegate actuator, a spring acts to open the wastegate, and oil pressure acts to close the wastegate. On the oil output side of the wastegate actuator sits the density controller, an air-controlled oil valve which senses upper deck pressure and controls how fast oil can bleed from the wastegate actuator back to the engine. As the aircraft climbs and the air density drops, the density controller slowly closes the valve and traps more oil in the wastegate actuator, closing the wastegate to increase the speed of the turbocharger and maintain rated power. Some systems also use a differential pressure controller which senses the air pressures on either side of the throttle plate and adjusts the wastegate to maintain a set differential. This maintains an optimum balance between a low turbocharger workload and a quick spool-up time, and also prevents surging caused by a bootstrapping effect.

Wastegate chatter myth

There is confusion in the automotive world about so called "wastegate chatter" or "turbo flutter". A noise created on lifting off the throttle in a turbocharged car, commonly described as a chipmunk or a rattlesnake, is often stated incorrectly as being a result of the turbo's wastegate closing.

The noise is in fact the air compressed by the turbo passing back through the compressor wheel of the turbo after the airflow is abruptly halted by the throttle plate closing, called compressor surge. However, in some cases, i.e. where the throttle plate doesn't open fast enough or is set up to only react to high boost, some chatter will remain. Surge can occur on diesels when the turbo is attempting to pressurize the air at a higher pressure ratio than the compressor wheel can flow at a given speed. Diesel engine

Diesel engine

A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

s have no use for a blow off valve

Blowoff valve

A blowoff valve or dump valve is a pressure release system present in most turbocharged engines.Its purpose is to prevent compressor surge, and reduce wear on the turbocharger and engine...

as they do not have a throttle plate.

The chatter noise is very noticeable on World Rally Car

World Rally Car

World Rally Car is a term used to describe racing automobiles built to the specification set by the FIA, the international motorsports governing body, and used to compete in the outright class of the World Rally Championship...

s, where anti-lag

Anti-lag

An anti-lag system is a system used on turbocharged engines to minimize turbo lag.- Overview :ALS was first used in the early days of turbocharged cars in Formula One racing circa mid to late 1980s, until fuel restrictions made its use unsuitable...

is used.

A compressor stall like this can cause excess stress and wear on the turbo's shaft or bearings under higher load applications of the turbo (around 15 psi (1 bar) and greater depending on the trim and flow rate of the compressor side).

Actual wastegate flutter occurs instead under partial boost conditions such as partial throttle near the boost threshold. It sounds like FftFftFft not ShuShuShu and is caused by the rapid opening and closing of the wastegate at boost levels near the spring pressure. It is commonly heard more clearly and may be more prominent on cars with modified intake silencers, up-pipes, and or downpipes, and is not harmful.

Wastegate sizing

Wastegate sizing is inversely proportionate to the desired level of boost and is somewhat independent of the size or power of the engine. One vendor's guide for wastegate sizing is as follows:

big turbo/low boost = bigger wastegate
big turbo/high boost = smaller wastegate
small turbo/low boost = bigger wastegate
small turbo/high boost = smaller wastegate