Volvo FM VGT diesel engine with EGR emissions technology
Variable-geometry turbochargers (VGTs), occasionally known as variable-nozzle turbochargers (VNTs), are a type of turbochargers, usually designed to allow the effective aspect ratio (A/R ratio) of the turbocharger to be altered as conditions change. This is done with the use of adjustable vanes located inside the turbine housing between the inlet and turbine, these vanes affect flow of gases towards the turbine. The benefit of the VGT is that the optimum aspect ratio at low engine speeds is very different from that at high engine speeds.
If the aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum. Because of this, VGTs have a minimal amount of lag, a low boost threshold, and high efficiency at higher engine speeds.
A cut open VGT turbocharger (VW Golf, Diesel)
Exhaust side with variable-geometry guide vanes
charge air side with compressor wheel
Turbo shaft storage
Turbo shaft storage
History
The rotating-vane VGT was first developed under Garrett and patented in 1953.[1]
One of the first production cars to use these turbochargers was the 1988 Honda Legend; it used a water-cooled VGT installed on its 2.0-litre V6 engine.
The limited-production 1989 Shelby CSX-VNT, with only 500 examples produced, was equipped with a 2.2-litre Chrysler K engine with a Garrett turbo called the VNT-25 (because it used the same compressor and shaft as the fixed-geometry Garrett T-25).
In 1991, Fiat incorporated a VGT into the Croma's direct-injected turbodiesel.[2]
The Peugeot 405 T16, launched in 1992, used a Garrett VAT25 variable-geometry turbocharger on its 2.0-litre 16-valve engine.
The 2007 Porsche 911 Turbo has twin variable-geometry turbochargers on its 3.6-litre horizontally-opposed six-cylinder gasoline engine.
In 2007, Acura introduced the RDX with Variable Geometry Turbocharger following a (VFT) design.
The 2015 Koenigsegg One:1 (named after its power-to-weight ratio of 1:1) uses twin variable-geometry turbochargers on its 5.0-litre V8 engine, allowing it to produce 1361 horsepower.
Common designs
The most common implementations of VGTs are Variable-Nozzle Turbines (VNT), Sliding Wall Turbines, and Variable Flow Turbines (VFT).
Variable-Nozzle Turbines are common in light-duty engines (passenger cars, race cars, and light commercial vehicles), the turbine's vanes rotate in unison, relative to its hub, to vary its pitch and cross-sectional area. VNTs offer higher flow rates and higher peak efficiency compared to other variable geometry designs.[3]
Sliding Wall Turbines are commonly found in heavy-duty engines, the vanes do not rotate, but instead, their effective width is changed. This is usually done by moving the turbine along its axis, partially retracting the vanes within the housing. Alternatively, a partition within the housing may slide back and forth. The area between the edges of the vanes changes, leading to a variable-aspect-ratio system with fewer moving parts.[4]
Variable Flow Turbines are another simplified version of a VGT when compared to a VNT. This design uses a two-volute turbine housing with a blend gate located in the neck. The gate can vary the flow between the scrolls to average the optimal A/R ratio. In low flow conditions exhaust gas is routed through the primary volute and under peak flow it is directed through both the primary and secondary. This design has a lower flow rate compared to VNT types so a wastegate may be incorporated with this design.[5]
VGTs may be controlled by a membrane vacuum actuator, electric servo, 3-phase electric actuation, hydraulic actuator, or pneumatic actuator using air brake pressure.
Unlike fixed-geometry turbines, VGTs do not require a wastegate.[6] Although VGTs do not require a wastegate, some applications requiring a high mass air flow ratio will benefit from an additional wastegate most commonly found in high performance spark ignition engines.[7] This is in contrast to diesel engines.
Variable Geometry Nozzle Turbine (VNT)
Sliding Wall VGT
Use
VGTs tend to be much more common on diesel engines, as lower exhaust temperatures mean they are less prone to failure. Early gasoline-engine VGTs required significant pre-charge cooling to extend the turbocharger life to reasonable levels, but advances in technology have improved their resistance to high-temperature gasoline exhaust, and they have started to appear increasingly in gasoline-engine cars.[1]
Typically, VGTs are only found in OEM applications due to the level of coordination required to keep the vanes in the most optimal position for whatever state the engine is in. However, there are aftermarket VGT control units available, and some high-end aftermarket engine management systems can control VGTs as well.
In trucks, VGTs are also used to control the ratio of exhaust recirculated back to the engine inlet (they can be controlled to selectively increase the exhaust manifold pressure until it exceeds the inlet manifold pressure, which promotes exhaust gas recirculation). Although excessive engine backpressure is detrimental to overall fuel efficiency, ensuring a sufficient EGR rate even during transient events (such as gear changes) can be sufficient to reduce nitrogen oxide emissions down to that required by emissions legislation (e.g., Euro 5 for Europe and EPA 10 for the USA).
Another use for sliding-vane turbochargers is as a downstream exhaust brake, so that an extra exhaust throttle valve is not needed. The mechanism can also be deliberately modified to reduce the turbine efficiency in a pre-defined position. This mode can be selected to sustain a raised exhaust temperature to promote "light-off" and "regeneration" of a diesel particulate filter (this involves heating the carbon particles stuck in the filter until they oxidize away in a semi-self-sustaining reaction - rather like the self-cleaning process some ovens offer). Actuation of a VGT for EGR flow control, or to implement braking or regeneration modes in general, requires hydraulic actuators or electric servos.
VGTs offer improved transient response over conventional fixed geometry turbochargers. This makes VGTs ideal for use in vehicles where power demand is very dynamic. In situations where engine load is constant like in stationary generators, fixed geometry turbochargers can provide higher efficiency over VGTs.[8] This is due to the added exhaust resistance created from the tolerances of the moving parts within a VGT.
Manufacturers
Several companies manufacture and supply rotating-vane variable-geometry turbochargers, including Garrett, BorgWarner, and Mitsubishi Heavy Industries. This design is mostly limited to small engines and light-duty applications (passenger cars, race cars and light commercial vehicles).
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.
A turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft propulsion. The word "turbofan" is a combination of the preceding generation engine technology of the turbojet, and a reference to the additional fan stage added. It consists of a gas turbine engine which achieves mechanical energy from combustion, and a ducted fan that uses the mechanical energy from the gas turbine to force air rearwards. Thus, whereas all the air taken in by a turbojet passes through the combustion chamber and turbines, in a turbofan some of that air bypasses these components. A turbofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of these contributing to the thrust.
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:
Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum in the cylinder through its downward motion.
Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. the compressed air-fuel mixture is ignited by a spark plug or by heat generated by high compression, forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust port.
Thrust vectoring, also known as thrust vector control (TVC), is the ability of an aircraft, rocket or other vehicle to manipulate the direction of the thrust from its engine(s) or motor(s) to control the attitude or angular velocity of the vehicle.
Garrett Motion Inc., formerly Honeywell Transportation Systems and Honeywell Turbo Technologies, is an American company primarily involved in engineering, development and manufacturing of turbochargers and related forced induction systems for ground vehicles from small passenger cars to large trucks and industrial equipment and construction machinery. It originated as part of Garrett AiResearch's Industrial Division in Phoenix, Arizona, in 1954, after which they entered a contract to provide 5,000 turbochargers for the Caterpillar mining vehicle. It manufactured turbochargers for railroads and commercial trucks. The business produced approximately $3.6 billion in revenue in 2021. Garrett Motion is also involved in motorsports providing turbochargers and forced induction systems, solutions and related equipment to racing teams and various forms of automobile racing and professional competitions. In 2004, the business became part of American industrial conglomerate Honeywell International, Inc., as their Transportation Systems division. In 2018, it was spun off to become an independent company under the Garrett Motion name with corporate headquarters in Rolle, Switzerland.
Mazda has a long history of building its own diesel engines, with the exception of a few units that were built under license.
Power Stroke, also known as Powerstroke or PowerStroke, is the name used by a family of diesel engines for trucks produced by Ford Motor Company and Navistar International for Ford products since 1994. Along with its use in the Ford F-Series, applications include the Ford E-Series, Ford Excursion, and Ford LCF commercial truck. The name was also used for a diesel engine used in South American production of the Ford Ranger.
The Shelby CSX is a limited-production high performance automobile based on the turbocharged intercooled Dodge Shadow and Plymouth Sundance. These cars were offered by Shelby Automobiles Inc. from 1987 through 1989. The CSX serial number was established by AC Cars, in Surrey, England. The purpose of that serial number was to identify which chassis were to be exported to Shelby in the U.S. CSX stood for "Carroll Shelby Export".
A propelling nozzle is a nozzle that converts the internal energy of a working gas into propulsive force; it is the nozzle, which forms a jet, that separates a gas turbine, or gas generator, from a jet engine.
A wastegate is a valve that controls the flow of exhaust gases to the turbine wheel in a turbocharged engine system.
A compressor map is a chart which shows the performance of a turbomachinery compressor. This type of compressor is used in gas turbine engines, for supercharging reciprocating engines and for industrial processes, where it is known as a dynamic compressor. A map is created from compressor rig test results or predicted by a special computer program. Alternatively the map of a similar compressor can be suitably scaled. This article is an overview of compressor maps and their different applications and also has detailed explanations of maps for a fan and intermediate and high-pressure compressors from a three-shaft aero-engine as specific examples.
A twincharger refers to a compound forced induction system used on some internal combustion engines. It is a combination of an exhaust-driven turbocharger and a mechanically driven supercharger, each mitigating the weaknesses of the other.
A jet engine performs by converting fuel into thrust. How well it performs is an indication of what proportion of its fuel goes to waste. It transfers heat from burning fuel to air passing through the engine. In doing so it produces thrust work when propelling a vehicle but a lot of the fuel is wasted and only appears as heat. Propulsion engineers aim to minimize the degradation of fuel energy into unusable thermal energy. Increased emphasis on performance improvements for commercial airliners came in the 1970s from the rising cost of fuel.
In turbocharged internal combustion engines, a boost controller is a device sometimes used to increase the boost pressure produced by the turbocharger. It achieves this by reducing the boost pressure seen by the wastegate.
The Volvo D5 is a type of turbocharged diesel engine developed by Volvo Cars for use in its passenger cars. The D5 engine is based on the Volvo Modular diesel engine. The D5 displaces 2.4 liters; a smaller series of two-litre engines were developed in 2010 and marketed as the Volvo D3 and D4.
The N series is Honda's first automotive diesel engine, an inline-four for medium-sized vehicles. It uses common rail direct injection, which Honda brands as i-CTDi. The most notable feature is the aluminium block, which uses proprietary technology in the manufacturing process to provide light weight and high rigidity. Roller chains drive two overhead camshafts. A variable-geometry turbocharger and intercooler are used.
The YD engine is a 2.2 and 2.5 L inline-four diesel engine from Nissan. It has a cast-iron block and aluminium head with chain driven twin overhead camshafts. The engine shares much of its architecture with the QR petrol engine.
The Mercedes-Benz OM642 engine is a 3.0 litres (2,987 cc), 24-valve, aluminium/aluminium block and heads diesel 72° V6 engine manufactured by the Mercedes-Benz division of Daimler AG as a replacement for the Mercedes straight-5 and straight-6 cylinder engines.
A variable geometry turbomachine uses movable vanes to optimize its efficiency at different operating conditions. This article refers to movable vanes as used in liquid pumps and turbocharger turbines. It does not cover the widespread use of movable vanes in gas turbine compressors.
↑ Khac, Hoang Nguyen (2017-11-20). "Design of diesel engine's optimal control maps for high efficiency and emission reduction". S2CID67274667.{{cite journal}}: Cite journal requires |journal= (help)
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A cut open VGT turbocharger (VW Golf, Diesel)
Exhaust side with variable-geometry guide vanes
charge air side with compressor wheel
Turbo shaft storage
Turbo shaft storage
