Turboaanjaer: Verskil tussen weergawes
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Die hoofdoel van die klep is om skade aan die enjin vanweë 'n drukstuwing te vermy en om te verseker dat die Turbo altyd teen 'n hoë spoed bly draai. Die kleppe kan ook gebruik word om die drukverhoging te beheer op 'n soortgelyke wyse as die afvoersluis maar word selde gebruik om praktiese redes. Die lug word gewoonlik na atmosfeer afgeblaas of kan alternatiewelik na die turbo se inlaat gehersirkuleer word. Die hersirkulasie verminder die blaasklank wat die turbo voortbring. |
Die hoofdoel van die klep is om skade aan die enjin vanweë 'n drukstuwing te vermy en om te verseker dat die Turbo altyd teen 'n hoë spoed bly draai. Die kleppe kan ook gebruik word om die drukverhoging te beheer op 'n soortgelyke wyse as die afvoersluis maar word selde gebruik om praktiese redes. Die lug word gewoonlik na atmosfeer afgeblaas of kan alternatiewelik na die turbo se inlaat gehersirkuleer word. Die hersirkulasie verminder die blaasklank wat die turbo voortbring. |
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===Brandstofdoeltreffendheid=== |
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Aangesien die turbo-aanjaer die spesifieke kraglewering van 'n enjin beïnvloed, sal die enjin ook groter hoeveelhede afvalhitte vrystel. Dit kan probleme veroorsaak in motors wat nie van meet af aan ontwerp is om die hoë hittelading te hanteer nie. Hierdie ekstra afvalhitte saam met die laer [[kompressieverhouding]] van turbo-aangejaagde enjins dra by tot 'n effens laer [[termiese doeltreffendheid]], wat 'n klein maar direkte impak op die oorhoofse [[brandstofdoeltreffendheid]] het. |
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Selfs al word die saamgeperste lug verkoel in 'n [[tussenverkoeler]] is die totale saampersing in die [[verbrandingskamer]] groter as in 'n [[natuurlike geaspireerde enjin]]. Om [[enjinklop]] te vermy en steeds die maksimum krag uit die enjin te tap, is dit soms gebruiklik om ekstra brandstof in te voer slegs om beter verkoeling te bewerkstellig. Die oortollige brandstof word nie verbrand nie maar absorbeer slegs die hitte. Terwyl hierdie gebruik wel lei tot verhoogde kraglewering is dit ten koste van brandstofekonomie en verhoogde uitlaatgasse. |
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<!-- Moet nog vertaal word |
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==Verwysings== |
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===Fuel efficiency=== |
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* [http://www.automobilemag.com/features/news/0602_turbocharger_history/index.html Happy 100th Birthday to the Turbocharger], Don Sherman, Automobile Magazine, February 2006 |
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Since a turbocharger increases the specific [[horsepower]] output of an engine, the engine will also produce increased amounts of [[waste heat]]. This can sometimes be a problem when fitting a turbocharger to a car that was not designed to cope with high heat loads. This extra waste heat combined with the lower [[compression ratio]] (more specifically, expansion ratio) of turbocharged engines contributes to slightly lower [[thermal efficiency]], which has a small but direct impact on overall [[fuel efficiency]]. |
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It is another form of cooling that has the largest impact on fuel efficiency: charge cooling. Even with the benefits of [[intercooled|intercooling]], the total compression in the [[combustion chamber]] is greater than that in a [[naturally-aspirated engine]]. To avoid [[Engine knock|knock]] while still extracting maximum power from the engine, it is common practice to introduce extra fuel into the charge for the sole purpose of cooling. While this seems counterintuitive, this fuel is not burned. Instead, it absorbs and carries away heat when it changes phase from liquid mist to gas vapor. Also, because it is more dense than the other inert substance in the combustion chamber, [[nitrogen]], it has a higher specific heat and more heat capacitance. It "holds" this heat until it is released in the [[exhaust gas|exhaust]] stream, preventing destructive [[Engine knock|knock]]. This thermodynamic property allows manufacturers to achieve good power output with common pump fuel at the expense of fuel economy and emissions. The [[stoichiometric]] Air-to-Fuel ratio (A/F) for combustion of gasoline is 14.7:1. A common A/F in a turbocharged engine while under full design boost is approximately 12:1. Richer mixtures are sometimes run when the design of the system has flaws in it such as a catalytic converter which has limited endurance of high exhaust temperatures or the engine has a compression ratio that is too high for efficient operation with the fuel given. |
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Lastly, the efficiency of the turbocharger itself can have an impact on fuel efficiency. Using a small turbocharger will give quick response and low lag at low to mid RPMs, but can choke the engine on the exhaust side and generate huge amounts of pumping-related heat on the intake side as RPMs rise. A large turbocharger will be very efficient at high RPMs, but is not a realistic application for a street driven automobile. Variable vane and ball bearing technologies can make a turbo more efficient across a wider operating range, however, other problems have prevented this technology from appearing in more road cars (see [[Variable geometry turbocharger]]). Currently, the [[Porsche 997#Turbo|Porsche 911 (997) Turbo]] is the only gasoline car in production with this kind of turbocharger. One way to take advantage of the different operating regimes of the two types of supercharger is [[Twin-turbo|sequential turbocharging]], which uses a small turbocharger at low RPMs and a larger one at high RPMs. |
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The engine management systems of most modern vehicles can control [[boost (automotive engineering)|boost]] and fuel delivery according to charge temperature, fuel quality, and altitude, among other factors. Some systems are more sophisticated and aim to deliver fuel even more precisely based on combustion quality. For example, the Trionic-7 system from [[Saab Automobile]] provides immediate feedback on the combustion while it is occurring using an electrical charge. |
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The new 2.0L [[Gasoline direct injection|TFSI]] turbo engine from [[Volkswagen]]/[[Audi]] incorporates lean burn and direct injection technology to conserve fuel under low load conditions. It is a very complex system that involves many moving parts and sensors in order to manage airflow characteristics inside the chamber itself, allowing it to use a stratified charge with excellent atomization. The direct injection also has a tremendous charge cooling effect enabling engines to use higher compression ratios and boost pressures than a typical port-injection turbo engine. |
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===Automotive design details=== |
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The [[ideal gas law]] states that when all other variables are held constant, if pressure is increased in a system so will temperature. Here exists one of the negative consequences of turbocharging, the increase in the temperature of air entering the engine due to compression. |
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A turbo spins very fast; most peak between 80,000 and 200,000 RPM (using low [[inertia]] turbos, 150,000-250,000 RPM) depending on size, weight of the rotating parts, boost pressure developed and compressor design. Such high rotation speeds would cause problems for standard [[ball bearing]]s leading to failure so most turbo-chargers use [[fluid bearing]]s. These feature a flowing layer of oil that suspends and cools the moving parts. The oil is usually taken from the engine-oil circuit. Some turbochargers use incredibly precise ball bearings that offer less friction than a fluid bearing but these are also suspended in fluid-dampened cavities. Lower friction means the turbo shaft can be made of lighter materials, reducing so-called ''turbo lag'' or ''boost lag''. Some car makers use water cooled turbochargers for added bearing life. This can also account for why many tuners upgrade their standard journal bearing turbos (such as a T25) which use a 270 degree thrust bearing and a brass journal bearing which only has 3 oil passages, to a 360 degree bearing which has a beefier thrust bearing and washer having 6 oil passages to enable better flow, response and cooling efficiency. |
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Turbochargers with [[foil bearing]]s are in development which eliminates the need for bearing cooling or oil delivery systems, thereby eliminating the most common cause of failure, while also significantly reducing turbo lag. |
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To manage the ''upper-deck'' air pressure, the turbocharger's exhaust gas flow is regulated with a [[wastegate]] that bypasses excess exhaust gas entering the turbocharger's turbine. This regulates the rotational speed of the turbine and the output of the compressor. The wastegate is opened and closed by the compressed air from turbo (the upper-deck pressure) and can be raised by using a [[solenoid]] to regulate the pressure fed to the wastegate membrane. This solenoid can be controlled by [[Automatic Performance Control]], the engine's [[electronic control unit]] or an after market boost control computer. Another method of raising the boost pressure is through the use of check and bleed valves to keep the pressure at the membrane lower than the pressure within the system. |
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Some turbochargers (normally called [[variable geometry turbocharger]]s) utilise a set of vanes in the exhaust housing to maintain a constant gas velocity across the turbine, the same kind of control as used on power plant turbines. These turbochargers have minimal amount of lag, have a low boost threshold (with full boost as low as 1,500 rpm), and are efficient at higher engine speeds; they are also used in diesel engines. <ref>{{cite web |
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| last = Parkhurst |
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| first =Terry |
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| title = Turbochargers: an interview with Garrett’s Martin Verschoor |
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| publisher = Allpar, LLC |
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| url =http://www.acarplace.com/cars/turbochargers.html |
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| accessdate = [[12 December]] [[2006]]}}</ref> In many setups these turbos don't even need a wastegate. The vanes are controlled by a membrane identical to the one on a wastegate but the level of control required is a bit different. |
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The first production car to use these turbos was the limited-production [[1989]] [[Shelby CSX|Shelby CSX-VNT]], in essence a [[Dodge Shadow]] equipped with a 2.2L [[petrol engine]]. The Shelby CSX-VNT utilised a turbo from [[Garrett Systems|Garrett]], called the VNT-25 because it uses the same compressor and shaft as the more common Garrett T-25. This type of turbine is called a '''Variable Nozzle Turbine (VNT)'''. Turbocharger manufacturer Aerocharger uses the term 'Variable Area Turbine Nozzle' (VATN) to describe this type of turbine nozzle. Other common terms include Variable Turbine Geometry (VTG), Variable Geometry Turbo (VGT) and Variable Vane Turbine (VVT). A number of other [[Chrysler Corporation]] vehicles used this turbocharger in 1990, including the [[Dodge Daytona]] and [[Dodge Shadow]]. These engines produced 174 horsepower and 225 pound-feet of torque, the same horsepower as the standard intercooled 2.2 liter engines but with 25 more pound-feet of torque and a faster onset (less turbo lag). However, the Turbo III engine, without a VATN or VNT, produced 224 horsepower. The reasons for Chrysler's not continuing to use variable geometry turbochargers are unknown, but the main reason was probably public desire for V6 engines coupled with increased availability of Chrysler-engineered V6 engines. <ref>[http://www.allpar.com/mopar/22t.html Allpar turbo engine history]</ref> |
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The 2006 [[Porsche 997|Porsche 911 Turbo]] has a twin turbocharged 3.6-litre flat six, and the turbos used are [[BorgWarner]]'s Variable Geometry Turbos (VGTs). This is significant because although VGTs have been used on advanced diesel engines for a few years and on the Shelby CSX-VNT, this is the first time the technology has been implemented on a production petrol car since the 1,250 Dodge engines were produced in 1989-90. Some have argued this is because in petrol cars exhaust temperatures are much higher (than in diesel cars), and this can have adverse effects on the delicate, moveable vanes of the turbocharger; these units are also more expensive than conventional turbochargers. Porsche engineers claim to have managed this problem with the new 911 Turbo. |
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=== Motorcycles=== |
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Using turbochargers to gain performance without a large gain in weight was very appealing to the Japanese factories in the 1980s. [[Suzuki]], [[Yamaha]] and [[Kawasaki]] chose the route of an inline four with a turbo unit. However [[Honda]] uprated their CX500 Vee twin along with an upgraded chassis and an added fairing and so produced their flagship performance model. It raised the standard machines power from 50BHP to 82BHP at 8,000rpm, using a maximum boost of 18.5psi. It was no faster than the current 750's of the day and weighed a not inconsiderable 574lb (curb weight). [[Turbo lag]] was a problem with this machine, its performance in town and urban riding with its low compression ratio and when off boost was underwhelming. Fuel injection, watercooling, and a 2 inch turbo spinning to 200,000 rpm was not enough to impress the buying public. Honda's Hi-tec approach and even a capacity lift to 650cc was not enough to reverse the trend. The other Japanese factories fared little better, though of all the 'fours' Kawasaki's Gpz 750 was perhaps the best. |
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It looked much like its non boosted version (86 BHP) and still aircooled, but put out 112 BHP, putting it into the performance range (if not handling) of its stablemate GPZ900 (Ninja). |
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The Suzuki's Turbo was the XN85 (its quoted BHP) this extracted from only 650cc. It had something of its [[Katana]] relatives looks, 16inch front wheel and monoshock rear suspension, but was soon overshadowed by the release of Suzukis own GS750ES later in 1983, it was only in production until 1986. |
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Yamaha stayed with a carburetter for their turbo model, the standard engine put out 73BHP the XJ650Turbo however put out 90BHP at 8,500rpm, and was released at the 1981 Tokyo Motorcycle Show. |
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==Properties and Applications== |
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===Reliability=== |
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Turbochargers can be damaged by dirty or ineffective oil, and most manufacturers recommend more frequent oil changes for turbocharged engines; many owners and some companies recommend using [[synthetic oil]]s, which tend to flow more readily when cold and do not break down as quickly as conventional oils. Because the turbocharger can get hot when running, many recommend letting the engine idle for one to three minutes before shutting off the engine if the turbocharger was used shortly before stopping (most manufacturers specify a 10-second period of idling before switching off to ensure the turbocharger is running at its idle speed to prevent damage to the bearings when the oil supply is cut off). This lets the turbo rotating assembly cool from the lower exhaust gas temperatures, and ensures that oil is supplied to the turbocharger while the turbine housing and exhaust manifold are still very hot; otherwise [[Coke (fuel)|coking]] of the lubricating oil trapped in the unit may occur when the heat soaks into the bearings, causing rapid bearing wear and failure when the car is restarted. Even small particles of burnt oil will accumulate and lead to choking the oil supply and failure. This problem is less pronounced in [[diesel engine]]s, due to the lower exhaust temperatures and generally slower engine speeds. |
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A [[turbo timer]] can keep an engine running for a pre-specified period of time, to automatically provide this cool-down period. Oil coking is also eliminated by [[foil bearings]]. A more complex and problematic protective barrier against oil coking is the use of watercooled bearing cartridges. The water boils in the cartridge when the engine is shut off and forms a natural recirculation to drain away the heat. It is still a good idea to not shut the engine off while the turbo and manifold are still glowing. |
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In custom applications utilizing tubular headers rather than [[cast iron]] manifolds, the need for a cooldown period is reduced because the lighter headers store much less heat than heavy cast iron manifolds. |
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===Lag=== |
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[[Image:Twinturbo.JPG|thumb|250px|right|A pair of turbochargers mounted to an [[Inline 6]] engine ([[Toyota JZ engine|2JZ-GTE]] from a [[Toyota Supra|MkIV Toyota Supra]]) in a [[dragster]].]] |
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A [[lag]] is sometimes felt by the driver of a turbocharged vehicle as a delay between pushing on the accelerator pedal and feeling the turbo ''kick-in''. This is symptomatic of the time taken for the exhaust system driving the turbine to come to high pressure and for the turbine rotor to overcome its [[rotational inertia]] and reach the speed necessary to supply boost pressure. The directly-driven compressor in a [[supercharger]] does not suffer this problem. (Centrifugal superchargers do not build boost at low RPMs like a positive displacement supercharger will). Conversely on light loads or at low RPM a turbocharger supplies less boost and the engine is more efficient than a supercharged engine. |
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Lag can be reduced by lowering the rotational inertia of the turbine, for example by using lighter parts to allow the spool-up to happen more quickly. Ceramic turbines are a big help in this direction. Unfortunately, their relative fragility limits the maximum boost they can supply. Another way to reduce lag is to change the [[aspect ratio]] of the turbine by reducing the diameter and increasing the gas-flow path-length. Increasing the upper-deck air pressure and improving the [[wastegate]] response helps but there are cost increases and reliability disadvantages that car manufacturers are not happy about. Lag is also reduced by using a [[foil bearing]] rather than a conventional oil bearing. This reduces friction and contributes to faster acceleration of the turbo's rotating assembly. Variable-nozzle turbochargers (discussed above) also reduce lag. |
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Another common method of equalizing turbo lag is to have the turbine wheel "clipped", or to reduce the surface area of the turbine wheel's rotating blades. By clipping a minute portion off the tip of each blade of the turbine wheel, less restriction is imposed upon the escaping exhaust gases. This imparts less impedance onto the flow of exhaust gases at low RPM, allowing the vehicle to retain more of its low-end [[torque]], but also pushes the effective boost RPM to a slightly higher level. The amount a turbine wheel is and can be clipped is highly application-specific. Turbine clipping is measured and specified in degrees. |
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Other setups, most notably in [[V engine|V-type engine]]s, utilize two identically-sized but smaller turbos, each fed by a separate set of exhaust streams from the engine. The two smaller turbos produce the same (or more) aggregate amount of boost as a larger single turbo, but since they are smaller they reach their optimal RPM, and thus optimal boost delivery, faster. Such an arrangement of turbos is typically referred to as a [[Twin-turbo#Parallel Twin-Turbo|parallel twin-turbo]] system. |
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Some car makers combat lag by using two small turbos (such as [[Kia]], [[Toyota]], [[Subaru]], [[Maserati]], [[Mazda]], and [[Audi]]). A typical arrangement for this is to have one turbo active across the entire rev range of the engine and one coming on-line at higher RPM. Early designs would have one turbocharger active up to a certain RPM, after which both turbochargers are active. Below this RPM, both exhaust and air inlet of the secondary turbo are closed. Being individually smaller they do not suffer from excessive lag and having the second turbo operating at a higher RPM range allows it to get to full rotational speed before it is required. Such combinations are referred to as a [[Twin-turbo#Sequential Twin-turbo|sequential twin-turbo]]. Sequential twin-turbos are usually much more complicated than a single or parallel twin-turbo systems because they require what amounts to three sets of pipes-intake and wastegate pipes for the two turbochargers as well as valves to control the direction of the exhaust gases. An example of this is the current [[BMW E60]] [[BMW 5 Series|5-Series]] 535d. Another well-known example is the 1993-2002 Mazda RX-7. Many new diesel engines use this technology to not only eliminate lag but also to reduce fuel consumption and produce cleaner emissions. |
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Lag is not to be confused with the boost threshold; however, many publications still make this basic mistake. The boost threshold of a turbo system describes the minimum engine RPM at which there is sufficient exhaust flow to the turbo to allow it to generate significant amounts of boost{{Fact|date=February 2007}}. Newer turbocharger and engine developments have caused boost thresholds to steadily decline to where day-to-day use feels perfectly natural. Putting your foot down at 1200 engine RPM and having no boost until 2000 engine RPM is an example of boost threshold and not ''lag''. Howewer, the term lag is used for boost threshold by many manufacturers themselves so as not to confuse common man with many words. |
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Electrical boosting ("E-boosting") is a new technology under development; it uses a high speed electrical motor to drive the turbocharger to speed before exhaust gases are available, e.g. from a stop-light. The electric motor is about an inch long. <ref>{{cite web |
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| last = Parkhurst |
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| first =Terry |
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| title = Turbochargers: an interview with Garrett’s Martin Verschoor |
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| publisher = Allpar, LLC |
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| url =http://www.acarplace.com/cars/turbochargers.html |
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| accessdate = 12/12/2006}}</ref> |
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[[Auto racing|Race cars]] often utilise an [[Anti-Lag System]] to completely eliminate lag at the cost of reduced turbocharger life. |
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On modern [[diesel engine]]s, this problem is virtually eliminated by utilising a [[variable geometry turbocharger]]. |
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===Boost Threshold=== |
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Turbocharger starts producing boost only above a certain rpm (depending on the size of the turbo) due to a lack of exhaust gas volume to overcome the [[inertia of rest]] of the turbo propeller. Power suddenly increases after that particular rpm when turbo propeller starts spinning. So power Vs rpm curve of a turbocharged engine has a steep increase in power at boost threshold rpm. There have been many advancements in technology to reduce boost threshold rpm below idle speed rpm of the engine, so as to virtually eliminate the boost threshold. |
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===Automotive Applications=== |
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Turbocharging is very common on [[diesel engine]]s in conventional automobiles, in [[truck]]s, [[locomotives]], for marine and heavy machinery applications. In fact, for current automotive applications, non-turbocharged diesel engines are becoming increasingly rare. Diesels are particularly suitable for turbocharging for several reasons: |
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* [[Naturally-aspirated engine|Naturally-aspirated]] diesels will develop less power than a gasoline engine of the same size, and will weigh significantly more because diesel engines require heavier, stronger components. This gives such engines a poor [[power-to-weight ratio]]; turbocharging can dramatically improve this P:W ratio, with large power gains for a very small (if any) increase in weight. |
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* Diesel engines require more robust construction because they already run at very high [[compression ratio]] and at high temperatures so they generally require little additional reinforcement to be able to cope with the addition of the turbocharger. Gasoline engines often require extensive modification for turbocharging. |
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* Diesel engines have a narrower band of engine speeds at which they operate, thus making the operating characteristics of the turbocharger over that "rev range" less of a compromise than on a gasoline-powered engine. |
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* Diesel engines blow nothing but air into the cylinders during cylinder charging, squirting fuel into the cylinder only after the intake valve has closed and compression has begun. Gasoline/petrol engines differ from this in that both fuel and air are introduced during the intake cycle and both are compressed during the compression cycle. The higher intake charge temperatures of forced-induction engines reduces the amount of compression that is possible with a gasoline/petrol engine, whereas diesel engines are far less sensitive to this. |
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Today, turbocharging is most commonly used on two types of engines: Gasoline engines in high-performance automobiles and diesel engines in transportation and other industrial equipment. Small cars in particular benefit from this technology, as there is often little room to fit a larger-output (and physically larger) engine. [[Saab Automobile|Saab]] is a leader in production car turbochargers, starting with the [[1978]] [[Saab 99]]; all current Saab models are turbocharged with the exception of the [[Saab 9-7X|9-7X]]. The [[Porsche 944]] utilized a turbo unit in the 944 Turbo (Porsche internal model number 951), to great advantage, bringing its 0-100 km/h (0-60 mph) times very close to its contemporary non-turbo "big brother", the [[Porsche 928]]. |
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In the 1980s, when turbocharged production cars became common, they gained a reputation for being difficult to handle. The tuned engines fitted to the cars, and the often primitive turbocharger technology meant that power delivery was unpredictable and the engine often suddenly delivered a huge boost in power at certain speeds. Some drivers said this made cars such as the [[BMW 2002]] and the [[Porsche 911]] exciting to drive, requiring high levels of skill. Others said the cars were difficult and often dangerous. As turbocharger technology improved, it became possible to produce turbocharged engines with a smoother, more predictable but just as effective power delivery. |
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[[Chrysler Corporation]] was an innovator of turbocharger use in the [[1980s]]. Many of their production vehicles, for example the [[Chrysler LeBaron]], [[Dodge Daytona]], [[Dodge Shadow]]/[[Plymouth Sundance]] twins, and the [[Dodge Spirit]]/[[Plymouth Acclaim]] twins were available with turbochargers, and they proved very popular with the public. They are still considered competitive vehicles today, and the experience Chrysler obtained in observing turbochargers in real-world conditions has allowed them to further turbocharger technology with the [[PT Cruiser]] Turbo, the [[Dodge SRT-4]] and the [[Dodge Caliber]] SRT-4. |
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[http://www.barber-nichols.com/products/specialty_products/turbo_alternators/default.asp Turbo-Alternator] is a form of turbocharger that generates electricity instead of boosting engine's air flow. On [[September 21]] [[2005]], [http://www.foresightvehicle.org.uk/ Foresight Vehicle] announced the first known implementation of such unit for automobiles, under the name [http://www.greencarcongress.com/2005/09/tigers_exhaust_.html TIGERS] (Turbo-generator Integrated Gas Energy Recovery System). |
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===Aircraft Applications=== |
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Turbochargers are used in reciprocating aircraft engines which are designed for high altitude use. As an aircraft climbs in altitude, the density of the air surrounding it decreases. As the density of the air decreases, so does the drag on the airframe, but so does the power of the engine. With this in mind, turbochargers were developed for aircraft to keep the pressure of the air entering the engine equivalent to a normally aspirated engine at sea level. In this case the system is called a ''turbo-normalizer''. Other systems use the turbocharger to boost the engine manifold pressure to much higher than sea level pressures; in the area of 35 to 45 [[inches of mercury]]; and this is called ''turbo-boosting''. In either case, an automatic or manually-controlled [[wastegate]] is used to vary the turbocharger output according to operating conditions. |
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===Implementations=== |
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The most common implemenations of a turbocharger involve mounting the unit to the downpipe of a vehicle under the hood towards the firewall of the vehicle. |
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A rear mount implementation is used when there is insufficient engine bay room; it may be used in place of the stock muffler. The turbo returns the boosted air (which is pulled in from a filter mounted somewhere in the rear) to the front of the vehicle and optionally through an intercooler, and then to the intake of the engine. Wiring and oil lines must be run to the rear of the vehicle and an auxiliary oil pump must be used to return oil from the turbo to the engine. According to Horsepower TV (2/3/2007), you can expect a loss of 1 psi using a rear mount turbo, because of loss due to the long pipe routings, and also about a 100°F drop in intake air temperature. The decrease is due to the cooler exhaust gases (thus a cooler turbo unit) and the cooler intermediate pipe between the turbo and the intake. Benefits include easier maintenance, because the unit is more accessible. |
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==Relationship to Gas Turbine Engines== |
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Prior to World War II, [[Sir Frank Whittle]] started his experiments on early [[turbojet]] engines. Due to a lack of sufficient materials as well as funding, initial progress was slow. However, turbochargers were used extensively in military aircraft during World War II to enable them to fly very fast at very high altitudes. The demands of the war led to constant advances in turbocharger technology, particularly in the area of materials. This area of study eventually crossed over in to the development of early [[Gas Turbine|gas turbine engines]]. Those early turbine engines were little more than a very large turbocharger with the compressor and turbine connected by a number of [[Combustion Chamber|combustion chambers]]. Consider also, for example, that [[General Electric]] manufactured turbochargers for military aircraft and held several patents on their electric turbo controls during the war, then used that expertise to very quickly carve out a dominant share of the gas turbine market which they have held ever since. Other companies such as [[Garrett]] make both gas turbine engines and turbochargers. |
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== Advantages and Disadvantages == |
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=== Advantages === |
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* More specific power over naturally aspirated engine. This means a turbocharged engine can achieve more power from same engine volume. |
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* More thermal efficiency over both naturally aspirated and supercharged engine. That means more mileage for same power output. Due to fall in temperature of exhaust gases in a turbocharger, thus energy recovered is used to boost the intake. However, a turbocharger does load the engine by creating back pressure, but not as much as a supercharger's mechanical drag. |
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* Weight/Packaging. Smaller and lighter than alternative forced induction systems and can be more easily fitted in an engine bay. |
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* Responsiveness if a correctly sized turbocharger is used{{Fact|date=May 2007}}. A turbocharger that is properly matched to the engine can/will provide power almost as instantly as a supercharger would. This results in a flatter power-curve. |
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===Disadvantages=== |
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* Lack of responsiveness if an incorrectly sized turbocharger is used. If a turbocharger that is too large is used it reduces throttle response as it builds up boost slowly. However you have more peak power. |
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* Boost threshold. Turbocharger starts producing boost only above a certain rpm due to a lack of exhaust gas volume to overcome [[inertia of rest]] of turbo propeller. This results in low torque at low revs, and hence reduces the usable power band of the engine. Also may result in sudden oversteer during cornering. |
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* Cost. Turbocharger parts are costly to add to naturally aspirated engines. |
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==References== |
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* {{cite journal |
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| url=http://www.automobilemag.com/features/news/0602_turbocharger_history/index.html |
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| |title=Happy 100th Birthday to the Turbocharger |
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| |author=Don Sherman |
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| journal=[[Automobile Magazine]] |
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| date=February 2006 |
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}} |
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<references/> |
<references/> |
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== |
== Eksterne skakels == |
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*[http://auto.howstuffworks.com/turbo.htm Artikel oor hoe turbo-aanjaers werk] |
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*[[Boost gauge]] |
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*[http://www.hot4s.com/tech_turboengines.php Fotos van 5 kragtige turbo enjins] |
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*[[Boost controller]] |
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*[[Twin-turbo]] |
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*[[Intercooler]] |
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*[[Turbo timer]] |
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*[[Supercharger]] |
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*[[Blow off valve]] |
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*[[Forced Induction]] |
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== External links == |
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*[http://auto.howstuffworks.com/turbo.htm How turbochargers work at HowStuffWorks.com] |
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*[http://www.hot4s.com/tech_turboengines.php Photos of 5 turbo engines over 500hp] |
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[[Kategorie:Voertuigtegnologie]] |
[[Kategorie:Voertuigtegnologie]] |
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Wysiging soos op 15:56, 12 Junie 2007
'n Turbo-aanjaer is 'n meganiese induksietoestel aangedryf deur uitlaatgas wat gebruik word in binnebrandenjins om die werkverrigting te verbeter deur saamgeperste lug in die verbrandingskamers in te dwing. Dit maak dit moontlik om meer brandstof per slag te verbrand wat lei tot 'n groter kraglewering.
Beginsel van werking
'n Turbo-aanjaer bestaan uit 'n turbine en 'n kompressor wat aan 'n gemeenskaplike as gekoppel is. Die turbine-inlaat ontvang die uitlaatgasse vanaf die verdelerpyp op die enjin-uitlaat wat die turbine se wiel laat draai. Die rotasie van die uitlaatgasse dryf die kompressor aan wat die lug saampers en dit na die inlaatverdeelpyp voer.
Die doel van 'n turbo-aanjaer is om die doeltreffendheid van 'n enjin se kraglewering te verbeter deur een van die hoofbeperkinge daarvan te oorkom. 'n Natuurlik geaspireerde enjin gebruik slegs die afwaartse slag van 'n suier om 'n lae druk te skep om lug by die silinder in te suig. Die getal lug- en brandstofmolekules bepaal die beskikbare potensiële energie om suier afwaarts te dwing tydens die kragslag. Gegewe dat die atmosferiese lugdruk relatief konstant bly sal daar dus 'n beperking wees tot die hoeveelheid lug en gevolglik die hoeveelheid brandstof wat in die verbrandingskamer ingesuig kan word. Die vermoë om die silinder met lug te vul word na verwys as die volumetriese doeltreffendheid. Aangesien die turbo-aanjaer die lugdruk verhoog voor dit die silinder binnegaan en die hoeveelheid lug wat ingelaat word grootliks 'n funksie van druk en tyd is, sal meer lug ingelaat word as die druk verhoog word. Die funksie van die turbo-aanjaer is dus om hierdie inlaatdruk op 'n beheerbare manier te verhoog.
Die gebruik van 'n kompressor om die inlaatdruk na die silinder te verhoog word dikwels na verwys as meganiese induksie. Sentrifugale drukaanjaers werk op dieselfde manier as 'n turbo-aanjaer; die verskil is egter dat die energie om die kompressor aan te dryf in die geval van 'n drukaanjaer vanaf die enjin se krukas verkry word in plaas van die uitlaatgas soos in die geval van 'n turbo-aanjaer. Om hierdie rede is turbo-aanjaers meer doeltreffend, aangesien hulle turbienes hitte-enjins is, wat die kinetiese energie van die uitlaatgas wat andersins vermors sou word, omskakel na nuttige werk. Die energie is anders as wat algemeen aanvaar word nie geheel en al verniet nie. Die turbo-aanjaer veroorsaak 'n terugdruk wat deur die enjin oorkom moet word. Drukaanjaers gebruik weer die uitsetkrag van die enjin om 'n verhoging in kraglewering te verkry wat 'n vermindering van die enjin se totale moontlike kraguitset veroorsaak.
Geskiedenis
Die turbo-aanjaer is deur die Switserse ingenieur Alfred Buchi uitgevind wat werk gedoen het op stoomturbienes. Hy het in 1905 aansoek gedoen om die patent vir die interne-verbrandingturbo-aanjaer. Dieselskepe en -lokomotiewe wat toegerus is met turbo-aanjaers het hul verskyning in die 1920's begin maak. Een van die eerste geruike van turbo-aanjaers wat nie in Diesel-enjins gebruik is nie het plaasgevind toe Sanford Moss, 'n ingenieur van General Electric, 'n turbo op 'n V12 vliegtuigenjin geïnstalleer het. Die enjin het die voordeel gehad dat dit nie soveel krag verloor het soos ander vliegtuigenjins wat met binnebrandenjins as hulle hoog gevlieg het nie.
Turbo-aanjaers is vir die eerste keer in vliegtuigenjins gebruik tydens die 1930's voor die Tweede Wêreldoorlog. Die hoofdoel vir die aanwending van turbo's in vliegtuigenjins was dan om die hoogte waarteen die vliegtuie kon vlieg te verhoog deur te vergoed vir die laer atmosferiese druk by hoë hoogtes. Vliegtuie soos die Lockheed P-38 Lightning, Boeing B-17 Flying Fortress en B-29 Superfortress het almal uitlaatgas gedrewe "turbo-aanjaers" gebruik om die kraglewering van hul enjins op hoë hoogtes te verhoog. Dit is belangrik om kennis te neem dat die oorgrootte meerderheid vliegtuie van hierdie tydperk beide rataangedrewe sentrifugale drukaanjaers asook uitlaatgasgedrewe turbo-aanjaers op dieselfde enjin gebruik het.
Turbo-Diesel vragmotors is in Europa en Amerika (veral Cummins) na 1949 vervaardig. Die turbo-aanjaer het groot opslae in 1952 gemaak toe Fred Agabashian die voorste wegspringplek behaal het tydens die kwalifiserende rondtes van die Indianapolis 500 en voorgeloop het totdat meganiese probleme sy motor gebreek het.
Na aanvanklike vroeëre minder suksesvolle pogings deur General Motors met turbo-aangejaagde passasiersmotors het BMW die herlewing van turbo-aanjaers in 1973 ingelui met die 2002 Turbo met Porsche kort op hulle hakke met die bekendstelling van die 911 Turbo by die Paryse Motorskou in 1974. Buick was die eerste van GM se afdelings wat die turbo weer heringestel het in die 1978 Buick Regal, gevolg deur Mercedes-Benz met die 300D en Saab 99 in 1978. Die wêreld se eerste passasiersmotor met 'n turbodiesel is ook in 1978 bekendgestel deur Peugeot met die loods van die Peugeot 604. Vandag word byna alle passasiersvoertuie met Dieselenjins met Turbo-aanjaers toegerus.
Alfa Romeo was die eerste Italiaanse vervaardiger met 'n motor met 'n turbo-aanjaer met hul Alfetta GTV 2000 Turbodelta in 1979. Pontiac het 'n motor met 'n turbo in 1980 bekendgestel gevolg deur Volvo in 1981. Renault het 'n nuwe rigting ingeslaan deur 'n turbo-aanjaer in hul kleinste en ligste motor, die R5 te installeer in 1980.
In Formule Een staan die tydperk tussen 1977 tot 1989 as die "Turbo Era" bekend. Dit was die tydperk toe enjins met verplasings van 1500 cc kraglewering van tussen 746 tot 1119 kW kon bereik. Renault was die eerste vervaardiger om turbotegnologie in 1977 in F1 te gebruik. Turbo-aanjaers het die sport oorgeneem, maar die FIA het besluit dat dit die sport te gevaarlik en duur gemaak het en het beperkinge begin plaas op die druktoename in 1987 en is turbo-aanjaers in 1989 uiteindelik geheel en al verban.
In tydrenne is turbo-aangedrewe enjins met 'n verplasing van meer as 2000cc al lank die gunsteling kragbron by die Groep A/Wêreldtydrenkampioenskap (topvlak) mededingers vanweë die uitstaande krag-tot-gewig verhouding (en besonderse hoë wringkrag) wat bereikbaar is. Die FIA het eerder as om die tegnologie in tydrenne te verban, beperkings geplaas op die inlaatdeursnee en sodoende die druktoename beperk.
Die sukses van klein, turbo-aangedrewe, vierwielaangedrewe voertuie in tydrenne, wat begin het met die Audi Quattro het gelei tot die ontwikkeling van padvoertuie soos die Lancia Integrale, Toyota Celica GT-four, Subaru Impreza WRX en die Mitsubishi Lancer Evolution.
Ontwerpbesonderhede
Komponente
'n Turbo-aanjaer het vier hoofkomponente:
- Die turbinewiel
- Die stuwer
- Koniese omhulsels vir elke wiel
- Die sentrale roterende spil
Die omhulsel rondom die kompressor se stuwer en turbine versamel en stuur die gasvloeie deur die wiele. Die grootte en die vorm van die omhulsel bepaal baie van die werkverrigtingseienskappe van die turbo-aanjaer. Die oppervlakte van die koniese deel vanaf die spil tot die wye tuit word uitgedruk as 'n verhouding. Sommige vervaardigers verskaf 'n basiese samestelling met verskeie keuses van bogenoemde verhouding. Dit laat die ontwerper toe om 'n doelgemaakte ontwerp daar te stel in terme van die werkverrigting, reaksiesnelheid en doeltreffendheid na gelang van die spesifieke ontwerpdoelwit. Die turbine- en stuwerwiel groottes dikteer ook die hoeveelheid lug of uitlaatgas wat deur die stelsel kan vloei en die relatiewe doeltreffendheid van hul werking. 'n Algemene reël is dat hoe groter die turbine- en kompressorwiele hoe groter die lugvloeikapasiteit. Mates en vorms, asook die kromming van- en die aantal lemme op die wiele wissel. Die as verbind die stuwer en turbine aanmekaar. Die as moet ook laers bevat om wrywing te verlaag.
Drukverhoging
Die drukverhoging verwys na die toename in die absolute inlaatverdeelpyp se druk wat deur die turbo-aanjaer veroorsaak word. Dit is presies gelyk aan die druk soos op 'n drukmeter aangedui word. Die drukverhoging word beperk om die enjinstelsel binne sy bedryfsbestek te hou en word beheer deur 'n afvoersluis wat uitlaatgasse verby die uitlaatturbine laat vloei. In sommige motors hang die maksimum drukverhoging af van die brandstof se oktaangehalte en word elektronies beheer deur 'n klopsensor.
Baie dieselenjins het nie so 'n afvoersluis nie omdat die hoeveelheid uitlaatgas direk beheer word deur die hoeveelheid brandstof wat ingespuit word en klein veranderinge in die drukverhoging maak nie 'n groot verskil aan die enjin se werkverrigting nie.
Afvoersluis
Die vinnig draaiende kompressor turbine trek 'n groot hoeveelheid lug in en forseer dit deur die enjin. As die turbo-aanjaer se uitsetvloei die enjin se volumetriese vermoë oorskry sal die inlaatverdeelpyp se druk te hoog word. Die rotasiesnelheid van die turbine kan ook te hoog word en daarom moet die uitlaatgas wat dit aandryf beheer word. Vir die doeleinde is die gebruik van 'n afvoersluis die mees algemene meganiese manier om die spoed te beheer. Die stelsel word dikwels deur 'n bykomstige elektroniese beheerstelsel bygestaan. Die hoofdoel van die afvoersluis is dus om van die uitlaatgas rondom die turbine te lei wanneer die verlangde inlaatdruk verkry is. Die meeste passasiersvoertuie se afvoersluise word by die turbo-aanjaer ingebou.
Stuwingsvermydings-, Stort- of Afblaaskleppe
Turbo-aangedrewe enjins wat met 'n vol-oop smoorklep en teen hoë omwentelinge werk vereis 'n groot hoeveelheid lug om te vloei tussen die turbo en die inlaat van die enjin. As die smoorklep toegemaak word sal die saamgeperste lug na die smoorklep beweeg sonder 'n plek om heen te gaan. Dit kan 'n stuwing tot gevolg hê wat die druk van die lug tot so 'n mate verhoog dat die enjin beskadig kan word. Die skielike drukverhoging kan ook 'n terugvloei na die turbo se kompressor veroorsaak wat die kompressor se wiel skielik sal rem. As die smoorklep weer oopgemaak word sal die terugdruk ook veroorsaak dat die kompressor stadig versnel en dus die reaksiesnelheid van die enjin beïnvloed. Om hierdie verskynsel te verhoed word 'n klep tussen die turbo en die inlaat geïnstalleer om die oortollige lug af te blaas. Die kleppe word gewoonlike geaktiveer deur die enjin vakuum of deur elektroniese beheermetodes.
Die hoofdoel van die klep is om skade aan die enjin vanweë 'n drukstuwing te vermy en om te verseker dat die Turbo altyd teen 'n hoë spoed bly draai. Die kleppe kan ook gebruik word om die drukverhoging te beheer op 'n soortgelyke wyse as die afvoersluis maar word selde gebruik om praktiese redes. Die lug word gewoonlik na atmosfeer afgeblaas of kan alternatiewelik na die turbo se inlaat gehersirkuleer word. Die hersirkulasie verminder die blaasklank wat die turbo voortbring.
Brandstofdoeltreffendheid
Aangesien die turbo-aanjaer die spesifieke kraglewering van 'n enjin beïnvloed, sal die enjin ook groter hoeveelhede afvalhitte vrystel. Dit kan probleme veroorsaak in motors wat nie van meet af aan ontwerp is om die hoë hittelading te hanteer nie. Hierdie ekstra afvalhitte saam met die laer kompressieverhouding van turbo-aangejaagde enjins dra by tot 'n effens laer termiese doeltreffendheid, wat 'n klein maar direkte impak op die oorhoofse brandstofdoeltreffendheid het.
Selfs al word die saamgeperste lug verkoel in 'n tussenverkoeler is die totale saampersing in die verbrandingskamer groter as in 'n natuurlike geaspireerde enjin. Om enjinklop te vermy en steeds die maksimum krag uit die enjin te tap, is dit soms gebruiklik om ekstra brandstof in te voer slegs om beter verkoeling te bewerkstellig. Die oortollige brandstof word nie verbrand nie maar absorbeer slegs die hitte. Terwyl hierdie gebruik wel lei tot verhoogde kraglewering is dit ten koste van brandstofekonomie en verhoogde uitlaatgasse.
Verwysings
- Happy 100th Birthday to the Turbocharger, Don Sherman, Automobile Magazine, February 2006