This page will contain wikis about Topaz, as they become available.|
This article is about the mineral or gemstone, for other uses see: Topaz (disambiguation).Topaz 4 Carat Oval Shape Topaz Gemstone Ring Enhanced with Azotic(r)Treatment Heart Cut Sky Blue Topaz Ring
The mineral topaz is a silicate of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. It crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. It has an easy and perfect basal cleavage and so gemstones or other fine specimens should be handled with care to avoid developing cleavage flaws. The fracture is conchoidal to uneven. Topaz has a hardness of 8, a specific gravity of 3.4-3.6, and a vitreous lustre. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. They may also be white, gray, green, blue, or reddish-yellow and transparent or translucent. When heated, yellow topaz often becomes reddish-pink. It can also be irradiated, turning the stone a light and distinctive shade of blue. A recent trend in jewelry is the manufacture of topaz specimens that display iridescent colors, by applying a thin layer of titanium oxide via physical vapor deposition.
Topaz is found associated with the more acid rocks of the granite and rhyolite type and may be found with fluorite and cassiterite. It can be found in the Ural and Ilmen mountains, Czech Republic, Saxony, Norway, Sweden, Japan, Brazil, Mexico, and the United States.
Etymology and historical/mythical usage
The name "topaz" is derived from the Greek topazos, "to seek," which was the name of an island in the Red Sea that was difficult to find and from which a yellow stone (now believed to be a yellowish olivine) was mined in ancient times. In the Middle Ages the name topaz was used to refer to any yellow gemstone, but now the name is only properly applied to the silicate described above.
According to Rebbenu Bachya, the word "Leshem" in the verse Exodus 28:19 means "Topaz" and was the stone on the Ephod representing the tribe of Dan.
Topaz is also the birthstone of November.Example of Heat Treated Topaz-Pink Topaz Pear Cut Ring
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Topaz is also the birthstone of November. The Turbo-charged engines took over the F1 field and ended the Ford Cosworth DFV era in the mid 1980s. According to Rebbenu Bachya, the word "Leshem" in the verse Exodus 28:19 means "Topaz" and was the stone on the Ephod representing the tribe of Dan. The project's high cost was compensated for by its performance, and led to other engine manufacturers following suit. In the Middle Ages the name topaz was used to refer to any yellow gemstone, but now the name is only properly applied to the silicate described above. Renault was the first manufacturer to apply turbo technology in the F1 field, in 1977. The name "topaz" is derived from the Greek topazos, "to seek," which was the name of an island in the Red Sea that was difficult to find and from which a yellow stone (now believed to be a yellowish olivine) was mined in ancient times. In Formula 1, in the so called "Turbo Era" of 1977 and onwards, engines with a capacity of 1500 cc could achieve anywhere from 1000 to 1500 hp (746 to 1119 kW) (Renault, Honda, BMW).
It can be found in the Ural and Ilmen mountains, Czech Republic, Saxony, Norway, Sweden, Japan, Brazil, Mexico, and the United States. Pontiac also introduced a turbo in 1980 and Volvo Cars followed in 1981. Topaz is found associated with the more acid rocks of the granite and rhyolite type and may be found with fluorite and cassiterite. Buick was the first GM division to bring back the turbo, in 1977, followed by the famed Mercedes-Benz 300D and Saab 99 in 1978. A recent trend in jewelry is the manufacture of topaz specimens that display iridescent colors, by applying a thin layer of titanium oxide via physical vapor deposition. BMW led the resurgence of the automobile turbo with the 1973 2002 Turbo, with Porsche following with the 911 Turbo, introduced at the 1974 Paris Motor Show. It can also be irradiated, turning the stone a light and distinctive shade of blue. Turbos were also leading at Le Mans in 1976.
When heated, yellow topaz often becomes reddish-pink. The Offy turbo peaked at over 1,000 hp in 1973, while Porsche dominated the Can-Am series with a 1100 hp 917/30. They may also be white, gray, green, blue, or reddish-yellow and transparent or translucent. Offenhauser's turbocharged engines returned to Indianapolis in 1966, with victories coming in 1968. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. Both of these engines were abandoned within a few years, and GM's next turbo engine came more than two decades later. Topaz has a hardness of 8, a specific gravity of 3.4-3.6, and a vitreous lustre. Its Turbo Jetfire was a 215 in³ (3.5 L) V8, while the Corvair engine was a 140 in³ (2.3 L) flat-6.
The fracture is conchoidal to uneven. The Oldsmobile is often recognized as the first, since it came out a few months earlier than the Corvair. It has an easy and perfect basal cleavage and so gemstones or other fine specimens should be handled with care to avoid developing cleavage flaws. The A-body Oldsmobile Cutlass and Chevrolet Corvair were both fitted with turbochargers in 1962. It crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. The first production turbocharged automobile engines came from General Motors. The mineral topaz is a silicate of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. The turbocharger hit the automobile world in 1952 when Fred Agabashian qualified for pole position at the Indianapolis 500 and led for 100 miles before tire shards disabled the blower.
This article is about the mineral or gemstone, for other uses see: Topaz (disambiguation).. Turbo-Diesel trucks were produced in Europe and America (notably by Cummins) after 1949. Mineral galleries. It is important to note that turbosupercharged aircraft engines actually utilized a gear-driven centrifugal type supercharger in series with a turbocharger. Mindat with location data. Aircraft such as the Lockheed P-38 Lightning, Boeing B-17 Flying Fortress and B-29 Superfortress all used exhaust driven "turbo-superchargers" to increase high altitude engine power. Webmineral. The primary purpose behind most aircraft-based applications was to increase the altitude at which the airplane can fly, by compensating for the lower atmospheric pressure present at high altitude.
Turbochargers were first used in production aircraft engines in the 1930s prior to World War II. The engine was tested at Pike's Peak in Colorado at 14,000 feet to demonstrate that it could eliminate the power losses usually experienced in internal combustion engines as a result of altitude. One of the first applications of a turbocharger to a non-Diesel engine came when General Electric engineer, Sanford Moss attached a turbo to a V12 Liberty aircraft engine. Diesel ships and locomotives with turbochargers began appearing in the 1920s.
His patent for the internal combustion turbocharger was applied for in 1905. The turbocharger was invented by Swiss engineer, Alfred Buchi, who had been working on steam turbines. On September 21, 2005, Foresight Vehicle announced the first known implementation of such unit for automobiles, under the name TIGERS (Turbo-generator Integrated Gas Energy Recovery System).. Turbo-Alternator is a form of turbocharger that generates electricity instead of boosting engine's air flow.
Special attention to engine cooling and component strength is required because of the increased combustion heat and power. Most applications produced by the major manufacturers (Beech, Cessna, Piper and others) increase the maximum engine intake air pressure by as much as 35%. For this reason, such aircraft are sometimes refered to as being turbo-normalised. In aftermarket applications, aircraft turbochargers sometimes do not overboost the engine, but rather compress ambient air to sea-level pressure.
As the aircraft climbs, the wastegate is gradually closed, maintaining the manifold pressure at or above sea-level. In the interests of engine longevity, the wastegate is usually kept open, or nearly so, at sea-level to keep from overboosting the engine. The wastegate is controlled manually, or by a pneumatic/hydraulic control system, or, as is becoming more and more common, by a flight computer. Most modern turbocharged aircraft use an adjustable wastegate.
Small car turbos are increasingly being used as the basis for small jet engines used for flying model aircraft—though the conversion is a highly specialised job—one not without its dangers. Contemporary examples of turbocharged performance cars include the Dodge SRT-4, Volkswagen GTI, Subaru Impreza WRX, Mazda RX-7, Mitsubishi Lancer Evolution, and the Porsche 911 Turbo. 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. Saab has been the leading car maker using turbochargers in production cars, starting with the 1978 Saab 99.
Small cars in particular benefit from this technology, as there is often little room to fit a larger-output (and physically larger) engine.
Turbocharging is very common on diesel engines in conventional automobiles, in trucks, for marine and heavy machinery applications. Many diesel engines do not have any wastegate because the amount of exhaust energy is controlled directly by the amount of fuel injected into the engine, and slight variations in boost pressure do not make a difference for the engine. This is limited to keep the turbo inside its design operating range by controlling the wastegate which shunts the exhaust gases away from the exhaust side turbine. Boost refers to the increased manifold pressure that is generated by the intake side turbine.
On modern diesel engines, this problem is virtually eliminated by utilising a variable geometry turbocharger. Race cars often utilise anti-lag to completely eliminate lag at the cost of reduced turbocharger life. 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. Newer turbocharger and engine developments have caused boost thresholds to steadily decline to where day-to-day use feels perfectly natural.
The boost threshold of a turbo system describes the minimum turbo rpm at which the turbo is physically able to supply the requested boost level. Lag is not to be confused with the boost threshold, however many publications still make this basic mistake. An example of this is the current BMW E60 5-Series 535d. Sequential turbochargers are usually much more complicated than single or twin-turbocharger systems because they require what amount 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.
Such combinations are referred to as "sequential turbos". 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. Below this rpm, both exhaust and air inlet of the secondary turbo are closed . Early designs would have one turbocharger active up to a certain rpm, after which both turbochargers are active.
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. Some car makers combat lag by using two small turbos (like Toyota, Subaru, Maserati, Mazda, and Audi). Such an arrangement of turbos is typically referred to as a "twin turbo" setup. 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.
Other setups, most notably in V-type engines, utilize two identically-sized but smaller turbos, each fed by a separate set of exhaust streams from the engine. Turbine clipping is measured and specified in degrees. The amount a turbine wheel is and can be clipped is highly application-specific. This imparts less impedance onto the flow of exhaust gasses 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.
By clipping a minute portion off the tip of each blade of the turbine wheel, less restriction is imposed upon the escaping exhaust gases. 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. Lag is also reduced by using a precision bearing rather than a fluid bearing, this reduces friction rather than rotational inertia but contributes to faster acceleration of the turbo's rotating assembly. Increasing the upper-deck air pressure and improving the wastegate response help but there are cost increases and reliability disadvantages that car manufacturers are not happy about.
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. Unfortunately, their relative fragility limits the maximum boost they can supply. Ceramic turbines are a big help in this direction. 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.
Conversely on light loads or at low rpm a turbocharger supplies less boost and the engine is more efficient than a supercharged engine. (Centrifugal superchargers do not build boost at low RPM's like a positive displacement supercharger will). The directly-driven compressor in a positive-displacement supercharger does not suffer this problem. 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.
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. Diesel engines are usually much kinder to turbos because their exhaust gas temperature is much lower than that of gasoline engines and because most operators allow the engine to idle and do not switch it off immediately after heavy use. In custom applications utilising 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. It is still a good idea to not shut the engine off while the turbo and manifold are still glowing.
The water boils in the cartridge when the engine is shut off and forms a natural recirculation to drain away the heat. Turbos with watercooled bearing cartridges have a protective barrier against coking. A turbo timer is a device designed to keep an automotive engine running for a pre-specified period of time, in order to execute this cool-down period automatically. Even small particles of burnt oil will accumulate and lead to choking the oil supply and failure.
Not doing this will also result in the critical oil supply to the turbocharger being severed when the engine stops while the turbine housing and exhaust manifold are still very hot, leading to coking (burning) of the lubricating oil trapped in the unit when the heat soaks into the bearings and later, failure of the supply of oil when the engine is next started causing rapid bearing wear and failure. This lets the turbo rotating assembly cool from the lower exhaust gas temperatures. Saab, in its owner manuals, recommends a period of just 30 seconds. After high speed operation of the engine it is important to let the engine run at idle speed for one to three minutes before turning off the engine.
The use of synthetic oils is recommended in turbo engines. Replacing a turbo that lets go and sheds its blades will be expensive. As long as the oil supply is clean and the exhaust gas does not become overheated (lean mixtures or retarded spark timing on a gasoline engine) a turbocharger can be very reliable but care of the unit is important. Turbocharger manufacturer Aerocharger uses the term 'Variable Area Turbine Nozzle' (VATN) to describe this type of turbine nozzle.
This type of turbine is called a Variable Nozzle Turbine (VNT). It utilised a turbo from Garrett, called the VNT-25 because it uses the same compressor and shaft as the more common Garrett T-25. The first car manufacturer to use these turbos was the limited-production 1989 Shelby CSX-VNT. The vanes are controlled by a membrane identical to the one on a wastegate but the level of control required is a bit different.
In many setups these turbos don't even need a wastegate. These turbochargers have minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds. Some turbochargers 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. 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.
This solenoid can be controlled by Automatic Performance Control, the engine's electronic control unit or an after market boost control computer. 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 regulates the rotational speed of the turbine and the output of the compressor. 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.
Turbochargers with foil bearings are in development which eliminates the need for bearing cooling or oil delivery systems. Some car makers use water cooled turbochargers for added bearing life. Lower friction means the turbo shaft can be made of lighter materials, reducing so-called turbo lag or boost lag. Some turbochargers use incredibly precise ball bearings that offer less friction than a fluid bearing but these are also suspended in fluid-dampened cavities.
The oil is usually taken from the engine-oil circuit and usually needs to be cooled by an oil cooler before it circulates through the engine. These feature a flowing layer of oil that suspends and cools the moving parts. Such high rotation speeds would cause problems for standard ball bearings leading to failure so most turbo-chargers use fluid bearings. A turbo spins very fast; most peak between 80,000 and 150,000 rpm (using low inertia turbos, 190,000 rpm) depending on size, weight of the rotating parts, boost pressure developed and compressor design.
Compressed air from a turbo may be (and most commonly is, on petrol engines) cooled before it is fed into the cylinders, using an intercooler or a charge air cooler (a heat-exchange device). It is not uncommon for a turbocharger to be pushing out air that is 90 °C (200°F). When a gas is compressed, its temperature rises. The pumping-effect heating can be alleviated by aftercooling (sometimes called intercooling).
The higher temperature is a volumetric efficiency downgrade for both types of engine. This increase in charge temperature is a limiting factor for petrol engines that can only tolerate a limited increase in charge temperature before detonation occurs. A main disadvantage of high boost pressures for internal combustion engines is that compressing the inlet air increases its temperature. This last factor makes turbocharging aircraft engines considerably advantageous—and was the original reason for development of the device.
However, for operation at altitude, the power recovery of a turbocharger makes a big difference to total power output of both engine types. This disadvantage does not apply to specifically designed turbocharged diesel engines. A disadvantage in gasoline engines is that the compression ratio should be lowered (so as not to exceed maximum compression pressure and to prevent engine knocking) which reduces engine efficiency when operating at low power. This engine rpm is referred to as the boost threshold.
Because it is a centrifugal pump, a typical turbocharger, depending on design, will only start to deliver boost from a certain rpm where the engine starts producing enough exhaust gas to spin the turbocharger fast enough to make pressure. For automobile use, typical boost pressure is in the general area of 80 kPa (11.6 lbf/in²), but it can be much more. However, there are some parasitic losses due to heat and exhaust backpressure from the turbine, so turbochargers are generally only about 80% efficient, at peak efficiency, because it takes some work for the engine to push those gases through the turbocharger turbine (which is acting as a restriction in the exhaust) and the now-compressed intake air has been heated, reducing its density. For example, at 100% efficiency a turbocharger providing 101 kPa (14.7 lbf/in²) of boost would effectively double the amount of air entering the engine because the total pressure is twice atmospheric pressure.
The energy from the extra fuel leads to more overall engine power. The increase in pressure is called "boost" and is measured in pascals, bars or lbf/in². The additional fuel is provided by the proper tuning of the fuel injectors or carburetor. This greatly improves the volumetric efficiency of the engine, and thereby creates more power.
The compressor increases the pressure of the air entering the engine, so a greater mass of oxygen enters the combustion chamber in the same time interval (an increase in fuel is required to keep the mixture the same air to fuel ratio). But because of "turbo lag" (see below), engines with mechanical superchargers are typically more responsive. Because the turbine of a turbocharger is in-itself a heat engine, a turbocharger equipped engine will normally compress the intake air more efficiently than a mechanical supercharger. The term supercharger is very often used when referring to a mechanically driven turbocharger, which is most often driven from the engine's crankshaft by means of a belt (otherwise, and in many aircraft engines, by a geartrain), whereas a turbocharger is exhaust-driven, the name turbocharger being a contraction of the earlier "turbosupercharger".
The compressor and turbine spin on the same shaft, similar to a turbojet aircraft engine. A turbocharger also has a turbine that powers the compressor using wasted energy from the exhaust gases. All superchargers have a gas compressor in the intake tract of the engine which compresses the intake air above atmospheric pressure, greatly increasing the volumetric efficiency beyond that of naturally-aspirated engines. A turbocharger is an exhaust gas driven supercharger.
. A key advantage of turbochargers is that they offer a considerable increase in engine power with only a slight increase in weight. A turbocharger is an exhaust gas driven compressor used in internal-combustion engines to increase the power output of the engine by increasing the mass of oxygen entering the engine. For other meanings of turbo, see turbo (disambiguation).
This article describes the internal combustion engine component often known as a turbo. Automobile magazine (February 2006).. Happy 100th Birthday to the Turbocharger. Don Sherman.
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. 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. 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. 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.
Gasoline engines often require extensive modification for turbocharging. 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. Naturally-aspirated diesels have lower power-to-weight ratios compared to gasoline engines; turbocharging will improve this P:W ratio.