Turbocharger
A turbocompressor or also called turbo is a supercharging system that uses a centrifugal turbine to drive, through a coaxial shaft with it, a compressor wheel to compress gases. This type of system is usually used in alternative internal combustion engines, both in diesel and gasoline engines.
In some countries, the tax burden on cars depends on the displacement of the engine. Since a turbocharged engine has a higher peak horsepower than another of the same displacement, a turbocharged model would pay less tax than a non-turbocharged engine of the same horsepower.[citation needed].
Timeline
- In 1902, on December 17, Louis Renault patents the Turbocompressor.
- In 1936 Cliff Garrett founded The Garrett Corporation in California, United States.
- In 1940 turbo technology is applied to marine, industrial and locomotive installations.
- In 1953 Caterpillar tests the first food turboa developed by the Garrett company.
- In 1962 the first mass production car manufactured in the US. UU. in having a factory turbocharger (the Oldsmobile Jetfire Turbo Rocket).
- In 1966 turbocharged engines are used for the first time in the 500 Miles of Indianapolis.
- In 1977, turbocharged engines are used for the first time in the F1, introduced by the Renault team. The first victory of a turbo engine was two years later. They were banned by the regulations in 1989 and reintroduced in 2014.
- In 2003 Ford launched the Focus RS naftero with turbocharged engine. Caterpillar uses Garrett turbos in series, for its trucks with ACERT engines.
Operation
In engines supercharged using this system, the turbocharger consists of a turbine driven by the exhaust gases from the internal combustion engine, on whose axis a centrifugal compressor is fixed that takes air at atmospheric pressure after passing through the air filter. air and compresses it to introduce it into the cylinders at greater than atmospheric pressure.
The exhaust gases radially affect the turbine, exiting axially, after giving up a large part of their internal energy (mechanical + thermal) to it.
Air enters the compressor axially, exiting radially, with the negative side effect of a more or less considerable increase in temperature. This effect is largely counteracted with an intercooler.
This increase in pressure manages to introduce a greater amount of oxygen (mass) into the cylinder than the normal mass that the cylinder would inhale at atmospheric pressure, obtaining more torque in each useful stroke (expansion stroke) and therefore More power than an atmospheric engine of the same displacement, and with an increase in consumption proportional to the increase in air mass in the gasoline engine. In diesels, the mass of air is not proportional to the fuel flow, excess air always enters as the fuel supply to the cylinder is by injection, for this reason it is in this type of engine where its maximum application has been found (turbodiesel engine).
The smallest and lowest boost pressure turbochargers have a maximum pressure of 0.25 bar (3.625 PSI), while the largest reach 1.5 bar (21.75 PSI). In competition engines, pressures of 3 and 8 bars are reached depending on whether the engine is gasoline or diesel.
Since the energy used to compress the intake air comes from the exhaust gases, which would be discarded in a naturally aspirated engine, it does not detract from the engine power when the turbocharger is working, nor does it cause losses outside the turbo's working range, unlike other intake compressors, such as mechanical (volumetric) compressor systems, where the compressor is driven by a pulley connected to the crankshaft.
Operation on different types of motors
Diesel
In diesel engines the turbocharger is more widespread because a diesel engine works with excess air as there is no throttle, on the one hand; This means that for the same unit displacement and the same engine speed (3000 rpm to 5000 rpm) much more air enters a diesel cylinder.
On the other hand, and this is the most important thing, the pressures reached at the end of the compression stroke and especially during the work stroke are much higher (40 to 80 bars) than in the Otto cycle engine (engine gasoline) (15-25 bars). This high pressure, necessary to reach the high temperature required for the auto-ignition or auto-ignition of the diesel, is the origin of the fact that the force of the exhaust gases, at the same regime, unit displacement and load required to the engine is much greater. in diesel than in gasoline.
Gasoline
In recent times, supercharging in gasoline engines has become more widespread as a technique to take advantage of small displacement engines. This in order not to reduce performance as a result of lower consumption requirements. The operation is almost always similar to that of diesel engines, however here supercharging plays a very important role because it must be carried out precisely with exact amounts with margins of error of +/- 0.50 cm/3, in this case. As there is a butterfly in the air intake manifold, the proportion of air and fuel in the injection system must be regulated, as well as the value of the compression ratio calculated in order to maximize performance and improve consumption. Indirectly these engines can operate at higher altitudes without significant loss of power.
It is also necessary to calibrate the moment of the turbocharger actuation due to its delay (turbo-lag). Generally this occurs because its performance depends on the speed at which the exhaust gases are expelled, which in turn depend on the RPM of the same engine, almost always it will have optimal performance in mid-range regimes (from 3000 to 5000 rpm), in turn this also depends on its blowing pressure, which in common cars is almost always calibrated in a few bars or psi, while in competition vehicles they will always depend on more PSI or Bars due to higher demands which may vary. For example, rally cars must sometimes rely on restrictor plates on the turbo itself to maintain an even power figure, plus special gears that keep the same revving regardless of idle or throttle stroke, in order to that you have the necessary power both in HP and in Torque (torque) which in turn causes those striking flares and explosions of the same vehicles as well as their characteristic engine tone.
Its operation is perceived with a sharp whistle that indicates that the main part itself is rotating according to the speed of the exhaust gases, in turn in some engines when you stop accelerating you can distinguish a hissing similar to that of the air brakes on a truck, an indication that the turbo is returning to a slow spin according to the engine idle.
Among the first brands to implement turbochargers in small displacement engines more frequently at the beginning of the XXI century were the belonging to the Volkswagen Group subsequently developed systems that would implement the combination of the fuel stratified charge and in turn a combination of turbocharger and supercharger that allows obtaining a relatively high power without sacrificing fuel consumption, since the second can work at the beginning since it is powered by the same engine.
Subsequently, more automotive brands joined the concept, including Ford, who developed the so-called Ecoboost Engines for most of their engines, both large and small, and in almost all their models, with the same purpose of obtaining more power without spending more fuel than necessary while reducing emissions.
Intercooler
Air, when compressed, heats up and loses density; that is, in the same volume we have less air mass, so it is capable of burning less fuel and, consequently, less power is generated. In addition, as the intake temperature increases, the danger of detonation, knocking, or self-ignition increases, and the useful life of many components is reduced due to excess temperature, and overstressing of the thermal group.
To reduce this problem, a "heat exchanger" or "intercooler". This system reduces the temperature of the air, thus increasing its density, which is introduced into the combustion chamber.
On the negative side, heat exchangers cause a pressure drop, thus decreasing the density of the air, although in many cases it is necessary to install one to avoid detonation or autoignition.
- There are three types of interspers:
- Air/air: in these compressed air exchanges its heat with external air.
- Air/water: compressed air exchanges its heat with a liquid that can be refrigerated by a radiator or, in some applications, with ice in a deposit located inside the car.
- Criogenics: the mixture is cooled by evaporating a gas over an air/air exchanger.
Turbo response time (turbolag)
Turbocharged engines suffer from a greater turbo response time lag (known as "turbolag" colloquially) at 50% power draw than atmospheric engines (NA-Naturally Aspirated or Natural Aspiration) or with mechanical compressor, because the performance of the turbocharger depends on the pressure exerted by it. This delay is influenced by the group's inertia (its diameter and weight) and the volume of the manifold between the turbine and the exhaust gas outlet from the cylinder.
A turbocharger does not perform the same way at different engine speeds. At low revs, the turbocharger does not apply pressure as the small amount of gases does not push hard enough to generate a significant amount of inertia to be considered turbocharging response. A smaller turbocharger prevents response lag, but exerts less force at high revs. Various engine manufacturers have designed solutions to this problem.
- Atwin turbo": it is a system with two different size turbochargers. At low revolutions only the small one works, due to its fastest response, and the big one works only at high revolutions, as it exerts greater pressure.
- Abiturbo in parallel": it is a system with two small turbochargers of identical size. Being smaller as a single turbocharger, they have a lower rotational inertia, so they start to generate pressure to lower revolutions and the delay of response is diminished.
- AAsymmetric turbocharger"It consists of putting a single small turbocharger on a bench (the front in the V6 engine placed transversally) leaving the other free. The idea is not to get a great power, but the answer is fast. This system was invented by Swedish manufacturer Saab and used in the Saab 9-5 V6.
- Asequential biturbo": consists of two identical turbochargers. When there is little volume of exhaust gases all this volume is sent to a turbocharger, and when this volume increases, it is divided between the two turbochargers to achieve greater power and a lesser response time. This system is used in the Wankel engine of the Mazda RX-7.
- Avariable geometry turbocharger"VTG): consists of a turbocompressor that has a mechanism of "alloys" called mobile links that open and close by changing the speed of exhaust gases when entering the turbine. The lower flow of exhaust gases (low revolutions) closes the passage between the links causing the gases to increase the speed by entering the turbine; to higher flow (high revolutions) we need more step and these open. This allows us to have a very linear working pressure throughout the turbocharger's working regime. In diesel engines it is very common but in gasoline engines only Porsche has developed a turbo that supports more than 1000 °C in the Porsche 911 turbo model (2007).
Mazda also has a prototype electric turbo. The car's electrical system cannot give enough flow to the engine at high revs, but it can at low revs; so both complement each other. At low load and revs, the electric assist allows for a rapid build-up of pressure and then the turbine can supply full power to compress the air. This system saves much more energy than combining it with a mechanical compressor driven by the engine.
Fiat Auto, S.P.A., formerly Fiat Group Automobiles (FGA) created and developed the mechanical turbo + compressor system during the 1980s. The vehicle in which it was developed and implemented was the Lancia Delta (MKI), manufactured between 1985 and 1990. Reaching its maximum exponential and development in the Lancia Delta Integrale WRC.
Overboost
The period during which the system produces a boost pressure higher than normal at full load, with the aim of increasing engine torque, is known as Overboost.
Currently this system, with the appropriate electronic control, can take into account different applications.
Turbocharger Evolution
The philosophy of applying turbochargers has been changing: from prioritizing power at high revs to prioritizing that the car responds well throughout the rev range of use.
The valve called waste-gate prevents excessive pressures from damaging the engine. The waste-gate or unloading valve is what regulates the amount of exhaust gases that leak from the turbo exhaust snail directly into the vehicle exhaust by opening the valve, thus the more gases leaked, the less turbo pressure, with the valve closed the maximum turbo pressure is reached as all the exhaust gases pass through the snail.
The dump valve (also called "dump valve" or "blow off" in English) opens a leak in the intake manifold when you stop accelerating to that the pressure generated by the enormous inertia of the turbo does not saturate these conduits, avoiding at the same time the sudden deceleration of the turbine, extending its useful life.
Currently we have several supercharging systems.
- Monoturb systems with fixed geometry, monoturb systems with variable geometry (management by vacuum or electronic actuator).
- Biturb, sequential systems (one large and one small).
- Side biturbo systems (both of the same size).
- Triturbo systems, with different configurations.
- Audi 3.0 TDI and BMW 3.0 diesel engines.
- Tetraturbo systems. It is currently mounted by BMW in its M50D 3000 cc diesel with 400 hp.
It is also worth noting the hybrid turbo system to increase the vehicle's power without the need to make adaptations. These are internally upgraded turbos over the original housing to get better performance than the original turbo. It is a product patented by ATC in Spain since 2015 and is available for practically all vehicles with supercharged engines.
Cooling
Normally the turbocharger is usually cooled with its own system by oil that circulates while the engine is running. If the engine is shut down suddenly after intensive use and the turbocharger is very hot, the oil that cools the turbocharger bearings remains stagnant and its temperature rises, which can start to carbonize, reducing its lubricating capacity and shortening the life of the turbocharger. turbocharger life.
The turbo timer is a system that keeps the oil circulating in the turbocharger for a period of time after the engine has been turned off. Some models work with sensors that detect the intensity in the use of the turbocharger to allow its forced lubrication for a reasonable time after the engine has been turned off.
Advantages of using a turbocharger
- It allows to increase the power of a motor by 50%, without the need to make further changes.
- It contributes to the recovery of energy, as it uses the engine's exhaust gases as a propeller.
- Adds little volume and weight to the engine, allowing it to fit into an existing vehicle without large external modifications.
- Because it depends on the pressure between exhaust gases and the environment is self-adjusted at any altitude above sea level.
- It allows to reduce the fuel consumption used (this obtaining more energy per liter of fuel).