By using a turbo, engine manufacturers can downsize the cylinder capacity of their engines to reap the fuel economy and emissions benefits of the lighter weight, smaller engine, without sacrificing performance.
These benefits are why, in its recent turbo forecast , Honeywell predicted that million cars with turbocharged engines will be produced during the next five years.
By , 47 percent of all new vehicles are expected to have a turbo fitted. Here are some things you may or may not know about the turbocharger that is giving your car that extra boost! Fuel Frugality: By integrating a turbocharger with a downsized engine, automakers can improve fuel efficiency by as much as 40 percent in diesel applications and 20 percent in gas applications as compared to a larger naturally-aspirated gas engine with similar output performance.
Even in diesel engines they run hotter than the temperature of molten lava. Going Green: By Honeywell expects that 7 percent of all cars on the road will be hybrids — at least 2 percent of which will be turbocharged. They still give go-fast cars an extra boost of power, but increasingly, automakers use them on smaller engines to boost power when needed but with better overall fuel economy.
A turbocharger is basically an air pump, pushing extra oxygen into the engine as needed so it can burn more fuel to make more power. Engines contain pistons, which move up and down in cylinders. These turn a heavy central crankshaft, the same way your legs move up and down to power a bicycle.
What makes it all move is a vapour of air and gasoline at the top of the piston. The burned gases are then expelled as exhaust. Each piston slides down at the start of its cycle, creating a vacuum. In a non-turbo engine, known as naturally-aspirated, air rushes in when the intake valve opens, but it can only fill the cylinder at atmospheric pressure.
The turbo is powered by the exhaust gases. As exhaust passes through the turbo, it spins one fan, called the turbine. This in turn spins the second fan, called the compressor, which draws in fresh air, pressurizes it, and forces it into the engine. The difference between atmospheric pressure and the amount of air pressure the turbo provides is known as boost, and is measured in pounds per square inch psi.
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 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.
Many new diesel engines use this technology to not only eliminate lag but also to reduce fuel consumption and produce cleaner emissions. 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 turbo RPM at which the turbo is physically able to supply the requested boost level. 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 engine RPM and having no boost until engine RPM is an example of boost threshold and not lag. Race cars often utilise anti-lag to completely eliminate lag at the cost of reduced turbocharger life. On modern diesel engines, this problem is virtually eliminated by utilising a variable geometry turbocharger. Boost refers to the increase in manifold pressure that is generated by the turbocharged in the intake path or specifically intake manifold that exceeds normal atmospheric pressure.
This is also the level of boost as shown on a pressure gauge, usually in bar, psi or possibly kPa. Colloquially also referred as "pounds of boost".
This is representative of the extra air pressure that is achieved over what would be achieved without the forced induction. Boost pressure is limited to keep the entire engine system including the turbo inside its design operating range by controlling the wastegate which shunts the exhaust gases away from the exhaust side turbine. 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.
Turbocharging is very common on diesel engines in conventional automobiles, in trucks, 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:. 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 has been the leading car maker using turbochargers in production cars, starting with the Saab All current Saab models are turbocharged. 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. An oil supply for the bearings is still needed, usually provided by an electric pump.
Starting such home-built jets is usually achieved by blowing air through the unit with a compressor or a domestic leaf-blower. Making these engines is not an easy task- unless the combustion canister design is correct the engine will either fail to start, fail to stabilise once running or even over-rev and destroy itself.
Most modern turbocharged aircraft use an adjustable wastegate. In the interests of engine longevity, the wastegate is usually kept open, or nearly so, at sea-level to keep from overboosting the engine.
As the aircraft climbs, the wastegate is gradually closed, maintaining the manifold pressure at or above sea-level. In aftermarket applications, aircraft turbochargers sometimes do not overboost the engine, but rather compress ambient air to sea-level pressure.
For this reason, such aircraft are sometimes referred to as being turbo-normalised. Special attention to engine cooling and component strength is required because of the increased combustion heat and power. The turbocharger was invented by Swiss engineer Alfred Buchi, who had been working on steam turbines.
His patent for the internal combustion turbocharger was applied for in Diesel ships and locomotives with turbochargers began appearing in the s. 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. The engine was tested at Pikes Peak in Colorado at 14, feet to demonstrate that it could eliminate the power losses usually experienced in internal combustion engines as a result of altitude.
Turbochargers were first used in production aircraft engines in the s prior to World War II. 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.
Aircraft such as the Lockheed P Lightning, Boeing B Flying Fortress and B Superfortress all used exhaust driven "turbo-superchargers" to increase high altitude engine power.
One way to decrease turbo lag is to reduce the inertia of the rotating parts, mainly by reducing their weight. This allows the turbine and compressor to accelerate quickly, and start providing boost earlier.
One sure way to reduce the inertia of the turbine and compressor is to make the turbocharger smaller. A small turbocharger will provide boost more quickly and at lower engine speeds, but may not be able to provide much boost at higher engine speeds when a really large volume of air is going into the engine. It is also in danger of spinning too quickly at higher engine speeds, when lots of exhaust is passing through the turbine.
Most automotive turbochargers have a wastegate , which allows the use of a smaller turbocharger to reduce lag while preventing it from spinning too quickly at high engine speeds. The wastegate is a valve that allows the exhaust to bypass the turbine blades. The wastegate senses the boost pressure. If the pressure gets too high, it could be an indicator that the turbine is spinning too quickly, so the wastegate bypasses some of the exhaust around the turbine blades, allowing the blades to slow down.
Some turbochargers use ball bearings instead of fluid bearings to support the turbine shaft. But these are not your regular ball bearings -- they are super-precise bearings made of advanced materials to handle the speeds and temperatures of the turbocharger.
They allow the turbine shaft to spin with less friction than the fluid bearings used in most turbochargers. They also allow a slightly smaller, lighter shaft to be used. This helps the turbocharger accelerate more quickly, further reducing turbo lag. Ceramic turbine blades are lighter than the steel blades used in most turbochargers. Again, this allows the turbine to spin up to speed faster, which reduces turbo lag.
Some engines use two turbochargers of different sizes. The smaller one spins up to speed very quickly, reducing lag, while the bigger one takes over at higher engine speeds to provide more boost. When air is compressed, it heats up; and when air heats up, it expands. So some of the pressure increase from a turbocharger is the result of heating the air before it goes into the engine.
In order to increase the power of the engine, the goal is to get more air molecules into the cylinder, not necessarily more air pressure. An intercooler or charge air cooler is an additional component that looks something like a radiator , except air passes through the inside as well as the outside of the intercooler.
The intake air passes through sealed passageways inside the cooler, while cooler air from outside is blown across fins by the engine cooling fan. The intercooler further increases the power of the engine by cooling the pressurized air coming out of the compressor before it goes into the engine. This means that if the turbocharger is operating at a boost of 7 psi, the intercooled system will put in 7 psi of cooler air, which is denser and contains more air molecules than warmer air.
A turbocharger also helps at high altitudes , where the air is less dense. Normal engines will experience reduced power at high altitudes because for each stroke of the piston, the engine will get a smaller mass of air.
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