Turbocharging has become a standard device for most gasoline and diesel engines. Research is still ongoing on ways to improve the designs of turbochargers for better performance at lower manufacturing costs. Even though vibration-induced stresses and bearing performance are major failure factors. For this reason, a rotodynamic analysis should be an important part of the turbocharger design process—well, maybe!
In an automobile engine, power is produced in the combustion chamber with an intake fuel/air mixture, right? After the compression, it releases the mixture as exhaust gas, which becomes waste products and even causes pollution to the atmosphere. But instead of making the exhaust gas useless, the turbocharger makes use of it to make the engine run faster. Let me explain.
In this reading, we’ll explore what a turbocharger is, its history, diagram, function, application, parts, types, and how it works.
What Is A Turbocharger?
A turbocharger is a turbine-driven, force-induction device that increases the efficiency and power output of internal combustion engines by forcing extra compressed air into the combustion chamber. This hot air induction seems to work because the compressor can force more air and proportionately more fuel into the combustion chamber than normal atmospheric pressure.
A turbocharger is a device fitted to a vehicle’s engine in order to improve the overall efficiency and increase the performance of the engine. turbochargers were originally known as turbosuperchargers because all forced-induction devices are classified as superchargers. A supercharger is a term given to a mechanically driven forced induction device.
A turbocharger and a conventional supercharger differ in that a turbocharger uses an engine’s exhaust gas to power a turbine. In contrast, a supercharger receives mechanical power from the engine crankshaft through a belt. However, turbochargers are more efficient but less responsive. The term twin-charger refers to an engine with a turbocharger and a supercharger.
History Of A Turbocharger
In a brief history of turbochargers, credit goes to the founder, Alfred J. Buchi (1879–1922), who was employed in an automotive engineer workshop by the Gebruder Sulzer Engine Company of Winterthur, Switzerland. The project was developed a year before World War I and was patented in Germany in 1905. He continued the enhancement of the project until his death after four decades.
Some other engineers also deserve to be credited for the turbocharger project. Some years earlier, Sir Dugald Clark (1854–1922) was a Scottish inventor of a two-stroke engine. he experimented with separating the compression and expansion stages of internal combustion using two separate cylinders.
His experiment worked like supercharging, increasing both airflows into cylinders and the amount of fuel that could be burned. Other engineers like Louis Renault, Gottlieb Daimler, and Lee Chadwick, also take part in the supercharging systems.
Diagram Of a Turbocharger
Functions Of Turbocharger
The primary function of a turbocharger is to increase the working efficiency of an automobile engine. below are the reasons why Turbo will always exist, despite a few of its limitations.
- Extra oomph is provided without increasing the engine capacity.
- Make the engine run faster without an increase in fuel consumption.
- Make use of carbon dioxide (exhaust gas) instead of causing pollution.
Applications Of Turbocharger
A turbocharger is commonly used in automotive engines like trucks, cars, trains, aircraft, and construction equipment. modern release of Otto cycle and Diesel cycle internal combustion engines feature turbochargers.
Gasoline and Diesel-Power Cars
As earlier mentioned, turbocharged cars are common for petrol and diesel-powered cars to increase their power output for a given capacity. It also increases fuel efficiency, allowing a smaller displacement engine. These engines lose weight by about 10%, save up to 30% in fuel consumption, and still deliver the same peak horsepower.
The first turbocharged passenger car was the Oldsmobile Jetfire. It uses a 215-cu in all aluminum V8s and on Chevrolet products called Corsairs. It was initially called the Monza Spyder cooled flat six-cylinder engine.
Diesel cars vastly rely on turbochargers for the improved efficiency, drivability, and performance of diesel engines. It was produced on a passenger car that was a Garrett-turbocharged Mercedes and introduced in 1978.
Trucks
For the same benefit, diesel truck engines have featured turbocharging since 1938.
Aircraft
Over the years, the effect of turbochargers also increases the efficiency of airplanes.
Motorcycles
Most Japanese companies have produced high-performance motorcycles that feature turbocharged engines since the early 1980s. Although there are few turbocharged motorcycles out there, this is because of the abundance of larger displacement. A naturally aspirated engine is available that offers the torque and power benefits of a smaller displacement engine with a turbocharger but returns more linear power characteristics.
Parts of Turbochargers
Below are the major parts of a turbocharger and their functions:
- Cartridges (fully assembled and balanced turbocharger cores)
- Vacuum actuators and pneumatic actuators
- Electronic actuators (electric servo drives)
- Compressor housings (the housings of the turbocharger cold section/part)
- Turbocharger repair kits (spare part kits/sets for a quick minor repair)
- Compressor wheels (turbocharger compressor wheels)
- Shaft and wheels (turbocharger shafts with turbine wheels and turbine rotors)
- Nozzle Ring Housings (Housings for VNT geometry control elements)
- Bearing Housings (Cartridge housings, Turbo core housings)
- Backplates (turbocharger cores plate from compressor side)
- VNT Nozzle Rings (Rings with nozzles for VNT turbochargers, VNT geometry control nodes)
- Heat shields (turbocharger core heat shields)
- Gasket kits (turbocharger gasket kits/sets)
- Actuator sensors (pressure sensors, position sensors)
- VNT Gaskets (internal gaskets for VNT turbochargers)
- Turbine housings (the housings of the turbocharger hot section/part)
- Electronic actuator parts (electric motors, shafts, and gears of turbocharger servo drives).
Types of Turbochargers
The following are the common types of turbochargers:
Single Turbo
The single turbo is the simplest, most common, and cheapest type of turbocharger that exists. It has limitless variability, and being a smaller turbo, it provides better low-end grunt as it spools faster. The single turbo has a ball bearing and journal bearing, which provide less friction for the compressor and turbine to spin on.
The benefits of single turbochargers are that smaller engines are also allowed to feature a turbo; cost-effectiveness is also considered; simplicity is also considered; and they are easy to install. It also increases engine efficiency.
Some limitations still occur despite its advantages, which include having a fairly narrow effective rpm range. Single turbos make sizing an issue since one has to choose between better high-end power and good low-end torque. Finally, the response may be slow compared to other turbo types.
Twin Turbos
The twin turbo is another option that allows a single turbocharger for each cylinder bank (v8, v12, etc.). Alternatively, a single turbocharger could be used for low rpm and bypassed to a larger turbocharger for high rpm.
Two similar-sized turbos, where one is used at low rpm and both are used at higher rpm (14, 16). BMW x5 M and x6 M use twin-scroll turbos, one on each side of the v8. The benefit of twin turbo is when it’s sequential or on the turbo at low rpm and both at high rpm.
It allows wider, flatter torque curves and better low-end torque, but the power won’t taper at high rpm like a single turbo. Limitations with these turbochargers include cost and complexity, as the component is almost doubled. And there are other alternatives for achieving a similar result that is lighter.
Twin-Scroll Turbo
In almost every way, twin-scroll turbochargers are better than single-scroll turbos because, while using two scrolls, the exhaust pulses are divided. For instance, in four-cylinder engines having firing orders of 1 3 4 2, cylinders 1 and 4 may be fed to one scroll of a turbo. Whereas cylinders 2 and 3 are fed to separate scrolls.
The purpose of these types of turbochargers is that there is overlap in the cylinder. Let’s say the cylinder is ending its power stroke as the piston reaches the bottom dead center, and the exhaust valve will open. During this time, cylinder two ends its exhaust stroke by closing the valve and opening the intake valve.
A traditional single-scroll turbomanifold is quite different; the exhaust pressure from cylinder one will interfere with cylinder two pulling in the fresh air because both exhaust valves are temporarily open. This reduces how much pressure reaches the turbo and interferes with how much air the second cylinder pulls in.
Variable Geometry Turbocharger (VGT)
The variable geometry types of a turbocharger are common on diesel engines, but their production is limited. This is because of its cost and exotic material requirements. Internal vanes within the turbocharger alter the area-to-radius A/R ratio to correspond with the rpm.
That is, at a low rpm, a low A/R ratio is used to increase exhaust gas velocity and quickly spool up the turbocharger. If the revs climb, the A/R ratio increases in order to increase the airflow, which results in low turbo lag. It also leads to a low boost threshold and a wide and smooth torque band.
The benefit of this type of turbo is that a wide, flat torque curve is produced. Which is effective at a very wide rpm range. It requires a single turbo, simplifying a sequential turbo setup into something more compact.
Its limitations include the fact that it only works with diesel engines because the exhaust gases are lower and the head won’t damage the vanes. Using the turbo on a gasoline engine, high-cost exotic metals will be used in order to maintain reliability.
Variable Twin-Scroll Turbocharger
The variable twin-scroll turbo is significantly cheaper than VGTs, making it a preferable choice for gasoline turbocharging. It combines a VGT with a twin-scroll setup; thus, at a low revolution, one of the scrolls is completely closed, forcing all the air into the other.
As the engine speeds up, a valve opens to allow air into the other scroll, and good high-end performance is obtained. The advantages of the turbocharger are that it allows a wide, flat torque curve and it’s more robust in design than the VGT. Cost and complexity are also its limitations and technology has been unwanted before.
Electric Turbochargers
With the application of an electric motor in a turbocharger, it enhances its features and provides an instant boost to the engine. Low-end torque is easily produced, and lag is eliminated. This turbocharger is just the best of all; perhaps a new version might bring it down.
its benefits are that a wider effective rpm range with even torque throughout is produced. Wasted energy is recovered as an electric motor is connected directly to the exhaust turbine. And as mentioned earlier, turbolag and insufficient exhaust gases can be virtually eliminated by rotating the compressor with electric power when needed.
Complexity and cost are some of the disadvantages of the turbocharger, as the electric motor is now included. Packaging and weight are also an issue, especially with the addition of a battery onboard, which supplies sufficient power to the turbo when needed. Similar benefits can be obtained from other types, like VGTs or twin scrolls.
How A Turbocharger Works
Having a basic knowledge of how a jet engine works and understanding cars with turbochargers will be much easier. Let me explain: a jet engine sucks fresh air at the front and uses it in the chamber to mix and burn with fuel. It then blasts hot air through its back.
The hot roars past a turbine made of a compact metal windmill, which drives the compressor (air pump) at the front of the engine. the engine uses it to push air into the engine to make the fuel burn properly.
A similar process is applied to the turbocharger on a car piston engine. exhaust gases are used to drive the turbine, which spins an air compressor that pushes extra air into the cylinders. It causes more fuel to be burned in seconds, which is why a turbocharged car can produce more power. That is more energy per second.
The shaft that connects the two halves of a turbocharger is what makes them. One of them has a turbine that spins when hot exhaust gases pass by, and the other has a turbine that draws air in and compresses it for the engine.
This compression offers extra power and efficiency to the engine. As more air enters the combustion chamber, more fuel is added, which produces extra power. Note that compressed air is hot and less dense, and it rises over radiators.
This hot air is less effective in helping fuel burn. Because of this, the air coming from the compressor needs to be cooled before entering the cylinders. This is why the hot air from the compressor passes over a heat exchanger that removes extra heat before it enters the combustion chamber.
Advantages
Below are the benefits of turbochargers:
- Extra power is offered to the engine.
- Free power is given to the engine using waste exhaust gases. It does not require any engine power to drive it.
- It’s used in both diesel and gasoline engines.
- Improve the fuel efficiency of engines.
Disadvantages
Despite the advantages of turbochargers, two main limitations still exist. Below are the disadvantages of the turbocharger:
One of the big issues with a turbocharger is known as turbolag. This happens when the throttle is pressed down; it takes time for the engine to speed up. That is, turbochargers take time to reflect the engine speed. When the engine’s speed is low, there are not enough exhaust gases to spin the compressor and offer the power needed. The required exhaust will be created after the throttle is pressed. This effect is reduced by downshifting to a lower gear, but expert drivers sometimes notice the split delay in response.
The second limitation of turbochargers is that they do not occur in everyday driving conditions. It happens only when the engine is pushed to its limits. The heat produced from the exhaust gasses gets very hot and causes the turbocharger to start glowing red. This is why most turbocharged sports cars are designed with vents at the side of the engine. This vent keeps air circulation constant and cools the parts.