In today’s day and age, the term turbocharger has become rather common in the Indian car market. This has primarily happened because many car makers like Hyundai, Kia, Mahindra, Tata, Skoda, Volkswagen and even Maruti Suzuki have introduced turbocharged petrol engines for their vehicles. So, is this the first time turbochargers have been offered on cars in India?
No, as turbochargers have long been offered with diesel engines. However, mass market car makers have only started offering them with petrol engines in the last decade, which has made them quite popular among regular car buyers. But, what exactly does a turbocharger do? To answer this question, we have put together this article which will answer all your doubts about the use of a turbocharger in a car.
History of Turbochargers
The first turbocharger design can be traced back to 1905, when a Swiss engineer named Alfred Büchi patented the first ever design for one. At the time, a turbocharger was developed for use in aircraft engines, to overcome the loss of power due to the thin density of air at higher altitudes. The first prototype was built in 1915, but it proved to be unreliable. In the following years, multiple designs for turbochargers came to light, but they were mostly used for aircraft or ship engines.
Automobile companies started research on turbochargers in the 1950s with their biggest challenge being the notorious ‘turbo lag’ and the bulky size of the whole system. The first cars to feature turbocharging were made by General Motors, the Oldsmobile Jetfire and the Chevrolet Corvair Monza, both of which were introduced in 1962. However, both cars were plagued by unreliability and throttle response issues.
In the following years, the potential of turbocharging was picked up on by car makers of the time. The turbocharger soon started making an appearance in motorsport, and the 1968 Indianapolis 500 was the first race to be won by a turbocharged engine. Soon after, Formula 1 also started using turbocharged engines, and the fist race victories came in the 1970s, however the first Formula 1 championship was won by a turbocharged car in 1983.
On the production cars front, the Porsche 911 Turbo and Saab 99 were the first cars to efficiently make use of turbochargers and extract more performance from their engines. The Mercedes 300 D was launched in 1970 and it too features a turbocharger. By the 1980s, turbochargers had appeared on many production cars and were seen as a quick way to increase the performance from a smaller engine, while still meeting emission regulations.
The Anatomy of a Turbocharger
Before we dive deep into the different parts of a turbocharger, it is important to understand a basic concept about an engine. Fuel and air is mixed and pushed into a cylinder, which is then ignited. The amount of power an engine can make is largely limited by the amount of air that can be pushed inside its cylinders. Naturally aspirated engines are reliant on atmospheric pressure to push air into their cylinders. However, if you can push more air inside an engine cylinder, you can increase the amount of fuel mixed with it to create more power. This is where a turbocharger comes in handy. It is essentially made up of two sections, the turbine and the compressor.
The Turbine
The turbine section of a turbocharger is positioned to meet the exhaust gases expelled from the engine. These gases are extremely hot and are highly pressurised and as they leave the engine, they are redirected towards the turbine housing of a turbocharger. Inside the housing is a turbine wheel and it looks like a small fan with many blades. These are angled to meet the exhaust gases at exactly the right angle, and this causes the turbine wheel to spin rapidly. The turbine in a turbocharger can spin upward of 1,00,000 RPM (revolutions per minute). This rotational motion is crucial for turbocharging, as it spins the common shaft which is attached to the compressor.
The Compressor
The turbine spins the common shaft which also spins the compressor wheel inside the compressor housing. The compressor wheel has a series of blades attached to it which are designed to draw in ambient air from the outside. As the air is drawn inside the compressor, it is forced outwards due to centrifugal force and it accelerates as it moves towards the outer edge of the compressor housing. The shape of the compressor housing is designed so that it converts this high velocity-low pressure air into low velocity-high pressure air, suitable for combustion inside the engine cylinder. This compressed air that is rich in oxygen is then redirected to the intercooler.
The Intercooler
When air is compressed inside the compressor housing of a turbocharger, its temperature rises. Hot air is not as dense as cold air, which means that it contains less oxygen molecules for a given volume of air. Therefore, the air from the compressor housing is passed through an intercooler, which is essentially a heat exchanger. Intercoolers can use either air or liquid to cool the air. By cooling the air, the intercooler increases the density of the air entering the engine and reduces the chances of pre-ignition or knocking. The air from the intercooler is redirected to the intake manifold, and from there it goes to the different cylinders of an engine.
Wastegate and Blow Off Valve
To prevent overboosting and damaging the turbocharger, a turbocharger features regulatory valves for the turbine and compressor to manage pressure.
Wastegate: It is a bypass valve which is located on the turbine side of the turbocharger. Once the engine has achieved the desired boost pressure (additional compressed air), the wastegate valve opens and diversts some of the exhaust gases directly into the exhaust and away from the turbine. This helps in moderating the amount of boost generated by a turbocharger, and it’s crucial in extending the lifespan of a turbocharger.
Blow Off Valve: This is a type of bypass valve which is found on the compressor side of the turbocharger, typically between the compressor outlet and the throttle body of an engine. When a throttle closes suddenly, such as during gear shifts, the turbocharger continues to spin and compress air. As the throttle is closed, this can create a pressure surge inside the intake manifold which can then create problems like turbo lag or even damaging the turbocharger. A blow off valve diverts this additional air to the atmosphere, or recirculates it back into the intake tract before the compressor. A blow off valve too is quite important for extending the lifespan of a turbocharger.
Different Types of Turbochargers
Turbochargers come in various configurations, and each type is designed for optimising performance in specific applications.
- Single Turbo: This is the most common type of turbocharger configuration and one turbo is used to boost the entire engine. It is cost effective, but can cause turbo lag in larger engines.
- Twin Turbo: Two turbochargers are used in this configuration. They can work identically at the same time and this configuration is called a Parallel Twin Turbo. Alternatively, one turbo can be configured for lower RPMs and another for higher, and this configuration is called Sequential Twin Turbo.
- Twin-Scroll Turbo: Instead of a single entry for exhaust gases inside the turbine housing, a twin scroll turbocharger separates the exhaust gases from different cylinder pairs. This helps in reducing exhaust gas interference and increasing turbine efficiency along with other benefits such as reduced turbo lag.
- Variable Geometry Turbocharger: Also known as VGTs, such a turbocharger has movable vanes inside the turbine housing. At lower RPMs, vanes of the turbine close to restrict the flow of exhaust gases and increase turbine speed, quickly spooling up the turbo. At higher speed, the vanes open up to reduce the back pressure and increase efficiency. VGTs offer an optimal boost pressure across a wide range of RPMs, and can effectively negate turbo lag.
- Electric Turbo: This is a new type of turbocharger and is not used commonly. However, such a turbocharger features an electric motor that can spin up the compressor. This is highly helpful at low RPMs as it virtually eliminates turbo lag and can also be used for energy recovery.
Advantages of a Turbocharger
Car makers use turbochargers with engines due to the their numerous advantages:
- Increased Power Output: This is the biggest advantage of a turbocharger as it can significantly increase the horsepower and torque output of an engine. It is especially beneficial as smaller engines can make more power without an increase in size.
- Improved Fuel Efficiency: The use of a smaller engine and a turbocharger to create the same amount of horsepower and torque compared to a larger naturally aspirated engine can result in a lower fuel consumption. This is because there are less internal friction forces at play and smaller engines can operate more efficiently at lower loads.
- Reduced Emissions: The increased oxygen in the cylinder leads to a more complete burning of the fuel inside the engine, which can result in lower emissions of unburnt hydrocarbons and carbon monoxide. Furthermore, downsizing an engine also helps in reducing overall CO2 emissions.
- Better Performance at Higher Altitude: At higher altitudes, naturally aspirated engines make less power due to the air being thinner and the overall scarcity of oxygen. Turbocharged engines can get around this problem due to forced induction.
- Engine Downsizing: Car makers are able to extract the same performance from a smaller engine using a turbocharger. This allows them to use smaller, lighter engines which are better for packaging and also reduce the overall weight of the vehicle.
- Enhanced Driving Experience: The increased torque from a turbocharger can be ideal for daily driving as most of it is made low down in the RPM range. This makes it easier to drive in city traffic. Furthermore, the increased horsepower also increases the overall performance of the car, making it a fun driving experience.
Disadvantages of a Turbocharger
Despite their vast number of advantages, turbochargers have some downsides as well:
- Turbo Lag: The biggest disadvantage of a turbocharger is the lag associated. At low RPMs, when the engine is not making enough exhaust gases to fully spin the turbo, the throttle response can feel sluggish and this is called turbo lag. Modern turbos have cut down on this problem to an extent, but turbo lag still exists in many cars today.
- Additional Heat Stress: Compressed air from the turbocharger can be quite hot and furthermore, the exhaust gases also heat up the turbocharger. This added heat stress needs to be managed using an intercooler and heat shields and over the long run, this heat stress can also decrease the life span of engine components.
- Increased Complexity: Turbochargers require several additional components to run properly and over time and such engines are more complex than naturally aspirated engines. Repairs of turbochargers can require specialised mechanics and parts.
- Reliance on Lubrication: Turbochargers spin at extremely high RPMs and require constant lubrication to function optimally. This places additional stress on the engine oil, requiring frequent top ups and a higher grade of oil.
- Durability Concerns: Modern turbochargers have proven themselves to be reliable, however older cars are still susceptible to turbocharger failure due to aggressive driving, poor maintenance and excessive heat. This is especially true for older diesel cars.
- Higher Repair Costs: A turbocharger is highly complex and is thus expensive. Furthermore, the additional elements such as an intercooler also raise the cost of the entire turbocharger system. This can lead to higher repair costs than usual in case of failure.
Conclusion
Once used as a tool for increasing the output of aircraft and ship engines, the turbocharger has come a long way in terms of propelling modern automobiles. The biggest upside behind using a turbocharger is that it harnesses the power of exhaust gases, which would otherwise simply be let out of the exhaust pipe, to increase the power output and the fuel efficiency of an engine. However, the biggest upside of using a turbocharger is that car makers can downsize their engines which leads to better overall efficiency. However, the use of turbocharger still has some downsides such as expensive repair bills, but ultimately, the advancements in turbocharger are slowly chipping away at its disadvantages.
FAQs about Turbocharger in Cars
Q. What is a turbocharger?
A turbocharger is a forced induction device that uses the exhaust gases from an engine to spin, which in turns spins an air compressor to compress air and send it to the intake manifold of an engine. The additional volume of air allows an engine to mix it with extra fuel, and the combustion of this additional air-fuel mixture inside the cylinders increases the horsepower and torque output of an engine.
Q. How is a turbocharger different from a supercharger?
A turbocharger uses the exhaust gases from an engine to spin the air compressor to force feed the engine with extra air. A supercharger also acts as a forced induction device, however, it is generally directly connected to the crankshaft of an engine which spins the compressor. A supercharger has more parasitic losses compared to a turbocharger, however, it is better optimised for a better response at low RPMs.
Q. Why do cars have turbochargers?
A turbocharger is used by car makers for many reasons. The primary reason is to increase the horsepower and torque output of an engine. Using a turbocharger allows engineers to squeeze more power out of a small engine, which is useful for better fuel consumption, lesser exhaust emissions and packaging the engine inside an engine bay.
Q. What does turbo lag mean?
Turbochargers use exhaust gases to spin the turbine, which in turn spins the air compressor. At low RPMs, the engine does not generate enough exhaust gases to properly spin the turbine of a turbocharger. This can lead to a delayed throttle response and this delay is called turbo lag. Modern turbochargers use various methods such as twin scroll turbos or variable geometry turbochargers to mitigate turbo lag.
Q. What is an intercooler?
When a turbocharger compresses air, the high pressure heats up the air. Hot air is not as dense and has less oxygen molecules. It needs to be cooled down before entering the engine cylinder. An intercooler is used to cool down this hot air, and it is basically a heat exchanger. An intercooler can use air or liquid to cool down the hot air from the turbocharger.
Q. What is a turbo wastegate?
Overboosting a turbocharger can lead to problems and also damage it. To prevent excess boost from building up, a turbocharger has a bypass valve on the turbine side. When the desired boost pressure is reached, the wastegate of the turbocharger opens up to divert excess exhaust gases directly into the exhaust system.
