Text: Mac Avendano / Photos: AutoIndustriya.com Team, BorgWarner, Honda, Honeywell, Volvo | posted October 22, 2013 10:21
Explaining the concept behind a turbocharger and its types
Before the mainstream use of turbochargers in the automotive industry, it was believed that using bigger displacements were the only solution to produce more power. However, developments among auto manufacturers have led to maximizing smaller engines for the same or better output. Among the technology used for the trend is the installation of turbochargers.
Turbochargers are making a comeback among auto manufacturers in hopes to squeeze out the most of smaller engines. Despite its conception in the 19th century, mainstream turbochargers only found its way inside the car’s engine bay during the 80s and 90s. However, back in the 80s, this feature was notorious for becoming too hot and blowing engines. Its use eventually faded along with the issues hounding it. With its reemergence these days, developments are continually made to prevent those effects and incidents from happening again.
To have a grasp on why this technology is prevalent among vehicles today, you should be able to understand the concept behind its use.
The idea behind turbochargers and superchargers
Turbochargers, along with superchargers, were developed to facilitate forced induction. This process delivers compressed air to the engine to boost its combustion, therefore maximizing engine power. Having a forced induction system also lessens the negative effects of operating at high altitude as it creates artificial air pressure for your engine. Despite delivering similar effects, the two systems differ in where they derive their energy. The supercharger relies on the engine shaft’s movement (therefore creating extra drag) while the turbocharger uses exhaust gases.
Basic components of the turbocharger
The turbo is made of these basic parts: turbine, compressor, and center housing. Before we move on to the different types of turbochargers, let us take a look how these basic components function:
The turbine converts heat and pressure into usable kinetic energy. The energy powers the rotation of the turbine wheel, shaft, and compressor wheel. Determining the turbine wheel’s size is essential in maximizing the capabilities of your turbocharger system: being too small can cause excessive back pressure and can choke the engine; being too big can result in increased lag and can add difficulty in achieving target boost.
The compressor, as the name implies, compresses fresh air and directs it to the throttle body. Being connected to the turbine wheel, the compressor wheel’s rotation is dependent on the speed of the turbine wheel. As a result of this process, boost is generated. The boost is the primary reason why turbochargers function as a supplement to naturally-aspirated engines.
The center housing is the mounting point of the turbocharger assembly. It is made of materials capable of enduring the heat and stress from the turbine. Likewise, it supports and lubricates the bearings of the turbocharger.
Other turbocharger components
Heat is generated as more pressure accumulates within the turbocharger system. The intercooler addresses this issue by cooling the air that passes through the system before entering the intake manifold.
The wastegate regulates the exhaust gas inside the turbocharger system. Inability to regulate the amount of exhaust gas present in the system will create an excessive amount of boost and can destroy engine components.
The blow-off valve eases off the system of extra pressure that accumulates during the vehicle’s operation. When the throttle is released, the trapped compressed air can only travel back to the compressor wheel. If that happens, a compressor surge may occur and damage the system due to excessive load. The blow-off valve works in the same fashion as the wastegate to address this situation.
How the turbocharger system works
After explaining the different components of the turbocharger system, we can now move on to the process of boosting your engine with it. To understand how it works, take a look at the following steps:
- The exhaust gas exits from the engine block and travels to the turbine wheel via a pipe.
- The exhaust gas propels the turbine wheel before exiting the system.
- The rotation of the turbine wheel turns the compressor wheel at the same speed, enabling it to suck ambient air into the system.
- The ambient air is compressed. It then travels towards the engine block. If an intercooler is present, the air passes through it first before proceeding to the engine block, cooling the compressed air in the process.
- The cool air that enters the engine is what you call a boost. It aids the combustion process giving the engine a more powerful output.
Types of turbochargers
As engineers continue to develop a better turbocharger, various types of this component came out. The growing variety suits different functions such as economic driving, performance racing, and offroading. These developments created different types of turbochargers. Here are some examples:
The journal bearing system is the traditional turbocharger. There have been debates over its continued use, and is often compared with the ball bearing system. It is considered easier to install and rebuild with minimal costs. However, it can take a longer time to cool down.
Turbochargers using a ball bearing system have enhanced mechanical and turbo efficiency. It has a rolling mechanism as opposed to the journal bearing’s sliding mechanism. This is commonly used for passenger cars due to the fuel efficiency and performance benefits.
Twin scroll turbo systems use two exhaust gas inlets and two nozzles, where one is smaller for quick response and the larger for peak performance. The set-up uses the exhaust manifold to separate the channels for cylinders allowing exhaust gases to flow freely.
Two-stage parallel turbo
This system involves two turbochargers working in sequence where the activation of each turbocharger depends on the engine speed. From 1-2,400 rpm, the primary turbocharger is activated; at 2,400-2,800 rpm, the second turbocharger is activated; and beyond 2,800 rpm, both turbochargers function. This system is recommended for diesel engines with displacements of 2.0 liters and above, and V engines.
Two-stage serial turbo
This system involves one small high pressure turbocharger and a large low pressure turbocharger. The fluid flowing in the turbochargers is controlled with bypass valves. When the engine runs from 1-1,500 rpm, the system works in full serial mode while leaving the compressor and bypass valves closed. If the engine exceeds 1,500 rpm, the bypass valve opens to allow more exhaust gas to the low pressure turbocharger.
Variable nozzle (geometry) turbo
Just as its name implies, variable nozzle turbochargers (VNT) use adjusting vanes that maximize the system’s output. VNTs can produce the following: higher torque levels; more power in a wider range; better acceleration; and cleaner combustion. This is why the use of VNTs in pick-up trucks is popular.
So there you have it. We hope that we were able to supplement your knowledge on turbochargers.