Turbocharger is a forced air induction device designed to increase engine power. It operates using the energy of the waste exhaust gases generated in the engine. It is an invention born from the idea of utilizing the wasted energy of exhaust gases, such as pressure, heat, and velocity. The concept of forced induction in naturally aspirated engines began to be used in race cars in the 1930s and is now widely applied in modern engines.

_{Turbocharger construction and flow of gases}

Engine power is directly proportional to the amount of air and fuel that can enter the cylinders. When all else is equal, a larger cylinder will allow more airflow, which results in greater engine power. In smaller engines, more air needs to be supplied to generate higher power and improve engine performance.

Currently, both diesel and gasoline engines use exhaust turbochargers, which are a form of forced air induction. The turbo, connected to the exhaust line right after the exhaust manifold, utilizes the energy from exhaust gases to operate.It compresses fresh air and sends it to the intake manifold, and then to the combustion chamber, improving combustion efficiency and increasing engine power.

A turbocharger works by directing the high-pressure exhaust gases from the exhaust manifold onto the turbine blades, causing them to spin. The compressor blades, located at the other end of the turbine shaft, draw in fresh air, compress it, and send it to the intercooler. From there, the pressurized air travels through the intake manifold to the combustion chamber. Turbochargers deliver fresh air at an absolute pressure of about 2 to 2.5 bar to the intake manifold. By recovering energy that would otherwise be lost in exhaust gases, the turbocharger enhances engine performance.

Types of Turbochargers

• Wastegate Valve-Free (Open) Turbocharger: This is the simplest turbocharger unit without boost pressure control. It is used in generators, construction machinery, and trucks.
• Wastegate Valve Turbocharger: Operates on the principle of air discharge at maximum pressure. It is predominantly used in passenger cars and light commercial vehicles.
• Exhaust Manifold-Integrated Turbocharger: Based on the principle of manufacturing the exhaust manifold and the turbocharger’s turbine housing as a single unit. It can be easily integrated into the vehicle’s engine without additional connection points or gaskets
• VGT (Variable Geometry Turbocharger): With its variable geometry feature, this is the most advanced system for maximum boost pressure control on a turbocharger. It is the best type of turbocharger for meeting exhaust emission regulations and is used in nearly all new-generation engines. It can be electronically or pneumatically controlled.

Turbocharger Components and Their Functions

_{The Parts of Turbocharger}

Turbine Blades (Turbine Wheel)

The turbine blades are a part of the turbocharger system that rotates due to exhaust gases. Exhaust gases strike the turbine blades, causing the turbo to spin. An increase in exhaust gas flow results in the turbine blades spinning faster.

Turbocharger Shaft

The turbocharger shaft is produced as an integrated piece along with the turbine blades. In other words, the turbine blades and shaft are manufactured as a single unit. As the turbine rotates with the help of exhaust gases, the shaft spins along with it. The turbocharger shaft operates within the turbo bearings.

Compressor Blades (Blower or Compressor Wheel)

The turbine blades and shaft, powered by exhaust gases, transmit motion to the compressor blades, which are connected via a coupling mechanism. As the compressor blades spin, they draw air from the atmosphere, creating intake airflow. While the turbine blades work with exhaust gases, the compressor blades perform the opposite function by pulling fresh air in and delivering it to the engine.In high-performance engines, the hot air leaving the turbocharger is passed through an intercooler (similar to a radiator) to cool down before reaching the engine.

Turbo Bearings

The turbocharger shaft, connecting the turbine and compressor blades, rotates at extremely high speeds with the support of turbo bearings. The bearings allow the shaft to spin at maximum efficiency while preventing wear and tear through continuous lubrication.

Labyrinth Ring

Labyrinth rings play a crucial role in turbocharger lubrication. Located on both the turbine and compressor sides, they prevent oil from leaking into the exhaust or intake sides. Their design ensures that oil remains within the bearing housing, maintaining effective lubrication as the turbo rotates.

Turbo Lag

After a turbocharger builds up a certain level of boost pressure, releasing the accelerator pedal causes the throttle valve in the intake manifold to close. This leads to high pressure building up in the system between the turbo and the engine, such as in the turbo pipes and intercooler. Due to this high pressure, the rapidly spinning turbo impeller slows down or stops completely. When the accelerator pedal is pressed again, the engine must first absorb this reverse pressure before the turbo can start spinning again and generate the required boost pressure. This process is known as Turbo Lag. This phenomenon can also be harmful to the turbine. To reduce turbo lag, many standard engines feature systems that release reverse pressure. In high-performance engines, a component called Blow-off Valve is used for this purpose.

Blow-off (Air Pressure Release)

The blow-off valve is placed between the turbo and the throttle valve. When the throttle valve closes, a hose connected after the throttle utilizes engine vacuum to activate the blow-off valve, releasing the excess reverse pressure from the turbo. By eliminating this unwanted pressure, the turbo impeller does not abruptly stop, allowing it to continue spinning. This ensures that, when the accelerator is pressed again, the turbo can rebuild pressure more quickly.

For a turbocharger to generate sufficient boost pressure, it must reach a certain rotational speed, which is directly proportional to the exhaust gas pressure leaving the engine’s exhaust manifold. The turbo, driven by exhaust gases rotating its turbine side, simultaneously spins the impeller on the intake side, supplying high-pressure air to the engine.Once the engine speed surpasses approximately 2000 rpm, the turbine blades reach optimal rotational speed, enabling efficient boost pressure production.

Although the period between idle speed (approximately 800 rpm) and reaching approximately 2000 rpm is often referred to as turbo lag, it is more of a natural operational phase rather than an actual delay. True turbo lag occurs when reverse pressure slows or stops the turbo impeller, even when the engine is already running at 2000 rpm or higher.