Analysis of the Principle of Engine Turbocharging-2

How does a turbocharger increase pressure?

Turbochargers are familiar to everyone. You can usually see words such as 1.4T, 2.0T, etc. on the rear of a car, which means that the engine of the car is turbocharged. Turbocharger (Turbocharger) is abbreviated as Turbo or T. Turbochargers use the exhaust gas of the engine to drive the turbine to compress the intake air, thereby increasing the power and torque of the engine and making the car more powerful.

The turbocharger is mainly composed of a turbine and a compressor, which are connected by a transmission shaft. The turbine's air intake is connected to the engine's exhaust manifold, and the exhaust port is connected to the exhaust pipe; the compressor's air intake is connected to the intake pipe, and the exhaust port is connected to the intake manifold. How is the supercharging achieved? It is mainly through the exhaust gas discharged from the engine that impacts the turbine to run at high speed, thereby driving the coaxial compressor to rotate at high speed, forcibly pressing the supercharged air into the cylinder.

Turbocharging mainly uses the energy of the engine's exhaust gas to drive the compressor to achieve intake air pressure increase. The entire process basically does not consume the engine's power and has good acceleration continuity. However, at low speeds, the turbine cannot intervene in time and has a certain lag.

What about superchargers?

Compared with turbocharging, the principle of supercharger is different. Supercharger mainly compresses air by driving a mechanical air compressor to rotate with the power of the crankshaft. Unlike turbocharging, supercharger will cause a certain degree of loss to the power output of the engine during operation.

Since the supercharger is directly driven by the crankshaft, it starts working when the engine is running. Therefore, at low speeds, the engine's torque output is also very good, and the air compression increases linearly according to the engine speed. There is no abruptness when the turbocharger intervenes, nor is there the low-speed hysteresis of the turbocharger. However, when the engine is running at high speed, the supercharger also causes a great loss of engine power, and the power improvement is not obvious.

How does a twin-turbocharged engine work?

A twin-turbocharged engine, as the name implies, means that one engine is equipped with two superchargers. If one engine uses two turbochargers, it is called a twin-turbocharged engine. For example, the BMW 3.0L inline six-cylinder engine uses two turbochargers.

In order to solve the turbo hysteresis of exhaust gas turbocharging, two identical turbines are connected in parallel on the exhaust pipe (one turbocharger is connected to every three cylinders). When the engine is at low speed, less exhaust can drive the turbine to rotate at high speed to generate sufficient intake pressure and reduce the turbo hysteresis effect. As we learned earlier, turbochargers have hysteresis at low speeds, but the boost value is large at high speeds, the engine power is significantly improved, and basically no engine power is consumed; while mechanical superchargers, the engine directly drives the turbine, there is no turbo hysteresis, but it loses some power and the boost value is low. Wouldn't it be better to combine them to complement each other's advantages?

For example, the 1.4-liter TSI engine equipped on the Volkswagen Golf GT, the designer combined the turbocharger and the supercharger together. The supercharger is installed on the engine intake system, and the turbocharger is installed on the exhaust system, thus ensuring that the engine can have a good boost effect at low, medium and high speeds.