I believe you all have experience when driving at ordinary times. I feel that the engine with "T" is very awesome and powerful. Why is a turbocharged engine powerful? How is it pressurized? Now let's learn about the working principle of the engine turbocharger.
The function of the throttle valve
There are two main components in the engine intake system, one is the air filter, which is mainly responsible for filtering impurities in the air; The second is the intake duct, which mainly introduces air into the cylinder. And there is a very important component in the intake pipe, which is the throttle valve.
The main function of the throttle valve is to control the amount of mixture entering the cylinder. How does it control the intake volume? The depth of the accelerator pedal we press while driving actually controls the size of the throttle opening. The deeper the accelerator pedal is pressed, the greater the throttle opening, the greater the amount of mixture entering, and the engine speed will increase.
The traditional wire throttle is connected to the accelerator pedal at one end and the throttle valve at the other end through a steel wire, with a transmission ratio of 1:1. This method has poor control accuracy. The current electronic throttle valve (electronic accelerator) uses position sensors to transmit data such as the force and amplitude of stepping on the accelerator pedal to the control unit for analysis, and then summarizes the driver's intention to step on the accelerator. The ECU then calculates the actual throttle opening and closing degree and issues commands to control the throttle motor, thereby achieving precise control of the throttle valve.
Is the length of the intake manifold variable?
We usually see that the length of the intake manifold of the engine seems to be fixed, but can its length be changed? In fact, by installing a control valve inside the intake manifold and opening and closing it, the intake manifold can be divided into two sections, thereby changing its effective length. What is the purpose of changing the length of the intake manifold? The main purpose is to improve the intake efficiency of the engine at different speeds, thereby enhancing the power performance of the engine at various speeds.
When the engine is running at low speed, the black control valve closes and the airflow is forced to flow into the cylinder from the long manifold, which can increase the velocity and pressure of the intake airflow, allowing better mixing of gasoline and air and more complete combustion (this is similar to the principle that flattening a water pipe with slow water flow will make the water flow faster). When the engine speed increases, the control valve opens, and the airflow bypasses the lower pipe and directly enters the cylinder. At this time, more air can be sucked in faster, increasing the intake volume at high engine speeds.
Why is the exhaust manifold "long" in a strange shape?
The exhaust system of a car mainly includes exhaust manifolds, three-way catalytic converters, mufflers, and exhaust pipes. The main function is to discharge the exhaust gas burned in the cylinder into the atmosphere.
Why do most of the exhaust pipes we see have strange shapes? This design is mainly aimed at minimizing the interference or backflow of exhaust gases discharged from each cylinder, which may affect the power performance of the engine.
Although the exhaust pipe is designed in a peculiar shape, in order to prevent turbulence, certain principles are still followed, such as the exhaust manifolds of each cylinder being as independent and equal in length as possible; Exhaust manifold should be as long as possible.
How is turbocharging done?
Turbocharging is not unfamiliar to everyone. You can usually see words such as 1.4T and 2.0T at the rear of the car, which indicates that the engine of this car is equipped with turbocharging. Turbocharger, abbreviated as Turbo or T. Turbocharging is the use of engine exhaust to drive the turbocharger to compress the intake air, thereby increasing the engine's power and torque, making the car more powerful.
A turbocharger is mainly composed of a turbine and a compressor, which are connected by a drive shaft. The intake of the turbine is connected to the engine exhaust manifold, and the exhaust is connected to the exhaust pipe; The intake port of the compressor is connected to the intake pipe, and the exhaust port is connected to the intake manifold.
How is turbocharging achieved? Mainly through the impact of exhaust gas from the engine on the high-speed operation of the turbine, it drives the coaxial compressor to rotate at high speed, forcing the pressurized air into the cylinder.
Turbocharging mainly uses the energy of engine exhaust gas to drive the compressor to boost the intake air. The entire process basically does not consume the power of the engine and has good acceleration continuity. However, at low speeds, the turbocharger cannot intervene in time and has a certain lag.
What is mechanical supercharging like?
Compared to turbocharging, the principle of supercharging (Super charger) is different. Mechanical supercharging mainly compresses air by driving a mechanical air compressor to rotate through the power of the crankshaft. Unlike turbocharging, mechanical turbocharging causes a certain degree of loss in the power output of the engine during operation.
Due to the fact that the supercharger is directly driven by the crankshaft, it starts working when the engine is running. So at low speeds, the engine's torque output also performs very well, and the air compression rate increases linearly according to the engine speed, without the sudden intervention of a turbocharged engine or the low-speed lag of a turbocharged engine. However, when the engine is running at high speeds, the mechanical supercharger also causes significant power loss to the engine, and the power improvement is not very significant.
How does a twin turbocharged engine work?
A twin turbocharged engine, as the name suggests, refers to an engine equipped with two turbochargers. If two turbochargers are used on an engine, it is called a twin turbocharged engine. The BMW 3.0L inline six engine uses two turbochargers.
In response to the turbo lag phenomenon in exhaust gas turbocharging, two identical turbines are connected in parallel on the exhaust pipe (one turbocharger is connected to every three cylinders). At low engine speeds, less exhaust can drive the turbines to rotate at high speeds to generate sufficient intake pressure and reduce the turbo lag effect.
As previously learned, turbochargers exhibit hysteresis at low speeds, but at high speeds, the boost value is high, resulting in a significant increase in engine power without consuming much of the engine's power; And the mechanical supercharger directly drives the turbocharger during engine operation, without the lag of turbocharging, but it consumes some power and has a lower boost value. Isn't combining them complementary to each other's strengths?
Schematic diagram of twin turbocharged engine (turbocharger+mechanical supercharger)
The 1.4-liter TSI engine equipped on the Volkswagen Golf GT combines a turbocharger and a mechanical supercharger. Install the mechanical supercharger onto the engine intake system and the turbocharger onto the exhaust system to ensure good turbocharging performance at low, medium, and high speeds.
