Turbocharging is a technology that uses the exhaust gas generated by the operation of internal combustion engine to drive the air compressor.
The turbocharged engine on the market is an engine that relies on the turbocharger to increase the intake of the engine. The turbocharger is actually an air compressor. It uses the exhaust gas from the engine as power to drive the turbine in the turbine chamber (located in the exhaust passage), and the turbine drives the coaxial impeller (located in the inlet passage). The impeller compresses the fresh air sent by the air filter pipe and then sends it to the cylinder. When the engine speed is accelerated, the exhaust gas discharge speed and the turbine speed are also accelerated simultaneously, the degree of air compression is increased, the air intake of the engine is increased accordingly, and the output power of the engine can be increased.
Mechanism and working principle of turbocharger
Turbocharging is driven by exhaust gases from the engine. The turbine consists of two parts, one is the fresh air booster end (compression pump wheel) and the other is the exhaust gas drive end (exhaust gas turbine). There is an impeller at both ends. There is a pressure relief trigger between the turbines on both sides of the same shaft. When the pressure of the compression turbine is too high, the pressure will push the trigger to open the valve of the exhaust gas turbine and reduce the air pressure, To prevent overpressure.
The support of turbine axle is shaft sleeve, and the bearing design inside the shaft sleeve can be divided into ball bearing and floating bearing. The rotating power of the turbocharger impeller comes from the exhaust gas. The exhaust gas drives the turbine, and on the other side of the turbine, the blades compress air. The turbocharger shell is made of nickel, chromium and silicon alloy, and the shaft is made of chromium and molybdenum alloy. More importantly, the turbocharger works at high temperature and high speed. In order to ensure its normal operation, oil and coolant are introduced into the turbocharger to ensure effective lubrication and cooling and improve working conditions.
The exhaust gas with high temperature and certain pressure discharged by the engine enters the supercharger and drives the impeller of the shaft to rotate at a high speed of tens of thousands or even hundreds of thousands of revolutions per minute. At idle speed, the impeller speed is 12000 rpm. At full load, the impeller speed can exceed 135000 rpm. Ordinary bearings can not withstand the high temperature and wear caused by such high speed, Therefore, the lubrication and cooling effect of engine oil in turbocharging system is very important. Diesel engines are also equipped with turbocharging systems, and the maximum boost value of diesel engines is generally higher than that of gasoline engines. It is also for the good heat dissipation needs of the turbocharger. Generally, vehicles equipped with the turbocharger are required to run at idle speed for a while before flameout.
The difference between turbocharging and supercharging
Turbocharging and supercharging are two different ways of intake supercharging. The main difference lies in the driving mode of supercharger. The earliest superchargers were all supercharged, which was called super supercharger when it was first invented. Later, after the invention of turbocharging, in order to distinguish the two. At first, the turbocharger was called turbo supercharger, and the supercharger was called mechanical supercharger. Over time, the two were simplified to turbocharger and supercharger respectively. The Germans call the supercharger kompressor because of German.
A / R value of turbocharger
The A / R value is often indicated in the turbocharger sales volume in the modification market to express the characteristics of the turbine. A means area, which refers to the narrowest cross-sectional area at the side inlet of the blade turbine receiving exhaust gas, R is radius, which refers to the distance between the center point of a (cross-sectional area) and the center point of the turbine body, and the ratio of area to the distance between the two center points, Is the A / R value.
The smaller the A / R value, it means that the inlet is relatively small, the starting inertia of turbine blade is low, the flow rate is relatively high, the low rotation response is relatively good, and the turbine hysteresis effect is not obvious. On the contrary, the larger the A / R value is, the larger the inlet is, the higher the blade inertia is, the slower the low rotation response is, and the turbine hysteresis is obvious, but it is much stronger at high rotation. In short, the A / R value of turbines that pay more attention to high rotational power output can reach about 0.7, while the A / R value of turbines that pay more attention to low rotational torque output is about 0.2. Porsche’s VTG variable turbine geometry blade technology achieves different turbine characteristics by changing the A / R value of the turbine.