Turbocharger classification
For a car to run fast, it must have strong power. At present, the power system of automobiles can be roughly divided into two categories: natural intake system and supercharged intake system. In European sports cars, except for BMW which still insists on using naturally aspirated engines, other automobile companies have adopted supercharging systems in order to improve the dynamic performance of their vehicles. For example, Mercedes-Benz sports cars use mechanical supercharging systems, and Saab has adopted supercharging systems. The pioneer of turbocharged. In recent years, Japanese cars have also begun to adopt turbocharging technology. The natural intake system is not equipped with any form of supercharger, but only uses the negative pressure generated by the downward piston to suck in the mixture. Although the natural intake system can obtain greater horsepower output through the variable valve timing system, the power increase is very limited. In order to effectively increase the output power of the engine, the use of a supercharging system can be said to be the most effective way.
The most common engine supercharging systems are mechanical supercharging and exhaust gas turbocharging.
Supercharged
The engine mechanically drives the supercharger for supercharging, which is called supercharging. When the engine uses mechanical supercharging, the supercharger is usually driven by the engine crankshaft through gears. Superchargers generally use centrifugal or Roots compressors, and some screw compressors are used. In recent years, new mechanical scroll superchargers have also been adopted abroad. Because driving the compressor consumes a certain output power of the engine, the thermal efficiency of the supercharged engine may not be improved, and sometimes it is lower than that of the non-supercharged internal combustion engine. When selecting boost pressure, first of all, it is necessary to ensure that the required average effective pressure can be achieved, and secondly, to obtain the lowest possible fuel consumption rate. These two requirements are often contradictory for mechanical supercharging. If the average effective pressure is pursued, it will inevitably lead to a decrease in mechanical efficiency and an increase in fuel consumption. Therefore, the selection of the boost pressure value should seek the best compromise between power and fuel consumption. Supercharged systems are currently more commonly used in European cars. Since a supercharged supercharger is continuously driven by the crankshaft, it does not move to produce a turbo lag phenomenon like turbocharging. Although supercharged can only increase the power output by about 10% and 20%, the smoothness and continuity are beyond the reach of turbocharged engines.
Exhaust gas turbocharging
The use of engine exhaust energy to drive a turbocharger is called exhaust gas turbocharging (referred to as turbocharging), as shown in the figure is an exhaust gas turbocharging system. The characteristic of exhaust gas turbocharging is that there is no mechanical connection between the turbocharger and the engine. They are connected by gas path. Because the work consumed by the compressor is part of the energy recovered by the turbine from the exhaust gas, a turbocharged engine can not only increase the power of the engine, but also increase its thermal efficiency and reduce fuel consumption. If you see the Turbo or T logo on the rear of the car, it means that the engine used in the car is turbocharged. The turbocharger is actually an air compressor. It uses the inertia of the exhaust gas discharged from the engine to push the turbine, and the turbine drives the coaxial impeller to compress the air sent from the air filter pipe, so that the air enters the cylinder after being pressurized. When the engine speed increases, the exhaust gas discharge speed and the turbine speed also increase simultaneously, and the impeller compresses more air into the cylinder. The increase in air pressure and density can burn more fuel. Increase the fuel volume and adjust the engine speed accordingly. The output power of the engine can be increased.