The principle of turbocharger

The general structure of the turbocharger, the exhaust gas turbocharger is mainly composed of a pump wheel and a turbine, and of course there are other control elements. The pump wheel and the turbine are connected by a shaft, that is, the rotor. The exhaust gas discharged from the engine drives the pump wheel, and the pump wheel drives the turbine to rotate. After the turbine rotates, the air intake system is pressurized. The supercharger is installed on the exhaust side of the engine, so the working temperature of the supercharger is very high, and the speed of the rotor of the supercharger is very high when it is working, which can reach hundreds of thousands of revolutions per minute, such a high speed and temperature The common mechanical needle roller or ball bearing cannot work for the rotor, so the turbocharger generally adopts a fully floating bearing, which is lubricated by oil, and the coolant is used to cool the supercharger. In the past, turbochargers were mostly used in diesel engines, because the combustion methods of gasoline and diesel are different, so the form of turbochargers used in engines is also different. A gasoline engine is different from a diesel engine. It is not air that enters the cylinder, but a mixture of gasoline and air, which is prone to detonation if the pressure is too high. Therefore, the installation of a turbocharger must avoid detonation, which involves two related issues, one is high temperature control, and the other is ignition timing control.
After forced supercharging, the temperature and pressure of gasoline engine compression and combustion will increase, and the tendency of knocking will increase. In addition, the exhaust temperature of gasoline engine is higher than that of diesel engine, and it is not suitable to increase the valve overlap angle (the time when the intake and exhaust valves are opened at the same time) to strengthen the cooling of exhaust gas, and reducing the compression ratio will cause insufficient combustion. In addition, the speed of the gasoline engine is higher than that of the diesel engine, and the air flow changes greatly, which is easy to cause the response lag of the turbocharger. In response to a series of problems arising from the use of turbochargers in gasoline engines, engineers have made targeted improvements one by one, so that gasoline engines can also use exhaust gas turbochargers. Because the speed of the gasoline engine of a car is higher than that of the diesel engine, the air flow rate is fast and the variation range is large, so its turbocharger has higher requirements. Modern car engines have generally adopted electronic injection systems. With the cooperation of electronic control technology and new materials, the application of turbochargers in gasoline engines will become increasingly common.
The exhaust gas turbochargers used in cars all use a single inlet turbine casing, which means that only the pressure energy of the exhaust gas is used, and no other auxiliary energy is required. Due to the large speed range of the car engine, the exhaust gas turbocharger must have a regulating device so that the engine can obtain a relatively constant boost pressure within a certain speed range. In addition, the gasoline engine is ignited, and its compression ratio is limited to a certain range, and if it is too high, it will cause deflagration. Therefore, there is also a deflagration detection and control mechanism to adjust the ignition advance angle at any time.
The exhaust gas turbocharger of a car is generally installed near the exhaust pipe, and the turbine and the impeller are installed in the turbine chamber and the supercharger respectively. The two are rigidly connected coaxially and rotate synchronously.
When supercharging is not required, such as at idle speed or when there is a premonition of detonation, a portion of the exhaust gas will leak through the bypass valve and not enter the turbocharger. When the engine speed reaches 2000 rpm, the solenoid valve closes the bypass valve to direct the exhaust flow to the turbine side, causing the turbine to turn. There is also a design that adjusts the angle of the turbine blades, and adjusts the speed of the turbine through the change of resistance, thereby changing the amount of boost.
Cooling the air can shrink the air to increase its density, pack more air into the same volume, and prevent deflagration. Therefore, the turbocharger of the car is equipped with an intercooler. This intercooler is generally cooled by air, installed in front of, beside the engine radiator or in a separate location, and is cooled by the oncoming air flow of the car or its own fan.
A key part of a turbocharger is the bearing. The bearing, named after the form of lubrication, is called a "full floating bearing" and operates at extremely high speeds and harsh working conditions. Therefore, it is very important to ensure lubrication. If the oil supply is slow due to low oil pressure, it can damage the bearings and cause the turbocharger to fail. This kind of failure does not occur in normal engine startup, but if the engine is started for the first time after changing the oil and oil filter, it will produce a slow oil supply, which will cause the bearing to lack oil lubrication. In this case, it is necessary to idle for about 3 minutes after starting, and it is not possible to directly increase the speed to the starting speed of the turbocharger. Similarly, do not stop the engine immediately after high speed and uphill, and continue to run the engine at idle speed for about 1 minute, so that the bearing of the turbocharger that is still idling will not be short of oil. Therefore, drivers of turbocharged vehicles must follow the manufacturer's instructions and pay great attention to the quality of the oil. It is not advisable to operate turbocharged vehicles as ordinary vehicles.