What is a turbocharger?
A turbocharger is actually an air compressor that increases the intake volume by compressing air. It uses the inertia impulse of exhaust gas emitted by the engine to drive the turbine inside the turbine chamber, which in turn drives a coaxial impeller. The impeller pressurizes the air sent by the air filter pipeline into the cylinder. When the engine speed increases, the exhaust gas discharge speed and turbine speed also increase synchronously, and the impeller compresses more air into the cylinder. The pressure and density of the air increase, which can burn more fuel. Correspondingly, increasing the amount of fuel and adjusting the engine speed can increase the output power of the engine.
Structural principle
Firstly, let's talk about the general structural principle of a turbocharger. The exhaust gas turbocharger is mainly composed of a pump wheel and a turbine, as well as other control components. The pump wheel and turbine are connected by a shaft, which is the rotor. The exhaust gas from the engine drives the pump wheel, which drives the turbine to rotate. After the turbine rotates, it pressurizes the intake system. The turbocharger is installed on the exhaust side of the engine, so the working temperature of the turbocharger is very high. Moreover, the rotor speed of the turbocharger during operation is very high, reaching tens of thousands of revolutions per minute. Such high speed and temperature make common mechanical needle or ball bearings unable to work for the rotor. Therefore, turbochargers generally use fully floating bearings, lubricated by oil, and cooled by coolant. Previously, turbochargers were mostly used in diesel engines because the combustion methods of gasoline and diesel were different, so the form of turbochargers used in engines was also different. A gasoline engine is different from a diesel engine in that it enters the cylinder not with air, but with a mixture of gasoline and air. Excessive pressure can easily cause detonation. Therefore, when installing a turbocharger, it is necessary to avoid detonation, which involves two related issues: high temperature control and ignition time control.
After mandatory turbocharging, the temperature and pressure during compression and combustion of gasoline engines will increase, leading to an increased tendency for detonation. In addition, the exhaust temperature of gasoline engines is higher than that of diesel engines, and it is not advisable to increase the valve overlap angle (the time when the intake and exhaust valves open simultaneously) to enhance the cooling of the exhaust. Reducing the compression ratio can also cause incomplete combustion. Moreover, gasoline engines have higher engine speeds than diesel engines, resulting in significant changes in air flow rate, which can easily cause delayed turbocharger reactions. Engineers have made targeted improvements to address a series of issues with the use of turbochargers in gasoline engines, enabling them to also use exhaust gas turbochargers.
Note
Due to the frequent operation of turbochargers at high speeds and temperatures, the temperature at the exhaust gas turbine end of the turbocharger is around 600 ℃, and the turbocharger rotor rotates at a high speed of 8000-11000r/min. Therefore, in order to ensure the normal operation of the turbocharger, the following points should be noted during use:
Do not leave in the car
After starting the engine, especially in winter, it should be allowed to idle for a period of time in order to fully lubricate the bearings with lubricating oil before the turbocharger rotor runs at high speed. So, after starting, do not forcefully hit the accelerator to prevent damage to the turbocharger oil seal.
Do not immediately turn off the engine
After running at high speed for a long time, the engine cannot be immediately turned off. During engine operation, a portion of the oil is supplied to the turbocharger rotor bearings for lubrication and cooling. After the running engine suddenly stops, the oil pressure quickly drops to zero, and the high temperature in the turbocharger turbine section is transmitted to the middle. The heat in the bearing support shell cannot be quickly carried away, while the turbocharger rotor is still rotating at high speed under the inertia. Therefore, if the engine suddenly stops in a hot engine state, it will cause the oil trapped in the turbocharger to overheat and damage the bearings and shaft. Be especially careful to prevent the engine from suddenly stalling after slamming the accelerator pedal a few times.
Clean
When disassembling the turbocharger, it is important to keep it clean and block all pipe joints with clean cloth to prevent debris from falling into the turbocharger and damaging the rotor. When repairing, be careful not to collide and damage the impeller. If the impeller needs to be replaced, a dynamic balance test should be conducted on it. After reinstallation, remove the blockage.
To be cleaned
Due to the frequent operation of the turbocharger at high temperatures, its lubricating oil pipeline is prone to partial coking of the internal oil due to the high temperature effect, which can cause insufficient lubrication of the turbocharger bearings and damage. Therefore, the lubricating oil pipeline needs to be cleaned after running for a period of time.
Pay attention to maintenance
Before leaving and after receiving the vehicle, the connection of each airway pipe should be checked to prevent looseness or detachment, which may cause the turbocharger to fail and air short circuit to enter the cylinder.
From this, it can be seen that after the engine is turbocharged, the structure of the components has been strengthened. From the perspective of use and maintenance, it is necessary to strengthen the mandatory maintenance work of the engine and pay attention to using the correct operating methods.