Turbocharger. diesel engine
Turbocharger VTG
All diesel engines, as well as some gasoline engines, of the AUDI A4 are equipped with a turbocharger. Two impellers are located on the turbocharger shaft in two separate housings. The turbine wheels are driven by exhaust gases. They ensure the rotation of the turbocharger shaft and thus both turbine wheels at a speed of 300,000 rpm. The turbocharger is lubricated from the engine lubrication system.
In a gasoline engine, the turbocharger is additionally cooled by liquid.
Due to the good filling of the cylinders with forced air, the engine power increases to 100%.
The turbocharger is designed to increase engine power (up to 100%) by increasing the air pressure in the intake manifold. Air does not just enter the cylinders, but is supplied to them under pressure. Along with the power boost creates an increase in engine torque. The increase in power, among other things, depends on the pressure of the injected air, which, as a rule, is 0.4-0.8 atm. The charge air pressure is constantly monitored and regulated by the engine control unit. This eliminates the possibility of exceeding the pressure above the set value. In accordance with the increase in air supply, the injection pump increases the fuel supply.
The compressor turbine is driven by the exhaust gases. Gases passing through a special casing (compressor casing), are fed to the compressor turbine. The turbine rotates on a shaft, at the other end of which there is a compressor wheel in a separate casing. It is he who supplies air under pressure to the pipeline.
Turbocharger with variable turbine geometry (VTG) has guide vanes, the position of which is regulated by the engine control unit by means of a solenoid valve and a vacuum actuator. This ensures optimum boost pressure throughout the entire rev range, resulting in higher torque and thus higher power, in particular at low revs.
An air cooler is located between the turbocharger and the engine intake duct (intercooler), which cools the air pre-compressed by the turbocharger. This increases engine power. cold air has a higher oxygen content due to its higher density.
The air pressure in the pipeline is limited by a special sensor. When the pressure limit is reached, the sensor opens the damper, thereby limiting the flow of exhaust gases to the turbine.
The compressor shaft is lubricated with engine oil, which is supplied through a specially designed hose. Shaft constantly «floats» In oil. Oil is drained from the compressor to the sump through the return hose.
Compared to a gasoline engine, the diesel engine does not need to reduce the compression ratio due to boost, which ensures full use of the injected fuel even at low speeds.
The turbocharger is an integral part of the exhaust manifold and cannot be separated from it.
The turbocharger is a precision mechanism. Therefore, if a malfunction occurs, it must be completely replaced.
Precautionary measures
The rotation speed of the compressor turbines is huge, and the operating temperature is very high. To avoid injury and damage to the turbocharger, observe the following precautions.
- Do not start the engine after removing any component of the turbocharger. The ingress of foreign objects on the turbine blades can lead to the failure of the latter. You also risk injury from objects ejected from the turbine.
- After removing any turbocharger components or air intake hoses, cover it with a clean rag.
- Do not give gas immediately after starting the engine, especially if it is not warmed up. Oil cannot instantly lubricate the turbine shaft.
- Never turn off the ignition immediately after stopping the vehicle. Do not press the accelerator pedal before stopping the engine. Immediately after the ignition is turned off, oil will no longer be supplied to the compressor shaft, and for some time it will rotate without lubrication.
- Before turning off the engine, let it idle for a few minutes, during which the turbine speed will decrease significantly.
- Change the oil, oil filter and air cleaner regularly. The use of old oil will lead to the formation of deposits on the compressor shaft and its failure. Thoroughly clean nearby surfaces before disconnecting oil supply and return hoses from the compressor. Store removed components in airtight containers.
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