Truck Encyclopedia: Turbocharger

●  What is the use of the small rod on the turbocharger?

The rod on the turbocharger is connected to the bypass valve (exhaust valve). The bypass valve is used to control the boost pressure, similar to the pressure cap on a pressure cooker. When the engine speed and exhaust volume are greater than a certain operating point, in order to prevent the boost pressure from continuing to increase, part of the exhaust gas is discharged from the bypass valve at the turbine.

For example, when the engine is at high speed and high load, and the turbocharger boost pressure is too high, the bypass valve opens, and part of the exhaust gas enters the exhaust pipe directly through the bypass valve, releasing part of the exhaust gas and reducing the turbine speed, thereby controlling the boost pressure.

When the bypass valve is closed, all the exhaust gas passes through the turbine, the turbine speed increases, and the boost pressure also increases. Therefore, by controlling the opening and closing degree of the exhaust bypass valve, the boost pressure of the turbine can be controlled.

Therefore, the small lever on the turbocharger is used to control the boost pressure.

● Why can a turbocharger increase low-speed torque?

The air-fuel ratio of a naturally aspirated engine is a fixed value. Therefore, the maximum torque can only be achieved at a certain speed. After adding a turbocharger, the intake volume is increased at low speeds, so the maximum torque can be reached earlier.

The turbocharged engine will pre-compress the gas before it enters the cylinder, increasing the density of the gas entering the cylinder and reducing the volume of the gas. Under the same cylinder working volume, the mass of the gas is greatly increased. At this time, the engine increases the amount of fuel injected according to the intake volume, thus achieving the purpose of increasing engine power and torque.

A turbocharger can increase the maximum torque of the engine, especially at low speeds.

●Will the turbocharger power coming from exhaust gas affect the engine power?

The turbocharger's boosting method determines that it will increase the exhaust resistance of the engine, so theoretically, it will have an impact. But compared with the power increase brought by the boost, it is not worth mentioning.

Therefore, the turbocharger has a positive impact on engine power.

From a technical point of view, when a diesel engine is equipped with a supercharger, the density of the air entering the cylinder increases, the intake pressure and temperature rise, and the temperature and pressure of the working fluid (fuel, air) at the end of compression increase accordingly, shortening the ignition delay period, which is beneficial to improving combustion quality and saving fuel to a certain extent.

In addition, the engine can be made more fuel-efficient by optimizing the combustion method, such as higher fuel injection pressure, optimized piston structure, lower friction resistance, etc. Therefore, fuel saving is not due to turbocharging, but more complete and more efficient combustion that makes the engine fuel-efficient.