Hello everyone, I'm Sir Lee. Starting from this issue, start a special series: Li Xie engine technology, in plain language, for you to interpret the advanced program and basic principles of the engine ~ it is not easy to write an article, if you need to reprint, please be sure to hang up the link to this article, plagiarism must be investigated ~
When introducing the engine earlier, two boosting techniques are mentioned several times in the work. Today Sir Li first interpreted one of them for everyone, that is, the variable section supercharger.
Turbochargers are mainly composed of a turbine, a compressor and an intermediate shaft connecting the two. The exhaust pipe of the engine is connected to the turbine, and the exhaust gas from the engine blows the turbine to rotate rapidly, and the compressor impeller rotates through the intermediate shaft, thereby compressing the intake air and increasing the amount of air entering the engine. The more air, the more oil can be burned, more energy can be released, and the engine output is higher.
The basic structure of a turbocharger
The size of the supercharger is diverse, and each supercharger has a range of applications. A small supercharger can rotate at high speed under a smaller airflow (i.e., when the engine is running at low power), but when the airflow is large (that is, when the engine is running at high power), the supercharger may be destroyed due to excessive speed. Conversely, the large supercharger can operate reliably under a large airflow (that is, when the engine is running at high power), but when the airflow is small (that is, when the engine is running at low power), the supercharger speed is too low and the boost effect is poor.
Variable-section supercharger can adjust the above problems to a certain extent, in order to make it easy for everyone to understand, here is a needle tube as an analogy. Push the needle tube at a constant speed to discharge the gas in the tube, when with the needle, the gas is not easy to discharge, the air pressure in the needle tube is large, the feeling is that a large force needs to be applied; when there is no needle, the gas is easy to discharge, the air pressure in the needle tube is small, and it feels that it can be pushed effortlessly.
Effect of flow section size on boost pressure
When the engine is running at low power, the flow section of the supercharger turbine is reduced, which is equivalent to the needle tube with a needle, the exhaust pressure becomes larger, and the turbine blade speed is high; when the engine is running at high power, the flow section of the supercharger turbine is increased, which is equivalent to the needle tube without a needle, and the exhaust pressure becomes smaller to protect the turbine blade from speeding.
Variable-section superchargers usually come in two forms of construction, which are described below.
VGT, or Variable Geometry Turbocharger, is a variable geometry supercharger. There are also manufacturers called VTGs, that is, Variable Turbine Geometry, variable turbine geometry. The names are similar, the basic structural principles are the same, and the supercharger suppliers BorgWarner and Holsett use this technology.
The turbine of the VGT can be sliding, also known as the sliding variable nozzle.
VGT supercharger construction
With a variable geometry actuator, the sliding variable nozzle is controlled to move along the axis of the intermediate axis.
Variable geometry actuator
The process of adjusting the supercharger geometry section from small to large is as follows:
—— The nozzle is fully closed, the sliding nozzle is located on the outermost side, the circulation section of the turbine is the smallest, the exhaust pipe pressure is the largest, the supercharger speed is the highest at this time, and the air boost pressure is the largest;
—— The nozzle is partially opened, the sliding nozzle moves inward, at this time the circulation section of the turbine becomes larger, the exhaust pipe pressure decreases, the supercharger speed decreases at this time, and the air boost pressure decreases;
- The nozzle is fully open, the sliding nozzle is located on the innermost side, at this time the turbine has the largest circulation section, the exhaust pipe pressure is the smallest, the supercharger speed is the smallest, and the air boost pressure is the smallest.
The process of geometric cross-sectional change
VNT, or Variable Nozzle Turbocharger, is a variable nozzle supercharger, and supercharger supplier Garrett (formerly known as Honeywell) employs this technology.
On the outside of the VNT's turbine blades, there is a coil of diverter vanes that can be adjusted.
Deflector vanes for VNT
The angle of the guide vane is controlled by means of a variable geometry actuator.
The angle of the inlet vane changes
—— The nozzle is fully closed, the spacing between the diversion blades is the smallest, the circulation section of the turbine is the smallest, the exhaust pipe pressure is the largest, the supercharger speed is the highest, and the air boost pressure is the largest;
——The nozzle is partially opened, the spacing between the diversion blades increases, the flow section of the turbine becomes larger, the exhaust pipe pressure decreases, the supercharger speed decreases at this time, and the air boost pressure decreases;
- The nozzle is fully open, the spacing between the diversion blades is the largest, the flow section of the turbine is the largest, the exhaust pipe pressure is the smallest, the supercharger speed is the smallest, and the air boost pressure is the smallest.
The principle and structure of the variable section supercharger believe that everyone has already understood, so what benefits can be brought by using this kind of supercharger?
- Higher output torque: Increase the intake airflow over a wide engine speed range by reducing the flow section. Especially for light engines with a wide speed range, variable-section superchargers are more suitable.
Increase torque
--Good low-speed responsiveness: By reducing the flow section and increasing the exhaust pipe pressure, the supercharger speed can be rapidly increased.
- Lower fuel consumption: Compared with ordinary deflating valve superchargers, variable-section superchargers have higher efficiency in the full speed range.
- Assist in the realization of EGR: EGR reduces the oxygen content in the cylinder by recirculating the exhaust gas into fresh air, thereby reducing the exhaust gas NOx generated during combustion. The exhaust gas can only be recirculated if the gas pressure in the exhaust pipe is higher than the gas pressure in the intake pipe. For some conditions that do not meet this condition, such as when the vehicle is running at low speed and high load, the gas pressure in the exhaust pipe can be increased by reducing the flow section, thereby achieving EGR.
Auxiliary EGR
Improve SCR conversion efficiency and reduce emissions: The main role of SCR is to reduce NOx through urea, but only at higher temperatures can good conversion efficiency be obtained. Increasing the flow section can reduce the intake air volume, and the reduction of the air-fuel ratio can increase the exhaust gas temperature, thereby improving the SCR conversion efficiency.
The variable-section supercharger has outstanding advantages in performance performance, but it also has disadvantages, that is, it is expensive. A variable-section supercharger costs two or three times as much as an ordinary vent valve supercharger of the same size. Domestic variable section superchargers are also being done by manufacturers, but due to the late start, the quality is not very stable.
At present, most engines use low-cost ordinary vent valve superchargers, if your car uses a variable-section supercharger, then your vehicle performance is likely to be better in the same class of cars.
For variable section superchargers have any questions, welcome to leave a message to discuss.
If this issue is helpful to you, please pay attention to and like it. I'm Sir Lee, a friend who accompanies you in an in-depth understanding of the engine.
Li Xie diesel engine: the vehicle 2L engine 4D20, the Great Wall Gun, Haval, Fengjun are all in use
Li Xie diesel engine: the car 2L engine π, SAIC Chase pickup truck, SUV, light passenger standard
Li Xie diesel engine: 2L engine FD20 for vehicles, supporting Foton Pioneer BAIC BJ40