Misunderstandings about turbochargers.
Misunderstandings about turbochargers.
High temperature is the biggest killer of turbochargers
The turbocharger has a simple structure, does not consume the power of the engine itself, and has a high boost value. These factors lead to a strong advantage of turbocharging. However, the principle of turbocharging makes it have the biggest hidden danger: high temperature. It is this hidden danger that has led to the delay in turbocharging entering the civilian field.
There are several sources of heat. The first is the exhaust gas temperature. As we mentioned earlier, the exhaust gas temperature of a gasoline engine can reach 750-900 degrees at full load, and it is also nearly 700 degrees under normal working conditions. These exhaust gases will cool down in the process of pushing the turbine to rotate. Where does this temperature go? It is absorbed by the turbine blades.
Secondly, the rotating shaft connecting the turbine and the impeller rotates at a high speed of more than 100,000 revolutions, and the friction between the rotating shaft and the bearing will generate a lot of heat. After Z, the intake impeller continuously sucks in air, compresses the air, and its own temperature will also increase. These factors add up to put the entire turbo in absolute "hot".
The turbine failure caused by high temperature is mainly due to the deformation and ablation of the turbine blade and the failure of the rotating shaft. Engineers have come up with a variety of ways to deal with this problem over the years, but there are basically two: use more heat-resistant materials and use more efficient cooling methods.
Does turbocharging really have "lag"?
"Turbo lag" used to be a shortcoming that Z was criticized by users. The so-called lag is the time it takes for the engine to output the corresponding power from the moment we step on the accelerator pedal. In fact, all engines will have this lag, just how much. Because if If you feel it carefully, you can feel it. The moment we step on the accelerator pedal, the engine needs to take in more air and adjust the amount of fuel injection, which takes time.
Because the early turbocharged engines were outstanding in terms of "lag", because it was widely recognized. So where does the hysteresis of the turbine come from? One is the inertia of the turbine's rotation, and it takes time to accelerate it; the other is the friction between the shaft and the bearing; the latter is the resistance formed by the impeller stirring the air. Among these three factors, the resistance generated by the impeller stirring the air is Z is the main one. It is precisely because the speed increase of the entire turbine rotor takes time. The larger the impeller and the greater the boost value, the longer the acceleration time required, and the more obvious the "hysteresis" formed.
There are many ways to improve the turbo lag. On the one hand, direct injection technology can be used to indirectly improve the torque characteristics at low speeds, so that the engine speed rises rapidly, increasing the exhaust energy to drive the turbo and reducing turbo lag. On the other hand, by reducing the supercharging value, the size and weight of the entire turbine rotor can be reduced, on the one hand, inertia and friction can be reduced, and more importantly, the impeller resistance can be reduced.
The early turbocharged engines lacked the help of direct injection, and in pursuit of performance, high turbocharged turbos were used, and the hysteresis was quite obvious. Today's turbocharged engines generally use direct injection technology, and in addition to low supercharging technology, the turbo lag has been greatly improved, and it is almost impossible to detect in daily ordinary driving. It can only be detected during rapid acceleration, but this What is the difference between this kind of lag and the slow power boost of a naturally aspirated engine during acceleration? (Unless you drive a large displacement naturally aspirated) The current "lag" phenomenon of low-supercharged direct-injection turbo engines cannot be compared with the earlier ones. Compared with the supercharged engine of the previous generation, it is only a preconceived idea because of the lag that has existed for many years.
