High temperature is the biggest killer of turbochargers.
The turbocharger is simple in structure, does not consume the power of the engine itself, and has high turbocharging value. These factors lead to the strong advantages of turbocharging. But turbocharging makes it one of the biggest dangers: high temperatures. It is also the hidden danger that turbocharging has not entered the civilian field.
There are several sources of heat. The first is the exhaust temperature. As we mentioned before, the exhaust temperature of gasoline engine can reach 750-900 degrees under full load and nearly 700 degrees under normal working conditions. These exhaust gases cool themselves in the process of propelling the turbine to rotate. Where does this temperature go? It is absorbed by the turbine blades.
Secondly, the shaft connecting the turbine and impeller rotates at a speed of more than 100,000 revolutions, and the friction between the shaft and the bearing generates a lot of heat. Finally, the intake impeller continuously sucks the air and compresses the air, and its temperature rises. Together, these factors make the turbocharger absolutely "hot".
The turbine failure caused by high temperature is mainly due to the deformation and ablation of turbine blades and the failure of rotating shaft. Over the years, engineers have come up with various ways to deal with this problem. Generally speaking, there are only two ways: using more heat-resistant materials and adopting more effective cooling methods.
Is turbocharging really "sluggish"?
"Turbine lag" is the most user criticized shortcoming. The so-called hysteresis is the time we need to step on the accelerator pedal to get the engine to output the corresponding power. In fact, all engines will have this lag. Because if you feel it carefully, you can feel it. When we step on the accelerator pedal, it takes time for the engine to breathe in more air and adjust the amount of fuel injected.
Because the early turbocharged engine is outstanding in its "lag" because it is widely recognized. Where does the price lag of turbocharger actuator come from? First, the inertia of turbine rotation, which takes time to accelerate; second, the friction between shaft and bearing; and finally, the resistance caused by impeller stirring air. In these three factors, the resistance produced by impeller stirring air is the most important. It is precisely because it takes time for the whole turbine rotor to speed up. The larger the impeller, the larger the boost value, the longer the acceleration time needed, and the more obvious the "hysteresis" formed.
There are many ways to improve the turbine hysteresis. On the one hand, direct injection technology can indirectly improve the torque characteristics at low speed, so that the engine speed can rise rapidly, increase the exhaust energy to drive the turbine, and reduce the turbine hysteresis. On the other hand, the size and weight of the whole turbine rotor can be reduced by reducing the turbocharging value. On the one hand, inertia and friction can be reduced, and more importantly, impeller resistance can be reduced.