Note: This post first appeared on our old site: TeamUV.org
Turbochargers are a class of superchargers that use a turbine and a compressor on the same shaft to increase the density of the intake air in an engine. Turbochargers come in all sizes and applications, for example: the turbocharger pictured above is for large marine vehicles, while the turbochargers that this article will be focused towards are the much smaller ones that can be found on some automotive engines. As mentioned before, the turbocharger increases the density of the air intake; this is generally accomplished by using the engine’s exhaust gases to spin a turbine which is connected by a shaft to a compressor which takes air from the environment and compresses it prior to feeding it into the engine. Why might one want to do this?
Now, to discuss some of the engineering analysis considerations associated with automotive turbochargers. Within the field of fluid mechanics, most of the considerations are energy related, such as: you must consider any pressure drop across the inlet (think an air filter), the pump work (power required to drive the turbocharger), obstructions to internal fluid flow (major losses associated with components in the flow path or minor losses associated with the changing geometry of the tubes – bends, curves, etc.), exit flow (does it pass through a nozzle, is it directly ducted to the engine intake, is there an expansion fitting), and any additional technologies at play such as intercooling).
From the standpoint of mechanics of materials, one interesting thing to consider would be the shaft inertial effects. What this refers to is the fact that the shaft has mass and that mass is spinning; the revolution of the shaft mass and mass of connected components puts cyclical stresses on the shaft which can lead to premature failure if the shaft is not designed properly.
Lastly, we can look at the turbocharger from the standpoint of control systems engineering: you may want to be able to vary the compressor speed in order to provide variable exit air density to provide for different ranges of engine speeds or to account for changes in elevation/altitude (this would mostly apply to airplane turbochargers), different climates, and so on.
Ultimately, turbochargers provide an excellent example of just how complicated any given system may be from an engineering standpoint as the above text hopefully displays; however, this is not the only purpose of this post, this post also aims to show some aspects of the thought process of an engineer and how truly many ways any given problem can be looked at (and how fascinating the options are)!