Eli5: why do diesel engines tend to be turbocharged rather than supercharged or even N/A?
In: 7
For gasoline engines, the limit for turbocharging or supercharging is autoignition of fuel, which limits the amount of boost and compression ratio. Diesels don’t really have to worry about that (as autoignition is basically the point), so they can boost up to the mechanical limits of the engine and the block materials. Boosting universally increases efficiency, so there’s no reason *not* to boost.
As for why they use turbos over superchargers; superchargers are less efficient because of mechanical losses and friction, and the only real advantage is in getting around turbo lag. However, with modern control systems and variable-vane turbocharging, plus the low speed range of diesel engines, there’s basically just no advantage to superchargers over turbos. Thus, everything gets a turbocharger.
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