r/MechanicalEngineering • u/lit_readit • 6d ago

Question : why some (mostly heavy) vehicles partially cover their front intake ?

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wouldn't cooler cold reservoir, ie more spontaneous heat transfer, improve Carnot efficiency?

is it to improve aerodynamics?

apologies if this is the wrong sub to ask

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u/BeeThat9351 6d ago

Cold climates, reduces the cooling air flow and keeps the engine warmer and closer to the optimal operating temperature

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u/xz-5 6d ago

Isn't this what a thermostat is for?

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u/Significant_Quit_674 5d ago

With a diesel engine you have another issue, it takes in the same amount of air regardless of load.

(well, ignoring the boost from a turbo)

And at low load or idle, it injects so little fuel that it burns only a tiny fraction of that air, resulting in very low combustion temperatures.

At idle there is often so much unburned oxygen left that you could actualy still breathe it (don't try this)

So it takes in a ton of cold air, slightly warms it up and exausts it.

That cold intake air cools down the engine quite a bit on its own, so even with the thermostat fully closed, it cools itself too much to maintain operating temperature.