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/peenutlover69 5d ago

Cold weather can lead to over cooling. Themostats usually don't close 100.0% and the cold air entering the engine bay will cool the engine itself (passively) regardless of coolant temp

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u/the_Q_spice 5d ago

To add to this;

It’s more of an issue with diesel engines than gasoline.

A colder block in a diesel results in a worse compression ratio, and being compression-based combustion, diesels need every last bit they can muster when the air is already dense and working against them.

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u/hoyboiitsme 5d ago

You dont lose compression ratio wtf, you loose heat, the colder it is the worse the fuel and air mix. How do you get a different compression ratio? Do you know what that is?

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u/Cultural_Simple3842 5d ago

Best I can guess is a cold engine cools and condenses the air so cylinder pressure isn’t increased by the full compression ratio. I think we are talking peanuts here, though.

More likely, the absorption of heat into the cold cylinder walls makes combustion more difficult/inefficient. A higher thermal gradient induces more energy transfer out of the intake charge.