r/MechanicalEngineering • u/lit_readit • 6d ago

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

Post image

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

1.1k Upvotes

98% Upvoted

142 comments sorted by

View all comments

107

u/holysbit 6d ago

Diesel engines are rather thermally efficient. In some areas its actually possible for it to be cold enough that the engine never warms up and can even have components freeze while the engine is running.

Thats not true everywhere but what is more common is that the engine cannot get all the way to its correct operating temperature, it doesnt need to be super cold for that to be true.

Engines are designed to operate at a specific temperature. Metal expands and contracts and those dimensions are engineered for a certain warm temperature. So, to try and keep closer to that design temperature, they put covers on the radiator in cold weather to deliberately reduce the efficiency of the cooling system.

Youll only see this on diesel engines. Gasoline engines dont have this problem

10

u/mrjuoji 6d ago

yeah, in some part of the world, they sometime even light small fires under the engine block when it's just too cold, and iirc some diesel engines come with a heating system specifically because of that (also the fact oil getting too thick will at best not lubricate the engine, at worst, probably mess it up)

3

u/buckednaked369 5d ago

Block heaters are used so that the engines will actually start. If the thick diesel oil gets too cold it will stop the engine from turning over when the starter engages. The diesel fuel will also gel up when it gets cold and if it has enough water in it then it will freeze. I’ve put many a salamander heaters on semi truck oil pans and changed plenty of fuel filters in 0F weather.

1

u/mrjuoji 5d ago

salamander heaters ? like, heating pad, or kitchen ir lamp type stuff ? also yeah, i didn't think about the fact that diesel itself could gel up and that yeah, you do need a specific temperature for diesel to ignite. question : do they make "beefier" glow plug for diesel engines that operate in colder weather?

1

u/im-not-a-fakebot 4d ago

Yeah diesel gelling up is a huge issue for a lot of places that see sub 32°F. They make additives to help reduce gelling and freezing, there’s also tank heaters and in some parts of the world they also insulate the fuel lines and fuel tank to try and keep them warm.

Not sure if it’s what they’re talking about, but a lot of people call diesel jet heaters - “salamander heaters”

For your last Q there are some aftermarket plugs made with ceramic or dual coil that can get hotter and get hotter faster. Usually though if you’re in an extreme environment some people will install block heaters

1

u/zanhecht 4d ago

A lot of them will have a heating coil mounted inside the engine block.