I'm familiar with the use of air intercoolers/charge air coolers to cool the intake charge (usually on turbocharged engines). But this BMW engine seems to use liquid to cool the intake charge. Which liquid is used (water?) and how exactly is it managed? Certainly looks pretty nifty.
If it's anything like the BMW M4 GTS, it's water. Purely and simply water atomised into the inlet tract.
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That is coolant running through the charge air cooler (inter cooler). Many engines just use the same coolant and water pump from the normal engine cooling system to circulate the coolant mixture through the charge air cooler. Since we are on the topic of BMW I will note that the N63 V8 uses a separate cooling system and pump for its charge air cooling.