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It’s pretty much like billiards. They just bounce. Different chemicals (types of molecule) are different phases at different temperatures e.g. nitrogen is a gas at room temp, water is liquid. Stuff that’s a gas at room temp just has less bonding forces (and often mass) than liquids or solids. So they don’t take as much heat to go fast. There’s a lot of heat even at room temp, and even at -40deg. The temperature for nitrogen to sit in one place is -210C or -346F.
No. The heat of combustion increases the gas temperature. But this temperature increase is relative to the mass of the gas. The heat is relative to fuel/oxygen mass combusted. (Combustion energy + Ideal gas law)
Add mass without adding combustion, you get lower pressure and temperature out. So you get less boost from the turbo and make more work for the compression cycle.
The major point of the turbo is to use wasted heat to add more oxygen by packing more air in. So it’s a bit of an odd question to answer. The point is there’s a lot of energy wasted in a naturally aspirated engine’s exhaust. Turbos mostly use that wasted energy, and not power from the crank.
Oh yeah, the turbo is going to have an efficiency ratio for converting exhaust pressure into boost. So that added backpressure on the exhaust is going to be offset in the intake stroke by that ratio. Not important to the point, hat a tidbit. These things are so complicated lol.