What cools a jet engine's combustion chamber liner?

The correct answer is that air streams cool the jet engine's combustion chamber liner. In a jet engine, air plays a crucial role in regulating temperatures within the combustion chamber. As air enters the engine, it is compressed and combines with fuel during the combustion process. However, before reaching the combustion chamber, a significant portion of this air is directed through cooling passages in the combustion chamber liner.

The design of the combustion chamber allows for this cooling air to absorb heat from the liner, which is exposed to extremely high temperatures due to the combustion of the fuel-air mixture. This cooling mechanism ensures that the materials of the liner do not exceed their thermal limits, maintaining structural integrity and performance efficiency.

The other options relate to processes that, while integral to the overall functioning of a jet engine, do not specifically pertain to the cooling function of the combustion chamber liner. Coolant fluid is typically used in other systems, fuel injection is focused on delivering fuel for combustion, and exhaust gases result from combustion but do not serve the purpose of cooling. The effective use of air streams helps maintain optimal operating temperatures in the combustion chamber, preventing damage and ensuring the engine operates smoothly and efficiently.