What does an overall compression ratio of 12:1 indicate in a gas turbine engine?

An overall compression ratio of 12:1 in a gas turbine engine signifies the total change in pressure from the engine's inlet to its outlet. The compression ratio is calculated by comparing the pressure of the air entering the engine (inlet) to the pressure of the air exiting the compressor stage (outlet). A higher compression ratio usually indicates that the engine can perform more efficient work, leading to improved performance and fuel efficiency.

In the context of gas turbine operation, this ratio is instrumental because it reflects how effectively the engine compresses incoming air before it enters the combustion chamber. A compression ratio of 12:1 means that the pressure at the blade exit in the engine is 12 times greater than the atmospheric pressure at the inlet, which can enhance the engine's ability to produce thrust and power.

While efficiency of fuel combustion, thrust produced, and engine weight are important factors in assessing engine performance, they are not directly indicated by the overall compression ratio itself. The compression ratio specifically addresses how much the pressure of the air is increased as it moves through the engine, making option A the correct choice.