How is thermal efficiency defined in gas turbine engines?

Thermal efficiency in gas turbine engines is defined as the ratio of useful work output to the energy input from fuel combustion. This definition captures the fundamental goal of a gas turbine engine, which is to convert the chemical energy stored in the fuel into mechanical energy or work.

By maximizing this ratio, we can assess how effectively the engine converts energy from fuel into work. A higher thermal efficiency indicates that more of the energy supplied by the fuel is being converted into useful work, which is crucial for improving performance and reducing fuel consumption. This concept is central to the design and operation of gas turbine engines, as it directly influences their efficiency, environmental impact, and operational costs.

The other choices do not accurately represent the definition of thermal efficiency in this context. For example, stating that it is the ratio of fuel combustion to energy output does not adequately describe how the energy is converted into work, while options that discuss cooling capability or weight do not relate to the efficiency of energy conversion in the engine.