Which of the following is NOT a common fuel used in gas turbine engines?

Coal is not a common fuel used in gas turbine engines primarily because of its physical properties and combustion characteristics. Gas turbines are typically designed for fuels that can burn cleanly and efficiently, such as kerosene, natural gas, and jet fuel. These fuels are in liquid or gaseous forms that easily atomize and mix with air, allowing for the high-speed combustion that gas turbines require.

Kerosene and jet fuel are both derived from petroleum and designed specifically for aviation applications, with properties such as a high energy density and low freezing point, making them ideal for high-performance engines. Natural gas is increasingly used due to its availability and cleaner combustion profile compared to liquid fuels. In contrast, coal presents challenges in terms of handling, storage, and the production of particulate emissions, which are detrimental to both engine performance and environmental standards. These reasons contribute to why coal is excluded as a common fuel in gas turbine applications.