What is the effect of water injection on air density?

Water injection into the intake air of a gas turbine engine has a cooling effect on the air density. When water is injected, it evaporates in the intake air stream, absorbing heat. This process is known as evaporative cooling. As the temperature of the air decreases, the density of the air increases. Cooler air is more dense, which means it can hold more mass in the same volume, allowing for improved performance in the engine.

This effect enhances the air mass flow rate into the engine, contributing to better combustion efficiency and overall performance, especially in high-temperature conditions. The combination of increased density and cooling contributes to the effectiveness of water injection as a means to augment thrust or prevent compressor stall in gas turbine engines.