What is the result of maintaining a higher turbine inlet temperature?

• A. Higher thermal efficiency
• B. Lower thermal efficiency
• C. No change
• D. Higher emissions

Answer: (A)

Raising the turbine inlet temperature increases the energy available to the expanding gas, so the turbine can do more work for the same pressure ratio. In a gas-turbine (Brayton) cycle, the compressor work is largely fixed by the compressor settings, while the turbine work rises as the inlet gas temperature goes up. That boost in turbine work relative to the fixed heat input leads to a higher net work output for the cycle, which translates into higher thermal efficiency.

Keep in mind that this comes with trade-offs in real systems, such as greater NOx emissions and tighter material/design limits due to the hotter hot gas. But the primary effect described here is the improvement in efficiency.