A gas turbine must be rotated at _______ speed before ignition begins.

• A. 10% of its maximum
• B. 120% of its maximum
• C. 20% to 30% of its maximum
• D. full

Answer: (C)

During start, the turbine needs some room for the air to flow and the pressure to build before combustion begins. Reaching a modest fraction of the maximum speed ensures enough compressor air and a stable pressure environment so the fuel–air mixture can ignite and stay burning. If ignition happens too early when the rotor is turning slowly, the airflow is insufficient, the flame may be unstable or go out, and surge risks increase. If ignition were attempted at very high speed, you’d risk unstable ignition conditions and mechanical strain from rapid acceleration. So the ignition is timed to a stage where there is adequate airflow and pressure—typically about 20–30% of maximum speed—allowing smooth light‑off and a safe transition to normal running.