What is surge margin in relation to compressor operation?

• A. The distance from the engine's current point to the surge boundary on the compressor map; adequate margin prevents surge.
• B. The percentage of time the engine operates near surge.
• C. The ratio of surge pressure to ambient pressure.
• D. The energy loss during surge.

Answer: (A)

Surge margin is the distance on the compressor performance map between the engine’s current operating point and the surge boundary (the surge line). This boundary marks where the compressor becomes unstable and surge can start. Keeping a sufficient margin means you’re operating well within the stable region, so the compressor won’t surge during transients or load changes.

That’s why the best description is that surge margin is this distance, and having adequate margin prevents surge. The other ideas—being a percentage of time near surge, a ratio of surge pressure to ambient pressure, or the energy loss during surge—are not how surge margin is defined.