In a high bypass ratio turbofan, which statement is true about its compressor and combustion chamber relative to a turbojet?

• A. Both larger
• B. Compressor larger, combustion chamber smaller
• C. Both smaller
• D. Compressor smaller, combustion chamber larger

Answer: (C)

In a high bypass ratio turbofan, most of the incoming air goes around the core in the bypass stream, while only a small portion goes through the core for combustion. Because the core handles a much smaller mass flow, the core’s compressor can be smaller and the combustion chamber can be smaller as well. The compressor size scales with how much air and how much pressure rise the core needs; with less core air, you don’t need as large or as many stages. Similarly, the combustor size is tied to the core air and fuel flow, which are reduced in a high bypass design. By contrast, a turbojet sends almost all inlet air through the core, requiring a larger compressor and combustion chamber to handle the higher core flow. So, the statement that both the compressor and combustion chamber are smaller in a high bypass turbofan than in a turbojet is the best fit.