What could cause a turbojet or turbofan engine to experience high exhaust gas temperatures with low rpm and high fuel flow?

High exhaust gas temperatures in a turbojet or turbofan engine, particularly when accompanied by low RPM and high fuel flow, can indicate issues with the turbine section of the engine. When there is turbine damage or a loss of efficiency, it may not effectively convert the high-temperature gases produced by combustion into usable mechanical energy to drive the fan and compressor stages of the engine. This inefficiency leads to increased energy retention in the exhaust gases, resulting in higher exhaust gas temperatures.

In a normally operating engine, efficient turbine performance ensures that not only is fuel consumed effectively but also that the heat generated is adequately converted into thrust. When the turbine is damaged or operates below its expected efficiency, combustion gases can escape heated without doing useful work, thus raising exhaust temperatures even when the engine is not operating at optimal speeds or fuel flow rates.

The other options, while they could influence engine performance, do not directly explain the specific scenario of high exhaust gas temperatures alongside low RPM and high fuel flow in the same manner that turbine damage does. Insufficient fuel supply would typically lead to lower exhaust temperatures. Improper engine calibration could affect performance but is less likely to specifically cause the combination of symptoms described, and environmental factors might impact engine efficiency overall but would not specifically lead to high exhaust