Core and engine efficiency
How much of the improvement in engine fuel burn from the first high-bypass turbofans (TF39, RB211 etc) to the current best (GE90-115, Trent 900) is due to increase in bypass ratio (propelling ever more air at slower speeds) and how much is due to improvements in high pressure turbine materials and cooling, allowing the engine to run hotter and have higher efficiency?
If you compare Rolls RB211 (entry into service 1972) and Olympus (entry into service 1976), how do engine inlet temperatures compare? And how do both compare to Trent 900 (EIS 2007)?
Suppose that someone wanted to design a low-bypass turbofan with the objective of picking the bypass ratio solely to optimize the fuel burn at cruise at Mach 2,00. What would the bypass ratio be, and how would the cruise fuel burn compare to the Olympus?