Originally Posted by
ApolloHeli
I am assuming you are referring to a turbine engine with separate gas generator and power output turbines (Ng and Nf are not linked).
Remember that the majority of air is used to shape the flame and cool the combustion gases before they interact with the turbines (because the combustion product typically peaks around 2100°C). The efficiency of the compressor blades to generate a flow of air through the engine varies as Ng speed changes, so the correlation is not linear (in fact it is very complex, because air pressure, temperature, engine speed, engine acceleration, etc all factor into the temperature of the engine).
Hopefully, a simple way to understand it is that ITT / TOT / T4 increases as the collective is increased because an increase of fuel flow to the nozzles will increase the energy input into the engine. The main product of this energy is heat, while secondary products are kinetic and mechanical energy.
Thank you for weighing in Apollo. I believe we are kind of saying the same thing aren’t we? I am implying that that compressor efficiency is directly related to Ng speed. So as Ng decreases compressor efficiency decreases and they are proportional in that sense. So even though fuel is decreased….. so is Ng …. So is compressor efficiency. So I understand how it would be a little cooler with the reduction in fuel but not a significant amount. Am i seeing this correctly?