Hi Homo Ludens,
things stay as follows, without "maybes":
- fuel temperature min limit: is based on fuel freezing point, engine margin, overall temperature accuracy error.
- fuel temperature max limit: one of the main causes for high fuel temperature is its use as means for cooling the oil, hydraulic fluid etc. As a consequence in some flight regimes, its temperature may rise above 100° C or more. Temperatures changes are manifested in modifications of fluid viscosity, dissolved gas concentration and other complex stuff. Above its maximum operating temperature, the cooling ability of fuel is greatly reduced thus leading to high oil and hyd fluid temp: this modifies the direction and rate of friction forces, hence considerably increasing wear processes. Every limitation, as reported by the FCOM, is strictly related to the engine type, fluid type and system type. The final value you get by the manufacturer (eg. 54° C for Airbus) takes into account all of these variables. That's it !
Hope this helps,
fredgrav
Last edited by fredgrav; 9th May 2010 at 19:58.