Your argument seems to hinge on one premise: that the Trent-engine equivalent of the GE90's Ps3 and P3B sensors (which you refer to as "FADEC's reference port lines") could have been blocked by the icy component in cold, waxy fuel (see your post, paragraphs f, g and h).
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Not quite what was said however....
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Obviously
post 79 on this thread was poorly worded so....for the purists and theoretical puritans:
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"the FADEC's reference ports" Long-winded version
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A FADEC has the following functions:
fuel-flow regulation (inc monitoring accelerations and decelerations)
automatic start sequence
transmitting eng data to panel insts
thrust management and protection of limits
prevention of overtemperature and overspeed
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Few would therefore dispute that it (the FADEC) determines HP fuel input to the engine. But how would it do that (i.e. schedule the fuel supply rate to the engine) - if it has no access to LP fuel-flow data? Therefore it has "reference ports". But how does the FADEC access these?
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Nine of Honeywell's LG-1237 Smart Pressure Transducers are used in the FADEC II (Full Authority Digital Engine Control) of the GE-90. The LG-1237's micro-controller measures air data (temps, density and pressures) for calibration, measurement and control of engine fuel flows. It also performs other measurement, control, communication, computation and self-test roles within the transducer.
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FADEC II uses these transducers to sense pressures within the engine's core stages and those external to the core. LG1237's provide the pressure measurement feedback required for the engine's closed loop control system (aka a bootstrapping system).
Internal algorithms determine the appropriate fuel flows (hence power output) and seek to optimize engine efficiency for a large number of variables. It provides a mechanism for detecting degraded performance or required maintenance that may occur as a result of normal erosion, service damage (such as bird, hail or water ingestion) or other transitory impediments such as icing within fuel, intakes or nacelles. LG1237 is
essential to the FADEC's primary function of determining (i.e. apportioning) the fuel-flow that goes to the engine and for bypassing any excess that may not be required.
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Functional Description
A bypass valve bypasses, to the input side of the pump, a portion of the pressurized fuel flow before it reaches the flow meter. An electronic control unit is included that receives the LG1237 signal and in response thereto adjusts the bypass valve until the measured fuel flow equals the FADEC's predetermined desired (i.e. appropriate for the conditions) fuel flow stored in the electronic control unit. The FADEC controls the operation of the engine including the fuel control system. In particular, the FADEC adjusts the area of the metering valve so that the fuel flow (Wfm) exiting the metering valve is delivered in accordance with the following equation.
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Wf=CA(ΔP)1/2
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where C is a fuel flow constant and A is the area of the metering valve. Though not shown, a linear variable displacement transducer, (LVDT), is mounted to the metering valve to provide a feedback signal to the FADEC indicative of the position of the metering valve.
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Summary
The objective is to provide a fuel system for delivering fuel from a fuel source to the combustor in a gas turbine engine by having a pump receiving LP fuel flows from the fuel source and producing a pressurized fuel flow that flows to a flow meter that will measure that fuel flow and generate an input signal (Wf). The FADEC's electronic control unit receives that Wf signal and in response thereto adjusts the bypass valve until the measured fuel flow (i.e. output) equals a predetermined desired fuel flow (wfm) stored in the electronic control unit. The bypass valve bypasses, to the input side of the pump, that calculated excess portion of the pressurized fuel flow before it reaches the flow meter.
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Thus, a fuel system is provided that controls fuel flow based on a measured and calibrated fuel flow requirement. Environmental calibration inputs are derived from the FADEC's LG1237 transducers.
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The contention is that anything stickily globular (i.e.
unctuous see #3) in that LP fuel supply could prove to be a "real ball of wax" - as far as the FADEC's computational algorithms go (all other
"air" pressures notwithstanding.