Aircraft Fuel Metering Unit Icing Prevention Design

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Solution Overview

Problem

Fuel metering units in aircraft engine fuel supply circuits are susceptible to icing, particularly at high flow rates, which can lead to blockage of the metering slot and risk of engine combustion chamber extinction due to ice particle agglomeration, especially when transitioning from high to low flow rates.

Innovation Solution

A fuel metering unit with a movable element and a metering slot having a flared profile, where the narrow passage section is obstructed in high flow rate positions to prevent ice agglomeration, and re-exposed in low flow rate positions to ensure uninterrupted fuel flow, using a combination of fixed and movable elements with strategically positioned edges and lumens to control the flow and prevent blockage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a metering slot with an exponential passage profile is used to achieve high accuracy in fuel metering at low flow rates, then measurement precision is improved, but the narrow width portion of the metering slot becomes susceptible to blockage by ice particles at high flow rates, worsening reliability

Engineering Contradiction:

Improvefuel metering accuracyVSAvoidresistance to ice particle blockage

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The metering slot is divided into two distinct portions: a first portion with a narrow width optimized for low flow rate metering accuracy, and a second portion with a wide width designed to prevent ice particle blockage at high flow rates. This segmentation allows each portion to fulfill its specific function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different sections of the metering slot are given different geometric properties - the first portion has a narrow width for precision metering while the second portion has a wide width for ice particle resistance. This local differentiation of geometric quality resolves the contradiction between precision and reliability.

Inventive Principle:

Principle #3Local quality

2Productivity

If the metering slot is exposed at high flow rates to maintain fuel flow, then productivity is improved, but ice particles can agglomerate in the narrow portion, worsening reliability and causing potential engine extinction

Engineering Contradiction:

Improvefuel flow rateVSAvoidice particle agglomeration risk

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The metering slot is segmented into a first portion for precision metering and a second wide portion for high flow operation. During high flow rates, fuel passes through the wide second portion which prevents ice particle agglomeration, while maintaining adequate flow productivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The wide second portion of the metering slot acts as an intermediary passage that mediates between the need for high fuel flow productivity and the need to prevent ice particle blockage. It provides a safe passage for high flow rates without ice agglomeration risk.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If the narrow portion of the metering slot is used for low flow rates, then measurement precision is improved, but transitioning from high to low flow rates carries the risk of extinction due to ice blockage, worsening reliability

Engineering Contradiction:

Improvelow flow rate metering accuracyVSAvoidextinction risk during flow transition

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The design preliminarily addresses the transition risk by providing a wide second portion of the metering slot that prevents ice particle deposition during high flow rates. This preliminary prevention ensures that when transitioning to low flow rates, the narrow first portion remains free of ice blockages, maintaining both precision and reliability.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The wide second portion of the metering slot, which might seem to add complexity, actually converts the potential harm of ice blockage into a benefit by providing a safe passage for high flow rates that prevents ice particle agglomeration, thereby protecting the precision metering function of the narrow first portion during transitions.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS9777644B2Fuel meter protected from icing

Publication Date: 2017.10.03 SAFRAN AIRCRAFT ENGINES SAS

AI summary

A fuel metering unit including a movable element including at least one fuel passage section opening upstream towards a fuel supply conduit and opening downstream towards a conduit of use through a metering slot with a flared profile having a narrow passage section flaring as far as a wide passage section, the movable element being able to be moved with respect to a fixed element between a low flow rate position in which the metering slot is for a large part obstructed and a high flow rate position in which the metering slot is for a large part exposed, the metering slot being made in the fixed element or in the movable element and its obstruction being obtained by covering the slot with a wall of the movable element or of the fixed element.