Anti-coking Injector Arm with Coaxial Fuel Ducts

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Solution Overview

Problem

In aircraft turbojet engines, the fuel injector arms are prone to coking due to high temperatures, especially when the secondary fuel circuit has a low flow rate, leading to non-homogeneous carburation, performance loss, and potential component damage.

Innovation Solution

Reversing the fuel circuit configuration so that the peripheral duct is part of the primary circuit and the central duct is part of the secondary circuit, with the fuel from the primary circuit circulating around the secondary circuit fuel to prevent stagnation and coking, utilizing the cooler primary fuel to thermally protect the secondary fuel.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the secondary circuit fuel duct is positioned centrally and insulated thermally, then coking is prevented through insulation, but the device complexity and manufacturing cost increase due to required thermal insulation layers

Engineering Contradiction:

Improveprevention of fuel cokingVSAvoidthermal insulation structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The primary circuit fuel, by circulating continuously through the peripheral duct, automatically performs the cooling function that would otherwise require thermal insulation. The fuel serves dual purposes: delivery and thermal protection of the secondary circuit

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

Instead of insulating the secondary circuit from the hot environment, the invention inverts the approach by having the primary circuit fuel actively cool the secondary circuit from the outside, reversing the traditional insulation concept

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If thermal insulation is added to the injector arm, then fuel coking is prevented, but the mass of the injector arm increases

Engineering Contradiction:

Improveprevention of fuel cokingVSAvoidinjector arm mass

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The circulating primary circuit fuel provides self-generated thermal protection, eliminating the need for additional insulation mass. The system uses its own operational fluid to prevent coking without external additions

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The invention converts the potentially harmful high-temperature environment into a beneficial cooling mechanism by using the temperature differential between primary and secondary circuit fuels to create automatic thermal protection

Inventive Principle:

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

3Productivity

If the secondary circuit flow rate is reduced at certain speeds, then fuel consumption is optimized, but coking occurs in the secondary circuit duct

Engineering Contradiction:

Improvefuel consumption efficiencyVSAvoidsecondary circuit duct cleanliness

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The primary circuit fuel acts as an intermediary cooling medium that protects the secondary circuit duct from coking, allowing the secondary circuit to operate at low flow rates without direct exposure to coking risks

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The continuous flow of primary circuit fuel provides beforehand thermal protection to the secondary circuit duct, preventing coking before it can occur during low-flow operation

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This configuration eliminates the need for expensive thermal insulation and prevents fuel coking, ensuring consistent performance and reducing the risk of component damage by maintaining fuel flow and cooling the secondary circuit fuel.

Implementation Method 1

the fuel in the primary circuit, introduced at a much lower temperature than that of the air coming from the high pressure compressor, cannot be subject to coking and allows the fuel in the secondary circuit when it stagnates in the central duct to cool

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

circulating it around the central duct in which the fuel of the secondary circuit now circulates makes it possible to avoid coking in this conduit

Methodology Applied

Scientific EffectConvection: Convection

Data Source

PatentEP1770333B1Anti-coking injector arm

Publication Date: 2010.07.21 SN DETUDE & DE CONSTR DE MOTEURS DAVIATION (S N E C M A)

Figure 1
Figure 2~4

AI summary

The injector has an injector arm with two ducts that are coaxial and supports a spray head, where a peripheral duct (29) of annular section surrounds a central duct (28). The peripheral duct connects a primary fuel circuit that delivers fuel continuously, and the central duct connects a secondary fuel circuit that delivers fuel at a specific rate. The spray head has distributor, and an arrangement of channels that enables a fuel flowing in the central duct to be ejected as a diverging jet situated outside the jet of fuel coming from the peripheral duct. An independent claim is also included for an injector system for injecting fuel into a combustion chamber of a gas turbine engine.