Staged Combustion Contrail Optical Depth Control
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Solution Overview
Problem
Current aircraft gas turbine engines with staged combustion systems produce contrails that can contribute to climate impact due to their optical depth, which is influenced by soot emissions, and existing lean combustion methods may not effectively manage this impact.
Innovation Solution
A staged combustion system with pilot and main injectors that adjust fuel flow ratios based on atmospheric conditions to control soot emissions, using rich pilot injectors for low power and lean main injectors for high power, managed by a fuel metering system and electronic engine controller to optimize contrail optical depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If lean combustion is used to reduce soot emissions, then contrail optical depth is reduced, but combustion stability and flame hold are compromised
Solution Approach 1:
The combustion system is segmented into multiple zones with different fuel-air ratios. The combustor includes a first combustion zone with a first fuel-air ratio and a second combustion zone with a second fuel-air ratio that is richer than the first. This segmentation allows each zone to perform its specialized function: the lean first zone controls soot emissions and contrail optical depth, while the richer second zone ensures combustion stability and flame hold.
Solution Approach 2:
Different regions of the combustor are given different local combustion characteristics. The first combustion zone operates with a leaner fuel-air ratio optimized for reducing soot emissions and contrail formation, while the second combustion zone operates with a richer fuel-air ratio optimized for combustion stability. This local quality differentiation resolves the contradiction by allowing each zone to optimize for its specific function rather than requiring uniform combustion throughout.
2Reliability
If rich combustion zones are used to ensure stable flame, then soot emissions increase, leading to increased contrail formation
Solution Approach 1:
The combustion system separates the functions of flame stability and soot control into different zones. The richer second combustion zone provides the necessary flame stability and combustion reliability, while the leaner first combustion zone minimizes soot emissions and contrail formation. This functional segmentation resolves the contradiction by allowing each zone to optimize for its primary function.
Solution Approach 2:
The invention converts the potentially harmful effect of rich combustion (soot production) into a beneficial arrangement by confining it to a specific zone where it serves combustion stability, while using lean combustion in another zone to minimize soot emissions for contrail reduction. The harmful soot-producing rich combustion is 'disguised' as a localized feature that serves a necessary function without compromising overall emission performance.
3Object-generated harmful factors
If staged combustion with multiple zones is used to control soot, then device complexity increases, but emission control is improved
Solution Approach 1:
The combustor is divided into a first combustion zone and a second combustion zone with different fuel-air ratios, allowing control of soot emissions through staged combustion. This segmentation enables emission control while maintaining a relatively simple overall structure by using straightforward zonal differentiation rather than complex active control systems.
Solution Approach 2:
The invention controls soot emissions by changing the fuel-air ratio parameter across different combustion zones. The first combustion zone operates with a leaner fuel-air ratio to reduce soot, while the second zone operates with a richer ratio for stability. This parameter change approach provides effective emission control through relatively simple means of adjusting fuel distribution rather than requiring complex device modifications.
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
The system effectively reduces or increases contrail optical depth by varying soot production, thereby mitigating climate impact by controlling ice particle formation and radiative forcing.
Implementation Method 1
Combustion of hydrocarbon fuels in aero engine combustion systems produces a hot exhaust stream composed primarily of nitrogen, oxygen, carbon dioxide and water vapour. In addition to these major components, a quantity of soot is also produced in locally-rich flame zones
Implementation Method 2
Initially-dry soot particles become activated by adsorption of oxidised sulphur, leading to scavenging of water molecules when relative humidity over water is in excess of 100 percent
Implementation Method 3
Following this, immersion freezing occurs, producing an ice nucleus
Implementation Method 4
Further depositional growth of the ice crystals may then proceed, in dependence upon the amount of water vapour, initially in the exhaust plume and subsequently in ambient air
Implementation Method 5
as the plume continues to mix out, ice mass is lost via sublimation
Data Source
AI summary
A gas turbine engine for an aircraft. The gas turbine comprises a staged combustion system having pilot injectors and main injectors, a fuel metering system configured to control fuel flow to the pilot injectors and the main injectors, and a fuel system controller. The controller is configured to identify an atmospheric condition, determine a ratio of pilot fuel flow rate for the pilot injectors to main fuel flow rate for the main injectors in response to the atmospheric condition, and inject fuel by the pilot injectors and the main injectors in accordance with said ratio to control an index of soot emissions caused by combustion of fuel therein.