Periodic Reporting for period 3 - FINCAP (Fuel INjector Coking and Autoxidation Prediction)
Période du rapport: 2020-05-01 au 2021-08-31
The FINCAP objective is to develop a robust theoretical framework to allow prediction of the build-up of surface carbonaceous deposits in jet fuel injection systems so that fuel injectors for advanced engines such as the VHBR may be designed with an acceptable maintenance frequency and their life span predicted.
Modern Very High Bypass Ratio (VHBR) engine designs are under development within CleanSky2 Engine ITD3. These engines are designed to operate at increasingly higher pressure and temperature ratios in order to improve thermal efficiency. Hotter cycles and consequently core engine temperatures are also accompanied by increased levels of nitrous oxide (NOx) emissions which therefore require the development of more complex fuel injector and combustion design such as lean burn combustor concepts. This is in order to achieve the ACARE objective of CO2, NOx and noise reduction4. Lean burn systems have main and pilot fuel circuits in the injector, which will result in a range of fuel flow regimes being exposed to these higher temperatures. Hotter cycles will have higher heat sink requirements, lower fuel flow rates (increased efficiency) and different fuel flow regimes compared with current fuel system designs, all of which are driving a need for an improved predictive capability in coke formation modelling.
The overall objective of this programme has been to develop a coking prediction modelling capability to support optimised (improved) designs rules at component and system level. This is to support improved engine performance and reduced emissions in line with industry targets. This work was undertaken by a combination of numerical methods, physical and chemical modelling and measurements at a range of TRL levels from 3 to 6 used to validate the results of the model developed.
The FINCAP project has developed new experimental methods to detect fuel ingress in lean burn injector designs, which significantly simplifies the testing requirements to confirm no ill effect of design alterations.
The final modelling capability produced can predict the initial rates of deposit formation from thermal CFD models of critical components in the injector design and has been provided to the Topic Manager for incorporation into the future design of lean burn systems.
Modern Very High Bypass Ratio (VHBR) engine designs are under development within CleanSky2 Engine ITD3. These engines are designed to operate at increasingly higher pressure and temperature ratios in order to improve thermal efficiency. Hotter cycles and consequently core engine temperatures are also accompanied by increased levels of nitrous oxide (NOx) emissions which therefore require the development of more complex fuel injector and combustion design such as lean burn combustor concepts. This is in order to achieve the ACARE objective of CO2, NOx and noise reduction4. Lean burn systems have main and pilot fuel circuits in the injector, which will result in a range of fuel flow regimes being exposed to these higher temperatures. Hotter cycles will have higher heat sink requirements, lower fuel flow rates (increased efficiency) and different fuel flow regimes compared with current fuel system designs, all of which are driving a need for an improved predictive capability in coke formation modelling.
The overall objective of this programme has been to develop a coking prediction modelling capability to support optimised (improved) designs rules at component and system level. This is to support improved engine performance and reduced emissions in line with industry targets. This work was undertaken by a combination of numerical methods, physical and chemical modelling and measurements at a range of TRL levels from 3 to 6 used to validate the results of the model developed.
The FINCAP project has developed new experimental methods to detect fuel ingress in lean burn injector designs, which significantly simplifies the testing requirements to confirm no ill effect of design alterations.
The final modelling capability produced can predict the initial rates of deposit formation from thermal CFD models of critical components in the injector design and has been provided to the Topic Manager for incorporation into the future design of lean burn systems.
The FINCAP project has developed a series of experimental data sets, and modelling capabilities to assess the formation of fuel break down deposits in fuel injectors with application specifically to lean burn fuel injectors required for the UHBR engine.
The lowest scale assessments of fuel performance were made in static reactors and permitted the generation of validation data for the expansion of the available chemical kinetic models for fuel autoxidation in FINCAP WP3 and WP5. The FINCAP project developed improvements to the available models in the literature, covering a wider range of application temperatures and chemistries, specifically: improvement to the Basic Autoxidation Mechanism (BAS) through the addition of hydroperoxide reactions, sulphur speciation and the impact of metal contamination on the fuel behaviour. This model development has been continued in a follow on UK funded programme, PINES, and is increasing the level of reaction steps to include the agglomeration phase of deposit formation. A PhD studentship has been externally funded in relation to this work also. This work has been published in two journal papers and presented at the CRC aviation fuels meetings in Washington, US. The strategy adopted within FINCAP is to generate the best available chemical kinetic model at key milestone points in the project.
Laboratory investigations into the impact of fuel chemistry and surface roughness on deposition have taken place in FINCAP WP2 using available small scale facilities at the University of Sheffield. The analysis of fuel chemistry has included the impact of 100%SAF on thermal stability behaviour of fuels, along with a number of blending studies to provide important guidance of the relative improvement in performance by changing the fuel chemistry. The HiReTS rig was used to develop a dataset investigating the impact of surface roughness at a small scale. Experimental data on the deposit formation from TRL5, AFTSTU rig studies were used as validation data for the kinetic model developed when used with CFD codes developed in WP4.
This work was expanded to include additive layer manufactured (ALM) sub sections of the full lean burn injector geometry which were tested on a TRL5 level rig in conjunction with the topic manager. These studies involved working closely with the topic manager, and the ALM manufacturing specialists within the organisation.
The WP4 work involved the upgrading of the Topic Manager in-house CFD code, PRECISE to include mesh morphing, conjugate heat transfer and multi step chemistry reactions to allow the developed kinetic model for deposition to be coupled with the CFD solutions for flow and thermal fields in the injector design. A post processing tool to predict deposit growth rates has been developed and was compared against the results from WP2 at TRL5 scale.
Finally, WP6 designed and built a new rig facility and has generation of experimental results studying the effect of ingress into the tertiary cavity of the fuel injector.
The conclusion of this work provides evidence to support a root cause for the ingress into the tertiary cavity and a new test capability, flexible enough to handle a range of injector designs.
The lowest scale assessments of fuel performance were made in static reactors and permitted the generation of validation data for the expansion of the available chemical kinetic models for fuel autoxidation in FINCAP WP3 and WP5. The FINCAP project developed improvements to the available models in the literature, covering a wider range of application temperatures and chemistries, specifically: improvement to the Basic Autoxidation Mechanism (BAS) through the addition of hydroperoxide reactions, sulphur speciation and the impact of metal contamination on the fuel behaviour. This model development has been continued in a follow on UK funded programme, PINES, and is increasing the level of reaction steps to include the agglomeration phase of deposit formation. A PhD studentship has been externally funded in relation to this work also. This work has been published in two journal papers and presented at the CRC aviation fuels meetings in Washington, US. The strategy adopted within FINCAP is to generate the best available chemical kinetic model at key milestone points in the project.
Laboratory investigations into the impact of fuel chemistry and surface roughness on deposition have taken place in FINCAP WP2 using available small scale facilities at the University of Sheffield. The analysis of fuel chemistry has included the impact of 100%SAF on thermal stability behaviour of fuels, along with a number of blending studies to provide important guidance of the relative improvement in performance by changing the fuel chemistry. The HiReTS rig was used to develop a dataset investigating the impact of surface roughness at a small scale. Experimental data on the deposit formation from TRL5, AFTSTU rig studies were used as validation data for the kinetic model developed when used with CFD codes developed in WP4.
This work was expanded to include additive layer manufactured (ALM) sub sections of the full lean burn injector geometry which were tested on a TRL5 level rig in conjunction with the topic manager. These studies involved working closely with the topic manager, and the ALM manufacturing specialists within the organisation.
The WP4 work involved the upgrading of the Topic Manager in-house CFD code, PRECISE to include mesh morphing, conjugate heat transfer and multi step chemistry reactions to allow the developed kinetic model for deposition to be coupled with the CFD solutions for flow and thermal fields in the injector design. A post processing tool to predict deposit growth rates has been developed and was compared against the results from WP2 at TRL5 scale.
Finally, WP6 designed and built a new rig facility and has generation of experimental results studying the effect of ingress into the tertiary cavity of the fuel injector.
The conclusion of this work provides evidence to support a root cause for the ingress into the tertiary cavity and a new test capability, flexible enough to handle a range of injector designs.
Lean burn systems have main and pilot fuel circuits in the injector, which will result in a range of fuel flow regimes being exposed to these higher temperatures. Hotter cycles will have higher heat sink requirements, lower fuel flow rates (increased efficiency) and different fuel flow regimes compared with current fuel system designs, all of which are driving a need for an improved predictive capability in coke formation modelling. This technology has a higher efficiency than alternative designs which require additional cooling systems employing bleed air that is dumped overboard, and could yield around a 2% specific fuel consumption (sfc) improvement in association with heat exchanger weight and volume savings alone. Lean burn engine designs already in the market claim to have a 15% fuel consumption improvement compared to conventional designs. In summary, lean burn is essential to simultaneously meet NOx and other emissions requirements by the use of more complex and therefore sensitive systems. However, this is direct conflict with the need to increase oil heat to fuel for engine overall efficiency. Without improved design rules and optimisation, air cooling will have to be used which results in a severe performance penalty.
This CS2 action has delivered CFD tools to assist the design of these high temperature components, including models for the effect of fuel breakdown and deposition on the components. This will accelerate the design stage and improve the final product developed. Two FINCAP chemical mechanism models have been developed and included in the CFD add-on capability.
A new series of experimental devices to assess thermal stability have been developed from the conclusions of the programme. These will allow further validation of future development in modelling capability.
This CS2 action has delivered CFD tools to assist the design of these high temperature components, including models for the effect of fuel breakdown and deposition on the components. This will accelerate the design stage and improve the final product developed. Two FINCAP chemical mechanism models have been developed and included in the CFD add-on capability.
A new series of experimental devices to assess thermal stability have been developed from the conclusions of the programme. These will allow further validation of future development in modelling capability.