Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - FINCAP (Fuel INjector Coking and Autoxidation Prediction)

Teaser

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...

Summary

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 WP5 and WP6 of 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 is by a combination of numerical methods, physical and chemical modelling and measurements at a range of TRL levels from 3 to 6, to create 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.

Work performed

Activity in the WP2 commenced in M5 and will continue until M27. The main objective of this work package is to provide experimental data across a range of scales to validate models developed in WP4. In particular, the tests are designed to provide data on the effect of roughness, geometry and fuel quality. The main achievements in the first period of FINCAP have been:
• Completion of State of the Art report on experimental methods
• Down selection of geometries to test
• Discussion regarding manufacture of ALM components for testing
• Preparation of test matrix for AFTSTU scale experiments

The main achievements of WP3 in the first reporting period are:
• Generation of first improvement to the Basic Autoxidation Mechanism (BAS) through the addition of hydroperoxide reactions
• Establishment of quantum chemical methods for developing metals and antioxidant effects on hydrocarbon autoxidation
• Completion of initial phase of experimentation using surrogate laboratory hydrocarbons
The strategy adopted within FINCAP is to generate the best available chemical kinetic model at key milestone points in the project. At the kick off meeting, it was possible to propose an initial model using the existing Kuprowicz and Zabarnick model of 2007 (BAS) and update this with added complexity at regular intervals. WP3 has released kinetic scheme version 1.1 to WP4 for inclusion in the second period of FINCAP.

A list of objectives achieved for this work package in the first reporting period are as follows:
• Compiled and installed latest version of Topic Manager in-house CFD code, PRECISE
• Run test case files using PRECISE
• State of the art review of numerical modelling of chemically reacting flows and deposition
• Successful application and running of SURE scheme award for student placement over summer break
• Prepared cold flow models of geometries to be tested in WP2
• Prepared limited thermal models of geometries
• Carried out initial chemical kinetic modelling of simplest geometries

The main achievements within the work package 5 are:
• Design or adaptation of two, small scale devices for thermal stability assessment, one with an O2 headspace, and one without to compare the effects of limited or excess O2 availability.
• Proposed test plan

The work within the fuel ingress work package requires the design and build of a new rig facility and the generation of experimental results studying the effect of ingress into the tertiary cavity of the fuel injector. This work package has been delayed by the time taken to agree a statement of requirements for the rig.
The following achievements have been possible:
• Establishment of an operating envelope for the rig
• Conceptual design of the test rig

Final results

Modern Very High Bypass Ratio (VHBR) engine designs are under development within CleanSky2 WP5 and WP6 of 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. 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 designs5. 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 will deliver 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. So far within the study, the project had developed the first improvement to the mechanism (model FINCAP v1.1).

A new series of experimental devices to assess thermal stability are being developed from the conclusions of the programme so far. These will allow appropriate validation of any models developed within the project.