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Low NOx / low sOot injection system design for sPinning combuStion technology

Periodic Reporting for period 2 - LOOPS (Low NOx / low sOot injection system design for sPinning combuStion technology)

Reporting period: 2021-11-04 to 2022-11-03

Safran Helicopter Engines has recently developed and patented a new spinning combustion technology (SCT). This innovative technology improves ignition and blow-off capabilities and enables combustor weight reduction, without compromising turbine nor combustor lifetime. To further promote this highly promising technology, the next step is to assess SCT performances in terms of NOx and soot emissions. Indeed, new aeronautical technologies entering the market today must comply with international regulations and answer the public environmental concern about global warming and human health.
To assist Safran in this development phase, the LOOPS project aims to design, manufacture, test and model an advanced low-NOx and low soot/particles injection system for SCT. The technology is based on the multi-point injection concept, which has already demonstrated very good low-NOx capabilities. The challenge is to guarantee low soot emission as well, which may be detrimental to other pollutant reduction. Two injectors will be designed and evaluated in a systematic way for both NOx and soot emission using combined measurements and numerical simulation.
On the experimental side, the most advanced experimental diagnostics will be used, providing in particular and for the first time a complete and detailed characterization of the soot particles with their concentration and size distribution. On the numerical side, a significant contribution of LOOPS will be the assessment and application of accurate models for NOx and soot production in real helicopter engines.
The confrontation of measurements and simulation results will allow to evaluate the accuracy of the numerical approach and to better understand the underlying mechanisms of pollutant emissions. In addition to a new low-emission injector systems for SCT, outputs of the project will be guiding rules, as well as an engineering numerical tool for low-emission SCT, allowing to find the best compromise between competing phenomena.
During this first period of work, 2 designs of injectors were defined by GDTech in order to reach the objectives of swirls and cross sections given by Safran. These objectives are directly related to NOx and particulate emissions. To validate the two designs of injector, GDTech performed aerodynamic simulations of the injection systems in the test bed configuration at the test operating points. At least, reactive calculations were carried out by GDTech to check the stability of the flame and to anticipate the temperatures to which the bench will be exposed to during the tests.
As the designs of the injectors were validated by the results of the simulations, those were produced by additive manufacturing.
Concerning the experimental part, INSA Rouen has mainly fitted out the HERON test bench to integrate the injectors, to cool the combustion chamber. Moreover, INSA Rouen has set up on another bench the methodology of optical measurements which will be applied for the LOOPS project. The first tests will take place in January 2022.
CERFACS started to prepare numerical models but the main work will occur once the test results will be available in 2022.

During the second period of work, the experimental investigations of the injectors were carried out. At first, INSA Rouen performed the analysis of the global performances of the 2 injections systems to get the flame structure and first emission index of NO. Then INSA Rouen performed the detailed experimental investigations with laser diagnostics and get measurements of OH, soot, NO, kerosen, mean velocity for different operating points. The last tests concerning spray measurements will occured in february of 2023. In parallel to the tests, the CERFACS has started the development of numerical models for prediction of NOw and soot. For that purpose, Large Eddy simulations (LES) were carried out while new numerical tools were implemented and validated against the experimental results. The non reactive simulations for different operating conditions fit well with the experimental results so the fisrt reactive simulations could be performed. The development of the numerical models will continue in 2023 with the availability of test measurements (especially the definition of the spray).
The ambition of the LOOPS project is based on the following 4 pillars :
• Innovative injector
o Lean direct injection
o Multipoint injection
o Low Nox emissions
o Low soot emissions
• Unprecedented tests :
o Advanced time resolved laser diagnostics
o Hard and real operatin conditions (high pressures and temperatures)
• Advanced LES (AVBP) for modeling Nox & soot
o NOx emission accuracy in 2 phases burners
o Soot emission prediction for various parameter
• Advanced implemented simulation tool
o Full scale spinning combustion chamber
o NOx & soot emissions
o Effusion cooling, bleeding, primary and dilution holes
o Lean blow-off
The quantified targets compared to state-of-the-art aircraft entering into service as from 2014 are :
1. NOx emission reduction of 20 %
2. Soot emission reduction via Smoke Number decrease of 30%
Additive manufacturing of the 2 designs of injectors
Heron test bench preparation with well-known injectors
Simulation of injector system in test bench configuration