Thermo-Acoustic Instabilities and Shape Bifurcations of a Pilot-Only Spray Flame in a Staged Burner
Bibliographic record
Abstract
Abstract Aircraft engine manufacturers develop new combustion technologies to comply with stricter regulations on pollutant emissions, such as nitrous oxides or soot. Staged systems coupled with lean premixed combustion show promising prospects to reduce these emissions through correct mixing of the fuel ahead of the combustion chamber, but are more prone to thermo-acoustic instabilities. Hence, guaranteeing the stability over the entire operating range is more challenging. The thermo-acoustic behavior of lean staged systems is investigated experimentally on the laboratory-scale BIMER combustor, an atmospheric pressure test rig composed of a two-stage swirled injector reminiscent of industrial systems and fueled with liquid dodecane. It uses a simplex atomizer in the pilot stage, multipoint injection in the main stage, and can be externally forced using a siren device located upstream of the injector. This study focuses on the thermo-acoustic behavior of the pilot stage of the BIMER combustor. Flame response to acoustic perturbations at different preheating temperatures (ranging from 383 to 473 K) is assessed. To this end, flame describing functions (FDF) are measured using acoustic forcing, a photomultiplier with an OH* filter for heat release rate fluctuation measurements and the multimicrophone method to determine acoustic velocity fluctuations. An acoustic network model of the combustor using the L-ζ model for the injector is used to compute acoustic velocity fluctuations at the base of the flame. This model is parameterized using only the burner geometrical configuration, with no tuning to fit reference experimental data. The accuracy of the model prediction is discussed. Measurements also display flame shape bifurcations from V to Tulip-shape flames generated by acoustic forcing at certain frequencies and amplitudes. High-speed imaging of flame chemiluminescence in the visible range is used to describe these bifurcations. The role of acoustic forcing is highlighted through phase-averaging.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".