Stability and structure of lean swirling spray flames with various degrees of prevaporization
Bibliographic record
Abstract
Achieving full premixing and complete evaporation in lean prevaporized premixed combustors is challenging as it depends on the spray injector characteristics, prevaporisation strategy, and flow conditions. This article experimentally explores the stability and structure of a turbulent swirling n-heptane spray flame under various degrees of prevaporization. The results show that preheating the air to 343 K and 393 K has little effect on the lean blow-off velocity, while recessing the fuel injection significantly decreases the lean stability limit. To correlate these limits, various attempts to define a Damköhler number were made, but unlike previous studies with no prevaporisation, the difficulty in defining laminar flame speed in the present case does not allow a single correlation to work for all degrees of prevaporization. Four stable cases that differ in equivalence ratio, air preheat temperature, and fuel injection recess are investigated using one-dimensional PDA, OH* chemiluminescence and CH[Formula: see text]O-planar laser-induced fluorescence (PLIF). Cases without fuel injection recess or air preheat exhibit a conical-shaped heat release zone near the shear layers. Preheating the air to 393 K reduced the Sauter mean diameter, increased prevaporization, and enabled a second heat release zone downstream of the fuel injection. Recessing the fuel injection by 25 mm reduced droplet velocities and led to a semi-spherical instead of a conical heat release zone. The CH[Formula: see text]O-PLIF signal without injection recess was high along the central axis and its distribution resembled that observed for spray jet flames. In contrast, with recessed spray injection, CH[Formula: see text]O was mainly found outside the central recirculation zone and only appeared inside during lean blow-off; similar to previous work with premixed flames. These findings show that different methods of prevaporization, which only differ by subtle changes in droplet characteristics, strongly impact flame stability. The present data can be used for turbulent flame modelling focusing on sprays and finite-rate kinetics.
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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".