Experiments in laminar and turbulent premixed counter-flow flames at variable Lewis number
Bibliographic record
Abstract
This thesis examines preferential diffusion effects in laminar and turbulent premixed combustion. Stretched, fuel-lean, laminar flames of methane, propane and hydrogen are studied experimentally in a counter-flow flame configuration to investigate the effect of Lewis number on stretched flames. Laminar flame results show that a maximum reference flame speed exists for mixtures with Le >= 1 at lower flame-stretch values than the extinction stretch rate. A continually-increasing reference flame speed is measured for Le << 1 mixtures until extinction occurs when the flame is constrained by the stagnation point.Turbulent counter-flow flame experiments are then performed for these mixtures, using high-blockage turbulence-generating plates to produce turbulence intensities on the order of u'/sLo = 1 to 10. Measurements of average and instantaneous velocity within the turbulent flame are performed by time-resolved particle image velocimetry measurements. Average and instantaneous flame front position is also measured by Rayleigh spectroscopy.Measurements of average turbulent burning velocity demonstrate the ambiguity in definitions of the burning velocity and the difficulty of examining turbulent flame chemistry using averaged measurements. Instantaneous statistics are shown to be superior tools for studying turbulent combustion. The probability-density functions (PDF) of the local flamelet burning velocities for Le >= 1 mixtures show that the instantaneous flamelet burning velocities increase with increasing turbulence intensity and flame stretch. The PDF for the Le ~= 1 mixture has a sharply skewed shape at high turbulence intensity and has a sharp drop-off in probability at a velocity that corresponds with the experimentally-measured maximum reference flame speed from the laminar flame experiments. In contrast, in the Le << 1 turbulent flames, the most-probable instantaneous flamelet burning velocities increase with increasing turbulence intensity and can significantly exceed the maximum reference flame speed measured in counter-flow laminar flames at extinction.These results are reinforced by instantaneous flame position measurements. Flame front location PDFs show the most probable flame location to be linked to velocity PDFs. Furthermore, hydrogen PDFs are recognizably skewed as u'/sLo increases, indicating a tendency for the Le << 1 mixture to propagate farther into the unburned reactants. These results support the leading edge theory of premixed turbulent flame propagation for flames in which preferential diffusion effects are expected.In the study of turbulent flames, this work promotes the use of local, instantaneous statistics as a tool for describing experimental results and studying fuel chemistry.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| 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".