Characterization of reaction zone growth in an optically accessible heavy-duty diesel/methane dual-fuel engine
Bibliographic record
Abstract
The performance of dual-fuel engines in terms of fuel conversion efficiency and unburned hydrocarbon emission is strongly influenced by the turbulent flame propagation through the premixed natural gas. To improve dual-fuel engine design and provide validation data for numerical models, the fuel conversion process must be better characterized, specifically the reaction zone growth rate. In this work, high-speed imaging of OH*-chemiluminescence is performed in an optically accessible 2 L engine operated with port-injected CH 4 and direct-injected diesel for different diesel and CH 4 fueling rates and pilot injection pressures ( P pilot ). The cumulative histogram time series is introduced for directly comparing high-speed optical data of dual-fuel combustion with simultaneously measured apparent heat release rate. The cumulative histogram time series diagram is also used to evaluate a “global” reaction zone speed, S RZ,g , based on OH*-chemiluminescence images. The S RZ,g calculation normalizes the reaction zone area growth rate by the perimeter of the reaction zone to determine the velocity scale, while a “local” reaction zone speed, S RZ,l , is based on the local displacement of the reaction zone boundary per unit time. From the distribution of S RZ,l for each image frame, a previously proposed metric for determining the transition from pilot autoignition based on apparent heat release rate was validated and used to evaluate a single mean flame propagation speed, [Formula: see text]. Using these metrics, it was noted that increasing ϕ CH4 from 0.40 to 0.69 results in an increase in [Formula: see text] from 4 to 8 m/s and 8 to 14 m/s for pilot injection pressures of 300 and 1300 bar, respectively. The spatial distribution of S RZ,l also indicates that autoignition of the pilot jets is not simultaneous (arising from asymmetric injector geometry) and leads to an overlap of the autoignition and flame propagation processes. This is not considered in the conventional conceptual model of dual-fuel combustion and impacts calculation of [Formula: see text] for the small diesel injections commonly used for dual-fuel engines.
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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".