Effects of Cetane Number, Aromatic Content and 90% Distillation Temperature on HCCI Combustion of Diesel Fuels
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Bibliographic record
Abstract
<div class="section abstract"><div class="htmlview paragraph">The effects of cetane number, aromatics content and 90% distillation temperature (T90) on HCCI combustion were investigated using a fuel matrix designed by the Fuels for Advanced Combustion Engines (FACE) Working Group of the Coordinating Research Council (CRC). The experiments were conducted in a single-cylinder, variable compression ratio, Cooperative Fuel Research (CFR) engine. The fuels were atomized and partially vaporized in the intake manifold. The engine was operated at a relative air/fuel ratio of 1.2, 60% exhaust gas recirculation (EGR) and 900 rpm. The compression ratio was varied over the range of 9:1 to 15:1 to optimize the combustion phasing for each fuel, keeping other operating parameters constant.</div><div class="htmlview paragraph">The results show that cetane number and T90 distillation temperature significantly affected the combustion phasing. Cetane number was clearly found to have the strongest effect. An increase in cetane number or a decrease in the T90 distillation temperature advanced the combustion phasing. The cetane number effect is related to increased low temperature heat release (LTHR) with increasing cetane number. The T90 effect is primarily due to a change in the physical delay period associated with preparation of the fuel-air mixture. At a similar combustion phasing, the high CN fuels exhibited significantly longer combustion duration than the low CN fuels. The best fuel conversion efficiencies were generally achieved with the four low cetane number fuels (FACE No. 1-4) as optimized combustion phasing occurred at a higher compression ratio. However, the two fuels with high CN and low T90 (FACE No. 5 and 7) also produced high fuel conversion efficiencies, although at a slightly lower compression ratio. These two fuels (FACE No. 5 and 7) produced the lowest indicated specific HC (isHC) emissions. This is due to the combined effects of high fuel volatility and reactivity that resulted in a more efficient combustion process. FACE No. 8, which has high CN and high T90, produced notably higher isHC emissions when the combustion phasing was in the range of 0° to 10°CA, aTDC. FACE No. 6 and 8, which have high CN and high T90, produced higher isCO emissions when the combustion phasing was retarded. The isNO<sub>x</sub> emissions were extremely low (below 0.008 g/kWh) for all fuels. Aromatic content did not directly affect the combustion phasing or emissions behavior.</div></div>
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.000 | 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 it