Influence of Engine Speed on HCCI Combustion Characteristics using Dual-Stage Autoignition Fuels
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Bibliographic record
Abstract
<div class="htmlview paragraph">Homogeneous Charge Compression Ignition (HCCI) combustion characteristics of dual-stage autoignition fuels were examined over the speed range of 600 to 1700 rpm using a Cooperative Fuels Research (CFR) engine. A fuel vaporizer was used to preheat and partially vaporize the fuel inside the intake plenum. The air and fuel were well-mixed prior to entering the cylinder.</div> <div class="htmlview paragraph">Since low temperature heat release (LTHR) is known to be an important factor that affects HCCI combustion of fuels that exhibit dual-stage autoignition behavior, a detailed heat release analyses were performed on both time and crank angle bases. At the lower and upper speeds, the operating ranges were compared as a function of air/fuel ratio (AFR) and exhaust gas recirculation (EGR) from the knocking to misfiring limits.</div> <div class="htmlview paragraph">The AFR-EGR operating region was more limited at 1700 rpm than at 900 rpm for the commercial ULSD fuel. Combustion stability was problematic at higher engine speeds. Reduced LTHR at higher engine speeds was one source of the combustion instability. LTHR timing was sensitive to compression temperature and the LTHR magnitude was sensitive to available time for completion of LTHR reactions. Combustion timing (CA<sub>50</sub>) was advanced on a time basis, but it was retarded on a crank angle basis.</div> <div class="htmlview paragraph">For a range of diesel-like fuels including commercial ultra low sulphur diesel and n-heptane, two methods of combustion timing control, namely intake heating and intake pressure boosting, were examined over the engine speed range. It was found that significant variations in intake heating or pressure boosting were required to control the combustion timing. While cetane number was not correlated with heating requirements in this preliminary study, the higher cetane number fuels required less intake pressure boosting for combustion timing control.</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 | 0.003 |
| 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 | 0.001 |
| 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