Effects of Gasoline Composition on Compression Ignition in a Motored Engine
Bibliographic record
Abstract
This study presents a fundamental investigation of gasoline autoignition behavior in a compression ignition engine, which is of great importance for next generation engine designs that employ low temperature combustion strategies. A total of eleven full boiling range gasolines with different octane number and sensitivity have been tested in a motored engine and a constant volume combustion chamber at various pressures, temperatures, and oxygen concentrations. For quantification of intermediate temperature heat release (ITHR), a new method was applied to the engine data by examining the maximum value of the second derivative of heat release rate. Combustion phasing comparisons of single-stage ignition fuels with various octane sensitivity showed that fuel with less octane sensitivity became more reactive as intake temperature and simulated exhaust gas recirculation (EGR) ratio decreased, while fuel with higher octane sensitivity had a reverse trend. When low temperature heat release (LTHR) was not active, the amount of ITHR increased as the intake temperature and oxygen mole fraction increased. These ITHR trends, depending on octane sensitivity, were almost identical with the trends of combustion phasing, showing that ITHR significantly affects fuel autoignition reactivity and determines octane sensitivity. In addition, the strong dependence of ITHR on equivalence ratio enhanced the ϕ-sensitivity. For the similar combustion phasing, the higher octane sensitivity fuels exhibited faster rise rates of ITHR intensity than the lower octane sensitivity fuels, leading to more advanced hot-ignition phasing with increasing equivalence ratio. For two-stage ignition fuels, LTHR significantly enhanced ITHR, eventually advancing the autoignition timing. Both LTHR and ITHR were suppressed by increasing the simulated EGR ratio. The intake pressure boosting increased LTHR whereas the magnitude of ITHR for fuels with a lower research octane number (RON), which exhibited a great amount of ITHR, became saturated as the intake pressure increased. However, the average ITHR per crank angle increased with the intake pressure, showing concise and strong intermediate temperature reaction. With regard to physical property effects, higher aromatic content led to lower volatility and higher density, resulting in a slower liquid fuel evaporation process. The physical ignition delay was very sensitive to air temperature whereas oxygen dilution rarely affected the physical ignition delay. With regard to chemical property effects at the same RON, fuel with a higher aromatic content was more resistant to autoignite at high pressure and less sensitive to the oxygen dilution whereas the alkane-rich fuel was less sensitive to the temperature due to pronounced negative temperature coefficient (NTC) behavior. For the same RON and octane sensitivity, fuel with a higher amount of n-alkane was less sensitive to the oxygen dilution.
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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 | 0.001 |
| 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".