The effect of the addition of nitrogen oxides on the oxidation of propane: An experimental and modeling study
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Bibliographic record
Abstract
The oxidation of propane (C3H8), with the addition of different oxides of nitrogen (NO, NO2, and N2O) in concentrations of 0 – 2000 ppm, has been investigated for stoichiometric mixtures, at compressed temperatures of (TC) = 690 – 1420 K, and at compressed pressures of (pC) = 2.0 – 3.0 MPa using both a rapid compression machine and a high-pressure shock tube. These new ignition delay time (IDT) measurements, together with C3/NOx data available in the literature, provide a direct validation of NUIGMech1.3 which includes an updated C3/NOx sub-mechanism. The experimental results show that the mixtures with NO2 and NO/NO2 added have longer IDTs, inhibiting reactivity at TC〈 800 K, and shorter IDTs, promoting reactivity at TC〉 800 K, compared to the base C3H8/‘air’ mixtures indicating the complex chemical interactions involved. Both the inhibiting and prompting effects depend on the concentrations of NO and NO2 added and on the temperature regime. The addition of 1000 ppm NO2 significantly reduces the negative temperature coefficient (NTC) behavior of C3H8 in the temperature range 715–800 K compared to the addition of 200 ppm. Model predictions with 1000 ppm NO added, assuming no conversion of NO to NO2, are significantly slower than for both the 0 and 1000 ppm NO2 addition cases at TC < 800 K. Although NO and NO2 addition have different impacts on C3H8 oxidation at low-, intermediate, and high-temperatures, the addition of 1000 ppm N2O did not show any chemical effect at the conditions studied. NUIGMech1.3, with the updated C3/NOx sub-mechanism, reproduces the sensitisation effect of NOx on C3H8 with generally good agreement. Sensitivity and flux analyses have been performed to highlight the key reactions controlling ignition. The analyses show that competition between the reactions Ṙ+NO2↔RȮ+NO and Ṙ +NO2 (+M) ↔ RNO2 (+M) governs NOx sensitization on propane ignition. The inhibiting effect of NO and NO2 addition to propane stems from the nĊ3H7+ NO2↔ nC3H7Ȯ + NO and nC3H7Ȯ2 + NO ↔ nC3H7Ȯ + NO2 reactions, which compete for nC3H7Ȯ2 radicals, reducing the rate of isomerization of nC3H7Ȯ2 into Ċ3H6OOH1–3 (RȮ2 ⇌ Q˙OOH).
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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 | 0.000 |
| 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) | 0.000 | 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