A complete understanding of the mechanism of ammonia pyrolysis and oxidation in the full range of operating conditions displayed by industrial applications is one of the challenges of modern combustion kinetics. In this work, a wide-range investigation of the oxidation mechanism of ammonia was performed. Experimental campaigns were carried out in a jet-stirred reactor and a flow reactor under lean conditions (0.01 ≤ Φ ≤ 0.375), such to cover the full range of operating temperatures (500 K ≤ T ≤ 2000 K). Ammonia conversion and the formation of products and intermediates were analyzed. At the same time, the ammonia decomposition reaction, H-abstractions and the decomposition of the HNO intermediate were evaluated ab initio, and the related rates were included in a comprehensive kinetic model, developed according to a first-principles approach. Low-temperature reactor experiments highlighted a delayed reactivity of ammonia, in spite of the high amount of oxygen. A very slow increase in NH₃ consumption rate with temperature was observed, and a full reactant consumption was possible only ∼150–200 K after the reactivity onset. The use of flux analysis and sensitivity analysis allowed explaining this effect with the terminating effect of the H-abstraction on NH₃ by O₂, acting in the reverse direction because of the high amounts of HO₂. The central role of H₂NO was observed at low temperatures (T < 1200 K), and H-abstractions from it by HO₂, NO₂ and NH₂ were found to control reactivity, especially at higher pressures. On the other side, the formation of HNO intermediate via NH₂ + O = HNO + H and its decomposition were found to be crucial at higher temperatures, affecting both NO/N₂ ratio and flame propagation.

International audiencePropene is a significant component of Liquefied Petroleum Gas (LPG) and an intermediate in the combustion of higher order hydrocarbons. To better understand the combustion characteristics of propene, this study and its companion paper present new experimental data from jet-stirred (JSR) and flow reactors (Part I) and ignition delay time and flame speed experiments (Part II). Species profiles from JSR experiments are presented and were obtained at near-atmospheric pressure over a temperature range of 800-1100 K and for equivalence ratios from φ = 0.64 to 2.19. The new JSR data were obtained at lower dilution levels and temperatures than previously published. Also reported are species profiles from two high-pressure flow reactor facilities: the Princeton Variable Pressure Flow Reactor (VPFR) and the High Pressure Laminar Flow Reactor (HPLFR). The VPFR experiments were conducted at pressures of 6-12.5 atm, in the temperature range 843-1020 K and at equivalence ratios of 0.7-1.3. The HPLFR experiments were conducted at 15 atm, at a temperature of 800 K and at equivalence ratios of 0.35-1.25. The flow reactor data is at higher pressures and lower temperatures than existing data in the literature. A detailed chemical kinetic mechanism has been simultaneously developed to describe the combustion of propene under the experimental conditions described above. Important reactions highlighted via flux and sensitivity analyses include: hydrogen atom abstraction from propene by molecular oxygen, hydroxyl, and hydroperoxyl radicals; allyl-allyl radical recombination; the reaction between allyl and hydroperoxyl radicals; and the reactions of 1- and 2-propenyl radicals with molecular oxygen. The current mechanism accurately predicts the combustion characteristics of propene across the range of experimental conditions presented in this study, from jet-stirred and flow reactors and for ignition delay times and flame speed measurements presented in Part II. In comparison to a previous mechanism, AramcoMech 1.3, the current mechanism results in much improved performance, which highlights the importance of the new experimental data in constraining the important reactions