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Ozone addition is not only a promising method for combustion control and enhancement but also provides a reliable platform to benchmark low-temperature oxidation chemistry. Studies of ozone-doped combustion provide additional insight into combustion chemistry at lower temperatures. This paper studies the ozone-assisted low-temperature oxidation of propane in an atmospheric jet-stirred reactor (JSR) from 350 to 770 K. More than twenty species are measured and quantified using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). The experimental results show that even at temperatures as low as 450 K, the reaction of propane is initiated by Ö atoms that originate from the thermal decomposition of ozone. The reactivity of propane reaches a maximum at 650 K, decreases in the temperature range of 650 – 740 K, and then slightly increases from 740 to 770 K. The propane oxidation behavior observed in this study is effectively captured by NUIGMech1.3 combined with a Princeton ozone sub-mechanism. However, the mole fractions of certain species such as, CO, H 2 O, and H 2 O 2 are over-estimated by the mechanism at temperatures above 700 K. Kinetics analyses indicate that fuel oxidation and intermediate species formation are sensitive to the reaction temperature which determines the competing reactions involving propyl-peroxy radicals and the formation of ȮH and HȮ 2 radicals. These findings are significant in terms of improving the core mechanism and acquiring a deeper comprehension of the ozone-assisted low-temperature oxidation chemistry of alkanes. [ABSTRACT FROM AUTHOR]

Ammonia is a promising carbon-free fuel and has attracted massive attention nowadays. However, there are still large uncertainties in the mechanism of ammonia oxidation that motivate further fundamental investigations. In this work, oxidation experiments of ammonia were carried out in a jet-stirred reactor (JSR) equipped with synchrotron vacuum ultraviolet (SVUV) photoionization mass spectrometry and gas chromatography. Ammonia/O 2 /Ar mixtures were tested under wide-range operating conditions covering an oxidation temperature of 700–1200 K and an equivalence ratio of ϕ = 0.1–1.0. Important intermediates and products (e.g., NO, NO 2 , N 2 O, N 2 , H 2 , and H 2 O) were detected and quantified. A chemical kinetic model for ammonia oxidation was proposed by integrating the rate constants of critical reactions from different models. The results show that ammonia oxidation reactivity is quite strong at ultra-lean conditions, manifesting lower oxidization temperatures and greater oxidization rates. However, this behavior becomes weakened rapidly with the elevation of equivalence ratio, such that ammonia oxidation characteristics are highly similar between ϕ = 0.5 and 1.0. Meanwhile, important intermediates like NO 2 and N 2 O are only detected under ultra-lean conditions. Reaction pathway analysis for equivalence ratios shows that high oxygen concentration is beneficial to the formation of HO 2 , which leads to a huge amount of OH and promotes the dehydrogenation of ammonia. With the elevation of equivalence ratio, the dehydrogenation of ammonia becomes difficult and reactions NO+HO 2 =NO 2 +OH and NH 2 +NO 2 =N 2 O+H 2 O are suppressed, which answers for the vanishing of NO 2 and N 2 O at ϕ = 0.5 and 1.0. Reaction pathway analysis for oxidation temperatures also emphasizes the significance of HO 2 and its conversion pathway to OH, but they are also strongly influenced by equivalence ratios. The current work provides useful insights into ammonia oxidation and a reliable experimental database for modeling. [ABSTRACT FROM AUTHOR]

Comprehensive analysis of the low-temperature oxidation intermediates, including the reactive intermediates and isomers, is crucial to develop the low-temperature oxidation models of the fuels. In this aim, the complementary analysis by different analytic methods is needed. Furthermore, the cross check by different analytic methods increases the fidelity of the experiment data. In this work, we developed a jet-stirred reactor (JSR) system that coupled to the synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC) analysis. The JSR was designed to couple the SVUV-PIMS and GC, and the temperature homogeneity and mixing of the JSR was examined by a CFD simulation. The SVUV-PIMS system was developed to have a mass resolution of ca. 5000 at m/z 100. The GC system included a flame ionization detector (FID), thermal conductivity detector (TCD), and a mass spectrometer (MS). This newly developed setup was validated by repeating the oxidation data of n -heptane in the literature. A good agreement was observed between the two datasets. The low-temperature oxidation of n -butane was then studied to show the advantage of this setup, i.e., the simultaneous and comprehensive measurement of the low-temperature oxidation products. Specifically, the SVUV-PIMS enables the separation of the C/H/O composition of the intermediates, the measurement of formaldehyde and the peroxide intermediate, while the GC analysis gives a better separation of the oxygenated isomers and the quantification of the species that the SVUV-PIMS has difficult in quantifying. The experimental method developed in this work is valuable to study the fuel low-temperature oxidation chemistry, to reveal the species pool, and to provide reliable mole fraction data for the validation and development of combustion models. [ABSTRACT FROM AUTHOR]