Chemical Kinetics of <i>n</i>-Hexane-Air Atmospheres in the Boundary Layer of a Moving Hot Sphere

Mével, Rémy; Niedzielska, Urszula; Melguizo-Gavilanes, J.; Coronel, Stephanie; Shepherd, Joseph E.

doi:10.1080/00102202.2016.1211886

Cited by 11 publications

(8 citation statements)

References 30 publications

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“…They observed that the boundary layer development and flow separation have crucial impacts on the ignition process, which is consistent with the experimental results of Mével et al. (2016, 2019). Usually, ignition occurs between the front stagnation point and the location of flow separation, and the ignition position moves downstream as the particle temperature decreases.…”

Section: Introductionsupporting

confidence: 89%

Theoretical analysis on the ignition of a combustible mixture by a hot particle

Chen

2022

J. Fluid Mech.

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Mechanical spark is an important ignition source in various industrial processes involving combustible mixtures and it may cause serious safety issues. In this work, we analysed the ignition induced by hot particles in a combustible mixture. In Semenov's transient ignition criterion, we introduced a hypothetical heat loss coefficient accounting for the temperature inhomogeneity and obtained a revised ignition criterion which allows us to calculate the ignition delay time. Explicit expressions for the critical ignition temperature were derived and used to demonstrate the primary impacts of temperature inhomogeneity on the ignition process. Consistent with experimental and numerical results, the temperature inhomogeneity is intensified by either reducing the particle size or convective heat transfer at the particle surface, resulting in an increase of the critical ignition temperature. For flow separation on the particle surface, the boundary layer problem was solved based on a Blasius series. A temperature gradient for ignition was defined at the location of flow separation to reproduce the experimentally observed phenomenon that ignition prefers to occur first near the flow separation position. It is shown that the unsteadiness of particle cooling makes negligible contribution to the ignition process because of the exceedingly large density ratio between the particle and the ambient gas. In addition, the finite residence time of ignition for a fluid parcel due to its elevation from the particle surface leads to additional growth in the critical ignition temperature. However, such a correction appears to be inconsequential because the ignition of the fluid parcel restricted to the Frank–Kamenetskii region is close to the particle surface.

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Section: Introductionsupporting

confidence: 89%

Theoretical analysis on the ignition of a combustible mixture by a hot particle

Chen

2022

J. Fluid Mech.

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“…Regarding the effect of equivalence ratio, the effect of n-hexane addition in shortening the ignition delay time weakens for stoichiometric and rich mixtures, see Figure 9 and 10. This can be attributed to the self-inhibition property of hydrocarbons on the ignition process in the high-temperature range [40,31]. All three chemical kinetic mechanisms capture the main experimental features but significant deviations can be observed with relative error as high as 200% under certain conditions.…”

Section: Evaluation Of Reaction Model Performancementioning

confidence: 93%

“…The present study was carried out with nhexane because it can be studied with room temperature starting conditions. While numerous experimental data on ignition are available for methane- [28,29,30] and nhexane-based [31,32,33,34,35] mixtures, experimental data for dual-fuel methanen-alkane mixtures are scarce. Liang et al [36] studied the ignition delay-time of n-heptane-methane-based mixtures in a shock tube.…”

Section: Introductionmentioning

confidence: 99%

Ignition characteristics of dual-fuel methane-n-hexane-oxygen-diluent mixtures in a rapid compression machine and a shock tube

Wang

Grégoire

et al. 2019

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Ignition delay times of methane-n-hexane-oxygen mixtures were studied experimentally and numerically in a wide temperature range (640-2335 K) using both a rapid compression machine (RCM) and a shock tube (ST). The RCM results demonstrated a two-stage ignition and negative temperature coefficient (NTC) behavior. Increasing n-hexane concentration, pressure and equivalence ratio shortened the ignition delay time. For the ST experiments, the addition of 10% n-hexane (relative to methane) can reduce the ignition delay time dramatically. However, no further reduction effect can be achieved with increasing addition of n-hexane from 10% to 20%. In addition, increasing equivalence ratio reduces the effect of n-hexane addition on ignition delay time. Three detailed chemical mechanisms, CaltechMech, GalwayMech and LLNLMech, were evaluated based on a quantitative error analysis. LLNLMech and CaltechMech demonstrated the best performance in the RCM and ST temperature ranges, respectively. Chemical kinetic analyses showed that the addition of n-hexane to methane provides some chemical pathways not available for methane oxidation which result in the production of active radicals and eventually accelerate the ignition of the methane-oxygen mixtures. The crucial intermediate species for the ignition process are H 2 O 2 and H under RCM and ST conditions, respectively.

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“…This approach decouples the fluid mechanics from the chemistry, thereby making the modeling less computationally demanding. A similar method was explored by Mével et al (2016) to model the chemical kinetics around a moving hot sphere in an n-hexane environment.…”

Section: Chemistry Along Streamlinesmentioning

confidence: 99%