Chenglong Tang

Bouncing, coalescence, and separation in head-on collision of unequal-size droplets

The dynamics of head-on collision of unequal-size droplets were experimentally and theoretically investigated, with emphasis on identifying distinct collision outcomes and interpreting the size-ratio dependence. A unified regime diagram in terms of bouncing, permanent coalescence, and separation after coalescence was identified for hydrocarbon and water droplets in the parameter space of the size ratio and a collision Weber number. Experimental results show that the transition Weber number, Web-c, that separates the bouncing and permanent coalescence regimes, weakly depends on the size ratio, while the transition Weber number, Wec-s, that separates permanent coalescence and separation regimes, significantly increases with the size ratio. A theoretical model based on energy balance and scaling analysis was developed to explain the size-ratio dependence of Wec-s. The theoretical results show good agreement with the experimental data for tetradecane and decane droplets, with a moderate discrepancy for water ...

High methane natural gas/air explosion characteristics in confined vessel

The explosion characteristics of high methane fraction natural gas were investigated in a constant volume combustion vessel at different initial conditions. Results show that with the increase of initial pressure, the peak explosion pressure, the maximum rate of pressure rise increase due to a higher amount (mass) of flammable mixture, which delivers an increased amount of heat. The increased total flame duration and flame development time result as a consequence of the higher amount of flammable mixture. With the increase of the initial temperature, the peak explosion pressures decrease, but the pressure increase during combustion is accelerated, which indicates a faster flame speed and heat release rate. The maximum value of the explosion pressure, the maximum rate of pressure rise, the minimum total combustion duration and the minimum flame development time is observed when the equivalence ratio of the mixture is 1.1. Additionally, for higher methane fraction natural gas, the explosion pressure and the maximum rate of pressure rise are slightly decreased, while the combustion duration is postponed. The combustion phasing is empirically correlated with the experimental parameters with good fitting performance. Furthermore, the addition of dilute gas significantly reduces the explosion pressure, the maximum rate of pressure rise and postpones the flame development and this flame retarding effect of carbon dioxide is stronger than that of nitrogen.

Bis(borano)hypophosphite-based ionic liquids as ultrafast-igniting hypergolic fuels

A family of hydride-rich bis(borano)hypophosphite-based ionic liquids was developed, which showed good water stability at room temperature and unexpected hypergolic reactivity with oxidizers. These ionic fluids have exhibited the shortest ignition delay times so far, demonstrating their application potential as hypergolic fuels or additives in liquid bipropellants.

Study on the Effects of Dielectric Barrier Discharge on the Bunsen Flame Structure With OH-PLIF Technique

Nonthermal equilibrium plasma has been reported to be potentially applicable in many combustion scenarios. In this paper, the effects of dielectric barrier discharge (DBD) on the flame structure of a Bunsen flame have been investigated by using the OH planar laser-induced fluorescence technique. Results show that the increase of discharge intensity significantly enhances the local burning. In coaxial-cylinder DBD reactor, the flame structure can be varied from conic shape to M shape with discharge power increasing.

Kinetics of Hydrogen Abstraction and Addition Reactions of 3-Hexene by ȮH Radicals

Rate coefficients of H atom abstraction and H atom addition reactions of 3-hexene by the hydroxyl radicals were determined using both conventional transition-state theory and canonical variational transition-state theory, with the potential energy surface (PES) evaluated at the CCSD(T)/CBS//BHandHLYP/6-311G(d,p) level and quantum mechanical effect corrected by the compounded methods including one-dimensional Wigner method, multidimensional zero-curvature tunneling method, and small-curvature tunneling method. Results reveal that accounting for approximate 70% of the overall H atom abstractions occur in the allylic site via both direct and indirect channels. The indirect channel containing two van der Waals prereactive complexes exhibits two times larger rate coefficient relative to the direct one. The OH addition reaction also contains two van der Waals complexes, and its submerged barrier results in a negative temperature coefficient behavior at low temperatures. In contrast, The OH addition pathway dominates only at temperatures below 450 K whereas the H atom abstraction reactions dominate overwhelmingly at temperature over 1000 K. All of the rate coefficients calculated with an uncertainty of a factor of 5 were fitted in a quasi-Arrhenius formula. Analyses on the PES, minimum reaction path and activation free Gibbs energy were also performed in this study.

The correlation between the cylinder pressure and the ion current fitted with a Gaussian algorithm for a spark ignition engine fuelled with natural-gas–hydrogen blends

An investigation was conducted of the ion current characteristics at various excess air ratios λ in a spark ignition engine fuelled with natural-gas–hydrogen blends. The Gaussian mathematical method was employed to fit the pure ion current signal without a spark tail generated by the ignition discharge. The cylinder pressure was recorded, and the Pauta criterion static threshold was used to deal with the outlier errors in the testing data for given cycles. The results show that the spark tail and the ion current can be separated by fitting the ion current with the Gaussian method, and the fitted pure ion current includes the flame-front stage and the post-flame stage. The timing with respect to the flame-front peak exhibits an irregular variation with λ. The maximum current in the flame-front stage increases with increasing λ.The timing of the maximum current in the post-flame stage occurs earlier at the stoichiometric ratio than at other air-to-fuel ratios. The correlation coefficient between the ion current in the post-flame stage and the pressure data treated with the Pauta criterion method increases. In addition, there are high correlation coefficients between the ion current and the pressure.

Experimental Observation of Hypergolic Ignition of Superbase-Derived Ionic Liquids

The hypergolic ignition behaviors of four newly synthesized ionic liquids with dicyanamide anion (ionic liquids 1 and 3) and cyanoborohydride anion (ionic liquids 2 and 4) were experimentally investigated. The results showed that successful hypergolic ignition of both group ionic liquids were achieved with white fuming nitric acid and red fuming nitric acid. Two distinct flame initiation processes illustrated by several stages were observed for each group of ionic liquids. Specifically, the ionic liquid 1 drop showed immerging, exploding, and ignition: the drop immerged and reacted with the oxidizers underneath the liquid surface, producing gas vapor and white foam like intermediates on the surface; then, the surface exploded by fast accumulation of heat and vapor underneath, followed by flame kernels formation in the adjacent gas phase. The ionic liquid 2 drop showed bouncing and igniting: it just created a crater on the oxidizer surface and then sat on the Leidenfrost vapor layer generated by impaction ...