Enhancement of teprenone isomer separation by subcritical fluid chromatography using porous graphitic carbon column

Teprenone is a therapeutic anti-ulcer agent developed in Japan. As described in the Japanese Pharmacopoeia (JP) 17th Edition, gas chromatography/hydrogen flame ionization detection (GC/FID) and high-performance liquid chromatography/ultraviolet detection (HPLC/UV) have been used for the assay of active pharmaceutical ingredients (APIs) and teprenone capsules, respectively. The critical aspect of the assay is a separation of the structural isomers (mono-cis and all-trans) of teprenone. Herein, we propose an improved quantitative method for the quality control of teprenone in APIs and capsules via subcritical fluid chromatography/photo diode array detection (SubFC/PDA) using a porous graphitic carbon column. SubFC conditions, i.e., type and content of the organic modifier in the mobile phase, column temperature, injection volume, and flow rate, were optimized. The developed SubFC/PDA method was validated according to ICH guidelines Q2(R1) in terms of accuracy, precision (repeatability and intermediate precision), specificity, linearity, quantification range, robustness, and stability. Comparison of SubFC/PDA method with the GC/FID or HPLC/UV method (described in JP) revealed that the SubFC/PDA method gave better resolution and run time than the JP methods. The developed SubFC/PDA method is expected to be useful for pharmaceutical analysis or quality control of teprenone isomers.

Flame Stabilization and Blow-off of Ultra-Lean errortypeceH2-Air Premixed Flames

The manner in which an ultra-lean hydrogen flame stabilizes and blows off is crucial for the understanding and design of safe and efficient combustion devices. In this study, we use experiments and numerical simulations for pure errortypeceH2-air flames stabilized behind a cylindrical bluff body to reveal the underlying physics that make such flames stable and eventually blow-off. Results from CFD simulations are used to investigate the role of stretch and preferential diffusion after a qualitative validation with experiments. It is found that the flame displacement speed of flames stabilized beyond the lean flammability limit of a flat stretchless flame (ϕ=0.3) can be scaled with a relevant tubular flame displacement speed. This result is crucial as no scaling reference is available for such flames. We also confirm our previous hypothesis regarding lean limit blow-off for flames with a neck formation that such flames are quenched due to excessive local stretching. After extinction at the flame neck, flames with closed flame fronts are found to be stabilized inside a recirculation zone.

Stabilization of combustion of kerosene-air mixture by hydrogen injection

On aircrafts at high flight speeds, the ramjet engine (ramjet) is of greatest interest at present, the efficiency of which can be increased by using the thermochemical fuel conversion (TFC) technology. Some aspects of the operation of such an engine can be simulated numerically. In this work, a theoretical and experimental study of the processes in the combustion chamber is carried out, and a method is proposed for stabilizing the combustion of a keroseneair mixture by injecting molecular hydrogen into a direct-flow combustion chamber. An experimental setup created at TsAGI was used, on which the influence of the hydrogen temperature, the location and size of the mass supply area on the combustion process was studied. For a theoretical study, the corresponding numerical technology was applied based on the Navier-Stokes equations using the Spal-rt-Allmares turbulence model, implemented in a complex of computer programs developed at the Research Institute of Mechanics of Moscow State University. Numerical modeling solved two problems. The first concerned the conditions for the ignition of molecular hydrogen supplied to the flow-type igniter, and the second - the conditions for the stabilization of the combustion of a kerosene-air mixture by a hydrogen flame. Based on the results of calculations, it was found that the ignition process is facilitated by an increase in the temperature of hydrogen and the power of its injection. The position and size of the hydrogen source is less influential. In the course of a comprehensive study by the method of a full-scale and computational experiment, the characteristic features of the flow structure in the channel, including the formation of a detonation wave, were revealed, and the possibility of controlling combustion by hydrogen injection was shown.

Recent Progress in Hydrogen Flammability Prediction for the Safe Energy Systems

Many countries consider hydrogen as a promising energy source to resolve the energy challenges over the global climate change. However, the potential of hydrogen explosions remains a technical issue to embrace hydrogen as an alternate solution since the Hindenburg disaster occurred in 1937. To ascertain safe hydrogen energy systems including production, storage, and transportation, securing the knowledge concerning hydrogen flammability is essential. In this paper, we addressed a comprehensive review of the studies related to predicting hydrogen flammability by dividing them into three types: experimental, numerical, and analytical. While the earlier experimental studies had focused only on measuring limit concentration, recent studies clarified the extinction mechanism of a hydrogen flame. In numerical studies, the continued advances in computer performance enabled even multi-dimensional stretched flame analysis following one-dimensional planar flame analysis. The different extinction mechanisms depending on the Lewis number of each fuel type could be observed by these advanced simulations. Finally, historical attempts to predict the limit concentration by analytical modeling of flammability characteristics were discussed. Developing an accurate model to predict the flammability limit of various hydrogen mixtures is our remaining issue.