Gas separation processes in a diffusion module based on anodic aluminum oxide membrane elements

Anodic alumina membranes with an ordered microstructure have been synthesized and investigated. It was found that Knudsen diffusion is the predominant mechanism for gas penetration through the obtained membranes. The technology made it possible to obtain porous membranes with specified structural characteristics for the separation of gas mixtures. Designs of a diffusion element and a gas separation module based on membranes made of anodic aluminum oxide have been developed, and the features of mass transfer under various operating conditions have been studied. The membrane module without recirculation made it possible to concentrate the heavy component from the model helium-methane mixture (99 % / 1 %) up to 18 %. The membrane module with recirculation made it possible to concentrate a light component from a model helium-methane mixture (1 % / 99 %) up to 40 %.

Theoretical studies of natural gas vaporization of an air-methane mixture in a diesel engine cylinder

This article presents theoretical studies of the vaporization of natural gas of an air-methane mixture in a diesel engine cylinder. These studies were conducted in order to find a rational volume of methane supplied to the cylinder of a diesel engine. Having carried out a thermal calculation of the working processes of the gas engine, we obtained the size of the gas droplet supplied to the engine cylinder, which should have a size of no more than 0.405 mm. Having evaluated the experimental studies conducted in this area, the dependence of the nozzle diameter of the nozzle and the diameter of the gas droplet was revealed, it was determined that with a pressure drop on the gas nozzle equal to 0.2 MPa, the diameter of the gas droplet practically coincides with the diameter of the nozzle. Based on this, the diameter of the nozzle of the gas nozzle sprayer is not more than 0.35...0.4 mm. The conclusion of this article is that it is possible to determine the optimal volume of gas supplied and assess the real picture of the processes taking place in the cylinder of a diesel engine only. Keywords: INTERNAL COMBUSTION ENGINE, WORKING FLUID, FUEL, VAPORIZATION, GAS, COMBUSTION

Chemical Kinetic Study on Dual-Fuel Combustion: The Ignition Properties of n-Dodecane/Methane Mixture

The natural gas (NG)/diesel dual-fuel engine has attracted extensive attention in recent years, and the influence of ignition delay on the engine is very important. Therefore, the research on the ignition delay of NG/diesel dual fuel is of great significance. In this work, a simplified n-dodecane mechanism was used to study the effect of methane mixture ratio on the n-dodecane ignition process. The results showed that the ignition delay time increased with the increase of methane content by changing the mixing ratio of methane and n-dodecane. However, the effect of methane on the ignition delay time gradually decreases when the content of the n-dodecane mixing ratio is greater than 50%. It was also found that with the increase of n-dodecane content, the reduction degree of the ignition delay time of the whole reaction system decreased and the negative temperature coefficient (NTC) behavior increased. Moreover, when the initial pressure increased from 20 bar to 60 bar, the thermal effect of methane also increases from 7.03% to 9.55%. The relationship between ignition characteristics of methane-n-dodecane and temperature was studied by changing the initial temperature. Furthermore, the evolution of species in the ignition process of the whole reaction system was analyzed, and the decomposition of n-dodecane first occurs in the reaction n-C12H26 + O2 = R + HO2 to form R and free radicals; however, the reaction CH4 + OH = CH3 + H2O dominates with the increase of the methane mixing ratio and inhibits the ignition process. Through the analysis of reaction paths, sensitivity, and rates of production and consumption of methane/n-dodecane, it was explained how n-dodecane accelerates methane ignition through the rapidly formed free radicals.

Preparation and Evaluation of the Polyethylene Film Deposited With a Multilayer Graphene Membrane for Tensile Properties

This study aims to improve the tensile properties of the polyethylene film deposited with a multilayer graphene membrane, in order to establish the understanding of the influence of the methane to hydrogen ratio on the tensile properties of the multilayer graphene membrane. Multilayer graphene membranes were prepared using the chemical vapor deposition method. Four types of multilayer graphene membranes were prepared with different ratios of methane to hydrogen before depositing a membrane on the polyethylene film. Experiments showed that the tensile strength of the polyethylene films with multilayer graphene deposition increased 7 times and the Young’s modulus 5 times more than that of pure polyethylene films, when the ratio of methane to hydrogen was set to 35/100 sccm. A compromise between hydrogen and methane mixture is required to achieve uniform growth of graphene. Insufficient hydrogen cannot activate the surface bound carbon that is necessary for continuous growth. Continuous and well-defined multilayer graphene was synthesized when the ratio of methane to hydrogen reached up a proper value.

Spectral study of argon-methane mixture plasma jet generated by a DC plasmatron

We present the results of studying optical emission spectra of Ar:CH4 plasma produced on a DC plasmatron for graphene synthesis. We have identified the basic set of spectral lines and bands in the obtained spectra and shown that H lines and C2 bands appear due to direct excitation by an electron strike of corresponding neutral particles. C2 molecular bands were also identified in the spectra with intensity considerably lower compared to previous studies where He: C2H2 mixture was used as plasma-forming gas.

Analysis of Exploitation Parameters in Drainage Boreholes of the Longwall Demethylation System. Case Study

In hard coal mines with methane, there is often a need to apply demethylation in order to keep the methane concentration not exceeding 2% in the ventilation air. The basic demethylation method in longwall areas is through drainage boreholes made in the roof rocks of the coal bed, from top gate, in front of the longwall. The drainage boreholes are usually made in bundles, in a fan-shaped arrangement, with several boreholes in each bundle. The paper presents the results of measurements and tests of the efficiency of a bundle of four drainage boreholes drilled approximately 100 m in front of the longwall face. The efficiency of individual boreholes was analyzed in time and depending on the distance of borehole outlets from the longwall face. It was found that there is a large variation in the extraction of air-methane mixture by individual drainage boreholes, as well as large differences in the efficiency of individual drainage boreholes during the longwall extraction process.

Preparing Methane – Air Mixture Using Ejector

In this research, a two – dimensional numerical investigation is conducted to show the ability of the jet-ejector to prepare the air – methane mixture at different equivalence ratio. The basic dimensions (diameters ratio, throat length, angle α, and angle θ) of the jet-ejector are taken into account on calculating the equivalence ratio. The results showed that the ratio of the diameters has a higher effect than other parameters on preparing a mixture for equivalent ratios including both rich and lean mixture. The rest of the factors did not have a significant effect on the value of the equivalence ratio, and only had a role in preparing an equivalence ratio for rich mixture type.

Effects of methane ratio on MPDF (micro-pilot dual-fuel) combustion characteristic in a heavy-duty single cylinder engine

In this study, the characteristics of micro-pilot dual-fuel combustion with respect to the fuel mixture ratio in a single cylinder dual-fuel engine have been investigated. In order to analyze the characteristics of micro-pilot dual-fuel combustion, a metal engine and an optical single cylinder dual-fuel engine were used. The fuel mixture ratio was varied for experimental purposes; the diesel was directly injected into combustion chamber and the methane gas was supplied via intake port. The present study reports that increasing the methane mixture ratio from 0 to 97.67% changes the diesel combustion to pre-mixed combustion. As a result, the peak cylinder pressure was increased from 184 to 198 bar, and the rate of heat release was greatly advanced. In the MPDF condition, the nitrogen oxides emissions were reduced by about 90%p, and the fuel conversion efficiency increased about 5%p because of the low combustion temperature of pre-mixed combustion. However, for the same reason, the hydrocarbon emissions were increased about 95%p. The fastest combustion speed was found form the results of methane mixture ratio between 40 and 80%. In the condition of diesel combustion and micro-pilot dual-fuel combustion, the combustion periods of middle and initial were increased, respectively, resulting in the low combustion speed. The standard deviation of peak cylinder pressure, which represents the combustion variation, was correlated with initial combustion period. While the condition of methane gas mixture ratio between 40 and 80% shows the lowest combustion variation, the highest combustion variation was occurred by MPDF condition. Through the optical engine experiment, it can be found that the cycle to cycle combustion variation is ascribed to the turbulent flow and the variation of ignition position. The combustion images show that the unpredictable characteristics of the ignition position and slow flame propagation speed caused the combustion variation in micro-pilot dual-fuel combustion.

Исследование нелегированных нанокристаллических алмазных пленок, выращенных из газовой фазы в плазме СВЧ разряда

Undoped nanocrystalline diamond (NCD) films less than 1 μm thick grown on Si (100) silicon by microwave plasma-assisted chemical vapor deposition at a frequency of 2.45 GHz are studied. To obtain diamond dielectric films with maximum resistivity the deposition of films in three gas mixtures is investigated: hydrogen-methane mixture, hydrogen-methane mixture with the addition of oxygen and hydrogen-methane mixture with the addition of an inert gas. A relationship has been established between the growth conditions, structural and electrical properties of NCD films. It is shown that for the use of NCD films as effective dielectrics preliminary high-temperature annealing of the films is required, for example, in vacuum at a temperature of 600°C for one hour.