• Transactions of the Korean Society of Automotive Engineers
• /
• v.10 no.1
• /
• pp.32-44
• /
• 2002

Selective catalytic reduction of nitric oxide by methane in the presence of excess oxygen was investigated over copper and cobalt ion-exchanged ZSM-5 zeolites. Copper ion-exchanged ZSM-5(Cu-ZSM-5) has the limitations for commercial applications to lean-bum gasoline and diesel engines due to low thermal stability and resistance to water vapor and sulfur dioxide. But cobalt ion-exchanged ESM-5(Co-ZSM-5) is more active at high temperatures and also stable to water vapor and sulfur dioxide for catalytic reduction of nitric oxide by methane. The catalytic activity of Cu-ZSM-5 for NO reduction increases with increasing temperatures, reaches the maximum conversion of 23.0% at 350\"C. and then decreases with higher temperatures. In the meantime catalytic activities of Co-ZSM-5 show the maximum conversion of 25.8% at $500^{\circ}C$ Therefore Co-ZSM-5 catalysts have higher thermal stability at high temperatures. Catalytic activities of both zeolites were remarkably enhanced with the existence of oxygen in the exhaust. It is noted that the catalytic activity of Cu-ZSM-5 decreases with the increasing concentration of methane while the catalytic activity of Co-ZSM-5 decreases with increasing contents of methane in the exhaust. This may imply the existence of different paths of NO reduction by methane in the presence of excess oxygen fur Cu-ZSM-5 and Co-ZSM-5 catalysts. For binary metal ionexchanged ZSM-5, the primary ion-exchanged metal may be masked by secondary ion-exchanged component, which plays the important role for catalytic activities of binary metal ion-exchanged ZSM-5, Therefore CuCo-ZSM-5 catalysts show the similar volcano-shaped curves to Cu-ZSM-5 catalysts between the activity and temperature. It Is interesting that the activities of CoCu-ZSM-5 catalysts indicate almost no dependence on the concentration of methane in the exhaust.aust.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.17 no.6
• /
• pp.120-130
• /
• 2013

A study was conducted for the performance characteristics of methane taking recently the limelight in the world as a next-generation propellant, with the survey for state of the art in the development of methane/oxygen rocket engine being accompanied. Liquid methane as a rocket fuel has the favorable characteristics such as non-toxic, low cost, regenerative cooling capability, and potential for in-situ resource utilization (ISRU). The combination of liquid methane and liquid oxygen also provides the excellent performance including high specific impulse and low system mass. For these reasons, many researches have been actively carried out on the methane/oxygen engine, nevertheless, its technology readiness level is not that high enough just yet. Therefore, it is judged that it is the time to mitigate the technical gap with the space technology of advanced countries through a swift onset of the development of methane rocket engine.

• Journal of the Korean Applied Science and Technology
• /
• v.24 no.1
• /
• pp.67-73
• /
• 2007

Methane combustion over perovskite catalysts was investigated. For the preparation of catalysts, Co, Mn, Fe, and Ni were used as B-site components of the perovskite catalysts $(ABO_3)$ and La was used as A-site component. The effect of calcination temperature on methane combustion and perovskite structure was also investigated. The structure of perovskites, surface area, and adsorbed oxygen species were tested with XRD, BET apparatus, and $O_2-TPD$, respectively. The formation of perovskite structure was affected by the calcination temperature. The catalyst desorbing oxygen at a lower temperature showed better activity for the methane combustion, therefore, the oxygen species desorbing at lower temperatures is responsible for the methane combustion.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2000.02a
• /
• pp.97-97
• /
• 2000

In this thesis, the metastable state diamond thin films have been deposited on Si substrates from methane-hydrogen and oxygen mixture using Microwave Plasma Enhanced Chemical Vapor deposition (MWPCVD) method. Effects of each experimental parameters of MWPCVD including methane concentrations, oxygen additions, operating pressure, deposition time, etc. on the growth rate and crystallinity were investigated. SEM, XRD, and Raman spectroscopy were employed to analyze the growth rate and morphology, crystallinity and prefered growth direction, and relative amounts of diamond and non-diamond phases respectively. As a methane concentration below 4%, the deposited films having well-defined facets could be obtained. As the methane concentration increases over 4%, the shape of films gradually changed into a amorphos form. The best crystallinity of the film at 3% in the Raman spectroscopy. Addition of oxygen to the methane-hydrogen mixture gave an improved film crystallinity at 50% oxygen concentration due to its more effectiveness in the selective removal of the non-diamond phased compared to the of H atom. on the contrary, the growth rate generally decreased by oxygen to from the more stable CO and CO2 is responsible for such an effect. Upon increasing the operating pressure and time, increased of growth rate and crystallinity were increased simultaneously.

• 한국연소학회:학술대회논문집
• /
• 2003.05a
• /
• pp.247-253
• /
• 2003

Burning velocities of conventional methane flame and oxygen-enriched methane flame were determined by experimentally and numerically at atmospheric pressure in order to examine the validity of various detailed reaction mechanisms in oxygen-enriched flame. The schlieren system was adopted to obtain the burning velocity of flame stabilized on a circular nozzle. Premix code was employed to compute the burning velocity. Three reaction mechnisms were tested at several oxygen enrichment level, whose names are GRI 3.0, MB(Miller and Bowman) and LKY(Lee Ki Yong) reaction mechanism. Sensitivity analysis was also performed to discriminate dominantly affecting reaction on burning velociy. The results showed that conventional reaction mechanisms originally based on methane-air flame were underpredict the burning velocity at high oxygen-enrichment level. The modified GRI 3.0 reaction mechanism based on our experimental results was suggested and shows a good agreement in estimating the burning velocity and the NO number density of oxygen-enriched flame.

• Environmental Engineering Research
• /
• v.7 no.3
• /
• pp.185-189
• /
• 2002

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.28 no.2
• /
• pp.207-214
• /
• 2004

The burning velocities of conventional and oxygen-enriched methane flame in various equivalence ratio were determined by experiments. The validity of existing reaction mechanisms was examined in oxygen-enriched flame on the basis of the experiment results. Modified reaction mechanism is suggested, which was able to predict burning velocity of oxygen enriched flame as well as methane-air flame. Complementary study on reaction mechanisms shows the following results : Present experiment data were found to be more reliable in comparison with existing ones in a oxygen-enrichment condition. It was found that some modification in existing reaction mechanisms is necessary, since discrepancy between measurements and predictions is increasing with oxygen enrichment ratio. The sensitivity analysis was performed to discriminate the dominantly affecting reactions on the burning velocity in various oxygen enrichment and equivalence ratio. A modified GRI 3.0 reaction mechanism based on our experiment results was suggested, in which reaction rate coefficients of (R38) H+O$_2$<=>O+OH in GRI 3.0 reaction mechanisms were corrected based on sensitivity analysis results. This mechanism showed a good agreement in predicting the burning velocity and number density of NO in oxygen-enriched flame and would provide proper reaction information of oxygen-enriched flame at this stage.

• Bulletin of the Korean Chemical Society
• /
• v.23 no.6
• /
• pp.799-803
• /
• 2002

Partial oxidation of methane has been conducted over $CeO_2$and it has been found that $CeO_2$has an extraordinary catalytic activity in the reaction. Its activity was strongly dependent on the $CH_4/CO_2$ ratio. Total combustion was dominant with stoichiometric feed ratio$(CH_4/O_2=$ 2.0) but partial oxidation was achieved between the $CH_4/O_2$ ration of 3.8 4.3 and the period depended upon the feed composition. The proposed raaction mechanism it that oxygen vacancies in raduced deria are supplied with oxygen molecules from the reactant, and then activate adsorbed oxygen, followed by releasing activated axygen species reacting with methane to produce $H_2$ and CO.

• Bulletin of the Korean Chemical Society
• /
• v.23 no.5
• /
• pp.669-673
• /
• 2002

Ni catalyst (Ni: 15 wt%) supported on precalcined SiO2 has been investigated in reforming reactions of methane to synthesis gas. The catalyst exhibited fairly good activity and stability in partial oxidation of methane (POM), whereas it deactivated in steam reforming of methane (SRM). Pulse reaction results of CH4, O2, and CH4/O2 revealed that Ni/SiO2 has high capability to dissociate methane. The results also revealed that both CH4 and O2 are activated on the surface of metallic Ni, and then surface carbon species react with adsorbed oxygen to produce CO and CO2 depending on the bond strength of the oxygen species on the catalyst surface.

• Journal of the Korean Ceramic Society
• /
• v.27 no.3
• /
• pp.401-411
• /
• 1990

Deposition of diamond films on Si(100) from the mixtures of methane and hydrogen were investigated using hot W filament CVD method. The nucleation density could be increased thousandfold by surface treatment with SiC powder. Upon oxygen addition to the mixture, crystal facets became developed more clearly by selectively removing non-diamond carbons, but the film growth rate generally decreased. However, at a very high methane content(e.g. 10%), a small amount of oxygen addition has resulted in an increase in the film deposition rate presumably by promotion of methane decomposition. When the gas pressure was varied, the growth rate exhibited a maxiumum at around 20torr and the film crystallinity steadily improved with the pressure increase. The observed variation of the growth rate by oxygen addition was discussed in terms of its role in the pyrolysis and the subsequent gas phase reactions.