Methane Oxygen Research Articles

Liquid methane and liquid oxygen horizontal chilldown experiments of a 2.54 and 11.43 cm transfer line

This paper presents new cryogenic two-phase heat transfer coefficient data for the chilldown of large diameter, long propellant transfer lines using liquid oxygen (LOX) and liquid methane (LCH4). At the NASA Neil A. Armstrong Test Facility, as part of the Integrated Cryogenic Propulsion Test Article test campaign which included the first ever cryogenic-lander engine hotfire testing at thermal vacuum conditions, liquid oxygen (LOX) and liquid methane (LCH4) flow boiling data was gathered during propellant feedline conditioning. Ten horizontal chilldown tests were conducted on a 2.54 cm and 11.43 cm transfer line in two different thermal environments, using two cryogens, over the range of inlet pressure (100–450 kPa), mass flux (100–6000 kg/m2*s), Reynolds number (4 × 104–1.32 × 106), and equilibrium quality (−0.02–1.1). These tests report cryogenic chilldown data at the largest diameter lines ever reported. A total of 1,634 data points are added to the consolidated cryogenic chilldown database. Examination of both chilldown and boiling curves shows significant stratification in the larger diameter transfer line, even at highly turbulent Reynolds numbers. Higher inlet pressure always leads to faster chilldown times and higher heat transfer coefficients. Recently developed cryogenic quenching correlations are also compared with experimental results here to comment on the validity of applying the correlations to larger, longer transfer lines.

Porous Glass Microspheres from Alkali-Activated Fiber Glass Waste.

Fiber glass waste (FGW) was subjected to alkali activation in an aqueous solution with different concentrations of sodium/potassium hydroxide. The activated materials were fed into a methane–oxygen flame with a temperature of around 1600 °C. X-ray diffraction analysis confirmed the formation of several hydrated compounds, which decomposed upon flame synthesis, leading to porous glass microspheres (PGMs). Pore formation was favored by using highly concentrated activating alkali solutions. The highest homogeneity and yield of PGMs corresponded to the activation with 9 M KOH aqueous solution.

Repeatability of gaseous measurements across consecutive days in sheep using portable accumulation chambers.

Portable accumulation chambers (PACs) enable gaseous emissions from small ruminants to be measured over a 50-min period; to date, however, the repeatability of consecutive days of measurement in the PAC has not been investigated. The objectives of this study were 1) to investigate the repeatability of consecutive days of gaseous measurements in the PAC, 2) to determine the number of days required to achieve precise gaseous measurements, and 3) to develop a prediction equation for gaseous emissions in sheep. A total of 48 ewe lambs (c. 10 to 11 mo of age) were randomly divided into four measurement groups each day, for 17 consecutive days. Gaseous measurements were conducted between 0800 and 1200 hours daily. Animals were removed from perennial ryegrass silage for at least 1 h before measurements in the PAC, and animals were assigned randomly to each of the 12 chambers. Methane (CH4; ppm) concentration, oxygen (O2; %), and carbon dioxide (CO2; %) were measured at three time points (0, 25, and 50 min after entry of the first animal into the first chamber). To quantify the effect of animal and day variation on gaseous emissions, between-animal, between-day, and error variances were calculated for each gaseous measurement using a linear mixed model. The number of days required to gain a certain precision (defined as the 95% confidence interval range) for each gaseous measurement was also calculated. For all three gases, the between-day variance (39% to 40%) accounted for a larger proportion of total variance compared with between-animal variance, while the repeatability of 17 consecutive days of measurement was 0.36, 0.31, and 0.23 for CH4, CO2, and O2, respectively. Correlations between consecutive days of measurement were strong for all three gases; the strongest correlation between day 1 and the remaining days for CH4, CO2, and O2 was 0.71 (days 1 and 6), 0.77 (days 1 and 2), and 0.83 (days 1 and 5), respectively. A high level of precision was achieved when gaseous measurements from PAC were taken over three consecutive days. The prediction equation overestimated gaseous production for all three gases: the correlations between actual and predicted gaseous output ranged from 0.67 to 0.71, with the r2 ranging from 0.45 to 0.71. The results from this study will aid the refinement of the protocol for the measurement of gaseous emissions in sheep using the PAC.

Chemical modeling for methane oxy-combustion in Liquid Rocket Engines

Methane–oxygen burning is considered for many future rocket engines for practicality and cost reasons. As this combustion is slower than hydrogen–oxygen, flame ignition and stability may be more difficult to obtain. To address these questions, numerical simulation with realistic chemistry is appropriate. However the high pressure and turbulence intensity encountered in rocket engines enhance drastically the stiffness of methane oxy-combustion. In this work, Analytically Reduced Chemistry (ARC) is proposed for accurate chemistry description at a reasonable computational cost. An ARC scheme is specifically derived for typical rocket engine conditions. It is validated by comparison with its parent skeletal mechanism on a series of laminar flames. Then the numerical stiffness of chemistry is overcome with an original approach for time integration, allowing to run simulations close to the acoustic time step whatever the chemical stiffness. It is demonstrated on laminar cases that the flame structure is well preserved, and that numerical stability is ensured while decreasing significantly the computational cost. The performance of ARC with the fast time integration method is finally demonstrated in a 3D Large-Eddy Simulation of a lab-scale Liquid Rocket Engine combustion chamber, where a detailed flame analysis is conducted.

Transient shifts in hydraulic retention times improve the methane production from ruminal hydrolysates of agave bagasse

AbstractBACKGROUNDValorization of lignocellulosic wastes such as agave bagasse from tequila industries can be enhanced using efficient biomass pretreatments. However, the next challenge requires finding the best process conditions to produce methane and remove chemical oxygen demand (COD) from the pretreatment hydrolysates. In this work, an innovative feeding strategy based on alternating hydraulic retention times (HRT) was investigated to improve methane production from ruminal hydrolysates of Agave tequilana bagasse.RESULTSThe ruminal hydrolysate provided a substrate rich in volatile fatty acids (VFA) for direct use in the methanogenic process. The alternating feeding strategy increased the volumetric methane production rate by up to 25% (from 0.76 ± 0.05 to 0.95 ± 0.03 L CH4 L−1 d−1) compared to operating at a constant feeding rate, equivalent HRT of 15 h, and organic loading rate (OLR) of 8 g COD L−1 d−1. The alternating HRT operation improved VFA conversion without modifying the methane yield, and the COD removal was increased by 14%. The system stability, measured through the alkalinity index, was maintained during the proposed feeding strategy and after the increase in OLR.CONCLUSIONThe proposed feeding strategy is a promising tool for improving methane production from agave bagasse hydrolysates. The strategy was robust and easy to apply, which could expand its use for a wider variety of substrates. © 2021 Society of Chemical Industry (SCI).

Proton-conducting Ceramic Fuel Cells for Co-Producing Electricity and Fuel – A Design for Manufacture and Assembly (DFMA) Analysis

This work develops preliminary design for manufacture and assembly (DFMA) models of a novel, proton-conducting, anode-supported ceramic electrochemical cell for co-producing electricity and fuels simultaneously. These DFMA models can then be used to estimated future, expected costs incorporating the novel cell design under various manufacturing production scenarios. The cell electrochemically coverts oxygen (O2) in air and methane (CH4) fuel (the primary constituent of natural gas) into electricity, water, and higher-order hydrocarbons, such as ethane (C2H6). To do this, the cell integrates a methane coupling catalyst into the anode and thereby co-produces ethane (C2H6) and hydrogen (H2) at the anode. The ethane can then be converted into other fuels. The cell is part of a joint R&D effort by Argonne National Laboratory (ANL) and the Illinois Institute of Technology (IIT). The cell’s current technology readiness level (TRL) is about a one (1), i.e. laboratory-scale demonstration of the fundamental concept.Approach:Gaia Energy Research Institute (Gaia) collaborates closely with ANL and IIT to develop the DFMA models for this novel cell design. Gaia works closely with ANL and IIT to identify and analyze key electrochemical cell engineering performance data. Gaia then develops and deploys custom DFMA computer models and data sets. DFMA models center around the electrolyte-electrode assembly (EEA), or the ‘heart’ of the electrochemical cell, where the anode and cathode half-reactions occur. Gaia first develops a specific physical embodiment of the novel cell, then the cell’s bill of materials (BOM), and finally cost estimates for the electrochemical cell, fuel cell stack, and full-scale stationary fuel cell system. Gaia follows this methodology:1. Develop a specific design that physically embodies the EEA concept;2. Develop the EEA’s BOM to specify quantities of components and materials used;3. Identify, for all key materials, price quotes from one or more manufacturers;4. Calculate the minimum costs for the EEA based on materials costs alone;5. Ascertain the EEA’s primary cost drivers;6. Quantify the uninstalled capital costs for a full-size fuel cell stack and stationary fuel cell system incorporating the novel cell design.With the exception of the EEA, other parts of the fuel cell, stack, and system were assumed to be somewhat similar in design to more traditional stationary solid oxide fuel cell (SOFC) systems. Capital costs for the novel stack design were scaled linearly with stack power density. This work estimates stack and system costs for a 100 kWe net electric stack mass-produced at a rate of 50,000 systems per year.Results:Model results indicate that the fuel cell stack subsystem will cost about $478/kW and the entire fuel cell system will cost about $597/kW, including all BOP components. These stack costs are roughly 74% higher than a ‘plain vanilla’ SOFC subsystem, analyzed by the author for DOE in a prior analysis. These system costs are roughly 48% higher than the same ‘plain vanilla’ SOFC system previously analyzed. At the same time, these cost estimates are well below the DOE ARPA-E program goal of < $2,000/kW.Gaia observed an order of magnitude difference in price quotes for several of the specialty ceramic materials investigated. Price quotes from Praxair Specialty Ceramics were approximately double those of Trans-Tech Inc. The reasons cited for the extreme price differential were different manufacturing methods, specifically a chemical co-processing approach for Praxair and a solid-state material manufacturing process (SSMP) for Trans-Tech Inc. The pros and cons of each manufacturing approach are discussed in greater detail in this talk. This analysis assumes that SSMP is used with no degradation in cell performance and bases subsequent cost estimates solely on prices from Trans-Tech Inc., and not Praxair, at ANL’s request.The primary cost driver for the EEA appears to be the BZY-NiO anode substrate. The BZY and NiO anode substrate material is estimated to cost either 2.88 cents/cm2 [based on price quotes for BZY from TransTech Inc.] or 16.40 cents/cm2 [based on price quotes from Praxair Specialty Ceramics]. If the lower BZY cost estimate is taken based on price quotes from Trans-Tech Inc., 52% of the cost derives from the BZY. If the higher BZY cost estimate is taken based on price quotes from Praxair Specialty Ceramics Inc., 92% of the cost derives from the BZY. The secondary cost driver for the EEA appears to be the anode catalyst. The catalyst material is estimated to cost 2.45 cents/cm2. 94% of its cost is due to the material cost of the platinum. The EEA is estimated to cost 5.56 cents/cm2 or $278/kW of gross electric power from the cell or stack.

Towards recognizing the mechanisms of effects evoked in living organisms by static magnetic field. Numerically simulated effects of the static magnetic field upon simple inorganic molecules.

Background: Recognizing effects of static magnetic field (SMF) of varying flux density on flora and fauna is attempted. For this purpose, the influence of static magnetic field upon molecules of water, nitrogen, ammonia, carbon dioxide, methane and molecular oxygen was studied. Methods: Computations of the effect of SMF of 0.1, 1, 10 and 100T flux density were performed in a computer vacuum involving advanced computational methods. Results: It was shown that SMF polarizes molecules depending on applied flux density but it neither ionizes nor breaks valence bonds. Three-molecular conglomerates of very dense packing form systems involving supramolecular orbitals. These orbitals deteriorate with an increase in the SMF flux density developing highly polarized structures. They are entirely different from these originally formed out of SMF. Conclusions: Small inorganic molecules commonly present in living organisms of flora and fauna can substantially influence functioning of those organisms when exposed to SMF.

Subgrid scale modeling considerations for large eddy simulation of supercritical turbulent mixing and combustion

This paper presents a systematic investigation of large eddy simulation (LES) and subgrid scale (SGS) modeling with application to transcritical and supercritical turbulent mixing and combustion. There remains uncertainty about the validity of extending the LES formalism developed for low-pressure, ideal-gas flows to simulations of high-pressure real-fluid flows. To address this concern, we reexamine the LES theoretical framework and the underlying assumptions in the context of real-fluid mixing and combustion. Two-dimensional direct numerical simulations of nonreacting and reacting mixing layers of gaseous methane and liquid oxygen in the thermodynamically transcritical and supercritical fluid regimes are performed. The computed results are used to evaluate the exact terms in the LES governing equations and associated SGS models. Order of magnitude analysis of the exact filtered and subgrid terms in the LES equations and a priori analysis of the simplifications are performed at different filter widths. It is shown that several of these approximations do not hold for supercritical turbulent mixing. Subgrid scale terms, which are neglected in the LES framework for ideal-gas flows, become significant in magnitude compared to the other leading terms in the governing equations. In particular, the subgrid term arising from the filtering of the real-fluid equation of state is shown to be important.

Temporal dynamics of femtosecond-TALIF of atomic hydrogen and oxygen in a nanosecond repetitively pulsed discharge-assisted methane–air flame

The temporal dynamics of the spatial distribution of atomic hydrogen and oxygen in a lean methane–air flame, forced by a nanosecond repetitively pulsed discharge-induced plasma, are investigated via femtosecond two-photon absorption laser-induced fluorescence technique. Plasma luminescence that interferes with the fluorescence from H and O atoms was observed to decay completely within 15 ns, which is the minimum delay required for imaging measurements with respect to the discharge occurrence. During discharge, H atoms in the excited state rather than the ground state, produced by electron-impact dissociation processes, are detected at the flame front. It was found that the temporal evolution of H and O fluorescence intensity during a cycle of 100 µs between two discharge pulses remains constant. Finally, the decay time of O-atoms produced by the discharge in the fresh methane–air mixture was about 2 µs, which suggests a faster reaction between O-atoms and methane than in air.

Bubble dynamics and pressure field characteristics of underwater detonation gas jet generated by a detonation tube

An underwater detonation tube (DT) experiment is carried out in a water tank to investigate the bubble dynamics and pressure field characteristics of an underwater detonation gas jet. In the experiment, a 0.78 liter DT filled with a 0.29 MPa methane–oxygen mixture (equivalent to 0.85 mg of TNT, trinitrotoluene) is detonated. By means of high-speed photography and pressure field measurements, the jet process is divided into four different stages. The evolution patterns and features of the four stages are characterized according to the morphology of the detonation gas bubble, and the dimensionless parameters of the bubble dynamics are defined and calculated using image post-processing. The transmitted shock wave and pressure pulsations of the bubble oscillations are extracted using a low-pass filter with a cutoff frequency of 1000 Hz. The time intervals between consecutive pressure peaks are compared with the oscillation periods obtained from parameter studies of bubble dynamics. The bubble dynamics generated by the sudden release of detonation products in the first oscillation are found to be similar to those of underwater explosions. An expansion-necking structure is observed, formed by the impulsive release of the remaining detonation gas from the DT. A numerical simulation is conducted under the same filling conditions as the experiment to supplement the experimental results. The experiment demonstrates the feasibility of underwater detonation gas jets, which could provide an alternative means of generating pulsation bubbles.

Dedicated setup to isolate plasma catalysis mechanisms

Plasma catalysis, the combination of plasma and catalysis, is used to achieve efficient molecule conversion, supporting the flexibility of operating parameters and feed gases. By combining plasmas with conventional thermal catalysis, the temperature windows may be changed and the process may be made insensitive to catalyst poisoning. However, understanding plasma catalysis mechanisms is extremely difficult, due to the strong coupling between plasma, gas-phase chemistry and surface. A multitude of reaction pathways may be enhanced or reduced by the presence of a plasma that provides excited species as reaction partners. We developed a robust setup to analyse those processes, based on a parallel-plate atmospheric-pressure plasma jet that allows a plug flow design. The plasma chemistry is analysed by Fourier transform infrared absorption spectroscopy and mass spectrometry. The electrodes in contact with the plasma are temperature controlled and can easily be replaced to apply a catalyst on top of them. The basic characteristics of the setup are discussed and three examples for its application are given: (a) the analysis of methane oxidation using the plug flow scheme; (b) the plasma catalytic conversion of CO2, and (c) the plasma catalytic conversion of methane in methane–oxygen mixtures.

Light-Driven C-H Oxygenation of Methane with Chlorine Dioxide

Extensive efforts have been devoted towards the development of methods for the direct conversion from methane (CH4), ethane (CH3CH3), or other abundant natural gasses into useful products, such as the corresponding alcohols, aldehydes, ketones, and carboxylic acids, as liquid fuels and precursors of chemical and pharmaceutical products. Selective aerobic oxygenation of CH4 into liquid products without the concomitant formation of CO2 and CO has served as an elusive target reaction. The one-step transformation of CH4 into methanol (CH3OH) is carried out in nature using methane monooxygenases. However, under chemical conditions, the selective oxygenation of CH4 to CH3OH with molecular oxygen (O2) has been unknown because the oxidation of oxygenated products, CH3OH and formic acid (HCOOH) is much easier than that of CH4, leading to over-oxidation products such as CO and CO2.Here we show that chlorine dioxide radical (ClO2 •) acts as an efficient oxidizing agent in the selective oxygenation of methane under photoirradiation. A fluorous solvent, perfluorohexane (PFH, n-CF3(CF2)4CF3) was chosen as an ideal solvent for CH4 oxygenation for the following reasons. First, PFH is more inert than CH4. It is only comprised of strong C–F bonds and does not contain any C–H bonds; therefore, PFH does not react with CH3 • and Cl• intermediates in the oxygenation of CH4. Notably, PFH can dissolve gaseous substrates such as CH4, CH3CH3, and O2 very well. Additionally, oxygenated products such as CH3OH and HCOOH, as well as water, are insoluble in PFH. Thus, if a two-phase PFH/water system was used for the oxygenation of CH4, the reaction would occur in the fluorous phase, and the products would be transferred into the aqueous phase without further oxygenation to CO and CO2. Towards that end, herein, we report the two-phase photooxygenation of CH4 by molecular oxygen (O2) with chlorine dioxide radical (ClO2 •) in PFH/H2O under ambient conditions to produce oxygenated products such as CH3OH and HCOOH.The oxygenation of CH4 (1.0 mM) with ClO2 • (1.0 mM) did not proceed in the dark. In contrast, the photochemical oxygenation of CH4 with O2 occurred to form CH3OH and HCOOH under photoirradiation with a xenon lamp (500 W) in an aqueous solution at 298 K and 1 atm for 2 h. The yields of CH3OH and HCOOH were 5% and 25%, respectively, as determined by 1H NMR and gas chromatography-mass (GC-MS) spectroscopies. The conversion of CH4 was determined to be 30% by 1H NMR. The selectivity of the formation of CH3OH and HCOOH was >99%, based on the consumption of CH4.2 Further improvement of the product yield by employing a two-phase system instead by one-phase aqueous system, a CH4-saturated solution of PFH (1.0 mL) was added to an oxygen-saturated aqueous solution containing ClO2 • (1.0 mM) to prepare a two-phase system; oxygenation of CH4 (1.0 mM) in an aqueous liquid-liquid two-phase solution (1:1 v/v) comprised of PFH and distilled water was carried out under the same conditions. CH4 dissolved in the aqueous and fluorous phases was completely consumed following photoirradiation for 15 min. The product yields of CH3OH and HCOOH were improved to 14% and 85%, respectively, as determined by the 1H NMR analyses of the aqueous phase. The selectivity of the CH3OH and HCOOH formation was >99%, based on the initial concentration of CH4. The formation of further oxygenated products such as CO and CO2, was not observed under the present reaction conditions. The quantum yield of the photo-driven CH4 oxygenation was130%, as determined by actinometric measurements using monochromatized light. When CH4 was replaced with ethane (CH3CH3), light-driven oxygenation also occurred to yield CH3CH2OH (19%) and CH3COOH (78%) under the otherwise same reaction conditions. The photochemical oxygenation of methane is initiated by generation of chlorine radical and singlet oxygen from photoexcited state of ClO2 •, leading to the final products by aerobic radical chain processes. Thus, the present study provides an environmentally benign approach towards the photooxidation of organic compounds. The photochemical oxygenation using ClO2 • reported herein could be generalized to provide novel chemical reactions, which may have significant implications in synthetic, pharmaceutical and polymer chemistry.3 Ohkubo, K.; Hirose, K.; Shibata, T.; Takamori, K.; Fukuzumi, S. Phys. Org. Chem. 2017, 30, e3619.Ohkubo, K.; Hirose, K. Chem. Int. Ed. 2018, 57, 2126-2129.Ohkubo, K.; Asahara, H.; Inoue, T. Chem. Commun. 2019, 55, 4723-4726.

Reaction of Lavandula angustifolia Mill. to Water Treated with Low-Temperature, Low-Pressure Glow Plasma of Low Frequency

Lavandula angustifolia was watered with either deionized tap water treated with low-temperature, low-pressure glow plasma of low frequency in the air (LPGPA), under oxygen-free nitrogen (LPGPN), methane (LPGPM), carbon dioxide (LPGPC) or molecular oxygen (LPGPO). The crop yields were slightly dependent on the type of water used for watering. Notably, only plants watered with LPGPN showed a slightly higher crop yield. The plants also contained a higher level of protein and bioaccumulated magnesium. The type of water had a considerable and specific effect on the yield of isolated essential oils and their composition. The yield of essential oil decreased in the following order LPGPA = LPGPN (0.4 g/100 g dry mass) &gt; LPGPC = LPGPO (0.3 g/100 g dry mass) &gt; LPGPM = non-treated water (0.2 g/100 g dry mass). The composition of the isolated essential oils varied depending on the type of water used for watering, which influences their role as a fragrant component of cosmetics, and in herbal therapy and aromatherapy.

Thermal and Physical Properties of Methane Family Hydrocarbon and Oxygen Combustion Products in State-of-the-Art Arc Steel Furnace

The work deals with the particular combustion characteristics of methane family hydrocarbons (methane, ethane, propane, butane) and wet natural gas with process oxygen at carbon dioxide and water steam dissociation in a state-of-the-art arc steelmaking furnace. An algorithm is developed to calculate chemistry, the amount and concentration of combustion products at carbon dioxide and hydrogen dissociation, their physical and thermophysical parameters; heating power, balance and actual temperature, heat and pyrometric factors are evaluated considering heat transfer by radiation into unbounded medium. Based on the calculation results the recommendations are given for development of cold charge material heating conditions in order to minimize dusting, carbon oxide and hydrogen and charge material loss.

Recent Progress, Development Trends, and Consideration of Continuous Detonation Engines

The continuous detonation engine (CDE) is based on detonation waves and is a new jet engine concept that is expected to bring a technical revolution to current aviation and aerospace propulsion systems. Some scholars have also called this concept the continuously rotating detonation engine or rotating detonation engine. The advantages and application potential of the CDE have been widely recognized and verified with research focused in three directions: continuous detonation rocket engines, continuous detonation ramjet engines, and continuous detonation turbojet engines. This paper reviews recent progress (primarily in the last five years) of CDE from the perspective of engineering applications. Research on continuous detonation rocket engines has gone from concept exploration to mechanism research, and it is moving toward engineering applications. Large-scale prototype testing may be the next step, especially with experiments based on liquid methane and liquid oxygen that need further development. The continuous detonation ramjet engine is still in the conceptual design and principle exploration stages. To adapt to broader inflow conditions and working Mach numbers, the combination of different working modes of a CDE may be of further interest. The continuous detonation turbojet engine is still in the scheme demonstration stage. Significant research work is needed in terms of experimental, numerical, and theoretical analyses, especially toward finding individual phenomena, mechanism exploration, and multicomponent coupling test. The performance of continuous detonation with solid fuels will also benefit from additional investigations and verifications.

A computational study of CO oxidation on IrO2 (1 1 0) surface

Though, oxygen-rich iridium oxide (O-IrO2 (110)) surface exhibits excellent catalytic activity towards methane activation and oxygen evolution reactions, the CO oxidation mechanism on this surface remains elusive. Here, we used density functional theory calculations, ab initio molecular dynamics (AIMD), and microkinetic simulations to explore the CO oxidation reactions via Langmuir-Hinshelwood (L-H), Eley-Rideal (E-R), and Mars-Van Krevelen (MvK) mechanisms on O-IrO2 (110) surface. We find that the C-O coupling and CO2 desorption are the rate-determining steps in L-H and E-R mechanisms, respectively. The CO oxidation via the MvK mechanism on the IrO2 (110) surface is more difficult to proceed. Both AIMD and microkinetic simulation results demonstrate that CO2 can desorb from the O-IrO2 (110) surface at 400 K. The production temperature of CO2 on the O-rich IrO2 (110) surface via E-R mechanism is lower than that via the L-H mechanism. Therefore, we predict that the O-rich IrO2 (110) surface can accelerate the CO oxidation reaction rate.

Methane–oxygen detonation characteristics at elevated pre-detonation pressures

The detonation characteristics of methane–oxygen mixtures at pre-detonation pressures of 101–1,013 kPa were investigated in a detonation tube. Both pure methane–oxygen mixtures and mixtures with argon dilution were explored. Measurements made include cell sizes via soot foil, wave speed via high speed ion probes / pressure transducers, and temperature / H2O molar concentration profiles via 100 kHz absorption spectroscopy. Measured cell widths agreed with predicted cell widths based on a ZND length correlation. In addition, the power law fit of cell width with pre-detonation pressure agreed with previous data at less than 101 kPa. Measured detonation wave speeds agreed within 3% of Chapmen-Jouguet for all cases. H2O molar density and temperature were successfully captured up to 507 kPa. However, above 507 kPa pre-detonation pressure, low signal to noise ratio and poor spectral fits at the extreme conditions of the von Neumann spike resulted in unacceptable uncertainty. These results provide a unique dataset to validate kinetics models and high-fidelity computation fluid dynamics codes for methane-oxygen detonations at elevated pre-detonation pressures relevant to rotating detonation rocket engines.

Time and space resolved diagnostics for plasma thermal-chemical instability of fuel oxidation in nanosecond plasma discharges

An instability in a nanosecond pulsed dielectric barrier discharge plasma occurring in methane–oxygen–argon mixtures is experimentally observed and measured by 1D time-resolved in situ electric field measurements. This instability, which seems to be created by the positive feedback between plasma kinetics and plasma-assisted low temperature fuel oxidation, is studied using electric field induced second harmonic generation and direct ICCD imaging. The rapid formation of streamers from an originally uniform discharge appears to be caused by the chemical kinetics of plasma-assisted low temperature methane oxidation, which may be resulting in a new type of plasma instability: a thermal-chemical instability. The results also revealed that the occurrence of this possible thermal-chemical instability in a reactive flow drastically changes the plasma properties by forming multiple secondary discharges and possibly leads to micron-sized non-uniform electric distributions. Single shot uncalibrated measurements of the electric field of the micron sized streamers appears to show much greater strengths than the average electric field. Furthermore, one-dimensional data analysis shows the positive feedback loop between the streamers and the low temperature plasma assisted oxidation chemistry in the plasma thermal-chemical instability. The present finding advances the understanding plasma instability growth and provides a new way to control plasma uniformity in plasma-assisted combustion and plasma fuel reforming.

Role of instability on the limits of laterally strained detonation waves

The present work examines the role of instability and diffusive phenomena in controlling the limits of detonations subject to lateral strain. Experiments were conducted in mixtures with varying levels of cellular instability, i.e., stoichiometric methane–oxygen (CH4/2O2), ethylene–oxygen (C2H4/3O2), and ethane–oxygen (C2H6/3.5O2). These detonations were propagated in channels with exponentially enlarging cross-sections, following the recent works of Radulescu and Borzou (2018) and Xiao and Radulescu (2020). Steady detonation waves were obtained at the macro-scale, with the near-limit reaction zone structures characterized by significant unreacted gas pockets. The turbulent flame burning velocity of these pockets was evaluated to be 30 m/s to 70 m/s, which is larger than the theoretical laminar value by a factor of 2 to 7 and smaller than the CJ deflagration speed by a factor of 2 to 3. For all the mixtures tested, the characteristic D−K relationships, relating the detonation mean propagation speed with lateral flow divergence, were obtained directly from experiments and as well from the generalized ZND model with lateral strain rates using detailed chemical kinetics. The results showed that the degree of departure between experiments and the theoretical predictions increases significantly with the detonation instability level. As compared to the laminar ZND wave, the more unstable detonations are much more detonable than the more stable detonations, with substantially larger limiting divergence rates and maximum velocity deficits. Such enhanced detonability with detonation instability can be manifested in the significantly enhanced global rates of energy release with the notably suppressed thermal character of ignition for the more unstable detonations. This globally enhanced burning mechanism is found to be realized by the intensified auto-ignition assisted by the turbulent diffusive burning of the unreacted gas pockets, substantially shortening the characteristic reaction zone lengths. Finally, the relatively good universality of the D/DCJ−Keffλ relations implicitly suggests that cell size is also a function of the detonation wave stability, since it is controlled by the reaction zone thickness of unstable detonations.

Effect of Hydrogen, Carbon Monoxide, Synthesis Gas, and Steam Additives on the Characteristics of Matrix Conversion of Rich Methane–Oxygen Mixtures

An experimental study and detailed kinetic modeling of characteristics of the matrix conversion of a methane–oxygen mixture with the addition of hydrogen, carbon monoxide, synthesis gas, and steam have been carried out. It has been shown that the most significant effect on the product composition is provided by the admixture of steam, which reduces the yield of acetylene and at the same time increases the H2/CO ratio. The kinetic simulation results appear to agree well with the experimental data obtained.