Ammonia Pressure Research Articles

Investigation of NO emission characteristics from co-combustion of methane and ammonia at high-altitude areas

The high-altitude areas of China are abundant in renewable energy and have a natural advantage in ammonia production. Based on this advantage, this paper proposes a co-combustion strategy for methane and ammonia to reduce carbon emissions in these areas. However, the NO emission characteristics associated with this strategy remain uncertain. A custom-designed combustion system capable of simulating high-altitude environments was used to investigate the effect of ammonia mixing ratio, equivalence ratio, and pressure on NO emission in methane/ammonia/air flames. Additionally, chemical kinetic calculations were conducted to explore the mechanisms of how sub-atmospheric pressure influences NO emission. The results indicate that for stoichiometric flames, NO increases with the ammonia mixing ratio. In fuel-rich flames, NO remains nearly constant once the ammonia mixing ratio exceeds 10%. Sub-atmospheric pressure leads to higher NO, particularly in fuel-rich flames, where the increase can reach up to 24.4%. Analysis of nitrogen reaction pathways and key radical concentrations reveals that sub-atmospheric pressure has a minimal effect on nitrogen conversion pathways. The variation in NO is achieved by altering the pathway contributions and the concentrations of H, NH, and N. This work provides direction and guidance for improving the application of methane and ammonia co-combustion in high-altitude areas.

Monte Carlo simulation of an ammonia adsorption refrigeration system based on calcium chloride impregnated nanoporous carbon.

We use Monte Carlo simulations to investigate the effect of incorporating calcium chloride salt into nanoporous carbon on the performance of an ammonia-carbon adsorption refrigeration system. Simulations of ideal carbon slit-pores with pore sizes of 1, 2, and 3nm, each containing calcium chloride with ion densities of 0.0, 0.25, and 0.5nm-3, were carried out at temperatures between 0 and 30 °C and ammonia pressures up to 15.0 bar. The results reveal that ideal 1nm pores are able to achieve a good refrigeration performance using waste heat below 100 °C to drive the process, but adding salt to these pores increases the waste heat temperature required beyond 100 °C. However, ideal 2nm pores require the addition of 0.25nm-3 salt to achieve a similar performance, while the 3nm pores were unable to achieve a satisfactory refrigeration performance. Considering that real nanoporous carbons usually feature a variety of specific adsorption sites and non-ideal geometries that should have a similar impact to adding salt, these results indicate that nanoporous carbons with pores in the range of 1-2nm are likely to hold the most promise for adsorption refrigeration applications and that the addition of salt may not always be helpful.

Comparative performance assessment of different halide composites in sorption cooling system: A dynamic approach

The adsorption technique presents a promising approach for cooling, heat storage, and gas storage. This study focuses on the viability of adsorption in cooling applications, specifically utilizing various halide salts in conjunction with thermal energy, highlighting its potential as an energy-efficient solution for modern energy demands. A dynamic numerical model is developed and used to study the performance of transverse finned reactor-based adsorption cooling system (ACS) with different halide composite salts. The simulations are carried out at different supply pressures ranging from 3.55 bar to 7.28 bar corresponding to saturation pressure of ammonia at an evaporator temperature ranging from −5 ℃ to 15 ℃ during adsorption. The desorption process is simulated at different regeneration temperatures with a required desorption pressure of 17.28 bar corresponding to saturation pressure at condenser operating temperature of 40 ℃. The average cooling power produced in first 60 min of system operation at an evaporator temperature of −5 ℃ is 4.89 W, 207 W, 206 W and 925 W with the use of BaCl2, CaCl2, SrCl2 and MnCl2 composites respectively. The theoretical maximum coefficient of performance (COP) obtained are 0.31, 0.365, 0.308 and 0.552 with BaCl2, CaCl2, MnCl2 and SrCl2 respectively. The cooling power (CP) is increasing with increase in evaporator temperature. The shortest adsorption completion time is observed at 15 ℃ of evaporator temperature with all metal halides used. The lowest adsorption time is observed with MnCl2 composite salt and highest with BaCl2 composite salt. The regeneration time of all composite salt beds is decreasing with increase in regeneration temperature.

Study of GaN solubility in ammonothermal alkaline solution

The solubility of gallium nitride in supercritical ammonia containing an alkaline mineralizer, sodium amide, was investigated. Twenty dissolution processes were carried out at constant ammonia pressure and constant mineralizer concentration. In each process, the solubility of four ammonothermal GaN crystals was analyzed at four different temperatures and five different times. By analyzing the total mass loss of all crystals in a given process, the time interval at which the solubility of GaN stopped changing was determined, indicating the saturated state of the solution. Based on these data, the solubility curve was determined. Retrograde solubility was observed. The impact of surface preparation of GaN samples and its correlation with the quantity of dissolved material was investigated. It was shown that as-grown and optically smooth surfaces dissolved slower than mechanically treated (000-1) GaN surfaces. These are important data for ammonothermal crystallization processes using native GaN seeds with differently prepared (000-1) surfaces.

Performance of a High-Speed Pyroelectric Receiver as Cryogen-Free Detector for Terahertz Absorption Spectroscopy Measurements

The application of terahertz (THz) radiation in scientific research as well as in applied and commercial technology has expanded rapidly in recent years. One example is the progress in high-resolution THz spectroscopy based on quantum cascade lasers, which has enabled new observations in astronomy, atmospheric research, and plasma diagnostics. However, the lack of easy-to-use and miniaturised detectors has hampered the development of compact THz spectroscopy systems out of the laboratory environment. In this paper, we introduce a new high-speed pyroelectric receiver as a cryogen-free detector for THz absorption spectroscopy. Its performance is characterised by absorption spectroscopy measurements on a reference gas cell (RGC) with ammonia using a tunable THz quantum cascade laser at approximately 4.75 THz as the light source. It is shown that the receiver can record spectra up to 281 Hz without any artefacts to the observed spectral absorption profile, and the results reproduce the known pressure of ammonia in the RGC. This demonstrates that the pyroelectric receiver can be reliably used as an alternative to helium-cooled bolometers for absorption spectroscopy measurements in the THz range, with its main advantages being the high bandwidth, compactness, relatively low cost, and room-temperature operation. Its simplicity and high sensitivity make this receiver a key component for compact THz spectroscopy systems.

Investigation on the combustion of ammonia using direct high/medium-pressure-Otto injection approach in a diesel two-stroke marine slow speed engine

The urgent need to reduce exhaust gas emissions has led to increased research activities on the potential of using ammonia as fuel in marine engines. Various researchers have already investigated the combustion of ammonia specifically in two-stroke, slow-speed marine engines, and obtained promising results. In the available literature, both high-pressure direct injection-Diesel (HPDF) and low-pressure direct injection dual fuel - Otto (LPDF) two-stroke engines have been well-researched. This study numerically investigates the potential of using a direct high/medium pressure (Otto) ammonia injection strategy on a marine two-stroke engine. A diesel-fueled engine was retrofitted with ammonia injectors on the cylinder head. The effects of ammonia injection direction, timing, and injection pressure on the combustion efficiency, engine performance, and exhaust gas emissions were investigated to ensure optimum injection parameters. Ammonia substitution rate (ASR) ranging from 40 to 80 % was used in this study. The investigated injection strategy revealed flexibility in achieving the original pure diesel engine power over a wide range of injection pressures (700-200 bar). At 80 %, ASR CO2 emissions were reduced up to 80 % while NOx emissions attained Tier II emission limits. The results of this study are helpful in the development process of ammonia dual-fuel marine two-stroke engines.

Dynamic inversion and correction of ammonia pressure within the range 6611–6614 cm−1

Laser absorption spectroscopy is widely applied in gas concentration detection while the measurement accuracy would be affected by fluctuations in the environmental pressure (pressure fluctuations inside the gas cell under vacuum conditions). In this paper, a dynamic inversion and correction method of gas pressure without pressure sensors was proposed. Ammonia within the range of 6611–6614 cm−1 was selected as the research object. In contrast to previous reports, this method does not investigate the effect of pressure on gas concentration detection from a single point of view, or obtain pressure values from pressure sensors. Instead, the real-time temperature was measured to determine the broadening coefficient, which was then utilized along with full width at half-maximum (FWHM) of the spectral lines to calculate the real-time pressure value before correction. The directly acquired pressure has an error, and based on the error analysis, the pressure is corrected to get the corrected real-time pressure value. Finally, the effect of systematic error was eliminated by correcting the concentration using the corrected real-time pressure value and the measured real-time temperature. Experimental results show that the average residual of the corrected real-time pressure compared to the measured true values was 0.1993 torr with a standard deviation of 0.7387 torr. The correlation coefficient R2 between the inverted pressure value and the measured true value was 0.999, with a maximum fitting error of 1.19 %, error fluctuations within 2 %, and pressure uncertainty ranging from 0.545 % to 0.913 %. Furthermore, the ammonia concentration was corrected, and the maximum error compared to the standard ammonia concentration injected in the experiment was 1.025 % (with an effective optical path length of the detection gas cell of 15 cm). This work demonstrated the effectiveness of the proposed method in accurately inverting dynamic real-time pressure values and improving the accuracy of gas concentration measurement.

The equilibrium vapor pressures of ammonia and oxygen ices at outer solar system temperatures

Few laboratory studies have investigated the vapor pressures of the volatiles that may be present as ices in the outer solar system; even fewer studies have investigated these species at the temperatures and pressures suitable to the surfaces of icy bodies in the Saturnian and Uranian systems (<100 K, <10−9 bar). This study adds to the work of Grundy et al. (2024) in extending the known equilibrium vapor pressures of outer solar system ices through laboratory investigations at very low temperatures. Our experiments with ammonia and oxygen ices provide new thermodynamic models for these species’ respective enthalpies of sublimation. We find that ammonia ice, and to a lesser degree oxygen ice, are stable at higher temperatures than extrapolations in previous literature have predicted. Our results show that these ices should be retained over longer periods of time than previous extrapolations would predict, and a greater amount of these solids is required to support observation in exospheres of airless bodies in the outer solar system.

Vapor compression and energy dissipation in a collapsing laser-induced bubble

The composition of the gaseous phase of cavitation bubbles and its role on the collapse remains to date poorly understood. In this work, experiments of single cavitation bubbles in aqueous ammonia serve as a novel approach to investigate the effect of the vapor contained in a bubble on its collapse. We find that the higher vapor pressure of more concentrated aqueous ammonia acts as a resistance to the collapse, reducing the total energy dissipation. In line with visual observation, acoustic measurements, and luminescence recordings, it is also observed that higher vapor pressures contribute to a more spherical collapse, likely hindering the growth of interface instabilities by decreasing the collapse velocities and accelerations. Remarkably, we evidence a strong difference between the effective damping and the energy of the shock emission, suggesting that the latter is not the dominant dissipation mechanism at collapse as predicted from classical correction models accounting for slightly compressible liquids. Furthermore, our results suggest that the vapor inside collapsing bubbles gets compressed, consistently with previous studies performed in the context of single bubble sonoluminescence, addressing the question about the ability of vapors to readily condense during a bubble collapse in similar regimes. These findings provide insight into the identification of the influence of the bubble content and the energy exchanges of the bubble with its surrounding media, eventually paving the way to a more efficient use of cavitation in engineering and biomedical applications.

Effect of Machine Learning Algorithms on Prediction of In-Cylinder Combustion Pressure of Ammonia–Oxygen in a Constant-Volume Combustion Chamber

Road vehicles, particularly cars, are one of the primary sources of CO2 emissions in the transport sector. Shifting to unconventional energy sources such as solar and wind power may reduce their carbon footprints considerably. Consequently, using ammonia as a fuel due to its potential benefits, such as its high energy density, being a carbon-free fuel, and its versatility during storage and transportation, has now grabbed the attention of researchers. However, its slow combustion speed, larger combustion chamber requirements, ignition difficulties, and limited combustion stability are still major challenges. Therefore, authors tried to analyze the combustion pressure of ammonia in a constant-volume combustion chamber across different equivalence ratios by adopting a machine learning approach. While conducting the analysis, the experimental values were assessed and subsequently utilized to predict the induced combustion pressure in a constant-volume combustion chamber across various equivalence ratios. In this research, a two-step prediction process was employed. In the initial step, the Random Forest algorithm was applied to assess the combustion pressure. Subsequently, in the second step, artificial neural network machine learning algorithms were employed to pinpoint the most effective algorithm with a lower root-mean-square error and R2. Finally, Linear Regression illustrated the lowest error in both steps with a value of 1.0, followed by Random Forest.

Stabilisation of solid-state cubic ammonia confined in a glass substance at ambient temperature under atmospheric pressure.

Ammonia, a widely available compound, exhibits structural transitions from solid to liquid to gas depending on temperature, pressure, and chemical interactions with adjacent atoms, offering valuable insights into planetary science. It serves as a significant hydrogen storage medium in environmental science, mitigating carbon dioxide emissions from fossil fuels. However, its gaseous form, NH3(g), poses health risks, potentially leading to fatalities. The sublimation pressure (psub) of solid cubic ammonia, NH3(cr), below 195.5 K is minimal. In this study, we endeavoured to stabilise NH3(cr) at room temperature for the first time. Through confinement within a boric acid glass matrix, we successfully synthesised and stabilised cubic crystal NH3(cr) with a lattice constant of 0.5165 nm under atmospheric pressure. Thermodynamic simulations affirmed the stabilisation of NH3(cr), indicating its quasi-equilibrium state based on the estimated standard Gibbs energy of formation, . Despite these advancements, the extraction of H2(g) from NH3(cr) within the boric acid glass matrix remains unresolved. The quest for an external matrix with catalytic capabilities to decompose inner NH3(cr) into H2(g) and N2(g) presents a promising avenue for future research. Achieving stability of the low-temperature phase at ambient conditions could significantly propel exploration in this field.

Ammonia powered thermal-responsive smart window with spectral regulation of Cu2+ and sodium copper chlorophyllin

Thermal responsive windows are highly promising for the next-generation architecture for their self-powered solar transmittance. However, existing thermochromic techniques, include VO2- and hydrogel-based systems, have not been used for large-scale in window applications, because of the technical obstacles such as low luminous transmittance (Tlum), poor solar modulation ability (ΔTsol), high transition temperature (Tc) and high haze rate. To tackle those issues, a new thermal-responsive design, i.e., the Ammonia Pressure Powered smart (APPs) window, was proposed, with Cu2+ and sodium copper chlorophyllin (SCC) providing solar spectrum management. In comparisons to traditional thermochromic windows, the new concept of APPs window shows significant energy-related advances. Particularly, a feasible Tc (24–36 °C), outstanding ΔTsol (67 %), and high Tlum in both cold (84 %) and hot (47.4 %) states are reported in this study. In addition, outdoor experimental test of the APPs window demonstrated that it could produce a rational daylight level of both photopic effects and melanopic effects, whilst reduce the room temperature by about 4 °C on hot sunny day. Furthermore, energy simulations conducted for the APPs window in three different cities (Singapore, Hong Kong and Harbin) indicate its superior performance, compared to the double-layered low-e glazing windows, across various climatic conditions. With cost-effective materials and excellent performance, the authors believe that this new APPs window represents a smart and sustainable solution for the development of next-generation green buildings.

Flexible operation, optimisation and stabilising control of a quench cooled ammonia reactor for power-to-ammonia

This paper discusses the operation of an ammonia reactor for a Power-to-Ammonia (P2A) plant. We develop a dynamic model for an ammonia reactor system consisting of a three-bed quench cooled adiabatic reactor and a feed-effluent heat exchanger. The reactor bed model is formulated as a differential algebraic equations (DAE) system. We use the thermodynamic software Thermolib for rigorous modelling of the thermodynamic functions in the high pressure ammonia reactor. We present a case study of an ammonia synthesis loop in a P2A plant connected to a 250 MW renewable energy source with a capacity factor of 0.4. Static optimisation and stability analysis are performed for the reactor system, which located the optimal operating point close to instability. The dynamic simulations confirm the unstable operating regions as severe oscillations arise. A fluctuating energy supply from renewable sources requires the ammonia reactor to operate over a wide operating window from 20%–120% of nominal capacity. We formulate a realistic strategy for varying the supply of H2 and N2 (load) to the synthesis loop depending on the available energy. Open-loop simulations show that varying the synthesis feed flow cause oscillations in the ammonia reactor system. Therefore, we propose a regulatory control structure for stabilising the ammonia reactor. The optimisation algorithm determines the reactor set-point state by updating at changes to the synthesis loop load. Hereby, we achieved fast control and close tracking of the set-points for the ammonia reactor.

High pressure ammonia oxidation in a flow reactor

The present work deals with an experimental and modeling analysis of ammonia oxidation at high pressure (up to 40 bar), in the 600–1275 K temperature range using a quartz tubular reactor and argon as diluent. The impact of temperature, pressure, oxygen stoichiometry and presence of NO has been analyzed on the concentrations of NH3 and N2 obtained as main products of ammonia oxidation. The main results obtained indicate that increasing either pressure or stoichiometry results in a shift of NH3 conversion to lower temperatures. The effect of pressure is particularly significant in the low range of pressures studied. The main product of ammonia oxidation is N2, while NO, NO2 and N2O concentrations are below the detection limit for all the conditions considered. The experimental results are simulated and interpreted in terms of a literature detailed chemical kinetic mechanism, which, in general, predicts satisfactorily the experimental results.

Analysis of thermodynamics, kinetics, and reaction pathways in the amination of secondary alcohols over Ru/SiO2

This work considers the Ru-mediated amination of secondary alcohols with ammonia in vapor and liquid media. We map thermodynamic constraints, and we probe the impacts of species partial pressure, residence time, and reaction temperature on rate, selectivity, and catalyst stability. Alcohol amination consumes no H2, and H2 has no significant impact on amination kinetics; however, operating under H2 benefits Ru stability. Primary amine selectivity increases with ammonia pressure and alcohol conversion, and the latter observation is consistent with the formation of primary amines through a network of sequential reactions. Unfortunately, primary amines are susceptible to secondary deamination to form hydrocarbons. As is typical of processes that seek to isolate a reactive intermediate, the main selectivity challenge here is identifying residence times that are long enough to accumulate high substrate conversion but short enough to avoid secondary deamination. In general, moderate residence times will maximize the production of primary amines. Insights extend across a broad substrate scope, and we observe 70 – 90% yield of primary amines from linear, cyclic, and heterocyclic alcohols. That said, heterocyclic alcohols appear susceptible to product inhibition, so achieving high conversions requires longer residence times and/or increased ammonia pressures.

Physiological Responses of Methanosarcina barkeri under Ammonia Stress at the Molecular Level: The Unignorable Lipid Reprogramming.

Acetotrophic methanogens' dysfunction in anaerobic digestion under ammonia pressure has been widely concerned. Lipids, the main cytomembrane structural biomolecules, normally play indispensable roles in guaranteeing cell functionality. However, no studies explored the effects of high ammonia on acetotrophic methanogens' lipids. Here, a high-throughput lipidomic interrogation deciphered lipid reprogramming in representative acetoclastic methanogen (Methanosarcina barkeri) upon high ammonia exposure. The results showed that high ammonia conspicuously reduced polyunsaturated lipids and longer-chain lipids, while accumulating lipids with shorter chains and/or more saturation. Also, the correlation network analysis visualized some sphingolipids as the most active participant in lipid-lipid communications, implying that the ammonia-induced enrichment in these sphingolipids triggered other lipid changes. In addition, we discovered the decreased integrity, elevated permeability, depolarization, and diminished fluidity of lipid-supported membranes under ammonia restraint, verifying the noxious ramifications of lipid abnormalities. Additional analysis revealed that high ammonia destabilized the structure of extracellular polymeric substances (EPSs) capable of protecting lipids, e.g., declining α-helix/(β-sheet + random coil) and 3-turn helix ratios. Furthermore, the abiotic impairment of critical EPS bonds, including C-OH, C═O-NH-, and S-S, and the biotic downregulation of functional proteins involved in transcription, translation, and EPS building blocks' supply were unraveled under ammonia stress and implied as the crucial mechanisms for EPS reshaping.

The effect of ammonia partial pressure on the growth of semipolar (11–22) InGaN/GaN MQWs and LED structures

This paper presents the effect of ammonia partial pressure at a relatively low fixed V/III (∼765) growth atmosphere on the growth of multi-quantum well (MQW) structures and the light emitting diode (LED) emission wavelength. At fixed V/III ratio, ammonia partial pressure together with the consequent group III partial pressures are shown to influence the growth of InGaN/GaN MQWs in term of growth rate and the indium incorporation for the quantum well. It is also observed that the growth of InGaN quantum well (QW) behaves differently as compared to GaN quantum barrier (QB) at low V/III ambient. For the growth of InGaN QW, the data collected shows the existence of threshold point for ammonia partial pressure of ∼300 Pa. In the regime below the threshold value, the decomposition of InGaN due to severe dissociation of In-N bonds caused the growth rate to be extremely low. As the ammonia partial pressure increases above the threshold value, the growth rate of InGaN QW increases sharply together with an improvement in indium incorporation, as proven by the XRD and (11–24) asymmetric reciprocal space mapping (RSM) results. The XRD result is consistent with the atomic force microscopy (AFM) results. As the partial pressures increases, the RMS and peak-to-valley roughness increases which is credited to the increment in indium incorporation. Furthermore, “needle-like” structures can be observed over all samples when the MQWs were grown with limited ammonia partial pressure. During the growth for the LED structure with thin layers of InGaN/GaN, the partial pressure of ammonia became a dominating factor in the formation of well-abrupt layer interfaces. Through the XRD and room-temperature photoluminescence (RTPL) results, it is shown that abrupt layers can be formed at higher ammonia partial pressures, while indium clusters tend to form at a lower partial pressure, which are most probably due to the insufficient N concentration, while the electroluminescence (EL) results were consistent as well. Therefore, it is once again confirmed that the performance of the InGaN/GaN LED is highly governed by the partial pressures of the ammonia.

Synthesis of Colloidal GaN and AlN Nanocrystals in Biphasic Molten Salt/Organic Solvent Mixtures under High-Pressure Ammonia.

Group III nitrides are of great technological importance for electronic devices. These materials have been widely manufactured via high-temperature methods such as physical vapor transport (PVT), chemical vapor deposition (CVD), and hydride vapor phase epitaxy (HVPE). The preparation of group III nitrides by colloidal synthesis methods would provide significant advantages in the form of optical tunability via size and shape control and enable cost reductions through scalable solution-based device integration. Solution syntheses of III-nitride nanocrystals, however, have been scarce, and the quality of the synthesized products has been unsatisfactory for practical use. Here, we report that incorporating a molten salt phase in solution synthesis can provide a viable option for producing crystalline III-nitride nanomaterials. Crystalline GaN and AlN nanomaterials can be grown in a biphasic molten-salt/organic-solvent mixture under an ammonia atmosphere at moderate temperatures (less than 300 °C) and stabilized under ambient conditions by postsynthetic treatment with organic surface ligands. We suggest that microscopic reversibility of monomer attachment, which is essential for crystalline growth, can be achieved in molten salt during the nucleation and the growth of the III-nitride nanocrystals. We also show that increased ammonia pressure increases the size of the GaN nanocrystals produced. This work demonstrates that use of molten salt and high-pressure reactants significantly expands the chemical scope of solution synthesis of inorganic nanomaterials.

Optimizing Reaction-Absorption Process for Lower Pressure Ammonia Production

Optimizing Reaction-Absorption Process for Lower Pressure Ammonia Production

Design and Analysis of Novel CO2 Conditioning Process in Ship-Based CCS

In this work, CO2 conditioning processes for ship-based CCS sequestration are modelled using the software APSEN HYSYS V11. This study uses the captured CO2 gas from the 3D project as the feed. The feed stream contains water, H2S, and CO as contaminants. The purification processes for dehydration, desulfurization, and CO removal are reviewed. Two liquefaction approaches, the open-cycle and the closed-cycle liquefaction, are modelled and compared for transport pressures 7 and 15 bar. It is found that the energy requirement of the open-cycle process is higher than that of the closed-cycle liquefaction process. For the closed-cycle design, two refrigerants, ammonia and propane, are considered. Results show that the energy requirement of the process using ammonia is lower than that of propane. When comparing the two transport pressures, it is found that liquefaction at 15 bar requires less energy than 7 bar. On top of that, both refrigerants are unsuited for the liquefaction of CO2 at 7 bar, as their operating pressures are below 1 atm. Several optimization concepts are tested on the closed-cycle liquefaction design. The net power consumption of the closed-cycle liquefaction is reduced when CO2 is precooled using the intermediate pressure ammonia streams and the cold from the CO stripper.