Effect Of Oxygen Enrichment Research Articles

Studies on properties of laminar premixed oxygen-enriched NH3/H2/O2/N2 flames at elevated temperature and pressure

In this work, the effects of oxygen enrichment coefficient (Ω = 0.21 − 0.42) and initial temperature (Tu = 298 − 448 K) on the laminar burning properties of NH3/H2/O2/N2 flames are systematically investigated by using the spherical flame propagation method at equivalence ratios (Φ = 0.8 − 1.4) and initial pressure (Pu = 3 atm). LBV is analyzed by obtaining experimental data. In order to analyze flame instability, thermal diffusion and hydrodynamic instability are separated by linear stability theory. The thermal and chemical effects of oxygen enrichment on LBV and its effect on heat release rate are analyzed by numerical simulation. The results show that the laminar burning velocity (LBV) exhibits a positive correlation with both the oxygen enrichment coefficient and the initial temperature. The temperature index (α) exhibits a non-monotonic variation in response to the initial temperature of the NH3/H2/O2/N2 flame. Leeff is insensitive to temperature and positively correlated with the oxygen enrichment coefficient. The NH3/H2/O2/N2 flame is mainly affected by hydrodynamic instability when the oxygen enrichment coefficient is large. The peak NHRR scales positively with the oxygen enrichment coefficient. Oxygen enrichment helps to contribute to the overall net reaction rate.

Effect of Oxygen Enrichment on Melting Behavior in Sintering Process

Effect of Oxygen Enrichment on Melting Behavior in Sintering Process

Evaluation of the effects of oxygen enrichment on combustion stability of biodiesel through a PSO-EMD-RBF model: An experimental study

<abstract> <p>In this study, we processed the flame images of biodiesel combustion in industrial furnaces, classified and evaluated flame states using digital image processing techniques, and proposed a combustion stability index (CSI) using the particle swarm optimization (PSO) algorithm. In order to more accurately predict the combustion stability under different oxygen concentrations, we proposed a method that combines the Multi-Input Radial basis function neural network (RBF-NN) with empirical mode decomposition (EMD). Initially, the EMD method was employed to decompose the original time series of CSI. Subsequently, a decomposition model incorporating initial parameters and CSI was established using the radial basis function. The results of the computations indicate that the EMD-RBF-NN model significantly outperforms existing models in enhancing the accuracy of CSI.</p> </abstract>

Effects of oxygen enrichment on diesel spray flame soot formation in O2/Ar atmosphere

In this study, diesel spray combustion at oxygen-enriched conditions (oxygen volume fraction of 21–70 %) with argon dilution is experimentally investigated in a constant-volume combustion chamber. Optical diagnostics are employed to study flame development, stabilization, and soot formation at oxygen-enriched conditions. To further verify the experimental observations, two-stage Lagrangian simulations are used to analyze the effects of oxygen on the formation and oxidation of soot precursors, polycyclic aromatic hydrocarbons. Results show that replacing nitrogen in air by argon leads to a 50 % reduction of the flame lift-off length, an increased soot flame temperature by 300 K, and higher soot concentrations. Flame morphology and structure still follow the classic conventional diesel combustion model in the oxygen range of 21–40 %, while changes are observed when oxygen levels are higher than 50 %. The width and length of the soot flame are shortened, and chemiluminescence from intermediate species like CO dominates the flame natural luminosity at the spray head, where the flame temperature reaches near 3000 K. Soot reduction mechanisms at high-degree oxygen-enrichment conditions are investigated. The intrinsic mixing-limited combustion of diesel sprays leads to unavoidable fuel-rich areas locally, but the shortened flame lift-off length and sufficient oxygen supply confines soot-forming conditions to a smaller, upstream region. The residence time of fuel parcels in this confined soot-forming area is shortened due to the larger local spray velocity. Thereafter, fuel parcels enter a high-temperature fuel-lean region, where the formed soot is oxidized rapidly.

Oxygen enrichment protects against intestinal damage and gut microbiota disturbance in rats exposed to acute high-altitude hypoxia.

Acute high-altitude hypoxia can lead to intestinal damage and changes in gut microbiota. Sustained and reliable oxygen enrichment can resist hypoxic damage at high altitude to a certain extent. However, it remains unclear whether oxygen enrichment can protect against gut damage and changes in intestinal flora caused by acute altitude hypoxia. For this study, eighteen male Sprague-Dawley rats were divided into three groups, control (NN), hypobaric hypoxic (HH), and oxygen-enriched (HO). The NN group was raised under normobaric normoxia, whereas the HH group was placed in a hypobaric hypoxic chamber simulating 7,000 m for 3 days. The HO group was exposed to oxygen-enriched air in the same hypobaric hypoxic chamber as the HH group for 12 h daily. Our findings indicate that an acute HH environment caused a fracture of the crypt structure, loss of epithelial cells, and reduction in goblet cells. Additionally, the structure and diversity of bacteria decreased in richness and evenness. The species composition at Phylum and Genus level was characterized by a higher ratio of Firmicutes and Bacteroides and an increased abundance of Lactobacillus with the abundance of Prevotellaceae_NK3B31_group decreased in the HH group. Interestingly, after oxygen enrichment intervention, the intestinal injury was significantly restrained. This was confirmed by an increase in the crypt depth, intact epithelial cell morphology, increased relative density of goblet cells, and higher evenness and richness of the gut microbiota, Bacteroidetes and Prevotellaceae as the main microbiota in the HO group. Finally, functional analysis showed significant differences between the different groups with respect to different metabolic pathways, including Amino acid metabolism, energy metabolism, and metabolism. In conclusion, this study verifies, for the first time, the positive effects of oxygen enrichment on gut structure and microbiota in animals experiencing acute hypobaric hypoxia.

Effect of oxygen enrichment on methane ignition

Oxygen-enriched combustion has attracted interest in the energy sector due to its increased thermal efficiency and low carbon capture cost compared to ‘air’ combustion. Experimental data on the ignition of oxygen-enriched mixtures are limited in literature. In this work, ignition delay times (IDTs) of various methane/oxygen mixtures diluted in argon/nitrogen were measured using a low- and a high-pressure shock tube over a temperature range of 1200 – 1700 K, three pressures of 1, 10, and 20 bar and an equivalence ratio range of 0.21 - 4. The oxygen mole fraction in the mixtures was varied from 19% (‘air’) to 90.5%, and dilution levels from 71% to zero. The reported IDTs were extracted from pressure and OH* emission profiles. To the best of our knowledge, this is the first comprehensive IDT study on the effect of oxygen enrichment on methane ignition. High-speed imaging experiments were performed to determine the possible presence of non-ideal ignition in these unconventional mixtures. The Bifurcation Damköhler number was found to be a good indicator of non-ideal ignition observed in some imaging experiments. Measured IDTs were compared with the predictions of AramcoMech 3.0 model as well as with GRIMech 3.0 and NUIGMech 1.1 for few cases. In general, AramcoMech 3.0 overestimated IDTs for the investigated methane mixtures. Brute force sensitivity analyses were conducted with AramcoMech 3.0 to identify reactions with a strong influence on IDT prediction for the investigated mixtures. Minor modifications were made to AramcoMech 3.0 resulting in improved predictions of ignition behavior in oxygen-enriched methane mixtures.

Effect of oxygen enrichment on the combustion characteristic and pollutant emissions of kerosene-biogas mixtures on a mini jet engine combustion chamber

There are many alternative fuel studies in gas turbine engines, which are widely used in aviation and energy production. Biogas has also become popular among alternative fuels, especially since it can be obtained from waste. Biogas not only provides a renewable energy source, but also helps to manage organic waste, reduce greenhouse gas emissions and promote sustainable practices in waste management and energy production. The most important issue for alternative fuel studies in gas turbine engines is maximum emission reduction with minimum efficiency loss. In this study, oxygen enrichment and alternative fuel simulation were performed on a mini gas turbine engine. The biogas/kerosene mixture was used together with the oxygen enrichment method, which is known to increase the flame temperature in the literature, due to the lowering effect of the biogas on the combustion chamber outlet temperature.As an alternative fuel, biogas was mixed with kerosene up to 50% in 10% increments. The geometry of the GTM-120 engine used in the study was simplified and validated with the combustion chamber outlet temperatures at 3 different rpms created with the fuel and air inlet conditions taken from the literature. While kerosene fuel is injected from 12 nozzles with Discrete Phase Method, k-e turbulence model and Discrete Ordinates radiation model are used. Alternative fuel was given from the nozzle surfaces as a mass flow inlet by calculating the flow rate so that the thermal power remains constant. All simulations were made with steady-state and 1600 iterations. As a result, it was observed that oxygen enrichment increased the flame temperature and NOX formation, while decreasing the CO emission.On the other hand, it has been observed that the CO2 in the biogas reduces both the temperature and NOX emissions due to its diluting effect, while at the same time increasing the CO emissions in the front region. Furthermore, the decrease in the total C/H mass also led to a reduction in the CO emission at the outlet. Another effect of the biogas was the reduction in the CO2 at the outlet. Thanks to this study, the use of alternative fuels and a decrease in pollutant emissions have been achieved by keeping the loss of engine efficiency at a minimum.With this study, it has been demonstrated that biogas can be used as an alternative fuel with kerosene by keeping the engine efficiency loss to a minimum and a decrease in pollutant emissions.

Effect of oxygen enrichment on sintering behavior of high proportion vanadium–titanium magnesite concentrates

Effect of oxygen enrichment on sintering behavior of high proportion vanadium–titanium magnesite concentrates

Effect of oxygen enrichment of Biogas-Hydrogen mixtures in a premixed combustor on the combustion instability and emissions

The effect of enrichment of a low calorific (50 % CH4-50 % CO2) biogas mixture with hydrogen and oxygen has been investigated on combustion stability and exhaust emissions in a premixed burner. The thermal power was kept constant at 5 kW, the equivalence ratio of 0.8, and a swirl generator (1) was placed at the burner outlet. Initially, hydrogen (H2) was added to the biogas at intervals of 10 % up to 40 % by volume. The addition of hydrogen to the biogas increased the heating value of the mixture and reduced the instabilities. It has been determined that biogas/hydrogen mixtures containing 20 % and 30 % H2 showed the lowest combustion instability and pollutant emissions. It has been observed that with the addition of 30 % hydrogen to the biogas, the CO emission value, which was 5532 ppm, decreased to 130 ppm. Also, 23 % and 25 % O2 enrichment were applied to fuel mixtures. It was observed that combustion instabilities increased with oxygen enrichment in both fuel mixtures and flashbacks occurred under acoustic perturbation. It has been determined that the mixture containing 20 % H2 as the flame, which has the lowest emission and is resistant to acoustic perturbation, is burned at the 23 % O2 ratio by volume.

焼結プロセスにおける酸素富化が焼結・溶融挙動に与える影響

焼結プロセスにおける酸素富化が焼結・溶融挙動に与える影響

Effect of Oxygen Enrichment on Methane Ignition

Effect of Oxygen Enrichment on Methane Ignition

Optical study of oxygen enrichment on methane combustion characteristics under high compression-ratio conditions

Natural gas is a promising fuel for IC engines with low carbon emissions, whereas its poor lean combustion performance at low load and low engine power output at high load remain a challenge for automobile manufacturers. Oxygen-enriched combustion can provide more opportunities for collisions between fuel and oxygen molecules; thus, methane combustion performance can be improved. In this work, using a high-compression-ratio optical engine, the effects of oxygen enrichment on methane combustion were comprehensively investigated, addressing the similarities and differences between high load and low load conditions. High-speed direct photography and simultaneous pressure were performed to capture detailed combustion evolutions. The results show that high oxygen concentration can greatly increase methane flame propagation speed under high energy density condition (high load). As a result, advanced combustion phase and high peak pressure are obtained by more concentrated heat release, which in turn are indicators for improvised thermal efficiencies. Under low energy density condition (low load), oxygen enrichment mainly acts as a promoter of the initial flame formation, which in turn are indicators for improvised combustion stability. A detailed comparison of flame characteristics confirms the different effects of oxygen enrichment on methane combustion under different energy density conditions. Besides, oxygen enrichment can significantly promote initial flame formation with a higher rate and lower cyclic variation, and a low degree of oxygen enrichment can also have a great effect. The current study shall give insights into the strategies for oxygen enrichment on methane engines’ performance at different loads.

HMB-CFD study of oxygen-enriched pulverised coal combustion in an ironmaking blast furnace

Pulverised coal injection (PCI) into blast furnace (BF) is a dominant technology for partial coke replacement and lowering production cost, and high oxygen enrichment is a recent promising technology for further increasing coal combustion and thus increasing pulverised coal rate (PCR) and lowering emissions. In this paper, a heat and mass balance (HMB) model and a three-dimensional computational fluid dynamics (CFD) model of pulverised coal flow and combustion in the lower part of the BF are combined to investigate the effect of oxygen enrichment on coal combustion in terms of operational feasibility and coal combustion efficiency, where the injection schemes such as blast volume, oxygen enrichment, PCR are designed using the HMB model; and the local detailed coal combustion is studied using the CFD model, including the effect of oxygen enrichment and PCR on in-furnace phenomena including gas-solid flow, temperature field and particularly, coal burnout. The CFD simulations reveal that the combustion efficiency is the result of the combined effects of oxygen enrichment and PCR. The high oxygen enrichment in the blast enhances gaseous combustion and coal combustion. The high PCR needs more time and distance for preheating and devolatilisation, which was detrimental to coal combustion near tuyere; on the other hand, more particles in combustion release more heat which is beneficial to the continued combustion of unburned particles. As a result of the combined effects, the inflection points could be found in some key phenomena, including gas temperature, particle temperature, O2 mass fraction, etc. This HMB-CFD study implies that it is highly necessary to consider both feasible operation windows and the detailed impacts of the oxygen enrichment on coal combustion under industrial BF conditions; and thus should be used in future PCI investigations.

An investigation of thermal radiation from laminar diffusion flames in a tri-coflow burner with central oxygen

In natural gas combustion processes, oxygen-enriched combustion is often used to improve heat transfer and thermal efficiency. In this investigation, a triple-port burner is employed to investigate the effect of oxygen enrichment on thermal radiation when introducing oxygen into the center of a normal coflow diffusion flame, while maintaining an outer coflow of air. Two fuels are investigated: methane, being the primary constituent of natural gas and having a low propensity for soot formation, and ethylene, which acts as a reference fuel with a much higher propensity for soot formation. The flow rates of air in the outer annulus and fuel in the inner annulus are held constant, while the flow rate of oxygen in the central tube is systematically increased. Total radiation, which is converted to radiation loss fraction, is measured using a wide-angle radiometer. Soot volume fraction and soot temperature are measured using two-color ratio pyrometry with a digital camera.For low flow rates of central oxygen when an inner oxygen-fuel flame is apparent, the thermal radiation is increased due to an increase in soot concentration. At these low flow rates, thermal radiation is increased by 20% for methane and 26% for ethylene, as compared to a normal coflow flame without central oxygen. The increase in radiation from these flames results in a decreasing, or relatively constant soot temperature in the soot laden region as the increased soot concentration radiates heat from the flame, even though gas temperatures upstream near the central oxygen flame are quite high. For relatively high flow rates of central oxygen, radiation from the tri-coflow methane flame increases by up to 31% compared to a normal coflow flame, while radiation from the ethylene flame monotonically decreases. For both fuels, when oxygen flow rates are high, soot concentration decreases (due to a change in flame shape and enhanced oxidation rates) and soot temperature increases. Product gases are the dominant emitters of radiation in the methane flames studied. Soot is the dominant radiant emitter in the ethylene flames until high flow rates of central oxygen reduce the soot concentration, such that high temperature product gases take over as the dominant radiant emitters. Overall, low flow rates of central oxygen can increase thermal radiation from the coflow methane flame by 20% due to increased soot concentration, and high flow rates of central oxygen can increase thermal radiation by 31% due to increased gas temperatures. However, the methane flames with central oxygen still emit at least 41% less radiation than the coflow ethylene flame. These results indicate that when considering the effect of oxygen enrichment on thermal radiation, the change in overall flame (gas and soot) emissivity can be just as important as the change in temperature.

Numerical simulation of iron ore sintering process with coke oven gas injection and oxygen enrichment

Abstract Oxygen enrichment is believed to improve productivity and reduce fuel consumption, while gas fuel injection is assumed to improve the product yield and quality in iron ore sintering process. It is important to understand the mutual effect of oxygen enrichment and gas fuel injection for combined usage of these two techniques. A mathematical model is developed to simulate the sintering process with coke oven gas (COG) injection and oxygen enrichment, particularly focusing on predicting the quality and yield of sinter production, as well as NO x emission. The model is validated by comparing the model predictions with sintering pot test data, and numerical simulations are carried out to investigate the mutual effect of oxygen enrichment and COG injection. The results show that, compared with the conventional sintering process, with 0.5% COG injection and 30% oxygen enrichment, the mean melt quantity index (MQI) is increased by 4.1% and the mean cooling rate (CR) is decreased by 62.5%, showing that the sinter quality is improved significantly. The sinter yield is increased by 44.5%, whereas the NO x emission is increased by 8.3%. With the increase of oxygen enrichment from 21% to 30%, the sinter yield increases prominently first and then decreases a little, attaining its maximum at 30% of oxygen concentration. In addition, increasing oxygen concentration will increase the conversion rate of coke-N to NO x . Therefore, excessive oxygen enrichment is not only bad for sinter strength and yield, but also increases NO x emission.

Examination of combustion characteristics of oxygen enriched synthetic gases mixtures at various acoustic frequencies

Abstract Synthetic gases attract the attention of researchers due to the increase in energy demand. H2 and CO gases are the main components of synthetic gases. In this study, three different gas mixtures were tested according to their H2/CO (3, 1.5, 0.5) ratios. Thermal power (3 kW), swirl number (1) and equivalence ratio (0.7) kept constants for all experiments. Three different oxygen ratios selected for the oxygen enrichment experiments. First, the gas mixture was burned with standard air. After that, the oxygen concentration in the oxidizer was raised to 23 % and 25 % for examining the effect of oxygen enrichment. The stability results showed that an increase of hydrogen content in the synthetic gas mixtures caused decreasing in the oxygen enrichment limit. The mixture, which can be enriched up to 25.8 % O2 while the H2/CO ratios are 0.5, can be increased up to 25.2 % O2 at a medium H2/CO ratio (1.5). In the case where the H2/CO ratio was increased to the high level (3) by increasing the hydrogen level, the oxygen enrichment limit decreased to 24.1 %. A stable flame did not occur after these oxygen enrichment values. In addition, dynamic pressure data were recorded for all mixtures under external acoustic enforcement. Increases in the hydrogen and oxygen ratio at the same time caused the flame instabilities. Thus, the flame extinguished under acoustic enforcement. In addition to these results mentioned, the emission values showed that oxygen enrichment caused the decrease in CO emissions but the increase of NOx values for all synthetic gas mixtures.

Oxygen enrichment effects on CH4-air turbulent flow characteristics in a coaxial swirl burner

ABSTRACT This paper reports results on the effect of oxygen enrichment on flow and turbulent flames in a coaxial swirl burner. The investigation was performed by S-PIV in CH4-air-O2 non-reacting and reacting flows. This work is the continuation of studies carried out previously by the authors on the same burner, with different new operating conditions. The burner consists of 2 concentric tubes, with a swirler located in the annular part through which the oxidant (air-O2) is supplied. The CH4 gas is delivered into the central tube and injected radially into the combustion chamber through small holes. The burner is placed in a parallelepiped combustion chamber with a volume of 120×50×50 cm3. The paper reports detailed results on mean velocity fields, profiles of the three velocity components (U,V,W) and velocity fluctuations (U’,V’,W’) in the case of a 150 Nl/min oxidant flow rate, a swirl number Sn = 1.4 and an equivalence ratio Φ = 1. Three cases of O2 addition were investigated, 21%, 25%, and 30% (in vol.) corresponding to 9.4 kW, 11.7 kW, and 14.5 kW of combustion power, respectively. In-depth analysis of the field velocity differences between reactive and non-reactive cases was carried out and showed a significant difference in flow velocities between reacting and non-reacting flows. The profiles of the mean velocities, fluctuations and velocity decays differed, and higher values were observed in the reacting case. The enrichment of air with oxygen affected the velocity fields and their fluctuations in both distribution and values. The addition of O2 increased the flame temperature, leading to a greater radial expansion and a reduction in the size of the recirculation zone. The maximum axial velocity increased significantly as a function of the O2 rate, whereas the swirling velocity varied only slightly. The velocity fluctuation results also revealed a difference in profiles and values depending on O2 enrichments and locations along the flow.

Experimental and Kinetic Study on the Effect of Oxygen Enrichment on Flame Propagation of Syngas Mixture in a Half-Open Pipe at Elevated Temperatures

Experimental and Kinetic Study on the Effect of Oxygen Enrichment on Flame Propagation of Syngas Mixture in a Half-Open Pipe at Elevated Temperatures

Comparison Between Pressure Swing Adsorption and Liquid Oxygen Enrichment Techniques in the Atacama Large Millimeter/Submillimeter Array Facility at the Chajnantor Plateau (5,050 m).

The Chilean workforce has over 200,000 people that are intermittently exposed to altitudes over 4,000 m. In 2012, the Ministry of Health provided a technical guide for high-altitude workers that included a series of actions to mitigate the effects of hypoxia. Previous studies have shown the positive effect of oxygen enrichment at high altitudes. The Atacama Large Millimeter/submillimeter Array (ALMA) radiotelescope operates at 5,050 m [Array Operations Site (AOS)] and is the only place in the world where pressure swing adsorption (PSA) and liquid oxygen technologies have been installed at a large scale. These technologies reduce the equivalent altitude by increasing oxygen availability. This study aims to perform a retrospective comparison between the use of both technologies during operation in ALMA at 5,050 m. In each condition, variables such as oxygen (O2), temperature, and humidity were continuously recorded in each AOS rooms, and cardiorespiratory variables were registered. In addition, we compared portable O2 by using continuous or demand flow during outdoor activities at very high altitudes. The outcomes showed no differences between production procedures (PSA or liquid oxygen) in regulating oxygen availability at AOS facilities. As a result, big-scale installations have difficulties reaching the appropriate O2 concentration due to leaks in high mobility areas. In addition, the PSA plant requires adequacy and maintenance to operate at a very high altitude. A continuous flow of 2–3 l/min of portable O2 is recommended at 5,050 m.

Effects of Oxygen Enrichment on Supersonic Combustion in a Mach 10 Scramjet

Scramjet engines are a suitable replacement for rockets in access-to-space systems, but, being air-breathing engines, their operational envelope is limited to altitudes where enough oxygen is available for combustion. Oxygen enrichment, in which fuel is premixed with oxygen, is a promising technique to overcome constraints in altitude due to low oxygen availability, and the difficulty to generate positive thrust at high Mach numbers. Large-eddy simulations of an inlet-fueled Mach 10 scramjet engine are performed to investigate the effect of oxygen enrichment on the flowfield and to characterize the turbulent combustion regimes. It is shown that combustion levels increase substantially with the addition of premixed oxygen, which leads to a considerable increase in combustion efficiency. It is shown that the mixing process is altered by oxygen enrichment in such a way that the observed increase in mixing efficiency is higher than the increase caused by premixing alone. Finally, the combustion regimes in the simulated engine are analyzed. This shows that combustion is mostly nonpremixed, and oxygen enrichment leads to an increase in premixed combustion, but without significantly altering turbulent combustion overall, which is distributed over a large range of regimes.