Conditions Of Oxygen Concentration Research Articles

Spatial distribution of volatile organic compounds in contaminated soil and distinct microbial effect driven by aerobic and anaerobic conditions

The vertical distribution of 35 volatile organic compounds (VOCs) was investigated in soil columns from two obsolete industrial sites in Eastern China. The total concentrations of ΣVOCs in surface soils (0–20 cm) were 134–1664 ng g−1. Contamination of VOCs in surface soil exhibited remarkable variability, closely related to previous production activities at the sampling sites. Additionally, the concentrations of ΣVOCs varied with increasing soil depth from 0 to 10 m. Soils at depth of 2 m showed ΣVOCs concentrations of 127–47,389 ng g−1. Among the studied VOCs, xylene was the predominant contaminant in subsoils (2 m), with concentrations ranging from n.d. to 45,400 ng g−1. Chlorinated alkanes and olefins demonstrated a greater downward migration ability compared to monoaromatic hydrocarbons, likely due to their lower hydrophobicity. As a result, this vertical distribution of VOCs led to a high ecological risk in both the surface and deep soil. Notably, the risk quotient (RQ) of xylene in subsoil (2 m, RQ up to 319) was much higher than that in surface soil. Furthermore, distinct effects of VOCs on soil microbes were observed under aerobic and anaerobic conditions. Specifically, after the 30-d incubation of xylene-contaminated soil, Ilumatobacter was enriched under aerobic condition, whereas Anaerolineaceae was enriched under anaerobic condition. Moreover, xylene contamination significantly affected methylotrophy and methanol oxidation functions for aerobic soil (t-test, p < 0.05). However, aromatic compound degradation and ammonification were significantly enhanced by xylene in anaerobic soil (t-test, p < 0.05). These findings suggest that specific VOC compound has distinct microbial ecological effects under different oxygen content conditions in soil. Therefore, when conducting soil risk assessments of VOCs, it is crucial to consider their ecological effects at different soil depths.

Enhanced dual-catalytic elimination of NO and VOCs by bimetallic oxide (CuCe/MnCe/CoCe) modified WTiO2 catalysts: Boosting acid sites and rich oxygen vacancy

It remains challenging to remove nitrogen oxides (NOx), benzene (C6H6), and toluene (C7H8) simultaneously under conditions of low oxygen and high SO2 concentration. Herein, CuCe, MnCe, and CoCe doped WTiO2 catalysts were designed. The prepared CuCe-WTiO2 catalyst consistently maintained more than 85% NO, 92% C6H6, and 91% C7H8 removal in 260–420 °C under 3.33% O2 and 1000 ppm SO2. The adequate charge flow between the catalyst surface and the gas molecules was enhanced, promoting SO2 tolerance of CuCe-WTiO2. More NH3, NH4+, and -NH2 were adsorbed with acid sites on the CuCe-WTiO2 surface. The high concentration of adsorption centers and superior redox properties effectively improved the co-catalytic efficiency. The primary intermediates in the reduction processes via the Langmuir-Hinshelwood and Eley-Rideal mechanisms were NO2, bridged nitrite (NO2–), and monodentate nitrite (NO2–). The generation of reactive chemisorbed oxygen (Oα) becomes more accessible with the transfer of electrons from Ce4+ to adsorbed O2. C6H6 and C7H8 are progressively oxidized by Oα and eventually completely mineralized to CO2 and H2O. This study is anticipated to offer a new option for co-catalytic removal of NO, C6H6, and C7H8.

Corrosion effect analysis on thermal-hydraulics of LBE/water spiral tube steam generator under oxygen-controlled environment

The advancement of utilizing liquid Lead-Bismuth Eutectic (LBE) as a cooling medium is hindered by its pronounced corrosive properties. The impact of LBE corrosion on the performance of heat exchangers is significant over the long term, however, this aspect has been largely overlooked in previous studies. Historically, there has been a dearth of LBE corrosion models that account for flow accelerated corrosion. Concurrently, precise numerical models and coupling methods for comprehending the interplay between LBE corrosion and thermal-hydraulics have not been developed. Nevertheless, these contents are pivotal for the advancement of liquid LBE cooling mediums. To delve into the flow and heat transfer characteristics of heat exchangers subjected to LBE corrosion, enhancements were made to capture the accelerated removal effect of LBE corrosion flow. Subsequently, a bidirectional coupling model encompassing LBE corrosion and flow heat transfer was formulated. The Computational Fluid Dynamics (CFD) method was employed to simulate the corrosion and flow heat transfer in a spiral tube steam generator under conditions of saturated oxygen concentration and an oxygen-controlled environment. The results indicate that the corrosion of liquid LBE forms an oxidation layer, which hinders the heat transfer in the spiral tube steam generator. This leads to a significant increase in the wall friction coefficient and a decrease in the surface Nusselt number. However, it does not have a significant effect on the water side evaporation process of the spiral tube steam generator. The implementation of an oxygen-controlled environment can effectively reduce the influence of LBE corrosion on the flow heat transfer of the spiral tube steam generator. Especially under high temperature conditions, it can reduce the near wall temperature of LBE change by up to 57.5% and the outlet temperature change by up to 61.5%. The oxygen-controlled environment results in prolonged local hypoxia time, with a more pronounced effect at higher temperatures.

Reverse combustion propagation in an oxygen-limited and -enriched N2/O2 flow for a bed packed with rice husk

Propagation characteristics of reverse combustion significantly impact the conversion of solid fuels in packed beds, especially under variable reaction atmosphere conditions. In this study, the propagation of reverse combustion was experimentally studied in an oxygen-limited and -enriched O2/N2 flow with an oxygen concentration range of 21–100 % for a bed packed with rice husk. The temperature profile measured by thermocouples along the bed height was processed to appreciate the driving mechanism of combustion front, as well as the reaction structure inside the bed. Besides, the contribution of volatiles gas-phase oxidation and char surface oxidation to reverse combustion was also evaluated. Results show that compared to the air case, an oxygen-enriched condition broadens the operating range of oxygen flow rate for the oxygen-limited reverse combustion. Under high oxygen concentration conditions, the low-temperature oxidation of rice husk inside the reaction front becomes enhanced. Such chemical reaction effect widens the whole reaction front thickness and thereby reduces the oxidation intensity in local regions, resulting in a faster ignition rate and a lower temperature for combustion front. It is found that this process is dominated by the gas-phase oxidation of volatiles, of which oxygen consumed is above 60 % of the supplied. As oxygen concentration increases, the gas-phase oxidation of volatiles becomes further enhanced. Correspondingly, the oxidation ratio of char is gradually approaching a limit, about 12 %, especially at the oxygen concentration above 50 %. These findings will facilitate a better fundamental understanding of driving mechanism of this special combustion process and thereby provide an important theoretical basis for efficient thermal conversion of solid fuels.

Estimating the Physicochemical and Antioxidant Properties of Hardy Kiwi (Actinidia arguta) Treated with 1-Methylcyclopropene during Storage

In fruit storage, new methods are being sought to extend the distribution period while maintaining the highest quality parameters of the fruit, i.e., the physical and chemical characteristics of the fruit, but also the health-promoting properties. One method is to treat the fruit with 1-MCP, which effectively inhibits fruit ripening, since the main reasons for limiting the distribution of minikiwi fruit are rapid ripening and the loss of firmness. It is also highlighted that minikiwi is a source of antioxidants, which, as highly reactive compounds, are quickly degraded during storage. This study evaluates the effectiveness of using 1-MCP to reduce minikiwi softening and maintain the high antioxidant properties of the fruit. In the experiment, minikiwi fruits of the ‘Ananasnaya’ cultivar were used. After harvesting, the fruits were treated with 1-methylcyclopropene at a concentration of 0.65 µL/L. Fruits treated in this way were stored in ordinary cold storage (NA) and under low oxygen concentration (ULO) conditions for a period of 12 weeks. The fruits’ physicochemical properties, sugar and acid contents and antioxidant potential, which consisted of ascorbic acid, polyphenols, phenolic acids, flavonols and flavan-3-ols, were evaluated. The application of 1-MCP is effective in reducing the loss of firmness in the minikiwi during storage, but the blocking of minikiwi ripening by 1-MCP makes the fruit less sweet and more acidic. Fruits treated with 1-MCP had higher antioxidant activity and a higher content of biologically active compounds. The effect of 1-MCP is stronger for flavan-3-ols, but slightly weaker for phenolic acids. Fruits treated with 1-MCP have a higher antioxidant potential than untreated fruit after a long period of storage.

Oxidative pyrolysis of plywood waste: Effect of oxygen concentration and other parameters on product yield and composition

Introducing a small amount of oxygen into the inert carrier gas will not only cause partial oxidation reaction, but also significantly change the composition and distribution of biomass pyrolysis products. The oxygen concentration greatly affects the balance between oxidation reaction and pyrolysis reaction. Therefore, it is very important to clarify the influence of oxygen concentration and other reaction conditions on oxidative pyrolysis. The results showed that the pyrolysis products yields remain constant when the oxygen concentration in the carrier gas ranges from 0 to 3 vol%; however, between 3 to 10 vol%, oxygen reacts with biochar to generate non-condensable gas and release heat, and the mass yield of bio-oil slightly declines. Compared with N2 atmosphere, the temperature corresponding to the maximum weight loss peak of pyrolysis under 10 vol% oxygen concentration shifts from 352.5 °C to 292.1 °C. With 10 vol% oxygen in the carrier gas, most of the oxygen transfers to non-condensable gas (6.8 vol%) and water (3.2 vol%). The proportion of 0–140 Da (acids, ketones, furans, BTX) in bio-oil decreases significantly. The biochar more porous structure and oxygen-containing functional groups. The study revealed the complex interactions among various parameters in oxidative pyrolysis.

Effect of oxygen concentration on the split injection combustion process of diesel spray injected into 2D piston cavity

The exhaust gas recirculation (EGR) technique effectively reduces NOx emissions, and the split injection can lower engine emissions. There is little research on the formation and oxidation of soot during fuel combustion by combining EGR and split injection. Therefore, the effect of oxygen concentration on the split injection strategies' flame characteristics was investigated by analyzing the integrated KL factor, the mean flame temperature, and the soot evolution. The experiment combines various conditions of single main injection, double main injection, high injection pressure, and low injection pressure, with pre-injection and without pre-injection, to discuss the influence of oxygen concentration on combustion characteristics. The 2D piston cavity has been used to form the impingement spray flame, and the two-color method has been used to analyze the combustion characteristics. Results reveal that there will not be fuel accumulation along the cavity groove between the first and the second main injection under low oxygen concentration with pre-injection conditions. Pre-injection reduces the soot oxidation rate under double main injection with low oxygen concentration. The ignition timing of the first main injection under double main injection with pre-injection conditions occurred in advance, even under low oxygen concentration conditions. The effect of oxygen concentration on the total flame area is not as significant as that of pre-injection or without pre-injection conditions. Considering all conditions, split injection (D160_50:50) without pre-injection has higher soot oxidation rate under 15% O2. The injection strategy (S160) without pre-injection can minimize soot and NOx emissions at a concentration of 15% O2.

The Small RNA-Binding Protein CcaF1 Promotes Formation of Photosynthetic Complexes in Rhodobacter sphaeroides.

In natural habitats, bacteria frequently need to adapt to changing environmental conditions. Regulation of transcription plays an important role in this process. However, riboregulation also contributes substantially to adaptation. Riboregulation often acts at the level of mRNA stability, which is determined by sRNAs, RNases, and RNA-binding proteins. We previously identified the small RNA-binding protein CcaF1, which is involved in sRNA maturation and RNA turnover in Rhodobacter sphaeroides. Rhodobacter is a facultative phototroph that can perform aerobic and anaerobic respiration, fermentation, and anoxygenic photosynthesis. Oxygen concentration and light conditions decide the pathway for ATP production. Here, we show that CcaF1 promotes the formation of photosynthetic complexes by increasing levels of mRNAs for pigment synthesis and for some pigment-binding proteins. Levels of mRNAs for transcriptional regulators of photosynthesis genes are not affected by CcaF1. RIP-Seq analysis compares the binding of CcaF1 to RNAs during microaerobic and photosynthetic growth. The stability of the pufBA mRNA for proteins of the light-harvesting I complex is increased by CcaF1 during phototrophic growth but decreased during microaerobic growth. This research underlines the importance of RNA-binding proteins in adaptation to different environments and demonstrates that an RNA-binding protein can differentially affect its binding partners in dependence upon growth conditions.

Two Birds with One Stone: Copper-Based Adsorbents Used for Photocatalytic Oxidation of Hg0 (Gas) after Removal of PH3.

CuX/TiO2 adsorbents with CuO as the active component were prepared via a simple impregnation method for efficient purification of phosphine (PH3) under the conditions of low temperatures (90 °C) and low oxygen concentration (1%). The PH3 breakthrough capacity of optimal adsorbent (Cu30/TiO2) is 136.2 mg(PH3)·gsorbent-1, and the excellent dephosphorization performance is mainly attributed to its abundant sur face-active oxygen and alkaline sites, large specific surface area, and strong interaction between CuO and the support TiO2. Surprisingly, CuO is converted to Cu3P after the dephosphorization by CuX/TiO2. Since Cu3P is a P-type semiconductor with high added value, the deactivated adsorbent (Cu3P/TiO2) is an efficient heterostructure photocatalyst for photocatalytic removal of Hg0 (gas) with the Hg0 removal performance of 92.64% under visible light. This study provides a feasible strategy for the efficient removal and resource conversion of PH3 under low-temperature conditions and the alleviation of the environmental risk of secondary pollution.

Experimental study on coal combustion by using the ilmenite ore as active bed material in a 0.3 MWth circulating fluidized bed

The oxygen-carrier aided combustion (OCAC) technology which improves the uniformity of oxygen distribution in the fluidized bed and subsequently enhances the combustion efficiency has attracted more and more attention. However, the existing studies on OCAC mainly focused on the combustion of methane or biomass. There were few studies on low-volatile fuels (such as coal), especially pilot-scale studies that have not been reported. In this work, the effectiveness of OCAC technology on coal combustion has been comprehensively evaluated in a 0.3 MWth pilot-scale circulating fluidized bed (CFB) combustor. The experimental parameters including oxygen carrier (OC) proportion, primary air ratio (A) and oxygen concentration have been carefully investigated. The CO, NOx, SO2 and particulate matter (PM) were measured in real-time from the outlet of the cyclone separator by a gas analyzer and electrical low pressure impactor (ELPI). The results showed that the CO emission from the exit of the cyclone was reduced when the inert bed materials were replaced with the ilmenite ore, especially under the conditions of low oxygen concentration and A. The OCAC technology exhibited good thermal buffering capacity and oxygen buffering capacity. Compared to sand as bed material, the SO2 and NOx emission in flue gas under OCAC decreased and increased, respectively, which is attributed to the more uniform oxygen distribution with more available oxygen in the combustor. Such properties also promoted the self-desulfurization reaction of coal ash. However, it also reduces the reducibility area in the combustor and thus weakens the reduction of NOx. Compared to the sand case, the PM emission under OCAC case is more diminutive, especially in the size of 0–0.4 μm, the PM concentration under OCAC case is much lower than that under sand case.

Soot combustion characteristics of oxygen concentration and regeneration temperature effect on continuous pulsation regeneration in diesel particulate filter for heavy-duty truck

The effects of oxygen concentration and regeneration temperature on continuous pulsation regeneration of DPF (diesel particulate filter) for heavy-duty truck are crucial. The regeneration performance characteristics of the oxygen concentration of 7.2%, 8.2% and 9.4% and regeneration temperature of 823 K, 873 K and 923 K are investigated in this paper. The pressure trend, temperature field change, regeneration reaction rate and the dynamic regeneration oxygen concentration are analyzed. The complete soot regeneration can be achieved of all the simulation cases with different oxygen concentration and regeneration temperature. Under the same oxygen concentration conditions, the higher the regeneration temperature has the wider range of high-pressure pressure region. The highest and the lowest pressure appear at the regeneration temperature/oxygen concentration condition of 923 K/7.2% and 823 K/9.4%. The maximum temperature is 1792.5 K under the condition of 923 K/9.4%. The dynamic reaction rates of the 9 simulation cases are diverse significantly in the inlet and outlet sections of the DPF. The difference between the maximum and minimum reaction rates is less than 0.001. The study results is able to determine the regeneration oxygen concentration and regeneration temperature for achieving complete regeneration of DPF.

Influence of Oxygen Concentration on Combustion Kinetics and Gas Products of a Polyurethane–Coal Mixture

Polyurethane materials are often used in mines to fill the geological structural areas for pretreatment and plugging. These areas are primarily high-incidence areas of coal spontaneous combustion (CSC). Polyurethane will promote the spontaneous combustion of the remaining coal because of its superior thermal insulation performance. Previous studies have focused on the effect of polyurethane on the spontaneous combustion of coal in air atmosphere, without considering the variation of oxygen concentration in the mining area. The paper investigates the effect of polyurethane on the spontaneous combustion of coal in the mining area under different oxygen concentration conditions according to the variation law of oxygen concentration in the mining area. Herein, thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) coupled methods were used to study the kinetics and gas release laws of a polyurethane–coal mixture. The critical temperature of coal increases with the decrease of oxygen concentration. When the oxygen concentration exceeds 10%, the shift of the thermogravimetric curve to the right is smaller, indicating that the oxygen concentration has less influence on the combustion of a polyurethane–coal mixture. When the oxygen concentration is less than 10%, the shift of the thermogravimetric curve toward a higher temperature is more prominent, indicating that the oxygen concentration has a greater influence on the thermogravimetric curve. Simultaneously, the maximum value of DTG increases with the increasing oxygen concentration. The main gas products of coal pyrolysis are CO2, CH4, and H2O, while those of polyurethane pyrolysis are mainly CO2, CO, CH4, and H2O during the pyrolysis process. The amount of CO2 during the pyrolysis of various proportions of coal and polyurethane is the main difference in the gas products. Coal can promote the pyrolysis of polyurethane to some extent. The characteristic temperature rises and falls as the proportion of polyurethane in the polyurethane–coal mixture changes. In the actual monitoring, small amounts of H2O, CO2, and CO gases appear in the starting phase, then a large increase in the amount of gases can be considered that polyurethane is involved in the relevant combustion reactions, which can avoid misjudgment of the spontaneous combustion of coal in the mining area.

Development of PEFC Low Pt-Loading Graphene Catalyst Layer By Electrospray Method for Increasing Output Power

Polymer electrolyte fuel cells (PEFCs) have various positive aspects for achieving carbon neutrality because carbon dioxide is not emitted during operation. However, there are several issues for practical use of PEFCs. One of the problems is its high cost due to the use of Platinum (Pt) for catalyst. Our previous study tried to reduce the amount of Pt in PEFC catalyst layer (CL) and realized low Pt-loading CL by using graphene as Pt support material (1). The graphene CL did not contain ionomer which prevent oxygen transport to the Pt surface. Therefore, we considered that graphene CL realizes smooth oxygen transport. However it was found that the proton transport resistance of graphene CL was about ten times that of CL containing ionomer (2). Since the proton transport resistance depended on the CL thickness, present study employed an electrospray (ES) method to fabricate thin CL. If the proton resistance in graphene CL is reduced, Pt can be used more efficiently. In this study, graphene CLs with various Pt-loading (mg/cm2) were fabricated by decal transfer method, gas diffusion electrode (GDE) method or ES method. The graphene CL was used in the cathode side. The performance and the proton resistance of fabricated CL were respectively evaluated by I-V measurement and impedance measurement. These were also compared with fabricated CLs using commercial Pt-supported Ketjen Blacks (KB/Pt CL). At the anode side, the CL with the Pt loading 0.20mg/cm2 and I/C 0.8 was used. Operation temperature was 80℃, relative humidity (RH) of supply gases was 80%, the flow rate of cathode gas was 2000 sccm with 1% oxygen concentration, and the flow rate of anode gas is 100 sccm. Relationship between fabrication method and the I-V performance was investigated. Figure 1 shows the I-V performance of KB/Pt CL with different fabrication method at 1% oxygen concentration. The CLs with the same Pt-loading (0.047mg/cm2) but different fabrication methods (transfer, ES) show similar I-V performance. This result indicates that fabrication method does not affect the I-V performance in case of KB/Pt CL. Figure 2 shows the I-V performance of graphene CL with different fabrication method at 1% oxygen concentration. The performance of graphene CL fabricated by ES method was higher than that with GDE method despite similar Pt-loading and proton resistance (Figure 3). In case of graphene CL, the structure is considered to depend on the fabrication method. The CL structure fabricated by ES method can improves water and oxygen transport in case of graphene CL. Figure 3 shows the proton transport resistance of the fabricated catalyst layers. The proton resistance is reduced in the smaller amount of Pt-loading CL. Additionally, the Pt-loading in graphene CL was proportional to the thickness of the CL because the weight of Pt relative to the that of graphene was constant (17.2wt%). Therefore, it was suggested that the proton resistance was reduced by fabricating a thinner catalyst layer.Comparing the I-V performance of KB/Pt CL 0.047mg/cm2 (Figure 1) and graphene CL 0.01mg/cm2 (Figure 2), the graphene CL shows high performance even though the Pt weight was about 1/5. These results indicate that fabrication of thin graphene CL with ES method enables to use Pt effectively. Higher performance of graphene CL was also confirmed under higher oxygen concentration condition. Figure 4 shows the I-V performance of graphene CL with ES (Pt-loading: 0.01mg/cm2) and KB/Pt CL with transfer method (Pt-loading: 0.2mg/cm2) at 21% oxygen concentration. Both of limiting current density were over 1 A/cm2. Even though the difference in Pt-loading was 1/20, the difference in I-V performance was small.References(1) K.Yada, et.al, ECS , #101A-1389, (2019).(2) M.Okano, et al., The 25th National Symposium on Power and Energy, C223(2021)(in Japanase). Figure 1

Simultaneous removal of organic matter and nitrogen by heterotrophic nitrification–aerobic denitrification bacteria in an air-lift multi-stage circulating integrated bioreactor

This study aimed to propose a novel air-lift multi-stage circulating integrated bioreactor (AMCIB) to treat urban sewage. The AMCIB combined the reaction zone and sedimentation zone, the alternating circulation of activated sludge in separate aerobic and anaerobic environments facilitates the enrichment of HN-AD bacteria. The preliminary study showed that AMCIB had high removal efficiencies for COD, NH4+-N, TN and TP under high dissolved oxygen (DO) concentration conditions, with average removal rates of 93.21 %, 96.04 %, 75.06 % and 94.30 %, respectively. IlluminaMiSeq sequencing results showed that the system successfully cultured heterotrophic nitrification-aerobic denitrification (HN-AD) functional bacteria (Pseudomonas, Acinetobacter, Aeromonas) that played a crucial role in sewage treatment, and Tetrasphaera was the central phosphorus removing bacteria in the system. Functional gene predictions showed that the HN-AD played a dominant role in the system.

Calibration method of multi-parameter compensation for optical dissolved oxygen sensor in seawater based on machine learning algorithm

Measurement accuracy of optical dissolved oxygen sensor in actual seawater field is affected by many environmental factors. Traditional sensor calibration method is carried out by combining laboratory calibration experiment with field environmental factor correction. First, the influence of temperature on the sensor measurement results is added to the laboratory calibration experiment and model research. The measurement results are then corrected according to salinity and depth environmental factors in the field measurement. However, the influence of these environmental factors on the dissolved oxygen measurement results presents a multi-parameter nonlinear coupling characteristic. Nonlinear machine learning method is used in this study to investigate coupling mapping relationship between seawater multi-environmental factors and measured data of the sensor. A calibration device for controlling temperature, salinity, hydrostatic pressure, and dissolved oxygen concentration conditions and a matching multi-parameter calibration experimental process is designed and established. Analysis of the coupling relationship between multi-parameter conditions and their influence on the measurement of dissolved oxygen concentration showed that the established multi-parameter compensation calibration model achieves a calibration error of ±1 μmol L−1. Compared with existing compensation results after independent calibration of multi-parameters, the proposed model demonstrates better accuracy and rationality. The calibration sensor is tested in the laboratory and seawater field to verify the validity of the calibration model. Dissolved oxygen concentration measured by the sensor is basically consistent with reference measurement data and Winkler analysis value. Results showed that the multi-parameter calibration method based on machine learning can meet calibration requirements of the dissolved oxygen sensor in seawater with improved scientific rationality and calibration efficiency. Furthermore, the proposed method can be extended to other in situ measurement sensors in seawater while considering various environmental factor corrections.

Experimental study on the flammability limit parameters of premixed methanol-gasoline vapor-air mixtures

In this research, the fire and explosion risks of methanol-gasoline blended clean fuels are assessed in experimental studies of the flammability limit parameters of methanol-gasoline vapors at different methanol proportions (M0∼M100) and initial temperatures (313–393 K). The experimental results show that when the proportion of methanol in the methanol-gasoline mixture increases, both upper and lower flammability limits increase. When the initial temperature increases, the lower flammability limit of a methanol-gasoline blend decreases, and a higher methanol volume fraction in methanol-gasoline mixtures corresponds to a more obvious decrease in the lower flammability limit. When the temperature increases from 313 K to 393 K, the lower flammability limit of M75 drops by 11.86%. Under the condition of inert gas dilution, the limiting oxygen concentration gradually decreases with increasing proportion of methanol in methanol-gasoline mixtures. Additionally, the explosion triangle of methanol-gasoline vapor expands to the lower left corner, which increases the deflagration hazard of methanol-gasoline mixture under low oxygen content conditions. The results of this research will help researchers evaluate the fire and explosion risks of related processes and devices and establish a technical index for the application of blended methanol-gasoline clean fuels.

Quantifying the Contribution of Ocean Mesoscale Eddies to Low Oxygen Extreme Events

AbstractOcean mesoscale eddies have been identified as drivers of localized extremely low dissolved oxygen concentration ([O2]) conditions in the subsurface. We employ a global physical‐biogeochemical ocean model at eddy‐permitting resolution to conduct a census of open‐ocean eddies near Eastern Boundary Upwelling Systems adjacent to tropical Oxygen Minimum Zones (OMZs). We track cyclonic and anticyclonic eddies with a surface signature over the period 1992–2018 and isolate their subsurface oxygen characteristics. We identify strongly deoxygenating eddies and quantify their contribution to low [O2] extreme events. Our results show that model simulated low [O2] extreme event frequency is 2–7 times higher in eddies versus non‐eddying locations, with regionally more than half of low [O2] extreme events outside of the permanent OMZs being associated with eddies. Our study highlights the need for further work to investigate the drivers, characteristics and potential ecosystem impacts of low [O2] extreme events.

Effects of Chemical Compositions and Cetane Number of Fischer–Tropsch Fuels on Diesel Engine Performance

Fischer–Tropsch synthetic (FT) fuels are expected to be an ideal alternative for diesel fuel to achieve higher thermal efficiency and reduction in exhaust emissions because of their characteristics of being aromatic-free, sulfur-free, and high cetane number. In this study, the effects of chemical compositions and cetane number of FT fuels on diesel engine performance were investigated by using a commercial GTL (Gas-to-Liquids) diesel fuel synthesized by the FT method and blended paraffinic hydrocarbon fuels made to simulate FT fuels with different chemical compositions and cetane numbers. At first, a commercial diesel fuel (JIS No.2) and GTL were examined by varying the intake oxygen concentrations with cooled EGR. Compared with diesel fuel, GTL shows shorter premixed combustion, smaller heat release peak, and longer diffusion combustion duration at both high and medium conditions due to the higher cetane number. Further, by using the GTL, a limited improvement in thermal efficiency and exhaust emission reduction of NOx have been obtained, but no significant reduction in the smoke emissions is achieved, even though FT fuels have been considered smokeless due to their aromatic-free characteristics. Next, three types of paraffinic hydrocarbon fuels with cetane numbers of 78, 57, and 38 were blended as simulated FT fuels and were examined under the same experimental apparatus and operation conditions. For the low cetane number simulated FT fuel (cetane number 38 fuel), the results show that the ignition delay and premixing period are significantly longer at low intake oxygen concentration conditions, meaning that the premixing of low cetane number fuel is more sufficient than other fuels, especially under the high EGR rate conditions, resulting in fewer smoke emissions. Furthermore, with CN38 fuel, an excellent indicated thermal efficiency was obtained at the high load condition. To summarize the results, the low cetane number FT fuel shows a potential to achieve higher thermal efficiency and reduction in exhaust emissions on commercial diesel engines with EGR.

Combined effects of intake oxygen enrichment, intake pressure and temperature on combustion behavior and emission characteristics of a small-scaled rotary engine

Intake oxygen enrichment has a promising potential to improve the combustion performance of a small-scaled rotary engine (RE) operating at high altitudes. However, the process is complicated because the intake temperature and pressure are sensitive to altitudes as well as the elongated rotor chamber. In this study, a three-dimensional CFD simulation model coupling with a suitable turbulent model and a reduced chemical kinetic mechanism was established and validated. The combined effects of intake oxygen enrichment as well as intake pressure and temperature under different altitudes on early flame growth, combustion behavior, and emission characteristics of small-scaled REs were numerically investigated. Results showed that intake oxygen enrichment promotes the formation of OH, O, H radicals, which leaded to the significant improvements of the early flame growth, especially for the flame near leading spark plug. The promotion effect due to intake oxygen enrichment became weak with increasing altitude. Moreover, the early flame growth duration at high altitudes was more dramatically shortened by intake oxygen enrichment than that at low altitudes. It is interesting to note that when oxygen concentration of 25% and 29% were applied to the small-scaled RE working at 2000 m and 3000 m altitude, respectively, the engine performance could be restored to the level of that working at sea level at the price of a smaller increment of NO emissions. Under high intake oxygen concentration conditions, the effect of altitude on indicated thermal efficiency of the engine could be ignored. Besides, increasing oxygen concentration significantly reduces HC and CO emissions, especially more significant reduction for HC emissions at higher altitudes. • Early flame growth of the rotary engine was analyzed numerically. • Early flame growth near LSP was more significantly improved by oxygen enrichment. • Effect of intake oxygen enrichment on rotary engine performance was quantified. • Oxygen enrichment significantly reduced HC and CO emissions.

Predicting the Oxidative Degradation of Raw Beef Meat during Cold Storage Using Numerical Simulations and Sensors-Prospects for Meat and Fish Foods.

Preventing animal-source food waste is an important pathway to reducing malnutrition and improving food system sustainability. Uncontrolled color variation due to oxidation is a source of waste as it prompts food rejection by consumers. Evaluation of oxidation–reduction potential (ORP) can help to predict and prevent oxidation and undesirable color changes. A new sensor and two modeling approaches—a phenomenological model and a reaction–diffusion model—were successfully used to predict the oxidative browning of beef ribeye steaks stored under different temperature and oxygen concentration conditions. Both models predicted similar storage durations for acceptable color, although deviating for higher and lower redness levels, which are of no interest for meat acceptance. Simulations under higher oxygen concentrations lead to a few days of delay in the redness change, as observed in practice, under modified atmosphere packaging. In meat juice, variation in ORP measured by the sensor correlated with the redness variation. However, in meat, sensors promote oxidation in the adjacent area, which is unacceptable for industrial use. This paper discusses the potential, limits, and prospects of the mathematical models and sensors, developed for beef. A strategy is proposed to couple these approaches and include the effect of microorganisms.