Scavenging Model Research Articles

A comprehensive phenomenological model for unburned fuel emission simulation applied to natural gas engines

The development of lean-burn concepts for internal combustion engines, utilizing a homogeneous air/fuel charge, aims to improve multiple aspects simultaneously, including thermal efficiency, fuel consumption, nitric oxide, and carbon monoxide emissions. However, the adoption of this technology may result in a notable increase in the emission of unburned hydrocarbons (uHC) compared to stoichiometric engines. The sources of uHC are diverse and their relative significance depends on fuel characteristics, engine operating conditions, and geometric features of the combustion chamber. This concern becomes more pronounced when considering engines fueled with natural gas, as methane has a high global warming potential compared to other pollutant emissions. This research proposes an enhancement to an existing simulation model that describes the primary mechanisms involved in uHC formation, which are filling/emptying of the piston top-land crevice volume and the flame wall quenching, with subsequent uHC post-oxidation. The improvements include the calculation of flame penetration into crevice volumes, the description of uHC production from non-piston crevices, and the introduction of a novel scavenging model. The uHC model is integrated into commercial software (GT-Power) as a “user routine”. Validation of the model is conducted with reference to three large bore engines (W31DF, W31SG, and W46SG) with bore sizes of 31 cm and 46 cm, fueled with natural gas, and operated under lean mixtures (λ > 2), employing different ignition methods (dual fuel mode or pre-chamber device). The uHC model is validated against engine-out measurements, exhibiting an average error of 10.0 % for W31DF, 19.4 % for W31SG, and 14.0 % for W46SG engines, respectively. The reliability of the uHC model is demonstrated by the absence of case-specific adjustments to its tuning constants, even when there are significant variations in engine load and geometric design of the crevice volumes.

Coupled effect of injection position variation on gas exchange stability of a free-piston engine

Gas exchange fluctuations may lead to operation instability of the free-piston engine (FPE), because the engine has a coupling effect between the gas exchange and the piston motion, which is different from a conventional engine. It is, therefore, important to study the gas exchange instability to ensure the stable operation of the engine. This study focuses the effect of variable piston position when injecting on the gas exchange stability of a looped scavenging FPE, and a systematic full-cycle gas exchange model is presented by developing a dynamic model, a combustion model, and a multidimensional scavenging model. Meanwhile, an iterative method between motion and scavenging is used to solve the model numerically for gas exchange simulation, and the effects of variable piston position when injecting on piston motion, thermodynamic in cylinder, and gas exchange process are studied. The results indicate that retarding injection induces instability of gas exchange duration which first increases and then decreases, and there is an injection position which is most conducive to the increase of capture efficiency of gas exchange, although the scavenging efficiency is lowest under this condition. This result also suggests that more complete exhaust may be achieved by a different injection position.

Wet scavenging of multi-mode 137Cs aerosols following the Fukushima accident: Size-resolved microphysics modeling with observed diameters

Wet scavenging was critical in the atmospheric transport of 137Cs aerosols following the Fukushima accident. The aerosol size diversity and related microphysical processes produce complex behaviors during wet scavenging. Such behaviors are difficult to investigate using traditional simplified size distributions, resulting in inaccurate modeling. This study establishes an improved size-resolved wet scavenging model that considers the activation process. Using this model, five monodisperse simulations with five representative observed diameters with realistic solubility setting are performed to investigate the spatiotemporal wet scavenging behaviors of 137Cs aerosols. One polydisperse simulation with an empirical size distribution is also validated against the observation. The results reveal that 137Cs aerosols with diameters of 0.6 and 2.0 μm are mainly subject to below-cloud scavenging, which makes a significant contribution to low-deposition areas (<300 kBq/m2). For 137Cs aerosols with diameters of 6.4, 15, and 30 μm, in-cloud scavenging dominates, and the resulting depositions make significant contributions in high-deposition areas. The polydisperse results satisfy the criteria for good performance and better agree with the size, and deposition observations than the five monodisperse simulations, whereas for the concentration, the results show a similar RANK2 with the best mono1 and mono2 cases and reach the satisfactory criteria. These findings reveal the complex behavior and wet scavenging process of multi-mode 137Cs aerosols, improving our understanding and modeling.

Ultrasonic assisted extraction of coumarins from Angelicae Pubescentis Radix by betaine-based natural deep eutectic solvents

This study focused on extracting coumarins from Angelicae Pubescentis Radix (APR) using deep eutectic solvents (DES). The process parameters were optimized using response surface methodology and characterized by projected scanning electron microscopy analysis. Methods: Eighteen types of DESs based on Choline chloride, Betaine, Sodium acetate, and Ammonium acetate were synthesized. The ultrasonic-assisted effect of these DESs on the yield of coumarins was investigated using high-performance liquid chromatography (HPLC). We studied and optimized the technological conditions for extracting coumarins from APR using a one-factor-at-a-time method and response surface methodology. Additionally, scanning electron microscopy was employed to observe the degree of fragmentation of APR powder before and after extraction with methanol solvent and DESs. The biological activity of DESs extract was evaluated using the free radical scavenging model of 1,1-diphenyl-2-picrylhydrazide (DPPH), while the molecular docking approach was used to explore the binding potential between the coumarins and superoxide dismutase (SOD) enzymes. The results indicated that the natural deep eutectic system with a molar ratio of betaine to ethylene glycol of 1:4 exhibited the most effective extraction. The optimum extraction conditions included a water content of 16.11 % in the DESs, a temperature of 43.52 °C, an extraction time of 59.61 min, and an extraction yield of 3.37 %. Furthermore, scanning electron microscopy revealed that the cells of APR powder obtained through ultrasonically assisted treatment with DESs exhibited the most severe breakage. The experiment demonstrated that the DESs extract exhibited a high scavenging capacity for DPPH free radicals. Conclusion: DESs present as an environmentally friendly solvent option for effectively extracting coumarins from APR, indicating promising potential for substitution of organic solvents.

Wound Healing, Anti-inflammatory and Antioxidant Potential of Quercetin Loaded Banana Starch Nanoparticles.

Quercetin belongs to the BCS Class IV of drugs, which means it exhibits low solubility and low permeability. Quercetin is a potent antioxidant drug candidate, but it has several drawbacks, such as a short half-life, poor stability, bioavailability, and solubility. These factors affect its reliability as a good wound-healing, anti-inflammatory, and antioxidant agent. Quercetin nanoparticles resolved these problems and offered high stability, high encapsulation efficacy, sustained and prolonged release, and enhanced accumulation at target sites with high therapeutic efficacy. Banana starch and quercetin were used to formulate a new composition of nanoparticles. Formulated QBSN were evaluated for their antioxidant, wound healing, and anti-inflammatory potential. QBSN showed a good antioxidant effect against the DPPH free radical scavenging model. Inhibition of DPPH free radicals reached up to 98 percent at 40 μl. Histopathological studies of treated tissues (wound and paw edema) confirmed the potential of QBSN. In the future, prepared nanoparticles may be the choice of drug formulation for wound healing, anti-inflammatory therapy, and antioxidant therapy.

Quantification of Total Polyphenols, Total Flavonoids, and Evaluation of Antioxidant Activity of the Aerial Part of Distichochlamys orlowii K. Larsen &amp; M.F. Newman

Distichochlamys orlowii K. Larsen &amp; M.F. Newman is a type of ginger endemic to Vietnam with high values of usage. This study aims to evaluate the total phenolic content, total flavonoid content, and antioxidant effect of the aerial part of Distichochlamys orlowii. The medicinal samples were extracted by ultrasonic method with different solvents including methanol, ethanol, ethyl acetate, and dichloromethane. The total phenolic content was evaluated using the Folin-Ciocalteu reagent and the total flavonoid content was evaluated by the aluminum chloride colorimetric method. The in vitro antioxidant effects of extracts were investigated through free radical scavenging models with DPPH and ABTS. The obtained results showed that the ethanol extract contained the highest content of total phenolic content and total flavonoid content with values of 12.81 ± 0.05% and 19.52 ± 0.23%, respectively. Meanwhile, the methanol extract exhibited the strongest DPPH and ABTS free radical scavenging activities with IC50 values of 243.89 ± 5.98 µg/mL and 33.58 ± 3.14 µg/mL, accordingly. The IC50 values of positive controls were 7,88 ± 0,25 µg/mL for the former assay and 9,74 ± 0,36 µg/mL for the latter assay. This is the first report on the chemical composition and antioxidant activity of the extracts from the aerial part of Distichochlamys orlowii.&#x0D; &#x0D; &#x0D; &#x0D;

Formulation and Evaluation of Quercetin-loaded Banana Starch Nanoparticles

Aims: Formulation and evaluation of quercetin-loaded nanoparticles Background: Nowadays, polymeric nanoparticles are one of the most chosen drug delivery systems for the treatment of life-threatening diseases such as cancer. Drug loading, drug entrapment, and drug release have been the challenges in nanoformulations till now. Various researchers are working to improve these limitations. Objective: Formulation of quercetin-loaded starch nanoparticles .Evaluation of drug loading, entrapment, size release, and activity of prepared starch nanoparticles Methods: In the present study, starch was isolated from a novel source, i.e., unripe banana fruit. Banana starch contains amylose and amylopectin in a certain ratio. Quercetin-loaded banana starch nanoparticles were prepared using the nano-precipitation method. Drug loading and drug entrapment were determined by different methods. Results: The enhanced water absorption capacity of prepared nanoparticles proved the breaking of intra-molecular bonding of amylopectin. In-vitro drug release of quercetin was found to be sustained for up to 12 hours from prepared nanoparticles. SEM was used to determine the particle size and morphology of prepared particles, which were found to be 67.67-133.27 and spherical, respectively. The antioxidant activity of prepared nanoparticles was evaluated by the DPPH scavenging model. The MTT assay for cytotoxicity studies was done using H661 lung cancer cell lines. Conclusion: In this research work, banana as a new source of starch was used to prepare quercetin nanoparticles by nano-precipitation method. The various factors of starch that affect the properties of nanoparticles such as water/oil absorption capacity, drug entrapment/loading, and drug release profile were studied. This study also revealed the effect of starch on particle morphology and size. The yield of prepared nanoparticles was lower than expected but particle size and shape were satisfactory. Prepared nanoparticles were evaluated for their antioxidant and cytotoxic potential. Finally, researchers felt the ratio of amylase and amylopectin were considerable factors in the selection of any starch for the formulation of any drug delivery system. This ratio affects the precipitation of nanoparticles, their properties such as oil/water absorption, drug entrapment, and loading as well as the drug release profile of the formulation.

Anthropogenic Iron Invasion into the Ocean: Results from the East Sea (Japan Sea).

Iron (Fe) is an essential micronutrient for phytoplankton growth, and its availability limits primary production in half of the global ocean. Traditionally, atmospheric input of natural mineral dust has been considered as a main source of Fe in the surface ocean. However, here we show that about 45% of the water-soluble Fe in aerosols collected over the East Sea (Japan Sea) is anthropogenic, which originates mainly from heavy fuel oil combustion, based on the analyses of various chemical tracers (Al, K, V, Ni, Pb, and 210Pb). It is striking that a tiny quantity of oil, less than 1% of the aerosols in mass, can constitute the majority of water-soluble Fe in aerosols due to its high Fe solubility. Furthermore, we show that a quarter of dissolved Fe in the East Sea is anthropogenic using a 210Pb-based scavenging model. Since this sea is almost fully enclosed (200-3000 m) and located at the forefront of the Asian human footprint, our results provide an insight that the marine Fe cycle may be already perturbed by human activities.

Ensemble of Below-Cloud Scavenging Models for Assessing the Uncertainty Characteristics in Wet Raindrop Deposition Modeling

This work is devoted to the development of an ensemble of below-cloud scavenging models of pollutant aerosol transport into the atmosphere. Among other factors contributing to the uncertainty of the forecasts of the dispersion and deposition of technogenic gas-aerosol releases in the atmosphere, precipitation scavenging is one of the least studied and, in case of precipitation, can be the dominant mechanism for aerosol deposition. To form the ensemble of below-cloud scavenging models, appropriate experimental data, raindrop-aerosol capture models, raindrop terminal velocity parameterizations, and raindrop size distributions were chosen. The pool of models was prepared and then evaluated to adequately describe the experimental data using statistical analysis. Rank diagrams were used to analyze the adequacy of meteorological ensembles; together with the ensemble distribution construction, they allowed selecting the groups of models with such properties as to produce unbiased estimates and dispersion corresponding to the dispersion of the experimental data. The model calculations of the concentration fraction deposited due to below-cloud scavenging were performed using a log-normal distribution with characteristics corresponding to those observed during the accidents at the Chernobyl NPP and Fukushima-1 NPP. The results were compared with those obtained using the models of the NAME and FLEXPART codes. The results of this work can be used to improve the current approaches applied for modelling the distribution of pollutants in the atmosphere in the case of emergency, enhancing the reliability of forecasts by taking into account uncertainties in the results. The formed multi-model ensemble will be included in the decision support system used in responding to releases of radioactive substances into the atmosphere.

Model behavior regarding in- and below-cloud 137Cs wet scavenging following the Fukushima accident using 1-km-resolution meteorological field data

Wet deposition remains an important source of uncertainty in modeling of the atmospheric transport of 137Cs following the Fukushima Daiichi Nuclear Power Plant accident. Its behavior is often difficult to investigate owing to the limited resolution of meteorological field data and inconsistent model implementations. This study investigated the detailed behavior of 25 combinations of in- and below-cloud wet scavenging models using high-resolution (1 km × 1 km) meteorological input. These combinations were all implemented in the Weather Research and Forecasting-Chemistry model, thereby enabling consistent evaluation. The 1-km-resolution simulations were compared with simulations obtained previously using 3-km-resolution meteorological field data. Results revealed that rainfall of <1 mm/h is critical for simulation accuracy. The 1-km results revealed better representation of rainfall than that revealed by the 3-km results, but with spatiotemporal variability in accuracy. Owing to their sensitivity to rainfall, single-parameter wet deposition models showed improvements in performance in the 1-km simulations relative to that in the 3-km simulations. The multiparameter models showed more robust performance in terms of both simulations, and the Roselle–Mircea model presented the best performance among the 25 models considered. Wind transport showed substantial influence on the removal of atmospheric 137Cs, and it was nonnegligible even during periods in which wet deposition was dominant. The 1-km-resolution simulations effectively reproduced local-scale 137Cs concentrations but with deviations in timing, mainly because of biased wind direction. These findings indicate the necessity for a refined wind and dispersion model for local-scale simulation of 137Cs concentration.

A multi-process coupling study of scavenging pressure effect on gas exchange of a linear engine

The linear engine is expected to operate with new gas exchange characteristics due to its unconstrained and adaptive dynamics. This study develops a simulation method that mutually transfers the coupling parameters between the piston motion model, generating model, combustion model, and scavenging model, and it iterates the calculation results of motion, combustion and scavenging for gas exchange predication. Then, the coupling effect of scavenging pressure fluctuation on gas exchange in a two-stroke linear engine is also investigated. The results indicate that unlike conventional engine systems, the linear engine reciprocation and compression ratio both increase first and then decrease with the enhancing scavenging pressure, namely the duration of gas exchange is shortened or prolonged, while the linear engine also provides high in-cylinder gas pressure for gas exchange, but the in-cylinder gas temperature reverses. The intake quality and escape amount of the cylinder both vary in positive correlation with the scavenging pressure, which leads to low trapping efficiency, although it cleans more exhaust. The results also find that high scavenging efficiency and fresh charge trapping efficiency can be obtained synchronously at an appropriately low scavenging pressure environment due to its adaptive motion.

Dispersion of Particle‐Reactive Elements Caused by the Phase Transitions in Scavenging

AbstractA generalized model of scavenging of the reactive radionuclide 239,240Pu was developed, in which the sorption‐desorption processes of oxidized and reduced forms on multifraction suspended particulate matter are described by first‐order kinetics. One‐dimensional transport‐diffusion‐reaction equations were solved analytically and numerically. In the idealized case of instantaneous release of 239,240Pu on the ocean surface, the profile of concentrations asymptotically tends to the symmetric spreading bulge in the form of a Gaussian moving downward with constant velocity. The corresponding diffusion coefficient is the sum of the physical diffusivity and the apparent diffusivity caused by the reversible phase transitions between the dissolved and particulate states. Using the method of moments, we analytically obtained formulas for both the velocity of the center mass and apparent diffusivity. It was found that in ocean waters that have oxygen present at great depths, we can consider in the first approximation a simplified problem for a mixture of forms with a single effective distribution coefficient, as opposed to considering the complete problem. This conclusion was confirmed by the modeling results for the well‐ventilated Eastern Mediterranean. In agreement with the measurements, the calculations demonstrate the presence of a maximum that is slowly descending for all forms of concentration. The ratio of the reduced form to the oxidized form was approximately 0.22–0.24. At the same time, 239,240Pu scavenging calculations for the anoxic Black Sea deep water reproduced the transition from the oxidized to reduced form of 239,240Pu with depth in accordance with the measurement data.

Metabolites of Colletrotricum species, an endophytic fungus isolated from Vernonia amygdalina Del possess antimicrobial and antioxidant activities

The endophytic fungus, colletrotricum species, isolated from the leaves of Vernonia amygdalina was investigated for its chemical constituents and biological activity. The pure fungus was grown using solid fermentation on rice medium and the metabolites were extracted using ethyl acetate. Further purification of the extract was carried out using vacuum liquid chromatography (VLC) and gel chromatography on Sephadex LH-20. The chemical constituents were detected by dereplication using HPLC-DAD. Antimicrobial assay of the Sephadex fractions EC3-1 and EC3-3 were evaluated using agar well diffusion assay against seven pathogenic microorganisms (Staphylococcus aureus, Escherichia coli, Salmonella typhi, Bacillus subtilis, Pseudomonas aeruginosa, Aspergillus niger and Candida albicans). EC3-3 was also subjected to antioxidant assay using DPPH free radical scavenging model. HPLC-DAD analysis of the VLC fractions revealed the presence of compounds like Hydroxybenzaldehyde, Cladosporin, Desmethyldichlorodiaportin and p-Hydroxybenzoic acid. EC3-1 and EC3-3 showed mild antimicrobial activity against S. aureus, S. typhi and A. niger strains, with minimal inhibitory concentrations ranging from 0.19 to 0.46 mg/mL. EC3-3 was found to exhibit very high ability to scavenge DPPH radicals with IC50 of 3.16 µg/mL compared to Ascorbic acid (IC50 of 50.72 µg/mL). HPLC analysis of EC3-3 revealed the presence of Palitantin, which has been shown to possess antimicrobial and antioxidant activity, and two unidentified major peaks. The endophytic fungus, Colletotrichum species isolated from Vernonia amydalina produced bioactive metabolites which exhibited antimicrobial and antioxidant activities thus projecting Vernonia amydalina as a potential source of fungal endophytes that can be further studied for generation of novel bioactive compounds.

Empirical Model of Uniflow Scavenging for Ultra-Long-Two-Stroke Marine Diesel Engines

_ Low-speed two-stroke diesel engines are widely employed in the marine industry, especially in tanks, owing to their advantages of fuel economy and reliability. However, with the emerging ultra-long-stroke trend, existing scavenging models, which are based on the configuration of cylinders with short strokes, are no longer applicable. In this study, we investigate the flow field and residual exhaust gas distribution in a cylinder using particle image velocimetry and computational fluid dynamics (CFD) simulations. The result shows a strong Burgers vortex structure upstream of the scavenger flow and dissipates gradually as it moves downstream. Furthermore, the scavenging process comprises three processes according to the detailed CFD analysis: displacement, mixing scavenging, and short circuit. Inspired by the results, a tailored empirical model of ultra-long-stroke uniflow scavenging comprising three sub-models is proposed. Specifically, a logarithmic relationship between the concentration level and scavenging deliver ratio is proposed to describe the mixing scavenging process. Finally, the model was validated against CFD results. The results demonstrate that the discrepancy in the scavenging efficiency curve predicted by this model and CFD is less than 1%, thereby demonstrating model reliability. Introduction Owing to the advantages of a large power range, high thermal efficiency, low fuel consumption rate, and good reliability, marine low-speed engines are widely used to provide power to civil ships (Heywood 1999). The market for low-speed engines is vast and is improving the performance of low-speed engines through research has great economic and environmental significance (Woodyard 2004). To meet the requirements of ship owners for lower fuel consumption and the IMO’s regulation of halving the greenhouse gas emissions of newly built ships, the ultra-long stroke of low-speed engines has become a trend (Lamas &amp; Vidal 2012). With an ultralong stroke, the combustion speed of low-quality fuel oil is slow, and an ultra-long-stroke cylinder can prolong the expansion process, improve the combustion process, and reduce the fuel consumption rate (Fenghua 2014). The ultra-long-stroke diesel engine further creates fuel savings of 3.5–7% based on the original low fuel consumption. Previously, ultra-long strokes could not be achieved, limited by materials and manufacturing processes. However, in recent years, with the advancement of materials and processes, ultra-long strokes have been widely adopted as they have demonstrated superior competitiveness.

Below-cloud scavenging of aerosol by rain: a review of numerical modelling approaches and sensitivity simulations with mineral dust in the Met Office's Unified Model

Abstract. Theoretical models of the below-cloud scavenging (BCS) of aerosol by rain yield scavenging rates that are 1–2 orders of magnitude smaller than observations and associated empirical schemes for submicron-sized aerosol. Even when augmented with processes which may explain this disparity, such as phoresis and rear capture in the raindrop wake, the theoretical BCS rates remain an order of magnitude less than observations. Despite this disparity, both theoretical and empirical BCS schemes remain in wide use within numerical aerosol models. BCS is an important sink for atmospheric aerosol, in particular for insoluble aerosol such as mineral dust, which is less likely to be scavenged by in-cloud processes than purely soluble aerosol. In this paper, various widely used theoretical and empirical BCS models are detailed and then applied to mineral dust in climate simulations with the Met Office's Unified Model in order the gauge the sensitivity of aerosol removal to the choice of BCS scheme. We show that the simulated accumulation-mode dust lifetime ranges from 5.4 d in using an empirical BCS scheme based on observations to 43.8 d using a theoretical scheme, while the coarse-mode dust lifetime ranges from 0.9 to 4 d, which highlights the high sensitivity of dust concentrations to BCS scheme. We also show that neglecting the processes of rear capture and phoresis may overestimate submicron-sized dust burdens by 83 %, while accounting for modal widths and mode merging in modal aerosol models alongside BCS is important for accurately reproducing observed aerosol size distributions and burdens. This study provides a new parameterisation for the rear capture of aerosol by rain and is the first to explicitly incorporate the rear-capture mechanism in climate model simulations. Additionally, we answer many outstanding questions pertaining to the numerical modelling of BCS of aerosol by rain and provide a computationally inexpensive BCS algorithm that can be readily incorporated into other aerosol models.

Investigation of the scavenging process in two-stroke uniflow scavenging marine engines by a real-time multi-stage model

The increasing demand of digital twin marine engine requires real-time physical models for prediction. In two-stroke uniflow scavenging marine engines, a real-time physical model for the scavenging process is rarely found since it is difficult to describe the complex in-cylinder air motion. Without an accurate prediction of the fresh air loss and residual burned gas in the cylinder, the precision of combustion and emission simulation cannot be guaranteed as well. In a marine engine digital twin system, the scavenging ratio and fresh air skip are the vital for the further simulation of combustion and emission. To predict them in real-time, a novel zero-dimensional (0D) multi-stage scavenging model is proposed in this article. In the cylinder zone, the complex gas motion is ideally divided to four stages: exhaust gas blowdown, perfect displacement, displacement-mixing, and perfect mixing. The duration of each stage is determined by the engine design and control parameters. Then, the thermodynamic conditions at each stage are simulated to obtain the mass of residual burned gas, fresh air inlet, and outlet. The results of the 0D model agree well with the results of the CFD simulation, and the mean relative errors of temperature, pressure, and total mass do not exceed 3%, 4%, and 2%, respectively, which indicates the potential for the two-stroke marine engine digital twin system. It could also be applied in a control-oriental engine model or engine diagnostics in the future.

Global simulation of dissolved &amp;lt;sup&amp;gt;231&amp;lt;/sup&amp;gt;Pa and &amp;lt;sup&amp;gt;230&amp;lt;/sup&amp;gt;Th in the ocean and the sedimentary &amp;lt;sup&amp;gt;231&amp;lt;/sup&amp;gt;Pa∕&amp;lt;sup&amp;gt;230&amp;lt;/sup&amp;gt;Th ratios with the ocean general circulation model COCO ver4.0

Abstract. Sedimentary 231Pa/230Th ratios provide clues to estimate the strength of past ocean circulation. For its estimation, understanding the processes controlling the distributions of 231Pa and 230Th in the ocean is important. However, simulations of dissolved and particulate 231Pa and 230Th in the modern ocean, recently obtained from the GEOTRACES project, remain challenging. Here we report a model simulation of 231Pa and 230Th in the global ocean with COCO ver4.0. Starting from the basic water-column reversible scavenging model, we also introduced the bottom scavenging and the dependence of scavenging efficiency on particle concentration. As demonstrated in a previous study, the incorporation of bottom scavenging improves the simulated distribution of dissolved 231Pa and 230Th in the deep ocean, which has been overestimated in models not considering the bottom scavenging. We further demonstrate that introducing the dependence of scavenging efficiency on particle concentration results in a high concentration of dissolved 230Th in the Southern Ocean as observed in the GEOTRACES data. Our best simulation can well reproduce not only the oceanic distribution of 231Pa and 230Th but also the sedimentary 231Pa/230Th ratios. Sensitivity analysis reveals that oceanic advection of 231Pa primarily determines sedimentary 231Pa/230Th ratios. On the other hand, 230Th advection and bottom scavenging have an opposite effect to 231Pa advection on the sedimentary 231Pa/230Th ratios, reducing their latitudinal contrast. Our best simulation shows the realistic residence times of 231Pa and 230Th, but simulation without bottom scavenging and dependence of scavenging efficiency on particle concentration significantly overestimates the residence times for both 231Pa and 230Th in spite of similar distribution of sedimentary 231Pa/230Th ratios to our best simulation.

The multi-field coupling effect of fuel injection duration on gas exchange stability for a free piston engine generator

• The detailed process of fuel injection duration affected the gas exchange stability through multi-field coupling effect was revealed. • Increasing the fuel injection duration is beneficial to improve scavenging efficiency, and the maximum scavenging efficiency is 97.9%. • Shortening the fuel injection duration is beneficial to improve the trapping efficiency, and the maximum trapping efficiency is 41.3%. • The afterburning effect and the backflow phenomenon were found. • The EGR mass fraction is inversely proportional to the fuel injection duration. Free piston engine generator (FPEG) is a new energy conversion plant to substitute for conventional combustion engine. However, the fluctuation of gas exchange is a key problem to induce the FPEG to run unsteadily and restrict its engineering application. This paper presents a study to explore the multi-field coupling effect of fuel injection duration on the gas exchange stability of a diesel compression-ignition, direct-injection, looped scavenging FPEG. A full-cycle gas exchange model of the FPEG is carried out by coupling the zero-dimensional dynamics, multi-dimensional combustion model and scavenging model, and an iterative calculation method is proposed for numerical simulation of the model. Meanwhile, the effect of injection duration schedule lasting from 0.50 ms to 0.80 ms on the scavenging and gas exchange is analyzed. The results show that the shorter injection duration brings about higher fresh trapping efficiency due to its faster reciprocating frequency which reduces the available time for fresh gas to flow out of the cylinder during gas exchange process, and the trapping efficiency is 41.3 % and the operating frequency achieves 36.6 Hz in the injection duration of 0.5 ms condition. However, the influence of injection duration on exhaust gas cleaning is opposite, and the scavenging efficiency varies in positive correlation with the injection duration, because the long injection leads to low motion velocity and causes the exhaust port to be opened and closed slowly, which provides long exhaust time of the residual burned gas in the cylinder. The maximum scavenging efficiency occurs in the injection duration of 0.8 ms condition and features with 97.9%. Suggesting, relatively high scavenging efficiency and trapping efficiency can be obtained at the same time under appropriate injection duration condition.

IN-VITRO FREE RADICAL SCAVENGING AND ANTIOXIDANT ACTIVITY OF JATROPHA CARCUS

To evaluate the in vitro free radical (FR) scavenging activity of leaves Jatropha carcus petroleum ether, ethanol, aqueous extracts of J. carcus were prepared, with successive extraction in Soxhlet apparatus. Each extract was selected to study the FR scavenging activity by superoxide scavenging assay and 2, 2-diphenyl-1 picrylhydrazyl hydrazyl (DPPH) radical scavenging assay method. It was found that aqueous extract contained carbohydrates, glycosides amino acids flavonoids, tannins, alkaloids and steroids; ethanolic extract contained glycosides amino acids flavonoids, tannins, alkaloids and steroids. Radical scavenging activity of plant extracts against stable DPPH was determined spectrophotometrically. Extract solutions were prepared by dissolving 0.025 g of dry extract in 10 ml of methanol. The solution of DPPH in methanol was prepared daily. The samples were kept in the dark for 15 min at room temperature and then the decrease in absorption was measured. Ethanolic extract of Jatropha carcus had showed 71.8±0.69 % inhibition in superoxide scavenging model. Aqueous extract also showed almost similar activity (67.8±0.58 % compared to ethanolic extract), while petroleum ether extract showed poor inhibition of superoxide scavenging activity. The antioxidant capacity of various solvent fractions of Jatropha carcus was found to decrease in this order:ethanolic ˃ aqueous ˃ petroleum ether. All results showed antioxidant activity in dose dependent manner at concentration 10 to 30 μg/ml. Strong antioxidant activity of ethanolic extract statistically similar to ascorbic acid indicates strong antioxidants in this extract. All extracts showed dose and time dependent inhibition of superoxide scavenging activity.

DES Based Efficient Extraction Method for Bioactive Coumarins from Angelica dahurica (Hoffm.) Benth. &amp; Hook.f. ex Franch. &amp; Sav.

In this study, a simple and environmentally friendly method was developed for the extraction of seven active coumarins from Angelica dahurica (Hoffm.) Benth. &amp; Hook.f. ex Franch. &amp; Sav.(A. dahurica) based on deep eutectic solvents (DESs). Among the 16 kinds of DES based on choline chloride, the DES system with the molar ratio of choline chloride, citric acid, and water as 1:1:2 had the best extraction effect. Ultrasonic-assisted response surface methodology (RSM) was used to investigate the optimal extraction scheme. The results showed that the optimal extraction conditions were a liquid–solid ratio of 10:1 (mL/g), an extraction time of 50 min, an extraction temperature of 59.85 °C, and a moisture content of 49.28%. Under these conditions, the extraction yield reached 1.18%. In addition, scanning electron microscopy (SEM) was used to observe the degree of powder fragmentation before and after extraction with different solvents. The cells of A. dahurica medicinal materials obtained by DES ultrasonic-assisted treatment were the most seriously broken, indicating that DES had the highest efficiency in the treatment of A. dahurica. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) DPPH radical scavenging model was used to evaluate the biological activity of DES extract. The results showed that DES extract had better scavenging ability of DPPH free radical. Therefore, DES is a green solvent suitable for extracting coumarin compounds of A. dahurica, with great potential to replace organic solvents.