Droplet Scale Research Articles

The impact of carbon quantum dots derived from spent coffee grounds on the droplet combustion of diesel/n-butanol blend

As global concerns surrounding climate change mount and fossil fuel reserves diminish, the application of additives in internal combustion engines is increasingly prevalent. Butanol and carbonaceous nanomaterials, such as carbon quantum dots (CQD), are being employed as additives to increase engine efficiency and mitigate the emission of pollutants. Nevertheless, understanding the impact of these additives on combustion behavior at the droplet scale through combustion assessments before their use in engines is crucial. In this study, our main objective was to assess the impact of incorporating CQD dispersed in n-butanol as additives to conventional diesel fuel on the combustion characteristics at the droplet scale. CQD were obtained from spent coffee grounds (SCGs) using n-butanol as a solvent. The product obtained was mixed with Colombian commercial diesel (10 % vol. palm oil biodiesel), and its combustion was evaluated using the droplet combustion method. Before the CQD synthesis, SCGs were characterized by thermogravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM). CQD were characterized via Fourier transform infrared (FTIR) spectroscopy, Transmission Electron Microscopy (TEM), UV–vis, and fluorescence spectroscopy. Results indicated that adding n-butanol and CQD to commercial diesel leads to a 5.4 % and 16.5 % increase in droplet ignition delay, respectively. These additives also cause droplet contraction and expansion cycles, resulting in unstable combustion. However, CQD reduces the frequency of microexplosions caused by boiling n-butanol inside the droplet, which mitigates instabilities during droplet combustion. Including CQD can enhance fuel evaporation by increasing the density of nucleation sites for bubble formation and preventing micro-explosions, thereby leading to stable combustion. These attributes can significantly influence the performance of blends in Compression Ignition (CI) Engines.

Electrocombustion Characteristics of Iron Particle-Laden Methanol and Ethanol Droplets in a Direct Current Field

ABSTRACT This study investigates the electrocombustion and atomization behavior of single droplets (2.5 wt.% Fe) of ethanol (EtOH) and methanol (MeOH) fuels at the droplet scale. The experiments utilize a system with two opposing plate electrodes of varying distances (200, 150, and 100 mm) and both negative (↓) and positive (↑) polarizations within a vertical direct current (DC) electric field. The results show that for EtOH and EtOH/Fe droplets, the flame envelope changes to a spherical form at (↓) and (↑) polarizations at 100 mm plate spacing, while for MeOH and MeOH/Fe droplets, the flame envelope changes to a spherical form at (↓) and (↑) polarizations at 200, 150 and 100 mm plate spacing. Increasing electric field strength reduced the micro-explosion tendency of Fe particles in the flame region and the micro-explosion intensity of Fe particles was found to be higher in ethanol droplets than in methanol. No systematic relationship could be established between the electric field effect and the presence of Fe particles. The MeOH/Fe/150(↑) droplet exhibited the lowest extinction time of 1050 ms. The electric field fundamentally alters the secondary atomization process of the fuel droplets. Notably, the diameter regression of all MeOH-based fuel droplets deviates significantly from a linear relationship. The investigation into the combustion behavior of pure EtOH, MeOH, and their Fe-blended counterparts within an electric field environment suggests that MeOH and MeOH/Fe fuels exhibit superior combustion characteristics. However, further research is necessary to fully elucidate these findings.

Molecular interaction of cyclodextrins with cellulose nanocrystals: A new venue for improving the functional properties of Pickering emulsions

The design of functional delivery systems is essential for storing and releasing active components. Inspired by the structure of Nepenthes mirabilis, cellulose nanocrystals (CNC) cooperate with cyclic α-cyclodextrins (α-CD), β-cyclodextrins (β-CD), and γ-cyclodextrins (γ-CD) to form nanocomposites at different mass ratios for the delivery the Mosla chinensis essential oils (EO)-loaded Pickering emulsions (PE), respectively. Characterization methods including FT-IR, TG, XPS, AFM, XRD, and three-phase contact angle were used to analyze the structure of the nanocomposites. The molecular docking and molecular dynamic simulation results revealed that the most hydrogen bonds were formed between β-CD and CNC, but the tendency for γ-CD and CNC to bond with hydrogen bonds was stronger in the molecular dynamic simulation. Subsequently, the physicochemical properties of emulsions stabilized by CNC/CDs nanocomposites were characterized through particle size, potential, microstructure, long-term stability, rheology, and aqueous phase distribution indexes. The results showed that the different mass ratios CNC/α-CD and CNC/β-CD nanocomposites stabilized PE had smaller droplet scales and better stability. While CNC/γ-CD nanocomposites had a negative effect on the emulsion. The in vitro release results showed that the emulsions stabilized by CNC/CDs nanocomposites had a slow-release rate for EO by diffusion. The simulated gastrointestinal release showed that CNC/β-CD-PE had the highest bioavailability. Moreover, CNC/β-CD-PE reduced the minimal inhibitory concentration of EO by a mechanism that disrupts the membrane structure of bacteria. Therefore, the introduction of β-CD may be an effective alternative in regulating the physical properties, function, and stabilization of CNC-based PE. These findings provide a scientific basis for the rational structural design of delivery systems for the encapsulated aroma molecules.

Enhancing Droplet Combustion Dynamics in Trimethyl Borate-Based Blends: Exploring Energetic Phenomena

ABSTRACT Trimethyl borate (TMB) is an excellent alternative to alter the combustion of conventional fuels due to the combination of boron, stable methyl groups, and oxygen, which can improve the combustion behavior in many ways compared to alcohols and etheric hydrocarbon structures. In this research, the combustion and energetic phenomena trends of trimethyl borate blends was investigated on a droplet scale. The camera systems were used at the combustion characteristics look at how the size of the droplets, the structure of the flame, and the flame temperature changed over time. The additions of 20%, 40%, 60%, and 80% trimethyl borate fuel to gasoline were tested for their ability to burn. As the amount of TMB increased, high variations in droplet deformation and high breakups from the hemispheric geometry occurred. At this point, changes were observed in droplet shape change independent of mixing ratio. TMB droplet had the highest flame temperature of 600 K and the lowest extinction time of ~ 1270 ms. As the gasoline content of the droplets increased, the droplet flame temperature tended to decrease. Also, the shortest ignition delay time was observed for pure TMB and fuel droplets containing 40%, 60% and 80% TMB (~0.714 ms).

Droplet freeze desalination high fidelity modeling for sustainable water purification and diverse applications

Freeze desalination (FD) is an environmentally clean water purification technique that holds a great promise for low-energy consumption and with unlimited brine's salinity levels. The brine cooling induces freezing, rendering separation and removing contaminants. A high-fidelity molding using CFD is employed to explain the purification of ice from saline droplets in a sub-cold environment under natural free-convection. Comparisons were made with analytical predictions derived from experimentally acquired data through brine cooling in bulk and droplet scales. The procedural sequence employed facilitated the model's ability to accurately represent the ion diffusion and phase-change phenomena across various temperatures (−15 °C and − 25 °C), concentrations, partition & heat-transfer coefficients, and droplet volumes (3 μL to 9 μL). The salt concentration ranged from seawater (35 g/L) to RO (70 g/L) salinity levels. The model successfully accommodates the experimental temperatures observed during the equilibrium between the solid and liquid phases. The achieved desalination efficiency ranges from 20 % to above 40 %. Lastly, machine learning is implemented to identify the principal experimental parameters influencing desalination efficiency. In the suggested system, dynamic salinity/impurity and temperature profiles enable natural free convection brine cooling research. The current framework can study the purification/concentration efficiency of diverse range of mixtures subjected to freeze crystallization.

Combustion Behavior of Fuel Droplets with Metallic, Non-Metallic and Organo-Metallic Boron Additives

ABSTRACT There is considerable interest in the utilization of fuels derived from boron materials, with their high calorific value, in various applications ranging from propellants to pyrotechnics. Conversely, their impact on the combustion behavior of conventional hydrocarbon fuels remains largely unclear. In this study, ignition, combustion, micro-explosion and simultaneous atomization behaviors of gasoline-based alternative fuels containing metallic (28–35 µm MgB2), nonmetallic (1 µm amorphous boron, 10 µm AlB12 with 86–88% and 95–97% purity) and organo-metallic boron derivatives (triethyl borate (TEB) containing C2H5 groups and trimethyl borate (TMB) containing CH3 groups) were investigated. The experiments were carried out at droplet scale and recorded using a high-speed camera and a thermal camera. The findings revealed a systematic reduction in ignition delay for each gasoline fuel enriched with boron derivatives. 2.5%AlB12/G and pure TMB droplets were the fastest extincting fuel droplets (0.9678 s and 1.245 s, respectively). The highest maximum flame temperature was recorded as 626 K and 610 K for pure TMB and 80%TEB/G, respectively. Droplet diameter regression analyses showed that the diameters of fuel droplets containing predominantly metallic and nonmetallic boron derivatives decreased in accordance with the d 2 -law. This study demonstrated that cost-effective and easily producible amorphous boron and organometallic boron derivatives are promising energy carriers for hydrocarbon fuels.

A PHYSICAL MODEL FOR THE PREDICTION OF ALUMINUM OXIDE RESIDUES

This work proposes a new model to estimate the size of oxide residues produced during the combustion of aluminum. Such large oxide residues contribute to the two-phase loss performance in solid rocket motors. The model includes two physical mechanisms: deposition of oxide smoke from the surrounding flame and oxide creation on aluminum surface by heterogeneous reactions. Parametric numerical simulations at the aluminum droplet scale are performed to estimate the rate of deposition and surface production, in order to feed a zero-dimensional model of oxide lobe growth and final oxide residue. Results are in line with available measurements with an oxide residue-to-aluminum size ratio in the range 0.5 ~ 0.8, depending on conditions. The model suggests that surface reactions are important for low pressures and small particles, while deposition prevails otherwise.

Combustion Characteristics of r-GO/g-C3N4/LaFeO3 Nanohybrids Loaded Fuel Droplets

ABSTRACT Graphene oxide (GO), reduced graphene oxide (r-GO) and graphitic carbon nitride (g-C3N4) are two-dimensional carbon-based nanosheets that show promise in reducing emissions with their superior catalytic activity in capturing species such as NOx and CO2 thanks to their oxygen-based functional groups and active edges on their surfaces. These active surfaces also provide a scheme for the substitution of materials with high calorific value or high catalytic activity for combustion. This study focuses on the fabrication of functional nanohybrid structures customized for combustion with LaFeO3 metal oxide nanoparticles substituted on these nanosheets and their effect on the combustion behavior of gasoline. The fabrication of r-GO/g-C3N4/LaFeO3 nanohybrid structures was carried out by a two-step hydrothermal method. The structural characterizations of the samples were confirmed by SEM and XRD analyses and their chemical states were confirmed by Raman and XPS techniques. Combustion experiments were carried out by droplet scale combustion of gasoline-based nanofuel droplets containing dilute (0.2 wt.%) and high (0.7 wt.%) concentrations of GO, r-GO, g-C3N4, g-C3N4/LaFeO3 and r-GO/g-C3N4/LaFeO3 nanoparticles. The experimental process was recorded with a high-speed camera and a thermal camera. The nanofuel droplets containing 0.2 wt.% g-C3N4/LaFeO3 nanohybrid structures had the highest maximum flame temperature of 519 K, and the nanofuel droplets containing 0.7 wt.% r-GO/g-C3N4/LaFeO3 particles had the highest maximum aggregate temperature of 1177 K. The ignition delay time decreased for all droplets with 0.2 wt.% and 0.7 wt.% particle loadings. At 0.2 wt.% concentration, g-C3N4 doped fuel droplets exhibited the lowest extinction time, while at 0.7 wt.% concentration, the lowest extinction time was measured for r-GO/g-C3N4/LaFeO3 doped fuel droplets. Fuel droplets containing g-C3N4 particles had the highest burning rate and were the fastest extinguishing fuel droplets in the electric field. In this study, it has been demonstrated that the combustion rate and energy value of hydrocarbon fuels can be increased and soot formation can be reduced at the same time with the new generation of graphene-based functional materials to be created, and thus, many combustion problems can be solved simultaneously with these functional particles.

Multi-scale conditional diffusion model for deposited droplet volume measurement in inkjet printing manufacturing

The volume consistency of deposited droplets is regarded as a core quality evaluation to achieve zero-defect manufacturing (ZDM) in inkjet printed organic light-emitting diode (OLED). In order to improve the product quality, the causal links between printing defects and its causes should be determined. However, the collection of the defects quantified data remains a challenge due to the micrometer scale and few texture features of droplets. In this paper, an accurate measurement method for deposited droplets based on coherence scanning interferometry (CSI) is proposed. Firstly, time series signals for topography reconstruction are recorded when CSI scans droplets vertically at a constant speed. Then, a deep learning method, multi-scale conditional diffusion model (MS-CDM), is proposed to restore the time series signals’ distortions led by the chromatic dispersion. Furthermore, a self-supervised learning method is proposed to efficiently train the MS-CDM, since the labeled data is hard to be acquired in industrial environment. Finally, the printing experiment indicates the collaboration of different modules in intelligent close-loop to reduce Mura defects. The volume measurement experiments demonstrate the ability to accurately measure the volume of deposited droplets, and the measurement error reaches 1.3%. The performance experiment on several public datasets demonstrates the method’s promising feature representation ability for time series mainstream task, and the MS-CDM achieves the best performance compared to those baselines methods.

Atomization and combustion behavior of nanofuel droplets containing perovskite-type nanoparticles

Metal and metal oxide nanoparticles (NPs) are promising agents for reducing energy consumption and pollution in applications where combustion power generation is provided. This study focuses on the production of new generation perovskite-type metal oxide NPs with enhanced catalytic activity customized for combustion and investigation of their catalytic performance for gasoline. The droplet scale combustion experiments were carried out at ambient temperature, atmospheric pressure and under normal gravity, the experimental processes were recorded with an optical system consisting of a high-speed camera and a thermal camera with a spectral range of 7.5–14 μm, and the combustion and atomization behavior of the nanofuel droplets were characterized. Perovskite-type NPs were produced by sol-gel technique in varying stoichiometric ratios (LaMnO3, La1-XNdXMnO3, La1-XBaXMnO3, Nd1-XBaXMnO3, La0.5NdXBa0.5-XMnO3, x = 0, 0.3) to confirm their catalytic activity's effect on gasoline droplets' combustion behavior. Structural characterization of the obtained five different NPs was carried out by SEM and XRD techniques. Chemical analysis, surface area measurements, and spectral properties of the samples were determined by XPS, BET, and UV–Vis spectroscopy, respectively. The results showed that all perovskite-type NPs have particle size range of 25–40 nm. La0.7Nd0.3MnO3 NPs had the highest oxygen adsorption ability and La0.5Nd0.3Ba0.2MnO3 NPs had the largest surface area (393.4898 m2/g). Perovskite type NPs tended to increase ignition delay and extinction times. The maximum flame temperature of fuel droplets loaded with La0.5Nd0.3Ba0.2MnO3 NPs was 469 °C. This temperature was 274 °C higher than the maximum flame temperature of the pure gasoline droplet. The outcomes demonstrated that, with the right catalyst design, perovskite-type NPs can perform better as powerful oxidizers and high energy combustion catalysts.

Versatile Product Detection via Coupled Assays for Ultrahigh-Throughput Screening of Carbohydrate-Active Enzymes in Microfluidic Droplets.

Enzyme discovery and directed evolution are the two major contemporary approaches for the improvement of industrial processes by biocatalysis in various fields. Customization of catalysts for improvement of single enzyme reactions or de novo reaction development is often complex and tedious. The success of screening campaigns relies on the fraction of sequence space that can be sampled, whether for evolving a particular enzyme or screening metagenomes. Ultrahigh-throughput screening (uHTS) based on in vitro compartmentalization in water-in-oil emulsion of picoliter droplets generated in microfluidic systems allows screening rates >1 kHz (or >107 per day). Screening for carbohydrate-active enzymes (CAZymes) catalyzing biotechnologically valuable reactions in this format presents an additional challenge because the released carbohydrates are difficult to monitor in high throughput. Activated substrates with large optically active hydrophobic leaving groups provide a generic optical readout, but the molecular recognition properties of sugars will be altered by the incorporation of such fluoro- or chromophores and their typically higher reactivity, as leaving groups with lowered pKa values compared to native substrates make the observation of promiscuous reactions more likely. To overcome these issues, we designed microdroplet assays in which optically inactive carbohydrate products are made visible by specific cascades: the primary reaction of an unlabeled substrate leads to an optical signal downstream. Successfully implementing such assays at the picoliter droplet scale allowed us to detect glucose, xylose, glucuronic acid, and arabinose as final products of complex oligosaccharide degradation by glycoside hydrolases by absorbance measurements. Enabling the use of uHTS for screening CAZyme reactions that have been thus far elusive will chart a route toward faster and easier development of specific and efficient biocatalysts for biovalorization, directing enzyme discovery by challenging catalysts for reaction with natural rather than model substrates.

Study of the de Almeida-Thouless line in the one-dimensional diluted power-law XY spin glass.

We study the de Almeida-Thouless (AT) line in the one-dimensional power-law diluted XY spin-glass model, in which the probability that two spins separated by a distance r interact with each other, decays as 1/r^{2σ}. Tuning the exponent σ is equivalent to changing the space dimension of a short-range model. We develop a heat bath algorithm to equilibrate XY spins; using this in conjunction with the standard parallel tempering and overrelaxation sweeps, we carry out large-scale Monte Carlo simulations. For σ=0.6, which is in the mean-field regime above six dimensions-it is similar to being in 10 dimensions-we find clear evidence for an AT line. For σ=0.75 and σ=0.85, which are in the non-mean-field regime and similar to four and three dimensions, respectively, our data is like that found in previous studies of the Ising and Heisenberg spin glasses when reducing the temperature at fixed field. For σ=0.75, there is evidence from finite-size-scaling studies for an AT transition but for σ=0.85, the evidence for a transition is nonexistent. We have also studied these systems at fixed temperature varying the field and discovered that at both σ=0.75 and at σ=0.85 there is evidence of an AT transition! Confusingly, the correlation length and spin-glass susceptibility as a function of the field are both entirely consistent with the predictions of the droplet picture and hence the nonexistence of an AT line. In the usual finite-size critical point scaling studies used to provide evidence for an AT transition, there is seemingly good evidence for an AT line at σ=0.75 for small values of the system size N, which is strengthening as N is increased, but for N>2048 the trend changes and the evidence then weakens as N is further increased. We have also studied with fewer bond realizations the system at σ=0.70, which is the analog of a system with short-range interactions just below six dimensions, and found that it is similar in its behavior to the system at σ=0.75 but with larger finite-size corrections. The evidence from our simulations points to the complete absence of the AT line in dimensions outside the mean-field region and to the correctness of the droplet picture. Previous simulations which suggested there was an AT line can be attributed to the consequences of studying systems which are just too small. The collapse of our data to the droplet scaling form is poor for σ=0.75 and to some extent also for σ=0.85, when the correlation length becomes of the order of the length of the system, due to the existence of excitations which only cost a free energy of O(1), just as envisaged in the TNT picture of the ordered state of spin glasses. However, for the case of σ=0.85 we can provide evidence that for larger system sizes, droplet scaling will prevail even when the correlation length is comparable to the system size.

Effects of Spinel Oxide Combustion Catalysts on the Combustion Behavior and Secondary Atomization Mechanism of Gasoline Droplets

ABSTRACT The catalytic activity of Mg-based spinel oxide nanoparticles (NPs) on the combustion behavior of gasoline and their effects on the atomization behavior were determined by droplet scale combustion experiments. MgFe2O4, MgCo2O4 and MgMnO3 spinel oxide NPs were produced by the sol-gel technique and doped into gasoline. The particles with the highest surface oxygen were MgCo2O4 and MgFe2O4 NPs, while the NPs with the largest surface area were MgCo2O4 NPs (517.8433 m2/g). The size of the flame envelope tends to shrink as the oxygen concentration of the particles rises, but an increase in their surface area tends to shorten ignition delay periods. MgFe2O4 NPs increased the flame temperature by 163°C compared to the pure gasoline. While MgFe2O4 and MgMnO3 NPs increased the extinction time of gasoline, MgCo2O4 NPs decreased the severe time by about 75% with the violent micro-explosions they created. In this study, we focused on the production of spinel oxide agents customized for combustion with improved catalytic activity, high flammability, and different component designs, and the results showed that these particles can reduce the soot formation of conventional hydrocarbons.

Ferrofluid droplets in planar extensional flows: Droplet shape and magnetization reveal novel rheological signatures of ferrofluid emulsions

By subjecting a ferrofluid emulsion to an external magnetic field, the flow at the droplet scale is altered, resulting in significant changes in the emulsion's rheological behavior. We present the first study of the rheological response of a dilute ferrofluid emulsion under extensional flow. Our findings reveal that at the microscopic level, the droplets experience a field-induced internal torque that leads to a complex non-symmetric stress tensor. We identify the remarkable presence of shear stresses within a material experiencing a pure extensional flow.

Mass Transfer and Droplet Behaviors in Liquid-Liquid Extraction Process Based on Multi-Scale Perspective: A Review

Liquid-liquid extraction is an important separation technology in the chemical industry, and its separation efficiency depends on thermodynamics (two-phase equilibrium), hydrodynamics (two-phase mixing and contact), and mass transfer (molecular diffusion). For hydrodynamics, the dispersion size of droplets reflects the mixing of two phases and determines the mass transfer contact area of the two phases. Therefore, a deep understanding of the droplet dispersion mechanism can help guide process intensification. The mass transfer and droplet behaviors in the liquid-liquid extraction process are reviewed based on three scales: equipment, droplets, and the interface between two liquids. Studies on the interaction between mass transfer and other performance parameters in extraction equipment as well as liquid-liquid two-phase flow models are reviewed at the equipment scale. The behaviors of droplet breakage and coalescence and the kernel function of the population balance equation are reviewed at the droplet scale. Studies on dynamic interfacial tension and interaction between interfaces are reviewed at the interface scale. Finally, the connection among each scale is summarized, the existing problems are analyzed, and some future research directions are proposed in the last section.

Experimental studies on combustion and atomization characteristics of aliphatic and aromatic hydrocarbons droplets

This study focused on how the properties of alcohols (ethanol, methanol, n-butanol), ketones (acetone), alkanes (hexane), esters (ethyl acetate), methyl benzenes (toluene), and ethers (diethyl ether) shape individual combustion and atomization behaviors. The experimentation conducted at the droplet scale involved suspending fuel droplets on a ceramic wire and subsequently igniting them for analysis. Experiments were recorded with a high-speed camera and a thermal camera with a spectral range of 7.5–14 μm. The results showed that the flame of the oxygenated fuel droplets, unlike non-oxygenated fuels, has a high non-luminous region seen throughout the combustion process. The diameter reduction of the fuel droplets during combustion tended to obey the D2-law. Single and multicomponent fuel droplets are hemispherical for preheating (Stage I) and hemispherical in droplet disruption mode for combustion and droplet diameter decrease (Stage II). Hexane, diethyl ether, and ethyl acetate were the fuels that were extinguished in the shortest time among the fuels studied here with extinction times of 1.021 s, 0.925 s, and 0.885 s, respectively. Hexane, diethyl ether, acetone, and diesel droplets had the minimum ignition delay times according to the experimental conditions in this study. In terms of maximum flame temperature, ethyl acetate exhibited the highest value among oxygenated fuel droplets, reaching 155 °C, while toluene demonstrated the highest maximum flame temperature of 244 °C among all fuel types, including non-oxygenated fuels.

A novel droplet-based approach to study phase transformations in lyotropic liquid crystalline systems

HypothesisLyotropic liquid crystals (LLC) and their phase transformations in response to stimuli have gathered much interest for controlled and ‘on-demand’ drug applications. Bulk methods of preparation impose limitations on studying the transformations, especially induced by compositional changes, such as enzymatic changes to lipid structure. Here we hypothesise that controlled microfluidic production and coalescence of dissimilar aqueous and lipid droplets emulsified in a third mutually immiscible liquid will provide a new approach to the spatio-temporal study of structure formation in lyotropic liquid crystalline materials. ExperimentsSeparate lipid and aqueous droplets, dispersed in a fluorocarbon oil were generated using a microfluidic format. The chip, prepared as a hybrid polydimethylsiloxane (PDMS) and glass microfluidic device, was constructed to enable in-situ acquisition of time-resolved synchrotron small angle X-ray scattering (SAXS) and crossed polarised light microscopy of the coalesced droplets to determine the structures present during aging. FindingsJanus-like droplets formed upon coalesce, with distinct lipid and aqueous portions with a gradient between the two sides of the merged droplet. SAXS and polarised light microscopy revealed a progression of mesophases as the lipid portion was hydrated by the aqueous portion via the diffusion limited interface which separated the portions. Thus demonstrating, on a droplet scale, a new approach for studying the phase transformation kinetics and identification of non-equilibrium phase in droplet-based lyotropic liquid systems.

Effect of amide-functionalized carbon nanotubes as commercial diesel and palm-oil biodiesel additives on the ignition delay: A study on droplet scale

The wide use of diesel in transport and industry demands actions to reduce the emissions of harmful pollutants in the scenario of the energy transition to renewable energy, which is currently the trend in most countries around the world. Carbon nanomaterials added to diesel have been identified as a promising alternative for reducing particulate matter and NOx emissions. However, the stability of the dispersions of these nanomaterials in liquid fuels is an issue of major concern because it determines the applicability of nanofuels to internal combustion engines. That is why some alternatives, like carbon nanomaterial functionalization, have been explored to increase the stability of nanofuels, but the addition of these functionalized nanomaterials could have an effect on the combustion properties of the blends. This work explores for the first time the effect of using amide-functionalized carbon nanotubes on the ignition delay of blends of these nanomaterials (50 and 100 ppm) and Colombian commercial diesel (90 % petroleum diesel and 10 % palm-oil biodiesel) and palm-oil biodiesel. The characterization of the ignition delay was conducted on a droplet scale through the shadowgraph technique since this property is an indicator of the performance of real compression ignition engines in terms of combustion efficiency and pollutant emissions. Results showed that the addition of carbon nanotubes, either functionalized or not, increased the volumetric expansion of the droplets before ignition by up to 1.6 % in comparison with the raw fuels. Also, the addition of carbon nanotubes reduced the ignition delay of the blends in comparison to the raw fuels by about 18.3 % and 13.1 % for biodiesel with functionalized carbon nanotubes at 50 ppm and 100 ppm, respectively; 9.4 % and 11.8 % for biodiesel with no-functionalized carbon nanotubes at 50 ppm and 100 ppm, respectively; 12.3 % and 18.3 % for commercial diesel with functionalized carbon nanotubes at 50 ppm and 100 ppm, respectively; and 14.9 % and 14.7 % for commercial diesel with no-functionalized carbon nanotubes at 50 ppm and 100 ppm, respectively. However, the reduction for biodiesel with functionalized carbon nanotubes at 100 ppm was not significantly different from that of the biodiesel added with no-functionalized carbon nanotubes at 50 and 100 ppm. In the case of commercial diesel, despite the reduction of the ignition delay for all the nanofuels in comparison with the raw fuel, there was not a significant difference between the functionalized and no-functionalized blends.

Transient Calculation Studies of Liquid–Solid Collision in Jet Descaling

Sichuan is gradually being transformed and is utilizing groundwater and thermal resources. However, this investigation found that the high mineralization rate of geothermal resources in the Sichuan Basin is common and efficient, and environmentally friendly descaling technology is the key to promoting the utilization of thermal resources in low-yield oil and gas wells. Due to the high efficiency, low cost, and lack of pollution of high-pressure jet descaling, it has attracted more and more attention recently, but the mechanism of jet descaling is still unclear. The key to jet descaling is the stress concentration in the scale caused by the impact of droplets from the jet. In this paper, the process of jet descaling is simplified as a 2D droplet–scale collision with a detailed theoretical analysis of the stress on the scale. A circular droplet was simulated to impact the surface of the scale. By using numerical methods for transient calculations, we couple the pressure of the droplets and the scale strain. We acquired transient equivalent stress fields inside scales and pressure distributions inside the water droplet. As a result of the impact, areas of high stress in the scale appeared. Due to the stress superposition, the highest stress is concentrated in two areas: the contact edge and the shaft. These results can identify the mechanism for high-pressure jet descaling and help improve the efficiency of high-pressure water-jet descaling.

Hypergolic ignition of paraffin-based hybrid rocket fuels by sprays of liquid oxidizer

An experimental study is conducted to measure the ignition delay of ammonia borane doped paraffin wax with sprays of white fuming nitric acid as oxidizer. The injection pressure and injector diameter are varied to investigate the effects of spray characteristics on the ignition dynamics. A range of Weber (We) number for the oxidizer jet covering 100 < We <2700 and Reynolds (Re) number 1300 < Re <8900 is investigated, whereas the We number at the droplet scale varies from 0.8 < Wedrop <24.1. The sprays are characterized using phase-doppler anemometry to obtain the size and speed distribution of the oxidizer droplets across multiple positions. In addition to conventional high-speed imaging, the hypergolic ignition is also observed using Schlieren imaging and a high-speed mid-infrared camera. The results show that the ignition delay of a hypergolic hybrid fuel under spray conditions is unaffected by the mean droplet size of the oxidizer. The ignition delay decreases with increasing We number at the droplet scale and increasing droplet velocity. The variability in the ignition delay also decreases with Weber number and droplet velocity. The values obtained for the ignition delay when using a spray are generally higher than those from simple oxidizer drop experiments, highlighting the need to investigate the hypergolic ignition in configurations representative of engine conditions.