Release Rate Profiles Research Articles

Computational investigation of combustion and emission characteristics of HCCI engine fueled with Carbon-Free NH3 –H2O2 blend

A computational investigation is provided of the utilization of blends of NH3 and H2O2 as carbonless fuels for HCCI combustion. A Computational Fluid Dynamics (CFD) model is developed and validated to assess the engine’s performance under varying proportions of NH3 and H2O2, equivalence ratios, and inlet temperatures. The heat release rate profiles demonstrated dual peaks, which were rationalized as an initial fuel decomposition followed by a slow thermal explosion and then a fast depletion of the fuel after the generation of a pool of OH radicals through decomposition of H2O2. Findings suggest that an increase in mole fraction of H2O2 advances combustion. Increasing the H2O2 volume fraction also decreases combustion duration, while increasing the IMEP. In-cylinder peak pressure and Maximum Pressure Rise Rate (MPRR) increase with H2O2 mole fraction, leading to reduced thermal efficiency, particularly at higher equivalence ratios, and an increased danger of uncontrolled combustion (knocking). Additionally, higher inlet mixture temperatures were shown to result in an advancement in the start of combustion and a reduction in combustion duration, with a corresponding increase in peak pressure. This points to the possibility of potentially controlling the notoriously difficult-to-control HCCI combustion through intake temperature for NH3/H2O2 fuel blends. However, increased NOx emissions are observed for increased intake temperature and in any case the NOx emissions are orders of magnitude above current regulatory limits, which means that practical engine operation will only be possible with an aftertreatment scheme based on the de-NOx activity of NH3.

Inverse identification of a pollutant source in an apartment with multiple rooms by joint multi-zone model and CFD

In case a hazardous agent is accidentally released inside a building, both the pollutant source location and the temporal release rates must be determined in order to guide emergency actions. Inverse modeling based on either a multi-zone model or computational fluid dynamics (CFD) may help to find the pollutant source. This investigation proposed the inverse identification of both the release location and dynamic release rate profile of a pollutant source in an apartment with multiple rooms. In the first stage of the solution, the room containing the pollutant source was identified by the inverse multi-zone model; then, in the second stage, the occupant who released the pollutant was determined by the inverse CFD model. Both models solved for the possible pollutant release rate profiles with a regularized, inverted matrix at all candidate zones/positions based on information from a sensor. Next, the occurrence probability at each candidate zone/position was interpreted by the Bayesian probability model with input from another sensor. The results revealed that the two types of models could be used in conjunction to efficiently identify both the room in which the pollutant was released and the exact occupant who released it, as well as the dynamic release rate profile.

Effect of using borax decahydrate as nanoparticles additive in blends of spirulina biodiesel/diesel on combustion characteristics and knock intensity

Abstract In this extensive investigation, the impact of borax decahydrate as a fuel additive in a diesel single-cylinder engine was rigorously examined. Borax decahydrate was introduced at concentrations of 5, 15, 25 and 35 g in 500 ml of biodiesel, forming five unique fuel mixtures with conventional diesel: 90% diesel + 10% spirulina biodiesel (SB10), SB10 + 1 g borax decahydrate (SB10B1), SB10 + 3 g borax decahydrate (SB10B3), SB10 + 5 g borax decahydrate (SB10B5) and SB10 + 7 g borax decahydrate (SB10B7). The investigation encompassed four diverse loading conditions and yielded insightful findings. Notably, at full load, SB10B3 exhibited a higher cylinder peak pressure than diesel, reaching 69.25 bar. Heat release rate profiles demonstrated superior efficiency for SB10 at 50% load, with a cumulative heat release rate of 950 J/°CA, which is lower than the 1050 J/°CA of diesel. Knock intensity (KI) evaluations revealed that, although SB10 and SB10B1 exhibited higher KI than diesel at full load due to elevated peak pressure, SB10B7 showed no knocking across all loads, indicative of reduced in-cylinder combustion. This meticulous numerical analysis emphasizes the potential of borax decahydrate as a catalyst and enhancer, providing valuable insights into the combustion dynamics of these alternative fuel blends and their viability for sustainable and efficient engine performance. In summary, out of all the blends, SB10B3 could be a potential diesel fuel replacement fuel for compression-ignition engines.

Experimental study and modelling of real-scale vertical cable tray fires

Cables are one of the most important fire loads in nuclear power plants. It is therefore important to understand their fire behaviour and to predict their heat release rate curve. Electricité de France carried out a series of full-scale vertical cable tray fire experiments. Relevant measurement systems were used. The aim of this article is to give an overview of these experiments and their main results. Important aspects of the fire behaviour are discussed and compared with the literature. In addition, two models, namely the FLASH-CAT model and the ISO 18195 vertical cable tray model, are compared to the experiments and their ability to predict the heat release rate profile is discussed. The models are also compared with other real-scale experiments available in the literature. The ISO 18195 model shows good agreement with the different experiments for the heat release rate profile. The FLASH-CAT model obtains reasonable conservative results for the maximum heat release rate. However, the model significantly overestimates the growth rate in all the tests.

On the Three-Stage Explosion Characteristics of Diethyl Ether-Oxygen Mixtures

ABSTRACT In this article, the three-stage explosion limits of diethyl ether (a typical alternative fuel with a high cetane number and high energy density) are taken as the research object. A comprehensive and in-depth analysis of the double negative temperature coefficient (NTC) behavior of the cool flame region and hot ignition region, through the detailed kinetic analysis, have been carried out. The results show that with the increase of the equivalence ratio, the double NTC phenomenon becomes more remarkable. In very lean conditions, such as the equivalence ratio of less than 0.5, the boundary between the first NTC region and the second NTC region becomes obscure, and a deeper single NTC phenomenon is formed as these two NTC regions merge. The whole explosion limit curve shifts to higher pressure conditions with the increase of the addition of inert gas. The NTC phenomenon in the moderate temperature region becomes more significant and the boundary between these two NTC regions is more obvious. In addition, the hot flame explosion limit also shows such two NTC response. The heat release rate (HRR) profile exhibits three-stage, two-stage, single-stage ignition, or non-ignition depending on the initial conditions. To elucidate the differences in the ignition process between the different explosion limit regimes, the sensitivity and reaction pathway analyses are performed. This study not only provides insight into the oxidation characteristics of ether fuels, but also provides theoretical support for high-performance engines.

Development of optimal in vitro release and permeation testing method for rectal suppositories

Currently there are no compendial assays for testing drug release from rectal suppositories. It is therefore essential to study different in vitro release testing (IVRT) and in vitro permeation testing (IVPT) methods for identifying a suitable technique to compare in vitro drug release and to predict in vivo performance of rectal suppositories. In the present study, three different rectal suppository formulations of mesalamine (CANASA, Generic, and In-house) were studied for in vitro bioequivalence. All the different suppository products were characterized by performing weight variation, content uniformity, hardness, melting time, and pH tests. Viscoelastic behavior of the suppositories was also tested both in presence and absence of mucin. Four different IVRT techniques such as Dialysis, Horizontal Ussing Chamber, Vertical Franz cell, and USP apparatus 4. IVPT studies were performed using Horizontal Ussing chamber and Vertical Franz cell methods. Q1/Q2 equivalent products (CANASA, Generic) and a half-strength product were studied to understand the reproducibility, bio relevance, and discriminatory ability of the IVRT and IVPT methods. This study is the first of its kind where molecular docking studies were performed to determine the potential interactions of drug (mesalamine) with mucin, IVRT studies were conducted with and without the presence of mucin, and porcine rectal mucosa was used to perform IVPT tests. The USP 4 method and Horizontal Ussing chamber methods were found to be suitable IVRT and IVPT techniques, respectfully, for rectal suppositories. RLD (Reference Listed Drug) and Generic rectal suppositories were found to exhibit similar release rate and permeation profiles obtained from USP 4, and the IVPT studies, respectfully. Wilcoxon Rank Sum/Mann-Whitney rank test, conducted for the IVRT profiles obtained using USP 4 method, proved the sameness of RLD and Generic suppository products.

Numerical simulations of a PVC cable fire on long cable-trays in a mechanically ventilated large scale facility

Electrical cable-tray fires pose a known safety risk at nuclear power plants. As part of the OECD funded PRISME-3 experimental programme, IRSN aims to improve understanding of cable-tray fires in confined and ventilated environments. In this study, a PVC cable fire in horizontally stacked long cable-trays is simulated using the CALIF3S-Isis CFD code. A FLASH-CAT approach approximates the heat release rate profile and allows for flame front tracking, a potentially important characteristic for fires involving long cable-trays. A further equivalent simulation without flame-front tracking is also carried out, injecting the same total mass but this time over the combined upper surface areas of the cable trays. Comparisons suggest that the flame-front tracking approach reduces the maximum error seen in the CFD predictions of temperatures in the near-fire zone. A similar result is found for gas product concentrations. However, a quantitative analysis suggests that, in its current state, the implemented FLASH-CAT approach requires further improvements if it is to realise its potential to reduce errors in long cable-tray fire simulations. Suggested improvements relate to the mass loss rate per unit area profile implemented in the FLASH-CAT approach to improve the predictive capabilities of flame-front tracking methods.

In Vitro-In Vivo Correlations (IVIVC) for Predicting the Clinical Performance of Metronidazole Topical Creams Intended for Local Action.

The safety and efficacy of a generic medicine can be confirmed by demonstrating bioequivalence (BE) between the generic product and its reference listed drug (RLD) by measuring drug concentrations in the blood following administration. However, for topical dermatological products that are not absorbed into the systemic circulation, clinical trials in patients are required. The objective of this investigation was to use an in vitro method to predict in vivo performance by correlating in vitro release testing (IVRT) data with tape stripping (TS) data following the application of metronidazole (MTZ) creams to the skin of healthy human participants. Whereas IVRT is generally used to characterize the release of a drug from topical products across a synthetic membrane into a suitable receptor medium, TS involves the sequential removal of layers of stratum corneum (SC) with an adhesive tape to determine the amount of the drug in the skin. The resulting IVRT and TS data were correlated using the IVRT parameter of the apparent release constant (ARC), which is the slope obtained from the release rate profile, with the TS parameter of the area under the curve (AUC) obtained from a plot of the amount of drug per tape strip vs. the relative SC depth. A rank order relationship for these parameters was established for the reference and test products. A graph of AUC vs. ARC was plotted to establish a Level C in vitro-in vivo correlation (IVIVC). Although the ARC for T1 was slightly lower than that for the reference, the rank order was essentially consistent. A linear relationship was observed between the AUCs and ARCs. The equation derived was used to predict the AUCs for all the tested products based on their respective ARCs. The predicted AUC values based on the observed ARCs were similar to the observed AUCs. The lower and upper limits for the in vitro and in vivo parameters for BE were computed based on regulatory acceptance criteria. In order to predict BE from the IVRT studies, the values of the ARC should be between 30.50 and 47.67 when comparing test and reference cream products containing MTZ.

Development of an Intrauterine Device Releasing Both Indomethacin and Levonorgestrel During the First Months of Use: Pharmacokinetic Characterization in Healthy Women.

Post-placement menstrual bleeding pattern changes with intrauterine contraceptives (IUCs), including levonorgestrel-releasing intrauterine systems (LNG-IUS), can be a reason for avoidance or early discontinuation. Prostaglandins play an important role in menstrual bleeding and pain. The key drivers of prostaglandin synthesis are cyclooxygenase (COX) enzymes, which are inhibited by non-steroidal anti-inflammatory drugs. In this study, we report the findings from pharmacokinetic (PK) analyses undertaken with an LNG-IUS (LNG-IUS8) modified with an additional reservoir containing indomethacin (IND). The IND/LNG-IUS8 is a proof-of-concept device studied in a phase II proof-of-concept/dose-finding study. IND/LNG-IUS8 contains the same LNG content as the unmodified LNG-IUS8 (13.5 mg) but was prepared with three different IND doses (low, 6.5 mg; middle, 12.5 mg; and high, 15.4 mg), resulting in different daily release rates. Overall, 174 healthy, premenopausal women were randomized to one of the four treatment arms (low-, middle-, high-dose IND/LNG-IUS8 or LNG-IUS 8). Initial and residual IND and LNG content were collected and the amount of IND and LNG released in vivo over the period of use was calculated. A subset of 62 participants underwent dense blood sampling for PK analysis. Concentrations of IND and LNG in plasma were determined by validated liquid chromatography-tandem mass spectrometry methods and plotted over time. Descriptive statistics were calculated for plasma drug concentrations and PK parameters. High-dose IND/LNG-IUS8 initially released much higher levels of IND than expected based on in vitro release data, followed by a steep decline, with the reservoir emptied by 4.5 months. Middle- and low-dose IND/LNG-IUS8 demonstrated steady sustained release of IND over time, emptying after 7.4 and 8.4 months, respectively. Peak plasma concentrations of IND for low- and middle-dose IND/LNG-IUS8 remained below the 20% maximal inhibitory concentration (IC20) values for COX enzymes. The average daily IND release rate in vivo was 49 µg/day for low-dose and 112 µg/day for middle-dose IND/LNG-IUS8. The IND release rate profile and IND plasma concentrations in vitro both decreased steadily over time with low- and middle-dose IND/LNG-IUS8. The LNG release rate profile was comparable for all IND/LNG-IUS8 dose groups and LNG-IUS8. This PK study demonstrates that two different drugs can be released at different rates from an IUS designed with two drug reservoirs. Inclusion of IND does not impact the LNG PK profile. Low- and middle-dose IND/LNG-IUS8 were associated with a systemic IND exposure that should preclude the occurrence of adverse events typically observed after oral IND dosing. ClinicalTrials.gov identifier number: NCT03562624.

A parametric investigation of methane jets in direct-injection compression-ignition conditions

This work investigated the effects of ambient and injection conditions on the autoignition, flame evolution and combustion characteristics of the natural gas jets at direct-injection (DI) compression-ignition (CI) conditions. Methane (CH4, as a natural gas surrogate) was directly injected into an optically accessible constant-volume combustion chamber (CVCC). For the experiments, the ambient gas density within the CVCC was fixed at 24kgm−3, but other ambient conditions were varied, including ambient gas temperature (1060–1200K) and ambient oxygen concentration (10–21 vol.%). The effects of injection pressure (10–20MPa reservoir pressure) were also assessed at a fixed ambient temperature and ambient oxygen conditions of 1200K and 21 vol.%, respectively. High-speed schlieren imaging, heat release rate analysis and flame luminosity measurement were applied to the CH4 jet flames. The results show that the ignition delay decreases with increasing ambient temperature or ambient oxygen concentration but does not display an apparent trend with changing injection pressure. Optical images reveal that the CH4 jet combustion typically starts from a localised kernel before propagating downstream of the jet volume in most cases, other than the lower ambient oxygen concentration case. The optical results also reveal that after ignition, the CH4 jet flame recesses back towards the nozzle before stabilising at a lift-off distance. The jet becomes more lifted with a decreasing ambient temperature, a reducing ambient oxygen concentration, and an increasing reservoir pressure. The results also reveal that the heat release rate and flame luminosity profiles roughly correspond to the ignition and combustion characteristics of the CH4 jet flames.

Cytotoxicity evaluation of poly(ethylene) oxide nanofibre in MCF-7 breast cancer cell line

Biocompatible polymers have received significant interest from researchers for their potential in diagnostic applications. This type of polymer can perform with an appropriate host response or carrier for a specific purpose. The current study aims to fabricate and characterise poly(ethylene) oxide (PEO) nanofibres with different concentrations for cytotoxicity evaluation in human breast cancer cell lines (MCF-7) and to get an optimal PEO nanofibre concentration (permissible limit) as a suitable polymer matrix or carrier with potential use in diagnostic applications. The fabrication of PEO nanofibres was done using electrospinning and was characterised by structure and morphology, surface roughness, chemical bonding and release profiles. The functional effects of PEO nanofibres were evaluated with MTS assay and colony formation assay in MCF-7 cells. The results showed that viscosity plays a vital role in synthesising a polymer solution in electrospinning for producing beadless nanofibrous mats ranging from 4.7 Pa·s to 77.7 Pa·s. As the PEO concentration increases, the nanofibre diameter and thickness will increase, but the surface roughness will be decreased. The average fibre diameter for 5 wt% PEO, 6 wt% PEO and 7 wt% PEO nanofibres were 129 ± 70 nm, 185 ± 55 nm and 192 ± 53 nm, respectively. In addition, the fibre thickness for 4 wt% PEO, 5 wt% PEO, 6 wt% PEO and 7 wt% PEO nanofibres were 269 ± 3 μm, 664 ± 4 μm, 758 ± 7 μm and 1329 ± 44 μm, respectively. Contrarily, the surface roughness for 4 wt% PEO, 5 wt% PEO, 6 wt% PEO and 7 wt% PEO nanofibres were 55.6 ± 9 nm, 42.8 ± 6 nm, 42.7 ± 7 nm and 36.6 ± 1 nm, respectively. PEO nanofibres showed the same burst release pattern and rate due to the same molecular weight of PEO with a stable release rate profile after 15 min. It also demonstrates that the percentage of PEO nanofibre release increased with the increasing PEO concentration due to the fibre diameter and thickness. The findings showed that all PEO nanofibres formulations were non-toxic to MCF-7 cells. It is suggested that 5 wt% PEO nanofibre exhibited non-cytotoxic characteristics by maintaining the cell viability from dose 0–1000 μg/ml and did not induce the number of colonies. Therefore, 5 wt% PEO nanofibre is the optimal nanofibre concentration and was suggested as a suitable base polymer matrix or carrier with potential use for diagnostic purposes. The findings in this study have demonstrated the influence of cell growth and viability, including the effects of PEO nanofibre formulations on cancer progress characteristics to achieve a permissible PEO nanofibre concentration limit that can be a benchmark in medical applications, particularly diagnostic applications.

On multi-stage autoignition of n-propylcyclohexane at low temperatures

n-Propylcyclohexane (nPCH) has been widely used as a surrogate component representing alkylated cycloalkanes in conventional transportation fuels. Since the autoignition characteristics of nPCH at low temperatures have not been extensively studied in the literature, a series of rapid compression machine (RCM) experiments were conducted using nPCH/air mixtures over a wide range of engine-relevant conditions. Specifically, ignition delay times were measured over the compressed temperature range of TC = 615‒750 K, compressed pressures of pc = 10‒30 bar, and equivalence ratios of φ = 0.25‒2.0. For the first time, a three-stage ignition phenomenon of nPCH was observed at ultra-fuel-lean conditions (φ = 0.25). Using the chemical kinetic model of nPCH developed in our recent work (Combustion and Flame 238 (2022) 111944), experimental results were simulated to better understand the changes in temperature and heat release rate at each stage of autoignition. In addition, the simulated concentrations of key species (ȮH, HȮ2, CO, and CO2) and values of the heat production rate per reaction were analyzed to identify the controlling chemistry at each stage. The current model can well capture the three-stage, two-stage, and one-stage ignition for different mixtures.Based on experimental pressure traces, heat release rate (HRR) profiles of representative one-, two-, and three-stage ignition cases were derived, showing that the trends of the deduced HRR characteristics agree well with those predicted by RCM simulations using the current model. Moreover, the main heat production chemistry of different stages in the multi-stage ignition is summarized in this work. For the three-stage ignition, the low-temperature chain-branching reactions of nPCH oxidation dominate at the first stage, while the intermediate-to-high temperature chain termination reaction of Ḣ + O2 (+M) 〈=〉 HȮ2 (+M), the chain branching reaction of H2O2 (+M) 〈=〉 ȮH + ȮH (+M), and the reaction sequence of ĊH2CHO → CH2O → HĊO → CO play the major role at the second and third stages. When increasing the equivalence ratio from 0.25 to 0.5, a two-stage ignition is observed and its heat production chemistry is different from those of the three-stage ignition. The reactions related to the Ḣ-atom abstraction reaction from small species by O2 and ȮH radical and the formation reaction of C2 species (CHX1*O2J =〉 Ċ2H3 + CH2CO + C2H4) are dominant at the first stage, while the high-temperature reactions involving the competitive reactions of Ḣ + O2 (+M) 〈=〉 HȮ2 (+M) and Ḣ + O2 〈=〉 Ö + ȮH and the exothermic reaction of CO + ȮH 〈=〉 CO2 + Ḣ play an essential role at the second stage. When pressure increases from 10 bar to 20 bar, only one-stage ignition behavior is observed. The heat production analysis also shows that the high-temperature chemistry is dominated by the Ḣ-atom associated reactions, namely Ḣ + O2 (+M) 〈=〉 HȮ2 (+M) and Ḣ + O2 〈=〉 Ö + ȮH, as well as the CO conversion reactions such as CO + ȮH 〈=〉 CO2 + Ḣ.

Carnosic Acid Encapsulated in Albumin Nanoparticles Induces Apoptosis in Breast and Colorectal Cancer Cells.

Carnosic acid (CA) is a natural phenolic compound with several biomedical actions. This work was performed to study the use of CA-loaded polymeric nanoparticles to improve the antitumor activity of breast cancer cells (MCF-7) and colon cancer cells (Caco-2). CA was encapsulated in bovine serum albumin (BSA), chitosan (CH), and cellulose (CL) nanoparticles. The CA-loaded BSA nanoparticles (CA-BSA-NPs) revealed the most promising formula as it showed good loading capacity and the best release rate profile as the drug reached 80% after 10 h. The physicochemical characterization of the CA-BSA-NPs and empty carrier (BSA-NPs) was performed by the particle size distribution analysis, transmission electron microscopy (TEM), and zeta potential. The antitumor activity of the CA-BSA-NPs was evaluated by measuring cell viability, apoptosis rate, and gene expression of GCLC, COX-2, and BCL-2 in MCF-7 and Caco-2. The cytotoxicity assay (MTT) showed elevated antitumor activity of CA-BSA-NPs against MCF-7 and Caco-2 compared to free CA and BSA-NPs. Moreover, apoptosis test data showed an arrest of the Caco-2 cells at G2/M (10.84%) and the MCF-7 cells at G2/M (4.73%) in the CA-BSA-NPs treatment. RT-PCR-based gene expression analysis showed an upregulation of the GCLC gene and downregulation of the BCL-2 and COX-2 genes in cells treated with CA-BSA-NPs compared to untreated cells. In conclusion, CA-BSA-NPs has been introduced as a promising formula for treating breast and colorectal cancer.

Characterizing the role of fuel injection strategies on performance, combustion, and emissions in intelligent charge compression ignition (ICCI) mode

In a novel combustion mode, intelligent charge compression ignition (ICCI), the effects of fuel injection strategies were studied on a modified single-cylinder engine with the given engine load and speed. Commercial gasoline and diesel were used to represent low-reactivity fuel and high-reactivity fuel, respectively. The in-cylinder stratification, fuel–air mixture formation, heat release rate profile and combustion phasing were investigated in detail. Engine thermal efficiency, fuel consumption, gaseous and solid emissions were further studied. In the single-injection strategy and the multiple-injection strategy, different diesel injection timings were configured to find the influence of their changing trends on engine performance, combustion and emissions. In the single injection strategy, the diesel injection of 60 °CA BTDC can lead to the highest indicated thermal efficiency. In contrast, only a specific injection strategy influences the heat release in small-scale split injection. Using multiple injections of high-reactivity fuel and adjusting the combustion phasing decrease the excessive in-cylinder pressure and maximum pressure rise rate in the single injection. Meanwhile, alternate fuel injection to build a stratified environment in the cylinder can maintain the indicated thermal efficiency at a high level. The indicated thermal efficiency is close to 50% when the diesel first injection timing is 60 °CA BTDC, the second injection timing is 38 °CA BTDC or 100 °CA BTDC. The single diesel injection strategy of 60 °CA BTDC reaches the best emissions, in which the NOx emissions are lower than 0.5 g/kWh. The multiple split injection strategies can further reduce carbon monoxide and total hydrocarbon emissions.

Reaction Mechanisms Testing with Spatial and Thermal Resolutions of Methane/Air Flames

Spatial and thermal dispersals of hydroxyl (OH), formaldehyde (CH2O), and other minor species have been acquired using various detail reaction mechanisms in the weak flame of stoichiometric methane and air mixture at ambient pressure. The weak flame was simulated inside a microflowcombustor with a prescribed temperature profile which releases a very small amount of heat. A wide reaction zone (~ 1 cm) was observed for methane and air flames compared to normal/conventional flames. Detailed oxidation analysis was carried out based on the normal and weak flames simulations. The computational flame structure was assessed with the experimentalresults available in the existing literature. Numerical modeling under the experimental conditions with various detail mechanism predicts a similar wide reaction zone. However, the species production and consumption temperatures were observed to vary for the different mechanisms used in present studies. The GRI mech 3.0 shows a typical two-peak heat release rate profile. The initial breakdown of fuel is vital for such scatter. The production of OH radical governs the initial breakdown of fuel at the intermediate temperatures. The present investigation is pretty useful in understanding the chemistry of intermediate species for different fuel-air mixtures specially at intermediate temperatures 800–1200 K.

Pyrolysis and combustion characterisation of HDPE/APP composites via molecular dynamics and CFD simulations

Understanding and characterisation of the pyrolysis and burning behaviour of flame retardant (FR) polymers are essential towards optimising the end-product in terms of flammability, charring, toxicity and smoke reduction. This study proposes a modelling framework to study the combustion behaviour, pyrolysis kinetics and FR mechanisms of FR treated polymer composites. This numerical framework has utilised reactive molecular dynamics (MD-ReaxFF) simulations to characterise the pyrolysis kinetics, char formation and residues fragments of High-density polyethylene (HDPE) and Ammonium polyphosphate filled HDPE (HDPE/APP) composites. Through MD characterisation of the polymer breaking process, thermal degradation behaviours are described by reactions rates in Arrhenius form and subsequently imported into the computational fluid dynamics (CFD) models. The modelling framework has well-predicted the heat release rate (HRR) profiles, ignition time and combustion duration of the HDPE and HDPE/APP composites, where average relative errors less than 15% were achieved compared to thermogravimetric analysis (TGA) and cone calorimeter tests. The proposed numerical framework demonstrated the capability to capture the burning behaviour and flammability of FR treated polymer composites and identify the pyrolysis kinetics and FR mechanisms offered by the APP additives, such as dehydration and char formation.

Characterization and controlled release of pequi oil microcapsules for yogurt application

Pequi oil is a valuable product for food industries due to its high levels of unsaturated fatty acids and carotenoids. This work used the complex coacervation technique with cashew gum/chitosan and cashew gum/gelatin matrices to encapsulate pequi oil in the production of enriched yogurt. Both wall materials achieved good results in encapsulation efficiency (>80%), yield (>50%), and loading capacity (<50%). The FTIR data demonstrated the presence of electrostatic interactions, thereby confirming encapsulation, and TGA, DSC and Rancimat data verified the microcapsule's stability. The acid release and temperature resistance results showed greater stability at pH's close to the optimum condition of the coacervation process and at temperatures below 80 °C. Finally, the potential for its application in yogurts was realized, showing that the preparation procedure of yogurt influenced the oil release rate and fatty acid profile, and that the addition of microcapsules should be optimally done during the cooling step.

Thermal Efficiency Improvement for a Diesel Engine Achieved by High-Heels Heat Release Rate Profile

Thermal Efficiency Improvement for a Diesel Engine Achieved by High-Heels Heat Release Rate Profile

Laser ignition of iso-octane and n-heptane jets under compression-ignition conditions

This work aims to investigate the effect of laser-induced plasma ignition (LI) on combustion behaviours of iso-octane (a gasoline surrogate) at compression-ignition (CI) conditions. A high-energy laser was used to force the fuel ignition at a quiescent-steady environment inside an optically accessible constant-volume combustion chamber with 900K ambient gas temperature, 22.8kg/m3 ambient gas density and 21 vol.% O2 concentration. A diesel surrogate (n-heptane) was tested at a lower charge temperature of 735K to offset its higher fuel reactivity than the iso-octane, such that the flames of both fuels can have a similar lift-off length. Forced laser ignition was introduced either before or after the natural autoignition timing of the fuels. The laser was focused at the jet axis 15mm and 30mm from the nozzle. High-speed schlieren imaging, heat release analysis and flame luminosity measurement were applied to the flames. The high-speed schlieren imaging was used to monitor the flame structure evolution of the natural ignition and LI cases. Due to laser ignition, the flame lift-off lengths decrease, with which the uncertainties in the lift-off distances reduce by more than 80%. The laser-affected flame bases return back to the natural flame base locations. The uncertainties in the lift-off lengths also increase, as the flame stabilisation locations approach the natural lift-off distances. Under the test conditions of this work, the rates at which the iso-octane flames shift downstream are slower than the n-heptane cases. The heat release rate profiles show high heat release from the flames following the LI events, before transitioning to lower steady values. The flame luminosity measurements indicate a strong correlation between the LI affected lift-off length and increased soot formation. The luminosity levels decrease as the flame base shifts downstream over time.

Controlled Release of Molecular Intercalants from Two-Dimensional Nanosheet Films.

Solution co-deposition of two-dimensional (2D) nanosheets with chemical solutes yields nanosheet-molecular heterostructures. A feature of these macroscopic layered hybrids is their ability to release the intercalated molecular agent to express chemical functionality on their surfaces or in their near surroundings. Systematic design methods are needed to control this molecular release to match the demand for rate and lifetime in specific applications. We hypothesize that release kinetics are controlled by transport processes within the layered solids, which primarily involve confined molecular diffusion through nanochannels formed by intersheet van der Waals gaps. Here a variety of graphene oxide (GO)/molecular hybrids are fabricated and subject to transient experiments to characterize release kinetics, locations, and mechanisms. The measured release rate profiles can be successfully described by a numerical model of internal transport processes, and the results used to extract effective Z-directional diffusion coefficients for various film types. The diffusion coefficients are found to be 8 orders of magnitude lower than those in free solution due to nanochannel confinement and serpentine path effects, and this retardation underlies the ability of 2D materials to control and extend release over useful time scales. In-plane texturing of the heterostructured films by compressive wrinkling or crumpling is shown to be a useful design tool to control the release rate for a given film type and molecular intercalant. The potential of this approach is demonstrated through case studies on the controlled release of chemical virucidal agents.