Rich Mixtures Research Articles

Physical and Chemical Features of Hydrogen Combustion and Their Influence on the Characteristics of Gas Turbine Combustion Chambers

Hydrogen plays a key role in the transition to a carbon-free economy. Substitution of hydrocarbon fuel with hydrogen in gas turbine engines and power plants is an area of growing interest. This review discusses the combustion features of adding hydrogen as well as its influence on the characteristics of gas turbine combustion chambers as compared with methane. The paper presents the studies into pure hydrogen or methane and methane–hydrogen mixtures with various hydrogen contents. Hydrogen combustion shows a smaller ignition delay time and higher laminar flame speed with a shift in its maximum value to a rich mixture, which has a significant effect on the flashback inside the burner premixer, especially at elevated air temperatures. Another feature is an increased temperature of the flame, which can lead to an increased rate of nitrogen oxide formation. However, wider combustion concentration ranges contribute to the stable combustion of hydrogen at temperatures lower than those of methane. Along with this, it has been shown that even at the same adiabatic temperature, more nitrogen oxides are formed in a hydrogen flame than in a methane flame, which indicates another mechanism for NOx formation in addition to the Zeldovich mechanism. The article also summarizes some of the results of the studies into the effects of hydrogen on thermoacoustic instability, which depends on the inherent nature of pulsations during methane combustion. The presented data will be useful both to engineers who are engaged in solving the problems of designing hydrogen combustion devices and to scientists in this field of study.

Extensive study on the detonation cell size of biogas-oxygen mixtures

Detonation cell size is one of the most important and most widely used parameters to describe the detonation process of a given mixture. It is used in both safety analyses and the design process of experiments and engines utilizing detonative combustion. Although much research has been carried out to collect data on the detonation cell of a wide range of combustible mixtures, few studies have focused on biogas. The presented study aims to fill this gap. Several biogas compositions, initial pressures p0 and equivalence ratios Φ were tested, totaling 200 different cases. Both a decrease of initial pressure and a decrease of methane content in the biogas result in an increase in the detonation cell width. When the equivalence ratio is moved away from stoichiometric (Φ = 1) towards either lean or rich mixtures it is accompanied by an increase in detonation cell size. Additionally, ZND induction length and instability parameter χ were calculated. Induction length correlates linearly with the cell size and the χ shows that the cellular structure is expected to be very irregular. Because of that it does not suffice to report merely the average cell size. Thus, a more detailed statistical description is provided.

Experimental Investigation of the Biodiesel Direct Injection and Diesel Fuel as Premixed Charge on CI-Engine Emissions, Performance, and Combustion Characteristics

This study aims to investigate the use of waste cooking oil biodiesel blend (B30D70) in CDC mode and the use of different premixing ratios of diesel vapor (15%, 20%, 25% and 30%) through manifold injection at a manifold premixed temperature of 110 ⁰C in PCCI mode when using biodiesel blend (B30D70) as the main fuel and diesel as the premixed fuel. The experiments were carried out on 4-stroke, single-cylinder, air cooled, DI diesel engine which was modified to run in PCCI mode with adding a fuel vaporizer to create the external homogeneous mixture. The engine combustion parameters, performance, and emissions characteristics were fully discussed, and the results were compared with these of CDC mode fueled by diesel. The obtained results for the use of B30D70 fuel indicates a certain decrement for exhaust gas temperature, HC, and CO emissions, but with a penalty in brake thermal efficiency, NOx, and smoke opacity. The experiments revealed that the best results were indicated for 20% diesel vapor in PCCI mode as CO, HC, NOx, and EGT reduced by 34.62%, 43.75%, 2.65% and 8.53% respectively and almost has the same BTE compared to CDC mode fueled by diesel. While increasing PR to 25% and 30% decrease the volumetric efficiency leads to rich mixture and deterioration of combustion and increase CO, HC and smoke emissions.

Effect of CO<sub>2</sub> Additives on the Non-Catalytic Conversion of Natural Gas into Syngas and Hydrogen

Abstract—A kinetic analysis of the non-catalytic carbon dioxide reforming of CH4 has been carried out in the temperature range of 1500–1800 K under conditions of variable temperature behind the reflected shock wave. The stages of conversion of methane into synthesis gas, the characteristic time intervals corresponding to these stages, and the most important elementary reactions have been established. At the first stage, as a result of thermal pyrolysis, methane molecules are sequentially converted into ethane, ethylene, and then acetylene, the most stable hydrocarbon in this temperature range. At the second stage, acetylene is normally converted into CO and H2, being accompanied by the formation soot particles in the case of rich mixtures. The conversion of CO2 proceeds at the second and third stages, when CH4 conversion is almost complete. It occurs as a result of the interaction of CO2 molecules with H● atoms arising in the reacting system and leads to the formation of CO molecules and OH● radicals. Acetylene is predominantly consumed in the reaction with OH radicals. A high concentration of acetylene during methane reforming promotes the intensive formation of soot nuclei, for which acetylene makes the highest contribution to the rate of their surface growth. At the same time, acetylene itself is not a precursor of soot particle nuclei, which are mainly formed from \({{{\text{C}}}_{{\text{3}}}}{\text{H}}_{3}^{\centerdot }\) radicals.

Bioactive Oxylipins Profile in Marine Microalgae

Microalgae are photosynthetic microscopic organisms that serve as the primary food source in aquatic environments. Microalgae can synthesize a wide variety of molecules, such as polyunsaturated fatty acids (PUFAs) of the omega-3 and omega-6 series. Oxidative degradation of PUFA due to radical and/or enzymatic conversion leads to the formation of oxylipins, which are compounds known for their bioactive properties. In the present study, we aim to profile oxylipins from five microalgae species grown in 10-L photo-bioreactors under optimal conditions. During their exponential phase, microalgae were harvested, extracted and analyzed by LC-MS/MS to determine the qualitative and quantitative profile of oxylipins for each species. The five different selected microalgae revealed a high diversity of metabolites, up to 33 non-enzymatic and 24 enzymatic oxylipins present in different concentrations. Taken together, these findings highlight an interesting role of marine microalgae as a source of bioactive lipids mediators, which we hypothesize have an important function in preventive health measures such as amelioration of inflammation. The rich mixture of oxylipins may display advantages to biological organisms, especially by providing for human health benefits including antioxidant, anti-inflammatory, neuroprotective or immunomodulator activities. Some oxylipins are also well known for their cardiovascular properties.

CFD modelling of hydrogen and hydrogen-methane explosions – Analysis of varying concentration and reduced oxygen atmospheres

This paper evaluates the predictive capabilities of the advanced consequence model FLACS-CFD for deflagrations involving hydrogen. Two modelling approaches are presented: the extensively validated model system originally developed for hydrocarbons included in FLACS-CFD 22.1 and a Markstein number dependent model implemented in the in-house version FLACS-CFD 22.1 IH. The ability of the models to predict the overpressure and the flame arrival time for scenarios with different concentrations of hydrogen, and thus different Lewis and Markstein numbers, is assessed. Furthermore, the effect of adding methane or nitrogen on overpressure for different regimes of premixed combustion are investigated. The validation dataset includes deflagrations in the open or in congested open areas and vented deflagrations in empty or congested enclosures. The overpressure predictions by FLACS-CFD 22.1 IH are found to be more accurate than those obtained with FLACS-CFD 22.1 for scenarios with varying hydrogen concentrations and/or added nitrogen or methane in the mixture. The predictions by FLACS-CFD 22.1 IH for lean hydrogen mixtures are within a factor of 2 of the values observed in the experiments. Further development of the model is needed for more accurate prediction of deflagrations involving rich hydrogen mixtures as well as scenarios with other fuels and/or conditions where the initial pressure or temperature deviate significantly from ambient conditions.

NOx reduction based on N2 dilution in a swirled-stabilized magnesium flame

New sources of clean energy with reduced greenhouse gas emissions must be considered because of global warming. Among these alternative sources, metal fuels such as aluminum or magnesium are promising. The present study focuses on the impacts of an air dilution by N2 and of the equivalence ratio on the amount of nitrogen oxides (NOx) produced by a swirled-stabilized magnesium flame. A polydispersed aerosol of pure magnesium in the size fraction 50–70 µm was injected in the combustion chamber. Different air–fuel ratios – from 0.14 to 1.0 – were obtained by changing the mass flowrate of the injected fuel. Thermocouples and a pyrometer were implemented to monitor the gas and flame temperatures. On-line paramagnetic analyzers were used to measure the oxygen (O2) and NOx concentrations. For each dilution condition (0, 30 and 50 %), the NOx mole fraction versus the equivalence ratio follows a parabolic shape. The amount of NOx first increases when increasing the air–fuel ratio as the power dissipated by the flame increases, leading to the rise of the gas temperature. For the highest air–fuel ratios, the NOx production is disfavored in the rich mixture. The maximal NOx emissions are shifted to higher equivalent ratios when increasing the dilution level and it decreases by a factor 2 with a dilution of 50 %, for a constant value of the air–fuel ratio. The gas temperature in the flame decreases due to the N2 dilution. The NOx emissions become negligible for an equivalence ratio of 1 at a 50 % dilution. Nevertheless, under the tested experimental conditions, the level of NOx never exceeded 7 gNOx/kWh, which is lower than the maximal value of NOx emissions from a gasoline engine.

Characterization of Premixed Flames with Ethanol Fuel affected Magnetic Field Induction

The purpose of this study was to determine the effect of magnetic field induction on the characteristics of premixed ethanol combustion flames. Petroleum reserves will increasingly be depleted if alternative energy is not found. Therefore, various breakthroughs are needed to prevent an energy crisis from occurring. Simultaneously the researchers are also trying to find equipment that can save fuel consumption. To get a more effective and efficient flame, you can apply a magnetic field effect to the burning fire, especially in terms of the rate of burning of the fire. Fuel oil under normal conditions tends to be irregular and grouped together. By providing a magnetic field to induce the fuel oil, the hydrocarbon bonds will break and will make the chemical composition more homogeneous. The experimental research method is to heat ethanol until it is in the form of steam, then flow it to the burner which will then be given air which is controlled by the mass flow. The research began with the manufacture of magnetic induction from carbon steel wrapped in copper wire. Then testing the fuel by providing a magnetic field before the ethanol fuel enters the burner tip. The magnetic field helps the fuel ionization process, this ionization is needed so that the fuel can easily bind oxygen during the combustion process. If the ionization process goes well then the combustion process becomes more complete. In this ionization process, it will result in the formation of positively charged fuel molecules so that during combustion the combustion process will occur more quickly. The magnetic field will generate Far Infrared waves, which will strengthen the positively charged bonds in the fuel structure due to the ionization process and position these bonds in an orderly manner. This makes it easy for oxygen to react with fuel in the combustion process. With the electric motion force will increase the combustion temperature. The increase in temperature is caused by the process of ionization of the fuel due to the magnetic field generated by the electromotive force. The dynamic electromotive force causes the flame to increase when the current is flowing and decrease when the electric current is cut off. The resulting fire is more transparent, clearer and more visible. The direction of the N-S magnetic field causes the temperature to be higher than the direction of the N-N magnetic field. The magnetic field can affect the burning speed of the ethanol flame. In a poor mixture (ϕ <1) in the presence of magnetic influence, the rate of fire is lower without the influence of a magnetic field, but in a rich mixture (ϕ > 1) in the presence of a magnetic influence, the rate of fire is higher than without the influence of a magnetic field.

Experimental Study of Effect of Injection Timing on Port Fuel Injection Gasoline, Port Fuel Injection Compressed Natural Gas, and Direct Injection Compressed Natural Gas Engine Performance, Combustion, and Emissions Characteristics

Abstract Compressed natural gas (CNG) has gained popularity due to its wide availability, higher efficiency, and lower emissions compared to gasoline. However, the lower flame speed characteristics of CNG with conventional port injection reduce the CNG engine volumetric efficiency and power output. CNG's lower gas jet momentum during a low load operation creates a non-uniform air-fuel mixture that affects ignition and combustion quality. Direct injection of CNG with optimum injection timing is expected to improve volumetric efficiency, ignition quality, and combustion process. In this study, a comparative study on the effect of end-of-injection (EOI) timing on volumetric efficiency, thermal efficiency, combustion duration, and emissions was carried out in a single-cylinder port fuel injection (PFI) spark-ignition engine using gasoline and CNG, and direct injection (DI) spark ignition engine using CNG. The experiments were performed at two-part load operations of 20% and 40% throttle at 900 and 1500 rpm. Experimental results indicate that the PFI CNG engine is more influential in EOI timing than gasoline engines. The performance of the PFI CNG engine is improved when the injection occurs during the intake valve open period compared to the closed valve period with higher thermal efficiency, volumetric efficiency, and indicated mean effective power (IMEP). A shorter flame development angle and combustion duration were observed when EOI timing was in the open intake valve condition. DI CNG improved volumetric efficiency at advanced EOI timing compared to the PFI CNG engine. However, the combustion process is critically dependent on injection timing and air-fuel mixing duration. A three-dimensional computational fluid dynamics simulation was conducted to evaluate the effect of advanced and retarded EOI timing on DI CNG engine's in-cylinder turbulent kinetic energy development and in-cylinder equivalence ratio near the ignition point. An excess advanced EOI timing resulted in stratified rich and retarded EOI timing results in loss of turbulence energy, leading to a slightly rich and lean mixture for advanced and retarded EOI timing, respectively. Hence, an optimum EOI timing provides a conducive environment to initiate the combustion and flame front propagation. Further, advanced EOI timing was required at higher throttle opening and engine speed. The emissions in DI CNG were also greatly affected by EOI timing.

Kinetic study of plasma assisted oxidation of H2 for an undiluted rich mixture

Non-thermal plasma discharges are considered as an assisted method for supporting conventional thermal processes, because the discharge-generated radicals can be used to benefit them. In this regard, plasma assisted combustion has been investigated extensively, and plasma assisted fuel reforming has expanded its horizons to include plasma assisted chemical synthesis, in accord with a global megatrend—electrification. To scientifically advance this area, plasma-chemical kinetic studies must be conducted, and their mechanisms should consider both electron and gas temperatures to describe electron-induced and thermally-induced chemistry, respectively. Here we present a temperature-dependent plasma-chemical kinetic study for the plasma assisted oxidation of an undiluted rich H2/O2 mixture; it represents our continued effort to establish a foundational plasma assisted reaction mechanism for H2/O2 systems. A plasma-chemical kinetic model (KAUSTKin) and a modified plasma-chemical reaction mechanism were used for the zero-dimensional simulation; a temperature-controlled dielectric barrier discharge reactor was employed for the experiment. Non-linear oxidation behavior was observed in a range of 300–850 K for various discharge powers. To unravel the underlying mechanisms, analysis was broken down to a physical effect, described by the reduced electric field (E/N), and a chemical effect originating from the temperature dependence of the plasma assisted oxidation chemistry. We concluded that (i) the oxidation was initiated by the electron impact dissociation of H2, (ii) E/N governed the degree of H2 dissociation (and thus the degree of oxidation), (iii) the key intermediate was HO2, and (iv) a significant increase in the chain termination reaction, H + HO2 → H2 + O2, suppressed the oxidation (especially in the Negative Temperature Coefficient (NTC)-like regime of 600–725 K). The need to improve existing thermal reaction mechanisms for temperatures below 1000 K was emphasized, and a method for temperature-dependent plasma-chemical kinetic studies to provide a novel and complementary tool for this task was demonstrated.

Waters that Witness: How the Bible’s Rivers Help Convey its Message

The rivers mentioned in the Bible are often significant. This narrative-exegetical study focuses on the Mesopotamian rivers, along with the Nile and the Jordan, with the latter leading from the Hebrew Bible on into the New Testament. The paper explores the ways in which these rivers convey divine revelation and mission, asking what the rivers say in expressing that revelation and also what the rivers do as part of its drama. A rich mixture of themes emerge: enabling life and reminding of loss; the nature of power, hubris and vulnerability; transition into new beginnings through crossing the rivers and through washing in them; and ultimately hope for a renewed creation through the flow of life-giving divine presence. In a variety of ways - symbolic, instrumental, sacramental and participatory – the rivers speak and act as partners with their creator.

Environmental assessment of road transport fueled by ammonia from a life cycle perspective

Renewable energy penetration into the electricity market has been increasing over the last decades; however, it is a different story in the transport sector. Fossil fuels are still predominant; therefore, several alternatives are being studied to attain a low-carbon, more sustainable transport and, consequently, a sustainable society. Ammonia has the potential to be a viable option, and it is critical to study its environmental profile in this early phase to appraise its sustainability as a fuel for passenger road transportation. This work aimed to develop a life cycle assessment of an ammonia-fueled internal combustion engine passenger car from the cradle to the grave, considering 1 km traveled as the basis for comparison. The product system under study included four stages: (i) vehicle, (ii) infrastructure, (iii) energy production, and (iv) operation. Life cycle inventory data related to vehicle operation, specifically ammonia combustion, resulted from various simulations of a model that considered the effect of different operation modes and vehicle emission control strategies, which resulted in nine configurations. The results show that rich mixtures (with an equivalence ratio of 1.1) help to reduce both nitrogen oxides (NOX) and nitrous oxide (N2O) emissions. As for unburnt ammonia (NH3), the after-treatment system drastically diminishes these and NOX emissions. Data on infrastructure and other upstream processes was taken from the Ecoinvent 3.7.1 database, and the ammonia production was based on the life cycle inventory from previous research. The life cycle impact assessment was performed on OpenLCA software implementing the ReCiPe2016 Midpoint (H) v1.13 methodology. On average, per 1 km traveled in an ammonia-based ICEV represents 0.098 kg CO2-eq for global warming potential (GWP100), 30.755 g oil-eq for fossil depletion potential (FDP), 38.974 mg P-eq for freshwater eutrophication potential (FEP), 8.907 μg CFC-11-eq for ozone depletion potential (ODP), 0.906 g NMVOC-eq for photochemical oxidant formation potential (POFP), and 1.029 g SO2-eq for terrestrial acidification potential (TAP). These results show a significant reduction, above −70%, for GWP100, FDP, and ODP compared with the same vehicle fueled on gasoline.

A wavelet-based separation method for tonal and broadband components of low Reynolds-number propeller noise

Propeller noise generally exhibits a rich mixture of tonal and broadband components related to different physical mechanisms. Specifically, the tones are characterized by having deterministic and persistent characteristics, while the broadband counterpart has random behaviour. The separation is essential for the experimenters as they provide information on the different noise sources. In this framework, the study presents a novel wavelet-based method able to separate the noise emitted by a low Reynolds number propeller into its tonal and broadband components. The technique is applied to an isolated rotor operating under different loading configurations, including hover and cruise conditions. The acoustic pressure data are obtained in the anechoic tunnel (A-tunnel) of the TU Delft low-speed laboratory with a near-field polar and azimuthal distribution of microphones. The method is based upon a threshold varying procedure that separates the tonal and broadband components through the computation of two-point statistics. Advantages and drawbacks with respect to other methodologies already known from the literature are discussed. The application of the method provides the spectral content of the tonal and broadband components as well as the different polar and azimuthal directivity. Specifically, the observed dipole-like shape directivity for the tonal part and flatter broadband OASPL, confirm that the method can provide quite a good separation. Furthermore, the overall flow behaviour is inferred from the decomposition and validated through benchmarked flow visualizations.

Uncertainty quantification of the premixed combustion characteristics of NH3/H2/N2 fuel blends

Green ammonia is a candidate fuel to decarbonise shipping and other industries. However, ammonia features a lower reactivity compared to conventional fuels and is therefore difficult to burn. To resolve this issue, thermo-catalytic cracking of ammonia using waste heat is often employed to produce NH3/H2/N2 blends as fuel. However, on-site operational variations in this process can become sources of uncertainty in the fuel composition, causing randomness of the flame's physicochemical properties and challenging flame stability. In the present work, a surrogate model is built using the polynomial chaos expansion (PCE) method to investigate the impact of fuel composition variability on combustion characteristics at different operating conditions. Impacts of 1.5% deviation in the fuel composition on the flame properties for different initial pressures (Pi) and unburnt fuel temperatures (Tu) are investigated for a wide range of equivalence ratios covering lean and rich mixtures. The uncertainty effects defined by the coefficient of variation (COV) fluctuate for equivalence ratios greater than 1.1, while no fluctuation is observed in COV for near stoichiometric combustion conditions. It is shown that H2 variation in the fuel blend has the strongest effect (over 80%) on the uncertainty of all investigated physicochemical properties of the flame. The least affected property is the adiabatic flame temperature with variations of about 2.5% in richer fuel conditions. The results further show that preheating of the reactants can significantly reduce the COV of laminar flame speed. The consequences of these uncertainties upon different combustion technologies are then discussed and it is argued that moderate and intense low oxygen dilution (MILD) and colourless distributed combustion (CDC) technology may remain resilient.

Measuring the relative contribution to predictive power of modern nucleotide substitution modeling approaches.

Traditional approaches to probabilistic phylogenetic inference have relied on information-theoretic criteria to select among a relatively small set of substitution models. These model selection criteria have recently been called into question when applied to richer models, including models that invoke mixtures of nucleotide frequency profiles. At the nucleotide level, we are therefore left without a clear picture of mixture models' contribution to overall predictive power relative to other modeling approaches. Here, we utilize a Bayesian cross-validation method to directly measure the predictive performance of a wide range of nucleotide substitution models. We compare the relative contributions of free nucleotide exchangeability parameters, gamma-distributed rates across sites, and mixtures of nucleotide frequencies with both finite and infinite mixture frameworks. We find that the most important contributor to a model's predictive power is the use of a sufficiently rich mixture of nucleotide frequencies. These results suggest that mixture models should be given greater consideration in nucleotide-level phylogenetic inference.

Species structures in preheated ammonia micro flames

Species structure of ammonia (NH3) micro flames stabilized on a preheated 2-mm diameter tube is investigated using laser-induced fluorescence (LIF) measurements and numerical simulations with detailed reaction mechanisms. Nitric oxide (NO) and hydroxyl (OH) radicals are measured using single-photon absorption laser-induced fluorescence (LIF), while hydrogen atoms (H) are measured using two-photon absorption LIF (TPLIF). NO and OH are measured using nanosecond excitation pulses while both nanosecond and femtosecond methods are employed for TPLIF of H. 1-D and 2-D flame simulations are performed using Cantera and ANSYS FLUENT, separately, and the results are compared with the experimental data. It was observed that experimental H-atom signals increased with increasing equivalence ratio (ϕ), while the model predicted an opposite trend. Compared to the model predicted a rapid drop of OH as a function of ϕ, experimentally measured OH profiles exhibit opposite trends in different height locations of the flame. It is conjectured that the thermal dissociation of NH3 to generate reactive radicals such as H and OH is enhanced with preheating rich mixtures. Measured NO-LIF signal decreases with increasing ϕ, which agrees with the predicted trend by the simulation. NO reduction in fuel-rich flames is expected to be due to NHi radicals generated from excess NH3. A negative correlation is observed between NO and H/OH as a function of ϕ, which contradicts with the simulation that shows a positive relationship. This discrepancy implies that the effect of NH3 thermal dissociation has to be considered in the simulation of rich NH3 flames. This study helps to fulfill the fundamental knowledge gap of NH3 dissociation kinetics and the role of reactive intermediates in oxidation and NO formation pathways, hence an important step towards realizing practical combustion devices operating of NH3 as an energy carrier.

Thermodynamic Analysis of the Solubility of Sulfadiazine in (Acetonitrile 1-Propanol) Cosolvent Mixtures from 278.15 K to 318.15 K

Drug solubility is one of the most significant physicochemical properties as it is related to drug design, formulation, quantification, recrystallization, and other processes, so understanding it is crucial for the pharmaceutical industry. In this context, this research presents the thermodynamic analysis of the solubility of sulfadiazine (SD) in cosolvent mixtures {acetonitrile + 1-propanol} at 9 temperatures (278.15 K–318.15 K), which is a widely used drug in veterinary therapy, and two solvents of high relevance in the pharmaceutical industry, respectively. The solubility of SD, in cosolvent mixtures {acetonitrile + 1-propanol} is an endothermic process where the maximum solubility was reached in pure acetonitrile at 318.15 K and the minimum in 1-propanol at 278.15 K. Although the solubility parameters of acetonitrile and propanol were similar, the addition of acetonitrile to the cosolvent mixture leads to a positive cosolvent effect on the solubility of DS. As for the thermodynamic functions of the solution, the process is strongly influenced by enthalpy, and according to the enthalpy–entropy compensation analysis, the process is enthalpy-driven in intermediate to rich mixtures in 1-propanol and entropy-driven in mixtures rich in acetonitrile.

Concrete Performance Produced Using Recycled Construction and By-Product Industrial Waste Coarse Aggregates.

Concrete is classified as a multi-composite material comprising three phases: coarse aggregate, mortar, and interfacial transition zone (ITZ). Fine and coarse aggregates occupy approximately 70-85% by volume, of which coarse aggregate typically constitutes more than two-thirds of the total quantity of aggregate by volume. The current study investigates the concrete performance produced using various recycled construction and by-product industrial waste coarse aggregates. Six types of coarse aggregates: manufactured limestone, quartzite, natural scoria, by-product industrial waste aggregate, and two sources of recycled concrete aggregates with densities ranging from 860 to 2300 kg/m3 and with different strength properties were studied. To determine the coarse aggregate contribution to the overall concrete performance, lean and rich concrete mixtures (Mix 1 and Mix 2) were used. Mix 1 (lean mixture) consisted of a ratio of water to cement (w/c) of 0.5 and cement content of 300 kg/m3, whereas a higher quantity of cement of 500 kg/m3 and a lower w/c ratio of 0.3 were used for Mix 2 (rich mixture). The results showed that while the compressive strength for different aggregate types in Mix 1 was comparable, the contribution of aggregate to concrete performance was very significant for Mix 2. Heavyweight aggregate produced the highest strength, while the lightweight and recycled aggregates resulted in lower mechanical properties compared to normal weight aggregates. The modulus of elasticity was also substantially affected by the coarse aggregate characteristics and even for Mix 1. The ACI 363R-92 and CSA A23.3-04 appeared to have the best model for predicting the modulus of elasticity, followed by the ACI-318-19 (density-based formula) and AS-3600-09. The density of coarse aggregate, and hence concrete, greatly influenced the mechanical properties of concrete. The water absorption percentage for the concrete produced from various types of aggregates was found to be higher for the aggregates of higher absorption capacity.

Oxidation of Rich Propane Mixtures in a Temperature Range of 773–1023 K at Pressures of 1–3 atm

Oxidation of Rich Propane Mixtures in a Temperature Range of 773–1023 K at Pressures of 1–3 atm

A New Era of Intracluster Light Studies with JWST

Still largely unexplored, the diffuse light in clusters of galaxies traces the past and ongoing buildup of these massive structures. Here we present the first comprehensive study of the intracluster light (ICL) of the cluster SMACS J0723.3–7327 (z = 0.39) using the JWST Early Release Observations. These deep and high spatial resolution images allow the study of the ICL with a high signal-to-noise ratio up to a radial distance of ∼400 kpc, twice as far with respect to previous HST studies of intermediate-redshift clusters. This opens up the possibility of exploring the rich mixture of processes that are building the ICL. We find that the inner parts of this cluster (R < 100 kpc) are built through a major merger, while the outer parts (R > 100 kpc) are mainly produced by the tidal stripping of Milky Way–like satellites. We also find that the slope of the stellar mass density radial profile of the ICL of this cluster (α 3D = −2.47 ± 0.13) closely follows the predicted dark matter halo slope (α 3D,DM = −2.6 to −2), supporting the idea that both components have a similar shape and thus the potential of using the ICL as a tracer of the dark matter distribution in clusters of galaxies. Future JWST studies of the ICL are set to revolutionize our understanding of cluster formation and will be crucial to improve the gravitational lensing mass maps of these structures and thus accurately characterize the properties of the first galaxies.