Equivalence Ratio Research Articles

Flame propagation, explosion hazard, and pollutant emission characterization of typical clean fuels leaks in plateau low-pressure region

To accelerate energy transformation and sustainable development, various countries are rushing to lay hydrogen doped natural gas pipelines. However, the installation of pipelines will pass through plateau low-pressure region, and the impact of low-pressure environments on the flame propagation, explosion hazards, and pollutant emission characteristics of hydrogen doped natural gas is not yet clear. To solve this problem, a combination of constant volume combustion experiment and numerical simulations is used. The characterization parameters of flame, explosion and pollutant concentration of natural gas/H2/air under low-pressure environment are obtained, and their chemical reaction kinetics are analyzed. When the pressure drops, the laminar burning velocity (LBV) of them increases, and the Lewis number (Le) gradually increases by more than 1. Thermal diffusion is stronger than mass diffusion, and the growth rate of flame thickness exceeds 26 %. The effect of hydrodynamic instability enhances, causing an increment in the average size of flame cells, the critical instability radius, and the Markstein length (Lu). At the equivalent ratio (φ) of 1, there is a change from negative to positive in the Lu, and flame stability continuously strengthens. The explosion overpressure is reduced by 78 % to 90 %, the explosion temperature by 16 % to 20 %. As the φ increases, the LBV exhibits an inverted U-shaped relationship, reaching its maximum value near “φ = 1″. The flame stability first weakens and then strengthens. The explosion hazard is strongest in the range of ”φ = 1–1.2″. With a decrease in pressure, the total reaction rate of fuel consumption is reduced by more than 50 %. The continuous reaction distance is extended by 12 %. Changes in pressure have a relatively weak impact on the content of CO and CO2. The increase in the φ results in an increase in CO content of over 7 %. The content of CO2 reaches its maximum value around “φ = 1″. It is an essential reference for the safe delivery of hydrogen energy and the reduction of environmental pollution.

Hydrogen-natural gas fuel blending in a “rich burn” engine with 3-way catalyst

Interest in hydrogen (H2) fuels is growing, with industry planning to produce it with stranded or excess energy from renewable sources in the future. Natural gas (NG) utility companies are now taking action to blend H2 into their preexisting pipelines to reduce greenhouse gas (GHG) emissions from burning NG. Stoichiometric (“rich burn”) NG engines that operate on pipeline NG and will receive blended fuel as more gas utilities expand H2 production. These engines are typically chosen for their low emissions owing to the 3-way catalyst control, so the focus of this paper is on the change in emissions like carbon monoxide (CO) and nitrogen oxides (NOx) as the fuel is blended with up to 30% H2 by volume. The Caterpillar CG137-8 natural gas engine used for testing was originally designed for industrial gas compression applications and is a good representative for most “rich burn” engines used across industry for applications such as power generation, gas compression, and water pumping. A significant greenhouse gas (GHG) emissions reduction is observed as more H2 is added to the fuel. Increasing H2 in the fuel changes combustion behavior in the cylinder, resulting in faster ignition and higher cylinder pressures, which increase engine-out NOx emissions. Post-catalyst CO and NOx both decrease slightly with increasing H2 while operating at the optimal “air-fuel” equivalence ratio (λ). A “rich burn” engine with 3-way catalyst can tolerate up to 30% H2 (by vol.) while still meeting NOx and CO emissions limits. However, at elevated levels of H2, increased engine-out NOx emissions narrow the λ range of operation. As H2 is added to NG pipelines, some “rich burn” engine systems may require larger catalysts or more precise λ control to accommodate the increased NOx production associated with a H2-NG blend. Sudden step-increases in H2 cause dramatic changes in λ, resulting in large emissions of post-catalyst NOx during the transition. Comparable changes in H2 at elevated concentrations cause larger spikes in NOx than at lower concentrations. Better tuned engine controllers respond more quickly and produce less NOx during H2 step-transitions.

Thermal energy propagation characteristics and hazard effects of hydrogen cloud explosion

Hydrogen has advantages such as high energy density and zero carbon emissions, but it poses a risk of generating explosion fireballs in the air. The gas explosion process not only involves thermal radiation from the fireball but also heat conduction and convection caused by the diffusion of high-temperature products. In this work, the thermal parameters of hydrogen cloud explosion with different equivalence ratios and gas cloud radius in an unconfined space were investigated. The results show that the flame temperature-distance curve of a hydrogen explosion exhibited a ’Z’ type. The maximum distance of flame propagation is positively correlated with the peak thermal radiation flux and cloud radius and increases first and then remains steady with the equivalence ratio. When only considering thermal convection, the minimum injury distance of flame temperature is achieved, and the thermal radiation effect can promote the flame propagation speed. Under the q-t criterion, the effective thermal radiation radius of first-level damage at a gas cloud size of 1 m was 6.11 m at φ = 1.2, which was 1.89 times that of φ = 0.6. Compared with the thermal dose criterion, the thermal flux-time criterion results in a larger thermal injury radius. The propulsion effect of hydrogen explosion products can cause the hydrogen cloud in the premixed zone to diffuse outward. The critical distance of hydrogen diffusion within the lower explosion limit was also analyzed. This study provides significant guiding implications for preventing hazards in people and buildings.

Safety of psychotropic medications in pregnancy: an umbrella review.

Weighing risks and benefits of the use of psychotropic medications during pregnancy remains a challenge worldwide. We systematically assessed the strength of associations between psychotropic medication use in pregnant people with mental disorders and various adverse health outcomes in both pregnant people and foetuses. Systematic reviews with meta-analyses of observational studies investigating the association between exposure to psychotropic medication in pregnancy and any adverse health outcomes were included. Credibility was graded into convincing, highly suggestive, suggestive, weak or not significant. Quality of the meta-analyses and of individual studies were assessed with A Measurement Tool to Assess Systematic Reviews 2 (AMSTAR 2) the Newcastle-Ottawa Scale (NOS), respectively. We considered 21 meta-analyses encompassing 17,290,755 participants (AMSTAR 2 high = 1, low = 12, or critically low = 8). Evidence was suggestive for: (1) preterm birth in pregnant people with either any mental disorder (equivalent odds ratio 1.62 (95% confidence interval 1.24-2.12) or depression (1.65 [1.34-2.02]) receiving antidepressants during any trimester of pregnancy; (2) small for gestational age for pregnant people with depression receiving a SSRI during any trimester of pregnancy (1.50 [1.19-1.90]); and (3) major congenital malformation (1.24 [1.09-1.40]) or cardiac malformations (1.28 [1.11-1.47]) in babies for pregnant people with depression or anxiety receiving paroxetine during first trimester of pregnancy. Additional associations were supported by weak evidence, or were not statistically significant.This umbrella review found no convincing or highly suggestive level of evidence of adverse health outcomes associated with psychotropic medication use in pregnant people with mental disorders.

Non-invasive acquisition of vital data in anesthetized rats using laser and radar application.

The aim of this study was to verify the possibility of obtaining vital sign information using a laser and radar sensor in a manner that is non-invasive and painless for test animals. A dataset was obtained from respiratory movement of anaesthetized male F344 rats, signals of laser and radar sensors were recorded simultaneously with vital data acquired with an integrated multiple-channel intraoperative monitor. In addition, respiratory movements were also video recorded, and used as reference data of respiration rate (RR; ref-RR). Reference data for heart rate (HR; ref-HR) were obtained from the R wave of electrocardiogram data for each epoch. Signals recorded from the radar sensor (I- and Q-signals) were input to a computer, and HR (radar-HR) and RR (radar-RR) were estimated using the frequency analysis method. Among the six positions where respiratory movements were measured by the laser sensor, the number of peak counts matched the visual counts of respiratory movements in the video records. The respiratory movements were significantly the greatest over the most caudal rib in the dorsal (p < 0.001). The average radar-RR and ref-RR values showed correspondence (ref-RR, 69 ± 6.2 breaths/min; radar-RR, 68 ± 5.7 breaths/min (p = 0.04-1.00); equivalence ratio, 86%). The radar-HR data showed slight variability; however, there was 80% homology compared with the ref-HR values (ref-HR, 336 ± 19.6 beats/min; radar-HR, 348 ± 34.1 (p = 0.10-0.95)). Although comparison of the data under noradrenaline administration failed to track drug-induced changes in some cases, the HR and RR data of anesthetized rats measured from the radar sensor system showed comparable accuracy to other conventional methods.

Soot and Flame Structures in Turbulent Partially Premixed Jet Flames of Pre-Evaporated Diesel Surrogates with Admixture of OMEn

In this study, the soot formation and oxidation processes in different turbulent, pre-evaporated and partially premixed diesel surrogate flames are experimentally investigated. For this purpose, a piloted jet flame surrounded by an air co-flow is used. Starting from a defined diesel surrogate mixture, different fuel blends with increasing blending ratios of poly(oxymethylene) dimethyl ether (OME) are studied. The Reynolds number, equivalence ratio, and vaporization temperature are kept constant to ensure the comparability of the different fuel mixtures. The effects of OME addition on flame structures, soot precursors, and soot are investigated, showing soot reduction when OME is added to the diesel surrogate. Using chemiluminescence images of C2 radicals (line of sight) and subsequent Abel-inversion, flame lengths and global flame structure are analyzed. The flame structure is visualized by means of planar laser-induced fluorescence (PLIF) of hydroxyl radicals (OH). The spatial distribution of soot precursors, such as polycyclic aromatic hydrocarbons (PAHs), is simultaneously measured by PLIF using the same excitation wavelength. In particular, aromatic compounds with several benzene rings (e.g., naphthalene or pyrene), which are known to be actively involved in soot formation and growth, have been visualized. Spatially distributed soot particles are detected by using laser-induced incandescence (LII), which allows us to study the onset of soot clouds and its structures qualitatively. Evident soot formation is observed in the pure diesel surrogate flame, whereas a significant soot reduction with changing PAH and soot structures can be identified with increasing OME addition.

Influence of climate smart agriculture approach of barley and pea intercropping on yield, land equivalent ratio and profitability in the agro-climatic condition of Khyber Pakhtunkhwa

Influence of climate smart agriculture approach of barley and pea intercropping on yield, land equivalent ratio and profitability in the agro-climatic condition of Khyber Pakhtunkhwa

Pomegranate-Quinoa-Based Agroforestry System: An Innovative Strategy to Alleviate Salinity Effects and Enhance Land Use Efficiency in Salt-Affected Semiarid Regions.

Salinity is a major problem, impeding soil productivity, agricultural sustainability, and food security, particularly in dry regions. This study integrates quinoa, a facultative halophyte, into a pomegranate-based agroforestry with saline irrigation in northeast Morocco. We aim to explore this agroforestry model's potential in mitigating salinity's effects on quinoa's agronomic and biochemical traits and evaluate the land equivalent ratio (LER). Field experiments in 2020 and 2021 used a randomized block design with three replicates, including monocropping and agroforestry systems, two salinity levels (1.12 and 10.5 dS m-1), four quinoa genotypes (Titicaca, Puno, ICBA-Q4, ICBA-Q5), and a pomegranate control. Salinity significantly decreased total dry matter (40.5%), root dry matter (50.7%), leaf dry matter (39.2%), and root-to-shoot ratio (7.7%). The impact was more severe in monoculture than in agroforestry, reducing dry matter (47.6% vs. 30.7%), grain yield (46.3% vs. 26.1%), water productivity (47.5% vs. 23.9%), and total sugar (19.2% vs. 5.6%). LER averaged 1.86 to 2.21, indicating 86-121% higher productivity in agroforestry. LER averaged 1.85 at 1.12 dS m-1 and 2.18 at 10.5 dS m-1, reaching 2.21 with pomegranate-ICBA-Q5 combination. Quinoa-pomegranate agroforestry emerges as an innovative strategy, leveraging quinoa's salt resistance and agroforestry's potential to mitigate salinity impacts while enhancing land use efficiency.

FGM modeling considering preferential diffusion, flame stretch, and non-adiabatic effects for hydrogen-air premixed flame wall flashback

Preferential diffusion plays an important role especially in hydrogen flames. Flame stretch significantly affects the flame structure and induces preferential diffusion. A problematic phenomenon occurring in real combustion devices is flashback, which is influenced by non-adiabatic effects, such as wall heat loss. In this paper, an extended flamelet-generated manifold (FGM) method that explicitly considers the preferential diffusion, flame stretch, and non-adiabatic effects is proposed. In this method, the diffusion terms in the transport equations of scalars, viz. the progress variable, mixture fraction, and enthalpy, are formulated employing non-unity Lewis numbers that are variable in space and different for each chemical species. The applicability of the extended FGM method to hydrogen flames is investigated using two- and three-dimensional numerical simulations of hydrogen-air flame flashback in channel flows. The results of the extended FGM method are compared with those of detailed calculations and other FGM methods. The two-dimensional numerical simulations show that considering both preferential diffusion and flame stretch improves the prediction accuracy of the mixture fraction distribution and flashback speed. The three-dimensional numerical simulations show that the prediction accuracy of the flashback speed, backflow region, and distributions of physical quantities near the flame front is improved by employing the extended FGM method, compared with the FGM method that considers only the heat loss effect. In particular, the extended FGM method successfully reproduced the relationship between the reaction rate and curvature. These results demonstrate the effectiveness of the extended FGM method.Novelty and Significance Statement The novelty of this research is the development of a flamelet-generated mani-fold (FGM) method that explicitly considers preferential diffusion, flame stretch, and non-adiabatic effects. To the best of the authors’ knowledge, no studies have performed numerical simulations of pure hydrogen flames using such an FGM method. The developed FGM method was applied to numerical simula- tions of hydrogen-air premixed flame flashback at an equivalence ratio of 0.5 and reproduced the flashback speed of lean hydrogen-air premixed flame. The applicability of the FGM method to the numerical simulation of hydrogen-air flashback is reported first. This research is significant because the FGM method is one of the most widely used combustion models for premixed combustion, and the development of an accurate FGM method will contribute to the engineering field. The accurate prediction of the flame flashback attempted in this study is particularly important for the development of hydrogen-fueled combustion devices.

A facile strategy for synthesizing isosorbide-based polyurethane structural adhesives and core–shell rubber

A structural adhesive series of biomass-based polyurethane (Biomass-PU) is synthesized using polypropylene glycol (PPG2000), isosorbide-based polyol (RPO300) as polyols, isophorone diisocyanate (IPDI) as an isocyanate and 4-tert-butylphenol (BP) as a capping agent. Three different equivalent ratios of PPG2000/RPO300, 9/1 (Biomass-PU1), 7/3 (Biomass-PU2), and 1/1 (Biomass-PU3), are evaluated to determine the effect of isosorbide-based polyol content on the properties and the optimizing formulation of biomass-PU structure adhesive. The 9/1 ratio of PPG2000/RPO300 substantially leads to the improvement of impact strength by up to 35 MPa, and the PPG2000/RPO300 = 9/1 ratio exhibits better thermal properties and impact strength than those of other ratios. To achieve more compatibility between biomass-PU structure adhesive and core–shell rubber (CSR) toughener, novel CSRs are successfully synthesized using acryl-PU as a shell and biomass-based PU as a core. The chemical structure of biomass-PU structure adhesives is analyzed through FT-IR Spectroscopy and NCO% titration. Thermal properties are evaluated using TGA and DSC analysis. Their molecular weights are measured by GPC. Also, the core–shell rubber (CSR) with a polyurethane shell is prepared to reinforce the impact strength of Biomass-PU structure adhesive.

Analysis of 27 supervised machine learning models for the co-gasification assessment of peanut shell and spent tea residue in an open-core downdraft gasifier

The producer gas (PG) obtained through thermochemical processing of the various renewable biomass types contributes to Sustainable Development Goal-7 (SDG-7). Hence, this study examined 27 supervised and multiple-input single-output ML models in terms of performance metrics and accuracy to predict CO, H2, CH4, and CO2 compositions, as well as PG's HHV in the co-gasification of peanut shell (PS) and spent tea residue (STR). Multiple trial experiments were tested with various equivalence ratios (ERs) and mixing ratios (MRs) on a 90 m3/h gas-yield open-core, down-draft gasifier with air as the gasification medium. About 18 models were chosen after evaluating their performance metrics in estimating relevant parameters. The accuracy of those models is assessed based on 12 sample runs with varying ER and MR. The findings revealed that 16 models from the linear, neural network, support vector machine, Gaussian process, tree, and ensemble categories were reliable ML models. The chosen 16 models' R2 values for CO, H2, CH4, CO2, and HHVPG are above 0.931, 0.937, 0.962, 0.806, and 0.971, respectively, with the exception of TRE. Additionally, the models demonstrated a prediction accuracy of >95 % for all of the investigated parameters in the co-gasification of PS and STR when compared to random experimental runs.

Data-driven models for the prediction of H2 generation through chemical reaction and performance evaluation of on-board hydrogen fuelled sintering tube furnace

Hydrogen is emerging as a sustainable fuel for the future. In this present work, data-driven modelling tools viz. Radial Basis Function Neural Network (RBFNN) and Least Square Fit (LSF) method, are employed to determine the rate of production of H2 gas by the chemical reaction between aluminium and water in the presence of aq. NaOH. Reactions are carried out at NaOH concentrations of 1M–5M, water temperatures 303K–333K. Hydrogen gas obtained at 333K/4M is found to have a yield of ⁓88 % of the theoretical yield. The activation energy of the reaction is found to be 57.62 kJ mol−1. The fitted models are validated with experimental results for two unknown conditions. The correlation coefficient obtained for the RBFNN model is 0.999, which indicates the high reliability of the model. On-board production of H2 gas by the chemical reaction was used for heating a sintering tube furnace. The hot products of the combustion of hydrogen and air at various fuel-air ratios were used to heat the sintering tube furnace. The maximum thermal efficiency obtained for the furnace is 76.22 % at a fuel-air ratio of 1:60 corresponds to a fuel-air equivalent ratio (λ) of 0.57.

Investigating the explosive characteristics of hydrogen/ n-butane blended fuel: Experimental and kinetic insights

Investigating the explosive characteristics of H2/n-C4H10 mixtures is crucial for the safe utilization of this blended fuel. Our study focused on varying equivalent ratios and hydrogen blending ratios within a closed 20-L spherical explosion vessel. Additionally, the microscopic kinetics of the reactions were analyzed through chemical reaction simulation. Our findings indicate that the most violent explosion occurred at an equivalent ratio of 1.2. Increasing hydrogen content intensified combustion reactions, reducing flame thickness and inducing cellular structures along the flame front. This escalation also increased explosion pressure, flame temperature, and flame propagation speed, elevating explosion risk. Moreover, the equilibrium molar fraction of O2 and CO2 decreased while that of H2O increased with higher hydrogen blending ratios. Correspondingly, the heat release rate and generation rates of H•, O•, and OH• radicals increased. Notably, the peak time of C2H4 and CH4 consumption rates preceded. Additionally, R5: O2 + H• = O• + OH• and R978: C4H10 + H• = SC4H9 + H2 represented crucial promoting and inhibiting steps, respectively. These insights deepen our understanding of the explosion mechanism of H2/n-C4H10 mixtures, providing a theoretical basis for designing safer protective measures and evaluating explosion risks in industrial production.

Seismic response and damage evolution process of a bedded slope‒tunnel system via the continuum‒discontinuum element method

To investigate the failure evolution process and failure mechanism of the bedded slope‒tunnel system under earthquakes, this work examines a specific layered slope at a tunnel portal in southeast China and conducts a 2D dynamic analysis with the continuum‒discontinuum element method (CDEM). It investigates the slope's dynamic behavior and potential for instability by evaluating the wave patterns, acceleration, displacement, Hilbert‒Huang transform (HHT) spectral analysis, and equivalent crack ratio. The research results indicate that the analysis of acceleration and displacement over time provides insights into wave propagation within a slope. During minor earthquakes (< 0.3 g), the slope experiences dynamic amplification at the surface and elevation-dependent effects, which are less evident during stronger seismic events. This work also revealed a positive correlation between the tunnel's dynamic amplification and elevation. A method leveraging HHT energy analysis, in conjunction with the slope's equivalent fracture ratio, is introduced to trace the progression of seismic damage across temporal and spatial dimensions. The progression of seismic intensity is characterized by stages of local failure initiation, expansion, and eventual holistic failure. Similarly, the temporal dynamics of instability are categorized into phases of initial instability, acceleration, and eventual sliding. Furthermore, this work explores the impact of tunnels on slope stability by comparing the equivalent fracture ratios and dynamic displacement patterns of slopes both with and without tunnels, revealing the evolution process of seismic damage to slope‒tunnel systems. This work provides a reference for the seismic design of complex slope‒tunnel systems.

Laminar burning velocity, cellular instability, and the superadiabatic flame temperature phenomenon for NH3/syngas/air premixed flames

The laminar burning velocity (LBV) and cellular instability of ammonia/syngas/air were investigated using the spherically expanding flame method at an initial pressure of 3 atm and temperatures of 298–448 K. The impacts of equivalence ratio, temperature, and hydrogen ratio on LBV were scrutinized. The results demonstrate that the LBV varies non-monotonically with the equivalence ratio and increases with increasing temperature and hydrogen ratio. Flame instability was analyzed using flame uplift rate, Lewis number, thermal expansion ratio, flame thickness, critical radius, critical Peclet number and logarithmic growth rate of perturbation in combination with the schlieren images. Of these, the flame uplift rate is used to quantify buoyancy instability, a flame instability that has received little attention. At high pressures, lower LBV makes the flame susceptible to buoyancy instability. The flame uplift rate increases with increasing flame radius, suggesting that the buoyancy instability becomes increasingly significant as the spherical flame expands. The diffusional-thermal instability is weaker at the fuel-rich side and enhanced at the leaner side. As the hydrogen ratio increases, the flame instability increases. Hydrodynamic instability is not susceptible to temperature, which is only slightly weakened with increasing temperature. Additionally, the phenomenon of superadiabatic flame temperature (SAFT) in ammonia/syngas/air flames was first found and analyzed its temperature dependence. Increasing the initial temperature suppresses SAFT occurrence.

Wavelet optical flow velocimetry of a scramjet combustor using high-speed frame-straddling focusing schlieren images

Scramjet combustors feature ultra-high-speed turbulent reacting flows with high temperatures and intense luminescence. Measurement of velocity fields under such extreme conditions presents great challenges. The present work demonstrated a seedless velocimetry approach using focusing schlieren images (FSIs) of high spatiotemporal resolution in a scramjet engine. Two fuel mass flow rates (Case1 and Case2) were investigated with corresponding global equivalence ratios of 0.27 and 0.13, respectively. The FSIs enabled by the employment of a high-speed pulsed LED light source are characterized by an effective exposure of 100 ns, and a 500-ns frame-straddling time interval with full resolution of 1280 × 800 pixels recorded at 76 kHz. The 100-ns exposure allows for capturing of transient high-speed flow motion without blurring, and the 500-ns time interval ensures an appropriate spatiotemporal correlation between subsequent schlieren images for high-speed reacting flows. A wavelet-based optical flow velocimetry (wOFV) algorithm was developed and applied to the FSIs. In contrast to the correlation-based algorithms widely employed in PIV for distinct particles, the wOFV algorithm suits better FSIs with continuous variation in brightness. The maximal velocities in the main duct of the scramjet combustor were measured to be approximately 550 m s-1 and 1100 m s-1 for Case 1 and Case2, suggestively corresponding to subsonic and supersonic combustion modes, respectively. The measured velocity inside the cavity is generally below 200 m s-1 for both cases. Recirculation regions and their dynamic motions inside the cavity were well resolved. In summary, the development of the novel velocimetry approach holds great potential for applications in extreme flow conditions. Novelty and Significance Statement: Present work demonstrates a seedless velocimetry approach based on high-speed frame-straddling focusing schlieren imaging coupled with the novel wavelet optical flow velocimetry (wOFV) algorithm. Velocity field measurement realized in a scramjet combustor with high spatiotemporal resolution (1280 × 800 pixels at 38 kHz) for the first time, showing great abilities to accommodate wide velocity range and to resolve dynamic flow characteristics with potentials for broader future applications.

Assessing turbulence–flame interaction of thermo-diffusive lean premixed H2/air flames towards distributed burning regime

Simultaneous laser-induced fluorescence of OH radicals and particle image velocimetry, and quasi-simultaneous 1D Raman/Rayleigh and 2D Rayleigh scattering measurements are used to investigate the effects of Karlovitz number (by varying the equivalence ratio) and residence time (by varying the axial measurement location) on the internal flame structures of lean premixed hydrogen/air turbulent jet flames. The turbulent flow fields, instantaneous macroscopic flame structures, and thermochemical states of a set of lean premixed hydrogen/air turbulent flames with varying initial equivalence ratio of 0.3, 0.4, and 0.45 at a constant bulk velocity of 100m/s are discussed. With an increasing equivalence ratio, the Karlovitz number derived from the turbulent flow fields decreases rapidly from 7690 to 260 and 100, determined at a downstream location of x/D=7. At the highest Karlovitz number (i.e., the lowest equivalence ratio), a distributed burning is observed in the jet flame as turbulent transport dominates over molecular mixing, and the effects of differential diffusion and flame curvature are suppressed. With decreasing Karlovitz number, intense burning regions characterized by elevated local equivalence ratio, high water mole fraction, and super-adiabatic flame temperatures are observed in association with positive flame curvature. The same combustion diagnostics are applied to another lean premixed hydrogen/air turbulent flame with an initial equivalence ratio of 0.4 and a bulk velocity of 200m/s at selected downstream locations of x/D=3.5, 7, 10.5, and 14 to assess the effects of developing turbulence and residence time. Corresponding Karlovitz numbers are 680, 730, 775, and 690, as the local turbulent intensity changes along downstream locations. While flame structures reveal characteristics towards distributed burning at lower x/D, a locally intense burning region appears at higher x/D together with positive curvature. This is mainly because the turbulence develops with increasing x/D and the flame surface is more disturbed and curved by turbulent eddies with increasing turbulence length scales. The highly diffusive hydrogen is locally concentrated by positively curved flame surfaces, resulting in fuel-rich burning regions at a higher temperature. This indicates that, as velocity fluctuations increase in axial direction, turbulence can also promote thermo-diffusive instabilities to a certain extent, increasing the mixture inhomogeneity in temperature space by interacting with the differential diffusion effect of hydrogen at atmospheric pressure.Novelty and significanceThe novelty of the current work is the focus on turbulence–chemistry interactions of premixed hydrogen/air jet flames at high turbulence and ultra lean conditions. Comprehensive experimental results including the turbulent flow fields (particle image velocimetry), instantaneous flame structures (laser-induced fluorescence of OH radicals) and internal thermochemical states (quasi-simultaneous 1D Raman/Rayleigh and 2D Rayleigh scattering imaging) of hydrogen/air jet flames are analyzed and discussed. The data sets with well-characterized boundary conditions and high measurement accuracy, are crucial for validation and development of numerical simulation models.

Growth and water-needs analysis of sweet corn and peanuts in different cropping systems

Maize and peanuts are important food crops in Indonesia and are generally planted in monoculture and intercropping systems. The water required for monoculture and intercropping is believed to be different. However, comparison analysis of water requirements in monoculture and intercropping is rarely conducted. The research aimed to evaluate the growth and production of sweet corn and peanuts in monoculture and intercropping systems concerning water requirement and crop coefficient. The study was conducted at IPB Experimental Station in Leuwikopo, Bogor, Indonesia from September to December 2022. Sweet corn and peanuts were planted in different cropping systems, i.e., monoculture and intercropping. Water consumption of both cropping systems was evaluated in every growing stage. The experiment used a completely randomized block design and was repeated three times. Results showed that sweet corn growth was not significantly different among cropping systems, but yield from intercropping was lower than monoculture. Intercropped peanuts grew lower than monoculture but did not show any significant difference in yield among cropping systems. Water use efficiency in intercropping was higher than monoculture for both crops, indicating intercropping is a suitable cropping system for limiting soil water availability. The land equivalency ratio was 1.80, concluding that intercropping was more efficient than monoculture in land use by 80%. Keywords: climate change; crop coefficient; intercropping; land equivalent ratio; water use efficiency

Experiments on critical behavior of oblique detonation wave in stratified mixtures

Two-stage gas-gun ballistic experiments are performed to investigate the feasibility of stratified mixtures with variable global equivalence ratios Φglobal for the formation of sphere-induced oblique detonation wave (ODW) and quantify their critical behaviors, which include local quenching and transitional structure to ODW, by testing conventional detonation criteria for uniform mixtures. 2 Φglobal H2 + O2 + 3Ar mixtures are tested with different concentration gradients for each fuel-lean/fuel-rich global composition. Opposite responses are observed depending on the global equivalence ratio: the lean mixture of Φglobal = 0.7, which forms ODW in the uniform mixture, fails partly in the strongest stratification, whereas the richest mixture of Φglobal = 2.0 turns to ODW in the strongly stratified conditions. As elucidated in the authors' previous work, Chapman–Jouguet (C–J) theory, including the curvature effects, reproduces the wave angles of the stable ODWs, as well as provides a good prediction on the local quenching of ODW occurring in the area with less reactive composition. Comparison of different wave regimes observed in the explored conditions reveals that wave curvature governs the critical behaviors of ODW far away from the projectile, whereas the initiation structure around the projectile is also influenced by the non-dimensional diameter. Surface energy theory is proven to quantify well the initiation structure on the projectile using a local equivalence ratio. These results indicate a new possibility of controlling the methodology of ignition and stabilization of detonation in aerospace engines, in which perfect mixing is difficult and non-stoichiometric and non-uniform mixtures are expected.

Investigation of biochars derived from waste lignocellulosic biomass and insulation electric cables: A comprehensive TGA and Macro-TGA analysis

This study investigates the thermochemical decomposition and gasification performance of biochars produced from blends of waste lignocellulosic biomass and waste insulation electrical cables at varying temperatures. Characterization tests revealed changes, particularly in ash content (27.5 %–34 %) and elemental composition, with nitrogen content increasing notably in biochar samples compared to the original feedstock. Van Krevelen diagrams demonstrated a reduction in O/C and H/C ratios with increasing production temperature, resembling fossil fuels more closely. The thermogravimetric and the derived thermogravimetric profiles illustrated distinct degradation stages influenced by heating rates and production temperature. Macro-TGA tests provided insights into biomass residue behavior under gasification conditions, indicating higher reaction rates at elevated temperatures. Syngas analysis highlighted the impact of temperature and equivalence ratio on syngas composition, with higher temperatures favoring hydrogen-rich gas production. The observed trends in cold gas efficiency (42.61 %–50.40 %) and carbon conversion efficiency (45.83 %–50.40 %) underscore the significance of temperature control in maximizing gasification performance. Biochars produced at higher temperatures demonstrated superior gasification performance, suggesting potential for optimizing biochar production processes to enhance energy recovery and waste valorization.