Stoichiometric Concentration Research Articles

Insight of low flammability limit on sustainable aviation fuel blend and prediction by ANN model

Sustainable aviation fuel (SAF) blend has been confirmed to benefit for greenhouse gases reduction, and thus the property of blend fuel should be understanded the detail to support the utilization in aircraft. Low flammability limit (LFL) is a key property of jet fuel which should be sufficiently flammable to burn in combustor of aeroengine and meanwhile should be non-flammable for safety storage in fuel tank of aircraft. LFL of fuel could be influenced by integrating effects including molecule structure, intramolecular chemical bond energy and binding energy of molecule to molecule. Three types of theoretical models, based on different individual view including LFL of every pure hydrocarbon, stoichiometric concentration, and combustion enthalpy, present unsatisfactory simulation results, which can be deduced without integrating all potential influence factors together. The artificial neural network (ANN) approaches have been involved to bridge the relationship of the complex compositions in jet fuels with LFL. For providing adequate and available composition input, the boundary of fuel compositions has been extracted based on constrains of boiling point, flash point and freeze point coupling with statistic petroleum-based jet fuels. By clustering analysis, 43 critical classes of compositions, extracted as surrogate hydrocarbons based on with similar LFL within 1 % deviation, have been deployed as input matrix. ANN-LFL model, trained by only drop-in fuel with feature of Sigmoid function as an activation function, can distinguish drop-in fuel with non-drop-in fuel. ANN LFL model can predict LFL of drop-in fuel with 0.988 accuracy. The predict output value of non-drop-in fuel could present obvious deviation with traditional jet fuel. The optimization methodologies of ANN-LFL model could be improved the understanding of LFL and extend ANN in SAF utilization.

Experimental investigation on the dynamic response of vent plate under methane-air mixtures explosion load

The dynamic response study of explosion venting components is of great significance for the assessment of explosion disasters and the determination of damage. Based on the self-developed rectangular explosion venting device, a series of experimental investigations on the dynamic response and failure mode of calcium silicate vent plates under the methane explosion loads induced by a detonator were conducted. The results show that the vent plate mainly exhibits brittleness and presents a plastic hinge failure mode under the blasting loads. When the gas concentration is closer to the stoichiometric concentration, P2 (the peak overpressure generated by the vent plate rupture) and its pressure rise rate dP2/dt are higher. Conversely, when the methane concentration is closer to the upper or lower limits of the explosion, the explosion load tends to be static, the yield line of the vent plate is shorter, and there are fewer fragments generated by the failure of the plate. The pressure-displacement curve and the correlation diagram of failure modes proposed provide a reference for predicting the failure mode of light and fragile explosion venting components.

Synthesis of Chitosan and Ferric-Ion (Fe3+)-Doped Brushite Mineral Cancellous Bone Scaffolds.

Biodegradable scaffolds are needed to repair bone defects. To promote the resorption of scaffolds, a large surface area is required to encourage neo-osteogenesis. Herein, we describe the synthesis and freeze-drying methodologies of ferric-ion (Fe3+) doped Dicalcium Phosphate Dihydrate mineral (DCPD), also known as brushite, which has been known to favour the in situ condition for osteogenesis. In this investigation, the role of chitosan during the synthesis of DCPD was explored to enhance the antimicrobial, scaffold pore distribution, and mechanical properties post freeze-drying. During the synthesis of DCPD, the calcium nitrate solution was hydrolysed with a predetermined stoichiometric concentration of ammonium phosphate. During the hydrolysis reaction, 10 (mol)% iron (Fe3+) nitrate (Fe(NO3)3) was incorporated, and the DCPD minerals were precipitated (Fe3+-DCPD). Chitosan stir-mixed with Fe3+-DCPD minerals was freeze-dried to create scaffolds. The structural, microstructural, and mechanical properties of freeze-dried materials were characterized.

Theoretical prediction model for minimum ignition energy of combustible gas mixtures

Minimum ignition energy (MIE) is a crucial parameter for identifying the hazards of combustible gases. To rapidly obtain accurate MIE values for various gases, the shape of the ignition source was simplified to cylindrical. Based on theories of heat conduction and chemical reaction kinetics, a physical model of the ignition process was established. The spatial and temporal evolution of temperature was used as a basis for judging the success of ignition. A numerical algorithm was developed and maximum flame temperatures and MIE were calculated for several combustible gases (H2, CH4, C2H6, C3H8, C4H10, C2H4, C2H2). This model accurately predicted the U-shaped trend of MIE values with concentration for CH4/air and H2/air mixtures. It found that the MIE was minimal at the stoichiometric concentration, at 0.37 mJ and 0.017 mJ, closely aligning with experimental data. This numerical model has been validated for its accuracy and promises to make relatively precise theoretical predictions for the MIE values of uncommon combustible gases or mixtures of various gases.

Semiclathrate-based CO2 capture from pre-combustion fuel gas using tetra-n-butylammonium chloride: A thermodynamic, kinetic, and spectroscopic study

The primary objective of this study was to investigate the feasibility of pre-combustion CO2 capture using tetra-n-butylammonium chloride (TBAC) semiclathrate in a fuel gas mixture comprising CO2 (40%) + H2 (60%), with a primary focus on examining the thermodynamic, kinetic, and spectroscopic aspects of this process. Phase equilibria measured at various TBAC concentrations revealed that the CO2 + H2 + TBAC semiclathrates exhibited maximum thermodynamic stability at a stoichiometric concentration (3.3 mol%). CO2 concentrations in both the vapor and semiclathrate phases, along with gas consumption during and after semiclathrate formation, were measured to assess CO2 selectivity and gas uptake in the semiclathrate phase. Notably, CO2 enrichment was approximately 90% in the semiclathrate phase. In-situ Raman spectroscopy provided clear confirmation of the enclathration of both CO2 and H2 in the semiclathrate lattices, while powder X-ray diffraction analysis revealed the tetragonal (P42/m) structure of the CO2 + H2 + TBAC (3.3 mol%) semiclathrate. Furthermore, a high-pressure micro-differential scanning calorimeter was used to measure the dissociation enthalpies of the CO2 + H2 + TBAC (3.3 mol%) semiclathrate at various pressures. The comprehensive results obtained in this study strongly support the potential use of TBAC semiclathrate as a material for pre-combustion CO2 capture.

Flash sintering BaTiO3-0.01MgO-0.01Nb2O5-xBi2O3 ceramics with superior dielectric temperature stability via defect engineering

In this paper, Bi2O3 doped BaTiO3-0.01MgO-0.01Nb2O5 ceramics are designed to increase dielectric constant, reduce dielectric loss and improve temperature dielectric stability through inducing defects, and are prepared by flash sintering method to inhibit the volatilization of Bi element and ensure the element ratio. The microstructure, polarization mechanisms, dielectric properties and conduction mechanism of the ceramics are studied. The doping of Bi2O3 can enhance the relaxation behavior and dielectric properties. The defects evolution in BaTiO3-0.01MgO-0.01Nb2O-0.01Bi2O3 ceramics are studied. The results show that the BaTiO3 ceramics doped with different amounts of Bi2O3 can form defect dipoles {[BiBa∙‐MgTi″‐BiBa∙]×, [NbTi∙‐VBa″‐NbTi∙]×, [MgTi″‐VO∙∙]×} and oxygen vacancy, which enhance the short-range transition within the grain and inhibit the movement of free electrons at the grain boundary. The ceramics have excellent room temperature properties, high dielectric constant (εr = 2894) and low dielectric loss (tanδ < 0.03). The ceramics have superior temperature stability and satisfying the EIA X8R (Δεr/ε25 ≤ ±15 %, over the temperature range from −55 °C to 150 °C). It is found that flash sintering can effectively guarantee the stoichiometric concentration of bismuth element and obtain good properties of ceramics. This study demonstrates the potential of Bi2O3 doped BaTiO3-based ceramics synthetized by flash sintering as high-performance electronic device materials.

Tuning effect of DIOX on the thermodynamics and cage occupancy of CH4/CO2 + DIOX mixed hydrates

Hydrate technology could provide a novel approach to deliver convenient CO2-rich natural gas. The identification of a suitable and environmental-friendly promoter for enhancing CO2/CH4 hydrate kinetics is critical. In this study, we evaluated the thermodynamics, kinetics, and morphology of CH4/CO2 + DIOX mixed hydrates in the presence of a thermodynamic promoter 1,3-dioxolane (DIOX) at and below its stoichiometric concentration (SC, CDIOX = 5.56 mol%). Due to the thermodynamic preference of DIOX enclathration in mixed hydrates formation, a decrease in CDIOX in the unconverted solution was observed post nucleation below SC and the hydrates formed exhibit significant heterogeneity in cage occupancy. As CDIOX in the unconverted solution decreases, the DIOX concentration in hydrate (RDIOX) and the thermodynamic stability of the newly formed hydrates decreases. Based on the step-wise heating design, the thermodynamic stability of the hydrates formed below SC with high-RDIOX is close to that of hydrates formed at SC, while hydrates with low-RDIOX undergo dissociation at their P-T trajectories above the measured phase equilibria. Raman measurement indicates that the lower-RDIOX hydrates possess a higher CO2 composition. This study provides new insights into the tuning effect of DIOX on mixed hydrates formation and the basis for using low thermodynamic promoter concentration in hydrate-based technologies.

Investigation of Hydrate Formation and Stability of Mixed Methane-THF Hydrates: Effects of Tetrahydrofuran Concentration.

Effects of tetrahydrofuran (THF) concentration on the mixed methane hydrate formation, dissociation, and stability were investigated. The experiment was conducted at 286.2 K and 6 MPa in a quiescent reactor. The presence of THF below 2.5 mol% did not show the evidence of hydrate formation. However, the concentration above 2.5 mol% enhanced the methane formation rate and the methane consumption. Increasing the THF concentration decreased the induction time as the result of the decrease in the surface tension. Moreover, the methane uptake and formation rate increased with the THF concentration due to the higher degree of hydrate nucleation. The methane recovery after the dissociation experiment showed up to 96%. Furthermore, the hydrate stability increased, and the hydrate dissociation kinetics decreased with the increase in the THF concentration. The optimum THF concentration to enhance and improve the hydrate formation kinetics and stability is its stoichiometric concentration.

Совершенствование технологии внутрипластовой генерации СО2 с компенсацией технологических потерь концентрации химреагентов

The paper is about the enhanced oil recovery technology, based on in-situ carbon dioxide generation, after stoichiometric reaction between gas releasing chemical agent and gas producing one. Two ways of technology improvement are considered: for more uniform in-situ CO2 generation and for more safety when chemicals injection. Both ways require sufficient increase of buffer water, which divides reactive chemicals. Larger buffer water volumes, when being mixed with chemicals water solutions, sufficiently drop down chemical concentration. It also decreases CO2 concentration in water solution. Finally, chemicals and CO2 concentrations, for in- situ generation, decrease. To prevent such decrease, it is necessary to adjust, increase chemicals concentration, when preparing chemical water solution, so to consider further dilution in buffer water and to ensure required stoichiometric concentration in reservoir conditions. Increase of chemicals concentration can be also from decrease of chemicals solutions volumes. Quantitative estimates are given for increase of buffer water volumes, for impact of such increase on decrease of initial chemicals concentrations and decrease of CO2 concentration, in water solutions, as well. Working formulas are provided for calculations on buffer water volumes, adjusted, increased concentrations and decrease volumes of chemicals water solutions, at their preparation stage.

Seawater-based methane storage via mixed CH4/1,3-dioxane hydrates: Insights from experimental and molecular dynamic simulations

Natural gas is essential in the global energy landscape due to its clean-burning properties and widespread availability. While Solidified Natural Gas (SNG) offers a promising solution for non-explosive and long-term gas storage, it confronts issues tied to toxic additives and substantial water-related expenses. This work addressed these challenges by employing the environmentally benign promoter 1,3-dioxane to synthesize sII methane hydrate in artificial seawater. The concentration of 1,3-dioxane employed in this study spans 2.5 mol%, 4 mol%, the stoichiometric concentration of 5.56 mol%, and 7 mol%. The phase equilibrium points slightly downwards shift as the concentration of 1,3-dioxane increases. Under initial conditions of 10 MPa/283.2 K, the CH4/dioxane (4.00 mol%)/seawater system exhibited a methane storage capacity of 80.66 (±0.74) v/v, which closely approached the highest level of 83.54 (±1.48) v/v achieved in the stoichiometric 1,3-dioxane (5.56 mol%) system. The excess 1,3-dioxane (7.00 mol%) system exhibited the highest methane uptake rate of 2.11 (±0.06) v/v/min in the initial 10 min. In situ Raman spectroscopic analyses confirmed the early emergence of encaged guest molecules with increasing 1,3-dioxane concentration. Molecular dynamic simulations revealed that the aggregation of additional guest molecules impeded the formation of well-defined hydrate structures. These findings contribute to the advancement of methane storage in seawater-based hydrates.

Unlocking enhanced gas storage capacity in tuned methane hydrates: Exploring eutectic compositions and water-to-hydrate conversion

The tuning effect of gas hydrates has received widespread interest as a promising approach for energy gas storage due to its unique features for enhancing gas storage capacity and formation conditions. However, its practical application has been stagnant because the effect of various factors has still not been revealed to induce the tuning effect. Here, we provide the dominant factors and optimized conditions related to the tuning effect to achieve the practical enhancement of gas storage capacity under mild formation conditions (272.0 K, 2.35 MPa). Based on the tetrahydrofuran (THF)/trimethylene oxide (TMO) + CH4 hydrates, dominant factors that can affect tuning effects such as eutectic composition, the concentration of the promoter, formation methods, and conversion of water-to-hydrate were experimentally examined by employing the in-situ Raman spectroscopy. The tuning effects of hydrates formed from the aqueous solutions (water-borne) were slowly advanced, unlike all hydrates formed from iced particles (ice-borne) which extremely rapidly induced them. It suggests that the eutectic point was the primary factor in water-borne hydrates, whereas the tuning effect in ice-borne hydrates is mainly governed by the formation rate and stochastic nature. Interestingly, our experiments confirmed for the first time that the gas uptake of water-borne tuned gas hydrates may be higher than those of untuned hydrates (i.e. 5.56 mol% stoichiometric concentration). This work provides not only the dominant parameters but also promising strategies for the practical application of tuning effects to efficient hydrate-based gas storage.

The Spontaneous Vesicle-Micelle Transition in a Catanionic Surfactant System: A Chemical Trapping Study.

Typically, the formation of vesicles requires the addition of salts or other additives to surfactant micelles. However, in the case of catanionic surfactants, unilamellar vesicles can spontaneously form upon dilution of the micellar solutions. Our study explores the intriguing spontaneous vesicle-to-micelle transition in catanionic surfactant systems, specifically cetyltrimethyl ammonium bromide (CTAB) and sodium octylsulfonate (SOS). To gain insights into the changes occurring at the interface, we employ a chemical trapping method to characterize variations in the molarities of sulfonate headgroups, water, and bromide ions during the transition. Our findings reveal the formation of ion pairs between the cationic component of CTAB and the anionic component of SOS, leading to tight interfacial packing in CTAB/SOS solutions. This interfacial packing promotes vesicle formation at low surfactant concentrations. Due to the significant difference in critical micelle concentration (cmc) between CTAB and SOS, an increase in the stoichiometric surfactant concentration results in a substantial rise in the SOS-to-CTAB ratio within the interfacial region. This enrichment of SOS in the aggregates triggers the transition from vesicles to micelles. Overall, our study may shed new light on the design of morphologies in catanionic and other surfactant systems.

The critical mass for the unconfined vapour cloud explosion of compressed and liquid hydrogen

AbstractThe (unconfined) vapour cloud explosion (VCE) is a dramatic phenomenon that generates a severe pressure wave with a high potential to damage assets and produce injuries in the far field. This definition applies also to hydrogen. Nevertheless, no clear tools and methodology have been so far developed and tested for this highly reactive gas, and even advanced numerical simulations lack validation and suffer from large uncertainties. In this view, the comprehension of the physic which subtends this dramatic phenomenon for the specific case of hydrogen is still a central issue. This paper revises some of the most adopted theories on VCE based on classical acoustic theory and models for pressure wave propagation and provides a consequence‐based, threshold (minimum) value for the critical mass of hydrogen which is needed—at a stoichiometric concentration in air—for a vapour cloud to behave as a VCE. To this regard, any non‐stoichiometric hydrogen concentration in air or lower amount of hydrogen would decrease either the flame Mach number or the total energy, thus resulting in negligible overpressure. In this sense, the effects of buoyancy, diffusivity, and weather conditions on the dispersion of hydrogen should be taken into account. The results are valid either for compressed or cryogenic liquid tanks and can be adopted for the sake of distinction between hydrogen flash fire and VCE; for the hazard analysis of hydrogen production and storage; and more in general for the risk assessment of hydrogen systems.

Achieving outstanding mechanical/bonding performances by epoxy nanocomposite as concrete–steel rebar adhesive using silane modification of nano SiO2

Anchoring steel rebar in concrete structures is a common method in the building and construction industry. This research focuses on improving the mechanical/bonding properties of the prepared epoxy nanocomposite adhesive using surface treatment of SiO2 nano fillers by glycidoxypropyltrimethoxysilane (GPTMS). For this purpose, the nano silica particles were silanized via a facile sol–gel method at silane concentrations of 1, 5, 10 and 20X (i.e. X is stoichiometric silane concentration). The nanoparticles were characterized carefully by FTIR, TGA, XRD and XPS techniques. It was found that the highest GPTMS grafting ratio was obtained at silane concentration of 10X. The pure and silanized nanoparticles were added to a two-pack epoxy resin and were compared for tensile and compressive properties. It was found that surface modification of nano silica caused improvement in the strength, modulus, compressive strength and compressive modulus by 56, 81, 200 and 66% compared to the pristine epoxy adhesive and also 70, 20, 17 and 21% compared to the pure nano silica containing adhesive. It also caused 40 and 25% improvement in the pullout strength, 33 and 18% enhancement in the pullout displacement and 130 and 50% in adhesion energy compared to the pristine and raw silica-containing adhesives, respectively.

Coupling amino acid L-Val with THF for superior hydrogen hydrate kinetics: Implication for hydrate-based hydrogen storage

Hydrogen (H2) emerges as a promising future clean energy for the low-carbon and sustainable future due to its high energy density and no pollutant or greenhouse gas emissions after combustion. The advantage of H2 storage in solid-hydrate form is the requirement of only moderate pressure and temperature compared to compressed H2 storage and the relatively lower energy consumption compared to liquid H2 storage. However, the slow kinetics of H2 hydrate formation is one major challenge to breakthrough for the large-scale development of hydrate-based H2 storage. In this study, we introduced an environmental-benign kinetic promoter (L-valine, L-Val) and coupled it with a thermodynamic promoter tetrahydrofuran (THF) using stoichiometric concentration (5.56 mol%) to enhance H2 hydrate formation kinetics. 0.3 wt% L-Val coupled with 5.56 mol% THF yields the optimal kinetic enhancement, and the maximum volumetric H2 uptake (VH2) is 29.83 ± 1.22 volume of H2/volume of H2-THF hydrate (v /v). The reusability of L-Val is proved in five consecutive cycles of H2-THF hydrate formation and dissociation with consistently superior H2 uptake. Furthermore, it was identified that cooling rate (Rc) was an important factor determining the H2-THF hydrate formation kinetics. Lower Rc (0.05 K/min) shows an optimal promoting effect of VH2, which was 105.29% higher than that at higher Rc (0.3 K/min). A mechanism is proposed to explain the effect of Rc on H2-THF hydrate formation kinetics. The maximum gravimetric H2 (GH2) reported in our study reaches 0.26 ± 0.01 wt%, which was superior in current literature below 15.0 MPa. The results provide insights into speeding up H2 uptake in solid-hydrate form and have potential applications in hydrate-based hydrogen storage.

Explosion and vented explosion behaviors of low-concentration gas in large-scale pipes

The extraction, transmission, and use of low-concentration gas in coal mines are often challenged by potential accidents due to proximity to the combustion and explosion concentration limit. Water sealing of fire barriers and explosion venting devices guarantee the safe transmission of low-concentration gas. The propagation and venting of gas explosion under different concentrations are experimentally investigated in a DN500 mm pipe explosion propagation test system. The water sealing of fire barrier vented explosion field evolution of methane-air mixture at the stoichiometric concentration (9.5 vol%) is examined through Fluent numerical simulation to reveal the water sealing of fire barrier further vented explosion pattern of gas transmission pipelines under low concentrations. The explosion overpressure and flame propagation of low-concentration gas in pipes are observed and correlated. Based on their coupling relationship, the design basis for the installation location of the explosion venting device is derived. The vented explosion characteristics of low-concentration gas during pipe transmission are summarized, proving that this explosion venting technique enhances both the explosion venting device and explosion parameters. Our observations and analysis can offer useful clues to underground gas explosion and prevention in coal mines.

The study of homogeneity of the hexagonal Ti3AlC2 phase with inclusions of the titanium carbide

Maps of spatial distributions of Ti, Al, and C on two surfaces of the Ti3AlC2 hexagonal phase (the so-called MAX phase) with inclusions of the TiC phase and Al2O3 were obtained by means of the energy-dispersive X-ray spectroscopy. Volume fractions of phases were 0.848, 0.107, and 0.045, respectively. The sample was cut from the synthesized tablet. One of the analyzed surfaces of the sample was the free outer surface of the tablet (surface 1), and another surface was the cut (surface 2). Histograms of the concentration distributions of elements were plotted. For both surfaces, histograms of all elements have Gaussian forms with mean values of about their stoichiometric concentrations in Ti3AlC2 and TiC phases. Histograms for the carbon have maxima at 34–36 at. %, which is close to the stoichiometric content of the carbon in the Ti3AlC2 MAX phase (33 at. %), and at about 50 at. % that corresponds to the stoichiometric concentration of the carbon in the TiC phase. However, Gaussian standard deviations from these mean values are large (up to 7 at. %), which proves the existence of th vacancies and interstitials of the carbon in phases. The histogram for the aluminum on surface 1 has an additional distribution near zero value of the concentration, and the histogram for carbon on surface 2 has an additional distribution near 27.7 at. %. Both found particularities can be explained by supposing that the outer surface of the original tablet cools down more rapidly than its inner parts.

Fabricating core-shell of silane modified nano ZnO; Effects on photocatalytic degradation of benzene in air using acrylic nanocomposite

In this work, ZnO nanoparticles were surface modified using bis-(triethoxysilylpropyl)amine (BTPA) at different silane concentrations and applied as photocatalyst to water based acrylic film to degrade benzene in gaseous phase under UV/Vis lights. The pure and modified nanoparticles were characterized using FTIR, TGA, BET, XRD, XPS, I-V, photocurrent response and photoluminescence analysis. The results showed that the band gap of the nanoparticles decreased from 3.21 to 2.98 eV and the specific surface area increased by silanization at silane stoichiometric concentration (1X). The mechanical properties of the pure and modified ZnO containing acrylic nanocomposites were investigated. The results showed that addition of the modified nanoparticles (at 3 wt%) to the acrylic matrix increased the tensile strength by 197.9 and 123.3% and modulus by about 288.8 and 185.7% compared to the pristine and pure nanoparticle containing acrylic films. It was found that using silanized nanoparticles in acrylic film increased photocatalytic degradation of benzene in gaseous phase by about 20% compared to the pure nano ZnO containing nanocomposite. The benzene removal efficiency of about 97.28 and 85.39% was obtained for the modified acrylic nanocomposites (at 3 wt% photocatalyst loading content) under UV and visible light irradiations, respectively.

Molecular Design of Interfaces of Model Food Nanoemulsions: A Combined Experimental and Theoretical Approach.

The composition and structure of the interfacial region of emulsions frequently determine its functionality and practical applications. In this work, we have integrated theory and experiments to enable a detailed description of the location and orientation of antioxidants in the interfacial region of olive-oil-in-water nanoemulsions (O/W) loaded with the model gallic acid (GA) antioxidant. For the purpose, we determined the distribution of GA in the intact emulsions by employing the well-developed pseudophase kinetic model, as well as their oxidative stability. We also determined, by employing an in silico design, the radial distribution functions of GA to gain insights on its insertion depth and on its orientation in the interfacial region. Both theoretical and experimental methods provide comparable and complementary results, indicating that most GA is located in the interfacial region (~81.2%) with a small fraction in the aqueous (~18.82%). Thus, GA is an effective antioxidant to inhibit lipid oxidation in emulsions not only because of the energy required for its reaction with peroxyl radical is much lower than that between the peroxyl radical and the unsaturated lipid but also because its effective concentration in the interfacial region is much higher than the stoichiometric concentration. The results demonstrate that the hybrid approach of experiments and simulations constitutes a complementary and useful pathway to design new, tailored, functionalized emulsions to minimize lipid oxidation.

General estimation method for lower flammability limits of organic compounds: The simpler the better

Due to the lack of well-established procedures to estimate the lower flammability limit (LFL) of arbitrary fuel-air mixtures, we report therein a simple method derived from a relationship introduced over 80 years ago for C–H–O molecules and presently extended to molecules containing C–H–N–O–F–Cl–Br–I–Si–P–S elements. The LFL was usually found to represent a constant fraction α≃1/2 of the stoichiometric concentration of fuel, except for halogen compounds for which α increases with the fraction of halogen atoms in the fuel molecules. Interestingly, this extremely simple scheme, which could be then easily integrated into any molecule design workflow, indicates that LFL values are mainly determined by the element count on the fuel structure, in sharp contrast with the premises underlying quantitative structure–property relationship (QSPR) and group contribution (GC) approaches.