Flammability Limits Research Articles

A thick reaction zone model for premixed flames in two-dimensional channels

Direct interactions between the flow field and the chemical reaction in premixed flames occur when the reaction zone thickness is comparable to, or greater than flow length scales. To study such interactions, a laminar model is considered that has direct bearings to steadily propagating deflagrations in a Hele-Shaw channel with a background plane Poiseuille flow. The study employs asymptotic analyses, pertaining to large activation energy and lubrication theories and considers a distinguished limit where the channel width is comparable to the reaction zone thickness, with account being taken of thermal-expansion and heat-loss effects. The reaction zone structure and burning rates depend on three parameters, namely, the Peclet number, , the Lewis number, and the ratio of channel half-width to reaction zone thickness, . In particular, when the parameter is small wherein the reaction zone is thick, transport processes are found to be controlled by Taylor's dispersion mechanism and an explicit formula for the effective burning speed is obtained. The formula indicates that for , which interestingly coincides with a recent experimental prediction of the turbulent flame speed in a highly turbulent jet flame. The results suggest that the role played by differential diffusion effects is significant both in the laminar and turbulent cases. The reason for the peculiar dependence can be attributed, at least in our laminar model, to Taylor dispersion. Presumably, this dependence may be attributed to a similar but more general mechanism in the turbulent distributed reaction zone regime, rather than to diffusive-thermal curvature effects. The latter effects play however an important role in determining the effective propagation speed for thinner reaction zones, in particular, when is large in our model. It is found that the magnitude of heat losses at extinction, which directly affects the mixture flammability limits, is multiplied by a factor in comparison with those corresponding to the no-flow case in narrow channels.

Feasibility analysis of blending hydrogen into natural gas networks

Hydrogen fuel has the potential to mitigate the negative effects of greenhouse gases and climate change by neutralizing carbon emissions. Transporting large volume of hydrogen through pipelines needs hydrogen-specific infrastructure such as hydrogen pipelines and compressors, which can become an economic barrier. Thus, the idea of blending hydrogen into existing natural gas pipelines arises as a potential alternative for transporting hydrogen economically by using existing natural gas grids. However, there are several potential issues that must be considered when blending hydrogen into natural gas pipelines. Hydrogen has different physical and chemical properties from natural gas, including a smaller size and lighter weight, which require higher operating pressures to deliver the same amount of energy as natural gas. Additionally, hydrogen's small molecular size and lower ignition energy make it more likely to permeate through pipeline materials and seals, leading to degradation, and its wider flammability limits make it a safety hazard when leaks occur. In this study, we investigate these potential issues through simulation and technical surveys. We develop a gas hydraulic model to simulate the physical characteristics of a transmission and a distribution pipeline. This model is used throughout the study to visualize the potential impacts of switching from natural gas to hydrogen, and to investigate potential problems and solutions. Furthermore, we develop a Real-Time Transient Model (RTTM) to address the compatibility of current computational pipeline monitoring (CPM) based leak detection methods with blended hydrogen. Finally, we suggest the optimal hydrogen concentration for this model, and investigate the amount of carbon reduction that could be achieved, while considering the energy needs of the system.

Ammonia-methane combustion in a swirl burner: Experimental analysis and numerical modeling with Flamelet Generated Manifold model

Ammonia/methane flames gained significant attention since this is a probable step toward a sustainable, carbon-free economy in the near future. Therefore, three such flames were numerically and experimentally investigated in a swirl burner, focusing on robust modeling methods to facilitate the spreading of ammonia combustion in the industry. Chemistry was considered by the mechanism of Okafor and employed through the Flamelet Generated Manifold model. Both Particle Image Velocimetry and OH* measurements confirmed the appropriateness of the numerical model in all cases. It was demonstrated that the modeling approaches are applicable at both near stoichiometric conditions and close to the flammability limit of ammonia. The comparison of steady-state and the mean unsteady results implied that the steady calculations are appropriate only for the chemical conversion and fall behind in flow field modeling. The Root Mean Square velocity was identical up to the reaction zone for all cases, while its value decreased with the increase of ammonia concentration. The CO emission matched underpredicted experiments by a magnitude; however, the concentration was very low. Regarding the NOx emission, the CFD underpredicted it by a factor of two.

NOX EMISSION ON RECIPROCAL FILTRATION COMBUSTION OF BIOGAS: A CASE STUDY

Filtration combustion is an effective technique for dealing with low-calorific value fuels, such as derivative fuels from biomass, and simultaneously reducing pollutant emissions. In this study, combustion of biogas (22% of CO2) was investigated theoretically and experimentally by utilizing a reciprocal flow porous burner with heat exchangers inserted in the porous medium. Combustion of lean biogas-air mixtures is stabilized in a naturally transient process, in which a lean equivalence ratio range (0.1 ≤ Φ ≤ 0.9) and gas flow velocities of 0.2 and 0.3 m/s were employed, periodically switching gas flow direction. Reciprocal flow combustion has been compared with unidirectional combustion, using technical methane as reference gas. In this context, predicted temperature profiles inside the burner, as well as experimental results, have shown that the reciprocating system plays an important role in the combustion process, significantly improving flammability limits, efficiency, and emissions. As result, trapezoidal temperature distribution profiles have been obtained with peaks between 1200 and 1600 K, reaching high efficiency up to 90% and ultra-low emission of nitrogen oxides (≤ 2ppm).

Effects of hydrogen addition on combustion and flame propagation characteristics of laser ignited methane/air mixtures

In this study, effects of hydrogen addition on combustion and flame propagation characteristics of methane/air mixtures were investigated in a constant volume combustion chamber. Tested gas mixtures are 100% CH4, 05% H2 – 95% CH4, 10% H2 – 90% CH4 and 15% H2 – 85% CH4, and such mixtures were ignited using a passively Q-switched Nd:YAG laser ignitor which has a pulse energy of 12.3 mJ, pulse duration of 2.4 ns and wave length of 1064 nm. A Schlieren setup coupled with a high-speed camera enabled evaluating flame propagation behavior, while pressure curve analysis provided necessary data for characterization of combustion properties. Additionally, lean flammability limits of gas mixtures were also determined at the test conditions. The unique properties of hydrogen (such as low density, high reactivity, high diffusivity etc) widened lean flammability limit. Rate of pressure rise and measured pressure values increased with hydrogen addition, regardless of the air-fuel equivalence ratio (λ). Lastly, hydrogen addition uniformly affected flame propagation characteristics and flame luminosity. Combustion process became more stable with hydrogen addition.

Non‐Flammable Electrolyte with Lithium Nitrate as the Only Lithium Salt for Boosting Ultra‐Stable Cycling and Fire‐Safety Lithium Metal Batteries

AbstractLithium metal batteries (LMBs) attract considerable attention for their incomparable energy density. However, safety issues caused by uncontrollable lithium dendrites and highly flammable electrolyte limit large‐scale LMBs applications. Herein, a low‐cost, thermally stable, and low environmentally‐sensitive lithium nitrate (LiNO3) is proposed as the only lithium salt to incorporate with nonflammable triethyl phosphate and fluoroethylene carbonate (FEC) co‐solvent as the electrolyte anticipated to enhance the performance of LMBs. Benefiting from the presence of NO3− and FEC with strong solvation effect and easily reduced ability, a Li3N–LiF‐rich stable solid electrolyte interphase is constructed. Compared to commercial electrolytes, the proposed electrolyte has a high Coulombic efficiency of 98.31% in Li‐Cu test at 1 mA cm−2 of 1.0 mAh cm−2 with dendrite‐free morphology. Additionally, the electrolyte system shows high voltage stability and cathode electrolyte interphase film‐forming properties with stable cycling performances, which exhibit outstanding capacity retention rates of 96.39% and 83.74% after 1000 cycles for LFP//Li and NCM811//Li, respectively. Importantly, the non‐flammable electrolyte delays the onset of combustion in lithium metal soft pack batteries by 255 s and reduces the peak heat release by 21.02% under the continuous external high‐temperature heating condition. The novel electrolyte can contribute immensely to developing high‐electrochemical‐performance and high‐safety LMBs.

Combustion and emission characteristics of NH3/CH4/air in a model swirl combustor: Comparison between premixed and non-premixed modes

Ammonia (NH3) is a promising hydrogen carrier and can be used as carbon-free alternative fuel. However, NH3 combustion faces critical challenges, such as narrower flammability range and high NOx emission, which limits its applications. To extend the knowledge on NH3 combustion characteristics, intensive previous studies have been carried out, but most of them were concerned on premixed swirl flames. This work aims to experimentally provide a thorough comparison between premixed and non-premixed NH3/CH4/air swirl flames in terms of their flame structure, chemiluminescence spectrum, and pollutant emission characteristics at various NH3 volumetric blending ratios (XNH3) and global equivalence ratios (φ). The results show that, at a fixed φ of 0.85, the premixed combustion features a closely attached flame profile at any XNH3 of interest, while the non-premixed combustion exbibits a lifted flame appearance for all XNH3 conditions, hence a higher flammability limit of XNH3 is attained by the premixed combustion mode. At a fixed XNH3 of 50%, the non-premixed combustion tends to move the whole flammability range towards the rich direction slightly. Considering the monotonic relationship between chemiluminescence intensity of different excited radicals and operating parameters, OH∗/CH∗ intensity ratio is suggested to be used for sensing the change of XNH3 in both premixed and non-premixed combustion modes, while NH∗/CH∗ intensity ratio is recommended for sensing the change of φ. Comparing to premixed combustion, the non-premixed combustion produces a lower NO emission in the whole ranges of considered XNH3 and φ. Moreover, the NO emission profiles suggest the necessity of employing rich-lean technology for achieving acceptably low NO emission for both premixed and non-premixed combustion modes, while the latter shows a possibility to be operated in relatively leaner condition in the first stage.

Performance-based assessment of an explosion prevention system for lithium-ion based energy storage system

This work developed and analyzed a design methodology for Powin Stack™ 360 enclosures to satisfy the requirements for explosion prevention per NFPA 855. Powin Stack™ 360 enclosures are lithium-ion-based stationary energy storage systems (ESS). The design methodology consists of identifying the hazard, developing failure scenarios, and providing mitigation measures to detect the battery gas and maintain its global concentration lower than 25% of the lower flammability limit (LFL) to meet the prescriptive performance criterion of NFPA 69 – Standard on Explosion Prevention Systems. The UL 9540A test data is used to define the battery gas composition, release rate, and release duration to describe the failure scenario involving thermal runaway propagation. The ESS enclosure consists of individual stacks (compartments) with targeted airflow to ensure the cooling of batteries during normal operational conditions. This arrangement makes it difficult to use a standard exhaust ventilation methodology to design an explosion prevention system. An innovative approach is used to purge the battery gas from individual Powin Stacks™ and from the main enclosure during a thermal runaway event. The designed method is analyzed using a computational fluid dynamics (CFD) model to ensure it meets the intent of NFPA 69. The explosion prevention system functionality presented in this work is limited to removing flammable battery gas generated due to the non-flaring decomposition of batteries and does not consider its interactions with other fire protection features.

A reduced-scale experimental study of dispersion characteristics of hydrogen leakage in an underground parking garage

A medium-scale model (1/10) of an underground parking garage is designed and built to study the characteristics of the release and dispersion of hydrogen leaked from hydrogen fuel cell vehicles (HFCVs) in underground garages. Helium is used in place of hydrogen for safety reasons. The helium release experiments are conducted and the variations in helium concentrations at different locations and times in the garage model are obtained. The influence mechanisms of the leakage flow rate and nozzle diameter on the spatial and temporal distributions of the helium concentration are revealed. The experimental results show that the initial release rate of helium is the key factor affecting the distribution of helium concentrations. Both leakage flow rate and nozzle diameter have a significant influence on helium concentrations by affecting the initial release rate. If the release time is long enough, the helium concentrations will experience three stages during release, namely, rapid growth, slow growth and relatively stable. Furthermore, the beams of the garage can reduce the area on the ceiling where the hydrogen concentration exceeds the lower flammable limit (LFL). On the other hand, the beams can make it easier for local hydrogen concentrations to reach the LFL. This work can provide theoretical support for the design and construction of underground parking garages and the arrangement of hydrogen detectors.

Investigation on the reaction mechanism of methane combustion near flammability limits at elevated pressures and temperaturaes

Combustible gas explosions may occur at elevated pressure and temperature of wellbore conditions. To better understand and protect against wellbore explosion, it is necessary to study the combustion mechanism of methane at elevated pressure and temperature conditions. In this study, combustion mechanisms near the stoichiometric concentration as well as the flammability limit were investigated using a one-dimensional premixed laminar flame speed model based on the GRI 3.0 mechanism. The effects of initial pressure and initial temperature on flame temperature were analyzed. The main free radicals and reactions at different conditions were determined by sensitivity analysis. The reaction rates of the main reactions were comprehensively analyzed with previous experimental results of the flammability limit at different conditions. The mechanism of how initial pressure and initial temperature affects the flammability limit was determined. The results showed that the radical HO2 and its involved reaction HO2+CH3OH + CH3O play a crucial role in the methane combustion process at elevated pressure and temperature conditions. The initial pressure and initial temperature quantitatively affect the flammability limit mainly by affecting the reaction rates of the main reactions.

Improvement the flame retardancy, thermal conductivity and mechanical properties of silicone rubber via silane coupling agent modified CNTs‐β‐FeOOH

AbstractSilicone rubber with its odorless and non‐toxic, high and low temperature resistance and other advantages is widely used in many fields, but its shortcomings of flammability and low thermal conductivity limit its application and development. Therefore, the research on flame retardant and thermal conductive silicone rubber is practically valueable. In this study, iron oxyhydroxide (β‐FeOOH) was synthesized on carbon nanotubes (CNTs) by in situ growth and added to silicone rubber after surface modification with γ‐aminopropyltriethoxysilane (KH550). The results showed that the limiting oxygen index (LOI) of methyl vinyl silicone rubber (VMQ) with the addition of one part of KH550@CNTs‐β‐FeOOH increased to 29.8%, its peak heat release rate (pHRR) and total heat release (THR) decreased by 40.1% and 30.2%, respectively, and its thermal conductivity increased to 0.3680 W/m·k. The flame‐retardant performance and thermal conductivity of the VMQ composite were significantly improved. The improvement of its flame retardancy was mainly due to the catalytic carbonization of CNTs and β‐FeOOH, which promoted the formation of dense carbon layers. The carbon layer insulates the exchange of oxygen and combustible gases. In addition, the thermal conductive network constructed by KH550@CNTs‐β‐FeOOH in the composite effectively improved the thermal conductivity of VMQ.

Effects of trifluoroiodomethane and pentafluoroethane on combustion characteristics of flammable refrigerant propane

For the environmentally friendly refrigerant R290, the flammability is the biggest concern for its applications. In this paper, the inhibition of trifluoroiodomethane (R13I1) and pentafluoroethane (R125) on laminar burning velocity (LBV), lower flammable limit (LFL) and heat of combustion (HOC) of R290 have been researched. The laminar burning velocities were obtained at elevated temperature by an externally heated diverging channel method, and the lower flammable limits were measured in a glass tube under different humidity conditions. R13I1 showed a greater inhibition effect than R125 on the flammability of R290. The LBV decreased exponentially and the LFL increased markedly with addition of R13I1. The computation of LBV for R290/R13I1 mixtures showed an average relative error within 7.4%. The inhibition effectiveness of R13I1 on the LFL was reduced in wet air, mainly by the chemical effect of water molecules. And the linear relationship was found at LFL between calculated adiabatic flame temperature and the proportion of R13I1. The model was proposed to calculate the LFL and demonstrated a good prediction accuracy of 3.2% for LFL of R290/R13I1 mixtures. This study set out to investigate the inhibition of R13I1 and R125 on the flammability of R290 and assess the flammability of R290/R13I1 mixtures to provide low GWP and less flammable alternative refrigerants in air conditioners or heat pumps.

Prediction of Laminar Burning Speed of Propane/Hydrogen/Air Mixtures Using Power-Law Correlation and Two Machine Learning Models

Abstract Propane (C3H8) and hydrogen (H2) are regarded as alternative fuels that are favorable to the environment. Hydrogen gas's low energy density, storage, and transportation are the main issues with using it as an alternative fuel. Addition of hydrogen gas in the combustion of propane will also improve flame stability, broaden lean flammability limits, and reduces pollutant emissions. Thus, utilizing propane and hydrogen mixtures as fuel is a good choice. Laminar burning speed is a fundamental property of a combustible mixture and can be used to provide information regarding the mixture’s reactivity, exothermicity, and diffusivity. In this study, power-law correlation and machine learning methods were used to create models that predict the laminar burning speed of propane/hydrogen/air mixtures at various states. Two machine learning models are artificial neural network (ANN) and support vector machine (SVM). The data were generated by using CANTRA code and a chemical kinetic mechanism. For a wide variety of input values, the models were able to determine the laminar burning speed with great accuracy. The ANN model yields the best performance. The main advantage of these models is the noticeably faster computing time when compared to chemical reaction mechanisms.

Enhancing ammonia combustion using reactivity stratification with hydrogen addition

In this paper, we propose a new method to enhance the burning rate of ammonia through reactivity stratification by using the binary fuel of ammonia and hydrogen. It is found that stratification from the high-reactivity fuel, hydrogen, to the low-reactivity fuel, ammonia, can substantially increase the flame speed of the low-reactivity, ammonia/air mixture. Moreover, the enhancement can sustain for a certain period even when the flame is entirely within the original low-reactivity mixture, indicating a memory effect of the flame. Such sustaining effect is found to be caused mainly by ammonia decomposition and the associated hydrogen production initiated by the hydrogen and active radicals. The reactions of NHx+H as well as reactions involving HNO and N2H2 were found to be important for this process. The length scale of the flame speed sustenance is further investigated in terms of the stratification thickness, pressure, flame stretch and stoichiometry. Furthermore, the flammability limits of the low-reactivity fuel are found to be substantially extended by the reactivity stratification. These findings suggest a strategy to facilitate the direct combustion application of ammonia.

Analysis of the Method for Enhancing Safety by Predicting and Comparing Damage Ranges Due Owing to Chemical Leakages

To predict the extent of damage caused by leakages at a place where chemicals are wholesaled, four of the most commonly stored substances in the corresponding place were selected. Leakage volumes were increased by 50 ㎘, and methyl alcohol, ethyl acetate, and methyl ethyl ketone were confirmed by increasing the leakage volume to 100 ㎘ and to 160 ㎘ for toluene. A total of 92 scenarios were created by applying the region’s average temperature, wind speed, wind direction, and humidity over the last 10 years to confirm each substance’s diffusion distance. The prepared scenario was analyzed by applying ALOHA air dispersion models. Regarding toxicity, criteria were analyzed based on each substance’s PAC-1, PAC-2, and PAC-3 concentration, and a fire occurrence possibility range was used to maintain the concentration of the lower flammable limit. Under normal conditions, in the case of the same amount of leakage, the concentration of the lower flammable limit and PAC-1 was maintained farthest from toluene, but the danger distance of methyl alcohol was farther in PAC-2 and PAC-3. Results showed that the diffusion distance increases the log function with the amount of leakage. However, owing to the substances’ toxicity and physical characteristics, the PAC levels of some substances showed non-uniform results. In addition, diffusion widths differed for each substance. Therefore, to prescribe countermeasures for chemical leakages in storage locations, all substances being stored must be checked. Disaster prevention measures must also be established by considering not only diffusion distances of the substances but also their diffusion widths.

Experimental research on flammability characteristics and ignition conditions of hybrid mixture emissions venting from a large format thermal failure lithium-ion battery

When the concentration of gas is below its lower flammable limit and the content of the particles is below its minimum explosible concentration, it can be explosible. Thermal abuse tests for 50 Ah lithium-ion batteries were conducted under an inert atmosphere. The battery failure venting emissions were collected and their composition was identified previously. It still needs further research for the flammability characteristics and ignition conditions for hybrid mixture emissions venting from a large format lithium-ion battery thermal failure. In this study, the likelihood, severity, and kinetics of the batteries' hybrid mixture emissions flammability have been researched. To analyze battery emission flammability characteristics, five indexes have been investigated; they are ignition temperature (Tig), ignition time (τig), maximum explosion pressure (Pmax), pressure rise maximum rate ((dP/dτ)max), and size-normalized maximum rate pressure rise (KSt). Based on quantitative analysis for the hybrid mixture flammability characteristics, it indicates that particle size and gas content can impact hybrid mixture emission flammability characteristics. As for the mixture with finer particles, the optimum combustion condition of the particle and gas concentration pairs were 0.3 and 0.7. The ignition temperature for the optimum combustion conditions was 495 °C. The pressure rising velocity was 23 Mpa/s during ignition. High solvent content and low particle concentration are the conditions for optimum combustion. This indicates that the gas admixture solvent plays a major role in the combustion kinetics of the mixture emission. This research offers a fundamental perspective and provides preventive and protective thermal safety designs that are more suitable for large format commercial battery thermal systems.

Numerical investigation of the dispersion features of hydrogen gas under various leakage source conditions in a mobile hydrogen refueling station

The leakage and dispersion of hydrogen gas in a mobile hydrogen refueling station is being numerically investigated in this paper. The investigated geometry is derived from the mobile hydrogen refueling station in China. The numerical models are verified by experimental data. The hydrogen gas leaks from the hydrogen buffer tank in the form of momentum-dominated jet. The combustible danger region, the hydrogen concentration distribution, and the volume of hydrogen gas cloud are investigated. The effects of leakage positions and leakage flow rates on the characteristics and evolution of hydrogen diffusion in the mobile hydrogen refueling station and the open space are analyzed. The results show that the hydrogen concentration in the 3-way corner of the ceiling opposite the leakage orifice first reaches 0.4% and 4%. When the leakage orifice faces the sidewall of the truck container, the liquid hydrogen storage is completely surrounded by hydrogen gas clouds in the flammability limit. The maximum diffusion height of hydrogen at the lower flammable limit increased as the leakage flow rate increased, and the volume of hydrogen in the flammability limit increased virtually exponentially in the open space. The research findings provide a significant reference for potential explosion and risk assessment studies of mobile hydrogen refueling station.

Minimum ignition energy of hydrogen–ammonia blends in air

We present a numerical analysis to calculate the minimum ignition energy of hydrogen–ammonia blends in air at both under and over atmospheric pressure. Unlike previous calculations, we used the full compressible and reactive Navier–Stokes equations coupled with detailed chemical kinetics (San Diego mechanism for hydrogen, complemented with the San Diego chemistry for nitrogen). The effect of the size of the energy deposition region and the deposition time are considered to determine the most efficient method to ignite the mixture. Our calculations also evaluate the impact of the gas compressibility on the minimum ignition energy after a sudden energy deposition. The results are validated first by comparing the minimum ignition energy of pure hydrogen–air mixtures as a function of the equivalence ratio ϕ with available experimental data and previous numerical results. Then, fuel blends made of mixtures of hydrogen and ammonia (NH3) are considered to calculate the minimum ignition energy as a function of fuel composition, equivalence ratio and pressure. The full range of ammonia volumetric content in the blend is varied between the extreme cases of pure hydrogen and pure ammonia. For each fuel blend, we computed a wide range of equivalence ratios ϕ that, in the case of pure hydrogen at atmospheric conditions, ranged from ϕ=7 to ϕ≃0.07, near the lean flammability limit, to theoretically explain the experimental evidence of ultra-lean flames reported in the literature.

Lower flammability limits of H2/NH3/CH3OH mixtures under elevated pressures, temperatures and different blending ratios

The lower flammability limits (LFLs) of H2/NH3/CH3OH mixtures and related flame morphologies are experimentally investigated under elevated pressures, elevated temperatures, and blending ratios. The results show that the flame morphologies of LFLs are mushroom-like, darkening with an increase in initial pressures and remaining unchanged with an increase in initial temperatures. Except for the flame wrinkles at 10:0:0 and 5:5:0, there is little difference in the flame morphologies with blending ratios. When NH3:CH3OH = 1:1, the LFLs of 0 % H2 decrease with elevated pressures while the rest increase, and the LFLs steadily decrease as H2 increases. When H2:CH3OH = 1:1, the LFLs of 100 % NH3 decrease with elevated pressures while the rest increase, and the LFLs increase as the NH3 increases. The LFLs of 0–40 % CH3OH rise with the increasing pressure when H2:NH3 = 1:1, while the LFLs of 60 % CH3OH are almost unchanged and the LFLs of 80–100 % CH3OH decrease. Additionally, the LFLs increase at 50–100 kPa and decrease at 150–250 kPa as CH3OH increases. The LFLs of the mixtures decrease with elevated temperatures. The prediction formula of H2/NH3/CH3OH mixtures’ LFLs under elevated pressures, elevated temperatures, and blending ratios is established. The average absolute error (AAE) and average relative error (ARE) are 0.11 % and 1.54 %.

Effect of a palladium catalyst and initial pressure on methane-air catalytic combustion process in a helical coil microchannel: A molecular dynamics approach

Catalytic combustion is a flame-free process which occurs at low temperatures and reduces less release of nitric oxide (NOx). Although catalysts help reduce the release of toxic gases, they have detrimental environmental effects. Therefore, by simulation these reactions, a constraint on the flammability limits and improving their performance can be achieved. In this research, using the molecular dynamics (MD) simulation, the catalytic combustion process of air-methane was studied in a helical microchannel. Palladium (Pd) was used as the catalyst. The results show that adding a Pd catalyst further improved the simulated structure's thermal performance(TP). The heat flux(HF) and thermal conductivity (TC) of atomic samples increased from 2067 W/m2 and 1.28 W/m.K to 2096 W/m2 and 1.45 W/m.K with an increase in atomic ratio Pd catalyst from 1 to 4%. Finally, the combustion efficiency (CE) converges to 93% in the presence of 4% Pd catalysts. By increasing the initial pressure (IP) from 0 to 10 bar, the maximum density did not change much, and the velocity and temperature values decrease in terms of the limitation in atomic oscillations. Increasing the IP reduces the HF and TC from 2096 W/m2 and 1.45 W/m.K to 1981 W/m2 and 1.19 W/m.K. Regarding different types of combustion processes, such as catalytic combustion, were considered in different types of industrial applications, it is expected to study the effect of the parameters of the atomic ratio of Pd catalyst and the IP, propose an optimal mechanism to create catalytic combustion in real and practical samples.