Upper Flammability Limit Research Articles

Studies of the diluent, temperature and pressure effect on the lower and upper flammability limits of ammonia in air

Ammonia safety and environmental protection research forms the basis for its role as a clean energy carrier. In this work, an experimental study was conducted in this work to analyze the effect of different inhibitors (nitrogen, argon and water vapor) on the flammability limits (FLs) of ammonia at elevated temperatures and pressures. In addition, the influence of diluents on the compositions and flame temperature changes was evaluated, and the temperature sensitivity coefficients of the elementary reactions and the ROP of free radicals and partial products at the FL concentrations were analyzed. The findings indicated that water vapor provided the strongest flame retardant effect on ammonia in three inhibitors. Within a certain temperature and pressure range, the FLs of ammonia in ammonia/diluent/air can be predicted using the extended Le Chatelier equation. The flame temperature decreased at the lower flammability limit (LFL) concentrations and increased at the upper flammability limit (UFL) concentrations of ammonia with increasing initial pressure. As the initial temperature increases, the flame temperature decreases during ammonia combustion. The influence of ammonia concentration on flame temperature is greater than that of diluents dilution. The elementary reactions H+O2<=>O+OH (R1) and NH2+NO<=>NNH+OH (R82) were the primary reactions that increased the flame temperature at the FL ammonia concentrations in ammonia/diluent/air. Conversely, NH2+NO<=>N2+H2O (R80) and H+O2(+M)<=>HO2(+M)(R15) were the main reactions that decreased the flame temperature. H, OH and NH2 radicals played a crucial role in the combustion reaction process at ammonia FL concentrations. At the LFL concentrations of ammonia, the molar fraction of the OH radical showed the greatest variation, while at the UFL concentrations of ammonia it was NH2 radical. The elementary reaction NH3+OH<=>NH2+H2O (R158) was the primary reaction that consumed OH radical and promoted the formation of NH2 radical. Free radical concentrations decreased with increasing pressure and temperature, while the change rate of free radical ROP accelerated with increasing pressure. In addition to nitrogen and water, the partial products were mainly nitric oxide at the LFL concentrations, while at the UFL concentrations were mainly hydrogen.

Comparative study on the thermal runaway characteristics of Li(NixCoyMnz)O2 batteries

Lithium-ion batteries (LIBs) generate substantial gas during the thermal runaway (TR) process, presenting serious risks to electrochemical energy storage systems in case of ignition or explosions. Previous studies were mainly focused on investigating the TR characteristics of Li(NixCoyMnz)O2 batteries with different cathode materials, but they were conducted in isolation. In this study, the thermal runaway characteristics of prismatic cells that use Li(NixCoyMnz)O2 (with x ranging from 0.33 to 0.9) cathode materials in an inert environment, which are commonly used or proposed for energy storage applications, are examined. The findings of this research show that the normalized gas generation rate remains consistent, regardless of the battery capacity or experimental chamber volume, with a value of 0.1 ± 0.03 mol∙Ah⁻1. High-capacity cells have short jetting durations, and a high nickel content leads to increased mass loss rates. The flammability limits of the gases expelled during thermal runaway, represented by the lower flammability limit (LFL), remain stable at 8 ± 1.8 % with minimal variations. However, the upper flammability limit (UFL) varies significantly, ranging from 30 % to 60 %. Increasing the battery capacity or reducing the experimental chamber volume increases the explosion index. The explosive, combustibility, and jetting duration characteristics of the emitted gases from five different battery chemical compositions provide valuable insights for risk assessment in future electrochemical energy storage systems.

Model for estimating the effects of pressure and dilution on the flammability limits of fuels in constant-volume systems at subatmospheric pressure

The fire and explosion hazard of a fuel is closely related to its flammability limits. These limits are affected by pressure but are typically investigated at atmospheric pressure. However, fuel in aircraft tanks during flight is at subatmospheric pressure, and most industrial processes are often conducted at nonatmospheric pressure. Inert gases are often added to mixtures to mitigate the flammability risks associated with oxidation and fuel storage processes; however, predicting the behavior of such mixtures is challenging. Building on two prior models, this study established a comprehensive model based on reported heat capacities to estimate flammability limits in fuel–air–diluent mixtures at various initial pressures. The accuracy of the model was validated through comparison with measured flammability limits for propylene with added nitrogen or added carbon dioxide at subatmospheric pressures. The predictions closely aligned with the measurements, with the deviations of lower and upper flammability limits (ΔL and ΔU, respectively) being 0.01% – 0.29% and 0.09% – 0.30%, respectively, for nitrogen addition and 0.10% – 0.23% and 0.36% – 0.89%, respectively, for carbon dioxide addition; these results confirmed the model’s efficacy. In summary, the proposed model could be applied to reduce flammability risk in systems containing air and fuel at any pressure, regardless of the addition of inert gases.

Исследование зависимости температуры самовоспламенения от концентрации паров горючей жидкости

Purpose. The currently used methodology for determining flammable liquid self-ignition temperature, which is well-known as the “drop method”, makes it impossible to obtain the dependence of self-ignition temperature on flammable liquid concentration that corresponds to theoretical concepts. It is related to the fact that while conducting experiments a flammable liquid is injected into the neck of an open heated vessel. The preliminary calculation of the required quantity of flammable liquid for creating its given concentration does not take into account the substance loss when it is injected into the reaction vessel. The main aim of the research is to improve the methodology for determining flammable liquid self-ignition temperature depending on the concentration of its vapors. Methods. To study the relationship between the volume of flammable liquid injected into the neck of the reaction vessel heated to a certain temperature and self-ignition temperature of this liquid the method of experimental data analysis was used. The experimental results were obtained with the help of the experimental method that involved injection of different volumes of flammable liquid and then recording flame presence or absence. Findings. A relationship was established between the fuel concentration in the vapor-air mixture and the volume of the injected sample. The methodology for determining the flammable liquid self-ignition temperature was corrected. Research application field. The results can be used in determining flammable liquids self-ignition temperature of various chemical composition, as well as in the educational process when students carry out a laboratory work on determining a flammable liquid self-ignition temperature depending on its concentration. Conclusions. The findings of the research allowed the authors to draw the following conclusions: 1) in the methodology for determining a flammable liquid self-ignition temperature when calculating the volume of the injected sample to create the required concentration of fuel in the vessel, the flammable liquid losses occurring on its injection into a heated reaction vessel were not taken into account. It is recommended to use a correction factor of 2 to take into consideration losses in calculation formulas. 2) to equally distribute the concentrations of the used fuel on the graph of the dependence under study within the lower and upper flammability limits, to calculate the volume of a flammable liquid, fuel concentration must be preset as follows: ϕ1 = 1,2ϕн, ϕ2 = ϕстех, ϕ3 = 1,8ϕстех, ϕ4 = 0,8ϕв. 3) the methodology for determining the self-ignition temperature of a flammable liquid is also valid in case of using high molecular weight aliphatic (non-cyclic) alcohols, for example, butanol, pentanol, hexanol.

Study of ethanol vapor explosion and prediction based on chemical kinetics under high temperature and pressure

AbstractThe study of the explosion parameters of ethanol–air mixture at high pressure and temperature is essential for the safe production of ethanol. However, the explosion characteristics of ethanol vapor at various pressures and temperatures are limited. The mechanism at the flammability limits of ethanol has not been clarified, and the corresponding prediction model is also lacking. In this study, chemical kinetics and machine learning are used to study the mechanism of ethanol explosion and build predictive models, respectively. Our findings show that an increase in the initial pressure has a more pronounced influence on the explosion pressure (Pex) and pressure rise rate (dp/dt) than an increase of temperature. The variation trend of the upper flammability limit (UFL) of ethanol is related to the different effects of temperature and pressure on OH radicals. H + O2&lt;&gt;OH + O and HO2 + CH3&lt;&gt;OH + CH3O had the greatest effect on the generation of OH radicals. The quantitative relationship between the H, O, and OH radicals and UFL was constructed by machine learning, providing a new research perspective for the prediction of the UFL of an inflammable fuel under different pressures and temperatures. The results of the study will provide theoretical and practical guidance for the prevention and control of explosions in the ethanol production process.

Investigating the effect of temperature, pressure, and inert gas on the flammability range of ethane/oxygen mixtures

The flammability limit is a critical parameter used to evaluate the risk of explosions from flammable gases and design appropriate explosion-proof measures. This study employs a combined approach of theoretical analysis and experimental determination to investigate the impact of temperature, pressure, and inert gas on the FL of ethane/oxygen mixtures in an environment of elevated temperatures and pressures. The findings demonstrate that the flammability range of ethane/oxygen mixtures progressively widens at elevated temperature and pressure conditions. At high pressures, the upper flammability limit (UFL) of ethane displays a quadratic-linear relationship with temperature, with a turning point at 200 °C. The impact of temperature and pressure on explosion risk is primarily achieved through their effect on the UFL. A new inerting capacity of added diluting gas, δ, is defined for inert gas, revealing that the inerting effect of diluting gas is enhanced under the influence of temperature or pressure. However, the inerting effect of nitrogen weakens as the initial pressure increases, while it strengthens as the initial temperature increases. The inerting effect of water vapor in the system of ethane/oxygen/nitrogen is superior to that of nitrogen. The combustion reaction kinetics of ethane and nitrogen near the UFL is influenced by high temperature, high pressure, and water vapor. The coupling effect of high initial temperature and pressure on the inerting effect of the two inert gases is less pronounced than that of single factors.

Upper and Lower Flammability Limits, Limit N2O Concentrations, and Minimum Inerting Concentrations of n-Alkane–N2O–Diluent Mixtures: An Experimental and Computational Study

Objectives: N2O is widely used in the chemical industry and laboratories; however, several fire/explosion accidents have been reported in facilities that handle N2O. This study aimed (i) to experimentally investigate the lower and upper flammability limits (LFL and UFL, respectively), limit nitrous oxide concentration (LN2OC), and minimum inerting concentrations (MICs) of fuel–N2O–diluent mixtures and (ii) to computationally estimate the UFLs of fuel–N2O–diluent mixtures. Methods: Herein, methane and n-propane and nitrogen (N2), argon (Ar), and carbon dioxide (CO2) were used as fuels and diluents, respectively. The LFL, UFL, LN2OC, and MICs of the fuel–N2O–diluent mixtures were experimentally determined using a closed cylindrical vessel, and their UFLs were computationally estimated based on the laws of conservation energy and mass and adiabatic flame temperatures. Results: Flammability-limit experiments revealed the following: (i) the LFLs of the CH4–N2O–diluent and C3H8–N2O–diluent mixtures were 2.5 and 1.4 vol %, respectively, (ii) the UFLs of the CH4–N2O–diluent and C3H8–N2O–diluent mixtures were 40.5 and 24.0 vol %, respectively, (iii) a nearly linear relationship between the UFL and diluent concentration was found, and (iv) the order of MICs in N2O atmosphere was consistent with the inerting ability of the diluents. Calculations based on overall combustion reactions and the laws of energy and mass conservation using six and five chemicals successfully estimated the UFLs of the CH4–N2O–diluent and C3H8–N2O–diluent mixtures with mean absolute percentage errors of ≤2.8% and ≤4.1%, respectively. Conclusions: The semiempirical model suggested herein allows accurate estimation of the UFLs of the tested fuel–N2O–diluent mixtures. These findings would contribute to reducing accident-induced losses in the chemical industry and laboratories handling N2O.

Investigation of the upper flammability limit of ethylene/propane mixtures in air at high temperatures and pressures

The upper flammability limit (UFL) of ethylene/propane mixtures was investigated using a self-built 20 L spherical explosion characteristic experimental device at initial temperatures ranging from 20 to 200 °C and initial pressures from 0.1 to 1.5 MPa. The effects of temperature, pressure, and ethylene blending ratio on the UFL were analyzed, and a mathematical function of the UFL as a function of temperature and pressure parameters was derived. The results show that the UFL of ethylene and propane displayed an almost linear incline as the temperature rose. Conversely, the ascending pattern of the UFL diminished for both gases as the pressure increased. At elevated temperatures and pressures, both propane and ethylene-propane mixtures demonstrated a bilinear correlation with temperature. Moreover, the impact of increasing pressure on the UFL of blended fuels became less pronounced as the proportion of ethylene in the blend increased. Furthermore, the synergistic effect of temperature and pressure on the UFL was much greater than the sum of the effects of the two individually. Thus, the explosion risk of ethylene/propane mixtures is elevated under the synergistic effect of high temperature and high pressure, and the risk is further increased with an increase in the ethylene blending ratio.

Investigation on the upper flammability limits of ethylene/air and propane/air mixtures at high temperature and pressure

This study investigates the upper flammability limits (UFLs) of propane/air and ethylene/air mixtures at various temperatures and pressures. The experiments were conducted in a 20 L spherical vessel with temperatures ranging from 20 °C to 200 °C and pressures between 0.1 MPa and 1.5 MPa. The UFL was found to have a different dependence on temperature and pressure, with a nearly linear relationship with temperature and a nearly logarithmic relationship with pressure. The synergistic effect of temperature and pressure on the UFL was found to be greater than the sum of the effects of the two alone, leading to an increased risk of explosion. To analyze the combustion reaction kinetics, a one-dimensional laminar premixed flame model was employed, and the mechanism of the influence of temperature and pressure on the UFL was explained using the chain reaction theory. This work provides valuable information for developing safety protocols and optimizing combustion processes in various industries, including chemical, petrochemical, and energy.

Effect of ignition energy on combustion characteristics of flammable working fluids

Working fluids with low global warming potential (GWP) will play an important role in the research and development of alternative working fluids for organic Rankine cycles and refrigeration cycles. However, the flammability of low GWP working fluid limits their development, and the energy of typical fire sources has a significant impact on their safe application. At present, there is a lack of relevant research on the effect of ignition energy on their flammability. In this paper, the effect of ignition energy on the combustion characteristics for propane (R290), fluoroethane (R161), 1,1-Difluoroethane (R152a), and 3,3,3-Trifluoropropene (R1243zf) was studied using a variable ignition energy system. The initial flame propagation process, flammability limit, and burning velocity were tested and analyzed in the range of 50 mJ to 20 J. The results showed that with the increase of ignition energy, the lower flammability limit (LFL) decreased and the upper flammability limit (UFL) increased, but their rate of change decreased with the increasing ignition energy. The effect of ignition energy on the flammability limit of R1243zf was significantly greater than that of the other three working fluids. In addition, the effect of ignition energy on flame propagation was mainly limited to the initial stage, and the burning velocity was independent of ignition energy. The mechanism of ignition energy on combustion characteristics was obtained. The research results have guiding significance for the safe application of flammable working fluids.

Mathematical model for describing the influence of initial pressure on the flammability limits of light hydrocarbons at subatmospheric pressures

Fuel in aircraft fuel tanks, as well as some industrial processes, are under conditions of reduced pressure. However, few models have been proposed for estimating the influence of the initial pressure on flammability limits at subatmospheric pressures. A model to describe this influence was derived in this study according to the assumption that the heat release rate is equal to the heat loss rate. Several assumptions used in the model simplification process were verified to accord with real situations. The experimental data on seven gaseous fuels, namely methane, ethane, ethylene, propane, propylene, n-butane, and n-butylene, were analysed to validate the proposed model. In general, the simulation results accord well with the data on flammability limits measured at subatmospheric pressures. In its extension to systems functioning at elevated pressures, the proposed model accurately estimated the lower flammability limit data for atmospheric pressures up to 30 MPa and the upper flammability limit (UFL) for atmospheric pressures from 0.1 to 0.9 MPa. However, large deviations were noted between the estimated and actual UFLs for atmospheric pressures from 0.1 to 24.9 MPa. Nevertheless, the proposed model accurately describes the variation trends of flammability limits over a wide pressure range.

Experimental determination of upper flammability limits of synthesized iso-paraffins (SIP), Jet fuel and their mixtures with air at atmospheric and sub-atmospheric pressures

Synthesized iso-paraffins (SIP) are compounds that can be blended with traditional aviation fuels up to 10% vol. to reduce greenhouse gas emissions. The safety properties of these fuels need to be determined to guarantee their reliable utilization. These properties include the upper flammability limit (UFL). The objective was to determine experimentally the UFL in air of SIP, jet fuel, and mixtures containing 10% (F10) and 50% (F50) of SIP on a mass basis, respectively. The initial conditions involved different initial temperatures and pressures. The experimental configuration followed the ASTM E681 standard. The temperature range was from 420 to 470 K and the pressure range was from 101.3 kPa to 20 kPa. The results show that the UFLs of the tested compounds have a second-order tendency with respect to pressure and constant temperature. The F10 mixture has a significant reduction of the UFL at 20 kPa. The experimental results were fitted by using regression models and empirical correlations which allow the determination of UFLs at different initial temperatures and pressures.

Investigation on combustion characteristics and thermal performance of a three rearward-step structure micro combustor fueled by premixed hydrogen/air

In order to achieve high and uniform wall temperature distribution in the micro combustor, a three-dimensional mathematical model of the premixed hydrogen/air mixtures in the micro combustors with rearward-step structure is established in this work. The effects of rearward-step structure, inlet velocity on combustion characteristics and thermal performance in the micro combustor are investigated. The results indicate that the rearward-step structure enhances the combustion intensity and stabilizes the flame in micro combustor. When the inlet velocity is 7.0 m/s, with the increase in the rearward-steps from one to three, the maximum combustion efficiency difference is about 2.28% and the percentages of improvements in lower and upper flammability limits are 20% and 3.5%, respectively. The achieved results show that the rearward-step structure increases the mean outer wall temperature and deteriorates the outer wall temperature uniformity in the micro combustor. When the inlet velocity is 5.0 m/s, the mean outer wall temperature and the temperature difference of the combustor with 3-steps are 6.3 K and 39.6 K higher than that of the combustor with 1-step, respectively. The maximum synergy degree in the micro combustor with 3-steps is 2.99% when the inlet velocity and equivalence ratio are 7.0 m/s and 1.5, respectively.

Experimental study on the influence of trifluoroiodomethane on the flammability of difluoromethane and propane

In this paper, an apparatus with a 12 L flask according to ASHRAE standards was used to study the influence of trifluoroiodomethane (R13I1) on the flammability of difluoromethane (R32) and propane (R290). The accuracy of this experimental system was verified by the tests of pure R290 and R32. The flammability limits of R32 + R290, R13I1 + R32 and R13I1 + R290 binary mixtures were measured at 60 °C and atmospheric pressure. The experimental data of R32 + R290 can be well predicted by Le Chatelier's formula with maximum absolute deviation of 1.0%. The flammability limit range of R13I1 + R32 reduces with the increase of the molar ratio of R13I1 to R32 and the critical suppression ratio is 0.2. As for R13I1 + R290, the upper flammability limit (UFL) has two inflection points while the lower flammability limit (LFL) always increases. The same phenomenon could be found in the experimental result of R13I1 + R32 + R290 mixture. An extended Le Chatelier model was used to correlate the experimental data of mixtures containing inert gas and the maximum absolute deviation is less than 0.8%. It is expected that the measured values will be useful for the safe application of R13I1/R32/R290 binary and ternary mixtures.

Laminar Burning Speeds and Flammability Limits of CH4/O2 Mixtures With Varying N2 Dilution at Sub-Atmospheric Conditions

ABSTRACT This paper presents experimentally determined laminar burning speeds () of premixed methane/oxygen/nitrogen mixtures at sub-atmospheric conditions obtained by using the constant-pressure spherical flame method. The goal of the conducted experiments was to investigate the effects of nitrogen dilution and pressure reduction on the laminar flame speed and flammability limits of methane/oxygen mixtures. Nitrogen content was varied between 3.1 and 79.3 volume percent. at a target pressure of 0.5 bar was investigated. Actual pressure levels ranged between 0.506 and 0.568 bar. Experiments at 1 bar were conducted as a benchmark case of the setup compared to results from literature. The laminar flame speed is found to increase with decreasing nitrogen content and decreasing pressure. The obtained results show good agreement with simulated data using the several chemical reaction mechanisms within 4.8% for near stochiometric mixtures. The upper flammability limit (UFL) is shown to be pressure-sensitive while the lower flammability limit (LFL) remains stationary for both pressure levels compared to reference data at 1 bar. Furthermore, the LFL is shown to stay at 6% vol methane content, independent of nitrogen dilution ratio.

Risk Assessment and Field Case Study on Oil/Natural Gas Explosion during High-Pressure Air Injection Process

Summary Air injection techniques have been widely applied in oil fields, but the associated safety issue of natural gas (NG) and oil explosion has been of great concern. In this study, explosion experiments of different NG compositions were conducted under high-pressure and high-temperature conditions (up to 15 MPa and 373 K) to reveal the necessary conditions for gas explosion in the air injection process. The experimental results indicate that the lower flammability limits (LFLs) and upper flammability limits (UFLs) of NGs change logarithmically with increasing pressure, which can significantly increase the explosion risk. The rise of temperature can also expand the flammability limit range. Based on the mechanisms and necessary conditions for NG and oil component explosion, fault tree analysis (FTA) models for explosion occurring during the air injection process were proposed that can provide valuable guidelines for designing anti-explosion procedures for field applications. Several explosion incidents that have occurred in air injection operations in different oil reservoirs are described, and the explosion mechanisms are analyzed. NG explosion can occur during air injection when NG is the main component present in the gas phase that can mix with air to form a combustible gas. For heavy oils with little NG, autoignited explosion of vaporized oil components can be the main reason for the incidents during the steam and air coinjection process because the autoignition temperature of heavy oil can be greatly reduced at high pressure.

Investigation on the flammability limit and limiting oxygen concentration of N2-diluted H2/CO/air mixtures at high temperature and pressure

H2/CO binary mixtures are common, and their combustion characteristics and reaction mechanism are important. Currently, there are few studies on the combustion characteristics of H2/CO mixtures at high temperature and pressure conditions, and they are mainly limited by the test conditions. In this work, a flammability limit test device was used to determine the flammability limit and limiting oxygen concentration of a combustible mixture with a composition of H2/CO = 1:1 at high initial temperature (∼80 °C) and high initial pressure (∼10 MPa) conditions. The effects of temperature and pressure on the flammability limit and limiting oxygen concentration were obtained, and the results showed that the initial temperature and initial pressure expanded the range and reduced the limiting oxygen concentration, which significantly increased the risk of combustion. As the pressure increased, the effect of pressure on the flammability limit and limiting oxygen concentration decreased. In addition, an obvious coupling effect of initial temperature and pressure on the upper flammability limit and the limiting oxygen concentration (<5 MPa) was found. Moreover, kinetic simulations of the CO/H2 mixture were carried out to verify the synergistic oxidation effect, which was explained using chain reaction theory. We found that the chain initiation reactions caused by H2 generated OH products and the heat required for CO oxidation. Lastly, we also observed oxygen competition between CO and H2, which decreased the CO conversion rate as H2 increased.

Predicting both lower and upper flammability limits for fuel mixtures from molecular structures with same descriptors

Knowledge of flammability limits values, including both the lower flammability limit (LFL) and upper flammability limit (UFL), is essential to maximise safety in process design and operational procedures. This study aims to develop theoretical models for predicting both lower and upper flammability limits for fuel mixtures from molecular structures with the same molecular descriptors. All samples were collected from a single reference and the “compounds out” strategy was employed to divide the training and the test set. Descriptors for pure compounds were calculated by Gaussian 16 and Multiwfn package. The developed LFL and UFL models were validated with rigorous internal and external validations. The results indicated the robustness, validity, and satisfactory predictivity of the established models. The applicability domain (AD) of the model was also defined. The established LFL and UFL models demonstrated that the higher dipole moment and van der Waals volume are, the higher LFL and lower UFL values are. The proposed models can be expected to predict the LFL and UFL values for other fuel mixtures for which experiment values are unknown, only based on molecular structures.

Fast, easy-to-use, machine learning-developed models of prediction of flash point, heat of combustion, and lower and upper flammability limits for inherently safer design

This study proposes easy-to-apply machine learning-developed models, which predict four flammability properties of pure organic compounds: the flash point, heat of combustion, lower flammability limit (LFL), and upper flammability limit (UFL). These flammability properties pose a strong impact on the inherently safer design of industrial processes. Similar to quantitative structure-property relationship (QSPR) or group contribution models, machine learning algorithms are utilized in this study to establish predictive models. Compared to previous models, this study uses readily available variables (i.e., the numbers of atomic elements, molecular weights, and normal boiling points) as default variables without the analysis of detailed molecular structures or the in-depth knowledge of chemistry. This study consists of two steps: Step (1) building multiple linear regression (MLR) models by incorporating default input variables and Step (2) building MLR models by incorporating interaction and transformed variables to improve the predictions from the models in Step 1. In Step 1, an optimal subset of predictors is identified by constructing an MLR model via the sequential floating backward selection (SFBS) algorithm. As a result of Step 1, the two constructed models of the flash point and heat of combustion are found to be adequate, while the predictability of LFL and UFL are insufficient. In Step 2, MLR models incorporating nonlinearity and interaction terms are constructed via the sequential floating forward selection (SFFS) algorithm by selecting the optimal subset of default variables. The results show that all the constructed models in Step 2 are adequate as predictive models; the mean absolute errors (MAEs) of the flash point, heat of combustion, LFL, and UFL are 7.31 (5.67 via the SFBS) [K], 60.6 (61.87 via the SFBS) [kJ/mol], 0.21 (0.19 via the SFBS) [vol.%], and 2.44 (2.33 via the SFBS) [vol.%], respectively. Compared to previous models, the approved models in this study provide highly competitive performance with enhanced simplicity and interpretability.

Experimental and Statistical ANOVA Analysis on Combustion Stability of CH4/O2/CO2 in a Partially Premixed Gas Turbine Combustor

Abstract The application of the oxy-fuel combustion technique could tackle the combustion process's environmental issues. Experiments were conducted on partially premixed air- and oxy-methane combustion flames stabilized over a novel perforated burner in the present work. The burner has a premixing ratio of 7.0. In oxy-fuel combustion, the experiments were performed at oxygen fractions (OF%: volumetric percentage of O2 in the oxidizer mixture) of 29%, 32%, and 36% and over a range of operating conditions necessary for a stable flame. The results of oxy-combustion flames were compared with the corresponding air-combustion flames at the same operating conditions. Two sets of statistical analyses were performed for further confirmation of the experimental results. The first set investigated the operating parameters’ effect, including OF and oxidizer Reynolds number (Re), on the upper flammability limits (UFL). Simultaneously, the second set studied the impact of OF and equivalence ratio on flame length. The experimental results revealed that the flammability limits get wider as the OF increases due to the resulting flame speed rise with O2-enrichment. The statistical analysis is conducted by analysis of variance (ANOVA) technique, which carries innovation and confirms that OF and Re significantly impacted the UFL. The visual flame length of oxy-flames was longer than its correspondents of air-flames due to the reduction of flame speed associated with the negative influence of CO2 dilution in oxy-flames. The statistical analysis showed a significant effect of OF and equivalence ratio on the visible flame appearance.