Carbon Dioxide Volume Fraction Research Articles

Cross-physical field prediction method for smoke field distribution in commercial building fire based on distributed optical fiber sensor

In modern commercial building spaces, the smoke generated during indoor fires poses a substantial safety threat to individuals attempting to evacuate. This study leveraged a distributed optical fiber temperature sensing system as the technological foundation. A series of commercial building space models were constructed by employing fire dynamics simulations, and a comprehensive database of simulated fire field information was established. The study built upon this database and proposed a method to establish influence pathways from existing temperature field detection data to three fire risk assessment parameters: carbon dioxide, oxygen, and visibility. The study utilized various machine learning algorithms and focused on selecting and constructing cross-physical field prediction models that optimized the performance of fire risk assessment parameters at the fire key plane. The findings demonstrated that the Multilayer Perceptron (MLP) algorithm model yielded the most accurate fit for carbon dioxide volume fraction, with a Mean Absolute Percentage Error (MAPE) of 3.80% between the model predictions and actual values. The Artificial Neural Network (ANN) algorithm showed superior fitting effects for oxygen volume fraction and visibility, with MAPEs of 1.37% and 3.10%, respectively. Furthermore, the study validated the generalizability of these optimal models by altering spatial scales, revealing robust performance. This study utilized a single optical fiber sensor to achieve dynamic prediction across different physical fields during fire incidents, expanding the application scope of optical fiber sensors in monitoring gas and visibility fields in commercial building fires. This not only enhanced the level of fire monitoring but also effectively reduce equipment costs. It provided effective data support for planning evacuation routes for individuals and rescue arrangements for firefighters, further ensuring personnel safety.

Experimental study on turbulent burning velocities of premixed flames for natural gas/air mixtures

Experiments on the spherical expanding flame of turbulent premixed natural gas/air mixtures were conducted in a fan-stirred turbulent combustor for the first time. As the belief that the methane burning velocity data can be obtained for natural gas is not justified, natural gas constitutes of 90% CH4, 7% C2H6 and 3% C3H8 by volume fraction was used. The operation conditions are equivalence ratio of 0.7–1.3, initial temperature of 300–400 K, initial pressure of 0.1–0.3 MPa, turbulence intensity of 1.0–2.7 m/s, oxygen volume fraction of 15–21% and carbon dioxide volume fraction of 0–20%. A self-developed program and post-processing procedure was developed to highly restore the real information of flame front without ignoring small local information. It was concluded that methane cannot be taken as a representative of natural gas for studying turbulent burning velocities. The increase of flame propagation speed with initial pressure is not as significant as that with initial temperature and turbulence intensity under low-intermediate pressure range. Dispersions exists for previous correlations relating to turbulent flame Reynolds number, Karlovitz number, Damköhler number, respectively, and a new correlation were proposed based on the ratio of Karlovitz number and Damköhler number. The new correlation was validated by both current and previous experimental data and its advantage and applicability were summarized. It will be validated by turbulent flames of various kinds of fuels over a wide range of working conditions in the further study.

An Experimental Study on a Dual-Fuel Generator Fueled With Diesel and Simulated Biogas

Abstract Diesel-fueled generators are widely used for power generation in remote and/or off-grid communities. In such communities, local organic waste streams can be used to generate biogas, which can be used to replace diesel used by diesel generators to lower fuel cost and reduce greenhouse gas (GHG) emissions. Diesel-powered generators can be easily retrofitted with a biogas dosing line in the engine intake to introduce biogas, but appropriate optimization would be of great help to further improve generator performance and reduce GHG emissions. The objective of this research is to demonstrate simplified optimization methods that can reduce GHG emissions (carbon dioxide and methane) from such retrofitted dual-fuel engines under various biogas compositions. The study was conducted on a modern 30 kilowatt (kW) generator using an electronically controlled, four-stroke, four-cylinder, direct injection, turbo-charged diesel engine. The engine was operated with the factory electronic control unit (ECU) and a programmable ECU which allowed for control of the fuel injections and exhaust gas recirculation valve. Biogas was simulated by using natural gas (with more than 95% methane by volume) which was diluted with either carbon dioxide or nitrogen. This study consisted of two areas. The first one was the comparison of the engine performance when operating with biogas using the factory ECU and the programmable ECU with user-optimized fuel injection. The second one was the influence of volume fraction of carbon dioxide or nitrogen in the biogas. Test results reinforced the importance of optimizing the diesel injections when the engine was operated in the biogas-diesel dual-fuel mode to ensure complete combustion and achieve a reduction in GHG emissions. Increasing nitrogen fraction had a minimal effect on the emissions but increasing carbon dioxide fraction caused the NOx and methane emissions to decrease, and the indicated thermal efficiency to increase.

Використання модельного газу в дослідженнях газового двигуна електростанції

Annotation – The analysis of scientific publications over the past ten years in the direction of creating gas ICEs in Ukraine, operating on natural gas, biogas or similar low-calorie fuels. The objectives of the work summarize the results of studies on the use of model gas in a gas internal combustion engine operating on a power plant drive. Developed recommendations on biogas additives to natural gas depending on the power plant load, and to develop a fuel control algorithm. The article provides recommendations on setting up the power system and automatic regulation of a gas engine running on a mixture of natural gas (methane) and biogas. To solve the tasks, a gas-electric installation with a rated power of 30 kW was tested. Initially, the installation was equipped with an 8-cylinder gasoline engine with spark ignition and an electric generator. The base ICE was converted to purely gas with a compression ratio of 8.5. In the physical modeling of biogas to natural gas additives in the model gas, the volume fraction of carbon dioxide increased to 30 % with a decrease in the load. By calculation, determined a similar ratio of compressed natural gas and biogas additives. For the calculation, it assumed that natural gas contains 90 ... 95 % methane, and biogas 60 % methane and 40 % carbon dioxide. The possibility of using biogas with 60 % methane as an additive to natural gas in piston ICEs with spark ignition has been confirmed. It was found that with a decrease in load, the biogas fraction increase and replace up to 85 % of natural gas. When working on biogas additives, the values of the concentrations of hydrocarbons and residual oxygen in the exhaust gases were determined to control the setting of the gas equipment of the internal combustion engine. Under operating conditions, three test modes selected for the power plant: idle, 50 % load, rated mode. The research results can serve as the basis for creating a control algorithm for the supply of biogas additives to natural gas, depending on load changes.

RELATED REGULATION OF BIOGAS SUPPLIES AND METHANE IN A GAS ENGINE

The results of experimental researches were received on a gas-electric installation with a rated power of 30 kW at 1500 rpm. The spark-ignited petrol drive engine (8-cylinder, 100 mm cylinder diameter, 88 mm stroke) was converted to a pure gas one. The compression ratio of 8.5 did not change. The gas fuel supply system consists of a supply line and an emergency shut-off circuit. The natural gas supply line was connected to the domestic main line through a special gas distributor. On the basis of HEINZMANN components, a system for dosing mixed gas fuel was developed, which, through a microprocessor control unit and an actuator, acted on the throttle valve of the gas mixer. In experimental researches, the composite fuel was a model gas – a mixture of natural and carbon dioxide gases, which was prepared in a zero pressure reducer before the gas mixer. With an increase in the volume fraction of carbon dioxide in the model gas by more than 34 %, a deterioration of the combustion process was observed in the steady state. In the article, based on the analysis of the experimental results of the operation of a piston gas engine on a model gas, an algorithm for the use of associated automatic control of biogas and methane feeds is substantiated. The transition from quantitative to qualitative regulation of the gas-air mixture has been substantiated. To do this, it is necessary to create two automatic control loops for the supply of air and a mixture of natural gas, which are interconnected through an external load. With the developed algorithm, as the load increases, the supply of natural gas increases, and the supply of biogas decreases. With an increase in the load of 75 % or more, a more intensive enrichment of the fuel mixture with natural gas occurs than at low and medium loads. The proposed algorithm for regulating the fuel mixture can be implemented using electromagnetic gas injectors for dosing the components of the composite fuel. Signals from sensors for oxygen and methane content in exhaust gases were selected as corrective links for the coupled control algorithm. Recommendations on the choice of tuning modes for oxygen and methane sensors have been developed.

Suppression effect of inert gases on aluminum dust explosion

The suppression mechanism of inert gases for 5 μm aluminum dust explosion was investigated in a confined cuboid chamber. The characteristic parameters of flame propagation and explosion severity parameters that were affected by the inert gases were systematically studied. The results indicated that the minimum inerting volume fraction of carbon dioxide was lower than that of nitrogen, thereby indicating that the suppression effect of carbon dioxide on aluminum dust explosion was superior to that of nitrogen. To reveal the suppression mechanism on a micro level, a kinetic model that considered the surface kinetic mechanism was proposed. The results revealed that as the inerting volume fraction of the inert gas increased, the heterogeneous reactions that promoted the generation of intermediate species were mostly suppressed, while the heterogeneous reactions that consumed intermediate species were facilitated. Thus, carbon dioxide and nitrogen exerted certain suppression effects on surface reactions in their characteristic ways.

RESULTS OF RESEARCH FOR THE USE OF THE BIOGAS AND METHANE MIXTURE IN A GAS POWER PLANT ENGINE

The analysis of scientific publications over the past ten years in the line of creating gas ICEs in Ukraine, operating on natural gas, biogas or similar low-calorie fuels has been carried out. The objectives of the work are to summarize the results of studies on the use of model gas in a gas internal combustion engine operating as a power plant drive, to develop recommendations on biogas additives to natural gas depending on the power plant load, and to develop a fuel supply control algorithm. It is possible to simplify labor intensity of experimental work with the help of model gas - a mixture of natural and carbon dioxide. The article provides recommendations on setting up the power system and automatic regulation of a gas engine running on a mixture of natural gas (methane) and biogas. To solve the tasks, research was carried out on a gas-electric plant with a rated capacity of 30 kW. The unit was originally equipped with a spark-ignited 8-cylinder petrol engine and an electric generator. The base ICE was converted to pure gas engine with a compression ratio of 8.5. In the physical modeling of biogas to natural gas additives in the model gas, the volume fraction of carbon dioxide was increased to 30 % depending on the external load. By calculation, we determined a similar ratio of compressed natural gas and biogas additives. For the calculation, it was assumed that compressed natural gas contains 90...95 % of methane, and biogas 60 % of methane and 40% of carbon dioxide. The possibility of using biogas with 60 % methane as an additive to natural gas in piston ICEs with spark ignition has been confirmed. It was found that with a decrease in load, the share of biogas can increase and replace up to 85% of natural gas. When working on biogas additives, the values of the concentrations of hydrocarbons and residual oxygen in the exhaust gases were determined to control the setting of the gas equipment of the internal combustion engine. Under operating conditions, three test modes have been selected for the power plant: idle, 50 % load, rated mode. The research results can serve as the basis for creating a control algorithm for the supply of biogas additives to natural gas, depending on load changes.

Study on Combustion Properties of Aviation Carpet under Low Ambient Pressure

The flame-retardant materials in the cabin of civil aircraft is possible to induce fire accident, which can cause certain threat to the operation safety of aircraft. The cabin pressure of civil aircraft is generally maintained at 75~84 kPa under normal transport condition, and the combustion behavior of aviation carpet will change under this pressure. Combustion properties of an aviation carpet, selected from civil aircraft, were studied at Guanghan City (520 m altitude) and Kangding airport (4290 m altitude), Sichuan province of China in this work, respectively. The results showed that the smoke density of the aviation carpets increased sharply and the decreasing rate of the oxygen volume fraction became more quickly under low pressure. Furthermore, the rising rate of carbon dioxide volume fraction also became rapidly with the decrease of the ambient pressure. The content of the carbon monoxide under low pressure was lower than that under normal pressure at the beginning of the combustion. However, the carbon monoxide production increased sharply when the combustion lasted for 4 minutes. In addition, the ignition time of the aviation carpet was shorter under low pressure.

Freeze Granulated Zeolites X and A for Biogas Upgrading.

Biogas is a potential renewable energy resource that can reduce the current energy dependency on fossil fuels. The major limitation of utilizing biogas fully in the various applications is the presence of a significant volume fraction of carbon dioxide in biogas. Here, we used adsorption-driven CO2 separation using the most prominent adsorbents, NaX (faujasite) and CaA (Linde Type A) zeolites. The NaX and CaA zeolites were structured into hierarchically porous granules using a low-cost freeze granulation technique to achieve better mass transfer kinetics. The freeze granulation processing parameters and the rheological properties of suspensions were optimized to obtain homogenous granules of NaX and CaA zeolites 2–3 mm in diameter with macroporosity of 77.9% and 68.6%, respectively. The NaX and CaA granules kept their individual morphologies, crystallinities with a CO2 uptake of 5.8 mmol/g and 4 mmol/g, respectively. The CO2 separation performance and the kinetic behavior were estimated by breakthrough experiments, where the NaX zeolite showed a 16% higher CO2 uptake rate than CaA granules with a high mass transfer coefficient, 1.3 m/s, compared to commercial granules, suggesting that freeze-granulated zeolites could be used to improve adsorption kinetics and reduce cycle time for biogas upgrading in the adsorption swing technology.

Effect of carbon dioxide content in biogas on turbulent combustion in the combustor of micro gas turbine

China has huge potential on biogas resources and the distributed energy system (DES) based on micro gas turbine provides an effective way for biogas utilization. In this work, turbulent combustion characteristics in the combustor of micro gas turbine for DES were numerically and experimentally studied, and the effect of carbon dioxide content in biogas on the turbulent flame was mainly analyzed. Turbulent flames structures of natural gas and three kinds of biogas under various equivalence ratios were measured by three-dimensional (3D) combustion diagnostic technique based on computed tomography of chemiluminescence (CTC). The results show that the carbon dioxide content in the fuel has a great influence on flame structure of turbulent combustion. The increase of carbon dioxide content in the fuel not only reduces turbulent combustion rate, but also makes the combustion stability worse. With the decrease of equivalence ratio, the effect becomes greater. With the increase of carbon dioxide volume fraction, combustion flame is gradually away from the outlet of the nozzle. When volume fraction of carbon dioxide is 50%, the distance between the combustion flame and the nozzle outlet increases the 100 mm. Furthermore, carbon dioxide weakens the effect of excess air on the CH* distribution and turbulent flame.

Separation of Carbon Dioxide from Real Power Plant Flue Gases by Gas Permeation Using a Supported Ionic Liquid Membrane: An Investigation of Membrane Stability.

The separation of carbon dioxide from coal-fired power plant flue gases using a CO2/N2-selective supported ionic liquid membrane (SILM) was investigated and the performance and stability of the membrane during operation are reported. The membrane is composed of a polyacrylonitrile (PAN) ultrafiltration membrane as a support and a selective layer of an ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM Tf2N). The feasibility of large-scale SILM production was demonstrated by the formation of a square-meter-scale membrane and preparation of a membrane module. A flat-sheet envelope-type SILM module containing 0.67 m2 of the membrane was assembled. Prior to real flue gas operation, the separation behaviour of the membrane was investigated with single gases. The stability of the SILM during the test stand and pilot plant operation using real power plant flue gases is reported. The volume fraction of carbon dioxide in the flue gas was raised from approx. 14 vol. % (feed) to 40 vol. % (permeate). However, issues concerning the membrane stability were found when SO3 aerosols in large quantities were present in the flue gas.

Gas sensing through evanescent coupling of spoof surface acoustic waves

An ultrasonic gas sensor based on evanescent coupling of spoof surface acoustic waves between two surface phononic crystals containing trapezoidal grooves on rigid slabs is theoretically and experimentally demonstrated. Sensing properties for carbon dioxide in dry air at 25 °C and 760 Torr are investigated as an example. Band structure analyses reveal two spoof surface acoustic wave bands with opposite parities when the separation of surface phononic crystals is 1.5 times the periodicity of grooves. The beat length varies with frequency and carbon dioxide volume fraction, where the increase of the latter results in red shift of a sharp intense output peak at 59.69 kHz at a rate of 17.70 mHz/ppm and 16.20 mHz/ppm for carbon dioxide volume fractions up to 10,000 ppm, as measured through Finite-Element Method simulations and experiments, respectively. Gas sensing can also be achieved by measuring the output acoustic intensity at constant frequency, which exhibits a steep decrease with carbon dioxide volume fraction up to 2000 ppm.

Precipitation of Spherical Vaterite Particles via Carbonation Route in the Bubble Column and the Gas-Lift Reactor

Spherical vaterite particles were produced by carbonation of calcium chloride solution with addition of ammonia to facilitate CO2 absorption. Synthesis of calcium carbonate was carried out in a bubble column or gas-lift reactor. The course of the reaction was monitored by pH measurements. Precipitated solids were analyzed by Fourier-transformed infrared spectroscopy, x-ray powder diffraction and scanning electron microscopy, and the particle size distribution was determined by a laser diffraction method. Synthesized calcium carbonate products were mainly vaterite. The calcium chloride concentration and carbon dioxide volume fraction in a gas phase had the main impact on the size of the produced particles in both reactors. A slight decrease in the mean particle size was observed for the highest mixing intensity. Both tested reactors can be applied to produce vaterite particles, although formation of homogeneous non-agglomerated spherical particles in a gas-lift reactor required careful selection of the process parameters.

Microbiological and Sensory Characteristics of Mould-Ripened Salami under Different Packaging Conditions.

SUMMARYThe preservation of mould-ripened salami was investigated during 48 days at 19-20 °C under different packaging conditions: (i) high barrier film filled with air, 100% N2 or under vacuum, (ii) biaxially oriented polypropylene film, (iii) microperforated polyethylene film and (iv) unpackaged. Sensory, texture profile, physicochemical and microbiological analyses were performed. Fungal quantification revealed two data groups. In group 1 (consisting of salami in microperforated polyethylene film, biaxially oriented polypropylene film and unpackaged) the conidium viability was relatively constant. In group 2 (salami preserved in high barrier film filled with air, 100% N2 or under vacuum) the conidium viability decreased due to the absence of oxygen and the high carbon dioxide volume fraction. SEM micrographs showed micromorphological changes in fungal structure; microperforated polyethylene film, biaxially oriented polypropylene film and unpackaged conditions preserved the conidial morphology, while high barrier film filled with air, 100% N2 or vacuum conditions collapsed the hyphae and most of the conidia. Salami packed in microperforated polyethylene film and biaxially oriented polypropylene film showed the most acceptable organoleptic characteristics and lower hardness and chewiness values after packaging.

Experimental investigation of corn cob pyrolysis

This paper presents experimental investigation of pyrolysis process of corn cob from Vojvodina (Republic of Serbia). The influence of temperature, reaction time, particle size, and heating rate on pyrolysis products yields was investigated. Studying of biomass pyrolysis kinetics led to the conclusion that thermogravimetry is an appropriate method for explaining decomposition of different biomass types. Experimental research showed that temperature increase leads to decrease in char yield and volatile yield. Mass yield of pyrolysis oil increased with higher heating rate. Methane volume fraction in pyrolysis gas increased with temperature increase, while the volume fraction of carbon dioxide decreased. Particle size affected the methane yield. It was shown that with the increase in particle size, the volume fraction of methane in pyrolysis gas decreased. Based on the char composition obtained after corn cob pyrolysis process, it was determined that char is rich in carbon (74.80%). Lower heating value of char was 26182.09 kJ/kg. High heating value of char contributes to economic justification for applying corn cob pyrolysis.

Study on flame-vortex interaction in a spark ignition engine fueled with methane/carbon dioxide gases

A numerical study on the in-cylinder flame-vortex interaction of gaseous spark ignited engine fueled with methane/carbon dioxide is carried out by means of large-eddy method. Evolution of in-cylinder turbulence in charge phase and flame-vortex interaction during combustion process is analyzed in great detail. It's found out that the large scale coherent structures are transformed into homogeneous small scale vortexes during the intake and compression stroke. The strong vortex cores are generated by interaction between flame and in-cylinder background turbulence. Those generated vortex cores wrinkle flame surface and augment turbulent flame speed. The contra-rotation between the two vortexes of vortex-pair in the unburned area results in the appearance of large scale flame wrinkles, which is because the vortex-pair movement leads to the local entrainment and hence stretchs of the flame surface. With the increase of volume fraction of carbon dioxide in the gases, the turbulent flame speed is decreased, the effect of vortex pair on the flame structure is weakened, and the level of the flame wrinkling is decreased correspondingly.

Large-eddy simulation of flame-turbulence interaction in a spark ignition engine fueled with methane/hydrogen/carbon dioxide

A three dimensional large-eddy simulation of in-cylinder charge and combustion process of a spark ignition engine was conducted. Partially stirred reactor combustion model and Arc and kernel tracking ignition model were implemented and applied to capture in-cylinder ignition and turbulent combustion. Interaction between flame and in-cylinder background turbulence for different mixtures of methane, hydrogen and carbon dioxide were studied. When a spark ignition engine is fueled with methane and carbon dioxide, its found that gas heating effect plays a dominant role in flame-induced turbulence. Increase of volume fraction of carbon dioxide has little effect on turbulent flame speed in each combustion phase defined by mean combustion progress variable, but it weakens gas heating effect owing to reduction in burnt temperature. Flame-induced turbulence produces small-scale vortices with high vorticity within gas preheating zone. When engine is fueled with methane, hydrogen and carbon dioxide, large volume fraction of hydrogen leads to high turbulent flame speed, which plays a dominant role in flame-induced turbulence. If volume fraction of hydrogen is small, flame-induced turbulence mainly is determined by gas heating effect due to large volume fraction of carbon dioxide. Flame-induced turbulence produces many vortex-pairs, which are the major sources of wrinkles of flame front. Rotation direction of vortex-pair determines whether the flame front bulges towards unburnt area or burnt area. Level of vorticity value and space size of vortex-pair affect sizes of wrinkles on the flame front.

Simulation of Mass Transfer in Anode Flow Field of a Passive Direct Methanol Fuel Cell

A three-dimensional model for anode side of a passive direct methanol fuel cell with perforated flow field was developed to investigate the mass transfer in anode flow channels. The model simulated the transient two-phase flow in channels. With this model, the distribution of methanol concentration and carbon dioxide volume fraction in channels was presented. The variation of species on the central surface of flow channels was also gained. Simulation results show that the mass transfer in anode flow field of passive direct methonal fuel cells is affected by comprehensive effects of diffusion and convection. The results also indicate that the methanol transfer in channels is influenced by the carbon dioxide.

Effect of Fuel Inject Angle on the Thermal Behavior of a 2D Axisymmetric Non-Premixed Methane–Air Flame in Vertical Cylinder Filled by Porous Media

The present manuscript is dedicated to the study of non-premixed combustion within a vertical cylinder filled by inert porous media using a turbulence model. A study of the effect of inlet gas angle on methane/air combustion is performed. Governing equations of Navier-Stokes, energy and the chemical species transport equations in a porous media with local thermal nonequilibrium assumption between the solid and fluid are solved. Distinct energy equations are considered for the porous burner and the fuel in it. Inlet velocity and excess air-to-fuel ratio are varied in order to analyze their effects on temperature, turbulent kinetic energy distribution and flame front location. The temperature field and species concentrations are presented in the premixed methane air combustion. The results show that an increase in angle of inlet gas enhances the mixing rate, the peak temperature, and water and carbon dioxide volume fraction inside the middle region of the chamber. The locations of the maximum temperature and product concentration shift closer to the combustor inlet with an increase in inlet angle. Furthermore, the temperature in porous burners is lower than free flame burners, and lower NOx and CO pollutant are achieved. KeywordsMethane/Air Flame; Turbulent Model; Numerical Simulations; Non-Premixed; Porous Media

Respiration Model of <i>Agaricus bisporus</i> under Modified Atmosphere Packaging Based on Enzyme Kinetics

The dynamic changes of the oxygen and carbon dioxide volume fraction，in modified atmosphere packaging ofAgaricus bisporuswere studied at different temperature. The respiration rate ofAgaricus bisporusunder modified atmosphere packaging at any instant of time were determined by improved permeable system. A respiration model, based on Michaelis-Menten type enzyme kinetics, was proposed for predicting respiration rates ofAgaricus bisporusas a function of O2and CO2volume fraction at the storage temperature. The model parameters were estimated by fitting the model to the experimental data by non-linear regression using Matlab. The effection on the model parameters of temperature was described by Arrhenius equation. The results suggest that, the low temperature and MAP could inhibit the respiration of mushroom, which is essential to the design of modified atmosphere package.