Air Coefficient Research Articles

Numerical Simulation Study of Combustion under Different Excess Air Factors in a Flow Pulverized Coal Burner

The basic national condition that is dominated by coal will not alter in the foreseeable future. Coal-fired boiler is the main equipment for coal utilization, and cyclone burner is a practical type of burner. There is a cyclone formation, a primary air duct inside the center air duct, and a secondary air duct. Introducing a small stream of pulverized coal gas or oil mist stream or gas directly into the reflux zone in the center duct ignites first a stable combustion and a small fluctuation of ignition pressure. In this paper, the variation of furnace temperature for cyclone pulverized coal burner corresponding to different excess air factors and the composition of gases such as O2, CO, CO2, and NOX produced by combustion were investigated using fluent software. A single cyclone pulverized coal burner from an actual coal-fired boiler is used, and a combustion zone applicable to the study of a single pulverized coal burner is established to study the actual operation of a single pulverized coal burner at different excess air coefficients. The findings indicate that the ignition position of pulverized coal combustion advances with decreasing α (Excess Air Factors); however, the length of the produced high-temperature flame gets shorter. As the value of α decreases, the burnout in the furnace decreases and the CO emission concentration increases, with a maximum CO mole fraction of 0.38% at α = 1.2 and a maximum CO mole fraction of 3.13% at the axial position when α decreases to 0.8. The furnace’s concentration of NOX, the NOX emission level decreases significantly with decreasing α. The NOX mole mass increases gradually with increasing α, and in the bottom portion of the primary combustion zone, more NOX is produced. The concentration of NOX in the chamber changes significantly after α exceeds 1.0, and the NOX at the outlet surges from 417.25 ppm to 801.07 ppm, which is attributed to the increase in the average temperature of the chamber, which promotes the generation of thermophilic NOX. The distribution pattern of O2 mole fraction along the furnace height cross-section at different excess air factors is basically the same, with a maximum at the burner inlet and a gradual decrease in the O2 content as it enters the combustion chamber to react with the pulverized coal in a combustion reaction. The value of α = 0.8 when the air supply is obviously insufficient, the fuel cannot be fully combusted, and only a small amount of CO2 is produced.

Moist air permeability characteristics of flexible contact gaskets used in refrigerators

Flexible contact gasket is a significant component affecting the sealing performance of the refrigerator. However, few studies were conducted on the permeability characteristics of moist air through refrigerator gaskets. The purpose of this study is to explore the permeability characteristics including permeation paths size, flow type, modeling and temperature-humidity-pressure-structure effect. The characteristic scale of the interface of permeation paths is observed as 10−5 m in the free-state by atomic force microscope. The equation of Knudsen number and contact stress relation is established to judgment the flow types. By comparing the critical and simulated contact stresses, it is inferred that moist air simultaneously occurs slip, transition and free-molecular flows. A multi-scale coupling model of permeation rate is constructed to obtain the apparent permeability coefficient characterizing the permeability intensity. The air pressure difference affects the permeability characteristics in the form of direct driving force and changing the contact stress of the interfaces. Free-molecular flow mainly occurs under the negative pressure condition with inhalation coefficient of 2.26 × 10−5∼2.84 × 10−5 m2, while the slip flow mainly occurs under the positive pressure conditions with exhalation coefficient of 2.87 × 10−5∼4.65 × 10−5 m2. The essence of enhancing the sealing performance of structural improvement is to increase the contact stress and length of permeation path. By increasing the height, increasing the inclination angle, adding the auxiliary edges and adding an auxiliary airbag, the inhalation coefficient of moist air, the exhalation coefficient of moist air and the inhalation coefficient of water vapor are decreased by 54.82 %, 51.46 % and 66.04 %.

Numerical study on effects of hydrogen doping of natural gas on the combustion characteristics in micro gas turbine combustor

The effect of hydrogen doping ratio on the flow and temperature fields in the combustor and the emission of the main pollutants (CO and NOx) for a constant excess air coefficient, a constant gas turbine power and different hydrogen doping ratios has been analyzed through numerical simulations for the application of natural gas blended hydrogen combustion technology in a 100 kW micro gas turbine. The combustion reaction principle used in the study is a simplified version of the GRI-Mech 3.0 mechanism, which includes 17 species and a total of 24 radical reactions. The simulation results show that the maximum temperature in the primary combustion zone of the combustor decreases as the hydrogen doping ratio gradually increases, the temperature distribution of the gas exiting the combustor becomes more uniform, and the gas gradually improves. The concentration and total emission of major pollutants gradually decrease.

Research on the performance of methanol/PODE dual fuel spark-assisted compression ignition combustion with different intake air adjustment

There is room for continued research and optimization on the exothermal processes and performance of methanol/polyoxymethylene dimethyl ether (PODE) dual fuel spark-assisted compression ignition (DF-SACI) with different air adjustment. The exothermal processes of methanol/PODE DF-SACI were investigated and optimized at varying methanol premix ratios (RM) and intake adjustment methods to maximize the promoting effect of spark ignition (SI). The results show that burning intensity progressively falls, while the ignition delay, CA50 and combustion duration progressively rise as excess air coefficient (λ) climbs. The resistance of high RM to lean combustion is weaker than low RM. As λ grows, the high-intensity exotherm is progressively transformed to the softer exotherm. Consequently, the exothermal energy from premixed compression ignition is progressively converted into the exothermal energy from DF-SACI. Subsequently, the exothermal energy from DF-SACI is progressively replaced by the exothermal energy of diffusion and SI combustion. By reducing air through intake variable valve timing (VVT), the optimal brake thermal efficiency (BTE) and RM under brake mean effective pressure (BMEP) of 0.4 MPa can be elevated to 40.67 % and 60 %, respectively. The optimal BTE for BMEP of 0.6 and 0.4 MPa are further enlarged from 42.82 % and 40.67 % to 43.52 % and 41.41 % by adjusting exhaust VVT, respectively.

Comprehensive pollutant emission prediction models from hydrogen-enriched methane combustion in a gas-fired boiler based on box-behnken design method

Hydrogen-enriched methane (HEM) combustion is an effective method for reducing the consumption of carbonaceous fuels. However, high adiabatic flame temperature of H2 can cause large NO emissions. To reduce the NO and CO2 emissions from HEM combustion, the Box-Behnken design (BBD) method combining response surface experimental design, analysis of variance, and multi-nonlinear regression models was adopted. The effects of the H2 doping ratio (XH2), preheated air temperature (Tair), excess air coefficient of burners arranged at the bottom (Ex,b), and their interactions on the NO, N2O, and CO2 emissions of a gas-fired boiler were investigated. According to the BBD method, the NO, N2O, and CO2 emissions prediction models with R2 exceeding 0.98 were proposed, respectively. The results showed that the increase of Tair had a positive effect on reducing NO emissions, as the NO exhausted from HEM combustion is mainly thermal NO. Compared with Tair and Ex,b, XH2 was the most significant factor affecting N2O and CO2 emissions, indicating that an increase in XH2 can significantly reduce greenhouse gas emissions. Additionally, the formation and consumption of N2O emissions presented a competitive mechanism at XH2 increased from 0 to 0.8, and CO2 emissions reduced with the increase of XH2, Tair, and Ex,b. Furthermore, a comprehensive emission prediction model with NO, N2O, and CO2 emissions was proposed. With the target of minimizing total NO, N2O and CO2 emissions, three groups of combinations for XH2, Tair, and Ex,b were obtained from the equal weight, entropy weight method, and criteria importance through the inter-criteria correlation method as 1:1:1, 24:9:17, and 21:11:18. The results showed that for minimize emissions, there is not much difference in the results calculated based on the optimal boundary conditions under different weights. For various reduction targets for nitrogen, carbon, and greenhouse gases, three groups of optimal combinations of XH2, Tair, and Ex,b were obtained and their accuracies were verified based on numerical calculations with relative errors below 6%. The proposed comprehensive pollutant emission prediction models are conducive to calculating the pollutant emissions of HEM combustion and guiding the investigation of prediction models considering other operating conditions.

Investigation on the Regulation of the Combustion Characteristics of a Propane/Air Mixture by Repetitive nSDBD Pretreatment.

This paper investigates the effect of the transient repetitive nanosecond surface dielectric barrier discharge (nSDBD) pretreatment on the combustion characteristics of combustible mixtures. A method of using nSDBD online pretreatment of a combustible mixture to regulate the combustion characteristics of the mixture is proposed. The study is conducted in a constant-volume combustion chamber at atmospheric pressure and temperature using a propane/air mixture as fuel. The discharge characteristics of repetitive nSDBD and the effects of pretreatment discharge energy and interval time between the pretreatment and ignition on combustion rate are discussed. The results show that (1) For 12.5 kHz pulses, the filament length generated with the annular dielectric barrier electrode discharge can reach up to 7 mm, and the number of discharge filaments per pulse can reach 40. (2) Pretreating mixtures using repetitive nSDBD at millisecond time scale can significantly improve the combustion process. (3) Repetitive nSDBD pretreatment can enhance the activity of the mixture near the surface of nSDBD electrode, which leads to obvious wrinkles on the flame surface and significantly improves the combustion rate. (4) The flame rise time decreases with the increase of discharge energy and increases with the increase of the interval time between the pretreatment and ignition. The effect of the repetitive nSDBD pretreatment on flame propagation during the flame development period becomes more pronounced with the increase of the excess air coefficient. The research results of the paper reveal the law of online regulation of combustion characteristics of combustible mixtures by the nSDBD, providing experimental data support for the mechanism research of online regulation of combustion characteristics of combustible mixtures by the nSDBD.

Numerical and experimental investigation of a solar air heater duct with circular detached ribs to improve its efficiency

A solar air heater duct (SAH-duct) SAH-duct has low thermal performance due to the low heat transfer coefficient of air which is the working fluid. Proper mixing of relatively hot and cold air with respect to the hot absorber plate of the SAH-duct can enhance heat transfer. It can be achieved by placing suitable hindrances in the path of airflow like detached ribs. This study presents the numerical investigation of an asymmetrically heated 2D rectangular SAH-duct with in-line arranged circular detached ribs. In the geometrical configurations of the detached ribs; blockage ratio d/H, clearance ratio c/d, and relative longitudinal pitch ratio P/d are varied as 0.04–0.48, 0.1–1.2, and 05–50 respectively at Reynolds number Re 3000–15000 to study their effect on the thermal-hydraulic performance of the SAH-duct. Local and space-averaged thermal-fluid properties like heat transfer coefficient, and friction factor, Nusselt number, pressure coefficient, etc. are discussed through the graphical illustrations and contour plots. The various dimensions of the ribs are varied to find the optimum geometrical configuration of the detached ribs.

Numerical simulation of hydrogen co-firing distribution on combustion characteristics and NOx release in a 660 MW power plant boiler

The article discussed the influence on furnace temperature distributions, combustion characteristics, and NOx release when hydrogen, coal, and sludge co-firing in a 660 MW power plant boiler by CFD. Non-premixed combustion model was chosen as the gas combustion model. As the height of the hydrogen injection position rises, the temperature difference in the main combustion region decreases from 297.22 K to 94.72 K. The co-combustion of hydrogen inhibits solid fuels' combustion. As hydrogen nozzles' height decreases, the NOx mass at the furnace outlet increases from 98.41 % to 160.38 %. When the excess air coefficient changes from 1.15 to 1.35, the temperature in the main combustion region significantly increases, while the temperature in the upper furnace decreases, and the heat flux of the main combustion region increases by 11.10 %, the heat flux of the total furnace decreases by 1.39 %, the NOx mass at the furnace outlet increases by 31.67 %. The optimum co-combustion method is injecting the hydrogen from the top hydrogen nozzles and the excess air coefficient is 1.15, the overall impact on the furnace is minimal in this way. The fundamental reason hydrogen affects co-combustion is the fuel characteristics’ difference between hydrogen and solid fuels.

Investigation effects of different calorific values and operating conditions on biogas flame: a CFD study

ABSTRACT This study investigates different biogas fuels’ and operating conditions’ effects on flame temperatures and emissions (CO, CO2, NOx, and soot). Different calorific values (15.580, 17.880, 20.430, 23.080, and 26.230 MJ/kg) were obtained by changing methane content. Furthermore, various gas pressure (0.5, 1, 2, and 3 atm), excess air coefficient (1.4, 1.8, 2.5, and 4), and oxygen values (21, 23, 25, and 27%) were simulated for 8.6 kW thermal capacity furnace. Increasing the calorific value of biogas fuels, CO, NOx, and soot emissions and flame length tend to increase, while CO2 decreases. Increasing gas pressure, flame temperature, and CO2, CO, and NOx decrease, while soot emissions tend to increase. As a result of the decrease in the air excess coefficient from 4.0 to 1.4, there is a increase in the flame temperature, flame length, and soot, CO, CO2, and NOx emissions. On the other hand, oxygen content from 21% to 27% oppositely affected these parameters, excluding flame length.

Применение методов машинного обучения для диагностики и управления режимами сжигания угольной пыли

The study examined the possibility of monitoring and identifying anomalies in the combustion process based on the patterns of flame visualization in the combustion space. Experimental studies were carried out on a semi-industrial stand to study the combustion of pulverized coal. Combustion images were classified using a deep learning algorithm for a finite number of corresponding excess air coefficients (α). Based on the excess air coefficient, we divided combustion modes into three main classes: efficient, ineffective and anomalous. This type of classification provides a simple approach to optimize the combustion process and alert the system in the event of critical events. The resulting model classified combustion modes with an accuracy in the range of 87–91 %.

МЕТОДИКИ ТЕПЛОВОГО РАСЧЕТА АППАРАТОВ ВОЗДУШНОГО ОХЛАЖДЕНИЯ

The methods of calculating the heat transfer coefficient in air cooling devices are considered. A com-parison of two methods for calculating the heat transfer coefficient from the outer surface of finned pipes to atmospheric air is performed using the example of air cooling apparatus

Towards optimized excess air ratio and substitution rate for a dual fuel HPDI engine

The diesel-piloted high-pressure direct-injection (HPDI) natural gas engine is a significant application of natural gas in heavy-duty engines. However, there is limited research focusing on quantitative optimization of the excess air coefficient and natural gas substitution rate of HPDI engines. In order to support the design and development of HPDI engines, this article investigates the effects of excess air coefficient and substitution rate on a dual fuel HPDI engine combustion performance and emission characteristics. Results show that increasing the excess air coefficient results in higher cylinder pressure, but it has minimal effect on the heat release rate. A higher excess air coefficient can also lead to higher nitrogen oxides (NOx) emissions, lower soot emissions, methane (CH4) and total hydrocarbon (THC) emissions significantly decrease at 50% loads (Case2 and Case4), but these increase at 70% loads (Case1 and Case3). Furthermore, increasing the substitution rate markedly reduces greenhouse gas emissions, though it comes with the drawback of heightened combustion instability, and there is a trade-off between engine combustion cycle variations and greenhouse gas emissions as the substitution rate changes. The above research findings will provide optimization guidance for the engineering development of HPDI engines.

Analysis of Exergy Efficiency and Influencing Factors of Tube Heating Furnace in Oilfield Enterprises

Abstract In the energy consumption of surface engineering systems in oilfield enterprises, heating furnaces account for a significant proportion. Therefore, it is necessary to analyze and study their operational performance. This paper conducts an exergy analysis on tubular heating furnaces from the perspective of energy quality. Firstly, an exergy balance model and exergy analysis evaluation criteria are established for the energy system of the heating furnace. Then, the internal and external exergy losses in the heating furnace's energy system are comprehensively considered to identify weak points in the energy system and reflect the utilization of energy quality. The exergy analysis results show that the highest proportion of exergy losses in the heating furnace system is attributed to the heat transfer process. The excess air coefficient, exhaust gas temperature, and external surface temperature of the furnace are inversely proportional to exergy efficiency. Based on the static exergy analysis results, measures to improve the exergy efficiency of the heating furnace are proposed: controlling the excess air coefficient within a reasonable range, reducing the exhaust gas temperature, and lowering the external surface temperature of the furnace. These measures can effectively enhance the energy utilization level of the tubular heating furnace and provide reference and assistance in meeting emission reduction requirements.

Measurement of the first Townsend coefficients in dry air

Density normalized ionization coefficients in dry air (79% N2, 21% O2) are measured by using a steady state Townsend technique (SST) over a range of reduced electric field (E/N) of 132–1056 Td. Previous measurements of the ionization coefficients of dry air were performed for low reduced electric fields namely smaller than 300 Td. The present study has extended this range to a fairly high range. The measurements at high values of E/N (>300 Td) are well agree with the Magboltz 2 version 11.14 code results. At lower values of E/N, the data is compatible in itself but the values are somewhat higher than the results of other groups as well as Magboltz 2 calculation results. The present work data is better agree with the Korff parametrization than the literature data.

Experimental and simulation analysis of the performance of premixed vertical ejectors

Infrared gas stoves have advantages such as rapid combustion speed and high thermal efficiency. The ejector, a pivotal component of the infrared gas stove, plays a crucial role in influencing the mixing ratio of gas and air. The vertical ejector is modeled and the simulation method is validated through experiments. The impact of structural parameters on the vertical ejector performance is investigated in this paper, like the contraction tube length, inlet diameter, and mixing tube length. The simulation results indicate that with the change in the contraction tube length, the excess air coefficient peaks at approximately 1.16. An increase in mixing tube length leads to a decreasing trend in the excess air coefficient. For ejectors with throat diameters of 9.8 mm, 11.2 mm, and 12.6 mm, their excess air coefficient reaches peak values at diffusion angles of 3.5°, 4.7°, and 5.0°, respectively. Furthermore, Response Surface Methodology is utilized to study the comprehensive influence of structural parameters on ejector performance and obtain the optimal structure. The excess air coefficient is 1.13 with the optimal geometric structure.

Обеспечение канцерогенной безопасности копченой рыбной продукции

The purpose of the study is to develop recommendations for rational smoke generation parameters that ensure the quality and environmental safety of smoked fish products. Objectives: to establish the influence of smoke generation parameters on the assessment of the carcinogenicity of smoked products; to evaluate the quality and safety of smoked products produced under optimal smoke generation parameters; to develop recommendations to ensure the quality and safety of smoked fish products. Research was carried out at the department of Management of Technical Systems at the Federal State Budgetary Educational Institution of Higher Education Dalrybvtuz (Vladivostok, Primorsky Region). The object of the study is the process of smoke generation. Analytical, physical and chemical methods, and mathematical modeling methods were used. To prepare smoke-drying smoke samples, 10 kg of alder sawdust with a moisture content of 30–35 % was prepared. Hot smoked smelt samples were obtained under optimal smoke generation conditions. The overall organoleptic index was 5. The content of individual polyaromatic hydrocarbons was: chrysene – 71 ng/kg; benz(a)anthracene – 70 ng/kg; benz(b)fluoranthene – 602 ng/kg; benz(a)pyrene – 64 ng/kg; benz(e)pyrene – 667 ng/kg; dibenz(a,c)anthracene – 57 ng/kg; dibenz(a,h)anthracene – 69 ng/kg, which corresponds to a generalized quality index of 0.99 (very good). During the study, the influence of smoke generation parameters on the assessment of the carcinogenicity of smoked fish products was established, and the dependence of the content of individual polyaromatic hydrocarbons on the excess air coefficient in the smoke generation zone was confirmed. Optimal smoke generation modes: smoke generation temperature 475 °C, excess air coefficient – 0.4. Rational smoke generation parameters: smoke generation temperature 450–500 °C, excess air coefficient – 0.3–0.6.

A novel coal purification-combustion system: Product and efficiency of coal purification process

A novel coal purification-combustion technology is presented to realize the efficient and clean utilization of coal under carbon peaking and carbon neutrality goals. Central to this technology is the implementation of a purification process, the product characteristics, and energy properties of which are the focus of this study. An experimental test of coal purification was conducted using Shenmu coal. The results demonstrate increased coal reactivity following the moderate temperature activation (MTA) process. The high temperature reduction (HTR) phase promotes the production of higher amounts of amorphous carbon, reduces aromatic carbon content, and further decreases fuel particle size. The composite combustion characteristic index(S) of the purified fuel reaches its peak when the excess air coefficient of secondary air (λ2) is 0.36. As λ2 increases from 0.1 to 0.36, the energy in the gas product of the purification system increases from 13700 kJ/kg coal to 25351 kJ/kg coal, while exergy increases from 6530 kJ/kg coal to 11030 kJ/kg coal. The energy efficiency of the purification process ranges from 74.74 % to 80.88 %, with exergy efficiency varying between 60.51 % and 70 %. These findings offer significant insights into refining the coal purification process, ultimately contributing towards maximizing the utility of coal resources.

Experimental study of emission characteristics for fully premixed combustion of dimethyl ether and hydrogen based on flame ions

The detection of flame ion current is a promising approach in fully premixed combustion. However, how to control the excess air coefficient (α) by ion current still needs an effective method. For this reason, the application of natural gas (12T), hydrogen-doped 12T (12T-H) and dimethyl ether (DME) in fully premixed combustion is experimentally studied in this paper. The emission characteristics of NOx, CO and CO2 from fully premixed condensing gas boilers (FPCGB) were analyzed. The detection voltage generated by the flame ion current is used to monitor the NOx emissions of different gas types. A novel combustion control method based on flame ion current is proposed. The results show that hydrogen addition can reduce NOx, CO and CO2 emissions of 12T. The highest NOx emission is observed at a hydrogen volume ratio (HVR) of 15 % in the experiment. The detection voltage gradually decreases with increasing HVR. The CO2 of DME is always lower than 12T. When α exceeds 1.21, 1.31 and 1.12, respectively, DME exhibits higher values in NOx, CO and detection voltage compared to that of 12T. In addition, two combustion characteristic values are identified and proposed for combustion feedback control. The peak voltage (Up) can be used as a parameter to identify the type of gas. The emission voltage (Ue) can be used to determine whether the NOx emission concentration exceeds the 40 ppm threshold.

Experimental study of a solid oxide fuel cell afterburner for a 30 kW generator module: A comparative performance analysis

A comprehensive performance test is conducted on a diffusion burner designed for a 30 kW-class methane solid oxide fuel cell (SOFC) power generation system. To facilitate this assessment, a test system is established, capable of simulating the gas composition and temperature of the anode and cathode at the outlet of the fuel cell stack under various typical operating conditions. The test results demonstrate the afterburner's exceptional robustness, minimal pressure loss, and low emission characteristics. Notably, the afterburner can be ignited and started at low load (6LPM, 20 % of the rated methane flow rate) and can achieve low-load heating (4LPM, at approximately 13 % of the rated methane flow rate) with a significant excess air coefficient of 46.2. Remarkably, the afterburner maintains its reignition capability under all operating conditions. Operational stability is observed with a water-to-carbon ratio below 3, displaying robust resistance to fluctuations in water vapor and airflow. Under generating condition, the afterburner exhibits self-ignition capabilities without the need for an external igniter following flameout. The pressure losses within both the anode and cathode flows remain well below 200Pa, while NOx and CO emissions are recorded at 1.7mg/kWh and 66.2mg/kWh, respectively, complying with the stringent EU EN676:2020 standards.

The influence of thermal diffusion on water migration through a porous insulation material

Excess water on pipes and equipment under porous insulation materials can lead to undesired corrosion. This work aims to clarify to what extent thermal diffusion affects the migration of water inside insulation materials subject to large temperature gradients. Since no experimental data is available on the thermal diffusion coefficients of humid air, revised Enskog theory for Mie fluids is used to estimate transport properties. Comparison to experimental data from literature shows that the theory reproduces the diffusion coefficient, viscosity and thermal conductivity of humid air within 8.7%, 5.0% and 3.5% respectively. The small discrepancies suggest that the theory can also provide reliable estimates of the thermal diffusion coefficients. In the investigated composition and temperature range, the theory predicts the Soret coefficient of water to be approximately ▪, while the Soret coefficient of oxygen varies from ▪ to +▪. A case study with heating of glass wool insulation containing humid air, encapsulating a cylindrical pipe is investigated. Non-equilibrium thermodynamics is used to consistently incorporate the Soret coefficients into the flux equations in a dynamic, non-isothermal model that includes diffusion, convection, thermal conduction and water sorption in the porous medium. With 50 K temperature difference across 5 cm of insulation, we find that at steady-state, thermal diffusion leads to a mole fraction of water in the gas phase that is about 1.5% higher at the hot location than if thermal diffusion is neglected.