Internal combustion engines with application in automobiles and other relevant industries constitute significant environmental pollution via the release of toxic exhaust gasses like carbon monoxide (CO), hydrocarbons ...Internal combustion engines with application in automobiles and other relevant industries constitute significant environmental pollution via the release of toxic exhaust gasses like carbon monoxide (CO), hydrocarbons (HC), particulate matter (PM), and nitrogen oxide (NO<sub>x</sub>). Engine researchers and manufacturers are challenged to develop external and internal measures to ensure environmentally friendly solutions to accommodate and conform to the growing list of emission standards. Therefore, this work presents an experimental investigation of the NO<sub>x</sub> emission profile of a diesel engine that is fuelled and fitted with waste frying oil-based biodiesel and catalytic converter. Using a single-cylinder, four-stroke air-cooled CI engine at a constant speed of 1900 rpm and different loadings of 25%, 50%, 75%, and 100%;fitted with a catalytic converter at the exhaust outlet of the engine and linked to a dynamometer and a gas analyser, an experiment was conducted at biodiesel/diesel volume blends of B0 (0/10), B5 (5/95), B20 (20/80), B30 (30/70), B70 (70/30), B100 (100/0);and 30% concentration (v/v), 0.5 litre/hr flow rate of aqueous urea from the catalytic converter. The results show an increasing NO<sub>x</sub> emission as the biodiesel component increased in the blend. The catalytic converter showed a downward NO<sub>x</sub> reduction with a significant 68% reduction in efficiency at high exhaust gas temperatures. It is concluded that the combined utilisation of waste frying oil-based biodiesel and the catalytic converter yields substantial NO<sub>x</sub> emission reduction.展开更多
Nitrogen oxides(NOx),significant contributors to air pollution and climate change,form aerosols and ozone in the atmosphere.Accurate,timely,and transparent information on NOx emissions is essential for decision-making...Nitrogen oxides(NOx),significant contributors to air pollution and climate change,form aerosols and ozone in the atmosphere.Accurate,timely,and transparent information on NOx emissions is essential for decision-making to mitigate both haze and ozone pollution.However,a comprehensive understanding of the trends and drivers behind anthropogenic NOx emissions from Chinadthe world's largest emitterdhas been lacking since 2020 due to delays in emissions reporting.Here we show a consistent decline in China's NOx emissions from 2020 to 2022,despite increased fossil fuel consumption,utilizing satellite observations as constraints for NOx emission estimates through atmospheric inversion.This reduction is corroborated by data from two independent spaceborne instruments:the TROPOspheric Monitoring Instrument(TROPOMI)and the Ozone Monitoring Instrument(OMI).Notably,a reduction in transport emissions,largely due to the COVID-19 lockdowns,slightly decreased China's NOx emissions in 2020.In subsequent years,2021 and 2022,reductions in NOx emissions were driven by the industry and transport sectors,influenced by stringent air pollution controls.The satellite-based inversion system developed in this study represents a significant advancement in the real-time monitoring of regional air pollution emissions from space.展开更多
The ultra-low NOx emission requirement(50 mg/m^(3))brings great challenge to CFB boilers in China.To further tap the NOx abatement potential,full understanding the fundamentals behind CFB boilers is needed.To achieve ...The ultra-low NOx emission requirement(50 mg/m^(3))brings great challenge to CFB boilers in China.To further tap the NOx abatement potential,full understanding the fundamentals behind CFB boilers is needed.To achieve this,a comprehensive CPFD model is established and verified;gas-solid flow,combustion,and NOx emission behavior in an industrial CFB boiler are elaborated;influences of primary air volume and coal particle size on furnace performance are evaluated.Simulation results indicate that there exists a typical core-annular flow structure in the boiler furnace.Furnace temperature is highest in the bottom dense-phase zone(about 950℃)and decreases gradually along the furnace height.Oxygen-deficient combustion results in high CO concentration and strong reducing atmosphere in the lower furnace.NOx concentration gradually increases in the bottom furnace,reaches maximum at the elevation of secondary air inlet,and then decreases slightly in the upper furnace.Appropriate decreasing the primary air volume and coal particle size would increase the CO concentration and intensify the in-furnace reducing atmosphere,which favors for NOx reduction and low NOx emission from CFB boilers.展开更多
A detailed numerical spray atomization,ignition,combustion and nitrogen oxides(NOx)formation model was developed for direct injection diesel engines by using KIVA3V code.Several modified or recalibrated sub-models inc...A detailed numerical spray atomization,ignition,combustion and nitrogen oxides(NOx)formation model was developed for direct injection diesel engines by using KIVA3V code.Several modified or recalibrated sub-models including a Kelvin-Helmholtz Rayleigh-Taylor(KH-RT)spray breakup model,a Shell ignition model,a single-step kinetic combustion model and a Zel’dovich NOx formation model were incorporated into KIVA3V.This modified model was validated by experimental data obtained from a John Deere 4045T direct injection diesel engine that was fueled with a natural soybean methyl ester,a yellow grease methyl ester,a genetically modified soybean methyl ester and No.2 diesel fuel.Errors between predictions of the brake-specific NOx and measured values were less than 1%at full load.For biodiesel fuels,either the Zel’dovich mechanism overpredicted NOx emissions,the ratio of NO to NOx should be less than diesel fuel,or both.As observed from the modeling results,the higher latent heat of vaporization and higher surface tension of biodiesel relative to diesel fuel did not result in increased NOx emissions.The higher viscosity of biodiesel could be one of the reasons for increased NOx,but its effect was relatively small compared with the effect of decreased spray cone angle and advanced start of injection timing on NOx.Decreased spray cone angle and advanced start of injection were the main reasons for increased NOx emissions of biodiesel.展开更多
This work presents a computational investigation of hydrodynamics,coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at different loads(630,440 and 300 MW;relative loads of 100%,70%and 48...This work presents a computational investigation of hydrodynamics,coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at different loads(630,440 and 300 MW;relative loads of 100%,70%and 48%)to clarify the effect of load change on the furnace processes.A computational fluids dynamics model was established;the flow field,temperature profile,species concentration and NOx emissions were predicted numerically;and the influence of burner tilt angles was evaluated.Simulation results indicate that a decrease in boiler load decreases the gas velocity,attenuates the airflow rotations,and increases the tangent circle size.The high-temperature zone and flame moved toward the side walls.Such behaviors impair air-fuel mixing,heat transfer and steady combustion in the furnace.In terms of species concentrations,a decrease in boiler load increased the O2 content,decreased the CO content,and decreased the char burnout rates only slightly.A change in boiler load from 630 to 440 and 300 MW increased the NOx emissions from 202 to 234 and 247 mg/m^(3),respectively.Burner tilt angles are important in coal combustion and NOx emissions.A burner angle of-15°favors heat transfer and low NOx emissions(<185 mg/m^(3))for the current tangentially fired boiler.展开更多
This paper presents designing sequence-to-sequence recurrent neural network(RNN)architectures for a novel study to predict soil NOx emissions,driven by the imperative of understanding and mitigating environmental impa...This paper presents designing sequence-to-sequence recurrent neural network(RNN)architectures for a novel study to predict soil NOx emissions,driven by the imperative of understanding and mitigating environmental impact.The study utilizes data collected by the Environmental Protection Agency(EPA)to develop two distinct RNN predictive models:one built upon the long-short term memory(LSTM)and the other utilizing the gated recurrent unit(GRU).These models are fed with a combination of historical and anticipated air temperature,air moisture,and NOx emissions as inputs to forecast future NOx emissions.Both LSTM and GRU models can capture the intricate pulse patterns inherent in soil NOx emissions.Notably,the GRU model emerges as the superior performer,surpassing the LSTM model in predictive accuracy while demonstrating efficiency by necessitating less training time.Intriguingly,the investigation into varying input features reveals that relying solely on past NOx emissions as input yields satisfactory performance,highlighting the dominant influence of this factor.The study also delves into the impact of altering input series lengths and training data sizes,yielding insights into optimal configurations for enhanced model performance.Importantly,the findings promise to advance our grasp of soil NOx emission dynamics,with implications for environmental management strategies.Looking ahead,the anticipated availability of additional measurements is poised to bolster machine-learning model efficacy.Furthermore,the future study will explore physical-based RNNs,a promising avenue for deeper insights into soil NOx emission prediction.展开更多
The Miller cycle is a program that effectively reduces NOx emissions from marine diesel engines by lowering the maximum combustion temperature in the cylinder,thereby reducing NOx emissions.To effectively investigate ...The Miller cycle is a program that effectively reduces NOx emissions from marine diesel engines by lowering the maximum combustion temperature in the cylinder,thereby reducing NOx emissions.To effectively investigate the impact of Miller cycle optimum combustion performance and emission capability under high load conditions,this study will perform a one-dimensional simulation of the performance of a marine diesel engine,as well as a threedimensional simulation of the combustion in the cylinder.A 6-cylinder four-stroke single-stage supercharged diesel engine is taken as the research object.The chassis dynamometer and other related equipment are used to build the test system,carry out the diesel engine bench test,and collect experimental data.The simulation results are compared with the test results,and the error is less than 5%.In this study,the authors will use simulation software to simulate several Miller cycle scenarios designed for early inlet valve closure and analyze the impact of the Miller cycle on combustion and emissions at 100%load conditions.By comparing the flow field distribution of the engine at 1500 r/min condition,it was found that proper EIVC can prolong the ignition latency period and homogeneous fuel-air mixture combustion acceleration,but it can reduce pressure and temperature within the piston chamber and NOx emission.However,the Miller cycle reduces end-of-compression temperatures,which increases combustion duration and exhaust temperatures,making it difficult to improve fuel economy at the optimum fuel consumption point,and closing the intake valves prematurely leads to excessive fuel expenditure.Furthermore,temperature and heat release rate within the piston chamber,NOx,and SOOT generation were significantly enhanced.展开更多
The components of combustion chamber (cylinder head-cylinder liner-piston assembly-oil film) were taken as a coupled body.Based on the three-dimensional heat transfer numerical simulation of the coupled body,a coupled...The components of combustion chamber (cylinder head-cylinder liner-piston assembly-oil film) were taken as a coupled body.Based on the three-dimensional heat transfer numerical simulation of the coupled body,a coupled three-dimensional calculation model for in-cylinder working process and the combustion chamber components was built with domain decomposition and boundary coupled method,which implements the coupled three-dimensional simulation of in-cylinder working process and the combustion chamber components.The model was applied in the influence investigation of the space non-uniformity in heat transfer among combustion chamber components on the generation of in-cylinder emissions:NOx.The results showed that the heat transfer space non-uniformity of combustion chamber components directly influences the formation of in-cylinder NOx.The main area being influenced was the accessory area on the wall,while the influence on the generation of NOx in the central area couold be omitted.展开更多
Supercritical carbon dioxide(S-CO_(2))Brayton power cycle power generation technology,has attracted more and more scholars'attention in recent years because of its advantages of high efficiency and flexibility.Com...Supercritical carbon dioxide(S-CO_(2))Brayton power cycle power generation technology,has attracted more and more scholars'attention in recent years because of its advantages of high efficiency and flexibility.Compared with conventional steam boilers,S-CO_(2) has different heat transfer characteristics,it is easy to cause the temperature of the cooling wall of the boiler to rise,which leads to higher combustion gas temperature in the furnace,higher NOX generation concentration.The adoption of flue gas recirculation has a significance impact on the combustion process of pulverized coal in the boiler,and it is the most effective ways to reduce the emission of NOX and the combustion temperature in the boiler.This paper takes 1000MW S-CO_(2) T-type coal-fired boiler as the research target to investigate the combustion and NOX generation characteristics of S-CO_(2) coal-fired boilers under flue gas recirculation condition,the influence of recirculated flue gas distribution along the furnace height on the characteristics of NOX formation and the combustion of pulverized coal.The results show that the recirculated flue gas distribution has the great impact on the concentration of NOX at the boiler outlet.When the bottom recirculation flue gas rate is gradually increased,the average temperature of the lower boiler decreases and the average temperature of the upper boiler increases slightly;The concentration of NOx at the furnace outlet increases.展开更多
Large size utility boilers develop rapidly in China, both their reliability and economics have reached better level. The operating situations of various existing boilers on the basis of different coals are analyzed, i...Large size utility boilers develop rapidly in China, both their reliability and economics have reached better level. The operating situations of various existing boilers on the basis of different coals are analyzed, it is held that, the notable energy imbalance of furnace exit, ever existing in the tangential firing boilers has been solved, with comparatively lower NOX emission concentration of gained. The higher NOX emission concentration and furnace slagging etc. problems existing in wall firing boilers are notable. The comprehensive analysis shows that, it is appropriate to choose lower furnace volume heat release rate and higher flame height in the type selection design of boilers, and sufficient margin should be kept in the selection of coal pulverizing mills.展开更多
Biogas fuel is a sustainable and renewable fuel produced from anaerobic digestion of organic matter. The biogas fuel is a flammable mixture of methane and carbon dioxide with low to medium calorific values. Biogas is ...Biogas fuel is a sustainable and renewable fuel produced from anaerobic digestion of organic matter. The biogas fuel is a flammable mixture of methane and carbon dioxide with low to medium calorific values. Biogas is an alternative to conventional fossil fuels and can be used for beating, transportation and power generation. CFD （computational fluid dynamic） analysis of the combustion performance and emissions of biogas fuel in gas turbine engines is presented in this study. The main objective of this study is to understand the impact of the variability in the biogas fuel compositions and lower heating values on the combustion process. Natural gas, biogas from anaerobic digester, landfill biogas, and natural gas/biogas mixture fuels combustion were investigated in this study. The CFD results show lower peak flame temperature and CO mole fractions inside the combustor and lower NOx emissions at the combustor exit for the biogas compared to natural gas fuel. The peak flame temperature decreases by 37% for the biogas landfill （COJCH4 = 0.89） and by 22% for the biogas anaerobic digester （CO2/CH4 = 0.54） compared to natural gas fuel combustion. The peak CO mole fraction inside the combustor decreases from 9.8 × 10-2 for natural gas fuel to 2.22 × 10-4 for biogas anaerobic digester and 1.32 × 10-7 for biogas landfill. The average NOx mole fraction at the combustor exit decreases from 1.13 × 10-5 for natural gas fuel to 0.40 × 10-6 for biogas anaerobic digester and 1.06 × 10-6 for biogas landfill. The presence of non-combustible constituents in the biogas reduces the temperature of the flame and consequently the NOx emissions.展开更多
To implement a real-time reduction in NOx,a rapid and accurate model is required.A PLS-ELM model based on the combination of partial least squares(PLS)and the extreme learning machine(ELM)for the establishment of the ...To implement a real-time reduction in NOx,a rapid and accurate model is required.A PLS-ELM model based on the combination of partial least squares(PLS)and the extreme learning machine(ELM)for the establishment of the NOx emission model of utility boilers is proposed.First,the initial input variables of the NOx emission model are determined according to the mechanism analysis.Then,the initial input data is extracted by PLS.Finally,the extracted information is used as the input of the ELM model.A large amount of real data was obtained from the distributed control system(DCS)historical database of a 1 000 MW power plant boiler to train and validate the PLS-ELM model.The modeling performance of the PLS-ELM was compared with that of the back propagation(BP)neural network,support vector machine(SVM)and ELM models.The mean relative errors(MRE)of the PLS-ELM model were 1.58%for the training dataset and 1.69%for the testing dataset.The prediction precision of the PLS-ELM model is higher than those of the BP,SVM and ELM models.The consumption time of the PLS-ELM model is also shorter than that of the BP,SVM and ELM models.展开更多
NOx and N2O emissions from an ultra-supercritical circulating fluidized bed(CFB)boiler were predicted using a two dimensional(2-D)comprehensive computational fluid dynamics(CFD)combustion model.This model was develope...NOx and N2O emissions from an ultra-supercritical circulating fluidized bed(CFB)boiler were predicted using a two dimensional(2-D)comprehensive computational fluid dynamics(CFD)combustion model.This model was developed from a three dimensional model for a supercritical CFB boiler previously constructed by our group.Based on an analysis of the NOx and N2O conversion processes in a CFB boiler,the primary formation and destruction reactions were introduced into the 2-D model and coupled.The resulting model was validated using data from the Baima 600 MW supercritical CFB boiler,and then applied to a 660 MW ultra-supercritical CFB boiler.The effects of excess air,the secondary air(SA)to(primary air(PA)plus SA)ratio and the SA injection height on NOx and N2O emissions were investigated.The results show that a higher excess air volume increases both NOx and N2O emissions,while increasing the SA/(PA+SA)ratio somewhat reduces both the NOx and N2O concentrations.On the basis of the results of this work,optimal locations for SA injection ports so as to lower NOx and N2O emissions are recommended.展开更多
Based on the investigation of NOx formation mechanism, a coal-fired utility boiler whose capacity is 1 004 t/h was studied. Excessive air coefficient, inclination of burner and the way of coal supply were investigated...Based on the investigation of NOx formation mechanism, a coal-fired utility boiler whose capacity is 1 004 t/h was studied. Excessive air coefficient, inclination of burner and the way of coal supply were investigated through experimental method. Resuits indicated that under the condition of same boiler efficiency and burn-off rate, the operation conditions adopting the lower excessive air coefficient, upward burners＇ inclination and pyramid coal-supply could reduce NOx emission.展开更多
In partially premixed combustion of gas turbine, the combustion temperature should be lowed in order to reduce NOx. One solution is lean premixed combustion. However, the problem is that large excess air ratio may mak...In partially premixed combustion of gas turbine, the combustion temperature should be lowed in order to reduce NOx. One solution is lean premixed combustion. However, the problem is that large excess air ratio may make the combustion unstable. A novel combustor with circumferential reverse flow of fuel gas is proposed for settling this problem. A 10 kw furnace is established to test performance of this combustor. Three factors such as primary air ratio, position of secondary air, total excess air ratio are studied. The emission characteristics and axial flame temperature distribution are studied. Basing on experimental results, the axial flame temperature and NOr emission increase with primary air ratio and axial length of second stream, and decrease with total excess air ratio. When the total excess air ratio is larger than 1.05, the combustor presents a lower temperature field and much lower NOx emission （less than 10 ppm）.展开更多
The development of maritime trade has greatly promoted the development of diesel engines.However,with the increasingly serious environmental problems,more and more attention has been paid to the exhaust emissions of h...The development of maritime trade has greatly promoted the development of diesel engines.However,with the increasingly serious environmental problems,more and more attention has been paid to the exhaust emissions of high-power marine diesel engines.The restrictions on SOx have been implemented globally,and the limitation of the NO,will be the next priority.This paper illustrates(a)Principle and research progress of NOx emissions-reduction technology of marine diesel engine;(b)Summary of advantages and disadvantages among various reduction technologies and their reduction effects;(c)The application effect of mainstream technology on board.Firstly,since exhaust gas recirculation(EGR)can achieve Tier-Ⅲ directly from Tier-Ⅰ without considering the increased fuel consumption.It is deemed as the most promising technology to reduce emissions by controlling combustion condition.However,EGR has shortcomings of excessive increase in ftiel consumption and generation of waste water,which need to be solved immediately.Secondly,selective catalytic reduction(SCR)is the most effective and straightforward means to achieve Tier-Ⅲ.Despite of the continuous optimization of SCR unit volume,the problem of scrap catalyst seriously limits its wide application.How to match the supercharger more efficiently is a key factor in choosing between high and low pressure SCR.Thirdly,nature gas(NG)engines are capable of achieving a reduction in NOx,but in order to meet the requirements of Tier-Ⅲ,it still needs to be assisted by other technologies.The emissions of hydrocarbon(HC)and CO in NG engines are huge defects that must be solved.Lastly,technologies such as the Miller cycle,Two-stage supercharging and mixed-water combustion can also reduce emissions but were rarely used alone.These technologies can be combined with EGR,SCR and NG engines to optimize the enginesJ economy and emission characteristics.展开更多
The effect of boiler combustion regulation on NOx emission of two 1025t/h boilers has been studied. The researches show that NOx emission is influenced by coal species, operation conditions, etc, and can be reduced by...The effect of boiler combustion regulation on NOx emission of two 1025t/h boilers has been studied. The researches show that NOx emission is influenced by coal species, operation conditions, etc, and can be reduced by regulating the combustion conditions. The effect of combustion regulation on boiler efficiency has also been checked.展开更多
This study focuses on a CFD modelling of biomass-derived syngas co-firing with coal in an older mid-sized PC-fired boiler of type OP-230 with low-emission burners on the front wall. The simulations were performed to d...This study focuses on a CFD modelling of biomass-derived syngas co-firing with coal in an older mid-sized PC-fired boiler of type OP-230 with low-emission burners on the front wall. The simulations were performed to determine whether the boiler can be retrofitted for the fulfilment of the prospective environmental protection regulations relating to levels of NO_X emissions. The improvement of the air staging via the dual-fuel technique was based on the indirect co-firing technology. The impact of two arrangements of dedicated syngas nozzles(below and above the existing coal burners), two syngas compositions and two heat replacements(5% and 15%) on the course of thermal processes in a furnace was tested. The reductions in NO_X emissions were predicted relative to the baseline when only coal is combusted. The highest reduction of about 38% was achieved with the syngas nozzles below the existing coal burners and 15% heat replacement. This arrangement of nozzles offers the residence time sufficient to co-fire coal with waste derived syngas. A lower reduction in NO_X emissions was obtained with the nozzles above the burners as the enlargement of local fuel rich zone near syngas injection becomes significant for 15% heat replacement. Results provide for the decreasing impact of methane content along with the increase of syngas heat input. The avoided CO_2 emissions through the syngas indirect co-firing with coal in the boiler are linear function of heat replacements.展开更多
Air worthiness requirements of the aircraft engine emission bring new challenges to the combustor research and design. With the motivation to design high performance and clean combustor, computational fluid dynamics ...Air worthiness requirements of the aircraft engine emission bring new challenges to the combustor research and design. With the motivation to design high performance and clean combustor, computational fluid dynamics （CFD） is utilized as the powerful design approach. In this paper, Reynolds averaged Navier-Stokes （RANS） equations of reactive two-phase flow in an experimental low emission combustor is performed. The numerical approach uses an implicit compressible gas solver together with a Lagrangian liquid-phase tracking method and the extended coherent flamelet model for turbulence-combustion interaction. The NOx formation is modeled by the concept of post-processing, which resolves the NOx transport equation with the assumption of frozen temperature distribution. Both turbulence-combustion interaction model and NOx formation model are firstly evaluated by the comparison of experimental data published in open literature of a lean direct injection （LDI） combustor. The test rig studied in this paper is called low emission stirred swirl （LESS） combustor, which is a two-stage model combustor, fueled with liquid kerosene （RP-3） and designed by Beihang University （BUAA）. The main stage of LESS combustor employs the principle of lean prevaporized and premixed （LPP） concept to reduce pollutant, and the pilot stage depends on a diffusion flame for flame stabili-zation. Detailed numerical results including species distribution, turbulence performance and burning performance are qualita-tively and quantitatively evaluated. Numerical prediction of NOx emission shows a good agreement with test data at both idle condition and full power condition of LESS combustor. Preliminary results of the flame structure are shown in this paper. The flame stabilization mechanism and NOx reduction effort are also discussed with in-depth analysis.展开更多
Moderate or Intense Low-oxygen Dilution(MILD)combustion has low emission potential in gas turbines.The present work has investigated the performance of MILD combustion with parallel-jet burner arrangement in dry and s...Moderate or Intense Low-oxygen Dilution(MILD)combustion has low emission potential in gas turbines.The present work has investigated the performance of MILD combustion with parallel-jet burner arrangement in dry and steam-diluted conditions.The combustion tests were conducted in atmospheric pressure at various equivalence ratios from LBO(Lean Blow Out)to near-stoichiometric conditions and steam-to-air mass ratios from 0 to 0.2.A simplified chemical reactors network(CRN)model based on MILD combustion concept has been established to study the effect of steam dilution on different pathways of NO production.The experimental results show that under the same adiabatic flame temperature,the reaction zone gradually moves downstream with the increase of steam content.For the high steam content(0.2 kg/kg),the reaction zone is widely distributed,and the distribution of reaction intensity in the reaction zone is more uniform.The average lift-off height of reaction zone is proportional to the steam content.For the steam content of 0.2 kg/kg,the average lift-off height reaches 2.5 times that of the dry conditions,which brings the risk of blowout.For the adiabatic flame temperature of 1650–1900 K,the emissions of NOxare below 3×10–6(at 15%O2,dry)when the steam content varies from 0 to 0.2 kg/kg,which indicates the ultra-low emissions can be obtained under large changes in steam content.For the inlet temperature of 381 K,as the steam content increases,the Prompt NO is dominant in the total NO production.Steam dilution results in a smaller operating range with lower CO emissions.When the steam content reaches 0.2 kg/kg,compared to the dry condition,the carbon monoxide emission increases significantly.In addition,the LBO equivalence ratio of combustion with larger steam content is significantly higher.展开更多
文摘Internal combustion engines with application in automobiles and other relevant industries constitute significant environmental pollution via the release of toxic exhaust gasses like carbon monoxide (CO), hydrocarbons (HC), particulate matter (PM), and nitrogen oxide (NO<sub>x</sub>). Engine researchers and manufacturers are challenged to develop external and internal measures to ensure environmentally friendly solutions to accommodate and conform to the growing list of emission standards. Therefore, this work presents an experimental investigation of the NO<sub>x</sub> emission profile of a diesel engine that is fuelled and fitted with waste frying oil-based biodiesel and catalytic converter. Using a single-cylinder, four-stroke air-cooled CI engine at a constant speed of 1900 rpm and different loadings of 25%, 50%, 75%, and 100%;fitted with a catalytic converter at the exhaust outlet of the engine and linked to a dynamometer and a gas analyser, an experiment was conducted at biodiesel/diesel volume blends of B0 (0/10), B5 (5/95), B20 (20/80), B30 (30/70), B70 (70/30), B100 (100/0);and 30% concentration (v/v), 0.5 litre/hr flow rate of aqueous urea from the catalytic converter. The results show an increasing NO<sub>x</sub> emission as the biodiesel component increased in the blend. The catalytic converter showed a downward NO<sub>x</sub> reduction with a significant 68% reduction in efficiency at high exhaust gas temperatures. It is concluded that the combined utilisation of waste frying oil-based biodiesel and the catalytic converter yields substantial NO<sub>x</sub> emission reduction.
基金supported by the National Key R&D Program of China(Grant No.2021YFB3901000)the National Natural Science Foundation of China(Grant No.42105094)the Shenzhen Science,Technology and Innovation Commission(Grant No.WDZC20220810110301001).
文摘Nitrogen oxides(NOx),significant contributors to air pollution and climate change,form aerosols and ozone in the atmosphere.Accurate,timely,and transparent information on NOx emissions is essential for decision-making to mitigate both haze and ozone pollution.However,a comprehensive understanding of the trends and drivers behind anthropogenic NOx emissions from Chinadthe world's largest emitterdhas been lacking since 2020 due to delays in emissions reporting.Here we show a consistent decline in China's NOx emissions from 2020 to 2022,despite increased fossil fuel consumption,utilizing satellite observations as constraints for NOx emission estimates through atmospheric inversion.This reduction is corroborated by data from two independent spaceborne instruments:the TROPOspheric Monitoring Instrument(TROPOMI)and the Ozone Monitoring Instrument(OMI).Notably,a reduction in transport emissions,largely due to the COVID-19 lockdowns,slightly decreased China's NOx emissions in 2020.In subsequent years,2021 and 2022,reductions in NOx emissions were driven by the industry and transport sectors,influenced by stringent air pollution controls.The satellite-based inversion system developed in this study represents a significant advancement in the real-time monitoring of regional air pollution emissions from space.
基金The authors acknowledge the support from the National Natural Science Foundation of China(grant No.22178095)。
文摘The ultra-low NOx emission requirement(50 mg/m^(3))brings great challenge to CFB boilers in China.To further tap the NOx abatement potential,full understanding the fundamentals behind CFB boilers is needed.To achieve this,a comprehensive CPFD model is established and verified;gas-solid flow,combustion,and NOx emission behavior in an industrial CFB boiler are elaborated;influences of primary air volume and coal particle size on furnace performance are evaluated.Simulation results indicate that there exists a typical core-annular flow structure in the boiler furnace.Furnace temperature is highest in the bottom dense-phase zone(about 950℃)and decreases gradually along the furnace height.Oxygen-deficient combustion results in high CO concentration and strong reducing atmosphere in the lower furnace.NOx concentration gradually increases in the bottom furnace,reaches maximum at the elevation of secondary air inlet,and then decreases slightly in the upper furnace.Appropriate decreasing the primary air volume and coal particle size would increase the CO concentration and intensify the in-furnace reducing atmosphere,which favors for NOx reduction and low NOx emission from CFB boilers.
基金This material is based on work supported by the U.S.Department of Agriculture Cooperative State Research,Education,and Extension Service under Project No.Hatch 10-311 AEFinancial support was also provided by the Kansas Agricultural Experiment Station(Contribution No.09-232-J from the Kansas Agricultural Experiment Station).
文摘A detailed numerical spray atomization,ignition,combustion and nitrogen oxides(NOx)formation model was developed for direct injection diesel engines by using KIVA3V code.Several modified or recalibrated sub-models including a Kelvin-Helmholtz Rayleigh-Taylor(KH-RT)spray breakup model,a Shell ignition model,a single-step kinetic combustion model and a Zel’dovich NOx formation model were incorporated into KIVA3V.This modified model was validated by experimental data obtained from a John Deere 4045T direct injection diesel engine that was fueled with a natural soybean methyl ester,a yellow grease methyl ester,a genetically modified soybean methyl ester and No.2 diesel fuel.Errors between predictions of the brake-specific NOx and measured values were less than 1%at full load.For biodiesel fuels,either the Zel’dovich mechanism overpredicted NOx emissions,the ratio of NO to NOx should be less than diesel fuel,or both.As observed from the modeling results,the higher latent heat of vaporization and higher surface tension of biodiesel relative to diesel fuel did not result in increased NOx emissions.The higher viscosity of biodiesel could be one of the reasons for increased NOx,but its effect was relatively small compared with the effect of decreased spray cone angle and advanced start of injection timing on NOx.Decreased spray cone angle and advanced start of injection were the main reasons for increased NOx emissions of biodiesel.
基金The authors acknowledge the support from the National Nature Science Foundation of China(No.51476058)and SINOPEC project(No.318015-6).
文摘This work presents a computational investigation of hydrodynamics,coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at different loads(630,440 and 300 MW;relative loads of 100%,70%and 48%)to clarify the effect of load change on the furnace processes.A computational fluids dynamics model was established;the flow field,temperature profile,species concentration and NOx emissions were predicted numerically;and the influence of burner tilt angles was evaluated.Simulation results indicate that a decrease in boiler load decreases the gas velocity,attenuates the airflow rotations,and increases the tangent circle size.The high-temperature zone and flame moved toward the side walls.Such behaviors impair air-fuel mixing,heat transfer and steady combustion in the furnace.In terms of species concentrations,a decrease in boiler load increased the O2 content,decreased the CO content,and decreased the char burnout rates only slightly.A change in boiler load from 630 to 440 and 300 MW increased the NOx emissions from 202 to 234 and 247 mg/m^(3),respectively.Burner tilt angles are important in coal combustion and NOx emissions.A burner angle of-15°favors heat transfer and low NOx emissions(<185 mg/m^(3))for the current tangentially fired boiler.
基金support from the University of Iowa Jumpstarting Tomorrow Community Feasibility Grants and OVPR Interdisciplinary Scholars Program for this study.Z.Wang and S.Xiao received support from the U.S.Department of Education(E.D.#P116S210005)Q.Wang and J.Wang acknowledge the support from NASA Atmospheric Composition Modeling and Analysis Program(ACMAP,Grant#:80NSSC19K0950).
文摘This paper presents designing sequence-to-sequence recurrent neural network(RNN)architectures for a novel study to predict soil NOx emissions,driven by the imperative of understanding and mitigating environmental impact.The study utilizes data collected by the Environmental Protection Agency(EPA)to develop two distinct RNN predictive models:one built upon the long-short term memory(LSTM)and the other utilizing the gated recurrent unit(GRU).These models are fed with a combination of historical and anticipated air temperature,air moisture,and NOx emissions as inputs to forecast future NOx emissions.Both LSTM and GRU models can capture the intricate pulse patterns inherent in soil NOx emissions.Notably,the GRU model emerges as the superior performer,surpassing the LSTM model in predictive accuracy while demonstrating efficiency by necessitating less training time.Intriguingly,the investigation into varying input features reveals that relying solely on past NOx emissions as input yields satisfactory performance,highlighting the dominant influence of this factor.The study also delves into the impact of altering input series lengths and training data sizes,yielding insights into optimal configurations for enhanced model performance.Importantly,the findings promise to advance our grasp of soil NOx emission dynamics,with implications for environmental management strategies.Looking ahead,the anticipated availability of additional measurements is poised to bolster machine-learning model efficacy.Furthermore,the future study will explore physical-based RNNs,a promising avenue for deeper insights into soil NOx emission prediction.
基金funded by the National Natural Science Foundation of China under Grant No.51505275.
文摘The Miller cycle is a program that effectively reduces NOx emissions from marine diesel engines by lowering the maximum combustion temperature in the cylinder,thereby reducing NOx emissions.To effectively investigate the impact of Miller cycle optimum combustion performance and emission capability under high load conditions,this study will perform a one-dimensional simulation of the performance of a marine diesel engine,as well as a threedimensional simulation of the combustion in the cylinder.A 6-cylinder four-stroke single-stage supercharged diesel engine is taken as the research object.The chassis dynamometer and other related equipment are used to build the test system,carry out the diesel engine bench test,and collect experimental data.The simulation results are compared with the test results,and the error is less than 5%.In this study,the authors will use simulation software to simulate several Miller cycle scenarios designed for early inlet valve closure and analyze the impact of the Miller cycle on combustion and emissions at 100%load conditions.By comparing the flow field distribution of the engine at 1500 r/min condition,it was found that proper EIVC can prolong the ignition latency period and homogeneous fuel-air mixture combustion acceleration,but it can reduce pressure and temperature within the piston chamber and NOx emission.However,the Miller cycle reduces end-of-compression temperatures,which increases combustion duration and exhaust temperatures,making it difficult to improve fuel economy at the optimum fuel consumption point,and closing the intake valves prematurely leads to excessive fuel expenditure.Furthermore,temperature and heat release rate within the piston chamber,NOx,and SOOT generation were significantly enhanced.
基金Sponsored by the National Natural Science Foundation of China (Grant No. 50576008,50876016,and 51006015)
文摘The components of combustion chamber (cylinder head-cylinder liner-piston assembly-oil film) were taken as a coupled body.Based on the three-dimensional heat transfer numerical simulation of the coupled body,a coupled three-dimensional calculation model for in-cylinder working process and the combustion chamber components was built with domain decomposition and boundary coupled method,which implements the coupled three-dimensional simulation of in-cylinder working process and the combustion chamber components.The model was applied in the influence investigation of the space non-uniformity in heat transfer among combustion chamber components on the generation of in-cylinder emissions:NOx.The results showed that the heat transfer space non-uniformity of combustion chamber components directly influences the formation of in-cylinder NOx.The main area being influenced was the accessory area on the wall,while the influence on the generation of NOx in the central area couold be omitted.
基金This paper is supported by the National Key R&D Program of China(2017YFB0601805).
文摘Supercritical carbon dioxide(S-CO_(2))Brayton power cycle power generation technology,has attracted more and more scholars'attention in recent years because of its advantages of high efficiency and flexibility.Compared with conventional steam boilers,S-CO_(2) has different heat transfer characteristics,it is easy to cause the temperature of the cooling wall of the boiler to rise,which leads to higher combustion gas temperature in the furnace,higher NOX generation concentration.The adoption of flue gas recirculation has a significance impact on the combustion process of pulverized coal in the boiler,and it is the most effective ways to reduce the emission of NOX and the combustion temperature in the boiler.This paper takes 1000MW S-CO_(2) T-type coal-fired boiler as the research target to investigate the combustion and NOX generation characteristics of S-CO_(2) coal-fired boilers under flue gas recirculation condition,the influence of recirculated flue gas distribution along the furnace height on the characteristics of NOX formation and the combustion of pulverized coal.The results show that the recirculated flue gas distribution has the great impact on the concentration of NOX at the boiler outlet.When the bottom recirculation flue gas rate is gradually increased,the average temperature of the lower boiler decreases and the average temperature of the upper boiler increases slightly;The concentration of NOx at the furnace outlet increases.
文摘Large size utility boilers develop rapidly in China, both their reliability and economics have reached better level. The operating situations of various existing boilers on the basis of different coals are analyzed, it is held that, the notable energy imbalance of furnace exit, ever existing in the tangential firing boilers has been solved, with comparatively lower NOX emission concentration of gained. The higher NOX emission concentration and furnace slagging etc. problems existing in wall firing boilers are notable. The comprehensive analysis shows that, it is appropriate to choose lower furnace volume heat release rate and higher flame height in the type selection design of boilers, and sufficient margin should be kept in the selection of coal pulverizing mills.
文摘Biogas fuel is a sustainable and renewable fuel produced from anaerobic digestion of organic matter. The biogas fuel is a flammable mixture of methane and carbon dioxide with low to medium calorific values. Biogas is an alternative to conventional fossil fuels and can be used for beating, transportation and power generation. CFD （computational fluid dynamic） analysis of the combustion performance and emissions of biogas fuel in gas turbine engines is presented in this study. The main objective of this study is to understand the impact of the variability in the biogas fuel compositions and lower heating values on the combustion process. Natural gas, biogas from anaerobic digester, landfill biogas, and natural gas/biogas mixture fuels combustion were investigated in this study. The CFD results show lower peak flame temperature and CO mole fractions inside the combustor and lower NOx emissions at the combustor exit for the biogas compared to natural gas fuel. The peak flame temperature decreases by 37% for the biogas landfill （COJCH4 = 0.89） and by 22% for the biogas anaerobic digester （CO2/CH4 = 0.54） compared to natural gas fuel combustion. The peak CO mole fraction inside the combustor decreases from 9.8 × 10-2 for natural gas fuel to 2.22 × 10-4 for biogas anaerobic digester and 1.32 × 10-7 for biogas landfill. The average NOx mole fraction at the combustor exit decreases from 1.13 × 10-5 for natural gas fuel to 0.40 × 10-6 for biogas anaerobic digester and 1.06 × 10-6 for biogas landfill. The presence of non-combustible constituents in the biogas reduces the temperature of the flame and consequently the NOx emissions.
基金The National Natural Science Foundation of China(No.71471060)Natural Science Foundation of Hebei Province(No.E2018502111)
文摘To implement a real-time reduction in NOx,a rapid and accurate model is required.A PLS-ELM model based on the combination of partial least squares(PLS)and the extreme learning machine(ELM)for the establishment of the NOx emission model of utility boilers is proposed.First,the initial input variables of the NOx emission model are determined according to the mechanism analysis.Then,the initial input data is extracted by PLS.Finally,the extracted information is used as the input of the ELM model.A large amount of real data was obtained from the distributed control system(DCS)historical database of a 1 000 MW power plant boiler to train and validate the PLS-ELM model.The modeling performance of the PLS-ELM was compared with that of the back propagation(BP)neural network,support vector machine(SVM)and ELM models.The mean relative errors(MRE)of the PLS-ELM model were 1.58%for the training dataset and 1.69%for the testing dataset.The prediction precision of the PLS-ELM model is higher than those of the BP,SVM and ELM models.The consumption time of the PLS-ELM model is also shorter than that of the BP,SVM and ELM models.
基金This work was supported by the National Key Research&Devel-opment Program of China(No.2016YFB0600202-2).
文摘NOx and N2O emissions from an ultra-supercritical circulating fluidized bed(CFB)boiler were predicted using a two dimensional(2-D)comprehensive computational fluid dynamics(CFD)combustion model.This model was developed from a three dimensional model for a supercritical CFB boiler previously constructed by our group.Based on an analysis of the NOx and N2O conversion processes in a CFB boiler,the primary formation and destruction reactions were introduced into the 2-D model and coupled.The resulting model was validated using data from the Baima 600 MW supercritical CFB boiler,and then applied to a 660 MW ultra-supercritical CFB boiler.The effects of excess air,the secondary air(SA)to(primary air(PA)plus SA)ratio and the SA injection height on NOx and N2O emissions were investigated.The results show that a higher excess air volume increases both NOx and N2O emissions,while increasing the SA/(PA+SA)ratio somewhat reduces both the NOx and N2O concentrations.On the basis of the results of this work,optimal locations for SA injection ports so as to lower NOx and N2O emissions are recommended.
基金Supported by the Youth Fundation of Shanghai University of Electric Power (F2004016)Shanghai Leading Academic Discipline Project (P1302)
文摘Based on the investigation of NOx formation mechanism, a coal-fired utility boiler whose capacity is 1 004 t/h was studied. Excessive air coefficient, inclination of burner and the way of coal supply were investigated through experimental method. Resuits indicated that under the condition of same boiler efficiency and burn-off rate, the operation conditions adopting the lower excessive air coefficient, upward burners＇ inclination and pyramid coal-supply could reduce NOx emission.
文摘In partially premixed combustion of gas turbine, the combustion temperature should be lowed in order to reduce NOx. One solution is lean premixed combustion. However, the problem is that large excess air ratio may make the combustion unstable. A novel combustor with circumferential reverse flow of fuel gas is proposed for settling this problem. A 10 kw furnace is established to test performance of this combustor. Three factors such as primary air ratio, position of secondary air, total excess air ratio are studied. The emission characteristics and axial flame temperature distribution are studied. Basing on experimental results, the axial flame temperature and NOr emission increase with primary air ratio and axial length of second stream, and decrease with total excess air ratio. When the total excess air ratio is larger than 1.05, the combustor presents a lower temperature field and much lower NOx emission （less than 10 ppm）.
基金The authors thank the financial support are as follow:Natural Science Foundation Committee of China(No.51709163)China Postdoctoral Science Foundation(No.2018T110382)Shanghai Sailing Program(No.17YF1407500).
文摘The development of maritime trade has greatly promoted the development of diesel engines.However,with the increasingly serious environmental problems,more and more attention has been paid to the exhaust emissions of high-power marine diesel engines.The restrictions on SOx have been implemented globally,and the limitation of the NO,will be the next priority.This paper illustrates(a)Principle and research progress of NOx emissions-reduction technology of marine diesel engine;(b)Summary of advantages and disadvantages among various reduction technologies and their reduction effects;(c)The application effect of mainstream technology on board.Firstly,since exhaust gas recirculation(EGR)can achieve Tier-Ⅲ directly from Tier-Ⅰ without considering the increased fuel consumption.It is deemed as the most promising technology to reduce emissions by controlling combustion condition.However,EGR has shortcomings of excessive increase in ftiel consumption and generation of waste water,which need to be solved immediately.Secondly,selective catalytic reduction(SCR)is the most effective and straightforward means to achieve Tier-Ⅲ.Despite of the continuous optimization of SCR unit volume,the problem of scrap catalyst seriously limits its wide application.How to match the supercharger more efficiently is a key factor in choosing between high and low pressure SCR.Thirdly,nature gas(NG)engines are capable of achieving a reduction in NOx,but in order to meet the requirements of Tier-Ⅲ,it still needs to be assisted by other technologies.The emissions of hydrocarbon(HC)and CO in NG engines are huge defects that must be solved.Lastly,technologies such as the Miller cycle,Two-stage supercharging and mixed-water combustion can also reduce emissions but were rarely used alone.These technologies can be combined with EGR,SCR and NG engines to optimize the enginesJ economy and emission characteristics.
文摘The effect of boiler combustion regulation on NOx emission of two 1025t/h boilers has been studied. The researches show that NOx emission is influenced by coal species, operation conditions, etc, and can be reduced by regulating the combustion conditions. The effect of combustion regulation on boiler efficiency has also been checked.
基金carried out in the framework of 3190/23/P and S/WZ/1/2015 works financed by Ministry of Science and Higher Education of Poland from the funds for science
文摘This study focuses on a CFD modelling of biomass-derived syngas co-firing with coal in an older mid-sized PC-fired boiler of type OP-230 with low-emission burners on the front wall. The simulations were performed to determine whether the boiler can be retrofitted for the fulfilment of the prospective environmental protection regulations relating to levels of NO_X emissions. The improvement of the air staging via the dual-fuel technique was based on the indirect co-firing technology. The impact of two arrangements of dedicated syngas nozzles(below and above the existing coal burners), two syngas compositions and two heat replacements(5% and 15%) on the course of thermal processes in a furnace was tested. The reductions in NO_X emissions were predicted relative to the baseline when only coal is combusted. The highest reduction of about 38% was achieved with the syngas nozzles below the existing coal burners and 15% heat replacement. This arrangement of nozzles offers the residence time sufficient to co-fire coal with waste derived syngas. A lower reduction in NO_X emissions was obtained with the nozzles above the burners as the enlargement of local fuel rich zone near syngas injection becomes significant for 15% heat replacement. Results provide for the decreasing impact of methane content along with the increase of syngas heat input. The avoided CO_2 emissions through the syngas indirect co-firing with coal in the boiler are linear function of heat replacements.
文摘Air worthiness requirements of the aircraft engine emission bring new challenges to the combustor research and design. With the motivation to design high performance and clean combustor, computational fluid dynamics （CFD） is utilized as the powerful design approach. In this paper, Reynolds averaged Navier-Stokes （RANS） equations of reactive two-phase flow in an experimental low emission combustor is performed. The numerical approach uses an implicit compressible gas solver together with a Lagrangian liquid-phase tracking method and the extended coherent flamelet model for turbulence-combustion interaction. The NOx formation is modeled by the concept of post-processing, which resolves the NOx transport equation with the assumption of frozen temperature distribution. Both turbulence-combustion interaction model and NOx formation model are firstly evaluated by the comparison of experimental data published in open literature of a lean direct injection （LDI） combustor. The test rig studied in this paper is called low emission stirred swirl （LESS） combustor, which is a two-stage model combustor, fueled with liquid kerosene （RP-3） and designed by Beihang University （BUAA）. The main stage of LESS combustor employs the principle of lean prevaporized and premixed （LPP） concept to reduce pollutant, and the pilot stage depends on a diffusion flame for flame stabili-zation. Detailed numerical results including species distribution, turbulence performance and burning performance are qualita-tively and quantitatively evaluated. Numerical prediction of NOx emission shows a good agreement with test data at both idle condition and full power condition of LESS combustor. Preliminary results of the flame structure are shown in this paper. The flame stabilization mechanism and NOx reduction effort are also discussed with in-depth analysis.
基金the financial support from the National Science and Technology Major Project(Grant No.2017-I-0009-0010)。
文摘Moderate or Intense Low-oxygen Dilution(MILD)combustion has low emission potential in gas turbines.The present work has investigated the performance of MILD combustion with parallel-jet burner arrangement in dry and steam-diluted conditions.The combustion tests were conducted in atmospheric pressure at various equivalence ratios from LBO(Lean Blow Out)to near-stoichiometric conditions and steam-to-air mass ratios from 0 to 0.2.A simplified chemical reactors network(CRN)model based on MILD combustion concept has been established to study the effect of steam dilution on different pathways of NO production.The experimental results show that under the same adiabatic flame temperature,the reaction zone gradually moves downstream with the increase of steam content.For the high steam content(0.2 kg/kg),the reaction zone is widely distributed,and the distribution of reaction intensity in the reaction zone is more uniform.The average lift-off height of reaction zone is proportional to the steam content.For the steam content of 0.2 kg/kg,the average lift-off height reaches 2.5 times that of the dry conditions,which brings the risk of blowout.For the adiabatic flame temperature of 1650–1900 K,the emissions of NOxare below 3×10–6(at 15%O2,dry)when the steam content varies from 0 to 0.2 kg/kg,which indicates the ultra-low emissions can be obtained under large changes in steam content.For the inlet temperature of 381 K,as the steam content increases,the Prompt NO is dominant in the total NO production.Steam dilution results in a smaller operating range with lower CO emissions.When the steam content reaches 0.2 kg/kg,compared to the dry condition,the carbon monoxide emission increases significantly.In addition,the LBO equivalence ratio of combustion with larger steam content is significantly higher.
