Soil NOx Emission Prediction via Recurrent Neural Networks

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.

Study on effect of heat transfer space non-uniformity of combustion chamber components on in-cylinder NOx emission formation in internal combustion engine

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.

Combined Effect of a Catalytic Reduction Device with Waste Frying Oil-Based Biodiesel on NOx Emissions of Diesel Engines

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 (NOx). 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 NOx 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 NOx emission as the biodiesel component increased in the blend. The catalytic converter showed a downward NOx 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 NOx emission reduction.

CPFD modeling of hydrodynamics,combustion and NOx emissions in an industrial CFB boiler

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.

Computational investigation of hydrodynamics,coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at various loads

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.

NOx Emission Reduction Technology for Marine Engine Based on Tier-Ⅲ:A Review

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.

Computational investigation of the effect of biodiesel fuel properties on diesel engine NOx emissions

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.

A Study of the Effect of the Miller Cycle on the Combustion of a Supercharged Marine Diesel Engine

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.

Influence of Recirculated Flue Gas Distribution on Combustion and NOx Formation Characteristics in S-CO_(2) Coal-fired Boiler

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.

Predictions of NOx/N2O emissions from an ultra-supercritical CFB boiler using a 2-D comprehensive CFD combustion model

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.

Experimental and Numerical Study on Co-combustion Behaviors and NO_(x) Emission Characteristics of Semi-coke and Coal in a Tangentially Fired Utility Boiler

The utilization of powdery semi-coke as a power fuel in pulverized coal-fired power plants has become a new and potential technique to consume the excess powdery semi-coke.The characteristic of low volatile results in poor combustion performance and high NO_(x) emission,and to co-fire with bituminous coal is a practical strategy to address this problem.However,the co-combustion characteristics and the inherent interaction between semi-coke and coal remain insufficiently understood.In addition,the influences of secondary air arrangement,the boiler operation load,and the fuel type on co-combustion process are still unclear,which is urgent to be further explored.In the present study,experiments and numerical simulations were jointly utilized to inquire into the co-combustion behaviors and NO_(x) emission features of semi-coke and coal.The results demonstrated that the"out-furnace method"was a suitable choice for small-capacity boiler when the proportion of semi-coke was 33%,due to the limited combinations of the semi-coke injection position.It was recommended that semi-coke was preferred to be injected from the middle layers of the furnace under the"in-furnace method"to improve the overall co-combustion performance.The critical value of the separated over fire air ratio in this study was 27.5%,over which a slight drop of carbon content in fly ash could come about.Moreover,the elevation in the proportion of separated over fire air gave rise to the significant decline of NO_(x) concentration.The constricted secondary air arrangement was preferred to be employed due to the high boiler efficiency.The separated over fire air and the surrounding air needed to maintain a wide-open degree to prevent the increase of NO_(x) emissions and the coking of nozzles.For the load reduction regulation method adopted in this study,the NO_(x) concentration first rose and then dropped,while the burnout ratio decreased obviously as the operation load was reduced.Different combinations of coal and semi-coke generated significant influences on co-combustion behaviors within the furnace.The NO_(x )generated by high-volatile fuel (bituminous coal) combustion was mainly affected by volatile-N,while the NO_(x )generated by low-volatile fuel (semi-coke) was mainly impacted by char-N.This study is of guiding significance for the efficient and clean utilization and beneficial to the large-scale application of powder semi-coke in power plants.

Real-world fuel efficiency and exhaust emissions of light-duty diesel vehicles and their correlation with road conditions

The real-world fuel efficiency and exhaust emission profiles of CO, HC and NOx for light-duty diesel vehicles were investigated. Using a portable emissions measurement system, 16 diesel taxies were tested on different roads in Macao and the data were normalized with the vehicle specific power bin method. The 11 Toyota Corolla diesel taxies have very good fuel economy of （5.9 ± 0.6） L/100 km, while other five diesel taxies showed relatively high values at （8.5 ± 1.7） L/100 km due to the variation in transmission systems and emission control strategies. Compared to similar Corolla gasoline models, the diesel cars confirmed an advantage of ca. 20% higher fuel efficiency. HC and CO emissions of all the 16 taxies are quite low, with the average at （0.05 ± 0.02） g/km and （0.38 ± 0.15） g/km, respectively. The average NOx emission factor of the 11 Corolla taxies is （0.56 ± 0.17） g/km, about three times higher than their gasoline counterparts. Two of the three Hyundai Sonata taxies, configured with exhaust gas recirculation （EGR） ＋ diesel oxidation catalyst （DOC） emission control strategies, indicated significantly higher NO2 emissions and NO2/NOx ratios than other diesel taxies and consequently trigger a concern of possibly adverse impacts on ozone pollution in urban areas with this technology combination. A clear and similar pattern for fuel consumption and for each of the three gaseous pollutant emissions with various road conditions was identified. To save energy and mitigate CO2 emissions as well as other gaseous pollutant emissions in urban area, traffic planning also needs improvement.

CFD Study of NO_x Emissions in a Model Commercial Aircraft Engine Combustor

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.

Effect of Steam Dilution on the MILD Combustion Characteristics of Methane in a Model Combustor

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.

Numerical Simulation of Combustion Characteristics in High Temperature Air Combustion Furnace

The influences of air preheating temperature, oxygen concentration, and fuel inlet temperature on flame properties, and NOx formation and emission in the furnace were studied with numerical simulation. The turbulence behavior was modeled using the standard k-ε model with wall function, and radiation was handled using discrete ordinate radiation model. The PDF （probability density function） /mixture fraction combustion model was used to simulate the propane combustion. Additionally, computations of NOx formation rates and NOx concentration were carried out using a post-processor on the basis of previously calculated velocities, turbulence, temperature, and chemical composition fields. The results showed that high temperature air combustion （HiTAC） is spread over a much larger volume than traditional combustion, flame volume increases with a reduction of oxygen concentration, and this trend is clearer if oxygen concentration in the preheated air is below 10%. The temperature profile becomes more uniform when oxygen concentration in preheated air decreases, especially at low oxygen levels. Increase in fuel inlet tempera- ture lessens the mixing of the fuel and air in primary combustion zone, creates more uniform distribution of reactants inside the flame, decreases the maximum temperature in furnace, and reduces NOx emission greatly.

Experimental investigations on combustion characteristics of syngas composed of CH_(4),CO,and H_(2)

The residual gas and remained raw gas in dual gas resources polygeneration system are quite complex in components(mainly CH_(4),CO,and H_(2)),and these results to the distinguished differences in combustion reaction.Experimental investigations on basic combustion characteristics of syngas referred above are conducted on a laboratory-scale combustor with flame temperature and flue gas composition measured and analyzed.Primary air coefficient(PA),total air coefficient(TA),and components of the syngas(CS)are selected as key factors,and it is found that PA dominates mostly the ignition of syngas and NOx formation,while TA affects the flue gas temperature after high temperature region and NOx formation trend to be positive as H_(2)/CO components increase.The results provide references for industrial utilization.