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Staged combustion technology is widely applied in modern low-emission energy and power systems. This study employs large eddy simulations (LES) to investigate the flame dynamics and emission characteristics in a staged two-phase partially premixed model combustor. To improve the suitability of the thickened flame model (TFM) for turbulent flames in the thin-reaction-zone regime, a new model for efficiency function is formulated such that the effects of small-scale turbulence on flame propagation are taken into account. The enhanced LES-TFM approach is then integrated with an efficient NOx model, in which an additional NOx transport equation is solved with pre-tabulated NOx formation source terms. Five LES runs are performed to investigate the evolution of flame dynamics and emission characteristics with staging ratios at the scaled cruise operating conditions, in which the optimal staging ratio is critical for NOx reduction. Results show that the trend of flame morphology and NOx emission predictions with staging ratios are consistent with the experimental results. The flame zones in the staged model combustor shift from a pilot-stage-only flame to a pilot-primary-stage flame, then to a primary-stage-only flame with decreasing fuel staging ratio. Due to the redistribution of the equivalence ratio and the NOx emission characteristics trade-off between the two-stage flows, there is an optimal staging ratio for NOx reduction in the staged model combustor. The proposed LES-TFM-NOx approach, which has both the benefits of efficient flame dynamics modeling with the global reaction mechanism and the advantages of prediction accuracy with the detailed mechanism for NOx emission, demonstrates its advantages in simulating flame and emission characteristics in low-emission combustion devices. [ABSTRACT FROM AUTHOR]

Moderate or intense low-oxygen dilution (MILD) combustion has the potential to enhance flame stability and control NOx emissions when using ammonia (NH 3) as fuel. However, the effects of a wide range of ammonia ratios on the combustion characteristics and NOx emissions of jet in a hot co-flow (JHC) ammonia-doped MILD combustion have not been thoroughly investigated. In this study, the combustion and NOx production characteristics of CH 4 /NH 3 hot co-flow combustion jets with a wide range of NH 3 contents (i.e. , ammonia ratios) are investigated systematically. The results indicate that all the simulated cases fall within the MILD combustion regime. The autoignition temperature increases, while the maximum temperature rise decreases monotonically with the increase of ammonia ratio. This suggests that the MILD combustion regime is more easily achieved with the addition of ammonia. The maximum temperature rise shows only slight changes when the ammonia ratio is less than 60%. This phenomenon occurs because the adiabatic flame temperature decreases with the blending of ammonia; however, the heat loss due to radiation is also reduced. Under most conditions, the emission index of NO (EINO) initially increases with the ammonia ratio when it is below 50%, but gradually decreases when it exceeds 50%. Additionally, the EINO decreases with an increase in hot co-flow temperature for a given ammonia ratio, indicating that the overall NO emission levels are suppressed by raising the hot co-flow temperature, despite the peaks of the NO rise. Changes in key chemical reaction pathways are also analyzed. It is found that hydroxyl (OH) radicals play a significant role during the dehydrogenation of NH 3 into NH 2 radicals. In ammonia-rich combustion, a higher ammonia ratio suppresses the conversion of NH i to HNO, while promoting the conversions of NH i to N 2 H 2 , NN, and N 2 O. This shift is advantageous for the conversion of NH 3 into N 2. [Display omitted] • Jets in hot co-flow combustion are simulated with a wide range of ammonia ratios. • Combustion regime and temperature variation are analyzed. • Emission index of NO (EINO) under different conditions are calculated. • Reaction pathways of NH 3 into NO with low and high ammonia ratios are compared. • Effects on NH i radical conversion to N-containing species are also discussed. [ABSTRACT FROM AUTHOR]

Hydrogen and ammonia, as currently popular zero carbon fuels, have received widespread attention. These two fuels have complementary advantages in combustion characteristics, cost, safety, etc. Based on the vase shaped micro combustor, a new structure proposed for application in micro thermophotovoltaic systems in our previous work. This article numerically investigated the combustion characteristics and NOx emission of non-premixed H 2 /NH 3 /Air in vase shaped micro combustor which proposed in our previous work. The variation patterns of flame temperature, wall temperature, flammability limit, and NOx emission with the blended ratio of NH 3 and equivalence ratio were obtained. It was found that the flame cannot move and stabilize when the mixing ratio is 0.6. The rate of production (ROP) and sensitivity of NO and N 2 O were analyzed. Four precursors of NO, HNO, NH, N, N 2 have been discovered. Under the conditions of this article, HNO is the key component affecting NO emissions. When the blending ratio is greater than 0.3, the lower reaction rate of HNO leaded to a decrease in NO. The elementary reaction R63: NH + NO N 2 O + H is the key elementary reaction that affects NO consumption and N 2 O generation. The blending ratio of 0.4 and the equivalence ratio of 1.2 are the optimized operating conditions with the highest comprehensive performance. • Combustion and emission characteristics of H 2 /NH 3 in vase shaped micro combustor. • H 2 /NH 3 non-premixed combustion limit in novel micro combustor was studied. • ROP and sensitivity of NO and N 2 O were analyzed. • HNO and R63 are key species and elementary reaction effect on the NO emission. [ABSTRACT FROM AUTHOR]

In the context of the growing use of hydrogen for decarbonization in combustion, understanding NO x emissions from hydrogen burners is crucial. This study focuses on the impact of partial premixing on NO x production in hydrogen flames using a coaxial injector with swirl. The goal is to expand conventional jet scaling laws to encompass additional physical phenomena. The flexible injection system employed allows the stabilization of various flame types depending on the operating conditions, and double-front flames are obtained in several configurations. Observing the limitations of known scaling laws, particularly in coaxial flows with low-velocity differences or swirl, we conduct experiments measuring NO x and flame volume. Two Large Eddy Simulations explore distinct flame configurations to deepen our understanding about coaxial jet and recirculating flames, especially in the presence of a secondary premixed front due to rich premixing. Our investigation delves into the relationship between NO production and strain rate, considering turbulent and strain-related timescales. Notably, the presence of a premixed flame front alters the velocity profile on the shear layer, and the observed relationship between strain and turbulence in jet flames does not hold for recirculating flames. Thanks to this new insight, we propose a novel formulation for NO x scaling in coaxial jets, leveraging existing literature on coaxial jet modeling. Additionally, we propose a simple model to represent the piloting strain rate for NO emission in recirculating flames. Intricate effects of both swirl and partial-premixing are then included in the derived NO x scaling laws. [Display omitted] • Nitrogen oxide (NO x) emissions are measured in many swirled hydrogen flames. • Large-eddy simulations are used to enlighten the formation mechanisms. • Scaling laws for NO x emissions are derived to work for different flame topologies. [ABSTRACT FROM AUTHOR]

Energy demand has increased gradually. Meeting the energy demand through available sources in the country leads to self-sufficiency. Alternate fuel production and implementation-based research have been more concentrated on encountering that demand for CI engine fuels. Here, transesterification produced biodiesel from the Ziziphus mauritiana seed oil is used. While running, the 5.2 kW CI engine with this new neat Ziziphus mauritiana biodiesel (ZMBD) has 8.7% lesser brake thermal efficiency and 4% and 33% higher NOx and smoke emissions than diesel at full load. Therefore, this biodiesel is blended with 10% and 20% by volume of camphor oil biofuel (COBF) to improve the performance. Also, exhaust gas recirculation (EGR) of 10% and 20% is employed for the better result-produced blend. At full load, 80% ZMBD with 20% COBF blend produced 6.9%, 19.8%, and 15.3% increased brake thermal efficiency, maximum heat release rate, and NOx emission and also 19.05%, 23.73%, 5.78%, and 19.75% drop in CO, unburnt HC, CO2, and smoke emission than ZMBD. With this blended fuel operation and 20% EGR employment is produced 52.99% reduction in NOx and a 13.96% reduction in smoke emission with 3.33% increased brake thermal efficiency compared to straight ZMBD. Therefore, this 80% ZMBD and 20% COBF blend with 20% EGR is recommended for the CI engine with improved performance and reduced NOx emission. [ABSTRACT FROM AUTHOR]

Decarbonization of gas turbine combustion creates a pressing demand for new technical solutions for the combustion process. While switching to hydrogen fuels may solve the problem of carbon emissions and associated pollutants, it can also lead to stability issues for swirl-stabilized combustors due to its increased reactivity. However, with jet flame burner systems, the required flashback safety can be achieved with high axial flow velocities even for premixed combustion of 100% hydrogen fuel. The development of such an engineering solution, however, requires significant effort to reach the maturity of today's swirl burners. This study examines the capacity of a premixed multitube jet burner to manage the chemical reactivity change over a range of volumetric blends from pure natural gas (NG) to pure hydrogen fuel. NOx emissions are measured and analyzed for atmospheric tests. The changes in emissions originate not only from altered combustion chemistry but also from changes in flame shape and turbulence intensity. To get a deeper understanding of the NOx formation process, a low-order model is designed and compared to the experimental data of technically and perfectly premixed combustion tests. Parameter variations of the low-order model are conducted to assess the influences on the NOx emission production of the multijet burner. The information on the combustion process required for the model is obtained computationally and experimentally. Therefore, flame images are recorded and analyzed. [ABSTRACT FROM AUTHOR]

Accurate prediction of nitrogen oxide (NOx) emission is crucial for effectively controlling pollution in municipal solid waste incineration processes. However, it is challenging to construct a NOx emission prediction model with high prediction accuracy and easy engineering application. To address this, this paper proposes a robust and easily applicable NOx emission trend prediction model oriented to engineering applications, utilizing the partial least squares (PLS) method with the time series reconstruction and exponential weighting (TS‐EW‐PLS). The model is verified using operational data from an actual waste incineration process, and comparative analysis with the PLS model showed that the TS‐EW‐PLS model achieved a remarkable improvement of 27–38 % in prediction performance. [ABSTRACT FROM AUTHOR]

Objective] Because of the limited arrangement of NOx emission measurement points in CFB units, the reductant injection amount is often inaccurate. Moreover, given that the pollutant generation characteristics of the units are different under different loads, higher requirements are placed on the accurate measurement of NOx emissions. To analyze the NOx emission prediction of circulating fluidized bed units, the Informer neural network model is used to model the NOx emission of a 350 MW supercritical circulating fluidized bed unit. [Methods] First, the overview of the circulating fluidized bed unit denitration system and the Informer neural network model theory were introduced. On this basis, the data of a circulating fluidized bed unit running continuously for 50 h were obtained as sampling data, 20 parameters related to NOx emissions were determined as input characteristic parameters of the prediction model, and the relevant parameter data were standardized. Second, the simulation experiment platform and model evaluation indicators were determined, the simulation experiment steps were clarified, and the simulation experiment flowchart was drawn. On this basis, simulation experiments on 6 different NOx emission long-sequence time series predictions with prediction lengths of 12, 24, 36, 48, 72, and 96 were conducted, and regression and error analyses were performed on the simulation results of the 6 long-sequence predictions. Finally, according to the same experimental plan and the same operating data, the Transformer, RNN, and LSTM models were used to predict NOx emissions, and the prediction results of the Informer neural network model were compared with the prediction results of the three models in terms of evaluation indicators and time consumption. The comparison results of the evaluation indicators of the four models were presented in a table, and the comparison results of time consumption were presented in a bar chart. [Results] Results showed that the Informer neural network model has good feature extraction and long-sequence input abilities through the attention and distillation mechanisms. The NOx emission prediction effect of this model is significantly better than those of the Transformer, RNN, and LSTM models in terms of prediction accuracy and time consumption. When the prediction length is 24, 36, 48, 72, and 96, the evaluation index value of the Informer neural network model is the smallest, and its prediction accuracy is better than those of the three comparison models. When the prediction length is 12, the sparse attention mechanism of the Informer neural network model cannot effectively extract the periodic characteristics of the input data. The prediction accuracy of the Informer neural network model is slightly worse than that of the LSTM model but is significantly better than that of the Transformer and RNN models. The average time consumption of the Informer neural network model is lower than those of the three comparison models, and the average time consumption is reduced by 60% compared with the RNN model, 84% compared with the LSTM model, and 94% compared with the Transformer model. [Conclusions] The Informer neural network model can provide effective technical support for the prediction of NOx emissions of circulating fluidized bed units. This research serves the innovation and practical education of students majoring in energy and power at the China University of Mining and Technology, helps train students' scientific research thinking, and provides a certain reference for the development of practical teaching of energy and power majors. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) is a carbon-free and hydrogen-rich fuel. NH3 co-firing in coal-fired boiler is an effective approach to reduce carbon emissions from the combustion source. However, it can lead to problems such as high NOx emissions and poor coal burnout. To address the issues above, this paper investigated the Fuel-N conversion and NOx emissions during co-firing 20%NH3 in gasifier (G-20% NH3) and in combustor (C-20%NH3) using a self-built mild gasification-combustion experimental rig. The research found that the co-firing NH3 in the gasifier can decrease the gasifier temperature. However, it has little effect on the coal gasification reactions in gasifier. Compared with a pure coal condition, the conversion ratio of coal-nitrogen was only reduced by 3.64%，and the conversion ratio of volatile matter and fixed carbon decreased by only 0.70% and 2.54%, respectively. Besides, the conversion of NH3 in the gasifier can reach 69.55% during the condition of G-20%NH3. The 68.88% of total fuel-N was conversed to N2 in the gasifier, with NH3-N converting to N2 was 67.73% in G-20%NH3. In addition, the NH3 co-firing in the gasifier promoted the transformation of coal-N and NH3-N to HCN, with the value of 0.36%. Moreover, the coal pyrolysis in the gasifier promoted the NH3 pyrolysis. Compared with pure coal, the NH3 co-firing in the gasifier increased the H2 concentration at the outlet of the gasifier by 69.23% than that of pure coal. The NH3 co-firing also decreased the temperature during the preliminary stage of combustion. Compared with pure coal, the NH3 co-firing in the gasifier and combustor decreased the temperature peak by 46 ℃ and 62 ℃, respectively. Simultaneously, the NH3 co-firing delayed the occurrence of temperature peaks. Additionally, the NH3 co-firing delayed the gasified char combustion in the combustor. The average temperature in the burnout zone increased by 135.8 ℃ and 72.8 ℃ during G-20%NH3 and C-20%NH3, respectively, compared to PC. It was more conducive to the burnout of pulverized coal. The NH3-cofiring in combustor had more significant promoting effects on the burnout of pulverized coal, in which the unburned carbon in fly ash decreased by 1.8% compared PC. However, the NH3 co-firing in gasifier was more effective in reducing NOx emissions. During the G-20%NH3, NO emissions were decreased by 23.51% compared to C-20%NH3. The study offers some innovative ideas and data reference for the development of low NOx emission technology for NH3 co-firing in coal-fired boiler.

Due to the introduction of large-scale renewable energy to the electric grid, the coal-fired units are running more under load cycling conditions and this has dramatically increased the difficulty of boiler in the control of NOx emissions. The real-time prediction of NOx emissions is of great significance to guide the efficient and clean operation of thermal power units under load cycling conditions. The CFD methods require huge computational cost to solve multiple coupled conservation equations, and hence, are infeasible to establish the complex nonlinear mapping relationship between boiler operating parameters and NOx emissions in a real-time manner. With the rapid development of big data analysis and artificial intelligence, data-driven models provide a new approach to realize the real-time prediction and control of boiler NOx emissions. Under load cycling conditions the boiler operating data has strong correlation in time sequence and complex spatial correlation characteristics. However, the traditional neural network methods cannot effectively capture these correlation characteristics, thus, greatly limiting their ability in the accurate prediction of boiler NOx emission. To resolve this problem, a boiler NOx prediction model based on the spatiotemporal attention graph convolutional network (AST-GCN) is proposed in this study. Not only can this model capture the spatial correlations among the boiler operating parameters, but also can it capture the dynamic relationship between the historical boiler operating data and NOx emissions. In addition, the attention mechanism embedded in the model can further improve the ability to adaptively extract the spatio-temporal correlation features from the boiler operating data, and increase the interpretability of the model. The prediction results based on the operating data of a 600 MW boiler demonstrate that the AST-GCN model exhibits a greatly improved prediction accuracy and generalization performance since it can effectively capture the spatial and time sequence correlations among the boiler operating parameters in comparison to the traditional neural network models.

The emission of heavy-duty vehicles has raised great concerns worldwide. The complex working and loading conditions, which may differ a lot from PEMS tests, raised new challenges to the supervision and control of emissions, especially during real-world applications. On-board diagnostics (OBD) technology with data exchange enabled and strengthened the monitoring of emissions from a large number of heavy-duty diesel vehicles. This paper presents an analysis of the OBD data collected from more than 800 city and highway heavy-duty vehicles in China using remote OBD data terminals. Real-world NO x and CO 2 emissions of China-6 heavy-duty vehicles have been examined. The results showed that city heavy-duty vehicles had higher NO x emission levels, which was mostly due to longer time of low SCR temperatures below 180°C. The application of novel methods based on 3B-MAW also found that heavy-duty diesel vehicles tended to have high NO x emissions at idle. Also, little difference had been found in work-based CO 2 emissions, and this may be due to no major difference were found in occupancies of hot running. [ABSTRACT FROM AUTHOR]

Low-temperature combustion (LTC) concepts, such as homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC), aim to reduce in-cylinder temperatures in internal combustion engines, thereby lowering emissions of nitrogen oxides (NOx) and soot. These LTC concepts are particularly attractive for decarbonizing conventional diesel engines using renewable fuels such as methanol. This paper uses numerical simulations and a finite-rate chemistry model to investigate the combustion and emission processes in LTC engines operating with pure methanol. The aim is to gain a deeper understanding of the physical and chemical processes in the engine and to identify optimal engine operation in terms of efficiency and emissions. The simulations replicated the experimentally observed trends for CO, unburned hydrocarbons (UHCs), and NOx emissions, the required intake temperature to achieve consistent combustion phasing at different injection timings, and the distinctively different combustion heat release processes at various injection timings. It was found that the HCCI mode of engine operation required a higher intake temperature than PPC operation due to methanol's low ignition temperature in fuel-richer mixtures. In the HCCI mode, the engine exhibited ultra-low NOx emissions but higher emissions of UHC and CO, along with lower combustion efficiency compared to the PPC mode. This was attributed to poor combustion efficiency in the near-wall regions and engine crevices. Low emissions and high combustion efficiency are achievable in PPC modes with a start of injection around a crank angle of 30° before the top dead center. The fundamental mechanism behind the engine performance is analyzed. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the interrelationships between key harmful emission components, nitrogen oxides (NOx), and particulate numbers (PNs) in diesel engine exhaust and the control actuators of diesel engines. This research involved conducting a series of experiments under fixed parameters within an engine brake laboratory environment to elucidate these correlations. The objectives of this study were to conduct a comprehensive review of the relevant emissions technology literature and a comparative assessment of particle measurement methods based on dilution ratios and develop innovative aerosol preparation principles tailored to condensation particle measurement. Additionally, this research involved designing and implementing an aerosol preparation unit based on the newly developed principles, along with the creation of test cell control programs using the AVL PUMA Open TST editor interface and Visual Basic. Furthermore, this study was concerned with conducting evaluations of fixed-parameter engine dynamometer tests to explore the functional relationships between the emission of 10/23 nm particles, NOx emissions, common rail pressure variations, and exhaust gas recirculation levels. This study aimed to enhance the understanding of diesel engine emissions dynamics and contribute valuable insights for developing more efficient and environmentally friendly engine control strategies. [ABSTRACT FROM AUTHOR]

The precise prediction of NOx generation concentration in coal‐fired boilers serves as the foundational cornerstone for the judicious optimization and control of selective catalytic reduction denitrification (SCR) systems. Owing to the intricate nature of the denitrification process within SCR, there exists a temporal delay in regulating the ammonia injection rate based on the monitored data of NOx concentration at the SCR inlet. Such delays can give rise to ammonia leakage and subsequent obstruction of the air preheater. In light of this, a predictive model, CEEMDAN‐LSTM‐SA, is proposed as an amalgamation of data decomposition and the LSTM (long short‐term memory) fusion self‐attention mechanism within a deep learning network, which is introduced to forecast the NOx emission concentration at the SCR inlet of coal‐fired units. To mitigate the impact of data outliers on the training effectiveness of the model, a clustering method coupled with a statistical testing strategy is initially applied to refine the dataset first. CEEMDAN data decomposition technology is leveraged to facilitate the breakdown of data, alleviating its non‐stationary and intricate characteristics. Subsequently, through spectral analysis, the decomposed components are grouped and aggregated to form novel data elements, which are then subjected to prediction by the constructed LSTM‐SA deep learning network. The ultimate NOx emission concentration prediction value is derived through a process of fusion. Upon scrutinizing and comparing the predictions derived from various models using coal‐fired power plant data, it is evident that the performance metrics of CEEMDAN‐LSTM‐SA predictions exhibit a mean absolute error of 7.425, mean absolute percentage error of 2.415%, root mean square error of 9.715, R‐squared (R2) value of.789, mean absolute relative error of 2.109%, and a Theil's information criterion of.016. In contrast to other models, including traditional self‐attention networks, LSTM, and LSTM‐SA combination networks, CEEMDAN‐LSTM‐SA proposed in this study demonstrates superior prediction accuracy and enhanced generalization capabilities. Consequently, this predictive model stands poised to furnish an efficacious framework for the SCR ammonia injection strategy within thermal power units. [ABSTRACT FROM AUTHOR]

This study investigates the co‐combustion of palm oil biodiesel fuel, as a renewable alternative for diesel fuel, inside natural gas flame to enhance the flame thermal specifications and NOx reduction. A power natural gas burner with a maximum heat capacity of 418,400 kJ/h was installed at the inlet of a laboratory furnace and biodiesel fuel was injected inside natural gas burner with a 100 μm in diameter solid cone nozzle. Flame temperature, thermal radiation, Infrared radiation, and CO, CO2 and NOx emission were measured. The results revealed that biodiesel injection increases the flame size and turns the non‐luminous blue flame into yellow‐colored flame. Furthermore, higher flash point and Sauter Mean Diameter of biodiesel promote the thermal decomposition of fuel droplets and increase the concentrations of Intermediate Soot Particles in the flame which in turn increases the flame emissivity coefficient and consequently flame thermal radiation. Also, the oxygen content of biodiesel fuel has an important role in the complete combustion of Intermediate Soot Particles to CO2 which increases the heat release of biodiesel combustion and raises the flame temperature. The average enhancement in thermal radiation and flame temperature were 5.6% and 43.38%, respectively. Finally, although biodiesel injection increases the flame temperature, it also increases the flame surface reaction and eliminates the hot spot region in the flame. Therefore, the rate of heat generation per unit volume of flame decreases and this decreases the rate of NOx emission as much as 10.84%. [ABSTRACT FROM AUTHOR]

Fuel can be produced from biomass, municipal solid waste, low-grade coal and other raw materials through anaerobic fermentation, pyrolysis gasification and other technologies. It can not only deal with solid waste, and make coal clean to use, but also generate utilizable gas, which has the dual benefits of energy and environmental protection. However, the produced gas has low calorific value, complex composition, more non-combustible components, and the composition changes greatly under the influence of raw materials and processes. There are some problems such as ignition difficulty, combustion instability, and difficult control of pollutants under traditional combustion. Flameless combustion is a mild combustion mode under low oxygen condition with low pollutant emission and high combustion efficiency, which helps to solve these problems. In this study, a detailed mechanism GRI Mech 3.0 and the eddy dissipation concept (EDC) model were used to simulate the flameless combustion process of three low caloric value gas by coupling the turbulent flow with the chemical reaction. The experimental data verify that the simulation method in this study can accurately simulate the flameless combustion in the actual burner. Subsequently, the numerical simulation of flameless combustion of biogas, biomass gasified gas and coal gasified gas was carried out, including temperature field, species, OH radical distribution and pollutant emission. The flameless combustion of biomass gasified gas and coal gasified gas was successfully realized by improving the burner. The results show that the temperature distribution of biomass gasified gas and coal gasified gas in flameless combustion is more uniform than that of natural gas and biogas, the reaction zone structure is larger, and NOx is close to "zero emission". The dilution of CO2 can promote flameless combustion, and CH4 will change the reaction zone and OH distribution, making the temperature distribution nonuniform. The horizontal comparison of flameless combustion of three low calorific value gas shows that even if the input power is the same, the lower the calorific value of gas, the lower the overall furnace temperature. However, the amount of flue gas is larger, so it is necessary to strengthen the heat utilization of flue gas to increase the thermal efficiency of the system.

[Display omitted] • The controllability of N and metal elements transformation was achieved. • Hydrothermal-pyrolysis offered DFW efficient utilization and control NO x emissions. • Hydrothermal pretreatment enhances biochar pore structure and surface area. • O-containing functional groups and doped metal Ca were enriched on the biochar. • Maximum P removal efficiency of wastewater by DFW biochar upped to 94%. Pyrolysis has emerged as a promising technology for valorizing digestate resulting from the anaerobic digestion of food waste. However, the high NO X emissions during pyrolysis limit its application. This study proposed a hydrothermal coupled pyrolysis process to control the element transfer in digestate during biochar production. The efficient reduction of NO X emissions and the improvement of biochar adsorbability were realized. The hydrothermal process reduced the nitrogen content in solid digestate by 49.10 %–81.79 %, thus reducing the NO X precursors in syngas and the N-containing substances in bio-oil. Additionally, the specific surface area and the total pore volume of biochar were enhanced from 25 m2/g to 60–73 m2/g and 0.06 cm3/g to 0.12–0.14 cm3/g, respectively. More defects, oxygen-containing functional groups, and doped Ca on the biochar resulted in a high phosphate removal efficiency of 94 %. The proposed technology provides an efficient and environmentally friendly way to utilize the digestate. [ABSTRACT FROM AUTHOR]

In this paper, the effects of different burner configurations on the characteristics of flameless combustion were evaluated by comparing the temperature field, NOx, OH, and H2CO at different burner inlet velocity and angles through a combination of experimental and numerical simulations. The results show that increasing the burner inlet angle and gas velocity is imperative in achieving the flameless combustion, increasing the re-circulation rate in the furnace, making the temperature distribution in the furnace uniform, and reducing the emission of NOx at the end of the furnace. During the simulation of flameless combustion, it was found that OH radicals and H2CO radicals were well correlated with the reaction exothermic zone, and the Reynolds number was positively correlated with the re-circulation rate in the furnace. With the increase of Reynolds number, the entrainment rate of flue gas increases, and the combustion state is closer to flameless combustion. When re-circulation rate Kv >2, combustion becomes flameless. Through the summary analysis of the data, it can be found that there is a critical Reynolds number for the burner to achieve flameless combustion, and flameless combustion occurs only when the Reynolds number is greater than 1.0·104. [ABSTRACT FROM AUTHOR]

Numerical calculations of the innovative flue gas recirculation (FGR) system through an inactive coal pulverizer for a 40% load of the OP 650 boiler at the Jaworzno III Power Plant were carried out. The research was conducted to determine the effect of FGR on the formation of NOx, CO emissions, and low-NOx waterwall corrosion. Using numerical modelling, the influence of the place of injection of recirculated flue gas on the formation of NOx was also investigated. The tests were carried out based on data from the boiler monitoring system and calculation results using a 0-dimensional model. Modelling of the FGR was performed for five variants. FGR equalized the temperature in the furnace, eliminating temperature peaks in the burner belt. Moreover, FGR did not increase the CO content in the flue gas and reduced the O2 concentration in the area zone of pulverized coal combustion. For FGR systems, the emission of NOx below 200 mg/m3n for 6% O2 in dry flue gas was kept. This proves that the recirculation helps to meet the BAT (best available techniques) requirements for NOx emissions. It has also been shown that FGR does not pose a risk of low-NOx corrosion in the next 20 years. [ABSTRACT FROM AUTHOR]

Several studies have aimed to predict and control carbon emissions from coal‐fired power plants. However, the highly complex combustion mechanisms in coal‐fired power plant boilers pose a significant challenge in direct modeling and optimization. To tackle this challenge, this study introduced a data‐driven approach along with model‐based process optimization to mitigate NOx emissions from coal‐fired power plants. The process involved collecting a 5‐month operational dataset containing 67 controllable parameters from a 500 MW coal‐fired power plant. Steady‐state data was isolated from the load output using a moving average method, followed by the application of an isolation forest algorithm to detect and remove anomalies. Correlation analysis was then used to evaluate parameter relationships and eliminate redundant ones. Subsequently, a NOx prediction model was developed, combining an extra tree regressor data‐driven prediction model with particle swarm optimization to optimize the most influential controllable parameters for reducing NOx emissions. Testing the proposed model across four different target loads consistently resulted in a reduction of over 20% in NOx emissions by optimizing boiler combustion parameters, representing a significant achievement in optimizing coal‐fired combustion. [ABSTRACT FROM AUTHOR]

To meet the requirements of achieving higher efficiency and lower NOx pollution, the flame temperature in gas turbine combustors increases continually; thus, the effusion-cooling technology has been used to ensure the combustor liner remains within the allowed temperature, by which the combustion characteristics and emission behavior are possibly influenced. In order to investigate the effects of dome cooling air flow on combustion characteristics and NOx emissions, three-dimensional combustion simulations for a swirl-stabilized can-type gas turbine combustor are carried out in this work by using the computational fluid dynamics (CFD) method. Through adjusting the ratio of the dome cooling air flow and the dilution cooling air flow, the characteristics of flow field, temperature distribution and NOx emissions under each work condition are analyzed. At different ratios of the dome-cooling air flow to the total air flow, the flow velocity field in the region near the center of the combustion chamber is not changed much, while the velocity field near the chamber wall shows a more significant difference. The temperature in the outer recirculation zone within the combustion chamber is effectively reduced as the dome cooling air flow increases. By analyzing the distribution characteristics of the concentration of OH*, it is demonstrated that the dome cooling air flow does not have a direct effect on the reaction of combustion. It is also found that as the ratio of the dome cooling air flow to the total air flow increases from 0 to 0.15, the value of the NOx emissions drops from 28.4 to 26.3 ppmv, about a 7.4% decrease. The distribution of the NOx generation rate in the combustion chamber does not vary significantly with the increasing dome cooling air flow. Furthermore, by calculating the residence time in different stages, when the the ratio of the dome cooling air flow to the total air flow varies from 0 to 0.15, the residence time in the pilot stage decreases obviously, from 42 ms to 18 ms. This means that reduction in residence time is the main factor in the decrease of NOx emissions when the dome cooling air flow increases. [ABSTRACT FROM AUTHOR]

The hydrogen carrier ammonia is considered a prominent carbon-free alternative fuel. This paper examines the impact of flue gas recirculation (FR) on combustion instability and emission behavior of premixed CH 4 /NH 3 /air swirl flame at different equivalence ratios (Φ) and ammonia mole fractions (χ NH 3 ). Experimental results show that FR is beneficial to suppressing the self-excited pulsating pressure and pulsating heat release rate of CH 4 /NH 3 /air flame, and the pulsating frequency decreases monotonically with the increase of FR. Under fuel-lean and stoichiometric conditions, FR is beneficial to suppressing NOx formation but will increase CO and NH 3 emissions. Under fuel-rich conditions, FR reduces CO emissions but increases NOx emissions. The NO emissions obtained from the chemical reactor network simulation are in qualitative agreement with the experimental results. The results show that the elementary reactions related to HNO and NHi radicals play a crucial role in the influence of FR on NO formation. • Flue gas recirculation (FR) suppresses combustion instability of CH 4 /NH 3 /air flame. • FR decreases NOx emission but increases CO emission under non-rich conditions. • FR increases NOx emission but decreases CO emission under fuel-rich conditions. • Chemical reactor network reveals the main reactions of FR affecting NO formation. [ABSTRACT FROM AUTHOR]

The low flame speed and NO x emissions of ammonia are the key to affecting combustion temperature, stability, flame structure, and pollutant control, limiting its application in power generation devices. This study proposes oxy-ammonia combustion (oxygen content in oxidant = 100%, NH 3 /O 2 combustion) as a novel method for significantly enhancing ammonia combustion. A method for measuring the laminar flame speed using the NH* distribution of the Bunsen burner flame is proposed, and the measured data is close to the constant volume combustion bomb. 21 kinetic models were collected and optimized after comparison with the experimental data of constant volume combustion bombs, and results show that Han et al.'s model has higher prediction accuracy for NH 3 /O 2 flames. The preheating temperature was relevant to gas turbine combustors (298.15–500 K), and the equivalence ratio ranged from 0.7 to 1.6. At this extreme condition (oxygen content in oxidant = 100%), the results show that the maximum laminar flame speed reaches 1.25 m/s at ambient pressure and temperature, which is approximately 18 times that of NH 3 /air combustion, mainly due to the increased reaction rates of OH, H, O and NH 2 radicals in the reaction zone (primary ammonia decomposition and H/O radical pool). The NO emission of NH 3 /O 2 combustion at stoichiometric conditions is about 7216 ppmv@15%O 2 , 1.5 and 13 times that of NH 3 /air and CH 4 /air combustion, respectively. NO production and consumption may follow the N 2 O and NNH mechanism, and HNO is an important precursor for NO formation. Increasing the preheating temperature has less effect on the reaction pathway directions in the reaction network of nitrogen conversion but affects the path flux significantly. [Display omitted] • Oxy-fuel combustion enhances the ammonia combustion to "m/s" level. • Active radical pools and ammonia primary decomposition determine flame speeds. • N 2 O–NNH mechanism dominates nitric oxide production and consumption. • Preheating and fuel-lean conditions promote ammonia primary decomposition. • HNO is the dominant precursor of nitric oxide and competes with NH radicals. [ABSTRACT FROM AUTHOR]

The influence of excess air coefficient, ignition timing, and injection timing were investigated to examine the combustion and emission performance of a hydrogen engine operating at low speed with low loads. Comprehensive experimental research was then undertaken to evaluate the engine performance across a wide range of loads and various combinations of factors. The experimental results show a substantial improvement in brake thermal efficiency (BTE) and a noteworthy reduction in NO X emissions with an increased excess air coefficient. Although the impact of injection timing on BTE is negligible, an appropriate injection timing delay effectively reduces NO X emissions. A lean mixture and a suitable ignition timing delay exhibit high thermal efficiency at a lower engine speed and simultaneously suppress knock. The BTE reaches 33.46% at a mean effective pressure of 10.0 bar. Improving the turbocharging capability under low-speed and high-load conditions is essential for enhancing the performance of hydrogen engines. • EOI has little impact on BTE but is effective in reducing NO X emissions at low load. • Larger excess air ratio can increase BTE and reduce NO X emissions greatly. • Increasing excess air ratio can suppress knock and improve BTE at high load. • Outward-opening injectors are used to decrease hydrogen injection pressure. [ABSTRACT FROM AUTHOR]

Artificial intelligence (AI), unlike natural intelligence, possesses the ability to problem-solving activities by machines. As AI-based models increasingly provide robust approaches to predicting air pollution, they are becoming more widespread. Intelligent transportation systems (ITS) are poised to be significant solutions for sustainable mobility. These systems, by appropriately enhancing mobility, will prevent the concentration of air pollution in a region through transportation. This study aims to examine AI-based models used in air pollution prediction and demonstrate the effectiveness of intelligent transportation systems in improving transportation-related air pollution. As a sample region, Kocaeli Province, which has highly polluted air, the amounts of transportation-related NOx pollutants emitted from light and heavy vehicles passing through the Dilovası district were modeled using Adaptive Neuro-Fuzzy (ANFIS) and Artificial Neural Networks (ANN). The results were compared with the outputs of the Calculations of Emissions from Road Transport (COPERT4) program. The evaluations revealed that ANFIS performed better in modeling NOx pollutants. Based on the prediction results, in case of exceeding the NOx limit, an intelligent transportation system redirecting vehicles to alternative routes was suggested. For the use of this system, scenarios proposing the redirection of cars in varying proportions, including single-plate, double-plate, and light vehicles, depending on route redirection, were proposed and evaluated. The evaluation of scenario results showed that redirecting a large number of cars to alternative routes with the assistance of ITS resulted in a significant decrease in emissions.

The most significant introduction of fluidized bed combustion technology took place about 50 years ago. Initially the combustion beds were of the bubbling type. Once the designs had reached commercial application, several drawbacks were discovered: Erosion on in-bed heat-exchanger tubes, insufficient combustion and desulphurization efficiencies with coal, unfavourable scale-up to electric utility-size. The problems were solved by applying circulating systems. The present text compares these bubbling and circulating designs. It is concluded that the bubbling bed may not be suitable for coal combustion, but for biomass and organic waste most of the drawbacks disappear, and the bubbling bed, being simpler, may have an economic advantage over CFB that should be considered. In addition, combinations of CFB and BFB are quite favourable in many applications.

Considering the pivotal role of ferroalloys in the steel industry and the escalating global emphasis on sustainability (e.g., zero emissions and carbon neutrality), the demand for ferroalloys is anticipated to increase. However, the electric arc furnace (EAF) of ferroalloy plants generates substantial amounts of nitrogen oxides (NOx) because of the high-temperature combustion processes. Despite the substantial contributions of many studies on NOx prediction from various industrial facilities, there is a lack of studies considering the environmental condition of the EAF in ferroalloy plants. Therefore, this study presents a deep learning model for predicting NOx emissions from ferroalloy plants and further can provide guidelines for predicting NOx in industrial sites equipped with electric furnaces. In this study, we collected various historical data from the manufacturing execution system of electric furnaces and exhaust gas systems to develop a prediction model. Additionally, an interpretable artificial intelligence method was employed to track the effects of each variable on the NOx emissions. The proposed prediction model can provide decision support to reduce NOx emissions. Furthermore, the interpretation of the model contributes to a better understanding of the factors influencing NOx emissions and the development of effective strategies for emission reduction in ferroalloys EAF plants. [ABSTRACT FROM AUTHOR]

Among many technical routes in solving the SCR (Selective Catalyst Reduction) deposition problem, a good mixer design can greatly improve the NO x conversion efficiency of the exhaust after-treatment system while avoiding urea deposition failures. This paper presents an anti-deposition mixer with novel conception which was optimized through CFD method, the more layers of wire mesh plates, the lower the evaporation efficiency is affected by the increase in injection volume. The new mixer with three layers of wire mesh plate shows better deposition resistance performance below 250℃through urea deposits boundary experiment, and it reduces the NO x emission value by 9.5% than conventional scheme under WHTC (Word Harmonized Transient Cycle) and WHSC (Word Harmonized Steady-state Cycle) test. By using the new mixer scheme in the after-treatment system, the problem of deposition under a variety of low emission temperature can be solved. • A new conception mixer make SCR system avoiding from urea deposition. • The new mixer scheme improve the engine emission limit of NO x by 9.5%. • The new mixer has excellent urea deposition resistance performance below 250 ℃. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) is being explored as a hydrogen carrier with no carbon emissions. However, if burned directly as NH3, rather than being completely decomposed back to N2/H2, the fuel-bound nitrogen comes with a potentially significant NOx emissions penalty. Indeed, several existing studies are showing ammonia combustion NOx emissions that exceed current natural gas fueled, DLN technologies by one to two orders of magnitude. Therefore, it is important to establish the theoretical minimum NOx emissions for an ammonia combustor, to determine how much NOx levels can be reduced via further technology development. In other words, the purpose of this work is not to analyze the performance of a specific combustor but, rather, the fundamental limits of what is achievable. This study quantifies this minimum NOx level for a two-stage combustor system for a given combustor exit temperature and residence time, with a constraint on unburned fuel levels. As expected, the optimum configuration is a rich front end combustor to burn and crack ammonia with significant H2 production, followed by an NO relaxation reactor, followed by a lean stage that consumes the remaining H2. The optimum residence time and stoichiometry of each zone are determined in the fast mixing limit, which essentially balances between NOx production in the primary and secondary zones. These results show minimum NOx levels are in 200-400 ppm range at 1 bar, but drop to levels of ∼25 ppm at 20 bar. These NOx emissions are dominated by NOx production in the primary stage which relaxes to equilibrium levels quite slowly. As processes controlling NOx relaxation to equilibrium in the primary stage dominate overall NO emission levels, combustor NOx sensitivities are essentially opposite that of natural gas fired, DLN systems. Specifically, NOx values drop with increased combustor residence time, increased pressure, and increased combustor exit temperature. These results also suggest that the most important strategy for NOx minimization is to provide sufficient relaxation time after the primary zone for NOx to approach equilibrium--this can be done via kinetic means to accelerate this relaxation rate, such as enhancing pressure or temperature, or increasing residence times. Indeed, this work shows that low pressure combustors specifically optimized for ammonia will have residence times that are one to two orders of magnitude larger than current natural gas systems. By doing so, NOx levels below 10 ppm may be achievable. Finally, we discuss the sensitivity of these values to uncertainties in ammonia kinetics. [ABSTRACT FROM AUTHOR]

This article presents a study that compares the performance and emission characteristics of a four‐stroke, four‐cylinder spark ignition (SI) engine fueled by gasoline and neat hydrogen. The engine was equipped with turbocharging to optimize ignition timing for power boosting and vaporized water–methanol injection to reduce emissions. Engine tests were conducted at speeds ranging from 2000 to 6000 rpm, with a fixed intake pressure and varying quantities of hydrogen and spark advance timings. The study compared the results of non‐turbocharged and turbocharged engines with water–methanol injection in terms of combustion, performance, and emissions. The findings showed that the turbocharged water–methanol hydrogen operation had a higher brake thermal efficiency (BTE) than its counterpart, while the brake power of the hydrogen engine operation increased with turbocharging but slightly decreased with water–methanol injection. Additionally, volumetric efficiency improved by 7% for turbocharged and 4% for water‐injected hydrogen engine operation compared to the counterpart. The cylinder pressure for turbocharging with water–methanol operation yielded 16.32% higher compared with counterpart gasoline engine operation. Finally, nitrogen oxides (NOx) emissions were reduced with turbocharging and water–methanol injection compared to the counterpart non‐turbocharged hydrogen engine operation. [ABSTRACT FROM AUTHOR]

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This experimental and numerical study investigates the stability and emission characteristics of the flameless combustion for various tangential and coaxial air entry configurations using biogas (60% CH4, 40% CO2) in an asymmetric vortex mesoscale furnace without preheating. It has examined three designs by varying the tangential and coaxial air entry (MF2T4A, MF4T4A, MF6T4A), global equivalence ratio (1.0), and thermal input (207 W) to highlight the impact of furnace configuration on flameless combustion. Temperature and exhaust species concentration measurements in the furnace and a visual inspection were used to conduct the investigation. It has demonstrated that the temperature and NOx emission generally decreases with decreasing O2. Interestingly, the non-premixed flameless combustion for MF6T4A configuration design behaves has an almost insignificant difference and is not very distinct from the other tangential entry configuration design cases. For example, these combustions are a fully flameless mode with a range of Φ = 1, producing an ultra-lower NOx due to the big mixing zone under this air–fuel arrangement. Furthermore, it is verified that the MF2T4A configuration design is the optimal design that provides a higher and uniform temperature, resulting in increased efficiency and ultra-low NOx emission. In contrast, for the case of coaxial entry without tangential configuration, it has combustion instability inside the mesoscale combustor due to an insufficient mixing zone under this coaxial air–fuel arrangement. Finally, the numerical analysis from computational fluid dynamics (CFD) is performed to predict and compare configuration design results. It found that the variations of NOx emissions depend on the variations of O2 and maximum temperature within the furnace rather than the average furnace temperature. Finally, the present study, non-premixed flameless combustion, approves that the tangential air-inlet configurations should be considered a critical operational parameter when designing furnaces. The results show that O2 (15%) recorded the maximum NOx emissions at 2.2 ppm, 0.92 ppm, and 0.52 ppm. In contrast, we recorded the lowest CO emissions at 0.0161 ppm, 1.29 ppm, and 130 ppm, in the cases of air entry configurations of MF2T4A, MF4T4A, and MF6T4A, respectively. Meanwhile, when the results reached the O2(5%) as the lowest concentrations in this research, NOx emissions were ultra-low values recorded between 1.20E-8 ppm and 1.27E-9 ppm. In contrast, CO emissions were different from each other and recorded a little high 692 ppm at 5% O2. [ABSTRACT FROM AUTHOR]

To enhance the combustion efficiency and reduce NOx emissions in large-scale semicoke and bituminous coal blends, an extensive numerical study was conducted. The focus of this study was to optimize the quaternary air vane angle (αv) through detailed analysis of the temperature and flow fields, turbulence–chemistry interactions, char burnout, and NOx formation in a carefully scaled 1:5 dual-swirl burner. The results showed that with increasing αv, the high-temperature flame region was narrowed and the peak temperature was reduced along with the broadened inner recirculation zone and the shrunken external recirculation zone due to better pulverized fuel-oxidant blending and reinforced convective heat transfer. The peak turbulent Damköhler number Dat evidently increased from 197.5 to 496 with increasing αv, which implied a strengthened homogeneous combustion. Additionally, the corresponding mixing time scales increased while the chemical kinetics time scales decreased, which denoted that an intense diffusing flame was generated with a strong turbulent intensity. The peak heterogeneous Damköhler number Das-O2 showed a reduction from 2.54 to 2.27, while the peak values of Das-CO2 and Das-H2O decreased from 0.1 to 0.077 and from 0.02 to 0.015, respectively. The char–O2 reaction was controlled by diffusion/kinetics; both char–CO2 and char–H2O reactions were determined by kinetics, and all gas‒solid reactions showed a kinetically controlled regime. With increasing αv, the enlarged inner recirculation region increased the residence time, and a higher dilution level lessened the peak temperature, which led to reductions in fuel-NOx and the thermal-NOx. The αv range of 30–45° (or swirl number Sn = 0.55–0.95) was suggested by taking the high burnout and low-NOx formation into account. [ABSTRACT FROM AUTHOR]

Although N 2 dilution is effective in reducing NO X emissions in hydrogen engines, it decreases thermal efficiency. Utilizing Ar with N 2 as a dilution gas can improve thermal efficiency while reducing NO X emissions. However, the specific effects and mechanisms of the mixed dilution of Ar and N 2 on the combustion and emission characteristics of hydrogen engines remain uncertain. This study examined the influence of Ar and N 2 on the combustion and NO X emissions by adding Ar and N 2 to the intake gas at various dilution rates. The examined cases were as follows: Case 1 (N 2 = 100%), case 2 (N 2 :Ar = 80%:20%), case 3 (N 2 : Ar = 50%:50%), case 4 (N 2 :Ar = 20%:80%), and case 5 (Ar = 100%). The findings indicate that increasing the N 2 ratio in the dilution significantly reduces NO X emissions, but it also reduces the combustion rate. In contrast, increasing the Ar proportion enhances combustion, resulting in higher peak values of the in-cylinder pressure, temperature, and heat release rate. In case 1 (N 2 = 100%), the NO X emissions decreased from 255 to 3 ppm when the dilution rate increased from 5% to 20%. However, this also caused a significant decrease in the thermal efficiency from 44.4% to 22%. This limitation can be mitigated by appropriately increasing the proportion of Ar. Optimal results, with lower NO X emissions (250–500 ppm) and higher thermal efficiency (47.6%–49.3%), were achieved with a dilution rate of 17%–27% and an Ar proportion of 80%–90%. • The effect of Ar/N 2 dilution on combustion and NO X emission of hydrogen engines. • The thermal efficiency increases with the increase of Ar proportion in dilution gas. • NO X emission decreases with the increase of N 2 proportion in dilution gas. • About DR 23%, Ar: N 2 = 80%：20%, low NO X emission and high thermal efficiency are obtained. [ABSTRACT FROM AUTHOR]

An injection mechanism which is split injection was found to reduce emissions in Diesel engines. In this mechanism, split injection proportion and split injection timing was varied and analyzed to reduce engine emissions. Injection proportion was varied at 25% of the pilot and 75% of the fuel as main injection and timing as 54° ATDC (after top dead center) and 40° ATDC for split injection. Since a homogeneous mixture occurs in this pilot injection, combustion is becoming complete for Diesel Engine. Hence, BTE was increased by 1.5% for timing 40° ATDC and 12° BTDC (before top dead center) and reduced by 1.4% for timing 54° ATDC and 12° BTDC. The reduction in BTE for 54° ATDC is because the increase in timing increases cooling effect of air and combustion rating was reduced. Also, combustion takes place at low temperature itself due to homogeneous mixture. So, NOx emission was also reduced by 8.4% and 18.6% for 40° ATDC and 54° ATDC injection timing respectively. The other emissions like HC and CO were also observed to be reduced upto 35% and 11% respectively due to increase in homogeneous mixture in Diesel Engine. [ABSTRACT FROM AUTHOR]

The study focused on the effects of the interaction between axial and radial secondary air and the reductive intensity in reduction region on combustion characteristics and NOx emission in a 30 kW preheating combustion system. The results revealed that the interaction and reductive intensity influenced the combustion in the down-fired combustor (DFC) and NOx emission greatly. For the temperature distribution, the interaction caused the position of the main combustion region to shift down as R2–12 (ratio of axial secondary air flow to radial secondary air flow) decreased or λ2 (total secondary air ratio) increased, and there was the interplay between both of their effects. As R3–12 (ratio of first-staged tertiary air flow to second-staged tertiary air flow) increased, the decrease in the reductive intensity also caused the above phenomenon, and the peak temperature increased in this region. For the NOx emission, the interaction affected the NOx reduction adversely when λ2 or R2–12 was higher, and the range of this effect was larger, so that the NOx emission increased obviously as they increased. The decrease in the reductive intensity caused the NOx emission increased under the homogeneous reduction mechanism, while was unchanged at a high level under the heterogeneous reduction mechanism. For the combustion efficiency, the interaction improved the combustion efficiency as λ2 increased when R2–12 was lower, while reduced it as λ2 increased excessively when R2–12 was higher. The proper decrease in the reductive intensity caused the combustion efficiency increased obviously, while was hardly improved further when the intensity decreased excessively. In this study, the lowest NOx emission was only 41.75 mg/m3 without sacrificing the combustion efficiency by optimizing the interaction and reductive intensity. [ABSTRACT FROM AUTHOR]

The hydroxyl radical (OH) is the most important oxidant on global and local scales in the troposphere. Urban OH controls the removal rate of primary pollutants and triggers the production of ozone. Interannual trends of OH in urban areas are not well documented or understood due to the short lifetime and high spatial heterogeneity of OH. We utilize machine learning with observational inputs emphasizing satellite remote sensing observations to predict surface OH in 49 North American cities from 2005 to 2014. We observe changes in the summertime OH over one decade, with wide variation among different cities. In 2014, compared to the summertime OH in 2005, 3 cities show a significant increase of OH, whereas, in 27 cities, OH decreases in 2014. The year-to-year variation of OH is mapped to the decline of the NO2 column. We conclude that these cities in this analysis are either in the NOx-limited regime or at the transition from a NOx suppressed regime to a NOx-limited regime. The result emphasizes that, in the future, controlling NOx emissions will be most effective in regulating the ozone pollution in these cities.

[Introduction] As the country has set ambitious targets in carbon peaking and carbon neutrality for the energy sector, there is a growing demand for technology improvements of low-carbon emission for power station gas turbines. It is urgent to explore the path of the key technology for this goal in China. The lean premixed combustion technology of gas turbine can make the air volume for combustion deviate from the theoretical air volume, which is the main technology to reduce NOx emission at present. At the same time, by mixing hydrogen in natural gas when combusting, it can effectively reduce the consumption of fossil energy and reduce carbon emissions. [Method] In this paper, a one-dimensional premixed free propagation flame model was established by Chemkin-Pro software, and the effects of different equivalent ratios, initial temperatures, initial pressures, and hydrogen-blended ratios on combustion temperatures, combustion rates, pollutant generation concentration, combustion free radicals, and chain reactions were compared. The temperature distribution, fuel component change and emission characteristics of combustion process were simulated. [Result] It is found that by mixing hydrogen in natural gas when combusting, fossil energy consumption and carbon emissions can be effectively reduced. However, the higher flame temperature brought by the lean premixed combustion of natural gas mixed with hydrogen will promote the generation of NOx, and at the same time, more CO will be produced at a lower equivalent ratio. [Conclusion] Based on the above research, the key data of hydrogen-blended combustion are obtained, which lays a foundation for the completion of hydrogen-blended combustion technology route.

Pulverized coal preheating combustion technology has been proven to be a clean and efficient combustion technology. In view of the limited space and load-bearing capacity around the large coal-fired boiler, a novel technology and system with a compact entrained-flow gasifier to preheat pulverized coal is proposed for the first time. The preheating characteristics in the gasifier and the combustion characteristics of the preheated fuel in the down-fire combustor (DFC) are studied on the novel self-built preheating combustion test rig. The migration and transformation of coal nitrogen during the preheating combustion are investigated. The results show that the experiment system can operate continuously and steadily with small fluctuations in pressure and temperature. The temperature gradient in the gasifier is large, and the high temperature zone is located near the burner plane. The maximum temperature can reach 1 115 ℃, while the outlet temperature of the gasifier decreases to 850 ℃. The high temperature coal gas and char produced by the entrained-flow gasifier are provided to the DFC continuously and steadily. The volume fractions (dry basis) of CO, H2 and CH4 in high temperature coal gas are 13.15%, 8.72% and 0.78%, respectively. Compared to the raw coal, the size of the preheated char decreases. The 50% cut particle size of raw coal is 43 μm, while the preheated semi-coke is 24 μm. The specific surface area increases from 4.05 m2/g to 216.44 m2/g after preheating. At the same time, the pore volume of the char particles increases, and the combustion characteristics are improved. During the preheating process, 96.33% of volatile matter and 40.23% of fixed carbon are released into high temperature coal gas. Also, 69.74% of coal nitrogen is transformed in the gas phase, and 47.67% is converted into N2, the rest into NH3 and HCN. Stable combustion could be achieved with preheated fuels in the DFC with no ignition delay and a uniform temperature distribution. Most of the NH3 and HCN and the nitrogen released from char are converted into N2 in the main combustion zone. There is no NO generation in the main combustion zone. The CO and NOx emissions at the outlet of the DFC are 8.17 mg/Nm3 (6% O2) and 143.02 mg/Nm3 (6% O2), respectively. The combustion efficiency is 99.75%. After the pulverized coal is preheated by the new entrained-flow gasifier and burn in the DFC, only 4.69% of coal N is converted into NO.

Low-temperature combustion (LTC) concepts, such as homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC), aim to reduce in-cylinder temperatures in internal combustion engines, thereby lowering emissions of nitrogen oxides (NOx) and soot. These LTC concepts are particularly attractive for decarbonizing conventional diesel engines using renewable fuels such as methanol. This paper uses numerical simulations and a finite-rate chemistry model to investigate the combustion and emission processes in LTC engines operating with pure methanol. The aim is to gain a deeper understanding of the physical and chemical processes in the engine and to identify optimal engine operation in terms of efficiency and emissions. The simulations replicated the experimentally observed trends for CO, unburned hydrocarbons (UHCs), and NOx emissions, the required intake temperature to achieve consistent combustion phasing at different injection timings, and the distinctively different combustion heat release processes at various injection timings. It was found that the HCCI mode of engine operation required a higher intake temperature than PPC operation due to methanol’s low ignition temperature in fuel-richer mixtures. In the HCCI mode, the engine exhibited ultra-low NOx emissions but higher emissions of UHC and CO, along with lower combustion efficiency compared to the PPC mode. This was attributed to poor combustion efficiency in the near-wall regions and engine crevices. Low emissions and high combustion efficiency are achievable in PPC modes with a start of injection around a crank angle of 30° before the top dead center. The fundamental mechanism behind the engine performance is analyzed.

This study aimed to investigate the interrelationships between key harmful emission components, nitrogen oxides (NOx), and particulate numbers (PNs) in diesel engine exhaust and the control actuators of diesel engines. This research involved conducting a series of experiments under fixed parameters within an engine brake laboratory environment to elucidate these correlations. The objectives of this study were to conduct a comprehensive review of the relevant emissions technology literature and a comparative assessment of particle measurement methods based on dilution ratios and develop innovative aerosol preparation principles tailored to condensation particle measurement. Additionally, this research involved designing and implementing an aerosol preparation unit based on the newly developed principles, along with the creation of test cell control programs using the AVL PUMA Open TST editor interface and Visual Basic. Furthermore, this study was concerned with conducting evaluations of fixed-parameter engine dynamometer tests to explore the functional relationships between the emission of 10/23 nm particles, NOx emissions, common rail pressure variations, and exhaust gas recirculation levels. This study aimed to enhance the understanding of diesel engine emissions dynamics and contribute valuable insights for developing more efficient and environmentally friendly engine control strategies.

As a combustor that can reduce pollutant emissions, the trapped-vortex combustor can not only reduce the length of the combustor because of its radial classification technology, but also its design concept is inseparable from RQL (Rich burn, Quench, and Lean burn). In this paper, the effects of cavity equivalence ratio and fuel injection cone angle on combustion performance and NOx emission were studied by numerical simulation. It is found that the trapped-vortex combustor achieves RQL combustion mode. The increase of the cavity equivalence ratio results in the non-uniform fuel distribution. However, the fuel injection cone angle in the primary region has little effect on the fuel distribution. With the increase of the cavity equivalence ratio, the combustion efficiency and NOx emission first decrease and then increase, and outlet temperature distribution factor is positively correlated with the cavity equivalence ratio. The difference is that the outlet temperature distribution factor and combustion efficiency show almost the same law with the increase of injection cone angle in the primary region, and the NOx emission decreases, but the reduction is not significant.