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Flame stability and pollutant emission performances of a porous burner fueled with ammonia/hydrogen blend were investigated numerically in this study. In this regard, a 2D solver based on finite volume method was developed in order to simulate reacting flow and heat transfer modes through a porous medium. Combustion characteristics in terms of porous structure, equivalence ratio and fuel component were studied and the pollutant emission trends were discussed. Flame stability limit was observed to be extended with increasing equivalence ratio regardless to ammonia fraction. Results proved that addition of ammonia in the fuel blend reduced the flame stability limits and thermal flame thickness but led to the enhanced NO emission. Increasing equivalence ratio led to a decrease in thermal flame thickness under fuel-lean conditions while it caused that the thickness of flame zone to be increased slightly under fuel-rich conditions. It was found that flame stability limits were extended as the mean pore diameter of the porous medium increased. The maximum amounts of NO concentration were achieved at stoichiometric conditions while, NO emission increased as equivalence ratio increased at fuel-lean conditions and it decreased as equivalence ratio increased at rich combustion regimes. [ABSTRACT FROM AUTHOR]

When semi-coke is co-combusted with bituminous coal with higher sulfur content in a circulating fluidized bed (CFB) boiler, the necessity of desulfurization in furnace increases. Meanwhile, limestone, which is a widely used desulfurizing agent, also has an effect on NO emission. In order to explore its effect during co-combustion, the combustion experiments were conducted in both a CFB test rig and a fixed bed reactor. The results show that blending semi-coke with bituminous coal will change the occurrence forms of nitrogen in the fuel and more fuel NO is released during the devolatilization stage. During the desulfurization process, CaO will be generated through the calcination reaction. It has catalytic effects on both the oxidation and reduction reactions of NO, and the catalytic strength in these two types of reactions decides the final effect on NO emission. For the blended fuel with 50% semi-coke and 50% bituminous coal (SC50BC50), the NO emission initially increases and then decreases as the Ca/S molar ratio increases from 0 to 4 at 900°C. Compared to the situation of burning semi-coke alone, semi-coke in the blended fuel has more opportunities to contact with CaO under the same Ca/S molar ratio, leading to the heterogeneous reduction reaction of NO enhanced. As the combustion temperature increases from 800°C to 1000°C, the effect of limestone on NO emission will change from promotion to inhibition. This is because the higher combustion temperature can intensify not only the catalytic reduction of NO precursors in the dense-phase region, but also the reaction between NO and unburnt char in the dilute-phase region in the CFB. Besides, the lower O2 concentration in the atmosphere is also favorable for enhancing the catalytic effect of CaO on the NO-char reduction reaction for semi-coke and SC50BC50, so the conversion of fuel-N/NO will be inhibited compared with the cases without limestone. The achievements of this study are beneficial for the coordinated control of NOx and SO2 during the co-combustion of semi-coke and bituminous coal. [ABSTRACT FROM AUTHOR]

To improve the NO modelling in turbulent flames, the flamelet/progress variable (FPV) model is extended by introducing NO mass fraction into the progress variable and incorporating an additional NO transport equation. Two sets of flamelet databases are tabulated with progress variables based on major species and NO mass fraction, respectively. The former is used for the acquisition of the main thermochemical variables, while the latter is employed for NO modelling. Moreover, an additional transport equation is solved to obtain the NO mass fraction, with the source term corrected using the scale similarity method. Model assessments are first conducted on laminar counterflow diffusion flames to identify lookup-related errors and assess the suitability of progress variable definitions. The results show that the progress variables based on major species and NO could correctly describe the main thermochemical quantities and NO-related variables, respectively. Subsequently, the model is applied to the large eddy simulation (LES) of Sandia flames. The results indicate that the extended FPV model improves the NO prediction, with a mean error for NO prediction at 55%, significantly lower than those of existing FPV models (130% and 385%). The LES with the extended FPV model quantitatively captures NO suppression in the mid-range of Reynolds numbers from 22 400 (Flame D) to 33 600 (Flame E), but underestimates the NO suppression at higher Reynolds numbers from 33 600 to 44 800 (Flame F). This underprediction is primarily attributed to the underestimation of local extinction levels in flames with high Reynolds numbers. [ABSTRACT FROM AUTHOR]

Carbon-free ammonia is a promising hydrogen energy carrier. Using ammonia as gas turbine fuel can effectively reduce carbon emissions. This study examines thermoacoustic instabilities of partially premixed CH 4 /NH 3 flame in a laboratory-scale swirl burner. Results show that as α NH 3 increases from 0 to 20%, the co-firing flame switches from stable mode to medium-frequency oscillation mode (105.4–151.2Hz) and then to low-frequency oscillation mode (36.7–44.1Hz). The oscillation intensity first increases and then decreases. Increasing α NH 3 and combustion chamber length will expand the unstable Φ range and enhance the pressure and heat release pulsation. When α NH 3 = 20%, CO 2 emissions are reduced by 12.5%, while NO increases sharply to over 1000 ppm. The flame is more likely to induce the low-frequency oscillation at high Φ. The shorter combustor can mitigate thermoacoustic instability. • Thermoacoustic instability of partially premixed CH 4 /NH 3 flame are studied. • Thermoacoustic frequency decreases as NH 3 ratio and equivalence ratio increase. • Thermoacoustic effect is weaker in short combustion chambers. [ABSTRACT FROM AUTHOR]

To improve energy savings and emission reduction in industrial heating furnaces, this study investigated the impact of various molar fractions of hydrogen on natural gas combustion and compared the results of the Non-Premixed Combustion Model with the Eddy Dissipation Combustion Model. Initially, natural gas combustion in an industrial heating furnace was investigated experimentally, and these results were used as boundary conditions for CFD simulations. The diffusion flame and combustion characteristics of natural gas were simulated using both the non-premixed combustion model and the Eddy Dissipation Combustion Model. The results indicated that the Non-Premixed Combustion Model provided simulations more consistent with experimental data, within acceptable error margins, thus validating the accuracy of the numerical simulations. Additionally, to analyze the impact of hydrogen doping on the performance of an industrial gas heater, four gas mixtures with varying hydrogen contents (15% H2, 30% H2, 45% H2, and 60% H2) were studied while maintaining constant fuel inlet temperature and flow rate. The results demonstrate that the Non-Premixed Combustion Model more accurately simulates complex flue gas flow and chemical reactions during combustion. Moreover, hydrogen-doped natural gas significantly reduces CO and CO2 emissions compared to pure natural gas combustion. Specifically, at 60% hydrogen content, CO and CO2 levels decrease by 70% and 37.5%, respectively, while NO emissions increase proportionally; at this hydrogen content, NO concentration in the furnace chamber rises by 155%. [ABSTRACT FROM AUTHOR]

The response of NO emission at 5.3 μm in the thermosphere to the geomagnetic storm on 24 April 2023 is analyzed using TIMED/SABER observations and TIEGCM simulations. Both the observations and the simulations indicate a significant enhancement in NO emission during the storm. Observations show two peaks around 50°S/N in the altitude–latitude distribution of NO emission and its relative variation. Additionally, the peak emission and enhancement are stronger on the nightside compared with the dayside. The peak altitude in the Northern Hemisphere is approximately 2–10 km higher than in the Southern Hemisphere; meanwhile, the peak altitude on the dayside is approximately 2–8 km higher than that on the nightside. Simulations reveal three peaks around 50°S, the equator, and 65°N, with peak altitudes at higher latitudes being slightly lower than those observed. In general, the altitude–latitude distribution structure of the relative variation in simulated NO emission matches observations, with two peaks around 50°S/N. TIEGCM simulations suggest that the increase in NO density and temperature during a geomagnetic storm can lead to an increase in NO emission at most altitudes and latitudes. Furthermore, the significant enhancement around 50°S/N is mainly attributed to the changes in NO density. [ABSTRACT FROM AUTHOR]

To investigate the combustion process and reduce Nitric Oxide (NO) emissions in the vertical heating flue of air-staged coke ovens, a three-dimensional computational fluid dynamics method was applied to simulate the combustion process. The model integrates the k-ε turbulence model with a multi-component transport combustion model. The impact of air staging on the flow field and NO emissions in the vertical fire chamber was assessed through comparative validation with experimental data. The impact of air staging on the flow field and NO emissions in the vertical fire chamber was assessed through comparative validation with experimental data. Based on this research, the effects of the excess air coefficient and air inlet distribution ratio on NO emission levels at the flue gas outlet were further investigated. Analysis of the flow field structure, temperature at the center cross-section, component concentration, and NO emission levels indicates that as the excess air coefficient increases, the NO emission levels at the flue gas outlet initially decrease and then increase, accompanied by corresponding changes in outlet temperature. At an air excess factor of 1.3 and an air inlet distribution ratio of 7:3, NO emission levels are at their lowest—53% lower than those in a conventional coke oven—and the temperature distribution in the riser channel is more uniform. These results provide a theoretical foundation for designing the air-staged coke oven standing fire channel structure. [ABSTRACT FROM AUTHOR]

Recently, many studies have been published in the field of using different biodiesels in diesel engines. However, the use of these fuels has not been used for different case studies. Moreover, scholars have not paid attention to factors like the price of utilized biodiesels and their costs, considerably. In the present paper, we are concerned with the use of palm oil as a cheap and abundant biodiesel in two different light and heavy diesel engines, and its environmental blueprint was also investigated for Helsinki. A CFD code was taken into consideration to estimate the amount of NO and PM emissions from different diesel engines. Although many different diesel engines can be utilized in a city, however, this research showed how an engine fueled by palm-based biodiesel can be balanced to satisfy the requirements related to the limitation of emissions for Helsinki, annually. It was found that, for this region, the 30% palm oil/diesel mixed fuel led to an insignificant increase in NOx emissions by 0.2% for the light-duty engine and a decrease of 0.7% for the heavy-duty engine whereas a significant decrease in PM emissions by 24 and 11.5% for light-duty diesel engine and heavy-duty diesel engine, respectively. The results of the presented paper demonstrated that there is a narrow border between the fuel waste amount and the exhaust NOx, highlighting the need for obtaining a balanced state between them for different cities based on their sources and their pollution status. [ABSTRACT FROM AUTHOR]

In the present study, the effects of water addition into intake air (WAIA) on combustion, engine performance, and NO emission in diesel engines were investigated numerically. Here, Ferguson's thermodynamic-based zero-dimensional single-zone cycle model was used and improved with new approaches for neat diesel fuel (NDF) and WAIA. After controlling the model's accuracy for NDF and WAIA, the effects of WAIA were first investigated in the Renault K9K diesel engine. For (5 and 7.5)% water ratios (WRs), effective power decreased by 4.26% and 7.37%, brake specific fuel consumption (BSFC) increased by 6.95% and 10.56%, and NO emission reduced by 12.43% and 16.39%, respectively. In the second application, the effects of (3, 6, and 9)% WRs on combustion, engine performance, and NO emission in the Renault M9R diesel engine were investigated at 4000 rpm by using this developed model. For (3, 6, and 9)% WRs, BSFC increased by 0.97%, 3.39%, and 8.25%, and NO emission decreased by 10.31%, 17.66%, and 34.20%, respectively. For (3 and 6)% WRs effective power increased, and NO emission decreased significantly without considerable deterioration in the BSFC at 4000 rpm. Cylinder pressure values and heat release rate increased for (3 and 6)% WRs and decreased for 9% WR. [ABSTRACT FROM AUTHOR]

New challenges posed to internal combustion engines require a fresh approach and the application of modern simulation methods. This study focuses on the numerical analysis of the co-combustion process of diesel fuel with butyl alcohol in a dual-fuel, self-ignition internal combustion engine based on a three-dimensional engine model developed in AVL Fire software. The influence of butanol content, ranging from 0 to 60 %, on engine performance and emissions was investigated. Increasing the amount of butyl alcohol burned with diesel fuel leads to a delay in ignition, decreases maximum cylinder pressure and temperature, and increases the rate of pressure rise and heat release rate. For alcohol content of 20 % and 40 %, there is an increase in pressure and indicated power compared to diesel fuel alone. The addition of butanol to diesel fuel reduces the specific emissions of nitrogen oxides and Soot in the dual-fuel engine. The most favorable case was with a 40 % butanol content. For DB40, the highest IMEP (0.69 MPa) and Ni (10.37 kW) values were obtained, along with the highest TE efficiency (43.64 %). In comparison to D100, lower NO and Soot emissions were achieved for this case by 35 % and 65 % respectively. [ABSTRACT FROM AUTHOR]

In the present study, premixed ammonia-methane combustion within a two-layer porous burner was investigated experimentally in order to evaluate the pollutant emissions. The effects of alumina spheres diameter, equivalence ratio and ammonia fraction on the flame stability limits, CO and NO pollutant emissions were considered. The tests were performed for equivalence ratios from 0.8 to 1, ammonia fraction from 20% to 80% and a range of alumina spheres diameters from 5 to 40 mm. Measurements illustrated that increasing the equivalence ratio improved the flame stability limits regardless of ammonia fraction while flame stability limits decreased with increasing the ammonia fraction. Results indicated that for the mixtures with ammonia content less than 50%, increasing ammonia fraction caused increase in NO emission regardless to the equivalence ratio, while for mixtures with ammonia fractions higher than 50%, the NO emission decreased slightly as ammonia content increased. Meanwhile, with increasing the ammonia fraction, CO concentration decreased at examined equivalence ratios. It was found that increasing equivalence ratio increased the NO emission, while CO concentration decreased as equivalence ratio increased. Measurements proved that decreasing the diameter of alumina spheres caused decrease of NO and CO quantities regardless to equivalence ratio. [ABSTRACT FROM AUTHOR]

In the present study, LESs of a modeled typical combustion zone of a 1000 MW S-CO2 coal-fired boiler using a hybrid flamelet/progress variable model are conducted for the first time. In the hybrid model, both the fuel-N from volatiles and char are considered, and two progress variables are used for major species and NO, respectively. The combustion and NO formation characteristics at different regions are qualitatively and quantitatively investigated. The results indicate that the mixture of primary air and secondary air, the high-temperature wall as well as the adjacent flame can promote the pulverized coal combustion (PCC) and NO formation. In addition, the effects of wall temperature and flue gas recirculation on PCC and NO formation are investigated. The results show that compared with the supercritical H2O boiler, a slight rise of 2.08% and 3.05% for temperature and NO production can be observed in the supercritical CO2 boiler due to a higher wall temperature; flue gas recirculation with a recirculation rate of 27% can effectively reduce the production of NO by 57.6% in the supercritical CO2 boiler.

The purpose of this study is to introduce an air nozzle on top of a top-fired heating furnace designed for oil shale retorting, using numerical simulations to delineate enhanced gas flow, heat transfer, and combustion in the furnace. Traditional heating flow fields, temperatures, and nitric oxide (NO) emission behaviors were carefully studied alongside furnaces fitted with various top jet systems. Our findings conclude that the introduction of top air supply leads to the development of a stable vortex pair in the combustion chamber, enhancing flame stability. Moreover, the incorporation of the top jet structure noticeably enhances the combustion chamberâs temperature and homogeneity, retaining the benefits of swirl combustion, optimizing high-speed entrainment effects, promoting gas flow stratification, and substantially reducing NO production. With the implementation of the top air supply, NO emission is reduced to below 50 mg/Nm3, while peak incomplete combustion heat loss decreases to less than 1%, which successfully helps achieve the goal of improving thermal efficiency, saving energy, and reducing emissions from the heating furnace.

The laminar burning velocity and NO formation process of ammonia-hydrogen combustion within a two-stage combustion chamber were investigated numerically in the present study. A chemical reactor network method involving perfectly stirred reactor, plug flow reactor, and partially stirred reactor configurations with the 24-species Xiao mechanism was implemented to simulate the premixed ammonia-hydrogen-air combustion process. The effects of inlet temperature and pressure conditions on the laminar burning velocity were investigated. Results proved that elevated pressure condition decreased primary flame thickness leading to lower laminar burning velocity while inlet temperature increased flame temperature which in turn increased the laminar burning velocity. Investigation of the effect of humidification on the laminar burning velocity showed that humidification can counteract the effect of high inlet temperature. The NO emission studies indicated a twofold impact of pressure on NO formation processes: preventing NO formation in the primary combustion zone, and promoting thermal NO formation in the lean combustion zone. The minimum amounts of NO emission were obtained at total equivalence ratios of 0.4. Humidification prevented the NO formation in the lean combustion through the competitive effect of H2O on O, whilst temperature effect was comparatively small. Humidity and pressure were optimized in the two-stage configuration achieve both low emission and high efficiency. [ABSTRACT FROM AUTHOR]

A hydrogen‐fueled multiple direct‐injection trapped vortex combustor is proposed to improve the unstable combustion and reduce NO emission. The effects of bluff‐body depth, bluff‐body height, and bluff‐body angle on the combustion flow characteristics are analyzed. NO emission is used as the main response value, the response surface method (RSM) is adopted to optimize the bluff‐body depth, bluff‐body height, and bluff‐body angle. The results show that the bluff‐body depth, bluff‐body height, and bluff‐body angle have significant effects on the NO emission, with the increase of the three parameters, NO emission first drops and then rises, but the effects on the pressure loss and outlet temperature distribution factor (OTDF) are very small. After optimization by RSM, the optimal bluff‐body parameters are the bluff‐body depth a = 56.5 mm, the bluff‐body height b = 128.9 mm, and the bluff‐body angle α = 77.6°. Under these circumstances, the maximum radial distances of the front concave vortex and the rear concave vortex reach 48 mm and 57 mm, respectively, which enhances the combustion stability. Furthermore, NO emission of 1.64 ppmv in the optimization structure is significantly optimized compared to NO emission of 4.32 ppmv in the original structure. [ABSTRACT FROM AUTHOR]

To enhance ammonia's flammability, blending methane with ammonia is a viable strategy to improve the laminar burning velocity of ammonia combustion. We conducted three-dimensional numerical simulations to investigate the thermal performance, the 2nd thermodynamic law efficiency, and NO emissions of a micro-combustor fuelled by ammonia/methane. Three key parameters are identified and examined. They include: 1) the inlet volume flow rate, 2) the CH4 mole blended ratio, 3) the N 2 dilution rate. It is found that increasing the inlet volume rate give rise to an increase of the combustor outer wall temperature, and so the thermodynamic second-law efficiency, but a reduction of NO emissions. For example, when the inlet volume flow rate is set to 14.4 mL/s, the wall temperature and 2nd law efficiency are increased by 36 % and 21 % respectively, but the NO emission is reduced by 15 %, in comparison with those in the presence of 7.2 mL/s inlet flow. While an increase of the CH 4 blended ratio (molar fraction) is shown to have limited impact on the thermal performances. This variation of such blended ratio is found to be associated with a notable 22 % reduction of NO emissions. Additionally, injecting N 2 as a dilution gas is shown to be not beneficial to the thermal performance. However, NO emissions are reduced. When the N 2 dilution rate is set to 0.6, the wall temperature is found to be reduced by 173 K. However, 47 % more NO reduction is observed in comparison with those in the presence of the N_2 dilution rate being set to 0.3. • 3D numerical investigation of a micro-combustor fuelled by methane/ammonia is conducted. • Entropy generation analyses of the ammonia/methane-fuelled micro-combustor are performed. • Examining the effect of blending methane with ammonia on thermodynamic performances is conducted. • NO emissions from the ammonia/methane-fuelled micro-combustor are evaluated. • A reduced chemical reaction mechanism of ammonia-methane combustion is proposed. [ABSTRACT FROM AUTHOR]

Burning hydrogen-rich syngas fuels derived from various sources in combustion equipment is an effective pathway to enhance energy security and of significant practical implications. Emissions from the combustion of hydrogen-rich fuels have been a main concern in both academia and industry. In this study, the NO and CO emission characteristics of both laminar and turbulent counterflow premixed hydrogen-rich syngas/air flames were experimentally and numerically studied. The results showed that for both laminar and turbulent counterflow premixed flames, the peak NO mole fraction increased as the equivalence ratio increased from 0.6 to 1.0 and decreased as the strain rate increased. Compared with the laminar flames at the same bulk flow velocity, turbulent flames demonstrated a lower peak NO mole fraction but broader NO formation region. Using the analogy theorem, a one-dimensional turbulent counterflow flame model was established, and the numerical results indicated that the small-scale turbulence-induced heat and mass transport enhancements significantly affected NO emission. Considering NO formation at the same level of fuel consumption, the NO formation of the turbulent flame was significantly lower than that of the laminar flame at the same level of fuel consumption, implying that the turbulence-induced heat and mass transfer enhancement favored NOx suppression. [ABSTRACT FROM AUTHOR]

During oxy-fuel combustion, the NO emission can be inhibited by the strongly reductive atmosphere caused by the high proportion of gasification reaction, which is a unique feature that differs from air combustion. The alkali and alkaline earth metals (AAEMs) contained in coal ash can catalyze gasification reactions, promoting the homogeneous reduction process of NO. Besides, AAEMs also suppress NO emission through catalyzing the NO heterogeneous reduction by char (CNO). Both catalytic effects of AAEMs have been studied at relatively low temperatures (below 1000 °C) in a simple atmosphere (pure CO2). However, the catalytic effect of AAEMs on NO reduction is still unclear during oxy-fuel combustion due to the more complex reaction atmosphere, higher reaction temperatures, and the presence of gasification reactions. In this work, the effect of different factors on the catalytic effect of AAEMs under O2/CO2 atmosphere is investigated. Results show that the order of the catalytic effect of AAEMs on NO reduction is Na > K > Ca > Mg, with the highest NO reduction efficiency of 30 % for Na. The catalytic effect of Na on NO reduction weakened as the temperature increases. When the temperature increased from 1373 K to 1573 K, the NO reduction efficiency (ηNO) of Na decreased from 30 % to 6 %. While the catalytic effect of Na on NO reduction strengthened as the oxygen concentration increases. When the O2 concentrations increased from 10 vol.% to 30 vol.%, the ηNO values of Na increased from 27 % to 35 %. The K-Na binary additive is more effective in reducing NO emissions than K and Na alone, with NO reduction efficiency as high as 46.8 % at a K/ Na is 1:2. Besides, the Raman test results reveal that K contributed to the conversion of amorphous carbon into a regular graphite crystal structure. Na disrupted the graphite structure resulting in more defective points appearing in the graphite lattice. These results are expected to provide a theoretical reference and new insights for the reduction of NO emission during oxy-fuel combustion.

The work presented here experimentally investigates the effect of pilot quantity (PQ) on combustion, performance and emission characteristics of an automotive diesel engine. All the experiments were performed at max torque speed of the test engine (1600 rpm) and 75 % of full engine load. Three PQs under consideration are 10 %, 20 % and 30 % of total fuel mass per cycle while maintaining the fixed pilot as well as main injection timings. The minimum PQ (10 %) considered in the study was found sufficient to enhance the in-cylinder thermodynamic conditions before main injection starts. Also, fuel injection pressure (FIP) was maintained constant at 500 bar initially. Obtained results showed that the pilot injection mode with 30 % PQ reduced nitrogen oxide (NO) emission as well as brake specific fuel consumption (BSFC) by 21.87 % and 1.46 % respectively compared to reference single injection mode while smoke emissions were increased by 77.64 %. In order to curb this negative effect of higher smoke emissions offered by pilot injection, FIP was increased from 500 bar to 700 bar and similar experiments were repeated. The experimental results demonstrated that higher FIP significantly reduced smoke emissions as well as fuel consumption under all the considered pilot injection modes with acceptable rise of NO emission which was still considerably lower than reference single injection mode. For e.g., when FIP was increased from 500 bar to 700 bar in case of pilot injection mode with 30 % PQ, smoke emissions and BSFC were reduced by 26.40 % and 2.14 % respectively, while NO emission was increased by 6.30 %. Therefore, it can be said that combination of pilot injection and high FIP leads to overall improvement in performance and emission characteristics of the test engine.

In this paper, the effect of H 2 addition to CH 4 on the NO emission of oxy-fuel, oxygen-enriched, and air-fuel MILD combustion is studied by numerical and chemical calculations. In the CFD section, the University of Lisbon MILD furnace is modeled. The results show that H 2 added to CH 4 is associated with a higher NO emission in the same oxidant composition. It is due to higher NO formation by NNH and thermal mechanisms. It can be found that by transformation from air-fuel to oxy-fuel MILD regimes, NO emission is reduced significantly. Moreover, the addition of H 2 prevents flame extinction that often occurs under MILD conditions when CO 2 replaces N 2. Reaction pathway analysis displays that dominant routes of NO emission in the H 2 -lean are N 2 O-intermediate for the air-fuel and oxygen-enriched conditions and NNH for the oxy-fuel MILD regime. In the H 2 -rich condition, the NNH mechanism plays the most important role in the NO production. • X H2,cr is known that in the higher values of it, NO emission increases dramatically. • H 2 added to CH 4 prevents flame extinction due to the replacement of CO 2 with N 2. • Change of diluent form N 2 to CO 2 reduces significantly NO emission under MILD regime. • H 2 -lean shows N 2 O-intermediate as main NO mechanism of air-fuel and oxygen-enriched. • NNH is the main route in the NO emission of CH 4 /H 2 -rich MILD regime. [ABSTRACT FROM AUTHOR]

This study analyzes the structure and emission of a biogas-hydrogen diffusion flame in a synthetic atmosphere composed by oxygen, nitrogen and carbon dioxide in a flameless regime. Particular attention is paid to the oxygen content in the oxidizer and the chemical effect of CO2 on the flame structure. The study is carried out in a laminar counter flow configuration over a wide range of strain rates. Detailed chemistry (GRI 3.0 mechanism) and complex thermal and transport properties are adopted in the calculations. The results obtained indicate that the structure of the flame, temperature and species, is very sensitive to the composition and to the amount of oxygen in the oxidizer stream. Pollutant species such as NO are reduced by a combination of decreased O2 content and increased CO2 volumes in the oxidant stream. The CO2 chemical effect is present as long as the O2 concentration is greater than 3% for the whole strain rate range. This effect leads to a decrease in temperature peaks, OH and NO. [ABSTRACT FROM AUTHOR]

Copyright of Gazi Üniversitesi Fen Bilimleri Dergisi Part C: Tasarım ve Teknoloji is the property of Gazi University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Pressurised oxy-fuel combustion (POFC) is a clean and efficient combustion technology with great potential. Due to the recycling of flue gas, the concentration of steam in the flue gas is higher than that of conventional combustion, which enriches the free radical pool in the flue gas and thus affects the emission of gaseous pollutants. Therefore, further research into the effect of high steam concentrations on NOx emission mechanisms in POFC is necessary. In this work, a fixed-bed reactor was used to conduct combustion experiments of volatiles and combined with chemical kinetic models to study the NO release characteristics for different pressures and steam concentrations in an O2/CO2 atmosphere at 800/900°C temperature. The results of the study indicated that the volatile nitrogen comes from the pyrolysis of part of pyrrole, pyridine, and all quaternary nitrogen in coal. The increase in temperature promoted the formation of NO during combustion. Higher pressure affects the main reaction pathway for NO formation, promoting NO consumption by HCCO and C2O groups while enhancing the overall NO reduction. Steam promoted NO consumption by NCO. In addition, steam increased the amount of H/OH groups during the reaction, which affected both NO formation and consumption. However, from the overall effect, the steam still inhibits the emission of NO. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, a modified catalytic converter was employed to treat the harmful exhaust gas pollutants of a twin-cylinder, four-stroke spark-ignition engine. This research mainly focuses on the emission reduction of unburnt hydrocarbons, carbon monoxide, and nitrogen oxides at low light-off temperatures. A sucrolite catalyst (sucrolite) was coated over the metallic substrate present inside the catalytic converter, and exhaust gas was allowed to pass through it. A scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectroscopy were used to investigate the changes in morphology, chemical compounds, and functional group elements caused by the reactions. Catalytic reactions were studied by varying the engine loads and bed temperatures, and the results were compared with those of the commercial catalytic converter. The results show that sucrose present in the catalyst was suitable at low temperatures while alumina was suitable for a wide range of temperatures. In the case of the modified catalytic converter, the maximum catalytic conversion efficiencies achieved for oxidizing CO and HC were 70.73% and 85.14%, respectively, and for reduction reaction at NOx was 60.22% which is around 42% higher than in commercial catalytic converter. As a result, this study claims that sucrolite catalyst is effective for low-temperature exhaust gas. [ABSTRACT FROM AUTHOR]

The simultaneous effect of the swirl number (SN) and equivalence ratio on NO and soot emissions in turbulent methane–air combustion was numerically investigated. The realizable k-ε model has been applied for modeling turbulence and eddy dissipation (ED) and probability density function (PDF) models were adopted for chemical reaction. The general gradient diffusion hypothesis (GGDH), high order algebraic model (HOGGDH), and simple eddy diffusivity model have been applied for modeling the turbulent heat flux (THF) vector. The Brooke–Moss model has been employed to predict the soot particle quantities. Comparing the results of the different numerical models (PDF and EDM with algebraic THF) with available experimental data indicated that employing the second-order models significantly leads to the modification of predicting temperature distribution in EDM. However, due to the effect of the PDF model on soot modeling, the PDF model provides more accurate results. The numerical simulations have been performed for various SNs (SN = 0–1.33) and equivalence ratios (0.125–0.75). In all of equivalence ratios the flame temperature and pollutants emission (NO and soot) were strongly affected by the SN. Also, the SN has different effects on NO and soot emission. Finally, for each of NO and soot emission, a correlation relative to effective combustion factors such as SN and equivalence ratio was presented. It is found that by increasing the equivalence ratio, the NO emission increases with a power of 2.3, and soot emission decreases with a power of 8.7. [ABSTRACT FROM AUTHOR]

The evolution of the power industry toward large‐scale automation and self‐monitoring provides the opportunity to optimize the technical and environmental performance of the plant with data‐driven methods with little changes in infrastructure. This article applies the artificial neural network (ANN) and genetic algorithm (GA) to predicting and optimizing NO emissions. Multiple linear regression models, correlation matrix, and research background are employed to find the most influential input features. The generated power, natural gas flow, the flow of gas recirculation fan, gas air heater temperature, and the amounts of oxygen in the stack are identified as the effective input features. Mean Square Error (MSE) and the coefficient of determination (R2) of best architecture (22 neurons in a hidden layer) are calculated 0.0117 and 0.96651, respectively. The Average Percentage Error (APE) is usually below 10%, meaning the model is in good agreement with real data. Finally, the Genetic Algorithm (GA) is used to minimize the amount of NO emissions. The ANN‐GA techniques reduce the NO emission by at least 32% for selected records, enabling us to optimally find the prominent features affecting NO emission by the operational conditions and low economic costs. [ABSTRACT FROM AUTHOR]

The influence of the blending ratio of pyrolyzed semi-char (SC) on the ignition, NO emission and burnout characteristics of lignite co-fired with SC was investigated in a 350 kW fuel-rich/lean combustion furnace. The flame temperature and concentrations of gaseous species including O2, CO, and NO, were measured in detail. The results indicated that the ignition characteristics of the blended fuel worsened with increasing SC blending ratio, such as an elongated ignition standoff distance. The addition of SC to lignite delayed the appearance of a stable flame boundary, and the stable combustion zone moved down, but the final combustion stability was gradually strengthened in the later combustion stage. NO emission concentration at the primary combustion zone (PCZ) outlet was the lowest at 472.6 mg/m3@6% O2 when the SC blending ratio was 25%. The combustion zone and reducing zone areas in PCZ were defined to evaluate the NO reduction characteristics, and quantitative analysis using a multiple linear regression model showed that heterogeneous reduction was more important than homogeneous reduction in lowering NO emissions. The Raman spectrum of the char sample indicated that the addition of lignite promoted the formation of small aromatic rings in the early ignition stage, corresponding to a higher char reactivity. The burnout ratio of pure lignite was maximal and was decreased by increasing the SC blending ratio. Synthetically, considering the ignition standoff distance, NO emission, and burnout ratio, the optimum SC blending ratio was estimated to be 25%. [ABSTRACT FROM AUTHOR]

Ammonia is an attractive clean fuel for its potential to reduce CO2 emission and fossil fuel consumption. However, ammonia combustion has been mainly discouraged by the low flammability and the high fuel NOx emissions. This study numerically investigates the effects of swirl intensity on combustion characteristics in swirl-stabilized ammonia/methane combustion. Large eddy simulation was performed by using OpenFOAM, and the accuracy of numerical results was validated by the experiment. The results show that swirl intensity will significantly affects the flow field and flame structure, and flame stability decreases with the swirl number increasing. The high swirl intensity leads to extinguishing at the flame root, while the low swirl intensity cannot generate the central recirculation zone to stabilize the flame. Selective non-catalytic reduction of NO (SNCR) is the key to controlling NO emission, the decrease of temperature will promote the reduction of NO, while the decrease of residence time will inhibit the reduction of NO. Meanwhile, SNCR will weaken the correlation between NO and OH in ammonia/methane combustion. NO emission will decrease with the swirl intensity increasing. In a word, medium swirl number (S ≈ 0.76) is proper to control NO emission and ensure flame stability.

Pyrolysis of biomass followed by combustion of pyrolytic vapors to replace fossil fuels is an economic low-carbon solution. However, the polycyclic aromatic hydrocarbons and N-containing species in biomass pyrolysis vapors result in the soot and NO emissions. The flue gas recirculation (FGR) technology, having the potential to reduce the soot and NO emissions, was introduced to the biomass pyrolysis-combustion system. In addition, it was numerically studied by simulating the biomass pyrolysis vapors based co-flow diffusion flames with CO2 addition. Both the experimental and simulated results showed that the FGR had significant suppression effects on the soot formation. When the FGR ratio (i.e., CO2 addition ratio) increased from 0% to 15%, the experimental and simulated soot volume fraction respectively decreased by 32% and 21%, which verified the models used in this study. The decrease in OH concentration caused by the CO2 addition was responsible for the decrease in the decomposition rate of A2 (A2+OH=A2–+H2O). Hence, more benzo(ghi)fluoranthene (BGHIF) was generated through A1C2H-+A2→BGHIF+H2+H, leading to the increase in inception rate. The decrease in benzo(a)pyrene (BAPYR) concentration was the major factor in the decrease in soot condensation rate. Moreover, the decrease in the C2H2 and OH concentrations was responsible for the decrease in the HACA surface growth rate. Furthermore, the simulated results showed that the NO concentration decreased by 0.4% when the content of CO2 was increased by 1 vol.%. The decrease in OH concentration suppressed the NO formation via decreasing reaction rates of N+OH=NO+H and HNO+OH=NO+H2O and enhanced the NO consumption via increasing reaction rate of HO2+NO=NO2+OH. [ABSTRACT FROM AUTHOR]

The major contribution to atmospheric air pollution is from the heavy vehicular emission. At present, it is rising at an alarming rate. These automotive pollutions can be reduced to a great extent by the exhaust gas after-treatment methods. Among these, catalytic converter (CC) is the major source to reduce regulatory emission in the internal combustion (IC) engine. Most catalytic materials work in some specific temperature ranges, and they are also costly. In this study, the zeolite 4A (ZSM 4A) and zeolite 5A (ZSM 5A) powder were converted into a solid mold and tested as a catalytic material in the converter. The experimental readings were taken with the fabricated CC at the exhaust with various loads (0, 4, 8, 12, and 16 kg) in the single-cylinder Kirloskar 5.2 kW diesel engine. Waste plastics were pyrolyzed into oil and blended with diesel in the 50:50 ratio of diesel plastic blend (DPB) for this study. Nitrogen oxide (NO) and hydrocarbon (HC) were reduced by 18% and 22% respectively for ZSM 5A and 12% and 16% respectively for ZSM 4A. [ABSTRACT FROM AUTHOR]

Biomass energy has drawn increased attention owing to its zero carbon emissions and large reserves. Pyrolysis instead of direct combustion is an efficient and clean way for biomass energy conversion. As a strong radiative species, H 2 O greatly affects the combustion processes. Despite the large concentration and fluctuation of H 2 O content in biomass pyrolysis gases (py-gas), radiation reabsorption effect has not been systematically investigated for py-gas combustion. In this study, one-dimensional simulations of premixed py-gas/air flames were conducted, using PREMIX code with both adiabatic and radiative models. The effects of H 2 O content and radiation reabsorption were examined. As H 2 O content in the py-gas mixture increased from 40% to 50%, the flame speeds decreased from 42.86 to 28.08 cm/s, while the relative differences caused by radiation reabsorption increased from 9.92% to 17.42%. Radiation reabsorption affected laminar flame speed primarily through the preheat-induced chemical effect, which was mainly controlled by HCO radical. The outlet mole fraction of NO was reduced by up to 13.56% when radiation reabsorption was considered. Reaction pathway analyses revealed that the NO emission was closely related to the outlet temperature and the peak NCO concentration, which were the limiting factors for the thermal-NO route and the fuel-NO route, respectively. [ABSTRACT FROM AUTHOR]

Ammonia co-firing is increasingly regarded as an effective strategy to reduce CO 2 emissions in coal-fired boilers. In this study, we introduce and evaluate two innovative fuel blending methods for ammonia-coal co-firing in a commercial 500 MW utility boiler: burner blending and in-boiler blending. Using computational fluid dynamics simulations, we investigated the effects of 20 % ammonia co-firing on heat transfer efficiency, fuel burnout rate, and pollutant emissions. The results show that while ammonia co-firing effectively reduces CO 2 emissions, it also leads to decreases in the furnace and furnace exit-gas temperatures due to the lower flame temperature and increased moisture production. Specifically, the total heat absorption by the water walls and heat exchangers decreased by 4.58 % in the burner blending method and 2.27 % in the in-boiler blending method compared to that with pure coal combustion. Although ammonia co-firing suppresses the generation of thermal NO, overall NO emissions increase significantly due to the substantial release of fuel NO. However, the in-boiler blending method demonstrated superior NO reduction, reducing NO emissions by 13.48 ppm compared to the burner blending method. In addition, the in-boiler blending method showed better combustion stability, achieving faster ignition and reducing the amount of unburned carbon in fly ash by 0.97 %, compared to that with the burner blending method. This is likely due to the higher concentration of combustible gases near the burner in the in-boiler blending system. These findings indicate that the in-boiler blending method is more effective than the burner blending method for ammonia-coal co-firing in a 500 MW utility boiler. This provides valuable insights into the implementation of ammonia co-firing in commercial boilers as part of efforts to achieve carbon neutrality. • Ammonia co-firing improved the combustibility of coal and reduced CO 2 emissions. • The influence of the ammonia co-firing blending method was evaluated. • In-boiler blending promoted faster ignition and reduced unburned carbon content. • Lower NOx emissions were produced from in-boiler blending than from burner blending. • In-boiler blending is preferable for ammonia co-firing in a tangential utility boiler. [ABSTRACT FROM AUTHOR]

Application of renewable methanol as an alternative fuel is a promising method for both CO 2 and NO emission reduction in thermal power plants fueled by coal. This work gives the first insight into coal-methanol co-combustion from the perspective of NO emission control with a wide range of methanol blending ratio (0%–100 %) involved. Air-staged strategy commonly applied in thermal power plants fueled by coal was considered, and the effects of some key parameters, including burnout air ratio, burnout air injection position and furnace temperature, were analyzed. Experimental results show a significant potential of NO emission reduction in coal-methanol co-combustion, as NO emission from methanol combustion is less than 30 % of that from coal combustion. The correlation between NO emission and methanol blending ratio is approximately linear. Air-staged strategy is still effective for NO emission reduction in coal-methanol co-combustion, and the effects of the key parameter is similar to that in coal combustion. Increase of burnout air ratio and delay of burnout air injection are beneficial, and NO emission can be reduced by more than 70 % compared with that under unstaged condition. Furnace temperature rise is harmful, whereas the corresponding NO emission increase is lower than 30 ppm (@6 % O 2). • NO emission is reduced by up to 70 % with methanol blending. • Effects of air staging are similar between co-combustion and coal combustion. • Furnace temperature rise causes NO emission increasing by up to 30 ppm. [ABSTRACT FROM AUTHOR]

The oxy-fuel combustion contributes to carbon capture, while the recirculation of flue gas brings about high concentrations of SO 2 and H 2 O, which can affect the transformation of minerals in high-alkali coal. The staged oxy-fuel combustion, as an effective method for NO x reduction, can also change the ash deposition behavior of high-alkali coal. Two kinds of diluting agents, including pure CO 2 for O 2 /CO 2 combustion and simulated "recycled flue gas" (CO 2 , SO 2 , and H 2 O) for O 2 /RFG combustion, were employed in the present work. The ash deposition and NO emission of high-alkali coal during the staged oxy-fuel combustion were simultaneously studied under O 2 /CO 2 and O 2 /RFG conditions. The conversion ratios of fuel-nitrogen to NO (C NO) and ash deposition efficiencies (E d) at different stoichiometric ratios in primary combustion zone (SR 1) and different oxygen concentrations were obtained. Afterwards, a series of tests were performed to further analyze the ash deposits. The experimental results show that as SR 1 increases from 0.6 to 1.2, C NO jumps from 2.0 % to 23.5 % (O 2 /CO 2 combustion) and from 1.9 % to 19.9 % (O 2 /RFG combustion). The additions of SO 2 and H 2 O can reduce the NO emission. With the rising SR 1 , E d under the O 2 /CO 2 and O 2 /RFG conditions decreases from 4.0 % to 2.6 % and from 4.8 % to 2.1 %, respectively. At high SR 1 , the CaSO 4 amount declines and the iron contributes less to the ash deposition. In O 2 /RFG combustion, the small sticky particles of sodium aluminosilicates on large particle surfaces reduce, and the large particles of calcium aluminosilicates shrink because some calcium produces CaSO 4. Moreover, the exposure of ferrous iron to H 2 O helps its oxidization so iron is harder to cause severe adhesion. As O 2 concentration rises from 21 % to 40 %, C NO shows an upward trend. Meanwhile, E d under the O 2 /CO 2 and O 2 /RFG conditions increases from 2.6 % to 3.7 % and from 2.3 % to 2.7 %, respectively. The present work is expected to provide some conducive information for the clean utilization of high-alkali coal and secure operation of boiler, as well as large-scale CO 2 capture. • Mixture of CO 2 , SO 2 , and H 2 O was used as "recycled flue gas" for O 2 /RFG combustion. • Ash deposition and NO emission of high-alkali coal were simultaneously focused on. • Different staged oxy-fuel conditions of high-alkali coal were investigated. • Additions of SO 2 and H 2 O can alleviate both the NO emission and ash deposition. • Effects of SR 1 and "recycled flue gas" on the ash deposition were summarized. [ABSTRACT FROM AUTHOR]

The article presents the results of numerical and analytical investigations of the influence of raw liquid natural gas (LNG) composition on parameters characterizing the combustion process. The high content of higher hydrocarbons influences the thermodynamic combustion process described with parameters like the adiabatic flame temperature, laminar flame speed and ignition delay time. A numerical study of the impact of LNG fuels on emission characteristics using the Cantera code has been performed. Results have shown that the change of grid natural gas to some types of liquid natural gas can result in an incomplete combustion process and an increase of emission of toxic compounds such as carbon monoxide and unburned hydrocarbons. For all investigated fuels the laminar flame speed rises by about 10% compared to natural gas, while the adiabatic flame temperature is nearly the same. The ignition delay time is decreased with an increase of ethane share in the fuel. The analysis of chemical pathways has shown that hydrogen cyanide and hydrogen formation is present, particularly in the high temperature combustion regimes, which results in an increase of nitric oxide molar fraction in flue gases by even 10% compared to natural gas. To summarize, for some applications, liquid natural gases cannot be directly used as interchangeable fuels in an industry sector, even if they meet the legal requirements. [ABSTRACT FROM AUTHOR]

The high-altitude areas of China are abundant in renewable energy and have a natural advantage in ammonia production. Based on this advantage, this paper proposes a co-combustion strategy for methane and ammonia to reduce carbon emissions in these areas. However, the NO emission characteristics associated with this strategy remain uncertain. A custom-designed combustion system capable of simulating high-altitude environments was used to investigate the effect of ammonia mixing ratio, equivalence ratio, and pressure on NO emission in methane/ammonia/air flames. Additionally, chemical kinetic calculations were conducted to explore the mechanisms of how sub-atmospheric pressure influences NO emission. The results indicate that for stoichiometric flames, NO increases with the ammonia mixing ratio. In fuel-rich flames, NO remains nearly constant once the ammonia mixing ratio exceeds 10 %. Sub-atmospheric pressure leads to higher NO, particularly in fuel-rich flames, where the increase can reach up to 24.4 %. Analysis of nitrogen reaction pathways and key radical concentrations reveals that sub-atmospheric pressure has a minimal effect on nitrogen conversion pathways. The variation in NO is achieved by altering the pathway contributions and the concentrations of H, NH, and N. This work provides direction and guidance for improving the application of methane and ammonia co-combustion in high-altitude areas., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)