Reduce NOx Emissions Research Articles

Inter-annual changes in transboundary air quality from KORUS-AQ 2016 to SIJAQ 2022 campaign periods and assessment of emission reduction strategies in Northeast Asia

Northeast Asia suffers from high concentrations of particulate matter (PM), prompting nations to actively implement emission reduction policies. This study evaluated the recent inter-annual changes in the chemical transformation and transboundary transport of PM over Northeast Asia, based on both ground and aircraft measurements, as well as WRF-Chem simulations, during two comprehensive campaigns: the Korea–United States Air Quality (KORUS-AQ) campaign in 2016 and the Satellite Integrated Joint Monitoring of Air Quality (SIJAQ) campaign in 2022, both conducted around the Korean Peninsula. Ground measurements in 2022 revealed significant reductions in air pollutants compared to 2016 levels. In the Beijing–Tianjin–Hebei region, PM2.5 and SO2 concentrations decreased by 47.2% and 73.9%, respectively, attributable to successful SOx and NOx emission reduction strategies. Similar trends were observed in downwind areas, including Seoul, where PM2.5 and SO2 levels declined by 30.0% and 41.4%, respectively. WRF-Chem model results indicated substantial decreases in sulfates, nitrates, and their precursors in both surface and upper atmosphere in 2022 compared to 2016. Moreover, model-calculated gas-to-particle conversion ratios, which peaked in the Yellow Sea in 2016, decreased by 15% in 2022 and shifted slightly eastward to the western Korean Peninsula. This shift suggests a potential decline in secondary PM formation processed in the Yellow Sea, coinciding with reduced long-range transport of gaseous pollutants. A comparison of model sensitivity experiments, accounting for both bottom-up emission changes and meteorological variations, revealed that while weather and climate factors such as precipitation and pressure patterns between 2016 and 2022 contributed to the overall decrease in PM concentrations, the primary driver was the reduction in emissions during this period. This study highlighted that the main driver of the substantial improvement in air quality over East Asia was the implementation of emission reduction policies targeting PM and its precursors in the main source regions in China.

Investigating combustion efficiency and NOx emission reduction in fluidized bed ammonia-coal co-firing

Ammonia, a carbon-free fuel, can significantly reduce CO2 emissions when co-fired with coal in power plants. Fluidized bed combustion, known for its excellent gas-solid mixing and low NOx emissions, is a promising method for ammonia-coal co-firing. However, challenges remain in optimizing ammonia injection and controlling nitrogen oxide emissions. This study investigates these aspects using a lab-scale fluidized bed reactor with flexible ammonia injection points. Key variables, such as ammonia co-firing ratios, injection location, temperature, and outlet oxygen concentration, are examined. The results show that with ammonia injection ratios up to 70 %, NO and N2O emissions slightly increase, while ammonia escape is maintained below 5 ppm. Air staging effectively controls NOx emissions, and higher temperatures promote N2O decomposition, but increase NOx levels. Ammonia injection does not raise unburned carbon content. Rate of production and sensitivity analyses highlight the role of OH radicals in ammonia conversion and identify the critical reactions affecting NO generation. This study highlights the feasibility of fluidized bed ammonia-coal co-firing technology.

Numerical simulation of natural gas-ammonia combustion characteristics in a U-shaped radiant tube

NH3, recognized as a carbon-free fuel and a high-energy–density renewable hydrogen carrier, holds promise as a low-carbon alternative fuel. However, its direct combustion is often posed with challenges such as a limited ignition zone and high NOX emissions. To address this, the present paper proposes a strategy to blend more reactive hydrogen-containing fuels with ammonia to enhance combustion stability and concurrently reduce NOX emissions. This study developed numerical models for natural gas-ammonia combustion within a U-shaped radiant tube. The dynamic characteristics of combustion flame flow fields inside the radiation tube were investigated across various mixing ratios, analyzing the effects of nitrogen-containing fuel temperature on NOX generation and elucidating NOX generation patterns under different mixing ratios. The findings indicated that a 30 % NH3 blending ratio in the radiation tube yielded uniform wall temperature distribution along its length, minimal circumferential temperature variation, and an outlet NOX emission of only 20.3 ppm. Furthermore, Pearson correlation coefficient calculations revealed strong correlations between NH3 concentration (0.97), URT temperature (0.88), and NOX generation rate (0.88) within the U-type radiation tube combustion flame and NOX emission content.

A novel approach of in-cylinder NOx control by inner selective non-catalytic reduction effect for high-pressure direct-injection ammonia engine

As an efficient hydrogen carrier and carbon-free fuel, ammonia shows great promise in realizing zero-carbon propulsions. However, challenges such as poor ignition stability, low combustion efficiency, and fuel-NOx emissions are yet to overcome. In this paper, the high-pressure direct-injection ammonia/diesel dual-fuel combustion mode (HPDF) with post injection strategy is proposed as a solution. The study reveals that HPDF combustion mode enables in-cylinder reduction of NOx, which is attributed to the selective non-catalytic reduction (SNCR) reaction. The results uncover that NH2, NH, and N radicals have a significant reducing effect on NO and NO2, while N2O serves as an important byproduct of the reduction reactions. Subsequently, the generated N2O can be further reduced to N2 through the involvement of O, H, and OH radicals. Building upon these findings, an innovative ammonia post injection method for reducing NOx emissions is explored. The post injection strategy effectively reduces the NOx emissions with only a minor decrease in indicated thermal efficiency, but an over-delayed post injection could also cause significant increase in N2O and unburned NH3 emissions. A post injection proportion of 20%-30% with appropriate post injection timing is found to achieve desired emission reduction. Overall, the HPDF combustion mode is a promising solution for ammonia engine, due to the high thermal efficiency and low nitrogen oxide emissions, as well as the ability to further reduce the NOx emissions through ammonia post injection strategy.

Experimental Studies on Utilization of Biogas with Biodiesel/Diesel Blends in a CI Engine

The present study covers the utilization of a gaseous alternative fuel, raw biogas, in a diesel engine. Biogas alone cannot run a diesel engine, because gaseous fuel cannot burn by compression. It can be supplied to the CI engines in dual fuel mode by using an air-biogas mixer device. In this work, it is aimed to investigate the performance and emission characteristics of a biogas-biodiesel/diesel dual fuel mode diesel engine by employing a venturi gas mixer device for providing a homogeneous mixture. The performance and emission characteristics of the engine operated by dual-fuel mode were experimentally investigated, and compared to diesel. The results indicated that biogas inducted at a flow rate of 1L/min was found to have better performance and lower emission, than that of the other flow rates. On the other hand, dual-fuel mode with a biogas flow rate of BD10 BG@1L/min showed an average reduction in BTE of 9.94% and an average increment of 8.82% in BSFC as compared to diesel. Whereas an increment in CO and HC by 5.18% and 3.01% respectively and an average reduction in NOx emissions by 14.91% as compared to diesel. Keywords: Alternative Fuel, Biogas, Biodiesel, Diesel Engine, Dual-fuel, Venturi Gas Mixer

Numerical simulation of co-firing LRC and ammonia in Pangkalan Susu 3 & 4 coal-fired steam power plant (CFSPP) capacity 210 megawatts

The effort to reduce CO2 and NOx emissions plays a crucial role in mitigating climate change, improving air quality, complying with environmental regulations, and promoting clean technology innovation. Ammonia, as an emission-free fuel, shows significant potential as a co-firing agent with Coal in coal-fired steam power plants (CFSPP). Previous studies have demonstrated promising results in emission reduction through ammonia co-firing. This research presents a numerical analysis based on Computational Fluid Dynamics (CFD) to investigate the co-firing of ammonia with low-calorific Coal (LRC) in the CFSPP Pangkalan Susu Units 3 and 4, with a capacity of 210 MW. The study employs fluid flow modelling and chemical reaction analysis using the Discrete Phase Model (DPM) to provide accurate predictions of temperature distribution and pollutant concentrations in pulverized coal boilers. Cofiring simulations were conducted with ammonia additions of 5 % and 15 % on a calorific basis. Injection experiments from each burner (A-D) were performed to identify the optimal injection location. The simulation results indicate changes in combustion characteristics, particularly in temperature distribution. The main finding reveals a temperature decrease when ammonia is added as a co-firing material, attributed to the higher H2O content, which leads to increased moisture losses. In terms of efficiency, co-firing showed a decline compared to the baseline combustion of 100 % LRC coal due to the more significant moisture losses. The highest reduction in CO2 emissions was observed when 15 % ammonia was injected from burner B in case #6, with a mass fraction value of 0.171 at the boiler outlet. Similarly, the most significant reduction in NOx emissions occurred with a 15 % ammonia co-firing from burner B, yielding a mass fraction value of 8.81E-04 at the boiler outlet. This co-firing technology is expected to enhance decarbonization efforts and optimize the use of renewable energy in the future.

Multiphase Reactions of Hydrocarbons Into an Air Quality Model With CAMx‐UNIPAR: Impacts of Humidity and NOx on Secondary Organic Aerosol Formation in the Southern USA

AbstractSecondary organic aerosol (SOA) mass in the Southern USA during winter‐spring 2022 was simulated by integrating Comprehensive Air quality Model with extensions (CAMx) with the UNIfied Partitioning‐Aerosol phase Reaction (UNIPAR) model, which predicts SOA formation via multiphase reactions of hydrocarbons. UNIPAR streamlines multiphase partitioning of oxygenated products and their heterogeneous reactions by using explicitly predicted products originating from 10 aromatics, 3 biogenics, and linear/branched alkanes (C9‐C24). UNIPAR simulations were compared with those using Secondary Organic Aerosol Partitioning (SOAP) model, which uses simple surrogate products for each precursor. Both UNIPAR and SOAP showed similar tendencies in SOA mass but slightly underpredicted against observations at given five ground sites. However, SOA compositions and their sensitivity to environmental variables (sunlight, humidity, NOx, and SO2) were different between two models. In CAMx‐UNIPAR, SOA originated predominantly from alkanes, terpenes, and isoprene, and was influenced by humidity, showing high SOA concentrations with wet‐inorganic salts, which accelerated aqueous reactions of reactive organic products. NO2 was positively correlated with biogenic SOA because elevated levels of nitrate radicals and hygroscopic nitrate aerosol effectively oxidized biogenic hydrocarbons at night and promoted SOA growth via organic heterogeneous chemistry, respectively. Anthropogenic SOA, which formed mainly via daytime oxidation with OH radicals, was weakly and negatively correlated with NO2 in cities. In CAMx‐UNIPAR, the sensitivity of SOA to aerosol acidity (neutral vs. acidic aerosol at cation/anion = 0.62) was dominated by isoprene SOA. The reduction of NOx emissions could effectively mitigate SOA burdens in the Southern USA where biogenic hydrocarbons are abundant.

Ground ozone rise during the 2022 shanghai lockdown caused by the unfavorable emission reduction ratio of nitrogen oxides and volatile organic compounds

Ground-level ozone (O3) pollution has shifted from a scientific issue to a key focus of governmental action in China. In recent years, the concentration of NO2 in Shanghai has shown a decreasing trend of 3.7% annually, but ozone concentrations have exhibited significant interannual variability, particularly with a noticeable increase in 2022. This study focuses on investigating the mechanisms behind the increase in ozone concentration during the COVID-19 pandemic control period in 2022 in Shanghai, utilizing a combination of ground observation data, observation-based models, and chemical transport models for analysis. The results indicate that during the lockdown period, the mean values of daily maximum 8-h average O3 concentrations (MDA8 O3) in Shanghai increased by 17 μg/m³, with emission-related factors contributing 65.3%, primarily due to a blanket reduction in VOCs and NOx emissions during the lockdown, with a reduction ratio close to 1:1. However, this reduction ratio and intensity are not sufficiently reasonable to alleviate ozone pollution. Meanwhile, adverse meteorological conditions further exacerbated this effect, contributing 34.7%, with temperature rise having the greatest impact. Results from the chemical transport model show that with the total reduction in NOx and VOCs emissions unchanged, the greater the reduction in VOC emissions and the better the reduction effect on ozone pollution, reducing MDA8 O3 by approximately 10 μg/m³, especially for the control of reactive compounds such as alkenes, aromatics, and OVOCs. However, if the reduction ratio of NOx is greater than that of VOCs, ozone concentrations may not decrease but instead increase. This indicates that ozone concentration is influenced not only by the intensity of emissions reduction but also by the ratio of emissions reduction between NOx and VOCs. Our study emphasizes the critical role of carefully designed strategies, focusing on controlling the ratio of VOCs to NOx and increasing the intensity of VOCs reduction, to effectively alleviate ozone pollution in urban areas.

Comparative analysis on pulverized coal combustion preheated by self-sustained purifying burner with coaxial and centrosymmetric air nozzle structures: Purification, combustion and NOx emission characteristics

To optimize secondary air nozzle structure in purifying burner, this study focused on the comparison of purification, combustion and NOx emission characteristics of pulverized coal preheated by a 30 kW purifying burner with coaxial and centrosymmetric structures. Centrosymmetric structure shifted the position of main burning region down in high-temperature reduction unit (HTRU), and the number of branches differently influenced the temperature in different regions with this structure. For reductive gas components, CO concentration with centrosymmetric structure was higher compared to coaxial structure, while the differences in H2 and CH4 concentrations were smaller. Centrosymmetric structure was more disadvantageous to improve physicochemical properties of pulverized coal compared to coaxial structure, and this structure with four branches further deteriorated its properties compared to two branches. In mild combustion unit (MCU), the temperature at top was lower with centrosymmetric structure, while was higher in the rest. Centrosymmetric structure more effectively reduced NOx emission compared to coaxial structure, but with slight sacrifice of combustion efficiency (η). Moreover, both two-branch and four-branch centrosymmetric structures realized ultra-low NOx emission (<50 mg·m−3) with high η of over 98.50%, and the former was more advantageous. With this optimal structure, η and NOx emission were 99.25% and 40.42 mg·m−3.

Experimental analysis and optimization of the variable valve timing on attaining high efficiency with low NOx emission of a direct-injected hydrogen engine

The direct-injection hydrogen engine (DI-H2ICE) has demonstrated zero carbon emissions with high brake thermal efficiencies (BTE). Due to the high stoichiometric air–fuel ratio of hydrogen, with a lean burn strategy the gas exchange process of a hydrogen engine is different to a gasoline engine, and the valve timing controlling strategy requires reinvestigation. In this research, the optimal variable valve timing (VVT) is investigated in a 2.0 L DI H2ICE. The intake and exhaust valve timing controlling strategies are analyzed experimentally over the whole operating map. A multi-indicator decision-making method is applied to determine the entropy weight of BTE and NOx emissions. Results indicate that BTE greatly benefits from advanced intake valve timing, and exhaust valve timing affects BTE through pumping losses. Advanced intake and exhaust valve timings are employed in the hydrogen engine to enhance the BTE until the NOx emissions rise rapidly at high loads. The retarded exhaust valve timing helps reduce NOx emissions and avoid the risk of abnormal combustion at high loads. Therefore, earlier IVO and later EVC are applied simultaneously for DI-H2ICE compared to the gasoline engine. A maximum power of 124.8 kW at an engine speed of 4500 rpm and a BTE of 42.57 % is achieved with optimized VVT. Furthermore, NOx emissions are controlled to under 20 ppm over nearly half of the engine operating map. The conclusions are valuable in the development of high-performance H2ICEs, the numerical simulation studies, and hydrogen fuel applications.

Assessing the effectiveness of SO2, NOx, and NH3 emission reductions in mitigating winter PM2.5 in Taiwan using CMAQ

Abstract. Taiwan experiences higher air pollution in winter when fine particulate matter (PM2.5) levels frequently surpass national standards. This study employs the Community Multiscale Air Quality model to assess the effectiveness of reducing SO2, NOx, and NH3 emissions on PM2.5 secondary inorganic species (i.e., SO42-, NO3-, and NH4+). For sulfate, ∼ 43.7 % is derived from the chemical reactions of local SO2 emission, emphasizing the substantial contribution of regionally transported sulfate. In contrast, nitrate and ammonium are predominantly influenced by local NOx and NH3 emissions. Reducing SO2 emissions decreases sulfate levels, which in turn leads to more NH3 remaining in the gas phase, resulting in lower ammonium concentrations. Similarly, reducing NOx emissions lowers HNO3 formation, impacting nitrate and ammonium concentrations by decreasing the available HNO3 and leaving more NH3 in the gas phase. A significant finding is that reducing NH3 emissions decreases not only ammonium and nitrate but also sulfate by altering cloud droplet pH and SO2 oxidation processes. While the impact of SO2 reduction on PM2.5 is less than that of NOx and NH3, it emphasizes the complexity of regional sensitivities. Most of western Taiwan is NOx-sensitive, so reducing NOx emissions has a more substantial impact on lowering PM2.5 levels. However, given the higher mass emissions of NOx than NH3 in Taiwan, NH3 has a more significant consequence in mitigating PM2.5 per unit mass emission reduction (i.e., 2.43 × 10−5 and 0.85 × 10−5 µg m−3 (t yr−1)−1​​​​​​​ for NH3 and NOx, respectively, under current emission reduction). The cost-effectiveness analysis suggests that NH3 reduction outperforms SO2 and NOx reduction (i.e., USD 0.06 billion yr−1 µg−1 m3, USD 0.1 billion yr−1 µg−1 m3, and USD 1 billion yr−1 µg−1 m3 for NH3, SO2, and NOx, respectively, under the current emission reduction). Nevertheless, the costs of emission reduction vary due to differences in methodology and regional emission sources. Overall, this study considers both the efficiency and costs, highlighting NH3 emissions reduction as a promising strategy for PM2.5 mitigation in the studied environment in Taiwan.

Effective utilization of waste plastics and ammonia as biodiesel to assess performance and emission

PurposeThis study aims to examine the environmental effects of plastic waste on the atmosphere and its implications for disaster waste management. It focuses on using ammonia, pyrolyzed plastic oil and the effectiveness of alumina nanoparticles as a catalyst.Design/methodology/approachThe research explores different combinations of conventional diesel and nano Al2O3 derived from pyrolyzed plastic oil (ranging from P10 to P40). Critical performance metrics evaluated include brake mean effective pressure (BMEP), brake specific fuel consumption, brake thermal efficiency and emissions of CO2, CO and NOx. The study specifically investigates the impact of adding 50 ppm of Al2O3 nanoparticles to these blends.FindingsThe findings indicate that using blended fuels with nanoadditives significantly lowers pollution. Specifically, the P30 blend with 50 ppm of Al2O3 nanoparticles greatly reduced CO emissions. Additionally, the same blend reduced NOx emissions and CO2 emissions. The P30 mix showed improved BMEP and brake thermal efficiency due to its density, calorific value and viscosity (6.3 bar). The P30 blend exhibited higher thermal efficiency due to decreased heat loss, whereas conventional diesel demonstrated the best mechanical efficiency due to its longer ignition delay.Originality/valueThis study highlights the potential of using Al2O3 nanoparticles and pyrolyzed plastic oil to reduce emissions and enhance the performance of internal combustion engines. It underscores the environmental benefits and implications for disaster waste management by converting plastic waste into useful resources and reducing air pollution.

Numerical research on structure and performance optimization of a pioneering water-cooled fully premixed gas-fired equipment

To meet ultra-low emissions, traditional diffused low-nitrogen gas combustion technologies are not effective or extremely laborious in controlling the emissions of NOx. Thus, this study innovatively proposes a water-cooled fully premixed gas combustion technology and explores its impact on pollutant emissions through numerical simulation. The effects of the burner inlet channel’s equivalent diameter (de), the relative positioning of two rows of buried tubes, and the burner type on combustion in the boiler are explored in-depth. As de decreases, a progressive reduction in NOx emissions is observed and an anti-backfiring effect is enhanced. Moreover, using a concave burner and placing buried tubes in the combustion chamber efficiently reduces the combustion temperature and thus NOx emissions. Finally, a ternary phase diagram is constructed to guide structural design optimization and clearly depicts the effect of Airflow channel width (SW), Dimensionless distance between the first row of buried tubes and the burner nozzle (D1), and Dimensionless longitudinal distance of buried tubes (D2) on NOx and CO emissions. Under the optimized structural condition, the water-cooled fully premixed gas combustion reveals great potential to synergistically control NOx emissions to as low as 11 mg/m3 and CO concentration to 10−6 mg/m3. This research provides valuable reference data for theoretical research and equipment design.

Study on the characteristics of urban background ozone pollution based on long-term observations from mountain sites in China during 2015–2022

In recent years, Chinese cities have faced persistent O3 pollution challenges. O3 concentrations at urban mountain sites, serving as proxies for urban background O3 levels, can help address data gaps in O3 research in China. This study, for the first time, analyzed O3 data from ten urban mountain sites during 2015–2022 using statistical methods like the Mann-Kendall test, Theil-Sen slope estimation, and Pearson correlation analysis to reveal characteristics and trends in urban background O3 and proposed a metric for assessing mountain sites as urban background stations. Results indicate that O3 at mountain sites were generally higher than at plain sites, regardless of mean, 10th percentile, or 90th percentile the average maximum daily 8-h average (MDA8) O3. Although mountain sites exhibited similar annual and diurnal variations as plain sites, their amplitudes were significantly lower. Significant upward trends (P < 0.05) in MDA8 O3 were observed mainly at plain sites, whereas trends at mountain sites were insignificant (P > 0.05) during 2015–2022. The increase in urban ground-level O3 was largely due to changes in VOCs and NOx emission structures, which reduce nighttime titration effects while enhancing daytime O3 production. The insignificant trends observed at mountain sites suggest that these mountain sites may be in NOx-limited or transitional regimes rather than VOCs-limited regimes, which is also associated with their lower NOx concentrations compared to plain sites. These findings suggest that if China continues to prioritize the reduction of NOx emissions, urban ground-level O3 could further increase and approach the O3 at mountain sites. Finally, this study proposes that the correlation in nighttime O3 concentrations between mountain and plain stations can serve as a valuable indicator for evaluating the suitability of mountain stations as regional background stations in urban areas. It recommends mountain sites in cities such as Changji, Nanping for urban background O3 monitoring stations.

Synergies quantification and evolution on air pollutant and CO2 emissions driven by different socio-economic effects

Realizing a synergistic reduction of air pollutant and CO2 emissions (APCE) is an important approach to promote a green socio-economic transformation in China, and it can provide a solid foundation for the achievement of clean energy production and climate action under a sustainable development goal framework. The objective of this study is to explore the quantitative relationship and evolution of synergies between APCE in industrial sectors driven by different socio-economic effects from 2007 to 2020 in China. The results indicated that the main sectors of pollutant emissions had consistency, however, large differences in the reduction efficiency of emissions exist among pollutants. The efficiency in reducing CO2 emissions was about 48% lower when compared with reductions of SO2 (95%), NOx (86%), and smoke and dust (83%) emissions from 2007 to 2020. The effects of improved technology were the main contributor to a reduction in pollutant emissions, but the synergies between APCE driving by it were not achieved. While the synergies between APCE driven by structure and final demand effects were significant. The synergies between NOx and CO2 emissions were stronger driven by final demand structure and type effects, with correlation coefficients of 1.06 and 1.13, respectively. Besides, the degree of synergistic reduction between APCE in most industrial sectors was around zero. Therefore, the efficiency of synergistic pollution reduction should be improved with the development of a synergistic governance system for industrial sectors. The structural decomposition analysis based on input-output model combined with the cross-elasticity analysis method to quantitively synergies between APCE from the consumption (demand) perspective, considering the connections between industrial sectors with socio-economic developing, which would contribute to the industrial synergistic reduction and green transformation as the consumption driven gradually increasing.

9E heavy-duty gas turbine ammonia-hydrogen mixture combustion characteristics and NOx emission characteristics research

In this study, we used the numerical simulation tool FLUENT to numerically simulate the combustion of ammonia-hydrogen fuel in the combustion chamber of a 9E heavy-duty gas turbine, and analysed the effects of different hydrogen blending ratios on the stability of ammonia combustion and NOx emissions. We found that an increase in the hydrogen mixing ratio in the fuel during the ammonia-hydrogen mixture combustion process contributes to the reduction of NOx emissions and has a positive effect on combustion stability.

Assessing the potential and energy distribution calibration of ethanol-biodiesel based RCCI mode of compression ignition engine in a plugin parallel hybrid electric vehicle

The focus of this research is to develop the resilient powertrain to combat the enforcement of stringent emission regulations and elevate its feasibility to power with the sustainable fuels to support the fuel crisis. The current solution in the reliable and adaptability point of view is the low temperature combustion engine-based hybrid electric powertrain powered with sustainable fuel is the better choice. The present work proposes the concept of an ethanol-biodiesel fuel based RCCI plugin parallel hybrid electric vehicles (PHEVs). The significant examination of this work in the aspects of optimal torque structure and injector control parameter calibration. The calibration of the RCCI engine torque structure operation is performed based on the multi-objective constraints of variance of indicated mean effective pressure and the maximum rate of pressure rise for the combustion stability. While the equivalence ratio and combustion temperature with emphasis on limiting the amount of NOx and soot emissions. The maximum ethanol energy share proportion of 66.98% has been achieved. The RCCI engine is most frequently operating in the torque zone of 10 Nm and then 17.81 Nm while the BLDC motor is most frequently operated in the range of 55 Nm even at max torque of 60 Nm. When comparing to a standard diesel hybrid setup, the ethanol-biodiesel fuelled RCCI setup has a 18%–19% reduction in harmful NOx emissions, with an equivalent decrease of 22.7% in fuel economy. This is achieved by only having a 13.4% more CO emission while a minimal increase in soot emission throughout the overall course of the driving cycle. The result of this work shows evidence that implementing an ethanol-biodiesel fuelled RCCI engine in a parallel hybrid configuration achieves a significant reduction in NOx emissions while achieving the performance targets and managing the fuel and battery energy utilization over a driving cycle efficiently.

Carbon-free power generation strategy in South Korea: CFD simulation for ammonia injection strategies through boiler burner configurations in tangentially fired boiler

To achieve carbon neutrality in power generation, incorporating ammonia-coal co-firing into coal-fired boilers effectively reduces CO2 emissions. Here, we aimed to optimize ammonia injection methods by investigating the feasibility of 20 % ammonia co-firing in a pulverized coal (PC) boiler through numerical simulations. These simulations aim to analyze the effects of different ammonia injection strategies and burner configurations on the combustion performance and NOx emission characteristics of a 500 MW tangentially fired PC boiler. Results showed that compared to using five burners, single-burner injection reduced outlet NO concentration by 22.72 ppm and unburned carbon content to 0.30 %, which is 0.80 % lower than multi-burner injection and even below the 0.45 % in coal-only combustion. The optimal case (burner A for ammonia injection) achieved a furnace outlet flue gas temperature of 1247.35 K, close to 1241.98 K in coal-only combustion, with the lowest NO emissions (193.89 ppm) among all ammonia co-firing cases. Positioning the single burner for ammonia injection revealed that utilizing the blending method with the ammonia injection burner, such as in the case of upper burner injection, increases both furnace temperature and high-temperature zone areas. However, employing in-boiler blending methods with lower-positioned burner ammonia injection distributes high-temperature zones more extensively. Comparing ammonia injection through coal and auxiliary oil burners, using only the lowest-level burner can significantly reduce NOx emissions while maintaining combustion and thermal efficiencies. This study is the first to simultaneously consider the number, position, method, and type of ammonia injection burners in large-scale commercial coal-fired boilers, providing a valuable reference for future research and practical boiler operations. This comprehensive analysis underscores how ammonia injection strategy and position can optimize ammonia-coal co-firing boiler performance.

Mathematical modeling and model predictive control research on coal powder burners for aggregate dryers

Aggregate drying is a crucial step in asphalt mixture production. Enhancing the model accuracy and controller performance of aggregate dryer burners is essential for consistent flame characteristics, reducing NOx emissions, and minimizing fuel consumption. This paper introduces a second-order nonlinear parametric model for coal powder burners that includes delay and noise. Model parameters were determined through experimental data using the Salp Swarm Algorithm, showing higher accuracy than models based on the least square method. A dual-layer model predictive control (MPC) based on this mathematical model was developed to improve the economic efficiency of the aggregate drying process. Simulation results showed that the dual-layer MPC saves 1.08 tons of coal every 10 h compared to a standard MPC. A full-scale prototype demonstrated average flame length, flame temperature, and NOx emissions of 4242.6 mm, 1729.4 °C, and 460.2 mg/m³, respectively, validating the accuracy of the proposed mathematical model and controller.

Experimental and numerical studies of NO reduction by ammonia in different methane flame positions

Blending ammonia with methane for combustion can reduce carbon emissions and improve the flame characteristics of ammonia combustion. However, blending ammonia with methane can easily lead to high concentrations of NOx emissions. This study investigates the impact of different ammonia and methane blending methods on the flame structure and NOx emission by experiments and CFD numerical simulation. The results indicate that simultaneous injection of ammonia and methane through the central fuel tube significantly alters the combustion flame structure and leads to high concentrations of NOx emission. As the ammonia ratio increases, the flame structure transitions from a bright flame to a layered flame with an inner yellow conical small flame surrounded by a light-colored outer flame. When the ammonia ration increases from 0 % to 20 %, NOx emission increase from 15 ppm to 323 ppm, nearly 22 times higher. When ammonia is injected into the methane flame from flame side, the flame above the injection position appears as an orange flame, and a significant reduction in NOx emission is obtained. When the ammonia ratio is 20 % and injected at heights of 20 mm 40 mm, and 60 mm above the fuel exit, the outlet NOx concentrations are 183 ppm, 140 ppm, and 153 ppm respectively, this represents reductions of 43.3 %, 56.6 %, and 52.6 %, respectively. The numerical simulation results indicate that the injection of ammonia leads to the formation of higher concentrations of NH2 and super-vapor H2O, resulting in an orange color flame. The gas temperature and oxygen concentration play a crucial role in NOx emissions. NOx emission is lowest when ammonia is injected into the higher temperature, lower oxygen environment at 40 mm.