Reduce NOx Emissions Research Articles

Energy, environmental, economic, and social assessment of photovoltaic potential on expressway slopes: A case in Fujian Province, China

Expressway slopes within the boundary of expressway construction land have the potential to be transformed from conventional land use to valuable utilization through the installation of photovoltaic (PV) systems. Considering the continuous increase in expressway mileage, the PV potential could be enormous; therefore, a method to quantify such potential is urgently needed. This study proposes a potential assessment method for expressway slope photovoltaics. First, the suitable locations of expressway slopes for installing PV systems are identified on the basis of publicly available digital maps, combined with the principles of PV site selection and geographic information systems. Then, the PVsyst model is used to simulate the power generation efficiency and power output of the PV systems and to evaluate their PV potential, contribution, and economic benefits. The implementation of the proposed method in Fujian Province, China, indicates that the installed capacity of PV systems could reach 16.3 GW, with an annual power output of 17,940 GWh, contributing to the peak shaving of power grids and regional energy supply. The reductions in CO2, SOx, and NOx emissions are 16.65 Mt, 8970 t, and 3947 t per year, respectively. Considering carbon trading, the payback period is shortened to 11.7 years, with the return on investment of 65.38 % and the net present value of 52.6 billion RMB over a 25-year operational period. Additionally, this project could create 19.88 % of jobs in the energy sector in Fujian Province, providing 27,861 jobs during the construction phase and 18,248 jobs during the operation and maintenance phase. Thus, this project is economically viable and generates positive energy, environmental, and social benefits, contributing to the promotion of local energy transition and sustainable development.

Health benefits of US light-duty vehicle electrification: Roles of fleet dynamics, clean electricity, and policy timing

We present a dynamic perspective to quantify the air quality-related health impacts of the electrification of light-duty vehicles in the United States between 2022 and 2050. Using a fleet turnover model and future electricity generation mix scenarios, we compare ambitious vehicle electrification to fleet renewal relying on newer internal combustion engine vehicles, without electric vehicles. The model includes vehicle-level pollutant emission factors and a reduced complexity air quality and valuation model and covers direct (tailpipe, brake wear, and tire wear) and indirect (production of electricity and liquid fuels) emissions of NOx, SO2, PM2.5, NH3, and VOCs, with a breakdown at the county level to identify geographical disparities in the distribution of health impacts. Short-term health benefits are mostly generated by reductions in NOx emissions from newer gasoline vehicles, while fleet electrification generates further benefits in the long term. The electricity mix plays a crucial role in the success of electrification policies. With continued grid decarbonization, electrification would reduce harmful air quality-related health impacts cumulatively by 84 to 188 billion USD over the study period, compared with fleet renewal without electric vehicles. In contrast, artificially freezing the 2022 grid would make electrification responsible for 32 to 71 billion USD additional health disbenefits compared with fleet renewal. Finally, we show that while fleet electrification achieves most of its benefits over fleet renewal in the long term, delaying the implementation of such policies would sacrifice meaningful cumulative benefits.

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.

Experimental multiple parameters optimization of the injection strategies for a turbocharged direct injection hydrogen engine to achieve highly efficient and clean performance

Improving the brake thermal efficiency (BTE) and reducing NOx emissions are two main goals for hydrogen-powered internal combustion engines to achieve efficient and clean performance. This paper focuses on the multiple parameters optimization of injection and ignition both experimentally and numerically based on a 2.0L turbocharged direct injection hydrogen engine. Firstly, the effects of single and split injection on engine performance, in-cylinder mixing and combustion characteristics are investigated. Secondly, the single-factor effect of split injection parameters and spark timing on engine performance are obtained with different engine speeds. Significant interaction effects are detected between these factors. Thus, a multi-parameter optimization is conducted based on the response surface methodology method to analyze the co-relationship of factors (split injection control parameters and ignition) on responses (BTE, NOx emissions, and knock intensity) at high-load. Finally, a maximum BTE of 43.03% and a reduction in NOx emissions by 71.19% are achieved with the help of model prediction at 2500 rpm and a load of 1.40MPa. Further optimization of other engine speeds is conducted, and the boundary of high-efficiency region (BTE>40%) covers over 50% of the load map after optimization. These results can provide valuable support for the performance improvement of efficiency and clean hydrogen engines.

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.

Flow field and emission characterization of a novel enclosed jet-in-hot-coflow canonical burner

The jet-in-hot-coflow is a canonical combustion setup, which has been used in several studies to study Flameless/MILD combustion and auto-ignition of fuels. However, the NOx and CO emission measurements from these combustion setups were not possible due to the entrainment of laboratory air and a lack of a well-defined physical system limit. These limitations have been overcome by a new enclosed jet-in-hot-coflow setup. The combustor was operated by injecting a mixture of CH4-Air in the central jet, and the coflow comprised of hot products from CH4-Air combustion in burners upstream. The coflow composition was further controlled by adding diluents such as N2 and CO2. Measurements were done using stereoscopic particle image velocimetry, suction probe gas analysis, thermocouples, and chemiluminescence imaging. Increasing central jet velocity and equivalence ratio led to lower NOx and a reaction zone that enlarged and shifted downstream. The reduction in NOx emission was attributed to the returning mechanism. Adding CO2 and N2 as diluents in the coflow resulted in a longer combustion zone and reduced temperatures in the combustion chamber, leading to decreased NOx production and increased reburning. These experiments provide relevant flowfield and emissions data for modelers and help characterize combustion regimes such as Flameless/MILD.

Efficient and low-NOx combustion in a grate-fired boiler by feeding biomass non-uniformly along grate width: An integrated modeling study with experimental validation

The distribution of air flows and fuel feeds are two crucial operational parameters determining the high-efficiency combustion and low-nitrogen emissions in biomass-fired grate boilers. However, current optimizations primarily focus on air distribution, with limited attention given to fuel feeds optimization. In this study, a three-dimensional integrated model was developed in FLUENT platform for simulating a grate-fired boiler with four feed inlets, in which the DPM model was adopted to track particle information in detail, and the Ergun model was used to account for the flow resistance generated by the thick packed bed, implemented in the form of a UDF code. The reliability of the model was validated through comprehensive on-site experimental data. It was found that key parameters such as temperature and ignition front of char are non-uniformly distributed along the width of the four grates. Specifically, a significant lag in volatiles release and char oxidation occurs near the water-cooled wall on both sides. On this basis, the optimization strategies on improving efficient and low-NOx combustion were proposed by redistributing the biomass fuel from near the sidewalls to the middle sections, and the optimal non-uniform feeding mode along the grate width was found. Results demonstrate that when the mass ratio of fuel between the middle and side grates is 0.30 to 0.20, yielding a maximum overall char burnout ratio of 84.74%. Additionally, the concentration of NO decreases from 163.2 mg/m3 of uniform feeding mode to 149.4 mg/m3 (at 11% O2). These predictions will provide reliable theoretical guidance for enhancing boiler efficiency and reducing NOx emissions in grate-fired boilers.

Nitrogen migration and gasification characteristics of pulverized coal using the novel gasification-combustion technology

This study proposes a feasible gasification-combustion technology for coal-fired boilers operating at low loads for the purpose of providing strong support for stable output of the power grid system that accommodates more renewable energy power. In this technology, a multi-nozzle impinging entrained-flow gasifier is used for the first time to preheat pulverized coal (PC), and the gasified fuel enters a down-fired combustor (DFC) for complete combustion with air-staged method. A 75 kW novel self-sustained gasification-combustion test rig was constructed. The stability and feasibility of the test rig were verified, and the gasification characteristics and nitrogen migration mechanism of PC under loads of 45 kW, 55 kW, 65 kW and 75 kW were investigated. The results demonstrated that the gasifier could continuously and steadily provide high-temperature gasified gas-char mixture to the combustor. The gas-char mixture, consisting of coal gas which was rich in high-concentration flammable gases (CO, H2, and CH4) and char with enlarged specific surface area, was easy to ignite, which could enhance the flame stability of boilers operating at low loads. Additionally, more than 61.6 % of coal-N was released in the gasifier. The liberated coal-N primarily transformed to N2 and NH3 instead of NOx, while the amount of NH3 produced was influenced by the gasification temperature. The gasified gas-char mixture entering the combustor achieved stable combustion with uniform temperature distribution. Before the injection of tertiary air, the released char-N and the NH3 in coal gas transformed primarily to N2, and there was no production of NO due to the strong reducing environment. The lowest NOx emission was 122.31 mg/Nm3 (@6% O2) at 65 kW, and the combustion efficiencies under all loads exceeded 99.62%, indicating that the gasification-combustion technology could enable efficient combustion and reduce NOx emission. Hopefully, the proposed technology could provide an innovative solution for the stable combustion of PC boilers at low loads and provide a feasible way to achieve clean combustion.

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-hour 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.

Towards cleaner energy: An innovative model to minimize NOx emissions in chemical looping and CO2 capture technologies

The urgent global challenges of climate change and environmental issues have catalyzed the development of CO2-capture-ready technologies incorporating fluidization, such as fluidized bed (FB) and circulating fluidized bed (CFB) combustion under oxy-fuel conditions, chemical looping combustion (CLC), chemical looping with oxygen uncoupling (CLOU), in-situ gasification chemical looping combustion (iG-CLC), and calcium (or carbonate) looping (CaL) systems. While these technologies have the potential to reduce CO2 emissions significantly, the persistent presence of nitrogen oxides (NOx = NO + NO2) as pollutants remains a critical environmental concern.This paper introduces a comprehensive fuzzy logic-based model for predicting NOx emissions (FuzzyNOx model) from solid fuel combustion in fluidized beds of chemical looping systems. This innovative model takes into account a wide range of operating parameters, including fuel type, fuel particle size, fuel moisture content, air/fuel ratio, and temperature. It also explores advanced coal and biomass combustion modes, including air-firing, oxyfuel, iG-CLC, and CLOU. Furthermore, it delves into the intricacies of two distinct facilities: the 5 kWth dual-fluidized bed Chemical-Looping-Combustion of Solid-Fuels (DFB-CLC-SF) facility at Czestochowa University of Technology, Poland, and the calcium looping dual-fluidized bed (CaL DFB) facility at Niigata University, Japan.Bituminous coal, semi-anthracite, and wood chips are utilized as fuels. Moreover, three various oxygen carriers (OCs) for chemical looping combustion were employed, namely ilmenite, copper oxide (60 % wt.) supported by carbonate waste from ore flotation, and copper oxide (60 % wt.) supported by ilmenite (20 % wt.) and fly ash. Bituminous coal, semi-anthracite, and wood chips are utilized as fuels.The developed knowledge-based fuzzyNOx model allows the optimization of operating parameters to reduce NOx emissions from CO2 capture technologies.

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.

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.

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

Purpose This 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/approach The 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. Findings The 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/value This 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.