Nitrogen Oxide Emissions Research Articles

Water and nitrogen availability define emissions of carbon dioxide and nitrogen oxides from desert soil differently

Nitrogen (N), phosphorus (P), and water, together and individually, limit soil biological processes in dryland ecosystems and therefore, the availability of each nutrient is a key determinant of ecosystem processes and functions. To assess the importance of each limiting factor for microbial activity in desert soil, we manipulated water, N, and P availability separately and combined. N, P, and NP were added at rates of 10 N or/and P g m−2 under two water regimes: one wetting event, and bi-weekly wetting–drying cycles in addition to natural rainfall. We measured soil respiration, nitrous (N2O) and nitric oxides (NOx) emissions in situ, and potential nitrification and mineralization in laboratory. Soil respiration increased by ∼30% with raised water availability but wasn't affected by nutrients availability. NOx and to a smaller extent N2O emissions, however, increased with nutrient availability but not with water. Average soil NOx flux increased up to ∼19 folds from 0.03 ± 0.01 μg N m−2 min−1 to 0.52 ± 0.10 μg N m−2 min−1 with the addition of N and N + P but only slightly with addition of P alone (p = 0.06). The removal of both water and NP limitation accelerated only NOx, but nor CO2 neither N2O emissions pointed on other than N and P limitation of soil heterotrophic processes in this alkali desert soil. The potential soil microbial activity was unaffected by the removal of neither water nor NP limitations. Our findings suggest that water primarily influences soil respiration and N availability soil NOx emissions while desert soil is a minor source of N2O. We conclude that heterotrophic and autotrophic microbial activities in desert soils are influenced differently by water and nutrients. Increasing precipitation would likely boost soil respiration and N mineralization rates, leading to decreased soil nutrient organic carbon stocks, while increased N deposition would accelerate gaseous N loss.

An amperometric high-temperature ammonia sensor based on a BaCo0.4Fe0.4Zr0.1Y0.1O3-δ triple conductor

Selective catalytic reduction (SCR) utilizing urea hydrolysis to generate ammonia (NH3) is the most efficient technology to reduce the emission of nitrogen oxides (NOx). NH3 detection is crucial in the closed-loop feedback system for the precise urea injection. In this work, a high-temperature NH3 sensor using a BaZr0.8Y0.2O3-δ (BZY) proton conductor as the electrolyte and a BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) H+/e–/O2– triple conductor as the sensing electrode (SE) is reported. The effect of the micromorphology of the BCFZY SE on the sensing performance is investigated by varying the sintering temperature of SE. The sensor shows high sensitivity to NH3 with response currents of 0.39, 1.31, 3.03, and 1.81 μA/ppm at 350, 400, 450, and 500 °C, respectively. Furthermore, the sensor shows excellent selectivity and repeatability. This work demonstrates that the BCFZY-based sensor has great potential for the high-temperature NH3 detection.

Urban air pollution evaluation in downtown streets of a medium-sized Latin American city using AERMOD dispersion model.

The transport sector is considered the largest contributor of air pollutants in urban areas, mainly on-road vehicles, affecting the environment and human health. Bahía Blanca is a medium-sized Latin American city, with high levels of traffic in the downtown area during peak hours. In this regard, it is necessary to analyze air pollution using an air quality model considering that there are no air pollutant measurements in the central area. Furthermore, this type of study has not been carried out in the region and since the city is expected to grow, it is necessary to evaluate the current situation in order to make effective future decisions. In this sense, the AERMOD model (US-EPA version) and the RLINE source type were used in this work. This study analyzes the variations of pollutant concentrations coming from mobile sources in Bahía Blanca's downtown area, particularly carbon monoxide (CO) and nitrogen oxides (NOx) during the period Jul-2020 to Jun-2022. It is interesting to note the results show the maximum concentration values detected are not directly associated with maximum levels of vehicle flow or emission rates, which highlights the importance of meteorological parameters in the modeling. In addition, alternative scenarios are proposed and analyzed from a sustainable approach. Regarding the scenario analysis, it can be concluded that diesel vehicles have a large influence on NOx emissions. Moreover, restrictions as strict as those proposed for a Low Emission Zone would be less applicable in the city than alternative temporary measures that modify traffic at peak hours.

Dielectric Properties of Materials Used for Microwave-Based NOx Gas Dosimeters.

Nitrogen oxides (NOx), primarily generated from combustion processes, pose significant health and environmental risks. To improve the coordination of measures against excessive NOx emissions, it is necessary to effectively monitor ambient NOx concentrations, which requires the development of precise and cost-efficient detection methods. This study focuses on developing a microwave- or radio frequency (RF)-based gas dosimeter for NOx detection and addresses the optimization of the dosimeter design by examining the dielectric properties of LTCC-based (Low-Temperature Co-fired Ceramics) sensor substrates and barium-based NOx storage materials. The measurements taken utilizing the Microwave Cavity Perturbation (MCP) method revealed that these materials exhibit more pronounced changes in dielectric losses when storing NOx at elevated temperatures. Consequently, operating such a dosimeter at high temperatures (above 300 °C) is recommended to maximize the sensor signal. To evaluate their high-temperature applicability, LTCC substrates were analyzed by measuring their dielectric losses at temperatures up to 600 °C. In terms of NOx storage materials, coating barium on high-surface-area alumina resolved issues related to limited NOx adsorption in pure barium carbonate powders. Additionally, the adsorption of both NO and NO2 was enabled by the application of a platinum catalyst. The change in dielectric losses, which provides the main signal for an RF-based gas dosimeter, only depends on the stored amount of NOx and not on the specific type of nitrogen oxide. Although the change in dielectric losses increases with the temperature, the maximum storage capacity of the material decreases significantly. In addition, at temperatures above 350 °C, NOx is mostly weakly bound, so it will desorb in the absence of NOx. Therefore, in the future development of a reliable RF-based NOx dosimeter, the trade-off between the sensor signal strength and adsorption behavior must be addressed.

Investigation of performance and emission characteristics using ethanol-blended gasoline fuel as a flex-fuel in two-wheeler vehicle mounted on a chassis dynamometer

Abstract This study investigated the performance and emissions of flex fuels in a 110-cc BS6-compliant fuel-injected two-wheeler without ethanol adaptation adjustments. The tests were carried out under controlled conditions on a chassis dynamometer at 1000, 2000 and 3000 r.p.m. using ethanol blends from 10% ethanol (E10) to 85% ethanol (E85). Parameters examined included brake power (BP) output, brake-specific fuel consumption (BSFC), peak in-cylinder pressure and exhaust temperature. Emissions, including carbon monoxide (CO), hydrocarbons (HC), nitrogen oxide (NOx) and unregulated emissions, were also assessed. As the percentages of the ethanol blend increased from E10 to E85, there was a noticeable improvement in power output. At 1000 r.p.m., the BP ranged from 2.4 to 4.6 kW for different blends. The BSFC and the peak in-cylinder pressure followed a similar pattern, indicating enhanced performance and fuel efficiency with higher ethanol concentrations. Interestingly, using E85 at 1000 r.p.m. resulted in a significant 41.08% reduction in exhaust temperature compared with E10, although this difference decreased with higher blend percentages. Furthermore, replacing E10 with E85 at 1000 r.p.m. reduced CO and HC emissions by 9.17% and 38.34%, respectively. In contrast, NOx emissions increased at all r.p.m. levels with higher-ethanol blends, peaking at a 415 parts per million increase at 3000 r.p.m. However, unregulated emissions decreased significantly with increased r.p.m. and ethanol content. In summary, the use of flex-fuel blends in a two-wheeler resulted in a modest increase in BP output, improved fuel efficiency and lower CO and HC emissions. These findings are vital for optimizing ethanol blend utilization in two-wheeler engines under low-load conditions, considering both performance and environmental aspects.

Numerical Investigation of In-Cylinder Combustion Behaviors in a Medium-Speed Diesel Engine

Abstract This study aims to advance understanding of in-cylinder combustion processes in medium-speed diesel engines, which are extensively employed in heavy-duty applications where electrification proves inefficient yet remains insufficiently examined in the literature. By modeling a four-stroke engine with dimensions of 210 mm bore and 310 mm stroke, operating at 900 rpm under full load, this research identifies distinct combustion characteristics that differentiate medium-speed engines from their high-speed counterparts. Key findings illustrate that super turbocharging in medium-speed engines enhances the combustion of the fuel–air mixture under elevated temperatures and pressures. Moreover, an increased stroke length promotes gas velocity and turbulence, facilitating fuel atomization and mixing. Notably, rapid fuel ignition occurs near the nozzle due to the high temperature of compressed air, reducing the ignition delay. As a result, the premixed combustion stage nearly disappears, with diffusion combustion dominating, especially pronounced with long-duration injection, a characteristic of medium-speed engines. The study also reveals a more uniform but elevated distribution of nitrogen oxide emissions in medium-speed engines, attributed to prolonged high-temperature conditions that both facilitate their formation. Early stages of diffusion combustion show high concentrations of incomplete combustion products. However, as the combustion process progresses, the conditions favor the complete oxidation of these products at high temperatures, resulting in decreased carbon-based pollutions. In addition, the larger combustion chamber and enhanced turbulence characteristic of medium-speed engines support efficient fuel and air mixing without necessitating the swirl effect required by high-speed engines, diminishing the dependence on wall impingement dynamics for air utilization. Consequently, efficiency optimization strategies for medium-speed engines, emphasizing adjustable injection parameters, encounter fewer constraints than those inherent to the spatial limitations of high-speed engines.

Effects of Blended Diesel-Biodiesel Fuel on Emissions of a Common Rail Direct Injection Diesel Engine with Different Exhaust Gas Recirculation Rates.

The aim of the study was to investigate the exhaust gas emissions and fuel consumption of a common rail direct injection (CRDI) diesel engine using mixed diesel (B10) and biodiesel (B20-B100) fuels. The study's primary objective was to determine the effects of blended diesel-biodiesel fuel on CRDI emissions based on different exhaust gas recirculation (EGR) rates, including carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2), nitrogen oxide (NOx), and hydrocarbon (HC) emissions, smoke opacity, exhaust gas temperature, and fuel consumption. The CRDI experiments involved adjusting the different engine speeds (1400-3000 rpm) and EGR rates (0 and 12.5%), which were analyzed to determine their impact on these parameters for both blended diesel and biodiesel fuels. The results showed that under the conditions of no EGR (0%), the CO and HC emissions and the smoke opacity were lower than those with a 12.5% EGR rate for all fuel types and all cases. With 12.5% EGR rate, the O2 emissions and the EGT of the CRDI diesel engine decreased, which resulted in significantly lower NOx emissions because of EGR into the combustion chamber. For the maximum engine speed of 3000 rpm and with no EGR, the CO and HC emissions and the smoke opacity were lower than those with a 12.5% EGR rate for all fuel types. With a 12.5% EGR rate at 3000 rpm, the O2 emissions and the exhaust gas temperature were reduced by 0.07% and 2.27%, respectively, and the NOx emissions were reduced by 2.54%. However, with EGR, the CO and HC emissions and the smoke opacity increased by 7.70%, 18.61%, and 0.4%, respectively. Furthermore, the fuel consumption of pure biodiesel (B100) at 3000 rpm with a 12.5% EGR rate was reduced by 2.81% compared to that with a 0% EGR rate. Because the temperature in the combustion chamber is high enough for the engine to run, the EGR reuses a portion of the exhaust gases and can help to minimize the quantity of fuel in the combustion chamber. As a suggestion based on these observations, biodiesel fuel should not exceed B80 because the viscosity and density of fuel that are too high may affect the fuel injection system, both the injectors, and the pressure pump, causing the injectors to be unable to work correctly. These findings can contribute to the development of strategies and technologies for reducing emissions and improving fuel efficiency in CRDI diesel engines.

The determination of the features of the process of mixture formation of hydrogen burner

The use of hydrogen fuel as an alternative source of individual heat supply is a rather promising direction in the development of thermal energy. However, due to the physical properties of hydrogen and the peculiarities of its combustion, several problems arise for the practical use of hydrogen heat generators. Such problems include ensuring flare stability and large emissions of thermal nitrogen oxides (NOX). For stable operation of the hydrogen burner, safe operation, and reduction of nitrogen oxide emissions when burning hydrogen, first, it is necessary to ensure high-quality pre-mixing with air. This work presents the first stage of research into the operation of a hydrogen burner for heat production in the Flow Simulation module of the SolidWorks software environment. For volume flow rates of air and hydrogen corresponding to capacities of 1, 1.5 and 2 kW and air excess coefficient α=1.6. The given design makes it possible to ensure uniform mixture formation (the volume fraction of hydrogen is approximately 18.5 % at the outlet cross-section of the burner and the speed at the outlet of the burner is 5.4, 8.1, and 10.8 m/s, respectively. The burner is a nozzle with a short premixing chamber First, hydrogen is supplied for mixing into the air flow through symmetrically located holes. After that, a vortex is created, which ensures high-quality mixing of gases with a short length of the burner, as well as a uniform distribution of velocity at the exit. The obtained results allow to proceed to the next stage – the study of hydrogen combustion processes in the combustion chamber of the contact heat generator, which would ensure the formation of a stable flame and low NOX emissions. In addition, this design can be used in the development of hydrogen burners for heating boilers to meet the needs of private homes and small businesses

Regulatory Insights for On-Board Monitoring of Vehicular NOx Emission Compliance.

Nitrogen oxide (NOx) emissions from heavy-duty diesel vehicles (HDDVs) have adverse effects on human health and the environment. On-board monitoring (OBM), which can continuously collect vehicle performance and NOx emissions throughout the operation lifespan, is recognized as the core technology for future vehicle in-use compliance, but its large-scale application has not been reported. Here, we utilized OBM data from 22,520 HDDVs in China to evaluate their real-world NOx emissions. Our findings showed that China VI HDDVs had a 73% NOx emission reduction compared with China V vehicles, but a considerable proportion still faced a significant risk of higher NOx emissions than the corresponding limits. The unsatisfactory efficiency of the emission treatment system under disadvantageous driving conditions (e.g., low speed or ambient temperature) resulted in the incompliance of NOx emissions, especially for utility vehicles (sanitation/garbage trucks). Furthermore, the observed intertrip and seasonal variability of NOx emissions demonstrated the need for a long-term continuous monitoring protocol instead of instantaneous evaluation for the OBM. With both functions of emission monitoring and malfunction diagnostics, OBM has the potential to accurately verify the in-use compliance status of large-scale HDDVs and discern the responsibility of high-emitting activities from manufacturers, vehicle operators, and driving conditions.

Cropland soil nitrogen oxide emissions vary with dairy manure incorporation methods

AbstractSoils contribute 15%–75% of total atmospheric nitrogen oxide (NOx) emissions in agricultural regions during the growing season. However, the impacts of cropland fertilizer management on spatially heterogeneous, temporally episodic NOx emission patterns are highly uncertain. We examine the effects of liquid slurry dairy manure application practices on soil NOx emissions in rainfed, corn‐soybean rotations during spring 2016 and 2017. Daily soil NOx emissions and weekly soil inorganic N measurements were performed in a randomized split–split plot design for 1–4 weeks following manure applications. NOx emissions and soil N with shallow‐disk injection and chisel‐disk manure incorporation methods were compared with unincorporated broadcast practices. Injected manure and chisel‐disk incorporation exhibited two–four times larger mean NOx emissions than those with unincorporated broadcast manure. Larger soil NOx emissions with manure incorporation practices were driven by the predominance of nitrification in these treatments with evidence of soil nitrate production. Soil NOx emission differences between treatments were detectable across order of magnitude changes in daily NOx emissions during two growing seasons. Larger soil NOx emissions associated with manure incorporation practices compared with unincorporated broadcast practices occur alongside larger N2O and smaller NH3 emissions, highlighting important air quality and climate impact tradeoffs for cropland manure fertilizer management choices.

Trends and drivers of anthropogenic NOx emissions in China since 2020

Nitrogen oxides (NOx), significant contributors to air pollution and climate change, form aerosols and ozone in the atmosphere. Accurate, timely, and transparent information on NOx emissions is essential for decision-making to mitigate both haze and ozone pollution. However, a comprehensive understanding of the trends and drivers behind anthropogenic NOx emissions from China—the world's largest emitter—has been lacking since 2020 due to delays in emissions reporting. Here we show a consistent decline in China's NOx emissions from 2020 to 2022, despite increased fossil fuel consumption, utilizing satellite observations as constraints for NOx emission estimates through atmospheric inversion. This reduction is corroborated by data from two independent spaceborne instruments: the TROPOspheric Monitoring Instrument (TROPOMI) and the Ozone Monitoring Instrument (OMI). Notably, a reduction in transport emissions, largely due to the COVID-19 lockdowns, slightly decreased China's NOx emissions in 2020. In subsequent years, 2021 and 2022, reductions in NOx emissions were driven by the industry and transport sectors, influenced by stringent air pollution controls. The satellite-based inversion system developed in this study represents a significant advancement in the real-time monitoring of regional air pollution emissions from space.

Experimental and simulation research on the lean combustion characteristics of direct-injection hydrogen engine

At a constant engine speed of 2000 r/min and 5 bar gross indicated mean effective pressure, experiments were carried out on a 1.5 L engine with a variable geometry turbocharger to examine the combustion and emission characteristics of a direct injection hydrogen engine under lean combustion conditions. Additionally, a CFD simulation model was established to investigate the formation process of the air-fuel mixture and the generation of nitrogen oxides (NOx). The findings demonstrated that the uniformity of the hydrogen-air mixture in the cylinder descended with a delay in SOI (start of injection), and that the thermal efficiency often rose initially before declining. When SOI was set at −80°CA ATDC, the engine achieved maximum indicated thermal efficiency, brake thermal efficiency, and output torque values of 40.8%, 36.22%, and 61.2 Nm, respectively. However, as the SOI was delayed, the combustion variability ascended, and when the SOI was delayed to −20°CA ATDC, there was a significant chance that abnormal phenomena like pre-ignition would occur. BTE achieves a maximum of 36.38% when λ is 2.2 and SOI is −40°CA ATDC. Under lean combustion conditions, temperature was a major factor in the generation of NOx, and homogenous combustion can substantially reduce NOx emissions. NOx emissions are always less than 100 ppm when SOI is before −80°CA ATDC.

Identification of NOx emissions and source characteristics by TROPOMI observations – A case study in north-central Henan, China

With the development of industries, air pollution in north-central Henan is becoming increasingly severe. The TROPOspheric Monitoring Instrument (TROPOMI) provides nitrogen dioxide (NO2) column densities with high spatial resolution. Based on TROPOMI, in this study, the nitrogen oxides (NOx) emissions in north-central Henan are derived and the emission hotspots are identified with the flux divergence method (FDM) from May to September 2021. The results indicate that Zhengzhou has the highest NOx emissions in north-central Henan. The most prominent hotspots are in Guancheng Huizu District (Zhengzhou) and Yindu District (Anyang), with emissions of 448.4 g/s and 300.3 g/s, respectively. The Gaussian Mixture Model (GMM) is applied to quantify the characteristics of emission hotspots, including the diameter, eccentricity, and tilt angle, among which the tilt angle provides a novel metric for identifying the spatial distribution of pollution sources. Furthermore, the results are compared with the CAMS global anthropogenic emissions (CAMS-GLOB-ANT) and Multi-resolution Emission Inventory model for Climate and air pollution research (MEIC), and they are generally in good agreement. However, some point sources, such as power plants, may be missed by both inventories. It is also found that for emission hotspots near transportation hubs, CAMS-GLOB-ANT may not have fully considered the actual traffic flow, leading to an underestimation of transportation emissions. These findings provide key information for the accurate implementation of pollution prevention and control measures, as well as references for future optimization of emission inventories. Consequently, deriving NOx emissions from space, quantifying the characteristics of emission hotspots, and combining them with bottom-up inventories can provide valuable insights for targeted emission control.

Assessing the Robustness of Ozone Chemical Regimes to Chemistry-Transport Model Configurations

In a previous study, we assessed the efficiency of reducing either traffic or industrial emissions on various ozone metrics for several cities in Europe, based on the Air Control Toolbox surrogate model. Here, we perform various model parametrisation sensitivity analyses in order to assess the robustness of our results. We find that increasing the model resolution has a limited impact on the ozone response to emission changes when focusing on concentration peaks but strongly changes the response of the ozone daily mean with a switch to a titration regime for all zones with significant nitrogen oxide (NOx) emissions. The impact of pollution imported from outside the simulation domain was also studied and we show that if the first lever for action on ozone peaks remains as the reduction of local and regional emissions, in order to achieve higher levels of reduction, it is necessary to act at a European level. We also explore more up-to-date temporal profiles and sectoral emission speciation and find a shift towards a more NOx-limited regime in a number of cities. Overall, these sensitivity tests show that most of the differences are simulated in cities with high NOx emissions and little solar radiation but do not change the overall conclusions that were previously obtained.

Impact of Ship Emission Control Area Policies on Port Air Quality—A Case Study of Ningbo Port, China

The implementation effectiveness of ship emission control area (ECA) policies can be effectively evaluated using econometric models. However, existing studies mainly focus on changes in SO2 concentrations in the air. In order to comprehensively assess the impact of ECA policies on air quality, this study takes Ningbo Port in China as an example and uses a regression discontinuity (RD) model to analyze the influence of ship emissions around the wharf on concentrations of SO2, NO2, and particulate matter (PM) in the air. The results indicate that individual ships’ activities within the monitoring area (within 300 m) make a relatively small contribution to the concentration of SO2 in the air and do not form a significant breakpoint. However, there is a noticeable breakpoint in the concentration of NO2 around the monitoring point as the ship approaches. At the same time, the variation range of PM2.5 is significantly greater than that of PM10, which aligns with the characteristics of PM emitted by ships. The experimental results have passed three robustness tests, demonstrating that the current policy on ship ECAs has a positive limiting effect on SO2 emissions and, to some extent, reduces PM emissions. However, further reductions in ship emissions may require more restrictions in nitrogen oxide emissions.

Multi-objective optimization for sustainable and economical polycarbonate production with reaction kinetics inference for real-world industrial process

Polycarbonate has a wide range of applications in electronic devices and medicine because of its remarkable properties such as transparency and mechanical strength. However, the polycarbonate production process using diphenyl carbonate leads to the inevitable generation of nitrogen oxide (NOx) from byproduct incineration. Therefore, it is essential to optimize the process conditions while simultaneously considering the production costs and NOx emissions. Herein, we propose a multi-objective optimization model for sustainable and economical polycarbonate production using a high-fidelity reaction model for real-world industrial processes. Additionally, a data-driven model was developed using industrial data to identify the operating conditions that minimize NOx emissions and maximize profitability. Four of the ten reaction parameters were selected through variance-based global sensitivity analysis, and the posterior distribution of each parameter was determined through Bayesian inference. In addition, NOx emissions were predicted using the data-driven model developed from industrial data. A process model with coefficients of determination above 0.7 and a data-driven model with R-squared value above 0.99 for pilot-scale experimental and industrial data were generated using our approach. The Pareto optimality, identified based on the developed models, suggested operating conditions that optimize both economic and environmental benefits. Consequently, NOx emissions could be reduced by 27.2%–27.4% and the unit costs of production could be reduced by 0.8%–1.6% compared with the base case.

Water-in-Biodiesel Emulsion with Hydroxy (HHO) Gas Fuel Enrichment for Single-Cylinder Diesel Engine Application

The rising issue of the depletion of fossil fuels opened a new pathway to seek alternative fuels to fulfil World Sustainable Development Goals (SDG). The application of high-blending biodiesel is possible however, it causes the diesel engine to perform poorly due to high viscosity, high fuel consumption, and increased NOx emission. To comply with the strict regulation, the idea of combining alternative fuels of high blending biodiesel, water-in-biodiesel emulsion, and hydrogen is seen as possible to solve the issue of each alternative fuel. Therefore, this study focused on the effect of high blending of biodiesel, water-in-biodiesel emulsion with hydroxy (HHO) enrichment in single-cylinder diesel engines on engine performance and exhaust emission. The fuel tested for this study are B10, B50, and an emulsion of B50 with the addition of HHO known as B50H and tested on engine speeds of 2400rpm under various loading conditions of 1kW, 2kW, 3kW, and 4kW. The result showed the B50H showed improvement in Fuel Consumption (FC) by 4%, 5% for Brake Thermal Efficiency (BTE), and reduced Nitrogen oxide (NOx) by 23% compared to B10 fuel. Thus, the combination of high blending of biodiesel, water-in-biodiesel emulsion, and HHO gas successfully improved diesel engine performance and reduced harmful exhaust emissions to promote clean and renewable energy, without depending on current diesel fuel.

Ammonia coverage ratio control of a novel two-cell SCR-DeNOX system configuration based on IA-ISMC

To respond the China’s “14th Five-Year Plan” on the control of nitrogen oxides (NOX) emission, urea-based selective catalytic reduction (SCR) system has been widely applied to reduce the NOX emission from the diesel engine. NO2 is no longer a factor to be ignored while refining the SCR-DeNOX system model because of the ship diesel engine's long-term low temperature and oxygen-rich condition, which provides abundant conditions for the creation of NO2. Therefore, a refined eight-state two-cell SCR-DeNOX model is established in this paper. Meanwhile, the trade-off between NOX emission and tailpipe ammonia (NH3) slip is one of the major challenges which SCR-DeNOX system is facing. While meeting NOX emission standards, the requirement of limiting NH3 slip to prevent secondary pollution is becoming increasingly urgent, which needs a better structure or controller. Therefore, a two-cell SCR-DeNOX system with a by-pass valve in front of the NH3 injection is designed, integral sliding mode control based on inversion algorithm (IA_ISMC) is proposed for each cell. Based on the FTP-75 test cycle, there are three points of view are presented. Firstly, compared with the traditional six-state model, simulation results from the refined eight-state SCR-DeNOX model are closer to the experimental data. Secondly, the introduction of the by-pass structure has a mild impact on the NOX conversion efficiency, but can largely limit the NH3 slip. Finally, the controller based on IA_ISMC effectively improves the tracking performance of NH3 coverage ratio and reduces the cost of NH3 injection. To sum up, the refined two-cell SCR-DeNOX system with a by-pass valve based on IA_ISMC can enhance SCR performance and lower costs.

Designing regional joint prevention and control schemes of PM2.5 based on source apportionment of chemical transport model: A case study of a heavy pollution episode

Fine particular matter (PM2.5) pollution still occurs frequently in China. Despite recognizing the importance of regional joint prevention and control (RJPC) for mitigating haze pollution, there is still a limited understanding of scheme design and effectiveness. In this study, with the Fenhe Plain in China serving as the case, the Integrated Source Apportionment Method (ISAM), incorporated into the Community Multiscale Air Quality Modeling System (CMAQ), was used to quantitively identify PM2.5 sources during a typical heavy pollution episode from Jan. 20th to 25th, 2021. Informed by source apportionment, we designed and assessed multiple RJPC scenarios for eliminating heavy pollution, yielding recommended RJPC schemes. Source apportionment results revealed a substantial increase in the contribution percentage of regions within a 350-km radius during the pollution episode compared to the non-polluted period. Sulfate was predominantly contributed from long-distance transport, whereas nitrate was chiefly contributed from closer regions. Ammonium exhibited higher local contributions than nitrate from the Fenhe Plain. Moreover, Taiyuan and Linfen were identified as PM2.5 exporters, whereas Sanmenxia, Jinzhong, and Luliang served as PM2.5 importers, and Yuncheng acted as a comprehensive city. The proposed specific RJPC schemes aimed at eliminating heavy pollution for the Fenhe Plain emphasized the importance of controlling emissions of particulate matter, ammonia, nitrogen oxides, and volatile organic compounds in areas within an approximate 350-km radius outside the Fenhe Plain, in addition to strengthening the local emission control. Nevertheless, only through the comprehensive and in-depth implementation of emission control measures across a larger area can PM2.5 compliance be achieved.

Impact of injection pressures on properties, microscopic behavior, and microexplosions in biodiesel-emulsified fuel with biosurfactant

Water in biodiesel emulsified fuel improves air–fuel mixing and reduces combustion temperature, thereby lowering nitrogen oxides (NOx) emissions in diesel engines. Studies on emulsified fuel formation often use chemical surfactants. However, biosurfactants, which are natural and eco-friendly, remain unexplored. Additionally, the common-rail fuel injection system increases the pressure, temperature, and shear forces of emulsified fuel, thereby altering its properties and emulsified fuel droplet size and distribution. This study investigates the influence of biosurfactant concentration (1–3 %) and fuel injection system pressures (34.5, 69.0, and 103.5 MPa) on emulsified fuel properties. We utilised microscopy and a customized MATLAB image-processing code, along with a hot-plate technique and high-speed camera, to analyze droplet size distribution and micro-explosion behaviours. The findings demonstrate that increasing the concentrations of biosurfactants from 1 % to 3 % leads to an increase in the density by 1.07 % and viscosity by 10.81 %% but lower surface tension by 16.499 % in emulsified fuel, subsequently reducing particle size, delaying micro-explosion, and lowering peak temperature. On the other hand, all fuel properties undergo a notable reduction after passing through the fuel injection system, with increases in fuel pressure and injection through the nozzle’s orifices. In the case of fresh emulsion, with initial values of 841 kg/m3 density, 2.35 mm2/s viscosity, and 26.9 mN/m surface tension, these properties decreased to 829 kg/m3, 2.05 mm2/s, and 25.23 mN/m respectively, under an injection pressure of 103.5 MPa due to increasing the heating and shear forces generated by the fuel injection system while particle size distribution decreased from 2-4 µm to 1–2 µm from the fuel tank to the injector spray. The micro-explosion time of droplets from the fuel tank and injector spray operated at 34.5 MPa, 69.0 MPa, and 103.5 MPa was found to be 1.72 s, 1.97 s, 2.21 s, and 2.34 s, respectively. Correspondingly, the peak temperatures recorded were 272 °C, 277 °C, 282 °C, and 288 °C respectively.