Reduction Of Nitrogen Oxide Emissions Research Articles

Effects of exhaust gas recirculation on nitrogen oxides, brake torque and efficiency in a hydrogen direct injection spark ignition engine

This study investigated the effects of exhaust gas recirculation (EGR) on emission and efficiency in a hydrogen direct injection spark ignition engine. EGR was supplied as the low-pressure (LP)-EGR system by controlling EGR valve from zero to 18.7% in terms of mass fraction. The result showed that EGR effect on nitrogen oxides (NOx) reduction became enlarged as higher engine speed due to increasing residual gas fraction. Also, under the same excessive air ratio (λ:2.2), EGR addition made NOx reduction from 89.9 to 98.7 % as varying engine speed. As NOx limit was low, the maximum brake torque was also reduced. However, by using appropriate EGR, NOx margin could be converted to increasing brake torque under the same NOx concentration level from 1.9% to 18.2% as varying engine speeds. From this result, to achieve the maximum output when reaching the turbocharger’s limit in a hydrogen engine and effectively reduce nitrogen oxide emissions, it is not only dependent on lean combustion but also effective to incorporate approximately 20% EGR into the operating strategy.

The combined effect of split fueling strategy and EGR on the combustion, performance, and emission characteristics of a CRDI biofuel engine

AbstractThe current research investigates the impact of a split fueling strategy combined with several flow rates of exhaust gas recirculation (EGR) on the combustion and emission characteristics of a diesel engine running on B20 waste cooking oil (WCO) biodiesel. A four‐stroke single‐cylinder common rail direct injection engine was employed for experiments. It operates with a B20 blend of WCO biodiesel at 600 bar pressure for varying pilot fueling conditions of 10%, 20%, and 30%. The B20 blend with 30% pilot fuel injection (B20P30) showed excellent performance and emission characteristics compared with B20 blend with 10% pilot fuel injection (B20P10) and B20 with 20% pilot fuel injection (B20P20). However, B20P30 had greater levels of nitrogen oxide (NOx) emissions than those by diesel. EGR discharge levels in 5% increments, ranging from 0% to 15% were introduced to address this issue. The experimental findings revealed that both cylinder peak pressure and heat release rate showed a reduction when the EGR flow rate was enhanced. The recirculation of exhaust gas into the combustion chamber led to a slight increase in the emission levels of hydrocarbon (HC), carbon monoxide (CO), and smoke, as well as a decrease in carbon dioxide (CO2). Nevertheless, the introduction of EGR significantly decreased NOx emissions by 22.94%, 35.05%, and 47.96% for EGR flow rates of 5%, 10%, and 15%, respectively, when compared with the engine operating without EGR. Overall, the two‐stage fueling strategy, B20P30 blended with 10% EGR corroborated to be beneficial in reducing NOx emissions with minimal performance penalties. Although there was a slight uptick in certain emissions, the overall trade‐off between emission reduction and performance was favorable. The culmination of this study is targeting the objectives of sustainable development goal 7 (clean energy) and goal 13 (climate action) to be achieved by 2030.

Effect of split injection strategy of diesel fuel on multi-stage heat release and performance of a RCCI engine fueled with diesel and natural gas

Reactivity controlled compression ignition (RCCI) combustion is a advanced low temperature combustion concept to reduce CO2 and brake the trade-off between NOx and PM emissions for next generation compression ignition (CI) engines. However, it leads to the more complex multi-stage heat release in diesel/natural gas (NG) dual fuel engines and is criticized for extra-high methane and carbon monoxide emissions. Using the existing methods, it is difficult to effectively quantify the contribution of the accumulated heat release (AHR) at each stage to the whole combustion process and to create their relevance to the performance and emissions in the RCCI engines.In this paper, experiments were conducted on a ship diesel/NG dual-fuel engine at a load of 25 %. A new identification and quantitative analysis method of multi-stage heat release is proposed, and the coupling effects of the diesel split injection parameters on the multi-stage heat release and performance in the RCCI engine were revealed. The results show that the new method is not only available for analyzing the combustion of traditional CI engines but also is more effective for identifying the multi-stage combustion in RCCI engines. For the increased pre-injection ratio (PR), as the start of first injection (SOI-I) and the start of second injection (SOI-II) advance, the AHR in Stage-I (Q-Stage-I) decreases, and the increased Q-Stage-III lead to the improved indicated thermal efficiency (ITE > 49 %). Meanwhile, methane (CH4), non-methane hydrocarbon (NMHC) and carbon monoxide (CO) emissions can be reduced by more than 50 %, while nitrogen oxides (NOx) emissions increase. The impact significance of SOI-II on Q-Stage-I and Q-Stage-III is higher, their values are + 65.88 % and −51.04 %, respectively, and the Q-Stage-II is mainly controlled by SOI-I. The impact significance of Q-Stage-III on ITE is the highest about + 69.43 %. Q-Stage-I shows a higher positive correlation with CH4, NMHC and CO emissions although the proportion of Q-Stage-I is far smaller than that of Q-Stage-II and Q-Stage-III. Therefore, the simultaneous reduction of incomplete combustion products and NOx emission can be achieved by reasonably adjusting split injection parameters.

Experimental investigation of multi-burner array with lean lifted spray flames in inline and inclined configurations

Lean combustion in gas turbines garners attention for emissions reduction, yet it faces stability challenges demanding careful design considerations. In this study, a novel CHAIRLIFT combustor concept, which integrates low swirl lean lifted spray flames known for substantial nitrogen oxides emissions reduction, into a Short Helical Combustors (SHC) arrangement, is investigated. A comprehensive experimental test campaign explores key parameters, including staggered arrangement offset, equivalence ratios, and air inlet temperature, to evaluate its performance. The results reveal exceptional stability in low swirl, lifted flames compared to moderate swirl flames with larger inner recirculation zones. The unwanted flow deflection of highly swirled flames in the SHC arrangement is effectively avoided with the investigated low swirl, lifted flames. The study emphasizes the significant influence of fuel droplet evaporation time on flame stability near the flame root under low air inlet temperatures. Furthermore, at high air inlet temperatures, the complex flame stability mechanism in inclined configurations is controlled by various parameters, including outer recirculation zone size, air inlet temperature, and additional vortices generated by pressure differences near the wall. OH∗ chemiluminescence results corroborate these stability mechanisms, showing that at lower temperatures, the flame stabilizes closer to the nozzle exit due to local rich pockets near the shear layer. Conversely, at the same tilt angle, higher air inlet temperatures lead to an increased flame lift-off height due to faster evaporation and enhanced mixing. Exhaust gas analyses confirm the potential of the investigated lean lifted spray flames in a multi-burner arrangement to achieve very low NOx emissions over a wide range of operating conditions for all investigated burner inclinations. These findings may facilitate the future development and optimization of lean combustion technology for aircraft engines.

Flue Gas Recirculation System for Biomass Heating Boilers—Research and Technical Applications for Reductions in Nitrogen Oxides (NOx) Emissions

The paper discusses the results of investigations of the change in thermal and emission-related parameters of a heating boiler fueled with biomass after a modification with a proprietary flue gas recirculation system made for this type of equipment. The results provide insight into the combustion process with a multistage flue gas recirculation that materially affected the boiler operation: a reduction in the mass concentration of nitrogen oxides (NOx) by reducing the combustion temperature. The authors also observed a reduction in the emission of particulate matters (PM) and carbon monoxide (CO). For the investigations, the authors used a heating boiler fitted with an automatic fuel feed (timber pellets) and a proprietary patented flue gas recirculation system (Polish patent Pat. 243395) for low power solid fuel heating boilers. Aside from the measurement of the mass concentration of the emitted pollutants, the research focused on the measurements of the temperature inside the combustion chamber, the temperature of the flue gas and the level of oxygen in the flue gas. The aim of the research was to confirm the validity of using the flue gas recirculation technique to reduce emissions of harmful substances from biomass heating boilers, as a technique not previously used for this group of devices. Moreover, the aim of the research was to test an original engineering solution, in the form of a flue gas distribution valve, and investigate its effect on reducing NOx emissions and improving other thermal and emission parameters of the boiler. The obtained research results confirm the validity of the chosen actions and provide a positive premise for the practical use of this technology in solid fuel heating boilers.

Evaluation of Incinerator Performance and Policy Framework for Effective Waste Management and Energy Recovery: A Case Study of South Korea

Waste incineration is a crucial component of waste management as it is the final stage of circular utilization and the initial phase of disposal. Effective waste management prioritizes energy recovery from waste and substantial waste volume reduction while committing to minimizing air pollutant emissions, particularly nitrogen oxides (NOx). This study involves an in-depth analysis of operational data from 44 incineration facilities in South Korea spanning 5 years, supplemented by empirical measurements from 14 sites. This study aimed to assess three key aspects of these incineration facilities: (1) waste volume reduction characteristics, (2) energy recovery capabilities, and (3) NOx emission reduction performance. We examined how these elements interact within the policy framework governing incinerator management in South Korea. Quantitatively, incinerating 100 tons of municipal waste resulted in a gain of 338.7 m3 in landfill capacity and recovery of 637.5 GJ of energy in the form of heat or electricity. Notably, South Korean incineration facilities significantly extend the lifespan of landfill sites, aligning closely with the objectives of the South Korean Ministry of Environment’s “No More Direct Landfilling of Household Waste Policy”. This positive outcome is further reinforced by the “Incineration Tax Reduction Policy”, which incentivizes active efforts toward energy recovery during incineration. Our study provides decision-makers with valuable insights for achieving a harmonious equilibrium between environmental sustainability and resource utilization, thereby contributing to the continuous improvement of policies aimed at South Korea’s vision of achieving a circular economy.

DIGITAL AND ENVIRONMENTAL REGULATION-DRIVEN TRANSFORMATION MANAGEMENT SYSTEM IN ENTERPRISE LOGISTICS ACTIVITIES

One of the most critical problems of the modern economy is the efficiency of the interaction of the logistics systems of enterprises with the elements of the logistics infrastructure. For a successful interaction, the transformation of the logistics activities of enterprises must be carried out logically and holistically, which is possible under the formation of an effective management system for this process. The proposed study examines the principles of forming this system based on the principles of the digital economy and the requirements for environmental regulation of activities. The research was carried out in two directions. The first direction was the study of the peculiarities and principles of the formation of the system of managing the logistics activity of the enterprise in the conditions of its transformation. A system of principles was formed to help regulate the process of managing the evolution of the enterprise's logistics activity. Another research direction was determining the influence of management decisions in enterprise logistics activities on the environment. For example, regarding the volume of product deliveries from Mareven Food Europe LLC to foreign consumers in 2021, a management decision was proposed that could lead to a reduction of nitrogen oxide emissions by 2.8 times in one year. The study can be useful in planning the transformation of enterprises' logistics systems, the requirements of the digital economy, and environmental regulation. Keywords: logistics activity, digital economy, environmental regulation, management system, management decision.

Numerical simulation of the aerodynamic flow of air and the results of the study of a burner device for burning synthetic gas

This work contributes to the ecological solution of synthetic gas combustion. The methods and tools that were used to research this topic are briefly described in the article. For the study, two programs were used and stabilizers were considered in terms of angular parameters. The angular stabilizers' dimensions and the optimal aerodynamic cross-section behind the stabilizer were calculated using numerical simulation in the ?COMSOL Multiphysics? program. This article also describes an experimental bench for burning syngas in a burner device. Due to the low-reaction characteristics of synthetic gas, its composition is variable. In this regard, to efficiently burn synthetic gas of various compositions, it is necessary to select the optimal angle of stabilizer inclination. During the experiments, the effect of angular stabilizers on the stabilization process, the efficiency of burning synthetic gas due to stable combustion, and the reduction of harmful emissions were investigated. Three different stabilizer angles (45?, 60?, and a semicircle) were presented on an experimental bench to find the optimal stabilizer angle for stable combustion with reduced nitrogen oxide emissions. As a result of the observation, it can be concluded that the combustion completeness of synthetic gas in burner devices depends not only on the angle of the stabilizer, but also on the coefficient of the incoming air, and this, in turn, affects the temperature level of the gases in the combustion zone.

Engine performance and emission characteristics of microwave-produced biodiesel blends

The main objective of this research is to investigate, experimentally, the effects of biodiesel blends on the performance and emissions of a Diesel engine. Measurements were carried out on a single-cylinder, four-stroke, and air-cooled compression-ignition engine, under half and full load conditions. Engine speed was varied from 1000-3000 rpm. Biodiesel was produced by transesterification process of sunflower oil with ethanol, using microwave-assisted heating reactor. Three biodiesel-diesel mixtures: containing 5%, 10%, and 20% by volume of biodiesel, respectively, have been tested and compared to pure diesel fuel. The effects of these biodiesel blends on the engine operating characteristics such as brake specific fuel consumption, brake power, brake thermal efficiency, brake mean effective pressure, and on carbon CO, CO2, and NOx emissions, have been investigated. It was noticed that, at full load, the specific fuel consumptions of biodiesel blends were higher compared to the pure diesel fuel, but no change was observed under ? load. An improvement in the brake thermal efficiency, under ? load, was obtained, but at full load, for medium and high speed, the thermal efficiencies of all biodiesel blends showed a decrease compared to pure diesel fuel. Concerning pollutants emissions, a decrease in CO emissions of all biodiesel blends was noticed. The best result in CO emissions was achieved by the mixture containing 10% by volume of biodiesel with an average reduction value close to 40%. In addition, a significant reduction in NOx emissions was observed for the three biodiesel blends.

ENHANCING PERFORMANCE OF BIODIESEL-HYDROGEN BLENDS OPERATED DI DIESEL ENGINE USING VARIABLE INJECTION TIMING

The study aimed to investigate the effect of injection timing (IT) on the combustion, emission, and performance characteristics of a single-cylinder, four-stroke, direct injection (DI) diesel engine. The engine was run on different fuel blends, namely, pure diesel, diesel blended with 20% mahua oil methyl ester (B20) with three hydrogen flow rates of 20, 22.5, and 25 liters per minute (lpm). The experiment was carried out at a rated speed of 2000 rpm. Four different injection timings (ITs) were applied, namely, 19°, 23°, 27°, and 31° bottom top dead center (BTDC), relative to the standard IT of 23° BTDC. The results showed that the optimal IT was 27° BTDC for B20-hydrogen (22.5 lpm) dual-fuel mode operation. This condition delivered the highest brake thermal efficiency (BTE) between 24.4 and 34.3% , the lowest brake-specific fuel consumption (BSFC) between 0.25 and 0.41 kg/KWh, and the minimum unburnt hydrocarbon (HC) emissions between 8 and 32 ppm, and carbon-monoxide (CO) emissions ranging between 0.002 and 0.389% . However, the concentration of nitrogen-oxides (NOx) emissions was slightly increased, ranging between 24 and 53 ppm compared to B20. Further modifications in the IT resulted in decreased brake thermal efficiency ranging between 13 and 31% , increased hydrocarbon emissions between 25 and 28% , and increased CO emissions between 70 and 96% for both 4° BTDC advancements and retardations. Moreover, both modifications reduced NOx emissions by 8-19% . Hence, based on this study's findings, employing an IT of 27° BTDC for 22.5 Ipm of hydrogen with a B20 dual-fuel mode of operation for the DI diesel engine to achieve optimal performance, combustion, and emission characteristics is recommended.

Numerical Study on Compact Design in Marine Urea-SCR Systems for Small Ship Applications

With increasingly stringent emissions legislation, such as that stipulated by the International Maritime Organization, for nitrogen oxide emission reduction in marine diesel engines, the imperative of curtailing nitrogen oxide emissions from marine diesel engines is intensifying. Consequently, the significance of aftertreatment technologies, including diesel particulate filters (DPFs) and selective catalytic reduction (SCR), is poised to grow substantially. In particular, a redesign is required to reduce the size of DPF and SCR systems for application in small ships. In this study, we varied the shape of the filters in DPF and SCR systems, aiming to achieve a distinct flow pattern and enable overall miniaturization. The performance metrics, including the nitric oxide (NO) reduction rate, NH3 slip rate, and pressure drop, of the redesigned models were compared with those of the conventional model. Computational fluid dynamics simulations were used to compare the performance of the redesigned model with that of the conventional model in terms of NO reduction and pressure drop. The redesigned system achieved a NO reduction rate of 6.9% below that of the conventional system, offering additional noteworthy benefits such as a 50% reduction in both pressure and overall length.

Ozone responses to reduced precursor emissions: A modeling analysis on how attainable goals can improve air quality in the Mexico City Metropolitan Area

High tropospheric ozone (O3) concentrations prevent the improvement of the air quality in the Mexico City Metropolitan Area (MCMA). Although the problem has improved considerably since the 1990s, a rebound in O3 levels in recent years has raised concerns about the deteriorating air quality. The nonlinear relationship between O3 formation and the emissions of its main precursors, i.e., volatile organic compounds (VOCs) and nitrogen oxides (NOx), is a challenge when measures are enacted for effective mitigation of the O3 problem. This study evaluated the reduction in precursors, VOCs and NOx, using an up-to-date regional air quality model (HERMES-Mex-WRF-CMAQ). For evaluating realizable scenarios, the decline in VOC achieved in Japan after policy implementation was the targeted VOC reduction (40 % from area sources), and the NOx reduction observed in the MCMA during the COVID-19 pandemic was the targeted NOx reduction (40 % from mobile sources). The analysis evaluated the O3 responses to changes in a single precursor and a combination of both during a period of high O3 concentrations (April 2019). The results showed that 40 % reduction in VOC emissions would decrease the O3 8-h maximum concentrations by 16 %. However, 40 % reduction in NOx emissions would increase O3 by >15 %. The simultaneous reduction of both precursors did not significantly affect O3 levels. The diagnosis of ozone sensitivity using the H2O2/HNO3 ratios reinforced the simulation findings, indicating that VOC emissions limited ozone formation in most MCMA areas. As the simulated scenarios were based on factual case studies, our research offers insights into the realistic aims of MCMA policies to reduce O3 levels.

Study on Control Strategies on NOX Emissions to Meet Real Driving Emissions.

The aim of this study was to fulfill the NOx emissions standards for a light-duty diesel vehicle under real driving emissions (RDE) testing conditions by implementing various control strategies. In this study, RDE tests were performed by adjusting the air mass quantity and postinjection quantity in order to analyze engine-out and tail-pipe nitrogen oxides (NOx) emissions for different phases of RDE. The results showed that reducing in air mass quantity enabled the engine to operate in higher exhaust gas recirculation (EGR) rate regions, resulting in a 32.5% reduction in engine-out NOx emissions and an 80.4% decrease in tail-pipe NOx emissions. Increasing the postinjection quantity primarily enhanced the NOx conversion efficiency for the urban phase by 7.5%, leading to a 22.6% reduction in tail-pipe NOx emissions. By employing both strategies, vehicles can comfortably meet the CN6b emission regulations by a substantial margin.

Prediction of Condensation in the Heat Exchangers of Engine Intake Systems according to External Environmental and Operating Conditions

Low-pressure exhaust gas recirculation (LP-EGR) systems are applied to diesel engines because they reduce nitrogen oxide emission by lowering the internal temperature of the cylinder by mixing the oxides with intake air. However, low-temperature ambient conditions include a large amount of vapor in the mixed gas flowing into the intercooler; when heat is exchanged, the water vapor condenses and is adsorbed on the surface of the intercooler fin to form a liquid film. Condensation occurs as the thermal resistance between the vapor and solid surface increases with the thickness of the liquid film and causing a corrosion due to condensation of the surface. In this study, the amount of condensation was predicted through calculations based on thermodynamic studies. Factors that can cause condensation inside the intercooler (fuel, air, and LP-EGR) were selected as variables. A mathematical formula was established to predict the convergence form of condensation or the amount of condensation over time at various temperature and relative humidity conditions. The formula predicted the condensation amount in the intercooler of the diesel engine, compared it to the actual amount of condensation in the test evaluation with an error of less than 4%. Additionally, because the formula can predict the amount of condensation by changing the heat exchange area of the intercooler, the application range of the formula was expanded to predict the condensation in the intercoolers of gasoline vehicles with different heat exchange areas and fuel types. The condensation error was within 2%, indicating a high consistency. Validation of the formula predicts a reliable amount of condensation under various operating and ambient temperature conditions, which means that both the time and cost of the test evaluation require the determination of the cause before solving the actual condensation problem.

Performance, emission, combustion, exergy, exergoeconomic and sustainability analyses of EGR incorporated CI engine fuelled with areca nut husk nano-additive dosed plastic oil–water-diesel emulsion blend

This first-of-a-kind research emphasizes the influence of exhaust gas recirculation (EGR) on engine characteristics, and exergy, sustainability, and exergoeconomic aspects of compression ignition engine, powered by plastic grocery bag-extracted plastic oil-diesel-water emulsion blend dosed with bio-nano-additive extracted from areca nut husk (D10EPO-15 ppm). Three EGR rates (5%, 10%, and 15%) were incorporated at varying engine loads. At 100% load, the EGR incorporation reduced the peak heat release rate and peak pressure up to 6.5 and 5.6%, respectively, in comparison to the base fuel without EGR. Up to 5.2 and 9.1% reduction in exhaust gas temperature and nitrogen oxide emission (NOx) was noticed with the EGR incorporation. However, carbon monoxide (CO), hydrocarbon (HC), and smoke emissions increased with the EGR incorporation. Nevertheless, considering the overall characteristics, 5% EGR was the most suitable one to have a lower NOx (3.4%) with a minimum penalty on CO (4.3%), HC (5.4%), and smoke (3.6%) emissions as well as fuel consumption (3%), at full load. Amongst the three EGR rates, 5% EGR incorporation also has the highest exergy efficiency (20.9%) and sustainability index (1.26). Exergoeconomic analysis also revealed the favorability of 5% EGR, and at full load, 5% EGR showed the lowest specific exergy cost inflow rate (0.8957 $/hr), the lowest specific exergy cost rate for shaft work (75.27 $/GJ), the lowest relative cost difference (3.99), and the highest exergoeconomic factor (9.95%).

Insights into soil NO emissions and the contribution to surface ozone formation in China

Abstract. Elevated ground-level ozone concentrations have emerged as a major environmental issue in China. Nitrogen oxide (NOx) is a key precursor to ozone formation. Although control strategies aimed at reducing NOx emissions from conventional combustion sources are widely recognized, soil NOx emissions (mainly as NO) due to microbial processes have received little attention. The impact of soil NO emissions on ground-level ozone concentration is yet to be evaluated. This study estimated soil NO emissions in China using the Berkeley–Dalhousie Soil NOx Parameterization (BDSNP) algorithm. A typical modeling approach was used to quantify the contribution of soil NO emissions to surface ozone concentration. The brute-force method (BFM) and the Ozone Source Apportionment Technology (OSAT) implemented in the Comprehensive Air Quality Model with Extensions (CAMx) were used. The total soil NO emissions in China for 2018 were estimated to be 1157.9 Gg N, with an uncertainty range of 715.7–1902.6 Gg N. Spatially, soil NO emissions are mainly concentrated in Central China, North China, Northeast China, the northern Yangtze River Delta (YRD), and the eastern Sichuan Basin, with distinct diurnal and monthly variations that are mainly affected by the temperature and timing of fertilizer application. Both the BFM and OSAT results indicate a substantial contribution of soil NO emissions to the maximum daily 8 h (MDA8) ozone concentrations by 8.0–12.5 µg m−3 on average for June 2018, with the OSAT results being consistently higher than the BFM results. The results also showed that soil NO emissions led to a relative increase in ozone exceedance days by 10.5 %–43.5 % for selected regions. Reducing the soil NO emissions resulted in a general decrease in monthly MDA8 ozone concentrations, and the magnitude of ozone reduction became more pronounced as reductions increased. However, even with complete reductions in soil NO emissions, approximately 450.3 million people are still exposed to unhealthy ozone levels, necessitating multiple control policies at the same time. This study highlights the importance of soil NO emissions for ground-level ozone concentrations and the potential for reducing NO emissions as a future control strategy for ozone mitigation in China.

NOx emissions prediction in diesel engines: a deep neural network approach.

The reduction of various nitrogen oxide (NOx) emissions from diesel engines is an important environmental issue due to their negative impact on air quality and public health. Selective catalytic reduction (SCR) has emerged as an effective technology to mitigate NOx emissions, but predicting the performance of SCR systems remains a challenge due to the complex chemistry involved. In this study, we propose using DNN models to predict NOx emission reductions in SCR systems. Four types of datasets were created; each consisted of five variables as inputs. We evaluated the models using experimental data collected from a diesel engine equipped with an SCR system. Our results indicated that the deep neural network (DNN) model produces precise estimates for exhaust gas temperature, NOx concentration, and De-NOx efficiency. Moreover, inclusion of additional input features, such as engine speed and temperature, improved the prediction accuracy of the DNN model. The mean absolute error (MAE) values for these parameters were 3.1°C, 3.04ppm, and 3.65%, respectively. Furthermore, the R-squared coefficient of determination values for the estimates were 0.912, 0.983, and 0.905, respectively. Overall, this study demonstrates the potential of using DNNs to accurately predict NOx emissions from diesel engines and provides insights into the impact of input features on the performance of the model.

Significantly alleviated PM2.5 pollution in cold seasons in the Beijing-Tianjin-Hebei and surrounding area: Insights from regional observation

PM2.5 pollution has been greatly alleviated in the Beijing-Tianjin-Hebei (BTH) and surrounding area since the implementation of Action Plans for blue skies. Regional air pollution covering multiple cities has recently become common, but an overview from a regional perspective is scarse. In this work, based on PM2.5 chemical composition data collected in “2 + 26” cities during four consecutive autumn-winter seasons (AWS, from October to next March) from October 2016 to March 2020, we determined the main components driving the increase in PM2.5 mass concentration within different PM2.5 concentration regimes. Regionally, in the low PM2.5 regime (daily concentration ≤ 75 μg/m3), the PM2.5 mass remained organic matter (OM)-driven during the four AWSs. In the high PM2.5 regime (daily concentration > 75 μg/m3), regional PM2.5 increase pattern rapidly transformed from OM-driven during the 2016–2017 AWS to secondary inorganics-driven during the latter three AWSs, with nitrate becoming the dominant component, driving PM2.5 increase in almost 90% cities in the region. These transitions not only reflect the effectiveness of policies to control emissions from coal combustion and biomass burning in recent years, but also highlight the need to further reduce nitrogen oxides emissions from diesel vehicles, non-road mobile machinery and industry. Besides, the control of sulfur dioxide and primary organic matter should not be neglected, given the substantial contribution of PM2.5 sulfate under stagnant and humid meteorological conditions, especially in the geographically central and southern parts of the region, and the need for in-depth air quality improvement if the PM2.5 concentration standards are tightened. Considering the dominance of nitrate in driving regional PM2.5 pollution, more research on nitrate formation and its atmospheric and climatic impacts is warranted.

Economic analysis and TOPSIS approach to optimize the CI engine characteristics using span 80 mixed carbon nanotubes emulsified Sapindus trifoliatus (soapnut) biodiesel by artificial neural network prediction model

The rise in fuel use within the vehicle sector leads to a corresponding escalation in energy demand. To achieve optimal operating conditions, it is necessary to reduce energy usage. For that, the primary objective of this study is to utilize an artificial neural network (ANN) and the optimization approach as a technique for order performance by similarity to the ideal solution (TOPSIS) to forecast the optimal features of a compression ignition (CI) engine. The experiment was performed with a four-stroke mono-cylinder compression ignition (CI) engine under different load situations. The study considers six operational parameters, including brake thermal efficiency (BTE), specific fuel consumption (SFC), as well as emission characteristics including carbon monoxide (CO), hydrocarbon (HC), Nitrogen oxides (NOx), and smoke. From the ANN results, the correlation coefficients for BTE, SFC NOx, smoke, HC, and CO were 0.9712, 0.9862, 0.964, 0.941, 0.998, and 0.978, respectively. The SNBD25 + 30 mg/L SP80 + 30 mg/L CNT blend exhibited the maximum closeness coefficient under various load conditions. The maximum closeness coefficient obtained from the TOPSIS optimisation approach under full load conditions is 0.982386. From the result of the ANN prediction technique, for TOPSIS optimised blend SNBD25 + 30 mg/L SP80 + 30 mg/L CNT a 13.84% increase in BTE, 11.21% decrease in SFC, 16.67% decrease in CO, 13.87% decrease in NOx, 19.23% decrease in HC, and 32.53% decrease in smoke. Based on the outcomes obtained from the ANN and TOPSIS methodologies, it can be concluded that the SNBD25 + 30 mg/L SP80 + 30 mg/L CNT blend exhibits superior performance in terms of reduced NOx emissions and enhanced efficiency, surpassing the other blends under consideration. The incorporation of carbon nanotubes (CNTs) into a system leads to an increase in the carbon-to‑oxygen ratio, resulting in a reduction in the generation of nitrogen oxides (NOx). The cost of a mixture consisting of SNBD25 + 30 mg/L SP80 + 30 mg/L blend is 20% lower than the cost of diesel on a per-litre basis.

Nonlinear effect of NOx concentration decrease on secondary aerosol formation in the Beijing-Tianjin-Hebei region: Evidence from smog chamber experiments and field observations

During the COVID-19 lockdown in the Beijing-Tianjin-Hebei (BTH) region in China, large decrease in nitrogen oxides (NOx) emissions, especially in the transportation sector, could not avoid the occurrence of heavy PM2.5 pollution where nitrate dominated the PM2.5 mass increase. To experimentally reveal the effect of NOx control on the formation of PM2.5 secondary components (nitrate in particular), photochemical simulation experiments of mixed volatile organic compounds (VOCs) under various NOx concentrations with smog chamber were performed. The proportions of gaseous precursors in the control experiment were comparable to ambient conditions typically observed in the BTH region. Under relatively constant VOCs concentrations, when the initial NOx concentration was reduced to 40% of that in the control experiment (labelled as NOx,0), the particle mass concentration was not significantly reduced, but when the initial NOx concentration decreased to 20 % of NOx,0, the mass concentration of particles as well as nitrate and organics showed a sudden decrease. A “critical point” where the mass concentration of secondary aerosol started to decline as the initial NOx concentration decreased, located at 0.2–0.4 NOx,0 (or 0.18–0.44 NO2,0) in smog chamber experiments. The oxidation capacity and solar radiation intensity played key roles in the mass concentration and compositions of the formed particles. In field observations in the BTH region in the autumn and winter seasons, the “critical point” exist at 0.15–0.34 NO2,0, which coincided mostly with the laboratory simulation results. Our results suggest that a reduction of NOx emission by >60% could lead to significant reductions of secondary aerosol formation, which can be an effective way to further alleviate PM2.5 pollution in the BTH region.