Nitrogen Oxide Emissions Research Articles

Impact of Biomass Fuel Feeding Ratio in Co-firing Circulating Fluidized Bed Boiler: A Computational Fluid Dynamics Study

Nowadays, our global population is on a notable rise, coupled with an annual surge in energy consumption. The prevailing reliance on fossil fuels, especially in electricity generation, has significantly contributed to environmental pollution and exacerbated global warming. The circulating fluidized bed, distinguished for its continuous operation and effective heat transfer in the combustion chamber, emerges as a prominent boiler type. Furthermore, the use of biomass fuel, recognized for its renewable and environmentally friendly characteristics, presents an attractive option. Hence, exploring a co-firing system incorporating both coal and biomass as fuel feeds for the boiler holds promise, necessitating optimization for efficient energy production and reduced gas emissions. This study employs computational fluid dynamics to simulate the intricate interactions of solid fuel and flue gas reactions within the boiler, utilizing the two-fluid method for multiphase flow simulation. The circulating fluidized bed boiler in focus employs subbituminous coal, woodchips as biomass sources, and sand as the bed material. Model validation against operational data, including bed temperature, flue gas velocity outlet, and carbon dioxide mass fraction, indicates minimal deviation. Examination of the biomass ratio's impact on fuel feed reveals a reduction in sulfur dioxide emissions with an increasing biomass ratio, attributed to the lower sulfur content in woodchips compared to coal. However, a heightened woodchip blending ratio results in diminished boiler efficiency due to the altered heating value of the mixed solid fuel. The optimized biomass-to-coal ratio in fuel feeding is determined as 59.15%, achieving a maximized boiler efficiency of 82.84% and minimized pollution gas emissions of sulfur oxide and nitrogen oxide in accordance with industrial standards.

Performance and Emissions Characteristics of Vehicle Fuelled with Blended Palm Biodiesel Before and After Engine Overhaul

Rapid industrialization and growth in population have resulted in a rapid increase in energy demand. Pollutant emissions from diesel engines have caused major impacts in disturbing the ecological system. The Malaysian government implemented the B10 biodiesel program for the transportation sector and B7 for the industrial sector in 2019 to drive the demand for palm oil and increase the sustainability of energy resources. For future implementation, the government is looking toward for higher percentage of blended biodiesel, such as B30 and above. This paper presented the effect of engine overhaul on the performance and emissions of a vehicle fuelled with blended biodiesel (B10, B20 & B30) by comparing before and after the engine overhaul. By using a vehicle Toyota Hilux 2.5L, the vehicle was attached to a chassis dynamometer for determining its performance such as brake power and brake specific fuel consumption (BSFC) at 45% and 90% of Acceleration Pedal Position (APP), respectively. The exhaust gas emissions were measured using a 5-channel analyser for determining the carbon dioxide (CO2), carbon monoxide (CO) and nitrogen oxide (NOx). The experiment was conducted in a steady-state condition with a constant speed of 30, 60, 90, and 110 km/h simulating rural, urban, and motorway speeds. The performance results revealed that blended biodiesel B10, B20 and B30, produced higher brake power, and lower brake-specific fuel consumption after engine overhaul. Emissions results showed that CO was increased at 45% APP but decreased at a higher 90% APP, and in most cases, NOx and CO2 emissions were decreased with an increase in speed for both APP.

Hydrogen as Fuel for ICEs: State of Art and Technological Challenges

The climate change, as the main consequence of the polluting emissions due to anthropic activities, is nowadays a well-known threat to human health as well as for the environment safety. Several plans and strategies have been announced by the governments to detach from fossil fuel-based energy and gradually reduce the carbon footprint of their economies. In this scenario, the road transport sector is turning out to be the main “technological gym” to test and improve new powertrain solutions to achieve as soon as possible the goal of the net-zero carbon emissions, at least in the tank-to-wheel (TTW) context. In view of this, the hydrogen as fuel is gaining ever more attention from the scientific community, both as the middle-term solution to achieve the abovementioned goal and as a prominent future energy carrier. In this review, the performance and main characteristics of the hydrogen-internal combustion engines (H2-ICEs) are discussed based on the most recent studies available in literature. A comprehensive overview of various topics is offered, from the production stage to the combustion anomalies, mixture formation strategies, and the challenge of reducing the nitrogen oxides (NOx) emissions under high load conditions.

Experimental research on vehicles equipped with a GMP Hybrid for the new Euro 7 emissions standard

With the increase the number of vehicles on European roads, the road transport has become the biggest source of air pollution in the cities of the old continent. According to European Commission estimates in 2018, more than 39% of NOx (nitrogen oxides) emissions and 10% of PM2.5 and PM10 emissions (mechanical particles with diameters of 2.5 and 10 micrometers) were attributed to road transport. It is known that, in order to limit to some extent, the uncontrolled increase in harmful emissions from road vehicles, the European Commission has gradually introduced new pollution standards to be met by manufacturers of new vehicles. In the second half of 2022, the Commission presented a new proposal to reduce pollutant emissions from new vehicles sold in the European Union (EU), defining the new Euro 7 pollution standards. Compared to Euro 6 by 2035, according to European Commission estimates, these new Euro 7 standards, together with a progressive increase in the number of electric vehicles sold, aim to reduce pollutant emissions from private vehicles and vans by around 35% for NOx emissions and around 13% for particulate emissions. Therefore, both the Euro 7 and CO2 emissions standard (CAFE) for vehicles have been designed to improve air quality in cities and reduce greenhouse gas emissions, including by increasing the use of electric vehicles. Starting from this hypothesis, the first part of the paper presents the experimental model developed in the AMESim simulation platform of a mid-size vehicle equipped with a hybrid GMP, tested on a roller bench, which simulates pollutant emissions in this new Euro 7 standard. In the second part of the paper, the simulation results and possible causes influencing hybrid GMP behavior leading to the evolution of pollutant emissions are analyzed. Finally, the paper formulates conclusions on the evolution of pollutant emissions.

Numerical analysis of flow and combustion of Coal-Ammonia blend in coal-fired furnace

Co-firing ammonia (NH3) in coal-fired power plants presents an attractive method to expedite the global decarbonization process. Nevertheless, the challenge lies in reconciling the need for higher temperatures within the furnace with the imperative of maintaining low nitrogen oxides (NOx) emissions, which limits the widespread use of NH3 as a fuel. In this article, the flow and combustion of coal-NH3 blends in a 3 × 700 MW tangentially-fired utility coal boiler furnace are investigated using Computational Fluid Dynamics (CFD). The impact of NH3 blending ratios is examined through numerically simulated combustion involving five co-firing ratios (CRs) of NH3, including 0%, 10%, 20%, 30%, and 50%. Various combustion properties are assessed, including the furnace’s temperature profile, flow distribution, species emissions, pollutant formation, and heat generation. To validate the approach, single coal and coal blend simulations performed depicted reasonable agreement in predicting furnace flame temperatures. The predicted flue gas temperature exhibited a decrease with an increase in NH3 CR, leading to a reduction in the furnace’s heat generation. Regarding flow characteristics, there was a notable increase in velocity as the concentration of NH3 was raised. The elevated NH3 content correlated with an observed rise in oxygen (O2) residue in the rear pass, coupled with a decrease in both carbon dioxide (CO2) and carbon monoxide (CO) concentrations. Pollutant formation, assessed in terms of nitrogen oxide (NO) emissions, revealed an increase in concentration with the rise in NH3 CR. Indeed, these findings suggest a promising strategy for adopting NH3 as a viable alternative to coal, representing an effective carbon-neutral fuel for the future.

Use of biofuels in marine diesel engines for sustainable and safe maritime transport

The article presents results of research on the use of fuel mixtures, containing with biodiesel fuel. The research was carried out on specialized sea vessels with a deadweight of 10,820 tons and 29,420 tons, which made passages in the waters of South America and the Caribbean, as well as in the Sulphur Emission Control Areas of Northern Europe. The operation of the ship's power plants (main and auxiliary engines) was provided both on marine fuel of petroleum origin and on a fuel mixture that consisted of petroleum fuel and biodiesel fuel. The experiments were carried out on marine medium-speed diesel engines 5DC-17A Daihatsu Diesel, 16V32 Wärtsilä-Sulzer and Volvo Penta TWD1645GE. Various kinds of marine fuels and as biodiesel fuel Fatty Acid Methyl Esters B99.9 FAME and B99.6 FAME were used. The concentration of biodiesel fuel in the fuel mixture was 5–20 %. The environmental friendliness of the work of sea vessels was assessed by the value of the emission of nitrogen oxides, sulphur, and carbon. As a result of the research, a variant of adjusting the sea crossing was proposed to ensure the continuous operation of the ship's power plant using biodiesel fuel.

An Estimate of the NOX Emissions of Euro 6 Diesel Passenger Cars with Manipulated Emission Control Systems

The motivation for conducting this research stems from the increasingly applied manipulations of emission control systems (ECSs), especially those in diesel passenger cars (PCs). The study aimed to investigate the influence of manipulations of exhaust gas recirculation (EGR) valves and a diesel exhaust fluid (DEF)-dosing system on the nitrogen oxide (NOX) emissions of a Euro 6 diesel vehicle and, through the quantification of vehicles with manipulated ECSs, estimate the emissions of Euro 6 diesel PCs. Portable emissions measurement system (PEMS) measurements were performed on a Euro 6 diesel vehicle at a constant speed and on real driving emission (RDE) routes. The speed-dependent functions of the NOX hot emission factor (EF) were calculated for seven different scenarios. The results showed that the NOX EFs for the worst-case scenarios were more than two orders of magnitude higher than those where all ECSs were active. Applying the calculated EFs and the survey answers on the percentage of manipulated PCs to the Croatian Euro 6 diesel PC fleet, the results showed that the emission levels were up to 46.3% higher than the emissions calculated by the official computer program COPERT v5.6.5, with a tendency towards significantly higher values. The main conclusion is that vehicle manufacturers, policymakers, and the general public need to be informed about the enormous damage that in-use vehicles with manipulated ECSs cause to the environment and human health, in order to prevent such actions.

An integrated approach for wastewater treatment and algae cultivation: Nutrient removal analysis, biodiesel extraction, and energy and environmental metrics enhancement

Human urine is rich in nitrogen and phosphorus, and the presence of these elements in wastewater significantly disrupts the biogeochemical cycle. Meanwhile, green algal biomass cultivation is unfeasible without these nutrients. Hence, the present study integrates wastewater treatment and algae cultivation to extract biodiesel and improve its performance through fuel modification. Chlorella vulgaris algae was cultivated in different dilution ratios of water and urine, and the nutrient removal rate was analyzed. Chlorella vulgaris algae biodiesel (CAB) was derived through Bligh and Dyer's method followed by transesterification, and its functional and elemental groups were analyzed. The various volume concentrations of CAB were blended with regular diesel fuel (RDF), and 10% water was added to a 30% CAB blended RDF to evaluate the combustion performance and environmental impacts. The results of the experiments demonstrated that the algae cultivation effectively removed the wastewater nutrients. The functional and elemental groups of CAB are identical to those of RDF. The engine characteristics of test fuels report that the CAB-blend RDF fuel mixtures generate low carbon footprints, whereas negative impacts have been drawn for performance metrics and oxides of nitrogen emissions. The water-emulsified fuel outweighed the unfavorable effects and promoted more efficient and cleaner combustion.

Lower soil nitrogen-oxide emissions associated with enhanced denitrification under replacing mineral fertilizer with manure in orchard soils

Emerging evidence suggests that replacing mineral fertilizers with organic livestock manure can effectively suppress reactive gaseous nitrogen (N) emissions from soils. However, the extent of this mitigation potential and the underlying microbial mechanisms in orchards remain unclear. To address this knowledge gap, we measured nitrous and nitric oxide (N2O and NO) emissions, microbial N cycling gene abundance, and N2O isotopomer ratios in pear and citrus orchards under three different fertilization regimes: no fertilization, mineral fertilizer, and manure plus mineral fertilizer. The results showed that although manure application caused large transient peaks of N2O, it reduced cumulative emissions of N2O and NO by an average of 20 % and 17 %, respectively, compared to the mineral fertilizer treatment. Partial replacement of mineral fertilizers with manure enhanced the contribution of AOA to nitrification and reduced the contribution of AOB, thus reducing N2O emissions from nitrification. Isotope analysis suggested that the pathway for N2O production in the soils of both orchards was dominated by bacterial denitrification and nitrifier denitrification. The manure treatment reduced the ratio of denitrification products. Additionally, the dual isotope mixing model results indicated that partially replacing mineral fertilizers with manure could promote soil denitrification, resulting in more N2O being reduced. N-oxide emissions were on average 67 % higher in the pear orchard than in the citrus orchard, probably due to the differences in soil physicochemical properties and growth habits between the two orchards. These findings underscore the potential of partially replacing mineral fertilizers with organic manure in orchards to reduce gaseous N emissions, contributing to the transition towards environmentally sustainable and climate-smart agricultural practices.

Review of Research on Asymmetric Twin-Scroll Turbocharging for Heavy-Duty Diesel Engines

<div>Asymmetric twin-scroll turbocharging technology, as one of the effective technologies for balancing fuel economy and nitrogen oxide emissions, has been widely studied in the past decade. In response to the ever-increasing demands for improved fuel efficiency and reduced exhaust emissions, extensive research efforts have been dedicated to investigating various aspects of this technology. Researchers have conducted both experimental and simulation studies to delve into the intricate flow mechanism of asymmetric twin-scroll turbines. Furthermore, considerable attention has been given to exploring the optimal matching between asymmetric twin-scroll turbines and engines, as well as devising innovative flow control methods for these turbines. Additionally, researchers have sought to comprehend the impact of exhaust pulse flow on the performance of asymmetric twin-scroll turbines. Drawing on a comprehensive review of prior research endeavors, this study presents a meticulous summary of the advancements made in asymmetric twin-scroll turbocharging technology, with a specific focus on its application in heavy-duty diesel engines. By analyzing and synthesizing the findings from these previous investigations, this work also identifies the existing challenges and outlines the future research priorities in this field. The continued exploration and optimization of asymmetric twin-scroll turbocharging technology holds immense promise in enhancing fuel economy and mitigating nitrogen oxide emissions. Consequently, this research contributes to the ongoing efforts aimed at achieving sustainable and environmentally friendly transportation solutions.</div>

Effects of Varying Equivalence Ratios on the Combustion Efficiency Characteristic of a Dual-Fuel Compression Ignition Engine by Changing Intake Pressures and Exhaust Gas Recirculation Rates

In general, a leaner mixture condition improves combustion efficiency in compression ignition (CI) combustion using diesel. However, in the case of leaner air–fuel mixture conditions, it disturbs flame propagation in spark ignition combustion using gasoline, i.e., low reactivity fuel, causing a decrease in combustion efficiency. Since dual-fuel combustion in a CI engine typically involves the use of high- and low-reactivity fuels together, the differing reactivity conditions in the cylinder become as important as the local equivalence ratio in the cylinder. Thus, there is a need to verify the effect of a leaner mixture condition on combustion efficiency in dual-fuel CI combustion. For this reason, this study experimentally evaluates the effects of varying equivalence ratios on the combustion efficiency of gasoline/diesel dual-fueled CI combustion in a 0.4-L single-cylinder engine under low-speed (1500 rpm) and low-load (total LHV 570 J/str) conditions. To vary the equivalence ratios, intake pressures and exhaust gas recirculation (EGR) rates were, respectively, changed under the part-load condition. The results emphasize that as the equivalence ratio becomes leaner by increasing the intake pressure, combustion efficiency worsens due to the low reactivity properties and certain flame propagation modes of gasoline combustion. On the contrary, increasing the EGR rate did not significantly influence combustion efficiency, but it effectively helped reduce nitrogen oxide (NOx) emissions. Based on these results, it is concluded that optimizing dual-fuel CI combustion to suppress NOx emissions is better achieved using EGR, rather than creating a leaner mixture condition.

Preliminary assessment of volatile organic compounds and hazardous gases dispersion at low winds: case study of Mellitah Gas Complex, Libya

Air pollution from industrial areas has become really worrying especially for city dwellers. The plume dispersion emitted from industrial sources is subject to several factors: temperature and emission rate velocity, wind speed and direction, source height, and atmospheric stability. This study aimed to evaluate the applicability of the dispersion coefficients correlated within a Gaussian plume approach to an industrial source in Libya (Mellitah Gas Complex) under low and moderate wind speeds. To this end, we have developed a specific code based on the Gaussian method to study the dispersion of (1) Volatile Organic Compounds (VOCs) from oil storage tanks and condensate storage tanks, and (2) sulfur oxides (SOx) and nitrogen oxides (NOx) emitted by the flaring process through three stacks of 80 m height. The emissions from multisource points and their dispersion have been predicted at calm wind conditions and the flammability and danger-prone toxic zones have been delimited around the studied site. The obtained results reveal that the emissions, particularly generated at low and moderate wind speeds, induce a dispersion with high concentration levels in the area surrounding the industrial site. The VOCs critical concentration region indicates a real risk of flammability at low-speed wind and stable atmospheric condition, from a height of 5 m above the ground. In fact, the VOCs concentration reach the Flammability Inferior Limit value of 0.018 m3 VOCs/m3 and these concentrations, appearing in the form of a plume, extend downstream to approximately 1000 m. The dispersion of NOx and SOx emissions downwind from the stacks are enhanced by wind speed; nevertheless, at 2 m height from the ground, the levels could exceed the limit value of 0.125 mg/m3, especially under the condition of unstable and very unstable atmospheric classes. From our findings, we recommend continuous monitoring campaigns inside and around the complex of Mellitah to ensure an environmentally secure zone that respects safety and health guidelines. Furthermore, enhanced simulations based on hourly weather conditions for extended area would be of great interest to accurately assess the air quality index in the region.

Using renewable alternative fuels and studying their impact on the performance and emissions of compression ignition engines

AbstractThis practical study examined the effect of engine torque on engine performance and emissions. The most important parameters of engine performance are thermal efficiency, brake power (BP), and specific fuel consumption. As for exhaust emissions, the most important of which are hydrocarbons (HCs), carbon monoxide (CO), and nitrogen oxides (NOx). The experiment was conducted for a single‐cylinder, four‐stroke compression ignition engine. Mixtures (B0, B10, B20, B30, and B40) were taken from biodiesel prepared from sunflower oil by the esterification method. The engine speed was fixed at 1700 rpm, and torque variable was from 0 to 10 N m. The results indicated a decrease in engine BP by an average of 19.5 W, a decrease in thermal efficiency by an average of 1.058%, while an increase in fuel consumption by an average of 0.095 kg/kW h−1 compared to diesel. As for exhaust emissions, HC emissions decreased by 5.8 ppm, while CO decreased by 0.0207%, and NOx emissions increased by 138.5 ppm compared to diesel, due to changes in the properties of biodiesel, such as high density, viscosity, and low calorific value compared to the properties of regular diesel

Assessment of the industrial emissions impact on the quality of atmospheric air in the Burlin district of West Kazakhstan region DEVELOPMENT

The article is devoted to the study of air pollution in the Burlin district of the West Kazakhstan region, where one of the main sources of air pollution is the Karachagan oil and gas condensate field, the main feature of which is the high content of hydrogen sulfide in natural gas from 4 to 4.3%. The analysis showed that the atmospheric air state in the specified area is determined by the characteristics of harmful emissions sources, composition, volumes of pollutant emissions and climatic characteristics of the territory, which determine the conditions for the polluting components dispersion. The qualitative and quantitative characteristics of the chemical composition of the atmospheric air in the study area, as well as the features of their changes over the years end climatic seasons, are largely determined by emissions of nitrogen oxides, carbon, sulfur dioxide, hydrogen sulfide, volatile organic compounds and inorganic dust into the atmosphere by oil and gas facilities. The anthropogenic influence of industry in this area is also evidenced by the calculated value of the integral coefficient of air pollution. At the same time, industrial enterprises, having increased the anthropogenic impact on the environment, have the ability to prevent negative environmental consequences. The system of industrial environmental control of the chemical composition of industrial emissions at the Karachagnak field facilities is carried out on an ongoing basis. The analysis showed that a reduction in emissions and, accordingly, a reduction in ground-level concentrations of air pollutants at the Karachagnak field facilities is ensured by a whole range of technological and organizational measures, among which the technology of high-pressure gas reinjection deserves special attention. It necessitates the need to carry out systematic work to study the ecological state of the territory of the Karachagnak field, using not only ground-based research methods, but also modern geoinformation and aerospace technologies that make it possible to dynamically assess the changes taking place, conduct a geo-ecological assessment and make a forecast for the development of the environmental situation in this area. territories. The work carried out contributes to further analysis of the regional assessment of the environmental state of the atmosphere of large industrial centers.

Biogas intake pressure and port air swirl optimization to enhance the diesel RCCI engine characteristics for low environmental emissions

Exhaust emission and combustion control in RCCI (reactivity-controlled compression ignition) focused mainly on the direct-injected fuel parameters, urging to investigate the advantages of port-fuel intake parameters. The engine was modified for port injection of Biogas at the valve and RCCI mode. The influence of port swirl ratio (PSR, 0 – 80%) and biogas injection pressure (BIP, 1 – 4 bar) on the diesel RCCI combustion and emissions was tested and optimized at varied loads and 1600 rpm in a port injection at the valve (PIVE) approach. Established kinetic mechanisms were combined with multi-objective optimization to further investigate, predict, and analyze emissions occurrence and trade-offs for reduced environmental impacts. The results show that the radiation absorption triggered by increased CO2 lowers combustion temperature, resulting in prolonged ignition. Setting the airflow to swirl lowers the in-cylinder pressure at elevated BIP while raising the heat generated across the BIPs. Increasing the PSR slows the combustion while BIP speeds up the process. BIP and PSR show great trade-off reduction ability among all emission parameters. The optimum unburned hydrocarbon, nitrogen oxide, particulate, and carbon monoxide emissions for the injection at the valve were found to be 109.58, 0.577, and 2.336 ppm, and 0.103%, respectively, at low-load, low-BIP, and high-PSR. The emissions were lowered by 6.58, 91.26, 80.65, and 13.45% compared to the premixed RCCI mode, respectively. Therefore, introducing low-pressure biogas amid high swirling air at the valve elevates the in-cylinder condition while lowering the emissions, mitigating their environmental implications.

RCCI combustion of ammonia in dual fuel engine with early injection of diesel fuel

Ammonia has gained considerable attention as a valuable, carbon-free alternative fuel for internal combustion engine (ICE) applications. The growing interest in ammonia's potential as an energy source stems primarily from its advantageous storage and transport properties. The reactivity-controlled compression ignition (RCCI) combustion mode presents a promising avenue for overcoming the challenges intrinsic to conventional diesel engines, such as elevated nitrogen oxides (NOx) and particulate matter (PM) emissions. Additionally, it addresses the limitations of both homogeneous charge compression ignition (HCCI) combustion (limited operational range) and premixed charge compression ignition (PCCI) combustion (diminished power output). The application of an ammonia-based RCCI combustion strategy emerges as a viable pathway for harnessing ammonia as a fuel. In this study, a numerical simulation on a single-cylinder heavy-duty engine operated in RCCI mode is conducted utilizing ammonia and diesel as fuels. The engine is operated at medium load and 910 RPM. The simulation results are validated against experimental data sourced from existing literature. The study investigates the impact of varying ammonia energy fractions, injection timing, and intake valve close temperature (TIVC) on key operational characteristics of the engine including in-cylinder pressure, heat release rate (HRR), combustion efficiency (CE), indicated mean effective pressure (IMEP), and emission levels. The results indicated that increasing the ammonia energy fraction within the RCCI combustion mode, transitioning from 30 % to 70 %, leads to a notable enhancement in IMEP, while maintaining low levels of carbon monoxide (CO), hydrocarbons (HC), unburned ammonia, and nitrous oxide (N2O) as greenhouse gases (GHG). Furthermore, increasing ammonia's energy fraction yielded a discernible reduction in NOx emissions and carbon dioxide (CO2). Conversely, the RCCI combustion mode attained superiority over the dual fuel combustion mode by simultaneously elevating CE and diminishing emissions of GHG, (CO2 and N2O) as well as unburned NH3.

Improving the performance of gasoline fuels by adding methanol and methyl tertiary-butyl ether along with metal oxides titanium oxide and magnesium oxide

These variables include the type of nanoparticle additives integrated into the fuel blend and the operational engine speed. The focus is on two specific oxygenated additives, methanol and isobutanol, in conjunction with Methyl Tertiary-Butyl Ether (MTBE) and two metal oxide nanoparticles, namely magnesium oxide and titanium oxide. The experimental framework entails testing these new fuel blends in a controlled environment, utilizing a four-stroke engine linked to a dynamometer and a speed analyzer. The tests are conducted at rotational speeds of 750 and 1250 rpm. The comprehensive data collected encompass a range of parameters, including engine power and torque, as well as the emissions of carbon dioxide (CO2), nitrogen oxides (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). The study meticulously analyzes data to build a robust model, significantly enhancing engine performance while substantially lowering emissions. It finds that adding specific additives to gasoline notably reduces carbon monoxide and hydrocarbons. Testing gasoline with methanol, MTBE, and titanium oxide at 750 RPM showed a notable shift in emissions: nitrogen oxide increased by 40.5%, while hydrocarbons, CO, and CO2 saw reductions of 17.5%, and from 2.4% to 7.8%–1.197% and 7.661%, respectively, underlining the need for careful fuel composition management for environmental benefits.

Hybrid rich- and lean-premixed ammonia-hydrogen combustion for mitigation of NOx emissions and thermoacoustic instabilities

The large-scale direct utilization of two carbon-free fuels, ammonia and hydrogen, is currently attracting significant interest in the context of the development of new gas turbine combustion technologies, with paying close attention to the reduction of nitrogen oxides and unburned ammonia emissions. Motivated by recent observations that rich-premixed conditions tend to mitigate excessive NOx emissions from ammonia combustion, and that uniformly blended ammonia-hydrogen fuel/air mixtures tend to increase NOx production exponentially, here we propose a hybrid configuration of hydrogen-doped rich-premixed ammonia-air flames (inner stage) and lean-premixed pure hydrogen-air flames (outer stage) in a radially stratified primary reaction zone. This fuel staging scheme offers a possible mechanism for chemical kinetics-controlled NOx abatement and asymmetry-induced thermoacoustic instability suppression. The relevance and feasibility of the unconventional premixing approach are rigorously evaluated based on detailed measurements of exhaust gas concentrations and self-excited pressure fluctuations, in conjunction with OH*/NH2*/NH* chemiluminescence and OH PLIF imaging measurements. We observe that drastically different non-homogeneous reaction regions can be stably established in a comparatively compact combustion volume without producing negative flame stabilization effects – such as blowoff of less reactive ammonia flames and flashback of more reactive hydrogen flames. As compared with the uniform-blend baseline condition, the hybrid staging method is shown to significantly mitigate total nitrogen oxides emissions, from 7764 to 310 ppmvd (96 % reduction), and achieving an approximately two-fold reduction in dynamic pressure amplitude. Interestingly, hydrogen-enriched rich-premixed ammonia flames are revealed to exhibit anomalous oscillatory states originating from the preferential diffusion of hydrogen molecules and reaction rate-dependent separation of reactive layers, enabling interacting non-homogeneous reaction zones with markedly different characteristic time scales to resist the growth of intense pressure perturbations.

Nitrogen and nitrous oxides emission characteristics of anoxic/oxic wastewater treatment process under different oxygen regulation strategies

Nitrous oxide (N2O) and nitrogen oxides (NOx) (i.e., nitric oxide (NO) and nitrogen dioxide (NO2)), which could be produced in wastewater treatment process and result in greenhouse effect and atmospheric pollution, respectively, have been studied limitedly in their emission characteristics and transformation mechanisms. In this study, intelligent oxygen regulation was applied in anoxic/oxic wastewater treatment process (I-A/O), and its effects on regulating NOx and N2O transformations were extensively explored by comparing it with conventional A/O process (C-A/O). Results showed that the average emission amounts of N2O and NOx in I-A/O were 7.45 ± 0.66 mg and 1.88 ± 0.10 mg, respectively. Satisfactory reduction of N2O by 29.28 %–45.08 % was achieved in I-A/O compared to that of C-A/O, but together with increased NOx emission by 83.19 %–120.57 %. Pearson correlation and transcriptional analysis suggested that NO2−-N reduction in the anoxic phase dominated N2O production, while no significant N2O production in the oxic phase was found. Hence, the reduced N2O production in I-A/O was mainly attributed to its efficient denitrification process. On the other hand, both the anoxic and oxic phases played important roles in NO production. More importantly, sufficient oxygen in I-A/O promoted the ammonia oxidation process, resulting in higher NO emission in I-A/O in the oxic phase. The imbalance in NO and N2O emissions was then amplified by the NOR enzyme, which mediates the conversion of NO to N2O in both the anoxic and oxic phases. Besides, carbon emission reduction by 31.32 %–36.50 % was obtained in I-A/O due to aeration consumption savings and greenhouse gas emissions reduction compared to C-A/O. Overall, intelligent oxygen regulation optimized the nitrogen transformation and achieved carbon emission reduction in A/O process, but special attention should be paid to the associated risk caused by increased NO emissions.

Analysis of the Impact of Agricultural Production Type and Traffic on Nitrogen Oxide Emissions

The protection of air from pollution is one of the basic principles of sustainable development, and this article analyzes the joint impact of various types of agricultural production and traffic on nitrogen oxide (NOx) emissions. The goal of this research is the development of a new methodology for assessing the combined impact of different types of agricultural production, traffic load, and traffic flow structure on the emission of nitrogen oxides. For the analysis of the joint impact of traffic and agricultural production, a new impact assessment methodology was developed, which is based on two selected impact prediction models. The following two models were used to predict the impact: the BioGrace model and the microsimulation model VISSIM. The developed methodology was applied to a case study in real field conditions. The results showed that the difference in the emission of NOx gases, depending on the type of agricultural production, indicates a reduction in NOx emissions in the walnut–winter-wheat system by 30%, compared to the production of winter wheat in an open field. The statistical analysis showed that there is no statistically significant difference between NOx emissions for different vehicle arrival scenarios for the same traffic load. The results of the joint impact show that the lowest NOx emission was found in walnut orchards and counted traffic. In this example, the difference between the one-hour emission load of three different agricultural types of production and traffic is not large; however, in the cumulative load, it can lead to significant differences. Emphasizing the importance of adopting new agricultural practices and the impact of traffic and the share of freight and heavy goods vehicles in agricultural production, we position them as a proactive and sustainable response to the critical ecological and agricultural challenges highlighted in European and Croatian policy.