Formation Of Nitrogen Oxides Research Articles

The preparation of SiO2/GO/PVA based hydrogel sensor and its application for rapid and sensitive detection of NH3

Gas sensors have received significant interest due to their miniaturization, low power consumption and high reliability. In this paper, hydrogel film with high sensing properties toward NH3 were prepared using silicon dioxide (SiO2), porous graphene oxide (GO) and polyvinyl alcohol (PVA). The morphology and structure of hydrogel were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectra (FT-IR) and specific surface area analysis. Compared with the conventional gas sensors based on planar GO sheets, the prepared porous SiO2/GO/PVA based hydrogel sensor could be used to detect NH3 with low concentration (10 ppm) and wide range of 10-1000 ppm. At the same time, a high response rate of 118% and an ultra-fast recovery (12s) were achieved. Finally, a sensing mechanism for SiO2/GO/PVA based hydrogel film was proposed: NH3 was adsorbed onto the surface of the film through hydrogen bonding and then reacted with the oxygen negative ions on the surface of the film to form nitrogen oxides. After degassing, oxygen was adsorbed on the surface of the film again to form oxygen negative ions. In addition, the film could monitor the freshness of fish over a period of 0-7 days, where the correlation between the resistance change and TVB-N was as high as 0.975. This work demonstrates the effectiveness of porous SiO2/GO/PVA based hydrogel film in improving gas-sensitive properties, providing a viable solution for food freshness detection, contamination tracking, and hazardous substances monitoring, etc.

Dynamic of mode transition in air surface micro-discharge plasma: reactive species in confined space

Abstract Flexible surface micro-discharge plasma is a non-thermal plasma technique used for treating wounds in a painless way, with significant efficacy for chronic or hard-to-heal wounds. In this study, a confined space was designed to simulate wound conditions, gelatin was used to simulate wound tissue. The distinctions between open and confined spaces were explored, and the effects of temperature, humidity, discharge power, and the gap size within the confined space on the plasma characteristics were analyzed. It was found that, temperature, humidity and discharge power are important factors that affect the concentration distribution of active components and the mode transition between ozone and nitrogen oxides. Compared to open space, the concentration of ozone in confined space was relatively lower, which facilitated the formation of nitrogen oxides. In open space, the discharge was dominated by ozone initially. As temperature, humidity and discharge power increased, nitrogen oxides in the gas-phase products were gradually detected. In confined space, nitrogen oxides can be detected at an early stage and at much higher concentrations than ozone concentration. Furthermore, as the gap of the confined space decreased, the concentration of ozone was observed to decrease while that of nitrate increased, and the rate of this concentration change was further accelerated at higher temperature and higher power. It was shown that ozone concentration decreased from 0.11 µmol to 0.03 µmol and the nitrate concentration increased from 20.5 µmol to 24.5 µmol when the spacing in the confined space was reduced from 5 mm to 1 mm, the temperature of the external discharge was controlled at 40 °C, and the discharge power was 12 W. In summary, this work reveals the formation and transformation mechanisms of active substances in air surface micro-discharge plasma within confined space, providing foundational data for its medical applications.

Numerical analysis of major reaction affecting to nitrogen oxide formation under Okafor reaction mechanism

Numerical analysis of major reaction affecting to nitrogen oxide formation under Okafor reaction mechanism

DEVELOPMENT OF NEW DESIGNS OF GP TYPE OIL-GAS BURNER DEVICES WITH NITROGEN OXIDES LOW EMISSION FOR OIL REFINERY FURNACES

The article discusses variants for new designs of GP type combined burner devices developed by the authors for oil refinery furnaces in order to reduce harmful emissions of toxic nitrogen oxides as one of the most dangerous chemicals. The main factors influencing the formation of nitrogen oxides during fuel combustion have been established. A classification of burner devices used in tube furnaces at oil refineries is given. Original designs of low-toxicity burner devices of the GP type, protected by patents for utility models differing from existing analogues in novelty and high environmental efficiency are recommended for implementation.

Investigation of [formula omitted] formation in non-premixed, swirl-stabilised, wet hydrogen/air gas turbine combustor

In line with the Paris Agreement and the United Nations Sustainable Development Goals, the use of fossil fuels is to be phased out in the coming decades. Fossil-free hydrogen is a promising candidate for decarbonising the energy sector. However, hydrogen combustion is known to produce undesirable emissions such as nitrogen oxides (NOx) and calls for mitigation measures such as steam-diluted hydrogen combustion, which is known to reduce the NOx emissions. This study focuses on improving the understanding of NOx formation in a swirl-stabilised, steam-diluted, non-premixed hydrogen/air combustion using high-fidelity large eddy simulation (LES) and zero-dimensional (0D) perfectly stirred reactors (PSR). The LES results are used to identify four salient points in the domain where the NOx chemistry is analysed in detail. These points are chosen in the main flame, flame tail, post-flame and central recirculation regions. Note, the high heat release rate (HRR) region is referred to as the main flame while the flame tail denotes the low-HRR and V-shaped flame region adjacent to the main flame. Based on the LES data at these chosen points, the contribution of the major NO production pathways such as the Zeldovich mechanism, extended Zeldovich mechanism, N2O route and the NNH route are studied and reveal different rates of production of NO (i.e. ROPNO). Also, the role of individual reactions in NO production and consumption is investigated. Furthermore, reaction pathway diagrams illustrating the chemical pathways leading to NO are visualised. The sensitivity of NO to each reaction is also reported. These analyses provide insights into the NO chemical pathways observed at the salient points across the domain. The dominance of the Zeldovich mechanism remains but is much less compared to that in dry hydrogen combustion as its contribution to ROPNO is less than 20% at all the points considered. However, the extended Zeldovich mechanism is significant at all the points. The NNH route is observed to be important in the flame regions. The major NNH reaction contributing to ROPNO in the flame regions is NNH+O⇌NH+NO. Furthermore, the complex NO chemistry at all the identified points is presented in great detail using the above-mentioned analyses and illustrations. This work highlights the possibility of combining a high-fidelity simulation and a simple 0D ideal reactor to decipher the nuances of NO chemical pathways in a practical swirl-stabilised gas turbine combustor and provide new understanding for assisting engineers in designing clean burners.

Mesospheric Ozone Depletion during 2004–2024 as a Function of Solar Proton Events Intensity

Solar proton events (SPEs) affect the Earth’s atmosphere, causing additional ionization in the high-latitude mesosphere and stratosphere. Ionization rates from such solar proton events maximize in the stratosphere, but the formation of ozone-depleting nitrogen and hydrogen oxides begins at mesospheric altitudes. The destruction of mesospheric ozone is associated with protons with energies of about 10 MeV and higher and will strongly depend on the intensity of the flux of these particles. Most studies investigating the impact of SPEs on the characteristics of the middle atmosphere have been based on either simulations or reanalysis datasets, and some studies have used satellite observations to validate model results. We study the impact of SPEs on cold-season ozone loss in both the northern and southern hemispheres using Aura MLS mesospheric ozone measurements over the 2004 to 2024 period. Here, we show how strongly SPEs can deplete polar mesospheric ozone in different hemispheres and attempt to evaluate this dependence on the intensity of solar proton events. We found that moderate SPEs consisting of protons with an energy of more than 10 MeV and a flux intensity of more than 100 pfu destroy mesospheric ozone in the northern hemisphere up to 47% and in the southern hemisphere up to 33%. For both hemispheres, the peak of winter ozone loss was observed at about 76 km. In the northern hemisphere, maximum winter ozone loss was observed on the second day after a solar proton event, but in the southern hemisphere, winter ozone depletion was already detected on the first day. In the southern hemisphere, mesospheric ozone concentrations return to pre-event levels on the ninth day after a solar proton event, but in the northern hemisphere, even on the tenth day after a solar proton event, the mesospheric ozone layer may not be fully recovered. The strong SPEs with a proton flux intensity of more than 1000 pfu lead to a maximum winter ozone loss of up to 85% in the northern hemisphere, and in the southern hemisphere winter, ozone loss reaches 73%.

Evaluation of the Mineral Manganese OXMN009 and OXMN009P in the Chemical Looping Combustion (CLC) Process Using Thermogravimetry

Indirect combustion with the chemical looping combustion (CLC) of solid oxygen carriers is one of the most promising technologies for capturing carbon dioxide (CO2) in energy production from fossil fuels since the separation of the generated CO2 is inherent to the process itself. Therefore, the cost associated with capturing this gas will be significantly reduced. This technology transfers oxygen from air to fuel through a metal oxide that acts as an oxygen carrier, avoiding direct contact between air and fuel. This oxygen carrier circulates in a fluidized bed reactor called a reduction reactor and an oxidation reactor. (1) This research work has focused on evaluating the behavior of oxygen carriers based on the original and improved manganese mineral (copper-impregnated mineral) named for this study, OXMN009 and OXMN009P, respectively. (2) Equilibrium experiments were carried out on a thermogravimetric balance (TGA) to evaluate the kinetic behavior of these oxygen transporters OXMN009 and OXMN009P, using the gases methane (CH4), carbon monoxide (CO), and hydrogen (H2). (3) The enhanced solid oxygen carrier OXMN009P exhibited good performance for the CLC process with gaseous fuels in terms of reactivity and combustion efficiency, having high reactivity and oxygen transfer properties due to copper impregnation. (4) The results show that OXMN009P has comparable reactivity to other manganese-based materials reported in the literature. It may be an effective option for carbon dioxide capture, as it uses metal oxides as the oxygen transporters (TO). (5) These oxygen transporters, OXMN009 and OXMN009P, are used in a cyclic process that prevents the formation of nitrogen oxides by keeping the air and fuel separate. (6) Thermogravimetric balance (TGA) experiments were conducted to evaluate the kinetic behavior of these copper-modified oxygen transporters. (7) It was found that OXMN009P improved the reactivity and oxygen transfer properties due to copper impregnation. The kinetic parameters obtained in the TGA indicate that the reaction is non-thermal and requires less energy to initiate. (8) The results show that OXMN009P has reactivity comparable to other manganese-based materials reported in the literature and can be an effective option for carbon dioxide capture.

Flame Characterization of Cofiring Gaseous and Solid Fuels in Suspensions.

This work characterizes technical scale flames of suspension firing of gaseous and solid fuel mixtures through in-flame measurements with focus on nitrogen oxide (NOx) formation. The aims are to investigate the impacts of substituting a solid fuel with a gaseous fuel on the important mechanisms for NOx formation and to highlight important considerations for burner design. The investigation was performed in a 100 kW test unit that fires mixtures of propane and lignite. The global emissions levels and in-flame compositions were measured. A detailed reaction model was used to interpret the experimental results. The study highlights the importance of the early release of volatile nitrogen to reduce the levels of NOx. The findings indicate that substituting lignite by propane is advantageous in terms of reducing NO emissions, primarily due to the diminished input of fuel-bound nitrogen to the flame. However, this holds true only if the flame temperature of the gaseous fuel does not increase excessively. Finally, introducing a relatively small quantity of solid fuel to a propane flame appears to alter the flame behavior to resembles that of the "solid fuel," with a longer and wider flame. Despite this, carbon monoxide and nitrogen oxide concentrations remain like gas combustion but more dispersed.

Full load optimization of a hydrogen fuelled industrial engine

There are a large number of applications in which hydrogen internal combustion engines represent a sensible alternative to battery electric propulsion systems and to fuel cell electric propulsion systems. The main advantages of combustion engines are their high degree of robustness and low manufacturing costs. No critical raw materials are required for production and there are highly developed production plants worldwide. A CO2-free operation is possible when using hydrogen as a fuel. The formation of nitrogen oxides during hydrogen combustion in the engine can be effectively mitigated by a lean-burn combustion process. However, achieving low NOx raw emissions conflicts with achieving high power yields. In this work, a series industrial diesel engine was converted for hydrogen operation and comprehensive engine tests were carried out. Various measures to improve the trade-off between NOx emissions and performance were investigated and evaluated. The rated power output and the maximum torque of the series diesel engine could be exceeded while maintaining an indicated specific NOx emission of 1 g/kWh along the entire full load curve. In the low-end-torque range, however, the gap to the full load curve of the series diesel engine could not be fully closed with the hardware used.

Investigation of the chemical mechanism of pollutant formation in co-firing of ammonia and biomass lignin

Ammonia (NH3) and biomass are recognised as renewable energy carriers with substantial promise for reducing carbon emissions. However, the issue of nitrogen oxides (NOX, including NO and NO2) and nitrous oxide (N2O) emissions from ammonia combustion and soot from biomass combustion, remains a pressing concern due to their detrimental impacts on the environment and human health. This study investigated the mechanism of pollutant formation during ammonia-lignin co-firing through reactive molecular dynamics (RMD) simulations. The results indicate that co-firing a certain amount of ammonia with lignin can reduce the formation of soot. This is mainly due to NH2 radicals converting a portion of polycyclic aromatic hydrocarbon (PAH) precursors into C–N compounds. However, it is necessary to maintain higher ammonia concentrations. Adding a small quantity of ammonia would decrease the extent of oxidative reactions within the system and fail to generate enough NH2 radicals to consume the carbon atoms forming PAH precursors, ultimately resulting in increased soot production. The impact of lignin on the formation of NOX and N2O during ammonia combustion has two main aspects: Firstly, the oxidising radicals formed during the initial decomposition of lignin promote the generation of N–O bonds, leading to an increase in the quantities of NOX and N2O during the initial reaction stage. Secondly, the carbon-containing products produced from lignin decomposition consume nitrogen atoms by forming N–C bonds, thereby diminishing available nitrogen atoms for nitrogen oxides formation. This study provides new insights into the formation of primary pollutants of ammonia and biomass co-firing on an atomic scale, which can help develop pollutant mitigation measures.

Numerical and experimental analysis of the formation of nitrogen oxides in a non-premixed industrial gas burner

Nitrogen oxides (NOx) formation in a non-premixed industrial gas burner is analyzed with Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics, using the Flamelet Generated Manifold (FGM) approach for chemistry and the Reynolds stress model for turbulence closure. Analysis and validation of the numerical methodology use both the RANS and the Large Eddy Simulation methods to study the Sandia flame D experiment. Four regimes of the gas burner, differing by thermal power, are studied experimentally and numerically, comparing measured and computed flue gas temperature and emissions. The flow features leading to NOx formation are analyzed. At low power, most NOx formation occurs in the flame core, where temperatures are highest. At high power, a significant amount of NOx forms where a secondary stream of oxidizer meets the high-temperature burnt gas stream. The NOx formation rate is modeled either by summing the contributions of the main paths relevant to the studied problem or via two variants of the FGM scalar transport approach. One of these variants features a correction to the transported scalar approach that enables accounting for the effects of non-adiabatic phenomena, e.g. heat radiation, on NOx formation without increasing the look-up table dimensionality and the required memory usage. The correction is shown to improve emission predictions over the baseline model, although quantitative differences between predicted and measured emission levels remain significant. The approach computing the NOx formation rate as by summing contributions yields the best agreement with measurements when the thermal path predominates, and the formation of nitrogen dioxide is negligible.

Combustor shape optimization and NO emission characteristics for premixed NH3-CH4 turbulent swirling flame towards sustainable combustion

Ammonia is considered an attractive carbon-free fuel for energy generation in aerospace gas turbine engines. However, ammonia is often used with methane fuel blend due to its low combustion limits. The formation of nitrogen oxides (NOx) during the combustion of ammonia-methane fuel blend is a fundamental problem of interest in the scientific community. To date, there have been several studies of ammonia-methane fuel blend, but none of them have considered the effect of combustor shape on NO emission. In this work, large eddy simulations (LES) are carried out at stoichiometric condition to analyze the flame structure and NO emission characteristics of the ammonia-methane premixed turbulent swirling flame in box and cylindrical shaped combustors. The fuel blend used in this study is 70% ammonia and 30% methane by volume. The LES solver employs a dynamic thickened flame (DTF) combustion model along with Okafor's reduced mechanism, which consists of 43 species and 130 elementary reactions. The flame shape and stabilization are discussed for both combustors, along with the effects of flowfield on the flame. The characteristics of the swirl stabilized flame are illustrated using several time-averaged and instantaneous contours of parameters, including heat release rate, local equivalence ratio, axial velocity, and NO emission. The effect of mixing and reaction rate distribution in the premixed configuration is studied quantitatively, subsequently identifying several flame regions. It is identified from the LES results that the NO emission is 1.6 times higher in the cylindrical combustor compared to the box combustor. While a typical V-shape flame is observed for both combustors, a flame tail also co-exits for the cylindrical combustor. The heat release rate in the flame tail is about 33% higher than the main flame which reignites the unburnt gases for a secondary combustion and generates NO. Thus, a box combustion chamber design is beneficial to minimize the NO emission. The residence time is also analyzed in both combustor to understand the oxidation process and identify the key reaction pathways for NH3/CH4 premixed flames.

Ammonia-enriched biogas as an alternative fuel in diesel engines: Combustion, performance and emission analysis

This study investigates the potential of ammonia as a secondary fuel in diesel engines, amidst the rising interest in alternative fuels and the growth of electric vehicles. Unlike hydrogen, with its higher flammability and safety concerns, ammonia offers a viable, sustainable fuel source. A single-cylinder diesel engine was utilized to assess engine performance and combustion characteristics using ammonia gaseous blends. Ammonia was combined with biogas to mitigate its corrosive effects and compensate for its lower heating value. Th entire best conducted with constant ammonia flow rate of 30 LPM. Diesel was mixed with biogas in compositions of 10 LPM, 20 LPM and 30 LPM, and tested under engine loads of 25%, 50%, 75%, and 100%. The blend with the highest ammonia concentration (B30B3) exhibited the largest heat release rate, highlighting a strong correlation between ammonia content and heat release levels. This is attributed to the premixed combustion phase and the accelerated flame speed associated with ammonia. An increase in ammonia content resulted in higher brake thermal efficiency and reduced brake specific fuel consumption. All ammonia-inclusive blends showed a decrease in hydrocarbon and carbon monoxide emissions, with the lowest emissions observed in the B30B3 blend. However, the high flammability of biogas in the B30B3 blend, compared to diesel, and enhanced fuel atomization, led to increased nitrogen Oxides formation. The results clearly indicate that combination of ammonia along with the biogas enhances the combustion and reduces greenhouse gas emissions. Findings of this study provides valuable insights into the use of ammonia as a sustainable alternative in diesel engines, offering a improved balance between combustion efficiency and environmental impact.

Experimental investigation of hydrogen enriched natural gas combustion with a focus on nitrogen oxide formation on a semi-industrial scale

Combustion of hydrogen-enriched natural gas is a valuable short-term strategy for reducing CO2 emissions from high temperature industrial heating. This paper presents several experiments on combustion characteristics and the formation of nitrogen oxides. The experiments included hydrogen contents up to 100% and fuel heat inputs up to 75 kW. Water-cooled lances were used to influence the furnace temperature. The analysis includes the distribution of furnace temperatures, the composition of flue gas, the cooling capacity of the lances under steady-state operating conditions, and OH*-chemiluminescence imaging of the near burner region. The presented results demonstrate the dependence of furnace conditions and NOX formation on various factors, such as different air inlet fluxes, furnace temperature, and fuel composition, for constant heat inputs. Efficiency increased by up to 5.5% and significant changes in flame shaped along with a maximum increase in NOX emissions when comparing natural gas to hydrogen was measured at 167%.

Advanced Numerical Analysis of In-Cylinder Combustion and NOx Formation Using Different Chamber Geometries

In diesel engines, emission formation inside the combustion chamber is a complex phenomenon. The combustion events inside the chamber occur in microseconds, affecting the overall engine performance and emissions characteristics. This study opted for using computational fluid dynamics (CFD) to investigate the combustion patterns and how these events affect nitrogen oxide (NOx) emissions. In this study, a diesel engine model with a flat combustion chamber (FCC) was developed for the simulation. The simulation result of the heat release rate (HRR) and cylinder pressure was validated with the experimental test data (the engine test was conducted at 1500 rpm at full load conditions). The validated model and its respective boundary conditions were used to investigate the effect of modified combustion chamber profiles on NOx emissions. Modified chambers, such as a bathtub combustion chamber (BTCC) and a shallow depth chamber (SCC), were developed, and their combustion events were analysed with respect to the FCC. This study revealed that combustion events such as fuel distribution, unburnt mass fractions, temperature and turbulent zones directly impact NOx emissions. The modified chambers controlled the spread of combustion and provided better fuel distribution, improving engine performance and combustion rates. The SCC (63.2 bar) showed peak pressure rates compared to the FCC (63.02 bar) and BTCC (62.72 bar). This study concluded that the SCC showed better results than other chambers. This study further recommends conducting lean fuel mixture combustion with chamber modifications and optimising fuel spray, such as by adjusting the fuel injection profile, spray angle and injection timing, which has a better tendency to create complete combustion.

Comparative Study of Key Reactions Affecting Nitrogen Oxide Formation in Methane Laminar Premixed Flame

Comparative Study of Key Reactions Affecting Nitrogen Oxide Formation in Methane Laminar Premixed Flame

Structure and nitric oxide formation in laminar diffusion flames of ammonia–hydrogen and air

In this work, we present an investigation of the structure and formation of nitrogen oxides (NOx) in an axisymmetric laminar diffusion flame in which an ammonia–hydrogen fuel stream is surrounded by co-flowing air. Green ammonia, produced using renewable energy, is a promising carbon-free fuel for replacing hydrocarbon fuels over a diverse range of combustion applications. A key challenge for ammonia combustion is to understand the kinetics of nitrogen oxide formation for designing low-NOx combustion systems. In this experimental study, ammonia fuel is blended with hydrogen to increase fuel reactivity, with a fuel composition range of 15%–100% hydrogen. NOx emissions and fuel slip are measured by downstream sampling of NO, NO2, N2O and NH3 with a Fourier Transform Infrared (FTIR) gas analyzer. Flame structure is visualized by planar laser-induced fluorescence (LIF) for NO, NH, and OH radicals, as well as OH* by filtered chemiluminescence. Species concentration profiles are compared to predictions from 2-dimensional axisymmetric numerical models of the laminar flame using recent kinetic mechanisms developed for ammonia combustion. No measurable ammonia slip was recorded for any fuel composition, in agreement with model predictions. Good agreement between predictions and measurements was obtained for exhaust nitrogen oxide concentrations and for in-flame radical profiles, although larger variation and deviations are observed for predictions of NO2 and N2O than for NO. Numerical predictions for spatial distribution of flame radicals and flame liftoff height also showed good agreement with LIF and chemiluminescence measurements. For high fuel hydrogen content, the measured NH and NO profiles are shifted inward toward the fuel outlet, away from the peak temperature contour. Reaction path analysis is used to illustrate the important contributions to NO creation and destruction, including the differing role of key reaction pathways with varying fuel hydrogen content.

Heat Transfer Analysis for Combustion under Low-Gradient Conditions in a Small-Scale Industrial Energy Systems

The issue of maintaining low-gradient combustion in the conditions of high heat extraction has been investigated numerically in this work. The analyses include the application of a convective boundary condition at the wall (with estimated boiling heat transfer coefficient); analysis of the Internal Recirculation Device’s impact on combustion products and heat transfer under low-gradient conditions; and comparison of both traditional and low-gradient combustion modes. It was shown that the Internal Recirculation Device material and geometry has a significant impact on the nitrogen oxide (NOx) formation mechanism, as NO2 emission becomes predominant and can rise up to several hundreds ppm. What is more, along with decrease in thermal resistance of the IRD, CO emissions also increase rapidly, even achieving over 2000 ppm. Additionally, the convective heat transfer rate decreased by about 25% after switching from traditional to low-gradient combustion, whereas the radiative mechanism increased by ≈40% compared to traditional mode. It should also be mentioned that the low-gradient combustion applied in this work achieved approximately 10% higher efficiency than conventional combustion.

Experimental investigation of the effect of ammonia substitution ratio on an ammonia-diesel dual-fuel engine performance

This research experimentally examines an ammonia-diesel dual fuel system, not widely covered in existing literature but acknowledged as an effective approach to reduce engine carbon footprints in alignment with global decarbonization trends, focusing on enhancing understanding of performance, combustion, and emission characteristics vital for designing and optimizing these engines for commercialization. The results indicate that in an ammonia-air mixture atmosphere, diesel undergoes a prolonged ignition process, enhancing the role of premixed combustion. Increasing ammonia substitution at constant speed and load reduces the weight of mixing-controlled combustion, leading to larger areas in the chamber where diesel flames cannot reach. Ammonia oxidation mainly occurs near the diesel flame, as overly lean ammonia-air mixtures fail to sustain stable flame propagation. This results in considerable unburned ammonia emissions, particularly in regions beyond diesel flame reach and engine crevices, adversely affecting combustion efficiency and diminishing the thermal efficiency advantages of such operation. Furthermore, while ammonia combustion contributes to fuel-borne nitrogen oxides (NOx) formation, the overall NOx emissions from ammonia-diesel engines are reduced due to lower combustion temperatures and the deNOx properties of amino groups. However, the partial oxidation of ammonia during the late expansion stroke generates significant levels of nitrous oxide (N2O), a greenhouse gas, in the emissions, counteracting the intended reduction of carbon dioxide. These experimental findings highlight the necessity of focusing on both improving in-cylinder combustion quality and developing effective aftertreatment systems for NH3 and N2O capture, as crucial steps towards enhancing the environmental performance and market viability of ammonia-diesel dual fuel engines.

Enhanced C2-CN sub-mechanism: Impact on NO/N2O and soot precursor yields during C2H2/HCN oxidation

The combustion of hydrocarbon-ammonia fuels poses challenges related to the formation of soot and nitrogen oxides (NOx) emissions. Various kinetic mechanisms have been developed to describe the pathways of soot and NOx formation, but limited attention has been paid to the role of the C2-CN species, such as HC3N and CH2CHCN, in influencing the yields of soot and NOx. To address this gap, we present a detailed C2-CN sub-mechanism integrated into a NOx and polycyclic aromatic hydrocarbons (PAHs) kinetic model. The rate constants of the barrierless association reactions of C2H+CN, C2H3+CN, C2H5+CN, and CH3+CH2CN were updated using the variable reaction coordinate transition state theory (VRC-TST). We numerically investigated the oxidation of C2H2 and HCN at equivalence ratios of 2.0 and 3.0, which are major precursors for NOx and PAHs, in a perfectly stirred reactor (PSR) employing two kinetic models (with/without the developed C2-CN sub-mechanism). By comparing the rates of production (ROPs) obtained via both models, we analyzed the formation pathways of NO/N2O and Benzo(ghi)fluoranthene (BGHIF). Our findings reveal temperature-dependent trends in the calculated rate constants of C2H5+CN and CH3+CH2CN associations (positive dependence) as well as C2H+CN and C2H3+CN associations (negative dependence). The peak mole fractions of BGHIF at equivalence ratio (φ) of 2.0 and 3.0 predicted by the updated mechanism were 18.4 % and 13.6 % lower than the base mechanism. This reduction can be attributed to an additional consumption channel of C2H2 (C2H2+CN=HC3N+H) predicted by the C2-CN sub-mechanism. Furthermore, the C2-CN sub-mechanism exhibited a stronger suppression effect on N2O formation compared with NO formation at φ=2.0 and 3.0. This limitation can be explained by an additional consumption channel of CN via CN+C2H2=HC3N+H, resulting in decreased NO/N2O through the reaction sequence CN→NO→N2O and CN→NCO→HNCO→NH2→HNO→NO→N2O.