NO Mole Fraction Research Articles

Chemical kinetic study of methane blended with ammonia cracked gas at elevated temperature and pressure

Ammonia (NH3) on-line cracking to produce hydrogen (H2) can avoid direct ammonia combustion and is an important method to enhance combustion performance and control nitrogen oxide (NOx) emissions. This work aims to study the effects of various ammonia energy ratios (ENH3) and cracking ratios (CNH3) on the combustion and NO emission characteristics of methane (CH4) blended with ammonia cracked gas under lean-burn condition. The results showed that methane co-combustion and ammonia cracking significantly enhance the laminar burning velocity (LBV). The chemical effect plays a dominant role in the enhancement of LBV, but its relative contribution gradually decreases with increasing ENH3 and CNH3. A linear relationship between LBV and (O+H+OH+NH2 + CH3)max was observed, with both the slope and intercept being functions of CNH3. At an ENH3 of 20 %, NO emission decrease with increasing CNH3. At an ENH3 of 80 %, NO emission first increase and then decrease. The percentage of thermal NO is less than 1 % under ambient condition and could increase to as much as 22 % under elevated condition (500 K, 10 atm). Additionally, there was a quadratic polynomial relationship between (O+H+OH+NH2)max and the final NO mole fraction within an equivalence ratio range from 0.4 to 0.8. The second-order coefficient exhibits a linear correlation with CNH3, while the first-order and constant coefficient show a quadratic polynomial correlation with CNH3.

NO and CO Emission Characteristics of Laminar and Turbulent Counterflow Premixed Hydrogen-Rich Syngas/Air Flames

Burning hydrogen-rich syngas fuels derived from various sources in combustion equipment is an effective pathway to enhance energy security and of significant practical implications. Emissions from the combustion of hydrogen-rich fuels have been a main concern in both academia and industry. In this study, the NO and CO emission characteristics of both laminar and turbulent counterflow premixed hydrogen-rich syngas/air flames were experimentally and numerically studied. The results showed that for both laminar and turbulent counterflow premixed flames, the peak NO mole fraction increased as the equivalence ratio increased from 0.6 to 1.0 and decreased as the strain rate increased. Compared with the laminar flames at the same bulk flow velocity, turbulent flames demonstrated a lower peak NO mole fraction but broader NO formation region. Using the analogy theorem, a one-dimensional turbulent counterflow flame model was established, and the numerical results indicated that the small-scale turbulence-induced heat and mass transport enhancements significantly affected NO emission. Considering NO formation at the same level of fuel consumption, the NO formation of the turbulent flame was significantly lower than that of the laminar flame at the same level of fuel consumption, implying that the turbulence-induced heat and mass transfer enhancement favored NOx suppression.

N2O Consumption by Thermal Decomposition and Reduction with CH4, C2H6 and NH3

ABSTRACTConsumption of nitrous oxide (N2O) by thermal decomposition and reduction with methane (CH4), ethane (C2H6), and ammonia (NH3) were investigated using a micro-flow reactor with controlled temperature profile. N2O mole fractions were measured using a gas chromatograph and mass spectrometers at the maximum wall temperatures from 900 to 1400 K. For N2O thermal decomposition, the measured N2O mole fraction was in good agreement with the prediction using the model proposed by Mulvihill, et al. The low-pressure limit of N2O (+M) = N2 + O (+M) was dominant and H2O showed the largest impact on N2O consumption as a third-body, followed by CO2 and Ar. New third-body coefficients were proposed from the comparison of measured N2O mole fractions with model predictions. For N2O reduction with respective fuels, experiments showed that N2O consumption became greater in the order of C2H6/N2O/Ar ≈ NH3/N2O/Ar > CH4/N2O/Ar > N2O/Ar mixtures. Chemical reaction analyses showed that N2O + H = N2 + OH is the dominant reaction for N2O consumption in all fuel/N2O cases. In the C2H6/N2O case, high rates of H radical production from the fuel radical (C2H5) at a low temperature was identified, resulting in a greater N2O consumption than the CH4/N2O case. In the NH3/N2O case, a reaction of N2O and the fuel radical (NH2) showed high contribution to N2O consumption. Additionally, NNH and H2, the products in N2H2 + H = NNH + H2, produce H radicals through subsequent reactions. These reactions create a cycle of production/consumption of H and OH radicals and promote consumption of NH3 and N2O.

Broadband ultrafast-laser-absorption measurements of NO[formula omitted] absorption cross-sections from 430 to 500 nm at high temperatures behind shock waves

This work presents broadband spectrally resolved measurements of the absorption cross-section of NO2 from approximately 430 to 500 or 580 nm, depending on temperature, with a spectral resolution of approximately 0.06 nm. An ultrafast-laser-absorption-spectroscopy (ULAS) diagnostic was developed and used to provide broadband (up to approximately 900 cm−1 per laser shot) cross-section measurements with sub-nanosecond time resolution. Cross-section measurements were acquired from 430 to 580 nm in a heated gas cell at temperatures of 296 K and 670 K and a pressure of 1.5 bar. Cross-section measurements were also acquired behind reflected shock waves at temperatures near 970 K, 1150 K, and 1450 K at pressures near 1.5 bar. A quantum-cascade-laser-absorption diagnostic for NO was used to measure NO mole fraction at 500 kHz and determine the extent of NO2 decomposition in shock-tube experiments. The measured cross-sections typically exhibit good agreement with prior measurements available at select wavelengths and conditions as well as with recently developed theoretical predictions at most wavelengths and temperatures studied. A detailed description of the experimental and data processing procedures that enabled the ULAS measurements despite pronounced variations in laser pulse energy and the absence of non-resonant wavelengths within the pulse bandwidth are also presented.

A simplified mechanism of hydrogen addition to methane combustion for the pollutant emission characteristics of a gas-fired boiler

The reaction mechanism of hydrogen-enriched methane (HEM) combustion is significant in the combustion process. In this study, four widely used reaction mechanisms for methane combustion are simplified to investigate the pollutant emission characteristics of a gas-fired boiler used for HEM combustion. The laminar burn velocity (LBV) and ignition delay time (IDT) of the four detailed and four simplified mechanisms are compared, and the simplified San Diego mechanism is identified as the optimal mechanism using relative error and population standard deviation analysis. The temperatures and key components of the simplified San Diego mechanism are also compared with those of the detailed San Diego mechanism under various XH2. Based on the simplified San Diego mechanism, a chemical reactor network model for gas-fired boilers is further established to investigate the pollutant emissions of HEM combustion, in which the hydrogen doping ratio XH2 ranged from 0 to 80% and the inlet air and fuel temperature Tin ranged from 300 K to 600 K. Results showed that at Tin = 300 K with XH2 ranging from 0 to 80%, the mole fraction of NO increase by 1.94 times because of the increase in peak flame temperature; moreover, the mole fractions of N2O, CO, and CO2 decrease by approximately 25%, 50%, and 52%, respectively. With XH2 ranging from 0 to 40% and Tin ≥ 500 K, the mole fraction of NO decreases because the reduction reaction of NO + H = N + OH is promoted, whereas when XH2 is further increased to 80%, the increased H promotes the increase in NO again. CO emissions decreased as XH2 increased from 0 to 80%, whereas they increased by approximately 1.3 times as Tin increased from 300 K to 600 K because of the CO2 decomposition. N2O emissions decreased by more than 25% as XH2 increased from 0 to 80%. Additionally, CO2 emissions decrease by 52% with an increase in XH2 and by only 5% with an increase in Tin, indicating that XH2 has a larger impact on CO2 emissions. The proposed optimal HEM combustion mechanism is conducive to improving the efficiency of numerical calculations.

Evolution of ammonia reaction mechanisms and modeling parameters: A review

Ammonia (NH3) has been suggested as a fuel to attain zero carbon emissions. However, dealing with ammonia needs careful studies to reveal its limits as a suitable and promising fuel for broad applications within large power requirements. Chemical reaction mechanisms, widely employed in the modeling of these applications, are still under development. Therefore, this review is aimed to shed light on the current mechanisms available in the literature, highlighting modeling parameters that directly affect reaction rates which in turn govern the performance of each reaction mechanism. The key findings denote that most of the reaction mechanisms have poor performance when predicting combustion characteristics of ammonia flames such as laminar flame speed, ignition delay time, and nitrogen oxide emissions (NOx). In addition, none of the mechanisms have been optimised efficiently to predict properly experimental measurements for all these combustion characteristics. For example, Duynslaegher's mechanism perfectly predicted the laminar flame speed at lean and stoichiometric conditions, while Nakamura's reaction mechanism worked properly at rich conditions for the estimation of laminar flame speed. Although the aforementioned mechanisms achieved good estimation in terms of laminar flame speed, they showed poor performance against NO mole fractions. Similarly, Glarborg's (2018) mechanism properly estimated NO mole fractions at lean and stoichiometric flames while Wang's mechanism performed well in rich conditions for such emissions. Other examples are presented in this manuscript. Finally, the prediction performance of the assessed mechanisms varies based on operating conditions, mixing ratios, and equivalence ratios. Most mechanisms dealing with blended NH3 combinations gave good predictions when the concentration of hydrogen was low, while deteriorating with increasing hydrogen concentrations; a result of the shift in reactions that require more research.

Axis-symmetric diesel spray flame model coupled with momentum flux distribution measurement and improved soot phi-T map

An axis-symmetrical diesel spray flame model coupled with momentum flux distribution measurement was developed as a tool for nozzle orifice development. Momentum flux distributions at several distances from the nozzle orifice exit are measured by a force sensor with a small-diameter aperture which traverses a cross-section. A theoretical momentum flux profile is determined by fitting with the measured momentum flux profile at the cross-section. The spray velocity profile and equivalence ratio profiles are quantified from the theoretical momentum flux profile. By interpolating the profiles of the measured cross-sections, the axis-symmetrical diesel spray flame model can calculate the equivalence ratio and other physical values as a function of the distance from the nozzle exit ( x) and the radius from the spray axis ( r). The equivalence ratio distribution in a cross-section involving the spray axis is converted into soot formation and oxidation distribution by coupling with the improved soot ϕ -T map. The conventional soot-NOx ϕ -T map did not show the borderline between the soot formation and oxidation. To quantify the residence time of the fuel element during soot formation, the narrow soot peninsula was expanded up to its maximum by replacing the soot yield with the soot particle diameter. Instead of contour lines for the of NO mole fraction, contour lines for the OH mole fraction were implemented to reveal the border between soot formation and soot oxidation on the ϕ -T map. The borderline appears clearly, consisting of a horizontal line in the lower-temperature region and a rising line in the higher-temperature region. The converted soot formation and oxidation regions in the axis-symmetric spray flame model exhibit a strong correlation with the measured soot distributions in a quasi-steady diesel spray flame. The shear-stress, which induces turbulence affecting soot formation/oxidation, is also quantified from the velocity distribution.

Concentration and Isotopic Composition of Atmospheric N2O Over the Last Century

AbstractTemporal changes in the magnitude and geographic distribution of different sources of nitrous oxide (N2O) are not well constrained. To better understand the dynamics of N2O in the atmosphere over the last century, we have reconstructed the mole fraction, δ15Nbulk, δ18O, and δ15NSP values of N2O from ice cores, firn air archives, and modern atmospheric samples. We have provided new firn air records from the Styx Glacier, Antarctica, and the North Greenland Eemian Ice drilling Project, and updated the firn air transport modeling of the published records. The composite reconstruction shows that the N2O growth rates were 0.26 ± 0.05, 0.15 ± 0.05 and 0.75 ± 0.01 ppb yr−1 during 1850–1930 (P1), 1931–1965 (P2) and 1966–2021 CE (P3), respectively. The temporal slope found in a linear least squares fit in δ15Nbulk and δ18O were −0.010 ± 0.025 and −0.004 ± 0.031‰ yr−1, −0.014 ± 0.013 and −0.009 ± 0.017‰ yr−1, and −0.040 ± 0.013 and −0.022 ± 0.005‰ yr−1 during P1, P2 and P3 phases, respectively. Overall, a significant long‐term trend was not observed in δ15NSP data. Two‐box model calculations using N2O mole fraction suggest that the total N2O flux (FT) at 2015 CE was 17.5 ± 1.1 TgN yr−1, where flux from the natural (FN) and anthropogenic (FA) sources were ∼60% and 40% of FT, respectively, and the contribution of FA was ∼30% of FT at 1900 CE. Estimated FA and δ15Nbulk of atmospheric N2O suggest that the anthropogenic emissions from continental regions were 12%, 25% and 76% of FA during P1, P2 and P3 phases, respectively.

Experimental study of the methane/hydrogen/ammonia and ethylene/ammonia oxidation: Multi-parameter measurements using a shock tube combined with laser absorption spectroscopy

Ammonia (NH3) is a promising hydrogen carrier and carbon-free fuel, which can be synthesized using renewable energy and has attracted increasing attention from both academic and industrial communities. This study selected six absorption lines and developed a laser absorption diagnostics system that can simultaneously measure the temperature, CO, CO2, H2O, NH3, and NO time-histories during the oxidation of CH4/H2/NH3 and C2H4/NH3 mixtures (equivalence ratio ϕ ≈ 1.2) behind reflected shock waves. Since the fuels were highly diluted to reduce the nonideal effects and heat release behind reflected shock waves, the maximum NO mole fraction was only ∼0.2% and led to a small absorption (< 2.0%). Therefore. the wavelength modulation spectroscopy (WMS-2f/1f) was used for the NO time-history measurements while the other species were measured using fixed-wavelength absorption spectroscopy. A total of thirteen kinetics models were used to interpret the measurements. The main differences between the model predictions and measured data lie in two aspects: the mixture reactivities and the NO production. Generally speaking, for both CH4/H2/NH3 and C2H4/NH3 mixtures, the Glarborg model performs the best in predicting the temperature and species time-histories but the differences still exist. The high-quality experimental data support further analyses and improvements. Detailed kinetics analyses based on the Glarborg 2018 model were performed. It indicates that H + O2 = O + OH is the most sensitive and promoting reaction for both mixtures, followed by the H-abstraction reactions of H2 and C2H4. Conversely, the H-abstraction reactions of CH4 and NH3 impede oxidation due to competition with promoting reactions for reactants (H, OH, or O). Moreover, subsequent reactions involving the produced CH3 or C2H3 radicals also have significant effects on oxidation. The reactions affecting the NO plateau were also selected as the basis to optimize the predicted NO plateau. Although updating the rate constants of some key reactions improved model performance for both mixtures, discrepancies still exist, particularly for the C2H4/NH3 mixture.

Performance Investigation of Currently Available Reaction Mechanisms in the Estimation of NO Measurements: A Comparative Study

Ammonia (NH3) has been receiving the attention of researchers as an alternative promising green fuel to replace fossil sources for energy production. However, the high NOx emissions are one of the drawbacks and restrictions of using NH3 on a broad scale. The current study investigates NO production/consumption for a 70/30 (vol%) NH3/H2 mixture using kinetic reaction mechanism concepts to shed light on the essential reaction routes that promote/inhibit NO formation. Sixty-seven kinetic reaction mechanisms from the literature have been investigated and compared with recently reported measurements at a wide range of equivalence ratios (ϕ) (0.6–1.4), atmospheric pressure and temperature conditions. Both numerical simulations and experimental measurements used the same combustion reactor configuration (premixed stabilized stagnation flame). To highlight the best kinetic model for the predicting of the NO experimental measurements of NO, a symmetric mean absolute percentage error (SMAPE) has been determined as a preliminary estimation by comparing both numerical and experimental measurements. The results found that the kinetic reaction mechanism of Glarborg showed an accurate prediction with a minor error percentage of 2% at all lean and stoichiometric conditions. Meanwhile, the kinetic model of Wang accurately predicted the experimental data with 0% error at ϕ = 1.2 and underestimated the mole fraction of NO at 1.4 ϕ with an error of 10%. The sensitivity analysis and rate of production/consumption of NO mole fractions analysis have also been implemented to highlight the most important reactions that promote/inhibit NO formation. At lean and stoichiometric conditions, Glarborg kinetic model shows that the kinetic reactions of HNO + H ⇌ NO + H2, HNO + O ⇌ NO + OH, and NH + O ⇌ NO + H are the most important reaction routes with considerable effect on NO formation for 70/30 (vol%) NH3/H2 mixture. In contrast, the reactions of NH2 + NO ⇌ N2 + H2O, NH2 + NO ⇌ NNH + OH, NH + NO ⇌ N2O + H, and N + NO ⇌ N2 + O significantly consume NO to N2, NNH, and N2O. Further, Wang’s mechanism illustrated the dominant effect of each HNO + H ⇌ NO + H2, N + OH ⇌ NO + H, NH + O ⇌ NO + H in NO formation and NH + NO ⇌ N2O + H, NH2 + NO ⇌ NNH + OH, and NH2 + NO ⇌ N2 + H2O in the consumption of NO mole fractions.

Combustion Characteristics of Natural Gas/Air Flat Premixed Laminar Flames in a Developed Matrix Burner

The natural gas flat flame characteristics are experimentally and numerically investigated under different equivalence ratios. A matrix burner is designed so that the natural gas-air mixture from the matrix burner makes up the flat flame. The combustion characteristics, such as the flame lift, the flame thickness, the gas temperatures, and the species concentration, are measured. The measured species concentrations are compared to the computed concentrations using different chemical kinetic mechanisms. The work was carried out at atmospheric pressure and room temperature at different equivalence ratios of 0.6, 0.8, 1, 1.2, and 1.4. A close agreement occurs between the experimental and the simulation results at lean and stoichiometric conditions with a mean absolute error value ranging from 0.9:3. At stoichiometric conditions, the maximum measured gas temperature, the flame thickness, and the minimum flame lift-off all coincide with the maximum simulated mole fractions of CO2 and NO. In addition, the centreline axial temperature is low just above the burner top (i.e., the flame lift region). However, those temperatures increase as the distance above the burner top increases.

Magnitude and seasonal variation of N2O and CH4 emissions over a mixed agriculture-urban region

Inventory estimates of N2O and CH4 emissions disregard temporal and spatial variabilities, which hinders the search for effective local strategies to lower greenhouse gas emissions. We have quantified the emissions of N2O and CH4 in a mixed agriculture-urban region using two independent approaches, i.e., the vertical gradient method (VGM) and the radon-tracer method (RTM), compared the estimated annual fluxes with the EDGARv6.0 emissions, revealed the seasonal variations of the VGM fluxes, and inferred the sources that most likely cause the seasonal variations based on the footprint analysis even though our methods cannot attribute different sources. We show that the annual RTM estimates represented by the mode of lognormal fit for N2O and CH4 are 0.4 g m−2 yr−1 and 12 g m−2 yr−1, and the VGM estimates are 0.6 ± 0.3 g m−2 yr−1 and 13 ± 4 g m−2 yr−1, respectively. Furthermore, the average EDGARv6.0 emissions constrained by the VGM and the RTM footprints are 1.3 g m−2 yr−1 and 0.9 g m−2 yr−1 for N2O, and 21 g m−2 yr−1 and 18 g m−2 yr−1 for CH4. Compared to our estimated fluxes, EDGARv6.0 N2O and CH4 emissions are both overestimated; for N2O, it is mainly caused by an overestimation of the chemical industry's emission. Moreover, in contrast to EDGARv6.0′s nearly constant monthly emissions throughout the year, the VGM estimates of N2O and CH4 show seasonal variations with relatively high values from March to September, which is most likely caused by agricultural activities. Our study demonstrates that large nighttime vertical gradients of atmospheric N2O and CH4 mole fractions at a tall tower can be used to derive surface fluxes by the VGM; taken together with the RTM fluxes, both the annual means and the temporal variations of N2O and CH4 emissions can be constrained on a regional scale.

Effects of X (X = H2S, SO2 and N2O) mole fractions on adsorption behavior and phase equilibrium properties of CO2 + X mixed gas hydrate

As a remedy for air pollution caused by flue gas, Hydrate Based Gas Separation (HBGS) technology is under development. Among many issues in HBGS, the prediction for the adsorption and dissociation conditions of hydrate and the impact from mixed gas on the formation of carbon dioxide hydrate are crucial to understand the sequestration and separation of CO2. In this work, the occupancy isotherms of the mixed systems of CO2 + H2S, CO2 + SO2 and CO2 + N2O with different mole fractions of H2S, SO2 and N2O in sI and sII hydrates are examined. The results show that X (H2S, SO2 and N2O) in flue gases can increase the absorption of mixed gas; CO2 + H2S in the sI and sII hydrates can be categorized as the one-site Langmuir type. The calculated abundance ratio of CO2 to X vary with the mole fraction of impurity gas and pressure, which provide the prerequisite information for prediction of gas recovery yield at different conditions during the CO2 + X gas separate process. The phase equilibria of clathrate hydrates of mixed gases are predicted and the hydration numbers are determined. The results show that the dissociation pressure of mixed hydrates decreases as the impurity gas mole fraction increases, indicating that SO2, H2S and N2O gases can all promote the formation of CO2 hydrate. Additionally, inspection indicates that the mixed flue gas can be efficiently separate by clathrate hydrate.

NOx Emissions of N-butanol and Methane in Low-speed Two Stroke Diesel Engines

This article firstly structures a detailed combustion reaction mechanism including methane N-butanol nitrogen oxide. According to two-stroke low-speed diesel engine’s parameter with the characteristics of engine firing, homogeneous charge compression ignition is selected as simulation model. At the same the output power and the excess air coefficient is 1.5, by means of the simulation calculation and analysis of reaction path and reaction mechanism, when N-butanol and methane are mixed in different proportions, the exhaust temperature in the reactor reduces with the increase of methane proportion in reactants. At the same time NO mole fraction increases with the proportion of CH4 in the mixed fuel decreases, but the NO2 mole fraction will increase with the proportion of CH4 in the mixed fuel increases.

Study on Laminar Combustion Characteristics of Ammonia/ Hydrogen Premixed Based on Chemical Reaction Kinetics

The combustion characteristics of ammonia/hydrogen premixed laminar flow and the effect of hydrogen on the combustion performance of ammonia fuel were studied. First, the corresponding model of ammonia/ hydrogen premixed laminar combustion is established by using GRI3.0 mechanism, Konnov mechanism, Mei mechanism, Okafor mechanism, and Otomo mechanism respectively. Second, the simulation results are compared with the experimental results. It is found that the Mei mechanism and Okafor mechanism are more suitable for ammonia/ hydrogen premixed laminar combustion. On this basis, the effects of equivalent ratio, hydrogen ratio, and initial temperature on laminar flame velocity, maximum combustion temperature, and NO mole fraction were studied. The results show that the laminar flame velocity, the maximum combustion temperature, and the mole fraction of NO first increase and then decrease with the increase of the equivalent ratio, and the laminar flame velocity reaches the maximum when the equivalent ratio is 1.1. At the same time, with the increase of hydrogen ratio and initial temperature, the maximum combustion temperature increases first and then decreases. The mole fraction of NO increased with the increase of hydrogen ratio and initial temperature. The results show that mixing hydrogen in ammonia can improve the combustion characteristics of ammonia.

Study on the Emission Characteristics in Renewable Energy Combustion under Different Working Conditions of Marine Two-Stroke Diesel Engine

In this paper, MAN 6S35ME-B9 two-stroke diesel engine is taken as the research object. By constructing a detailed combustion reaction mechanism including CH4, C4H10O, nitrides and other substances, CHEMKIN-PRO is used to simulate the same fuel mixing ratio and excess air coefficient. Under the condition of 1.5, the temperature, NO mole fraction and NH3 mole fraction in the reactor change and study the factors affecting the pollutant emission of marine diesel engine with the crank angle under different working conditions. The simulation shows that with the decrease of diesel engine speed, the maximum temperature of combustion reaction and the temperature at exhaust opening are obviously reduced. At the same time, mole fraction of NO and NH3 decreases with the decrease of rotational speed, and there is no nitride production in the combustion reaction at 25%.

Exergy analysis and NOx emission of the H2-fueled micro burner with slinky projection shape channel for micro-thermophotovoltaic system

In order to improve the energy output of the MTPV system and reducing the NOx emission, a novel micro burner with a slinky projection shape channel for the MTPV system is proposed. To conduct the numerical simulation, 3-D models with detailed H2/air reaction mechanisms and the extended Zeldovich mechanism of NOx generation are employed. The influence of the slinky projection amplitude, slinky projection fins number, and the basic oscillating channel radius on the energy conversion characteristics and the NOx emission is investigated. The increase of the slinky projection amplitude and slinky projection fins number can improve the energy output and exergy efficiency, as well as reduce the NOx emission. When the slinky projection amplitude is 0.4 mm and the slinky projection fins number is 42, the exergy efficiency reaches the maximum value of 70.3%, while the energy output of MTPV reaches the maximum value of 4.99 W at 10 m/s. Meanwhile, the decrease of the basic oscillating channel radius can significantly decrease the NO mole fraction at the outlet. Generally, an efficient technique to increase energy output and reduce NOx emission for the MTPV system is to introduce a micro burner with a slinky projection shape channel.

Stabilization of Low-NOx Hydrogen Flames on a Dual-Swirl Coaxial Injector

Abstract Hydrogen-fueled carbon-free energy is a growing prospect for the future of several industries, including the aeronautical and energy generation sectors. However, the transition to hydrogen comes with several challenges: flame stabilization due to the unique combustion properties of hydrogen compared to conventional fuels and control of nitrogen oxides (NOx) production due to the higher combustion temperature. In addition, the high flammability of hydrogen poses an increased risk of flashback in premixed configurations commonly used to generate low-NOx flames. As a consequence, research into strategies for low-NOx hydrogen combustion is developing, and several technologies are being considered for industrial use. Among these technologies, we consider here a dual swirl coaxial injector operated in nonpremixed conditions. This setup enables the stabilization of multiple types of flame structures that are parametrically investigated for their NOx emissions. The flame structure is observed using OH* chemiluminescence images collected using an intensified CCD camera equipped with a bandpass filter. Exhaust gas species mole fractions of NO, NO2, and O2 are measured using NDIR gas detectors and a paramagnetic sensor. This investigation reveals that stabilization of hydrogen-air flames on the double swirl injector is possible and that varying the flow parameters induces changes in structure that affect NOx emissions, independently of swirl level, residence time, and temperature that also play a role. The study is carried out at atmospheric pressure.

Impact of ammonia addition on soot and NO/N2O formation in methane/air co-flow diffusion flames

Ammonia (NH3) is receiving considerable attention as a potential substitute for carbon-containing fuels to reduce CO2 and soot emissions. Co-burning with hydrocarbons is a feasible solution to improve the combustion performance of NH3, which however, brings new challenges such as NO emissions. Hence, it is essential to investigate the detailed suppression/formation mechanisms of soot and NO during the co-burning of NH3 and hydrocarbons. In this study, the effects of NH3 addition in the fuel stream on soot and NO formations in a CH4/air co-flow atmospheric-pressure diffusion flame were numerically investigated using a 2D code and a combined chemical mechanism comprised of a model of polycyclic aromatic hydrocarbons (PAHs) up to five-rings and detailed nitrogen-containing reactions. The integral of reaction rates over the whole flame were obtained in both CH4 and CH4NH3 co-flow flames to quantitatively investigate how the NH3 addition affected the soot and NO formation pathways. The results showed that the addition of 10% NH3 in the fuel stream of a CH4/air diffusion flame had a strong suppression on soot formation, decreasing the peak soot volume fractions by 38.9%. It was found that the NH3 addition led to decreases in CH4 and H mole fractions close to the burner exit, and hence lowered the integral of reaction rate of R67 (CH4+H=CH3+H2) by 1.07×10−5 mol/s, which in turn reduced the A1 production mainly through the pathway of CH4→CH3→C2H6→C2H5→C2H4→C2H3→C2H2→C3H3→A1. NO and NH played an important role in the consumption of C1∼C2 species involved in A1 formation pathways. The NH3 addition led to an increase in the integrated rates of CH3+NH=CH2NH+H and C2H+NO=HCN+CO by 2.45×10−6 and 2.59×10−6 mol/s, respectively. The decrease of A1 mole fraction reduced the inception, condensation and HACA surface growth rates. The peak NO mole fraction was increased by two orders of magnitude, from 28 ppm in the CH4 flame to 3060 ppm in the CH4NH3 flame. A promoting effect of NH3 addition on N2O was observed in CH4NH3 mixtures, however, through different channels than that of CH4 flames. In addition, more CN species, such as CH2NH, H2CH and CH2CN, were produced in the CH4NH3 flame compared to the CH4 flame.

NH3 oxidation by NO2 in a jet-stirred reactor: The effect of significant uncertainties in H2NO kinetics

Understanding the kinetics of ammonia (NH3) is becoming increasingly important to a growing variety of applications — ranging from its role as a NOx reduction agent, a key intermediate during combustion of biomass and energetic materials (especially green propellants), and a potential carbon-free energy carrier and storage medium. This wide variety of applications calls for comprehensive NH3 kinetic models that are reliable over wide ranges of temperatures, pressures, and mixtures. Yet, many still consider the present understanding of its kinetics to be incomplete. For example, there are few experimental studies of NH3 oxidation by nitrogen-containing species, which offer the opportunity to probe relatively untested reactions (or combinations thereof) to enable a more comprehensive understanding of NH3 kinetics. To address this gap, we perform jet-stirred reactor experiments of NH3 oxidation by NO2 over an intermediate temperature range (700–1100 K). The mole fractions of NH3, NO2, NO, and O2 are measured through a combination of gas chromatography, chemiluminescence, and infrared absorption. Agreement among different diagnostics (≤4% for NH3 and ≤7% for NO2) and excellent experimental repeatability ensure high confidence in all species measurements. Comparisons of species measurements to model predictions revealed deficiencies in recent kinetic models, particularly for NH3 consumption and NO formation at elevated temperatures (≥900 K). Uncertainty-weighted kinetic analyses point to the importance of reactions that form (NH2 + NO2) and consume (H2NO + NO2, H2NO + OH) H2NO, both of which are uncertain and influential in this system (and many other NH3 oxidation systems). These and other reactions accentuated in the present dataset are also key reactions in NH3/air ignition and N2O formation, both of which remain outstanding challenges for NH3 combustion in engines. Consequently, resolving the modeling deficiencies observed for the present dataset appears especially important to predictive models to enable the use of NH3 as a fuel.