N2 Dilution Research Articles

Laminar burning velocity of NH3 at elevated preheating temperatures and with N2 dilution: Measurements and evaluation of kinetic models

Ammonia is a promising hydrogen carrier and carbon-free fuel. In this work, new laminar burning velocity data of ammonia under intensified preheating (773K–848K) and N2 diluted condition is provided. Temperature coefficient that reflects the exponentially positive effect of preheating is reevaluated and compared with literature data at lower preheating temperatures, which is in the range of 2.08–2.30 with an improved accuracy. In contrast, dilution is of a linearly negative effect. The laminar burning velocity decreases by more than 20% as the O2 content drops from 21% to 19%. Besides, 11 recently published kinetic models are evaluated based on the experimental data. The Otomo18 model makes the best prediction with a small relative difference (≤±5%). Accordingly, the effects of radiation heat loss and dilution are analyzed in detail. The former is found insignificant, and the latter is mainly attributed to the adiabatic flame temperature drop.

EFFECT OF ADDING N2/H2O TO ETHYLENE LAMINAR DIFFUSION FLAME ON SOOT FORMATION

Abstract The method of adding exhaust gas to fuel to reduce soot and NOX is called Exhaust Gas Recirculation (EGR). This paper was carried out to investigate the effect of adding N2 and H2O to the fuel side to dilute ethylene on soot generation in laminar diffusion flame by combining experiment and numerical simulation. In the experiment, the flame was optically detected, and the volume fraction of soot and temperature was reconstructed. The numerical simulation adopts a simplified GRI-Mech 3.0 ethylene 23-step combustion reaction mechanism. It introduces virtual species FX (F1H2O, F2H2O, F3H2O) to isolate the effects of H2O addition on thermal, transport, chemical, and density effects. The results show that the numerical values agree well with the experimental results. At the same dilution ratio, the direct involvement of H2O in the reaction affects the flame temperature and intermediate products, leading to a more significant suppressing effect on soot than N2 dilution. After decoupling the effects of H2O, it was found that there are two main reasons for the decrease of soot caused by the addition of H2O. The first is the dilution effect and thermal effect, which hinder the HACA reaction by reducing the concentration of intermediate component C2H2, greatly inhibiting the surface growth rate of soot, and playing a decisive role in reducing the formation of soot. The second is the chemical effect, which mainly enhances the oxidation process of soot by increasing the concentration of OH free radicals during combustion through the elementary reaction OH+H2↔H+H2O. Additionally, the degree of influence of various effects on soot was qualitatively determined as follows: dilution effect > chemical effect > thermal effect > density effect > transport effect.

Intrinsic kinetics of steam methane reforming over a monolithic nickel catalyst in a fixed bed reactor system

The intrinsic kinetics of steam methane reforming were experimentally investigated using a monolithic nickel-based catalyst in a specially designed fixed bed system. All kinetic tests were performed under various operating conditions: steam to carbon ratio of 2 to 5, methane volumetric concentration in feed gas of 3 % to 9 %, temperature of 500 to 650 °C, and typical biogas compositions with N2 dilution (carbon dioxide 35.7–55.6 %, methane 44.4–64.3 %, with 86–91 % nitrogen dilution). A deconvolution process was applied during the rate calculation and the reaction orders with respect to different gases were determined, coupled with thermodynamic system analysis. The reaction mechanism was then proposed and a Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model was established, followed by kinetic parameter estimations for the model and a further model validation with experimental data. Based on the model, the intrinsic kinetic of SMR reaction using monolithic catalysts was described. The validity and feasibility of applying the faster approach for kinetic parameter estimation were demonstrated, and this work is the first demonstration of a complex reaction system. Also, the reaction mechanism appeared to show a suitably high correlation with alternative and more sustainable methane sources (i.e. biogas).

Experimental study of nitric oxide distributions in non-premixed and premixed ammonia/hydrogen-air counterflow flames

This study reports an experimental investigation of quantitative Nitric Oxide (NO) distribution in both premixed and non-premixed NH3/H2-air flames using a counterflow burner at atmospheric pressure. One-dimensional (1D) NO laser-induced fluorescence (LIF) spectroscopy and Raman/Rayleigh spectroscopy were conducted to accurately resolve the quantitative 1D NO profile in terms of mixture fraction, temperature, and physical space. We calibrated a saturated NO-LIF model in 5 premixed lean H2/N2/NO-air flames with different seeded NO levels in a McKenna burner and validated its accuracy in three H2N2NO-air counterflow diffusion flames. The overall uncertainty of NO quantification was less than90 ppm. Our measurements were compared with simulations using different ammonia chemical kinetic models, revealing that current models have over 30% uncertainty in predicting peak NO concentrations (mole fraction) in 1D non-premixed and premixed flames and over 100% uncertainty in lower temperature regions. In premixed flames, measured NO concentrations fell within the intermediate range of current chemical kinetic models at lean and stoichiometric conditions, but were lower than the models at rich conditions. In non-premixed flames, all models overestimated the peak NO concentrations by more than 1000 ppm. It is noted that the measured peak NO concentrations increased with higher NH3/H2 ratios (from 4/6 to 8/2), strain rates (from 80 to 140 1/s), and N2 dilution ratios in a 1:1 NH3/H2 mixture (from 0 to 30%). Although most models could qualitatively predict the trends, they were inaccurate in quantifying NO. Additionally, the measured width of the NO profile in mixture fraction space expanded with increasing NH3/H2 ratio, N2 dilution ratio, and strain rate. While models could qualitatively predict this behavior, they consistently underestimated NO in the fuel-rich, lower-temperature region, resulting in a narrower NO profile width. The Manna model showed a better prediction of NO distribution in the fuel rich portion of non-premixed flames, accounting for NH3NO interactions at lower temperatures. These findings highlight the critical need to improve models to accurately predict NO concentrations in ammonia-containing flames and their behavior in fuel rich regions.

On the difficulty of interpreting NO-LIF measurements around 226 nm in confined ammonia flames

This paper addresses how NH3 and NO absorption along the laser axis disrupts NO-LIF measurements made around 225 nm in NH3/O2/N2 premixed flames confined at low pressure (10 kPa). Measurements were performed in 3 flames (equivalence ratio ϕ = 0.87, 1.1 and 1.3) with 24 % N2 dilution. Together with the LIF measurements, single-pass absorption measurements were obtained in all flames as a function of the height above the burner (HAB) and of the wavelength. A significant NH3 absorption of the laser beam is found in the pre-heat zone and flame front of each flame, as well as in the burned gas in the rich flame. In the lean flame, whatever the HAB, an additional significant absorption is due to the NO present in the gas surrounding the flame. Whereas NH3 absorbance only occurs inside the flame under all conditions, NO absorbance is mainly due to the high concentration of NO produced in the lean flame and spread in the entire confined vessel around the flame. From this analysis, relative NO rotational population profiles were recorded by measuring the temporal peak of the LIF signals (prompt-LIF) which were corrected for absorption to account for the available energy at burner's center. NO-LIF thermometry was conducted to determine the temperature in the flames through collecting excitation LIF spectra and performing spectral fitting using a dedicated software (thermo NO-LIF, https://pc2a.univ-lille.fr/thermo-no-lif/). The procedure developed to collect the NO profiles could not be transposed to determine the temperature in the lean flame. Indeed, the attenuation of the laser beam depends on whether the laser is tuned on a “cold” transition (strongly impacted by absorption outside the flame) or on a “hot” transition of NO, little affected. Thus, two tubes (with N2 flushing) were installed inside the vessel along the laser axis and surrounding the flame to suppress the NO absorbance.

The effect of CH4 addition on high-H2 syngas combustion characteristics under N2/CO2 dilution

The composition of biomass gas is complex, in order to promote the more extensive and efficient utilization of low-calorific syngas, it is necessary to master the basic combustion characteristics of low-calorific syngas under different compositions. In this paper, the effects of addition of CH4 (0% – 20%) on the combustion characteristics of laminar flow flame of high-H2 syngas (H2:CO = 3:1) were studied by experiments and numerical simulations under the dilution of N2 and CO2 (40%). The laminar burning velocity (LBV) and Markstein length are obtained by experiments. CHEMKIN-PRO software package was used to compare the prediction results of the four mechanisms with the measured data. Finally, GRI3.0 mechanism was selected as the simulation mechanism in this paper. The experimental results indicate that the LBV of N2 dilution is higher than that of CO2 dilution, and the flame is more stable, with adding CH4, the LBV of syngas mixtures is decreased, and the LBV of rich-fuel mixtures is decreased faster, but the stability of premixed flames of syngas is improved. Numerical simulation shows that the dominant branch chain reaction changes from R99 to R38 after CH4 is added, and the mole fraction of H, O decreases while the mole fraction of OH, CH3 increases. The dilution of CO2 results in a lower concentration of active radicals than N2 because CO2 inhibits the important reaction R99. The GRI 3.0 mechanism was used to simulate the formation of NO: the addition of CH4 promoted the formation of hot NO. The NO production of NNH and N2O intermediate mechanism is decreased, and a new way of N2 and CH reaction to HCN is increased. The dilution of CO2 can reduce NO emission more than that of N2. The insights gained from this study have practical implications in a variety of production applications. For example, optimizing mixture equivalence ratios can improve combustion efficiency, thereby increasing energy efficiency and reducing environmental emissions.

Detailed kinetic modeling of catalytic oxidative coupling of methane

The oxidative coupling of methane (OCM) at high temperature over monolithic Pt-based catalysts operated at short contact times is investigated as an attractive method for methane upgrading to higher value products like ethylene and acetylene. An experimental measurement campaign aiming at elucidating the effect of operation parameters on the catalyst performance revealed that lower N2 dilution, lower CH4/O2 ratio, and higher space velocities promote high C2 yields. A maximum C2 yield of 10 % with 94 % CH4 conversion was obtained at a CH4/O2 ratio of 1.1, 50 % N2 dilution, and a space velocity of 4.5 × 105 h−1. Since both heterogenous and homogenous gas-phase chemistry together are required for determining C2 formation pathways, a detailed OCM surface reaction mechanism over Pt is presented consisting of 26 species and 86 reactions that are consistent from the view of thermodynamics and micro-kinetic reversibility. The combination of this OCM surface mechanism with a detailed gas-phase mechanism allows a numerical micro-kinetic description of the experimental measurements. The simulations presented in this study suggest that C2 formation takes place in the gas-phase at temperature above 1200 K with both oxidative and pyrolytic pathways for methane dehydrogenation to form CH3 radicals, whose coupling results in C2H6, C2H4 and C2H2 formation. Furthermore, the simultaneous presence of sufficient oxygen content and heat are vital for high C2 species yields.

NO emission characteristics of air coflowed non-premixed ammonia jet flame at elevated ambient temperatures and with N2 dilution

Ammonia is promising carbon-free alternative fuel, while the poor combustion performance and severe NO emission hinder its application. In this work, a strategy combined with preheating and dilution was discussed, and NO emission characteristics of air coflowed non-premixed ammonia jet flame were experimentally investigated over 550–700 °C and with N2 dilution, using a novel preheating facility. Results show that the general excess air coefficient is significant for NO emission, but not the unique factor. NO emission monotonically increases with the general excess air coefficient, while the slope decreases. Ambient temperature is also of a remarkable effect, that NO emission decreases by about 100 ppm (15% O2, dry) when the ambient temperature rises from 550 °C to 700 °C. Besides, effects of dilution were considered with three specific strategies. Air coflow dilution is of a negative influence on NO emission, while, NH3 jet dilution promotes NO emission in contrast. The interaction between the two single-dilution strategies is limited, and the effect of double dilution seems to be a simple sum of that of the other two single-dilution strategies. In addition, flame liftoff was observed in experiments and a considerable decline of NO emission was detected with the flame regime transition. According to the experimental results, the combination of elevated ambient temperature and air dilution is evaluated to be a promising low NO emission combustion method of ammonia.

N2 and Ar dilution on the premixed biogas jet flame under external acoustic enforcement

In this study, combustion instabilities and flue gas emission changes under different dilutions of N2 (nitrogen) and Ar (argon) of a promising biogas mixture (70% CH4 - 30% CO2) in the fight against greenhouse gas emissions were investigated. In the experiments, additions were made from 0% to 50% at intervals of 10% for both gases. In order to detect the instability of the flame, external acoustic enforcements at different frequencies was applied through the speakers placed in the combustion chamber arms. The dynamic pressure fluctuation values were recorded. The results showed that low dilution ratios were effective in reducing flame instability for both inert gases. However, as the dilution ratio increased, the fuel/air mixture became leaner and blowoff occurred. In the case of comparing two different gases, it has been observed that the effect of argon gas on reducing dynamic pressure fluctuation is higher. Burner outlet temperature and brightness values of the flame decreased in both Ar and N2 dilution. CO and NOx emissions increased with increasing diluent volume for all dilution conditions. When the emissions of the two diluent gases are compared, the CO emission, which was 3134 ppm in the undiluted condition, increased up to 4949 ppm in 50% Ar dilution, while it increased to 4521 ppm in 50% N2 dilution.

Experimental and numerical investigations of high-temperature PEM fuel cells under different anode dilution levels and varying temperatures

This work investigates the effect of nitrogen in the anode gas mixture on the performance of HT-PEMFCs using experiments and simulations. It explores four H2/N2 ratios (100/0, 80/20, 60/40 and 50/50) at three temperatures (140 °C, 160 °C, 180 °C), and four current densities (0.1 A cm−2 to 0.4 A cm−2). The results demonstrate that N2 dilution negatively impacts fuel cells performance, but higher temperatures can mitigate this effect. Temperature influences electrochemical impedance spectroscopy, with initial ohmic resistance increase followed by a slight decrease. N2 dilution effects charge and mass transfer resistances. Current density has minimal impact on ohmic resistance but improves charge transfer resistance, especially at high frequencies. This understanding can optimize fuel cell performance, especially in ammonia-fueled systems with hydrogen and nitrogen mixtures or during anode gas recycling with significant nitrogen crossover.

Influence of steam dilution on ignition delay time of dimethyl ether/air mixtures at high pressure measured behind reflected shock waves

This work provides the first experimental data on ignition delay times of steam-diluted dimethyl ether/air mixtures at high pressure obtained behind reflected shock waves. Mixtures are prepared with 20 and 40vol% steam dilution and at equivalence ratios of 0.5, 1.0 and 2.0. The measurements comprise temperatures between 731 and 1314K and are recorded at nominal pressures of 15 and 35bar. The obtained experimental data is used for comparison and evaluation of predictions of common chemical-kinetic models. The effect of dilution on ignition delay time is furthermore studied numerically utilizing zero-dimensional reactor simulations with the chemical-kinetic model AramcoMech 3.0. Thermal and chemical effects of steam-dilution are analyzed in comparison to CO2 and N2 dilution. Steam dilution features a smaller heat capacity than CO2 at the investigated temperatures, which leads to a lower thermal effect and therefore shorter ignition delay time. The chemical effect of steam decreases ignition delay time at intermediate and high temperatures below the ignition delay time of a mixture with the same amount of N2 dilution. The chemical effect is mainly due to the high collision efficiency of H2O in the third body reactions H2O2 + H2O ↔ 2OH + H2O, H + O2 + H2O ↔ HO2 + H2O and CH3OCH3 + H2O ↔ CH3 + CH3O + H2O. At high temperatures the direct participation of H2O in reactions and its chemical conversion additionally exerts a further decreasing effect on ignition delay time.

Near-extinction transient behaviors of counterflow nonpremixed flames in a porous spherical burner at very low stretch rate

Near extinction transient behaviors of CH4/N2 versus O2/N2 counterflow nonpremixed flames were investigated by adopting a porous spherical burner with a large radius of curvature to achieve a very low buoyant stretch rate. By varying the oxygen concentrations in the oxidizer stream, four regimes were identified by three limits of sooting, instability, and extinction. The sooting limit was sensitive to flame temperature, and was characterized by two indexes of fuel injection velocity uF and oxygen concentration XO2. When decreasing uF, the sooting limit was different from high stretch flames because of appreciable heat loss toward the burner surface. In the instability regime, periodic holes were observed whose frequency decreased with XO2. Periodic holes were also found to occur with N2 dilution in the fuel stream, which were more regular with larger frequencies compared with the periodic holes in the diluted oxidizer streams. The edge propagation behaviors for periodic holes in diluted fuel streams were analyzed. The statistical average of the propagation speed of advancing edge (hole closing) Se decreased with increasing fuel concentration gradient, and the ratio of Se with the stoichiometric laminar burning velocity SLst of Se/SLst was larger than unity. Also, the stretch rate significantly affected the propagation speed of advancing edge flames. Determination of the propagation speed of the retreating edge (hole opening) had intrinsic difficulty in estimating the transient radial flow velocity, however, the approximated |Se/SLst| was larger than unity and decreased with the fuel mole fraction. Nitrogen dilution in the oxidizer stream was proven to be more effective than in the fuel stream for flame suppression of methane. This study could enrich the understanding of very low-stretch nonpremixed flames in a counterflow burner and provide information regarding low-stretch flame suppression, which may be relevant to microgravity flame behaviors.

Investigation of the impact of nitrogen and water vapor dilution in oxidizer stream on flame structure, soot production and extinction of a laminar ethylene-fueled co-flow diffusion flame

This paper discusses the effect of nitrogen (N2) and water vapor (H2O) dilution in oxidizer stream on the flame structure, and soot production and extinction of laminar ethylene (C2H4)-fueled co-flow diffusion flame (CFDF). The total oxidizer stream flow rate is kept constant while varying the flow rates of air, N2, and H2O to achieve the desired oxygen concentration called oxygen index (OI). As OI reduces, the flame starts to lift off from the burner surface and shows upward and downward oscillations before extinction through blow-off. The OI at which the flame blows off is called the limited oxygen index (LOI), and it depends on burner configuration, fuel, and oxidizer flow conditions. LOI value for C2H4-fueled laminar CFDF were found to be 12.4% and 14% when the diluent was N2 and H2O, respectively. The experiment and simulation results are presented from 21% O2 concentration in oxidizer to very low oxygen concentration in oxidizer close to extinction. Through quantitative measurements of soot volume fraction (SVF), the result shows a notable reduction in the peak concentrations of SVF as the OI decreases. This decrease is more pronounced with H2O than N2 dilution. One-dimensional (1D) opposed flow diffusion flame simulations are performed to understand various effects of the addition of diluents like H2O and N2. It is observed that in addition to inert, thermal and diffusion effect of H2O in reduction of flame temperature and temperature-dependent production rate of key species, H2O also affects flame chemistry through OH + H2 = H + H2O, 2OH = O + H2O. As a result there is a further drop in the concentration of active radicals (like H, O) which leads to quicker soot inhibition and flame extinction.

Simulation study of N2/Ar dilution gas to improve thermal efficiency and reduce NOX emissions in hydrogen engines

Although N2 dilution is effective in reducing NOX emissions in hydrogen engines, it decreases thermal efficiency. Utilizing Ar with N2 as a dilution gas can improve thermal efficiency while reducing NOX emissions. However, the specific effects and mechanisms of the mixed dilution of Ar and N2 on the combustion and emission characteristics of hydrogen engines remain uncertain. This study examined the influence of Ar and N2 on the combustion and NOX emissions by adding Ar and N2 to the intake gas at various dilution rates. The examined cases were as follows: Case 1 (N2 = 100%), case 2 (N2:Ar = 80%:20%), case 3 (N2: Ar = 50%:50%), case 4 (N2:Ar = 20%:80%), and case 5 (Ar = 100%). The findings indicate that increasing the N2 ratio in the dilution significantly reduces NOX emissions, but it also reduces the combustion rate. In contrast, increasing the Ar proportion enhances combustion, resulting in higher peak values of the in-cylinder pressure, temperature, and heat release rate. In case 1 (N2 = 100%), the NOX emissions decreased from 255 to 3 ppm when the dilution rate increased from 5% to 20%. However, this also caused a significant decrease in the thermal efficiency from 44.4% to 22%. This limitation can be mitigated by appropriately increasing the proportion of Ar. Optimal results, with lower NOX emissions (250–500 ppm) and higher thermal efficiency (47.6%–49.3%), were achieved with a dilution rate of 17%–27% and an Ar proportion of 80%–90%.

Effect of diluent N2 addition on NH3/H2/air combustion characteristics

As a clean energy source with high-energy hydrogen carriers, ammonia has a promising application prospect in gas turbine power production. The existence of N2 as an ammonia combustion product and as an ammonia decomposition product at high temperatures influences ammonia combustion characteristics. Accordingly, this paper measured the combustion characteristics of the NH3/H2/air flame by the method of a constant-pressure spherical flame under different N2 dilution ratios and different equivalent ratios (0.7–1.5), with initiating temperatures of 303 K and 500 K and an initiating pressure of 1 atm, respectively. The experimental results show that the influence of diluent N2 leads to a downward trend in the laminar burning velocities (LBVs) of the NH3/H2/N2/air mixture, and the dilution effect inhibits the propagation of the NH3/H2/N2/air flame. The laminar flame propagation of the mixture is aided by the initiating temperature increase. The existence of diluent N2 reduces the major branching reactions’ net reaction and net heat production rates while enhancing inhibition of the H/OH radical pool and the rate-limiting effect of the primitive reactions. The initiating temperature reduces the impact of the radical reactions on the flame rate and enhances the chemotaxis of NHi (i = 1, 2). The diluent N2 changed the NH3 consumption and effectively suppressed the NOx production, showing the NO emission potential of NH3/H2/N2/air mixtures combustion under fuel-rich conditions.

Effect of N2 and CO2 dilution on syngas/air deflagration characteristics in narrow gap disk burner

ABSTRACT This study explored the typical features of flame from syngas/air premixed flame in a narrow gap disk burner based on diluted N2 and CO2. Four concentrations (i.e. 10%, 20%, 30%, and 40%) of CO2 and five concentrations (i.e. 10%, 20%, 30%, 40%, and 50%) of N2 were adopted in this study. The experiment was conducted in a narrow gap disk burner with a clearance of 2 mm. The results showed that the addition of N2 and CO2 significantly reduced the brightness of flame, the flame propagation velocity, and the pressure resulting from the explosion. When the CO2 concentration reached 40%, the maximum pressure was reduced to 60.78 kPa, which was 41.5% lower than that without diluent. When the N2 concentration was increased to 50%, the maximum pressure was reduced to 67.01 kPa, but at this point, the inhibition effect on the maximum pressure was not as good as 40% of CO2. Additionally, the dilution effect of CO2 was more obvious than of N2. An analysis on the dilution mechanism found that reduced moles of critical radicals H, O, and OH were an important reason for the inhibition effect. However, with the increase of N2 and CO2 concentrations, the unstable flame propagation behavior in a later stage was not inhibited, but enhanced. The unstable propagation behavior was related to the flow field disturbance caused by heat loss.

Stabilization of air coflowed ammonia jet flame at elevated ambient temperatures

Ammonia is a promising carbon-free fuel, while, understanding of ammonia jet flame is still in lack. In this work, a novel facility was applied and air coflowed ammonia jet flames were achieved in an elevated ambient temperature range, 723–923K. Stabilization regimes and limits were investigated. Stable lifted flame with a classical triple structure was observed, and critical aerodynamic parameters were measured at three specific regimes, liftoff, reattachment and blowoff. Attached flame can only be retained under laminar conditions with flow Reynolds number <150. A linear correlation between velocities of fuel jet and coflow under critical conditions was uncovered, which is different from the literature research on methane flames. Effects of partially premixing and N2 dilution were considered. Partially premixing was found harmful to stabilization at 823K, while this influence becomes unclear at 923K. Differently, a linearly adverse effect was observed under both N2-diluted jet and coflow conditions at different temperatures.

Laser absorption study of the N2+ O → NO + N and NO + O → O2+ N Zeldovich reactions in shock-heated N2O mixtures

The fast decomposition of nitrous oxide (N2O) into molecular nitrogen (N2) and atomic oxygen (O) was leveraged to probe the N2 + O and NO + O Zeldovich reactions behind reflected shocks in experiments spanning 2000–6800 K and 0.04–1.67 atm in 1% and 5% N2O diluted in either argon (Ar) or N2, respectively. One infrared (IR) and two ultraviolet (UV) laser absorption diagnostic systems probed N2O and NO. The IR laser system probed N2O in isolation, while the two UV laser systems probed a combination of N2O, NO, and O2 using an online/offline method. The resulting absorbance time-histories were used to infer the NO rotational temperature and the number densities of N2O and NO. The number density time-histories were used to infer (1) the N2O dissociation rate to form N2 and O ( k d N 2 O − [ M ]), (2) the reaction rate of N2O and O to form two NO ( k d N 2 O − O , 1), (3) the NO + O Zeldovich reaction rate ( k z NO − O), and (4) the N2 + O Zeldovich reaction rate ( k z N 2 − O). The experiments were insensitive to the reaction rate of N2O and O to form O2 and N2 ( k d N 2 O − O , 2) at high temperatures. Generally, k d N 2 O − [ M ] was inferred from IR and UV offline data, with k d N 2 O − O , 1, k z NO − O, and k z N 2 − O inferred from UV online data in Ar and N2 dilution. Each inferred reaction rate shows consistency with literature, while extending data to higher temperatures with reduced uncertainty. The reduced uncertainty is sufficient to enable comparisons of the data to various high-temperature quantum chemistry models.

Characteristics of biomass gasification by oxygen-enriched air in small-scale auto-thermal packed-bed gasifier for regional distribution

To utilize the by-product oxygen produced by regional distributed water electrolysis plant for the creation of “hydrogen society” in Japan, a small-scale auto-thermal packed-bed gasifier using oxygen-enriched air was proposed. In this study, the packed-bed height, temperature distribution, syngas concentration, lower heating value (LHV) of syngas, tar content, cold gas efficiency (CGE), and carbon conversion were assessed to verify the feasibility of the scheme. The LHV improved from 3.85 to 4.66 MJ/Nm3, the tar content reduced from 0.81 to 0.17 g/Nm3, and the CGE increased from 81.22 % to 90.69 % as the oxygen concentration increased from 21 % to 25 %. Thermochemical calculations were further performed using FactSage 8.3 to explore the essence of O2-enriched effect. It was found that O2-enriched effect can be ascribed to the synergy of weakened N2 dilution and temperature increasing.

NOx reduction based on N2 dilution in a swirled-stabilized magnesium flame

New sources of clean energy with reduced greenhouse gas emissions must be considered because of global warming. Among these alternative sources, metal fuels such as aluminum or magnesium are promising. The present study focuses on the impacts of an air dilution by N2 and of the equivalence ratio on the amount of nitrogen oxides (NOx) produced by a swirled-stabilized magnesium flame. A polydispersed aerosol of pure magnesium in the size fraction 50–70 µm was injected in the combustion chamber. Different air–fuel ratios – from 0.14 to 1.0 – were obtained by changing the mass flowrate of the injected fuel. Thermocouples and a pyrometer were implemented to monitor the gas and flame temperatures. On-line paramagnetic analyzers were used to measure the oxygen (O2) and NOx concentrations. For each dilution condition (0, 30 and 50 %), the NOx mole fraction versus the equivalence ratio follows a parabolic shape. The amount of NOx first increases when increasing the air–fuel ratio as the power dissipated by the flame increases, leading to the rise of the gas temperature. For the highest air–fuel ratios, the NOx production is disfavored in the rich mixture. The maximal NOx emissions are shifted to higher equivalent ratios when increasing the dilution level and it decreases by a factor 2 with a dilution of 50 %, for a constant value of the air–fuel ratio. The gas temperature in the flame decreases due to the N2 dilution. The NOx emissions become negligible for an equivalence ratio of 1 at a 50 % dilution. Nevertheless, under the tested experimental conditions, the level of NOx never exceeded 7 gNOx/kWh, which is lower than the maximal value of NOx emissions from a gasoline engine.