Fuel Communications最新文献

The oxidation of ammonia was studied experimentally by monitoring the time history of the intermediate N₂O species using laser absorption spectroscopy. Experiments were conducted in a shock tube for mixtures of NH₃/O₂ diluted in ∼96.7% Ar for equivalence ratios of 0.54, 1.03, and 1.84. The equivalence ratios were determined accurately using spectroscopic measurements of NH₃ with another laser before each experiment. Experiments were performed at an average pressure of 1.2 atm and covered a temperature range of 1829 to 2198 K. For the same temperature, experiments revealed that increasing the equivalence ratio leads to less N₂O formation. The time-history profiles showed that N₂O is formed at the beginning of the experiments, mainly from the formed NO, until reaching a peak. The N₂O is then fully consumed, mainly via its reaction with H-atom. Characteristic parameters, such as the N₂O peak time and mole fraction, were extracted from the N₂O profiles and compared with 15 recent NH₃ kinetics models. The comparison revealed that none of the existing kinetics models were able to correctly predict both the peak N₂O time and mole fraction together. Two of the models were selected to perform a chemical analysis, and an improvement of the predictive capability of one model is proposed. The N₂O profiles reported herein are excellent validation targets that offer stringent constraints for the improvement of future NH₃ kinetics models.

Tap water from twenty-five houses using private water sources, in an area of ironic and fluoride mineralization (Abuja, Nigeria), was evaluated so to ascertain the extent of conformity with chemical clean water quality criterions, and how this is inspired through householder water treatment resolutions. The percentage of analyses surpassing water quality criteria were high, with 67% of tap water samples above one or more chemical criterions. The greatest exceedances for health-established criterions were iron (44%) and fluoride (40%). The concentration of iron in borehole water varied at different sites, between 0.01 mg/L and 2.95 mg/L with an average value of 1.02 mg/L while that of fluoride ranged from 0.47 mg/L to 1.84 mg/L with an average value of 1.28 mg/L. The Hierarchical cluster analysis revealed three common clusters in which the samples may be grouped. The carcinogenic threat was calculated with defined procedures by USEPA considering ingesting and dermal pathways. The CDI values for iron and fluoride varied from 6.80E-04 to 0.20 and 8.33E-02 to 0.12 for children, while adults’ index was 9.17E-04 to 1.56E-02 and 5.56E-02 to 1.44E-02, respectively. For Total Threat Index (TTI), adults and children are below 1.0 for both iron and fluoride in all the examined locations.

The adoption of ammonia/hydrocarbon fuel blends can be viewed as an intermediate step towards a hydrogen economy, hence the characterization of methane/ammonia flame product gas trends is essential for designing combustors for a broader range of low-carbon fuel blends while fulfilling strict NOx requirements. This paper describes the product gas content of laminar premixed ammonia/methane flames for a range of equivalence ratios and ammonia heat ratios ranging from 10% to 60%, using a strain stabilized burner at atmospheric pressure and room temperature. The optimal condition to reduce NOx emissions while maintaining below 100 ppm of unburnt NH₃ emissions was found to be at equivalence ratio of 1.20 for higher ammonia ratios, moving incrementally closer over 1.35 as the methane fuel content was increased. Meanwhile, the highest measured NO values were ∼6,950 ppm at an equivalence ratio of 0.9, peaking at heat ratios of 30% to 40% at this equivalence ratio. Detailed reaction mechanisms were evaluated against the experimental data and rate constants of NO production/consumption steps featuring both NH and HNO intermediates and thermal NOx reactions were updated for Okafor's mechanism. Changes in reaction rate constants improved the mechanism accuracy for NO emissions in lean to stoichiometric flames. Meanwhile, in the rich region, modelled NO values were less responsive to changes in reaction constants, suggesting the need for an alternative approach to improve NO predictions for rich, high methane content flames. However, N₂O performance in the rich region could be improved, highlighting the significance of the HNO+CO$\to$NH+CO₂ reaction.

Gas in thermally mature shale reservoirs is considered to exist as adsorbed volume in organic matter and free gas within pores and voids in natural fractures. Gas in-place is derived from summation of aforementioned volumes. Although industry has adopted laboratory-based adsorption isotherms, quantification is still uncertain and questions on recoverability still linger. This study reevaluated in-place adsorbed gas and post-stimulation recovery. Two proprietary laboratories, using small and large mesh sizes, generated different adsorption isotherms for comparable samples of a Middle East source rock. In addition, review of published experimental studies led to the realization that confining pressures as those in situ were seldomy replicated and derived isotherms exhibited wide variability. A hypothetical scenario, using benchmarked adsorption isotherms illustrated impacts of unreliable adsorbed volume quantification on total gas in-place. From analysis of well production for three shales, matrix transient linear flow persisted for extended periods without indicating influence of boundaries. The flow regime is often matched by considering only free gas porosity. Using a sector model with 1.0 nanodarcy (nD) system permeability in reservoir simulation, a considerable proportion of the adopted grid remained above a benchmarked average critical desorption pressure after long-term post-stimulation drainage. Thus, desorption could be of limited significance in shale production if the flow model was appropriate. This study illustrated uncertainties in traditional concepts for shale gas storage and recovery. Realistic quantification of in-place adsorbed gas was found to require tailoring of laboratory protocols to account for crushed sample sizes and confinement that should match subsurface conditions such as effective vertical stress.

Various interior techniques to enhance the local heat transfer are essential for improved performance of appliances. The high-pressure penalties created by these applied passive techniques cause high power consumption and lower the pumping power. This research presents the simulation of four (4) different compound angled dimples, which are presented in this research; Case 1: 90-Circular-45-Oval dimple (90-C-45-O); Case 2: 45-Oval-90-Circular dimple (45-O-90C); Case 3: 60-Oval-90-Circular dimple (60-O-90-C); Case 4: 90-Circular-60-Oval dimple (90-C-60-O). The oval dimple print diameter, D = 20 mm, and the circular dimple print diameter, d = 10 mm. The objectives are to investigate the influence of mixed geometries with varying locations and orientation angles of the dimples. The pressure drops and heat transfer measurements are extracted using the Star-CCM+ CFD simulation bench RANS model. It was revealed that friction factor ratio, (f/fo) increases with the Reynolds number, and at the minimum of Re 1000, a 25% increment is observed, while 71% increment is noted for 11,000 Re. Case 2 has optimal effects compared to cases 3, 2 and 1. The Nusselt number ratio (Nu/Nuo) increases with Re with at least a 26% increment at 1000 Re for Case 1. Case 4 dimple arrangement is observed to be least performing arrangement with 12 – 22% Nusselt number increment. Also, the thermal performance quantified by (Nu/Nuo) / (f/fo)^1/3 is the highest for the angle of Case 2 for all Re > 2000. The results thus contribute to engineering applications with thermal performance based on varying angle, and heat transfer enhancement.

In this work, we investigated the combustion characteristics of ammonia (NH₃) by blending it with various proportions of diethyl ether (DEE). We measured laminar flame speed of various NH₃/DEE blends (DEE, 10–40% by mole) using a constant volume spherical vessel at T_i = 298 K and P_i = 3 and 5 bar and Φ = 0.8–1.3. We developed a detailed kinetic model to describe the trends of the current and previously published experimental data. For the robustness of the model, we first developed a comprehensive diethyl ether kinetic mechanism to accurately characterize neat DEE oxidation behavior. We validated the kinetic model using a large pool of experimental data comprising shock tube, rapid compression machine, jet-stirred and flow reactors, freely propagating, and burner-stabilized premixed flames. The developed kinetic model performs remarkably in capturing the combustion behavior of pure DEE and NH₃. Importantly, our model captures the experimental data of laminar flame speed and ignition delay times of various NH₃/DEE blends over a wide range of conditions. We found that DEE is a promising candidate to promote the combustion characteristics of NH₃. A small portion of DEE (10%) enhances the laminar flame speed of NH₃ by a factor of 2 at P_i = 1 bar, T_i = 298 K, and Φ = 1.0. A further doubling of the DEE mole fraction to 20% did not enhance the laminar flame speed of NH₃ with the same propensity. At low temperatures, adding 5% DEE in NH₃ blend has significantly expedited the system reactivity by lowering the autoignition temperature. A further 5% increment of DEE (i.e., 10% DEE in NH₃) lowers the autoignition temperature by ∼120 K to achieve the same ignition delay time. The “NONO₂” looping mechanism predominantly drives such reactivity accelerating effect. Here, the reactions, NO + HO₂ = NO₂ + OH and NO₂ + H = NO + OH, appear to enhance the reactive radical pool by generating OH radicals. We observed that the HNO path is favored more with increasing DEE content which eventually liberates NO. Other key reactions in “NONO₂” looping mechanism are: CH₃ + NO₂ = CH₃O + NO, CH₃O₂ + NO = CH₃O + NO₂, C₂H₅ + NO₂ = C₂H₅O + NO, C₂H₅O₂ + NO = C₂H₅O + NO₂. In addition, CH₃ + NH₂(+M) = CH₃NH₂(+M) reaction is also one of the important cross-reactions which leads to the formation of HCN. Therefore, cross-reactions between the nitrogen and carbon family are crucial in accurately predicting autoignition timing. This work provides a detailed chemical insight into the NH₃ and DE