11 research outputs found
Evolution of N2O production at lean combustion condition in NH3/H2/air premixed swirling flames
In the development of ammonia - hydrogen blends as potential substitutes for fossil fuels, the retrofitting of existing devices running at very lean condition is one of the promising solutions for decarbonisation of the power sector. However, little is known about the impact of these conditions on the production of NOX, particularly N2O that is a potent greenhouse gas. Therefore, the influence of varying thermal power and Reynolds numbers on the flame and emission characteristics, especially N2O, of ammonia-hydrogen-air swirling flames has been evaluated for the first time through the use of spatially resolved OH*, NH* and NH2* chemiluminescence, spectrometry analyses and advanced emissions characterisation at a fixed lean equivalence ratio, Φ = 0.65, representative of the Dry Low NOX (DLN) approach in traditional stationary gas turbines. NO and NO2 emissions were found to be decreasing (from ∼ 5000 ppmv to ∼ 1000 ppmv; NO and from ∼ 150 ppmv to ∼ 50 ppmv; NO2) with increasing ammonia content (from 50% to 90%) in the fuel while N2O followed reverse trends (from ∼ 50 ppmv to ∼ 200 ppmv). More than 80% ammonia content in the fuel blends exhibited high amounts of unreacted ammonia fractions (∼ 100 to ∼ 1200 ppmv), which can be potentially linked to flame instability and/or low temperatures. Furthermore, any increasing or decreasing trends in NOX with ammonia fraction were made more extreme by increasing thermal power or Reynolds number due to the differences in relevant radicals (NH, OH, NH2 etc.) formation in the flames. Experimental results suggest the unviability of these blends at the conventional lean conditions utilised at the DLN power applications due to excessive NOX emissions. Detailed sensitivity analyses of N2O concentration at the flame and post flame zone has been carried out utilising Ansys Chemkin-PRO to identify and investigate the reactions responsible for N2O formation/consumption in the experimental flames. Results have identified the reaction NH + NO ↔ N2O + H as the major source of N2O production in the flame, while the reactions N2O + H ↔ N2 + OH and N2O(+M) ↔ N2 + O(+M) are responsible for N2O consumption at the post flame zone, with higher reactivity for the latter reaction at longer residence time and relatively lower temperatures
Ammonia combustion in furnaces: A review
Ammonia is a formidable chemical that has been investigated over 150 years for its use in the chemical processing field. The potential of the molecule to be used in farming applications has enabled a demographic explosion whilst its implementation in refrigeration technologies ensure continuous operation of cooling systems at high efficiencies. Other areas have also benefited from ammonia, whilst the use of the molecule in fuelling applications was scarce until the 2010s. A combination of factors that include climate change and energy dependency have reignited the interest of using ammonia as an energy vector that can potentially support applications that range from small devices to large power applications, thus supporting the transition to a net zero economy. Therefore, ammonia appears as a tangible option towards the reduction of emissions that can support a truly carbon-free energy transition in the coming years. As the recognition of the molecule increases, research areas based on combustion processes have also expanded towards the utilization of ammonia. The research around the topic has considerably augmented not only in the academic community, but also across governmental institutions and industrial consortia willing to demonstrate the potential of such a chemical. Therefore, this review approaches the latest findings and state-of-the-art research on the use of ammonia as a combustion fuel for furnaces. Different to other reviews, the present work attempts to gather the latest fundamental research, the most critical technologies evaluating ammonia for system operation, and novel approaches that suggest various breakthrough concepts that will ensure the reliable, cleaner consumption of the molecule as furnace fuel. Further, the present manuscript includes the latest research from all corners of the world, in an attempt to summarise the extensive work that dozens of groups are currently conducting. Finally, future trends and requirements are also addressed, providing guidance to those interested in doing research and development in ammonia-fuelling systems
A Dual Fluorescence–Spin Label Probe for Visualization and Quantification of Target Molecules in Tissue by Multiplexed FLIM–EPR Spectroscopy
Simultaneous visualization and concentration quantification of molecules in biological tissue is an important though challenging goal. The advantages of fluorescence lifetime imaging microscopy (FLIM) for visualization, and electron paramagnetic resonance (EPR) spectroscopy for quantification are complementary. Their combination in a multiplexed approach promises a successful but ambitious strategy because of spin label-mediated fluorescence quenching. Here, we solved this problem and present the molecular design of a dual label (DL) compound comprising a highly fluorescent dye together with an EPR spin probe, which also renders the fluorescence lifetime to be concentration sensitive. The DL can easily be coupled to the biomolecule of choice, enabling in vivo and in vitro applications. This novel approach paves the way for elegant studies ranging from fundamental biological investigations to preclinical drug research, as shown in proof-of-principle penetration experiments in human skin ex vivo
Analysis of the performance of kinetic reaction mechanisms in estimating N2O mole fractions in 70/30 vol% NH3/H2 premixed flames
To address the environmental concerns associated with fossil fuels, this study explores ammonia (NH3) blended with hydrogen (H2) as an alternative fuel. While offering reduced CO2 emissions and leveraging existing infrastructure, NH3-H2 combustion notably leads to the production of nitrogen oxides (NOx), including the greenhouse gas nitrous oxide (N2O). Understanding the flame structure and chemistry responsible for N2O formation and consumption is crucial. This study comprehensively investigates various kinetic reaction mechanisms, focusing on accurately estimating N2O mole fractions and identifying mechanisms that align closely with experimental data. Sixty-seven chemical kinetic mechanisms have been numerically analysed across various equivalence ratios (φ) ranging from 0.57 to 1.4, utilizing the Premixed Stagnation Flame Model via Chemkin-Pro software. Simulations in a Perfectly Stirred Reactor were also conducted for the kinetic models that demonstrated high accuracy within the burner-stabilized stagnation flame model and closely matched experimental measurements with minimal discrepancies. This was done to determine whether the tested models, which perform accurately, maintain their performance across different combustion configurations. A preliminary assessment was carried out using the Normalized Error Approach, taking into account the uncertainty of experimental measurements, to compare the numerical results with experimental data. This method is significant in determining whether the discrepancies between the model's calculations and the experimental results, considering the experimental uncertainties, are within an acceptable range of error. The sensitivity analysis along with rate of production/consumption of N2O investigation at several conditions of equivalence ratio (0.6,1,1.4) has been conducted to check the discrepancies among the mechanisms and shed light on the reactions that dominate the formation/consumption of N2O at different conditions. The study revealed that the kinetic model developed by Klippenstein et al. (2018) demonstrates remarkable accuracy in predicting N2O mole fractions across a range of conditions, specifically within the equivalence ratio range of 0.6 to 1.4. In this range, the normalised error values were observed to be less than 1, signifying that the experimental values align closely with the numerical expectations, considering the uncertainty. However, it is noteworthy that the model's accuracy appears to decrease in lean flame scenarios, particularly when the equivalence ratio falls between 0.57 and 0.585. In these conditions, higher normalised error values exceeding 1 were recorded, suggesting a possible deviation between numerical predictions and experimental observations. Along with that the rate of production/consumption analysis revealed the NH + NO ⇌ N2O + H reaction has a dominant role in the formation of N2O for all studied conditions, while the consumption of N2O is dominated by reactions N2O + H ⇌ N2 + OH and N2O (+M) ⇌ N2 + O(+M) at all investigated conditions
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
Experimental and numerical comparison of currently available reaction mechanisms for laminar flame speed in 70/30 (%vol.) NH3/H2 flames
To achieve net zero carbon emissions, ammonia is gaining traction as a promising alternative fuel. However, the combustion characteristics of ammonia need further investigation. The current study aims to analyze the laminar flame speed, a fundamental physio-chemical property of any combustible mixture, through experimental measurements and kinetic reaction mechanism analysis. The laminar flame speed of 70/30 (%vol) NH3/H2 at atmospheric pressure and ambient temperature across a wide range of equivalence ratios (0.6–1.4) was studied experimentally and compared to the performance of 36 kinetic reaction mechanisms to appraise their performance concerning laminar flame speed prediction for the measured NH3/H2 mixture. The absolute percentage error (APE) formula has been adopted for preliminary estimation based on the experimental measurements of the present study and numerical data. The study found that Duynslaegher et al. 2012 model shows good performance speed across lean and stoichiometry conditions with an APE value between 0%-6%. The mechanism of Nakamura et al., 2017 and Gotama et al., 2022 demonstrates a good estimation of laminar flame speed under rich conditions. The sensitivity analysis revealed that the reactions H+O2=O+OH, NH2+NH2=N2H2+H2, and OH+H2=H+H2O are the most crucial reaction with considerable effect in promoting the laminar flame speed at all conditions, while the reactions of H+O2(+M)=HO2+M, NH2+H=NH+H2, and NH2+O=HNO+H play an essential role in the retardation of laminar flame speed at all conditions. The effect of the aforementioned reactions varies for the equivalence ratio, mainly due to changes in adiabatic flame temperature
Impact of structural differences in hyperbranched polyglycerol–polyethylene glycol nanoparticles on dermal drug delivery and biocompatibility
Polyglycerol scaffolds and nanoparticles emerged as prominent material for various biomedical applications including topical drug delivery. The impact of slight structural modifications on the nanoparticles’ properties, drug delivery potential, and biocompatibility, however, is still not fully understood. Hence, we explored the influence of structural modifications of five structurally related polyglycerol-based nanoparticles (PG–PEG, SK1–SK5) on dermal drug delivery efficiency and biocompatibility. The PG–PEG particles were synthesized via randomly and controlled alkylated chemo-enzymatic approaches resulting in significantly varying particle sizes and interactions with guest molecules. Furthermore, we observed considerably improved dermal drug delivery with the smallest particles SK4 and SK5 (11 nm and 14 nm) which also correlated with well-defined surface properties achieved by the controlled alkylated synthesis approach. The consistently good biocompatibility for all PG–PEG particles was mainly attributed to the neutral surface charge. No irritation potential, major cytotoxicity or genotoxicity was observed. Nevertheless, slightly better biocompatibility was again seen for the particles characterized by alkyl chain substitution in the core and not on the particle surface. Despite the high structural similarity of the PG–PEG particles, the synthesis and the functionalization significantly influenced particle properties, biocompatibility, and most significantly the drug delivery efficiency
Evaluation of Tear Evaporation Rate in Patients with Diabetes Using a Hand-Held Evaporimeter
Diabetes is a very common disease and is considered a risk factor for many diseases such as dry eye. The aim of the current work was to evaluate the tear evaporation rate (TER) in patients with diabetes using a hand-held evaporimeter. This observational, case–control and non-randomized study included 30 male patients with diabetes (17 controlled and 13 uncontrolled) with a mean ± standard deviation (SD) of 33.1 ± 7.9 years. An age-matched (18–43 years; 32.2 ± 6.5 years) control group consisting of 30 male subjects was also enrolled for comparison. Subjects with thyroid gland disorder, a high body mass index, high blood cholesterol, or thalassemia, contact lens wearers, and smokers were excluded. The TER was measured after the completion of the ocular surface disease index (OSDI) by each participant. The OSDI and TER median scores were significantly (Wilcoxon test, p 2h, respectively) compared to the subjects within the control group (5.6 (7.0) and 15.1 (11.9) g/m2h, respectively). The median scores for the OSDI and TER measurements were significantly (Wilcoxon test, p 2h, respectively) compared to those obtained for patients with controlled diabetes (11.0 (8.0) and 27.3 (32.6) g/m2h, respectively). The tear evaporation rate in patients with diabetes was significantly higher compared to those obtained in subjects without diabetes. Uncontrolled diabetes patients have a higher tear evaporation rate compared to controlled diabetes patients. Therefore, diabetes can lead to eye dryness, since these patients possibly suffer excessive tear evaporation
Interactions of Hyaluronic Acid with the Skin and Implications for the Dermal Delivery of Biomacromolecules
Hyaluronic acid (HA) hydrogels are interesting delivery systems for topical applications. Besides moisturizing the skin and improving wound healing, HA facilitates topical drug absorption and is highly compatible with labile biomacromolecules. Hence, in this study we investigated the influence of HA hydrogels with different molecular weights (5 kDa, 100 kDa, 1 MDa) on the skin absorption of the model protein bovine serum albumin (BSA) using fluorescence lifetime imaging microscopy (FLIM). To elucidate the interactions of HA with the stratum corneum and the skin absorption of HA itself, we combined FLIM and Fourier-transform infrared (FTIR) spectroscopy. Our results revealed distinct formulation and skin-dependent effects. In barrier deficient (tape-stripped) skin, BSA alone penetrated into dermal layers. When BSA and HA were applied together, however, penetration was restricted to the epidermis. In normal skin, penetration enhancement of BSA into the epidermis was observed when applying low molecular weight HA (5 kDa). Fluorescence resonance energy transfer analysis indicated close interactions between HA and BSA under these conditions. FTIR spectroscopic analysis of HA interactions with stratum corneum constituents showed an α-helix to β-sheet interconversion of keratin in the stratum corneum, increased skin hydration, and intense interactions between 100 kDa HA and the skin lipids resulting in a more disordered arrangement of the latter. In conclusion, HA hydrogels restricted the delivery of biomacromolecules to the stratum corneum and viable epidermis in barrier deficient skin, and therefore seem to be potential topical drug vehicles. In contrast, HA acted as an enhancer for delivery in normal skin, probably mediated by a combination of cotransport, increased skin hydration, and modifications of the stratum corneum properties