Search Results (1,321)

Although hydrogen plays a crucial role in the EU’s strategy to reduce greenhouse gas emissions, its storage and transport are technically challenging. If ammonia is produced efficiently, it can be a promising hydrogen carrier, especially in decentralized and flexible conditions. The Horizon EU HySTrAm project addresses this problem by developing a small-scale, containerized demonstration plant consisting of (1) a short-term hydrogen storage container using novel ultraporous materials optimized through machine learning, and (2) an ammonia synthesis reactor based on an improved low-pressure Haber–Bosch process. This paper presents an initial version of a Python (v3.9)-based dashboard designed to visualize and optimize the simulation workflow of the ammonia synthesis process. Designed as a baseline for a future online, automated tool, the dashboard allows the comparison of three reactor configurations already defined through simulations and aligned with the upcoming experimental campaign: single tube, two reactors in parallel swing mode and two reactors in series. Pressures at the inlet/outlet, temperatures across the reactor, operation recipe and ammonia production over time are displayed dynamically to evaluate the performance of the reactor. Future versions will include optimization features, such as the identification of optimal operating modes, the reduction of production time, an increase of productivity, and catalyst degradation estimation. Full article

With increasingly stringent greenhouse gas emission regulations, carbon emissions from marine engines have become a major concern, driving the shipping industry to actively explore efficient and clean alternative fuels. Among the various candidates, ammonia has attracted considerable attention in recent years due to its carbon-free nature and potential as a high-quality clean fuel. However, its practical application in marine engines is constrained by several inherent drawbacks, including a high auto-ignition temperature, low flame propagation speed, and low calorific value. Blending ammonia with natural gas has been demonstrated as an effective strategy to enhance its ignition performance. In this study, the ignition characteristics of NH₃/C1–C4 alkane mixed fuels were systematically investigated using numerical simulations. Rate of production (ROP) analysis, reaction pathway analysis, and other kinetic evaluation methods were employed to elucidate the underlying ignition mechanisms. The results reveal that blending NH₃ with C1–C4 alkanes significantly shortens the ignition delay time. When X_CH ≥ 30%, at high initial temperatures, the ignition-promoting effect is most pronounced for NH₃/C₂H₆ mixtures. In contrast, under low temperature conditions, ignition performance progressively improves with increasing carbon chain length of the blended alkane fuel. The ignition delay time across different operating conditions is primarily governed by highly reactive radicals, including O, H, and OH. Elevating the initial temperature, pressure, and blending ratio promotes the earlier formation of these key radicals and increases their production rates. ROP analysis of OH radicals indicates that reaction R10 (O₂ + H ⇌ OH + O) contributes most significantly to OH generation. Furthermore, reaction pathway analysis of NH₃ shows that at lower initial temperatures, NH₃ dehydrogenation is dominated by reactions with OH radicals. At higher temperatures, a greater fraction of NH₃ participates in NO reduction reactions, thereby decreasing the proportion of NH₃ involved in dehydrogenation pathways. Full article

Anaerobic digestate (AD) has the potential to partially replace inorganic fertiliser, containing readily available nitrogen and other macro- and micronutrients. However, these properties vary with the feedstock. The objectives of this study were to analyse the chemical composition of AD materials and measure their effects on plant growth and greenhouse gas emissions. Anaerobic digestate came from a conventional reactor using vegetable waste and maize as feedstock (‘food AD’) and from a biogas system on a smallholder dairy farm using manure feedstock (‘manure AD’). Undigested cattle slurry (‘manure slurry’) and a complete mineral fertiliser were used as controls. These were applied to wheat plants grown in a glasshouse. Wheat grown with the food AD had a higher yield than the complete mineral fertiliser control, even when applied at a lower rate of nitrogen. Wheat grown with both the food AD and manure AD had macronutrient concentrations equal to or higher than the complete mineral fertiliser treatment. Furthermore, the wheat P concentration was significantly greater with the manure AD treatment, which was unrelated to a biomass dilution effect. However, food AD caused high ammonia emissions, and residual methane was emitted with manure AD, indicating incomplete digestion in the latter. Optimal yields and reduced greenhouse emissions were obtained with mixtures of AD and mineral fertiliser in a 1:1 ratio, indicating the potential to greatly reduce the costs and environmental impact of fertiliser application. Full article

Shipping is a high-energy-intensive sector and a major source of climate-relevant and harmful air pollutant emissions. In response to growing environmental concerns, the sector has been subject to increasingly stringent regulations, promoting the uptake of alternative fuels and emission control technologies. Accurate and diverse emission factors (EFs) are critical for quantifying shipping’s contribution to current emission inventories and projecting future developments under different policy scenarios. This study advances the development of load-dependent EFs for ships by incorporating alternative fuels, biofuels and emission control technologies. The methodology combines statistical analysis of data from an extensive literature review with newly acquired on-board emission measurements, including two-stroke propulsion engines and four-stroke auxiliary units. To ensure broad applicability, the updated EFs are expressed as functions of engine load and are categorized by engine and fuel type, covering conventional marine fuels, liquified natural gas, methanol, ammonia and biofuels. The results provide improved resolution of shipping emissions and insights into the role of emission control technologies, supporting robust, up-to-date emission models and inventories. This work contributes to the development of effective strategies for sustainable maritime transport and supports both policymakers and industry stakeholders in their decarbonization efforts. Full article

Sawdust represents a locally available lignocellulosic resource that may complement ruminant diets during periods of forage shortage. This study evaluated the feeding value of birch (Betula pendula) sawdust subjected to physical and chemical processing using a stepwise experimental approach. Steam-exploded and fresh sawdust were treated with 0, 4% ammonia, or 4% sodium hydroxide in a 2 × 3 factorial design and initially evaluated by in vitro gas production, dry matter digestibility, and fermentation pH. Based on these results, selected materials were further assessed for rumen dry matter and fiber degradation using the in sacco technique in cannulated dairy cows, with untreated and ammonia-treated wheat straw included for comparison. In addition, steam-exploded sawdust was compared with wheat straw and grass silage for in vivo digestibility in sheep. A pilot study also tested aspen (Populus tremula) sawdust in lactating cow diets. Steam explosion substantially reduced fiber fractions, particularly hemicellulose, and increased residual carbohydrates, resulting in higher gas production and in vitro digestibility compared with fresh sawdust (p < 0.05). Ammonia treatment markedly increased crude protein content, whereas sodium hydroxide primarily increased ash concentration. In sacco, steam-exploded birch showed similar or higher ruminal dry matter and neutral detergent fiber degradation compared with ammonia-treated wheat straw, while untreated fresh birch remained largely undegraded. In vivo, steam-exploded sawdust exhibited greater organic matter digestibility and net energy than untreated wheat straw but remained less digestible than grass silage (p < 0.0001). A pilot feeding test with lactating dairy cows demonstrated good acceptance of untreated aspen sawdust as a partial roughage substitute under non-standardized conditions. Overall, the results indicate that steam-exploded sawdust has potential as a complementary roughage source for ruminants when conventional forages are limited. Full article

The global transition toward net-zero emissions by 2050, encompassing the International Energy Agency’s Roadmap for the energy sector, the IMO’s revised strategy for the maritime industry, and broader climate guidelines, necessitates a profound transformation of both global energy systems and the shipping sector. In this context, energy vectors such as Liquefied Natural Gas, Green Hydrogen, and Ammonia are emerging as key elements for this shift. This review article proposes a comprehensive analysis of these vectors, contrasting their roles: Liquefied Natural Gas as a transitional solution and Hydrogen and Ammonia as long-term pillars for decarbonization. The research moves beyond a simple comparative analysis, offering a detailed mapping and evaluation of the global port infrastructure required for their safe handling, cryogenic storage, and bunkering operations. We examine their technical specifications, decarbonization potential, and the challenges related to operational feasibility, costs, regulation, and sustainability. The objective is to provide a critical perspective on how the evolution of maritime ports into energy hubs is a sine qua non condition for the secure and efficient management of these vectors, thereby ensuring the sector effectively meets the Net Zero 2050 climate goals. Full article

Nitric acid production is a cornerstone of the chemical industry, yet it presents considerable environmental challenges, primarily due to greenhouse gas emissions such as nitrous oxide (N₂O) and nitrogen oxides (NO_x). This manuscript critically examines the key performance indicators (KPIs) that define the gate-to-gate environmental sustainability of nitric acid plants. Quantitative metrics and related benchmarks achieved in modern plants, e.g., energy efficiency (ca. 2 GJ exported per ton of HNO₃) and NO_x/N₂O reduction (95–99%), are presented. Strategies to enhance these KPIs are discussed, including process integration, intensification, advanced emission control technologies, and operational optimization. Special attention is given to the chemical conversion processes of NO_x and N₂O, highlighting their roles in minimizing overall emissions. The review also synthesizes recent literature to showcase emerging trends, regulatory developments, and technological innovations that facilitate the transition toward more sustainable nitric acid production. Finally, the article identifies current research gaps and outlines future directions for the field. Full article

A plasma-assisted ammonia jet flame igniter was developed in this study to address the limitations of conventional spark ignition at high pressures. The effect of pressure on plasma discharge characteristics, optical emission spectra, and exhaust gas emission was systematically investigated, providing new insights into the mechanisms of plasma-assisted ammonia ignition under high-pressure conditions. The results indicate that increased chamber pressure elevates gas density, which in turn raises the voltage required to sustain an arc discharge at 0.4 MPa and markedly reduces the frequency of arc drift. Spectral analysis shows that higher pressure inhibits atomic oxygen lines (777.2 nm and 844.6 nm) while intensifying the molecular nitrogen bands between 350–450 nm. A corresponding decrease in electron excitation temperature is also observed. In terms of exhaust composition, hydrogen concentration demonstrates a bifurcated behavior, rising with pressure under fuel-rich conditions (the equivalence ratio φ > 1.2) and falling under fuel-lean conditions (φ ≤ 1). Conversely, NO concentration consistently decreases with increasing pressure across all test conditions. The ammonia concentration in the exhaust gas shows opposite pressure dependencies at different equivalence ratios. It increases with rising pressure for φ ≥ 1, while it decreases with increasing pressure for φ < 1. Full article

Tannins are known for their ability to modify digestion and reduce CH₄ emissions in ruminants. Novel forages able to tolerate water deficits often contain low-to-moderate levels of dietary tannins. The aim of the study was to compare the effect of tannic acid (hydrolysable tannin, HT) and Tannivin (quebracho, condensed tannins, CTs) added to a total mixed ration at a concentration of 2.5% on rumen fermentation over time using in vitro methods. The substrates were incubated with buffered rumen fluid at 39 °C for 0, 3, 6, 12, 24, and 48 h to study dry matter (DM) degradability, tannin disappearance, utilizable protein (uCP), and rumen fermentation parameters. In parallel, gas production was measured using the ANKOM-RF Gas Production System. Gas composition was determined after 24 and 48 h of incubation. DM degradability was influenced by the incubation time (p < 0.001), reaching approximately 50% after 48 h, with a similar course of degradability for both tannin types. Tannin disappearance was significantly influenced by the type of tannins and the incubation time (both p < 0.001), reaching 50% in HTs and 39% in CTs within the first 6 h of fermentation. Production of individual and total VFA and uCP increased during incubation (p < 0.001) but were not influenced by the tannin type. However, the formation of uCP was relatively stable over time. Ammonia-N production increased during the first 12 h of fermentation with both tannin types and the increase continued with HTs (p < 0.001). Gas and methane production increased during fermentation and the increase was more substantial in HTs (p < 0.001). Our results suggest that at moderate concentrations, tannins mainly affect protein metabolism, with a minor effect on rumen fermentation. Full article

Ammonia (NH₃) is a zero-carbon fuel and an attractive hydrogen (H₂) carrier for gas turbine power generation due to its high energy density, ease of storage, and transportation. This study numerically investigates NH₃/air combustion using a hybrid Well-Stirred Reactor (WSR) and Plug Flow Reactor (PFR) model in Cantera at pressures of 1–20 atm, temperatures of 1850–2150 K, and equivalence ratios (ϕ) of 0.7–1.2. The effects of pressure, equivalence ratio, and temperature on NH₃ conversion and NO formation are examined. Results show that NH₃ exhibits a non-monotonic conversion curve with pressure after the WSR, reaching a minimum near 5 atm, whereas NO formation decreases monotonically from 1 to 20 atm. Equivalence ratio sweeps show that NO decreases steeply as ϕ increases from 0.7 to ~1.1 as nitrogen is redirected toward N₂ and oxidizer availability declines; residual NH₃ increases rapidly for ϕ > 1.0, especially at high pressure. Increasing temperature accelerates NH₃ oxidation and raises NO formation, most strongly at low pressure where thermal and NH/OH pathways are least inhibited. These results indicate that co-tuning pressure and equivalence ratio near rich operation enables low-NO_x ammonia combustion suitable for advanced gas turbine applications. Full article

In the context of promoting strategies to mitigate the global warming effect resulting from greenhouse gas emissions produced by human activities, ammonia stands out as an important player in the decarbonization of various sectors, including transportation, energy, and other industries. Ammonia is an effective carrier of hydrogen, having three times the volumetric energy density of hydrogen itself. In this study, the authors present findings obtained from a group of experiments and simulations conducted on a diesel engine operating at a constant speed and under different loads, using a dual-fuel method in which ammonia was injected into the intake manifold to partially replace the original diesel fuel. The results demonstrate that it is possible to reduce fuel consumption and CO₂ emissions. NO_x dropped by 40.8% and soot by 13.4% under heavy load, while under light load, they dropped by 50.5% and 23.3%, respectively. Full article

Two-dimensional carbide crystals (MXenes) are emerging as a promising platform for the development of novel gas sensors, offering advantages in energy efficiency and tunable analyte selectivity. One of the most effective strategies to enhance and tailor their functional performance involves forming hetero-structured composites with metal oxides. In this work, we explore a chemiresistive effect in double-metal MXene of Ti_0.2V_1.8C and its composites with 2 mol. % SnO₂ and Co₃O₄ nanocrystalline oxides toward feasibility tests with alcohol and ammonia vapor probes. The materials were characterized by simultaneous thermal analysis, X-ray diffraction analysis, Raman spectroscopy, and scanning/transmission electron microscopy. Gas-sensing experiments were carried out on composite layers deposited on multi-electrode substrates to be exposed to the test gases, 200–2000 ppm concentrations, at an operating temperature of 370 °C. The developed sensor array demonstrated clear analyte discrimination. The distinct sensor responses enabled a selective identification of vapors through linear discriminant analysis, demonstrating the further potential of MXene-based materials for integrated electronic nose applications. Full article

This study examines the high-temperature degradation of Hastelloy C276, a corrosion-resistant nickel-based alloy, during exposure to combustion products generated by methane and 99% cracked ammonia. Using a high-pressure optical combustor (HPOC) at 4 bar and exhaust temperatures of 815–860 °C, standard tensile specimens were exposed for five hours to fully developed post-flame exhaust gases, simulating real industrial turbine or burner conditions. The surfaces and subsurface regions of the samples were analysed using scanning electron microscopy (SEM; Zeiss Sigma HD FEG-SEM, Carl Zeiss, Oberkochen, Germany) and energy-dispersive X-ray spectroscopy (EDX; Oxford Instruments X-MaxN detectors, Oxford Instruments, Abingdon, United Kingdom), while mechanical properties were evaluated by tensile testing, and the gas-phase compositions were tracked in detail for each fuel blend. Results show that exposure to methane causes moderate oxidation and some grain boundary carburisation, with localised carbon enrichment detected by high-resolution EDX mapping. In contrast, 99% cracked ammonia resulted in much more aggressive selective oxidation, as evidenced by extensive surface roughening, significant chromium depletion, and higher oxygen incorporation, correlating with increased NO_x in the exhaust gas. Tensile testing reveals that methane exposure causes severe embrittlement (yield strength +41%, elongation −53%) through grain boundary carbide precipitation, while cracked ammonia exposure results in moderate degradation (yield strength +4%, elongation −24%) with fully preserved ultimate tensile strength (870 MPa), despite more aggressive surface oxidation. These counterintuitive findings demonstrate that grain boundary integrity is more critical than surface condition for mechanical reliability. These findings underscore the importance of evaluating material compatibility in low-carbon and hydrogen/ammonia-fuelled combustion systems and establish critical microstructural benchmarks for the anticipated mechanical testing in future work. Full article

Ammonia is considered as a promising hydrogen carrier and a carbon-free fuel. Methods for improving ammonia combustion characteristics often involve its co-firing with more reactive fuels (natural gas, biofuels, etc.). Among the natural gas components, ethane is second most abundant. Therefore, the development of detailed chemical–kinetic mechanisms that accurately consider the interactions between ammonia and each component of natural gas is very important. Such mechanisms must be based on experimental data obtained under a wide range of conditions. In this work, NH₃/C₂H₆/O₂/Ar blends were studied in JSR (φ = 0.5–2.0, p = 1 atm, τ = 1 s, T = 800–1300 K) and in a shock tube (p = 7.3–8.6 atm, T = 1260–1590 K). Additionally, the structure of premixed flames was investigated (φ = 0.8–1.2, p = 1–5 atm). Eleven recently published detailed chemical–kinetic mechanisms were tested. The model Shrestha-2025 was updated to achieve better agreement with the entire set of experimental data. The effect of p and φ on intermediate species concentration was analyzed. Ammonia and ethane consumption pathways were also examined. Full article

Although tannins generally inhibit the growth of lactic acid bacteria, different strains vary significantly in their tolerance to this inhibitory effect. However, it remains unclear whether the differences in tannin tolerance among various lactic acid bacteria (LAB) lead to variations in the fermentation outcomes during the silage process and in vitro fermentation. Therefore, this study investigated the correlation between the fermentation effects of LAB with varying tannin tolerances and the tannin content of sorghum. Four LAB strains (Lactococcus garvieae, LG; Lactococcus lactis, LL; Lactiplantibacillus plantarum, LP; Pediococcus pentosaceus, PP) were selected and identified from whole sorghum and mulberry leaves, and their tannin tolerance was assessed. The results demonstrated that LG exhibited the highest tolerance to sorghum tannins, followed by LL and LP, while PP displayed the lowest tolerance. Upon addition of LAB to whole sorghum for silage, LG showed the most effective ability to lower pH, reduce ammonia nitrogen content, decrease neutral detergent fiber content, diminish microbial diversity, and enhance the abundance of firmicutes. Concurrently, during in vitro fermentation, they significantly reduced rumen fluid pH and suppressed gas emissions (CH₄, CO₂). Conversely, PP performed poorly across all parameters. These findings suggest that the fermentation effects of LAB on sorghum silage are closely related to their tannin tolerance. Full article