Search Results (147)

This study investigates the effect of hydrogen injection pressure on combustion, energy, and emission characteristics of a spark-ignition engine under stoichiometric operating conditions. Experiments were performed on a four-cylinder Nissan HR16DE engine at 2500 rpm and 0.48 MPa brake mean effective pressure using gasoline and hydrogen-enriched blends containing 10%, 20%, and 30% hydrogen by mass. Hydrogen was injected into the intake manifold at pressures of 1.2, 1.4, 1.6, and 1.9 bar, while spark timing was adjusted to maintain peak in-cylinder pressure at 14–15 CAD after top dead center. Results showed that hydrogen mass fraction had a much stronger influence on engine performance than injection pressure. Increasing hydrogen content intensified combustion, shortened ignition delay, increased heat release rate and in-cylinder temperature, and reduced brake-specific fuel consumption by up to 36% compared with pure gasoline. Hydrogen enrichment also reduced HC and CO₂ emissions, but increased NO_x emissions. Effect of injection pressure was secondary and depended on hydrogen concentration. Under the investigated conditions, the lowest tested pressure, 1.2 bar, was generally the most favorable, especially at lower hydrogen fractions. Overall, hydrogen injection pressure acted mainly as a mixture formation control parameter, while hydrogen mass fraction remained the dominant factor determining engine behavior. Full article

Ammonia, as a carbonless carrier of energy, presents considerable potential for hydrogen storage and production, as well as for power generation, thanks to its high energy density and relatively easy transportability. However, the practical adoption of ammonia in combustion systems faces major stability challenges—chiefly its low reactivity, slow laminar burning velocity, narrow flammability envelope, and high ignition temperature. These attributes increase the risks of flame instability, misfire, and incomplete combustion, which, in turn, can elevate levels of unburned ammonia and greenhouse gas emissions such as NOx—posing significant health and climate concerns. Stable ammonia combustion demands optimization of several interrelated factors: the air–fuel equivalence ratio, flame temperature, flow regime, and combustor design are critical for maintaining reliable operation. Particularly pivotal is the control of the air–fuel equivalence ratio; excessively lean conditions can trigger flameout. Modern systems utilize real-time monitoring of flame and exhaust properties to diagnose and prevent instabilities. Advanced combustion strategies, such as transitioning to diffusion or flameless (MILD) regimes, substantially expand the stable operating window, especially under lean conditions. Overall, sustaining stable ammonia combustion is essential for maximizing efficiency and emission control, and integrating aftertreatment (deNOx) technologies is crucial for sustainable, clean-energy implementation. Full article

Tree rings record environmental conditions and can serve as long-term biomonitors of urban pollution. This study evaluated the radial growth and chemical composition of Pinus greggii wood in three urban green areas of Mexico City: San Juan de Aragón Park (SJA), Sierra de Guadalupe State Park (GUAD), and Vivero Coyoacán National Park (COY). Tree ring chemical elements were analyzed at annual resolution for the period 2002 to 2022, and their relationships with atmospheric pollutant concentrations, including nitrogen oxides (NO_x), carbon monoxide (CO), ozone (O₃), and particulate matter (PM), of medium size or smaller than 10 µm, including the fractions PM_2.5 and PM₁₀, were assessed using a spatial scaling approach. Elemental concentrations were determined using X-ray fluorescence (XRF). Statistical analyses included analysis of variance (ANOVA), Theil–Sen trend estimation, and Pearson correlation with lag analysis (up to 3 years). The oldest trees were recorded in COY (52 years), while the youngest were recorded in GUAD (13 years). Distinct temporal patterns in elemental concentrations were detected among sites; for instance, peak concentrations of Fe (307 ppm), Cu (11 ppm), and Zn (51 ppm) occurred in GUAD in 2021, while Pb concentrations declined during 2019–2020 across all three sites. Significant correlations (p < 0.05) were identified between Cu, Fe, Zn, and Pb and the atmospheric pollutants (NO_x, PM_2.5, PM₁₀, O₃). Notably, O₃ showed significant positive correlations with Fe at SJA (up to r = 0.80) and GUAD (up to r = 0.46) with lags ranging from 0 to 3 years, suggesting delayed responses between atmospheric pollution and elemental deposition in tree rings. These findings highlight the sensitivity of P. greggii to urban atmospheric pollution and support its potential as a long-term biomonitoring tool, as well as its importance for informing policies aimed at improving air quality and promoting the sustainable management of urban green spaces. Full article

Ammonium bisulfate (ABS) fouling in air preheaters has become a critical challenge restricting the safe and efficient operation of coal-fired units. Optimizing the flow field of the outlet of the upstream SCR system is a potentially effective path to mitigate ABS fouling. In this work, CFD simulations were conducted on the SCR De-NO_x system and its succeeding flue ducts connected to the air preheater. The simulation results of the original design show that a significant velocity deviation exists at the inlet of the air preheater (with the CV₁ up to 53.2%), with a portion of the flue gas adhering to the walls, which could induce ABS fouling in the low-temperature region. By adding flow guide plates into the flue duct, the flow uniformity before the air preheater was expected to be effectively improved. Notably, considering the deposition characteristics of ABS and the operating characteristics of the rotary air preheater, this study proposed a novel evaluation indicator, radial variance coefficient (CV₂), which focuses on the velocity uniformity based on the annular sector unit, to indicate the risk of ABS deposition. The influence on velocity uniformity of different flow guide plate layouts was analyzed. Based on the multiple evaluation metrics including pressure drop and flow uniformity, the optimal layout scheme was then selected. After optimization, the radial variance coefficient decreased from 30.7% to 11.7%, with the pressure drop slightly increased from 50 Pa to 80 Pa. This study could help to reduce unit failure frequency and support efficient operation of coal-fired power plants. Full article

Urban business-to-business distribution in Casablanca relies heavily on light commercial vehicles (LCVs) operating in a constrained street environment where loading/unloading access, intersection capacity, and recurring bottlenecks jointly shape performance and environmental impacts. However, high-resolution freight origin–destination (OD) observations and junction calibration data are limited, which complicates direct estimations of congestion and externalities attributable to commercial activity. This study develops a reproducible, large-scale modeling workflow that couples tour-based freight demand generation in order units with simulation-based traffic assignment (SBA) on a metropolitan network and translates network performance into emissions and monetary losses. Warehouses are modeled as primary producers and commercial activity zones as attractors via sector-tagged production and attraction functions; the resulting order distribution is converted to OD vehicle trips using the tour-based trip generation procedure with the mean targets-per-tour fixed to one to ensure numerical stability, yielding a direct-shipment approximation appropriate for stress–response analysis. Junction impedance is represented through turn-type volume–delay relationships and node-level impedance procedures, and congestion is evaluated using vehicle kilometers traveled/vehicle hours traveled (VKT/VHT)-based indicators, delay-intensity measures, and link/node bottleneck rankings. Across demand-scaling scenarios, VKT increases from 302,159 to 1,017,686 veh·km/day, while network delay rises nonlinearly from 392.5 to 2738.4 veh·h/day, indicating saturation-driven amplification of time losses. The Handbook of Emission Factors for Road Transport (HBEFA)-compatible emission estimates scale with activity: total carbon dioxide (CO₂) increases from 154.1 to 519.5 t/day, and nitrogen oxides (NOx) and particulate matter (PM_2.5) totals rise proportionally under fixed fleet assumptions. Monetizing delay with a purchasing-power-adjusted value-of-time range yields a congestion cost per trip that increases from approximately 0.20 to 0.41 Moroccan dirham, MAD/trip (at 60 MAD/veh·h), consistent with rising delay intensity. Bottleneck extraction shows welfare losses to be structurally concentrated on a small persistent corridor set, led by ‘Boulevard de la Résistance’, with recurrent hotspots including ‘Rue d’Arcachon’ and ‘Rue d’Ifni’. The framework supports policy-relevant reporting of congestion, emissions, and welfare impacts under data scarcity, with explicit sensitivity bounds. Full article

This study investigates the combustion and emission characteristics of a marine low-speed two-stroke engine using diesel-ignited ammonia dual direct injection. Using a validated 3D CFD model, the impact of ammonia blending ratios (R_a) was systematically explored. Results indicate that the strategy of shifting energy from early diesel injection to late ammonia injection physically repositions the combustion phasing. Rather than ammonia delaying the heat release, this late injection strategy avoids the overly early combustion observed at low ammonia concentrations, thereby lowering peak in-cylinder temperatures while maintaining robust work extraction. Consequently, indicated power at the N90 condition increases by 3.5% (to 1689 kW) over the diesel baseline, with a minimum EISFC of 165.5 g/kWh. High-ratio ammonia blending achieves deep decarbonization: at N90, peak CO and soot emissions are reduced by over 90% and 95%, respectively. Additionally, NO_x emissions decrease by approximately 70% at N90 compared to the N20 peak, attributed to the thermal DeNO_x mechanism. However, the low-temperature environment introduces trade-offs, leading to increased ammonia slip (4 ppm at N90) and elevated N₂O emissions (peaking at N70). These findings clarify the mechanisms governing ammonia combustion and provide theoretical support for optimizing zero-carbon marine propulsion systems. Full article

CO₂ corrosion remains a critical challenge for the safe and reliable operation of Carbon Capture, Utilization, and Storage (CCUS) infrastructure. This review summarizes CO₂ corrosion implications from material selection, exposure time, CO₂ phase behavior, flow conditions, and impurities such as H₂O, O₂, SO_x, NO_x, and H₂S. CO₂ corrosion modeling has, since early works by de Waard in 1975, expanded to a wide range of models and software tools, many of which have already been reviewed and compared. This work provides a historical timeline and a comparative summary of models and software tools to assist in selecting models for CCUS applications. Modeling approaches are classified into empirical, semi-empirical, and mechanistic categories, with their assumptions, strengths, and limitations. CO₂ corrosion modeling has persistent challenges relating to data quality, data quantity, and parameter interactions, which reduce model accuracy, especially for machine learning approaches. The provided perspective emphasizes that machine learning and hybrid modeling approaches for CO₂ corrosion prediction are gaining popularity, and their effectiveness is currently limited by the quality and quantity of available corrosion data. The provided opportunities include recommendations for standardized experimental procedures and hybrid modeling strategies that combine physics-based insights from mechanistic modeling approaches with data-driven machine learning approaches. Full article

Cracked ammonia is attracting attention as a carbon-free energy carrier, yet trace residual ammonia after reforming can significantly affect nitrogen oxide (NOx) emissions. This study quantifies how residual ammonia from 0 to 10,000 ppm affects NOx formation using one-dimensional premixed flame simulations under gas turbine-relevant conditions (ϕ = 0.5 and 2.0, 673 K, 20 atm). NO formation is evaluated using integrated rate of production (ROP) analysis, reaction pathway analysis, and A-factor sensitivity analysis (defined as sensitivity to the pre-exponential factor in the Arrhenius rate expression). Under lean conditions (ϕ = 0.5), NO increases approximately linearly with residual ammonia. Even at 100 ppm, the dominant NO formation route shifts rapidly from thermal and N₂O mechanisms to fuel NO chemistry led by HNO. In contrast, under rich conditions (ϕ = 2.0), the final NO level remains below 10 ppm. Under rich conditions, residual ammonia and the higher flame temperature raise gross NO production in the reaction zone, yet strong DeNOx reactions in the post-flame region consume most of it, resulting in low net NO emissions. These mechanistic results inform cracking targets and the design of staged combustion strategies to minimize NOx formation when deploying cracked ammonia in practical gas turbine systems. Full article

The increased presence of harmful algal blooms (HABs) is a concern for many aquatic environments, especially with the increasing effects of climate change. Members of the dinoflagellate genus Dinophysis have been shown to produce toxins that can cause Diarrheic Shellfish Poisoning (DSP) in humans who consume infected shellfish. The advancing oyster aquaculture industry in Delaware will require the development of management practices and monitoring HAB species to protect environmental and human health. Temperature, nutrients, and prey abundance can be drivers of Dinophysis blooms. D. acuminata has been historically identified at high concentrations (>200,000 cells L⁻¹) in water samples from Rehoboth Bay, DE, USA. However, the reach of spring blooms and how far they extend to aquaculture sites have not been determined. This study monitored an emergent HABs threat of a toxin-producing dinoflagellate, Dinophysis acuminata, by assessing a transect during the first recorded winter bloom in Torquay Canal and analyzing concentrations of chemical nutrients of combined nitrate and nitrite, and orthophosphate. Pearson correlation coefficient analysis between cell density (cells L⁻¹) and environmental variables across all sites was conducted to determine significant relationships between water temperature, Chl-a concentration, conductivity, dissolved oxygen (DO), combined nitrate and nitrite concentrations (NO_x), and orthophosphate concentrations (PO₄³⁻). Genetic techniques and PCR were utilized to determine the presence of Dinophysis using genus-specific primers to monitor cell density or abundance within the sediments during winter months. There were no significant correlations between environmental variables, and nutrient concentrations did not exceed EPA regulations. Molecular analyses of benthic sediments detected Dinophysis spp., offering insight into potential bloom origins. Overall, there is limited ecological data on Dinophysis acuminata in Rehoboth Bay, DE, USA. The results of this study will help strengthen resources for monitoring HAB species and understanding potential risks to oyster aquaculture in Delaware. Full article

Obesity is closely associated with the development of insulin resistance (IR) and type 2 diabetes mellitus (T2DM), primarily due to dysfunctional adipose tissue expansion and the secretion of pro-inflammatory cytokines such as interleukin-1β (IL-1β). 14-Deoxy-11,12-didehydroandrographolide (deAND), a major diterpenoid component of Andrographis paniculata, has demonstrated notable antioxidant and anti-inflammatory activities. This study aimed to investigate the protective effects and mechanisms of deAND against IL-1β-induced IR in 3T3-L1 adipocytes. Network pharmacology analysis indicated that deAND targets several IR-related signaling pathways, particularly the MAPK and IRS-1/AKT pathways. The experimental results show that IL-1β stimulated p67phox membrane translocation and reactive oxygen species (ROS) production, contributing to impaired insulin signaling by activating ERK and JNK and reducing IRS-1/AKT phosphorylation, which ultimately decreased insulin-stimulated glucose uptake. Pretreatment with deAND effectively inhibited NOX2-derived ROS generation, suppressed ERK/JNK activation, restored IRS-1/AKT phosphorylation, and reversed the reduction in glucose uptake caused by IL-1β. These findings suggest that deAND can alleviate IR by inhibiting NOX2-mediated oxidative stress, restoring insulin signaling and improving glucose uptake, highlighting its potential as a therapeutic agent for obesity-related IR. Full article

A system-level study of a NO_x abatement process by means of non-thermal plasma (NTP) generated with dielectric barrier discharges (DBDs) is the framework of this article. With the goal of system improvement, the kinetic reaction simulation software ZdPlaskin is considered to select the most favorable operating conditions in order to optimize NO_x abatement (deNO_x). A parametric exploration of the performance, through variations in operating conditions (temperature, power injection pattern, and input gas mixture composition), requires highly numerous simulations; thus, the shortest possible computation times with robust results are of significant interest. As such, an analysis and filtering method is proposed and detailed to build a minimized chemical kinetic reaction set, allowing us to reliably analyze the impact of the selected operating conditions for the DBD reactor on treatment performance. Full article

The pathways and mechanistic aspects of H₂-SCR over precious metal-based catalysts is still under debate. This study focusses on low loaded platinum-based catalysts (0.07–0.3%) in a large temperature range (50–500 °C), with special focus on (i) the role of NH₃ as a possible intermediate species, (ii) the origin of the undesired N₂O emission and (iii) the platinum sites involved in the H₂-SCR deNO_X reactions. Up to 60 °C, the N₂O selectivity was close to 100%, with no influence of the presence of oxygen in the 50–100 °C temperature range. Ammonia formation was observed at relatively low temperatures (from 60 °C), but its reactivity was then limited. All these low temperature reactions were associated with the same platinum sites, probably a mix of edge and face sites. The maximum outlet NH₃ was observed around 100 °C and the role of the NH₃-SCR in the whole H₂-SCR process appeared very limited. On the contrary, the ammonia oxidation by O₂, which started near 120 °C, significantly contributed to the H₂-SCR process and appeared responsible for the second N₂O emission peak (150–500 °C). This reaction did not imply the same platinum sites and appears mainly dependant on the platinum particle size. Full article

As landfill mining becomes more widely applied, growing attention is being paid to the waste-to-energy conversion of landfill waste. Co-disposal of landfill waste with municipal solid waste represents one of the primary strategies for achieving energy recovery of landfill waste. In this paper, the emission characteristics of pollutants were systematically analyzed during the co-disposal of landfill waste and municipal solid waste in a full-scale municipal solid waste incineration. The study investigated the formation patterns of toxic PCDD/Fs and gaseous pollutants under different co-disposal ratios of landfill waste (0%, 15%, 25%, 35%, and 45%). In total, 136 PCDD/Fs were analyzed to investigate the influence of co-disposal ratios on PCDD/F formation in both flue gas and fly ash. The influence of varying co-disposal ratios on the phase and elemental composition of fly ash was also investigated. Co-disposal led to a significant reduction in the toxic PCDD/F concentration at the boiler outlet, mainly attributed to the higher sulfur content of LW compared to MSW. With increasing co-disposal ratios, the annual emission amounts of toxic PCDD/Fs in fly ash significantly increased. The ∑PCDD/∑PCDF ratio in both flue gas of boiler outlet and fly ash also increased, indicating an enhancement of the precursor formation pathway, while the de novo synthesis pathway was relatively suppressed. The fly ash exhibited a high proportion of highly chlorinated dioxins (degree of chlorination: 7.19–7.23), likely due to their low saturated vapor pressure. According to the Hagenmaier congener distribution, high co-disposal ratios (25–45%) suppressed the chlorination of DD/DF in fly ash but promoted the formation of gas-phase PCDFs. Different co-disposal ratios significantly influenced both the emission concentrations and removal efficiencies of air pollutants, including NOx, SO₂, and HCl. Although co-disposal did not alter the crystalline phase composition of fly ash, it led to an increased content of heavy metals such as Cu, Hg, and Pb. Full article

This study investigates the impact of hydrogen supplementation on the performance, efficiency, and emissions of a spark-ignition internal combustion engine, with a specific focus on knock phenomena. A Nissan HR16DE engine was modified to operate in a dual-fuel mode using gasoline (E95) and high-purity hydrogen. Hydrogen was injected via secondary manifold injectors and managed through a reprogrammable MoTeC ECU, allowing precise control of ignition timing and fuel delivery. Experiments were conducted across various engine speeds and loads, with hydrogen mass fractions ranging from 0% to 30%. Results showed that increasing hydrogen content enhanced combustion intensity, thermal efficiency, and stability. Brake specific fuel consumption decreased by up to 43.4%, while brake thermal efficiency improved by 2–3%. CO, HC, and CO₂ emissions were significantly reduced. However, NO_x emissions increased with higher hydrogen concentrations due to elevated combustion temperatures. Knock tendency was effectively mitigated by retarding ignition timing, ensuring peak in-cylinder pressure occurred at 14–15° CAD aTDC. These findings demonstrate the potential of hydrogen supplementation to reduce fossil fuel use and greenhouse gas emissions in spark ignition engines, while highlighting the importance of precise combustion control to address challenges such as knock and NO_x formation. Full article

Platinum- and/or palladium-containing silica-based supports were applied for the selective catalytic reduction of NO_x with hydrogen (H₂-SCR-DeNO_x). To obtain enhanced activity and N₂ selectivity below 150 °C, we varied the type and loading of noble metals (Pt and Pd both individually and paired, 0.1–1.0 wt.-%), silica-containing supports (ZrO₂/SiO₂, ZrO₂/SiO₂/Al₂O₃, Al₂O₃/SiO₂/TiO₂), as well as the H₂ concentration in the feed (2000–4000 ppm). All of these contributed to enhancing N₂ selectivity during H₂-SCR-DeNO_x over the (0.5 wt.-%)Pt/Pd/ZrO₂/SiO₂ catalyst in the presence of 10 vol.-% of O₂. H₂ was completely consumed at 150 °C. A comparison of the catalytic results obtained during H₂-SCR-DeNO_x,(H₂-)NH₃-SCR-DeNO_x, as well as stop-flow H₂-SCR-DeNO_x and temperature-programmed studies, revealed that in the temperature range between 150 and 250 °C, the continuously coupled or overlaying mechanism of NO reduction by hydrogen and ammonia based on NH₃ formation at lower temperatures, which is temporarily stored at the acid sites of the support and desorbed in this temperature range, could be postulated. Full article