Nitrogen oxides formation mechanisms and control strategies in ammonia high-pressure direct injection combustion of marine low-speed engines

We studied a newly developed high-pressure injection flexible knife, to offer potential procedural simplification in colorectal Endoscopic Submucosal Dissection (ESD). Animal study: open randomized controlled study using an anesthetized porcine model, five ESD novices alternated between the flexible high-pressure injection Knife (HPK) and a Standard Knife (SK). Clinical study: a prospective cohort study conducted in an expert center analyzed colorectal ESD performed with HPK or SK, with propensity score matching. Animal study: 41 gastric and 59 colorectal ESDs were performed. No significant differences were observed between HPK and SK. Operator satisfaction was significantly better with HPK. Clinical study: 379 colorectal ESDs were performed including 70 with HPK. After propensity score matching based on predictors of technical difficulty, 69 lesions per group (HPK vs. SK) were compared. Histological R0 resection rate was significantly higher with HPK than with SK (n = 64 (95.52%) vs. n = 56 (82.35%) p = 0.026), as was the curative resection rate (n = 62 (93.94%) vs. n = 53 (77.94%), p = 0.012). No significant differences were noted regarding procedural speed or perforation rates. HPK improves trainee satisfaction during animal ESD and yields superior histological and curative resection rates in complex colorectal ESD cases when used by experts, without increasing risks.

Parameter analysis of the cold-leg LBLOCA initiating event of the SCW-SMR reactor concept

Microscopic characteristics and fractal Representation of limestone reservoirs in the Taiyuan Formation, Ordos Basin

Formation mechanisms and play fairway prediction of deep tight-sand reservoirs: A case study of the Yingcheng Formation in the Fulongquan fault depression, Songliao Basin

• Solketal showed reduced soot formation and a slightly longer ignition delay. • The hydroxyl group likely contributes to solketal’s greater oxidative activity. • Solketal enhances fuel oxidation under low injection energy conditions. • Biodiesel–solketal blends confirm solketal’s oxidation-promoting effects. • Diesel R33 showed the best behavior at 3 wt% solketal, revealing a non-linear effect. The global energy transition drives an enhanced emphasis on innovative fuel design approaches. Novel renewable fuel components are being sought that are drop-in compatible and exhibit synergistic interactions within fuel components. Isopropylidene glycerin (solketal) is a promising candidate, offering favorable chemical and physical properties due to its high molecular oxygen content. This study investigates the soot formation tendency and ignition behavior of solketal in a high pressure and high temperature injection chamber. Its combustion characteristics under varying injection parameters and chemical influences were evaluated in comparison with 1,3-dioxolane and a reference fossil diesel fuel. Additionally, the influence of solketal in a binary biodiesel-solketal system and in Diesel R33 was examined. Solketal exhibited a soot-reducing effect alongside an increased ignition delay. Comparison with 1,3-dioxolane suggests that the enhanced oxidative reactivity is attributable to the hydroxyl functionality. This interpretation is supported by low-temperature combustion indicators and observations in the biodiesel-solketal system. The Diesel R33 results showed that a concentration of 3 wt% solketal provides the most favorable performance characteristics. This demonstrates how targeted blending strategies can unlock beneficial combustion effects. Such insights open promising pathways for developing advanced, future-ready fuel formulations

With the rapid increase in the exploitation of oil and gas resources, conventional oil and gas resources in most oil and gas fields in China are being depleted at an accelerating pace, and research on the exploitation of unconventional oil and gas resources has become a crucial approach to safeguarding national energy security. China is endowed with abundant low-permeability reservoir resources with great application potential, yet their exploitation is fraught with considerable challenges. Water injection into the formation is a routine practice during the exploitation of low-permeability reservoirs to maintain formation pressure and improve oil recovery efficiency. However, most low-permeability oilfields currently suffer from problems such as high water injection pressure and a high proportion of insufficient injection, which prevent the establishment of effective displacement in oil-water wells and lead to a sharp drop in formation pressure, consequently driving up the exploitation costs of low-permeability reservoirs. The application of suitable formation drag reducers for oil production in the exploitation process of low-permeability reservoirs can significantly reduce water injection pressure and enhance oil recovery efficiency. This paper aims to summarize and sort out the action mechanisms of pressure reduction and injection enhancement, the types of drag reducers, and the current research status of pressure reduction and injection enhancement. Furthermore, it proposes the development directions of drag reducers in the field of pressure reduction and injection enhancement, providing a certain technical reference for improving the exploitation efficiency of low-permeability oilfields.

Shale oil in continental faulted basins of eastern China, represented by Jiyang Depression, has achieved breakthroughs in productivity. However, challenges such as deep burial, high formation pressure, and poor crude oil mobility pose significant obstacles to achieving high and stable production. Hydraulic fracturing is required to form complex fracture networks for stimulation. Factors such as the lamellar structure of shale, geomechanical conditions, and fracturing operation parameters affect fracture propagation. Therefore, this study establishes a numerical model of fracture propagation in lamina-developed shale using the discrete element software PFC2D 6.0, conducts simulation analysis of fracture propagation laws under in situ stress conditions, and characterizes the influence of lamellar structure and construction technology on fracture complexity. The results show that, for lamina-developed shale, the initiation pressure decreases with increasing injection rate; as the difference between the two horizontal principal stresses increases, hydraulic fractures gradually tend to propagate toward the direction of the maximum principal stress; under high injection pressure, a complex network of short fractures is formed, while, under low injection pressure, the length of the main fracture is prompted to increase. High density (9–10 strips/100 mm) enhances lamina penetration, favoring extension toward maximum horizontal principal stress; low density (4–5 strips/100 mm) strengthens lamina guidance, with fractures propagating along laminae near the injection hole. This research clarifies the mechanisms of fracture initiation and propagation in laminated shale, providing theoretical and technical support for optimizing hydraulic fracturing designs.

We studied experimentally and computationally the structures and optical properties of sulfur (S), selenium (Se) and tellurium (Te) ring clusters. We encapsulated S, Se and Te into AFI, MOR, CHA and LTA zeolites via vapor adsorption or high-pressure injection from melt and studied Raman and optical absorption spectra (RS and OAS, respectively) of zeolite single crystals with incorporated S, Se and Te ring clusters. Importantly, strict orientation of the rings in zeolite crystals allowed us to study the polarization/orientation dependency of ring RS and OAS. The obtained experimental spectra are found to be in agreement with density functional theory results (DFT using the PBE0 functional and def2-TZVP basis sets) for S8, Se6, Se8, Se12, Te6 and Te8 ring molecules. The agreement is especially good for Te rings, while for S and Se rings harmonic frequency scaling factors are required. The S and Se rings display light-induced effects, which we attribute to the presence of conical intersections between their ground and excited electronic states, resulting in isomerization and subsequent fragmentation. We consider this effect using the Se6 ring example. This phenomenon is important for understanding photostructural changes not only in chalcogen clusters but also in bulk materials such as amorphous selenium.

This study aims to clarify the characteristics and genetic mechanisms of low-permeability to tight sandstone reservoirs. We carry out the research by integrating multiple data sources: core observation, cast thin sections, X-ray diffraction (XRD), scanning electron microscopy (SEM), high-pressure mercury injection (HPMI), and well logging data, focusing on the Paleogene Huagang Formation (E 3 h) of Structure Y, Xihu Sag. Results show that the E 3 h was deposited in a sandy braided river delta-lacustrine system, including subaqueous distributary channels, interdistributary bays, and shallow lake microfacies. Five major lithofacies are identified, with the massive medium sandstone lithofacies (MMLF) and massive fine sandstone lithofacies (MFLF) exhibiting the best physical properties (porosity 6%–15%, permeability 0.1–13.5 mD). The sandstones are mainly feldspathic lithic quartz sandstones, with interstitial materials dominated by clay minerals (avg. 4.34%) and matrix (avg. 3.68%), showing overall low porosity (5%–15%) and low permeability (avg. < 1.2 mD). Pore types are primarily residual intergranular and dissolution pores, with pore structure significantly controlled by lithofacies. Compaction is the main cause of porosity loss (avg. reduction rate 78%), while secondary pores formed by late organic acid dissolution (avg. dissolution pore surface porosity 1.6%) effectively improve reservoir quality, and abundant carbonate cementation (avg. 2.53%) leads to tightness. The reservoirs are in the late middle diagenetic stage A to B, having undergone an evolution from weak acidic leaching to acidic dissolution and finally to acid-alkaline transition cementation. Four diagenetic evolution types are classified, and reservoir quality is dually controlled by depositional environment (grain size, compositional maturity) and diagenesis (compaction, dissolution, cementation). The classification criteria, evolution mechanism, and proposed development adaptation scheme provide technical support for optimal well placement, reservoir reconstruction, and efficient exploitation of deep hydrocarbon resources in the Xihu Sag and similar offshore basins.

High-pressure hydrogen direct injection (DI) technology demonstrates significant potential for high thermal efficiency and ultralow emissions in engines. The hydrogen gas jet at an elevated nozzle pressure ratio (NPR) exhibits turbulent underexpanded jet behavior, manifesting shock wave formations and sequential shock cell structures in the near-nozzle zone. This work investigated transient shock cell evolution and Mach disk parameters during high-pressure hydrogen injection through a single-hole cylindrical injector. The injector inner pressure building-up process was tested, and a three-dimensional large-eddy simulation (LES) model was used to investigate the underexpanded jet. The results show that the inner pressure declines from the hydrogen tank to the injector, undergoing a pressure-building transient process, causing a delay in achieving stabilization. Moreover, shock cell development exhibits distinct transient characteristics. The Mach disk dimension parameters, i.e., cell core length L c, Mach disk width W disk, and Mach disk height H disk, demonstrate phased evolution: an initial growth phase followed by asymptotic stabilization. The turning points of L c, W disk, and H disk depend on the inner pressure-building process. Notably, the constant coefficient C H for H disk estimation requires empirical correction due to transient shock cell behavior. For NPR ≥ 90 of a single-hole injector, our data recommend C H = 0.85-0.9. The shock waves of the underexpanded gas flow induce a lower entrainment ratio within the near-nozzle region (Z/D < 8), resulting in minimal entrainment. Furthermore, this dynamic delay phenomenon becomes particularly pronounced when injection cycles are shorter. It is necessary to consider the dynamic hydrogen jet characteristic for better design and optimization.

Integrating THMCD coupling for CH4 production and CO2 storage in CO2-ECBM: A multiphysics modeling framework

To clarify the development characteristics and controlling factors of nanomicron pores in lacustrine shale, this study examines the Cretaceous Xiagou Formation shale reservoir in the Qingxi Sag of the Jiuxi Basin. The rock composition, pore types, and pore structure of continental shale were analyzed using whole-rock X-ray diffraction, laser confocal microscopy, nitrogen adsorption, nuclear magnetic resonance, and high-pressure mercury injection. The different pore reservoir properties were compared, and the factors influencing reservoir development were investigated. The findings indicate that the Xiagou Formation shale comprises a mixture of carbonate and terrigenous clasts, with the carbonate primarily consisting of micritic microcrystalline dolomite. The shale contains various pore types, including nanometer-scale intercrystalline pores, organic matter pores, clay mineral pores, micrometre-scale brittle mineral intergranular pores, millimeter-scale brittle mineral intergranular dissolution pores, and fractures. Organic matter pores exhibit a dispersed distribution and significant heterogeneity. Based on pore size distribution, continental shale pores are classified into three types: (1) isolated nanopores, (2) relatively concentrated nanopores, and (3) nanomicron multiscale composite pores, with the third type exhibiting the most favorable reservoir properties. The study concludes that high-quality reservoir pores in continental shale are primarily influenced by dolomitization and the dissolution of brittle mineral pores by organic acids.

Exploration of enabling ammonia rapid ignition and self-sustaining combustion with minimal pilot diesel in high-pressure direct injection ammonia/diesel dual-fuel mode

To assess the steam generator tube rupture (SGTR) accident scenario under compromised safety systems (e.g. post-earthquake conditions), as specified in the Organisation for Economic Co-operation and Development/Nuclear Energy Agency Committee on the Safety of Nuclear Installations’s International Standard Problem No. 52 project, a full-scale facility model was developed using the RELAP5 thermal-hydraulic code for numerical simulation. The computational results were systematically validated against experimental data obtained from the PKL (Primary Coolant Loop) Test Facility. The analysis demonstrated that RELAP5 accurately reproduces the primary progression of the SGTR accident, with the simulated accident sequence and key thermal-hydraulic parameters exhibiting strong agreement with empirical observations. During the early phase of the transient process, depressurization of the primary circuit facilitates secondary-side coolant ingress into the reactor core, thereby maintaining adequate core cooling throughout the initial and intermediate stages. Subsequent depletion of the steam generator inventory results in partial core uncovery, precipitating a rapid escalation in the core exit temperature. However, the coordinated actuation of the high-pressure safety injection system, accumulator, and low-pressure safety injection system effectively preserves core integrity, ultimately enabling a transition to a long-term cooling phase. These findings confirm that adherence to appropriate operational protocols can ensure reactor safety even under degraded safety system conditions.

This study evaluates the effectiveness of microfine cement (MF) to seal two laboratory-fabricated wellbore microannuli. The samples were characterized with their hydraulic apertures (158 and 85 µm). A rough cement surface paired with a transparent acrylic plate, acting as a steel surrogate, formed the basis of the experimental setup, with the acrylic enabling direct visual monitoring of MF behavior throughout the tests. Hydraulic aperture measurements were taken before and after each repair attempt, with MF injected at constant pressure and a 24 h curing period allowed between successive injections. Four injection cycles were completed per sample. The MF cement had a d95 = ~14 µm and a w/c of 1.45. Results show progressive reduction in hydraulic aperture from 158 µm to 20 µm and from 85 µm to 8 µm, but complete sealing was not achieved. Visual observations revealed that bleeding and filtration (plug formation) were the primary mechanisms limiting repair efficiency. These findings highlight the challenges of sealing rough microannuli with MF and suggest that aperture variability and particle filtration strongly influence repair outcomes. Higher injection pressures or alternative materials may be required for complete sealing.

Ammonia has emerged as a potential zero-carbon marine fuel owing to its compatibility with existing liquefied petroleum gas infrastructure and its potential role as a hydrogen carrier. Nevertheless, its practical application is challenged by low combustion speed, incomplete combustion, and nitrogen oxide (NO x ) emissions. This study investigated the combustion performance and emission characteristics of ammonia in a 12.5 l single-cylinder marine dual-fuel engine. The experimental configuration employed high-pressure ammonia injection and diesel micro-pilot (MP) ignition to overcome ammonia’s high self-ignition temperature and low energy density. By systematically varying ammonia and MP injection pressures and timings, the effects on thermal efficiency, combustion stability, and exhaust emissions were evaluated. The results demonstrated that higher ammonia injection pressures improved both efficiency and combustion stability, while optimized MP injection pressure enhanced diesel atomization and facilitated reliable ammonia ignition.

In the field of oil reservoir engineering, the development of large-dip-angle reservoirs poses significant challenges due to their strong heterogeneity, pronounced gravity effects, and inefficient water flooding sweep, all contributing to suboptimal oil recovery rates. This study aims to address these challenges by focusing on the core issue of optimizing water injection development strategies for such reservoirs. A numerical simulation mechanism model is constructed based on actual large-dip-angle reservoir A, and the impact of key parameters—including reservoir dip angle, permeability, injection–production well spacing, water injection intensity, and crude oil viscosity—on oil recovery is systematically analyzed under the “water injection at structural lows and oil production at structural highs” high-pressure water injection development mode. The simulation results reveal that the oil recovery rate increases with higher dip angles, permeability, injection–production well spacing, and water injection intensity; however, excessive water injection intensity or crude oil viscosity can lead to premature water breakthrough, reducing efficiency. Using the analytic hierarchy process, the primary controlling factors are ranked as permeability &gt; crude oil viscosity &gt; reservoir dip angle &gt; water injection intensity &gt; injection–production well spacing. Furthermore, development theory charts are established to guide the selection of appropriate water injection intensities for different injection–production well distances and permeabilities. This study offers valuable theoretical insights for optimizing water injection development in large-dip-angle reservoirs, thereby enhancing oil recovery and economic benefits and laying a foundation for future research and practical applications in similar reservoir settings.

To address the application limitations of traditional weakening techniques under complex geological conditions such as hard coal mine roofs, directional hydraulic fracturing (DHF) technology has become a key technical measure to ensure safety production by virtue of its core advantages of directional rock breaking. This paper systematically reviews the research status and development trends of underground DHF technology in underground coal mines, focusing on an analysis of the three key dimensions: directional fracturing methods, processes, and equipment. Regarding fracturing methods, three mainstream technologies based on manual slotting, linear arrangement drilling, and high-pressure water jet slotting have been sorted out. The paper compares their principles, advantages, and applicable scenarios, pointing out that a linear synergistic fracturing method using multiple fracturing holes with high-pressure water jet slotting demonstrates both precision and scalability, making it the most promising technological path at present. For fracturing processes, it elaborates on the standardized progress of the four core procedures: drilling construction, pre-treatment, high-pressure water injection, and effect verification, and analyzes the key bottlenecks in process optimization under complex geological conditions. In terms of fracturing equipment, technical characteristics and existing issues of drilling, slotting, high-pressure water injection, and monitoring devices are summarized. Aligning the development trends of mining engineering technology, the paper proposes that future directional hydraulic technology will evolve towards intelligent directional fracturing, multi-field coupled fracturing, and miniaturized precision fracturing. At the process level, it will develop towards integrated efficiency, adaptive dynamics, and green low-carbonization, while equipment will focus on breakthroughs in intelligent automation, high efficiency and reliability, and miniaturization and integration. These research results provide a reference for theoretical study, equipment development, and engineering applications of underground DHF technology, contributing to safe, efficient, and sustainable coal mining practices.

The efficiency and safety of CO2 geological sequestration together with CO2-enhanced coalbed methane recovery (CO2-ECBM) depend on the dynamic evolution of coal–water–gas interfacial wettability under the influence of reservoir pressure, temperature, and the formation water chemistry. The wettability has a direct impact on the migration ability of CO2 into coal seams and the stability of the adsorption-sequestration and desorption efficiency of coalbed methane. Research has often overlooked the effect of in situ formation water on wettability, which may hinder accurate prediction of multiphase flow mechanisms in realistic environments. This study simulates in situ interactions among the CO2 formation water and coal for 25 days. Thus, it shows the wettability evolution in four stages. These stages are initial hydrophobicity, rapidly wetting, slowly wetting, and dynamic equilibrium. The formation water is acidic and multi-ionic in nature. This affects wettability through many mechanisms. These include mineral dissolution and precipitation, catalytic oxidation, and pore surface feedback. The impact of these mechanisms is greater than in low-salinity system. Moreover, this can bring about faster equilibration (20 days). The cause of equilibrium is the precipitation of secondary minerals (Fe(OH)3, amorphous SiO2, CaSO4), which self-limit reactions and smooth surface irregularities. The findings were used to propose a pressure regime in phases. These include low-pressure injection 0–5 days, medium- to high-pressure injection 5–10 days, gradual pressure reduction 10–20 days, and injection switch-off after 20 days for safe storage of CO2 in the long term. Overall, this study reveals the evolutionary pathway of coal wettability under reservoir conditions. Furthermore, it links the stage transitions to multiple mineral reactions, organic modifications, and pore-structure feedback. The kinetics derived present a basis for stage-wise pressure control concepts in CO2 storage and the CO2-ECBM process, which is experimentally anchored.