Search Results (26)

Currently, there is limited experimental research on the stability of journal bearing-rotor systems under base motion, and the influence of rocking motion on the stability of such systems remains unclear. This study develops an experimental test rig for a journal bearing-rotor system and employs a six-degrees-of-freedom shaking table to apply complex alternating loads, with the aim of investigating the effects of rocking amplitude and frequency on the vibration characteristics of the shaft system. The experimental results show that, under the excitation of base roll and pitch motions, the critical speed of the sliding bearing-rotor system remains nearly unchanged, while the resonance amplitude increases significantly, and the instability speed occurs earlier. In addition, base rocking motion not only induces periodic and uniform changes in the vibration amplitude of the shaft system but also demonstrates a strong positive correlation between the amplitude of system vibration and the amplitude of base rocking. Full article

Low-cycle fatigue damage accumulation exhibits inherent nonlinear characteristics, particularly under variable-amplitude loading conditions, where loading sequence exerts significant influence on damage evolution. This investigation conducted strain-controlled variable loading fatigue tests on nickel-based superalloy specimens at 650 °C. Comparative microstructural analysis through scanning electron microscopy revealed distinct fracture features between variable-amplitude and constant-amplitude loaded specimens. A novel fatigue damage accumulation model was developed through three critical advancements: mathematical formulation of strain amplitude as an exponential function based on the damage equivalence principle, explicit integration of loading sequence effects, and systematic calibration using experimental data. Comparative analysis with existing fatigue damage models revealed that the proposed methodology demonstrates notable advantages in both prediction accuracy and implementation simplicity. Full article

Differences in exposures and resources to manage personal health contribute to persistent inequities in air pollution burden despite vast air quality improvements over the past 2–3 decades in the United States. These factors are, partly, linked to historic racist practices, such as redlining, a discriminatory housing policy that was practiced legally between 1935 and 1968. Using 100 m × 100 m resolution land-use regression predicted surfaces of PM_2.5 constituents (black carbon, nickel, vanadium, and copper) as pollution source indicators, we fit Bayesian generalized linear mixed-effects models to examine differences in source exposures over two study periods, 2008–2015 and 2016–2019, comparing (1) redlined to not redlined and (2) high-asthma to low-asthma neighborhoods. We examine redlining as an indicator of historical, and structural racism and asthma rates as an indicator of present-day community burden. Redlined areas saw near elimination of disparities in exposure to residual oil boilers and marine residual oil but persistent disparities in traffic. High-asthma neighborhoods continue to have disproportionately high exposures to both residual oil boilers and traffic, with no discernable disparities related to marine residual oil emissions. Overall exposure disparities are small, with PM_2.5 disparities by both asthma morbidity and redlining amounting to less than 1 µg/m³ and NO₂ disparities by asthma and redlining amounting to less than 2 ppb in the post-2016 period. For context, 2019 NYC average PM_2.5 and NO₂ were 8.5 µg/m³ and 20 ppb, respectively. Our findings suggest that local pollution policy should focus on reducing traffic and building boiler emissions in high-asthma neighborhoods to reduce exacerbations. Full article

European Union (EU) energy markets are changing rapidly. After the recent turmoil, a new wave of EU legislation is once again reshaping the way energy should be used in the EU, emphasizing not only the increasing importance of using renewable and local energy sources but also highlighting the importance of energy efficiency and decarbonization of high to abate sectors (including aviation and marine fuels). Heating and cooling account for about half of the total gross final energy consumption in the EU. This article explores the novel concept of using waste heat from the flexible Fischer–Tropsch (FT) process (FLEXCHX) in the existing district heating network, resulting in tri-generation: FT C5+ liquids, heat, and electricity. FLEXCHX provides operation flexibility and combines advanced biomass gasification, catalytic liquefaction, electrolysis, and waste heat recovery, allowing use of biomass residues in a more sustainable way. Our results, based on the Kaunas district heating (DH) system, show that this process could be integrated into the existing district heating network in Northern Europe and successfully compete with existing heat-only boilers and CHPs using biomass or municipal waste, resulting in more efficient use of biomass and savings accumulated up to EUR 200 million over the study period in the analysis (2020–2050), supplying up to 30% of the heat in the Kaunas DH system. Enriching the FT process with hydrogen (using electrolysis) could result in additional FLEXCHX utilization benefits by creating demand for cheap excess electricity that might otherwise be curtailed. Full article

The control system of oil-fired boiler units on ships plays a crucial role in reducing the emissions of atmospheric pollutants such as nitrogen oxides $\left({\mathrm{N}\mathrm{O}}_{\mathrm{x}}\right),$ sulfur dioxides $\left({\mathrm{S}\mathrm{O}}_2\right)$, and carbon dioxide $\left({\mathrm{C}\mathrm{O}}_2\right)$. Traditional control methods using conventional measurement sensors face limitations in real-time control due to response delays, which has led to the growing interest in combustion control methods using flame images. To ensure the precision of such combustion control systems, the system model must be thoroughly considered during controller design. However, finding the optimal tuning point is challenging due to the changes in the system model and nonlinearity caused by environmental variations. This study proposes a controller that integrates an internal model control (IMC)-based PID controller with the deep deterministic policy gradient (DDPG) algorithm of deep reinforcement learning to enhance the adaptability of image-based combustion control systems to environmental changes. The proposed controller adjusts the PID parameter values in real-time through the learning of the determination constant lambda ($\lambda$) of the IMC internal model. This approach reduces computational resources by shrinking the learning dimensions of the DDPG agent and limits transient responses through constrained learning of control parameters. Experimental results show that the proposed controller exhibited rapid adaptive performance in the learning process for the target oxygen concentration, achieving a reward value of −0.05 within just 105 episodes. Furthermore, when compared to traditional PID tuning methods, the proposed controller demonstrated superior performance, achieving a target value error of 0.0032 and a low overshoot range of 0.0498 to 0.0631, providing the fastest response speed and minimal oscillation. Additionally, experiments conducted on an actual operating ship verified the practical feasibility of this system, highlighting its potential for real-time control and pollutant reduction in marine applications. Full article

This study proposes and validates a novel combustion control system for oil-fired boilers aimed at reducing air pollutant emissions through flame image prediction. The proposed system is easily applicable to existing ships. Traditional proportional combustion control systems supply fuel and air at fixed ratios according to the set steam load, without considering the emission of air pollutants. To address this, a stable and immediate control system is proposed, which adjusts the air supply to modify the combustion state. The combustion control system utilizes oxygen concentration predictions from flame images via SEF+SVM as control inputs and applies internal model control (IMC)-based proportional-integral (PI) control for real-time combustion control. Due to the complexity of modeling the image-based system, IMC filter constant tuning through experimentation is essential for achieving effective control performance. Experimental results showed that optimal control performance was achieved when the filter constant $\lambda$ was set to 1.5. In this scenario, the peak overshoot $M_p$ was reduced to 0.19245, and the Integral of Squared Error (ISE) was minimized to 10.1159, ensuring a stable response with minimal oscillation and maintaining a fast response speed. The results demonstrate the potential of the proposed system to improve combustion efficiency and reduce emissions of air pollutants. This study provides a feasible and effective solution for enhancing the environmental performance of marine oil-fired boilers. Given its ease of application to existing ships, it is expected to contribute to sustainable air pollution reduction across the maritime environment. Full article

This study focuses on optimizing the thermal pyrolysis process to maximize pyrolysis oil yield using marine biomass or seaweed. The process, conducted in a batch reactor, was optimized using response surface methodology and Box–Behnken design. Variables like temperature, residence time, and stirring speed were adjusted to maximize bio-oil yield. The optimal conditions yielded 42.94% bio-oil at 463.13 °C, with a residence time of 65.75 min and stirring speed of 9.74 rpm. The analysis showed that temperature is the most critical factor for maximizing yield. The bio-oil produced contains 11 functional groups, primarily phenol, aromatics, and alcohol. Its high viscosity and water content make it unsuitable for engines but suitable for other applications like boilers and chemical additives. It is recommended to explore the potential of refining the bio-oil to reduce its viscosity and water content, making it more suitable for broader applications, including in engine fuels. Further research could also investigate the environmental impact and economic feasibility of scaling up this process. Full article

The coal found in the Zhundong Coalfield is highly suitable for power generation and gasification. However, the high sodium content within the coal leads to severe boiler slagging and contamination. Additionally, sodium disperses into the gaseous phase to form haze, adversely affecting the local atmospheric environment. This study delved into the distribution and occurrence characteristics and enrichment causes of sodium in the coal, employing sequential extraction experiments and testing methods such as XRF, ICP-OES and SEM-EDS. The findings of this research indicate the following: (1) With the increasing burial depth of coal seams, there is a noticeable decrease in the sodium content within the coal. Sodium is primarily distributed within the coal seam, with higher concentrations observed in the upper portions of the same coal seam. Furthermore, the distribution of sodium within the epipedon, overlying rocks and coal seam also exhibits a decreasing trend. (2) Sodium primarily exists in a water-soluble state within coal seams, with H₂O-Na accounting for over 70% of its composition. The ion-exchangeable sodium is higher than that in the roof, floor and gangue. Sodium exists in coal seams in both ionic and hydrated ionic forms. It is worth noting that the minerals within coal are not the primary carriers of sodium. (3) These coal seams were formed in a warm and humid shallow lake peat swamp environment, which is not significantly influenced by terrestrial or marine sources. The enrichment of sodium is primarily influenced by later hydrodynamic conditions. Full article

Pitch motion is the key factor affecting the performance characteristics of centrifugal pumps on board ships and exacerbates hydraulic excitation to induce the unsteady vibration of pump units. A hydraulic test platform with swing motion is established to explore the effects of pitch motion on a pump’s performance characteristics. An obvious hump zone exists in the head characteristic curve in the low-flow-rate condition due to the pitch motion. The pump head in the shut-off condition has a significant decrease due to the pitch motion, compared to the static state. The head decrease gradually increases as the maximum pitch angle increases or the pitch period shortens. Specifically, the head in the rated flow condition decreases by 6.3 % to reach a minimum at the maximum pitch angle of 20 degrees in a period of 5 s. Based on a multiple-reference coordinate system, a large eddy simulation with a shear-modified eddy viscosity model is employed to simulate inner flow characteristics under the influence of pitch motion. A distinct vortex flow appears near the blade suction surface and becomes increasingly turbulent as the pitch period shortens. The pitch motion intensifies the unsteady stretching and deformation of vortices. The periodic variations in fluid-induced pressure over time present parabolic features, and the amplitude in the frequency domain reaches its maximum value within a pitch period of 5 s. Full article

Numerical analysis and experimental studies were conducted to evaluate the performance of a selective catalytic reduction (SCR) system according to the load of a 1.5-ton marine boiler. There are post-treatment methods for reducing the exhaust gas emitted from ships, such as low-sulfur oil, scrubber, a desulfurization device to remove sulfur oxides (SOx) and particulate matter, an exhaust gas recirculation system, and SCR agents to reduce nitrogen oxides (NOx). Furthermore, there are methods of using eco-friendly natural gas fuels, such as liquefied natural gas (LNG), methanol, liquefied petroleum gas, and ammonia. In the case of LNG, SOx and particulate matter are hardly emitted, and only a small amount of NOx is emitted compared to an internal combustion engine. Therefore, SCR system technology that can remove NOx needs to be applied. As a result of this study, the boiler load increased, and the flow velocity through the outlet decreased. In addition, the NOx emissions of diesel fuel and LNG fuel were reduced by 100% to 0 ppm when the boiler load ratio was 50%. When the load ratio was 75%, the NOx emissions of diesel fuel were reduced by 77.4% to 40 ppm, and those of LNG fuel were reduced by 64.1% to 24 ppm. When the load ratio was 100%, the NOx emissions of diesel fuel were reduced by 66.1% to 60 ppm, and those of LNG fuel were reduced by 47.8% to 24 ppm. In addition, the results of the numerical analysis according to boiler load were almost identical to the experimental results. Finally, this study could design an optimal SCR system through numerical analysis, according to the important parameters of the SCR system. Full article

A small combustion chamber was developed and manufactured for empirical combustion testing of several alternative fuels developed to meet IMO emission limits for fuel oil used in ships. The combustion chamber consists of four independent tanks and a circulation system with a two-stage heating function owing to the high viscosity and temperature of ship fuel. A gun-type burner is mounted on the side of the combustion chamber, which possesses a cylindrical shape and a capacity of less than 300 L. This device was manufactured in accordance with several variables such that the basic stage performance and simulation tests of each fuel could be sufficiently completed before performing the combustion test to simulate the engines of large ships. To conduct an initial experiment using the developed combustion chamber, low-sulfur MGO with a sulfur content less than or equal to 0.05% was chosen, and ideal operating parameters were selected according to the measurement tests based on load control. The exhaust gas temperature differed by approximately 10.7% as a result of burning MGO at a burner load state of 80–100%. The use of a normal oxygen concentration of 4% helped remove approximately 14.31 ppm of nitrogen oxide and 1.91% of carbon dioxide. The maximum combustion efficiency was 70.17%, indicating the chamber’s potential for use in a variety of combustion tests of alternative fuels for ships in the forthcoming years. Full article

In marine gas turbines, variations in rotational speed occur all the time. To ensure adequate cooling effects on the turbine blades, the valves need to be adjusted to change the pressure upstream of the pre-swirl nozzle. Changing such pressure will have significant effects on the local or overall parameters, such as core swirl ratio, temperature, flow rate coefficient, moment coefficient, axial thrust coefficient, etc. In this paper, we studied the flow characteristics within the pre-swirl system of a marine gas turbine at low rotational speed by varying the pressure at the pre-swirl nozzle. The corresponding global Reynolds number ranged from Re = 2.3793 × 10⁵ to 9.5172 × 10⁵. The flow in the rotor-stator cavities was analyzed to find the effects of nozzle pressure on the radial velocity, core swirl ratio, and pressure. According to the simulation results, we introduced a new leakage flow term into the formulary in the references to calculate the values of K between the inner seal and the pre-swirl nozzle. The matching characteristics between the pre-swirl nozzle and the inclined receiving hole was predicted. Performance of the pre-swirl system was also analyzed, such as the pressure drop, through-flow capacity, and cooling effects. After that, the moment coefficient and the axial thrust coefficient were predicted. This study provides some reference for designers to better design the pre-swirl system. Full article

Due to the relatively cheap price of diesel, most Marine engines use diesel as Marine fuel, but its emissions contain a lot of carbon. To reduce carbon emissions, International Maritime Organization (IMO) has established an Energy Efficiency Design Index (EEDI) and Energy Efficiency Existing-Ship Index (EEXI). Currently, a popular way is to reduce EEDI by optimizing the heat transfer performance of exhaust gas boilers on new ships, but there is little research on the EEXI index of existing ships. For operating ships, the thermal conductivity of exhaust gas boiler materials and other parameters has been fixed, so the main factors affecting the heat transfer coefficient of the exhaust gas boiler are exhaust gas temperature and flow velocity. Therefore, this paper studies the influence of engine exhaust temperature and flow rate on boiler heat transfer coefficients and optimizes it to achieve the EEXI value required by IMO. Firstly, based on the conservation of mass and energy as the basic equation, a heat exchange model of the exhaust gas boiler is established by using the hybrid modeling method and lumped parameter method. Secondly, for the given boiler, since other parameters are basically unchanged, the input temperature and flow rate of the model are changed by the control variable method, and the temperature of the boiler outlet is simulated by the test algorithm. Through the simulation operation of an Aalborg OC-type boiler, the results show that when the exhaust gas flow velocity is 15 m/s, 17.2 m/s, 22.4 m/s and 25 m/s, respectively, the heat transfer coefficient at each flow velocity increases first and then slowly decreases with the increase of temperature, and there is an optimal temperature at each velocity, which is 230 °C, 227 °C, 225 °C and 224 °C, respectively. The innovation of this study lies in the research on the inlet temperature and flow rate of the exhaust gas boiler of the operating ship based on the EEXI, and the relevant results are obtained, which provides theoretical guidance for the operation management of the exhaust gas boiler of the operating ship. Full article

As a result of technological advancements in the 21st century, steam-driven ships, with an efficiency of between 36 and 38%, have been replaced by diesel-driven ships, with an efficiency of up to 55%. Accordingly, the manufacturers of the main boilers and steam turbines in ships have fought for their products to remain on the market by modernizing their construction in order to increase their competitiveness in relation to diesel drives. Based on a review of data in the literature, this article presents an analysis of the increased efficiency of ship boilers with the use of waste heat from boiler exhaust gas. This paper considers the utility of using this heat to heat up the water that supplies the boilers as well as the use of the heated air in the combustion process. The analysis takes into account the different types of heat exchangers used for these purposes and the different efficiencies of boilers made by the leading boiler manufacturers. The formulae and calculation methodologies used are applied in the following analysis of the impact of using waste heat to increase boiler efficiency. Full article

The application of water-fuel emulsion (WFE) in internal combustion engines enables to reduce the consumption of sulfurous fuel oils, thereby protecting the environment from emissions of sulfur and nitrogen oxides, as well revealing a great potential for the heat utilization of exhaust gases. The efficiency of utilization of exhaust gas heat in exhaust boilers (EGB) depends on their temperature at the outlet of EGB, id est. the depth of heat utilization. Exhaust gas temperature is limited by the rate of low-temperature corrosion (LTC), which reaches a level of 1.2 mm/year at the wall temperature of about 110 °C for the condensing heat exchange surfaces (HES) and reduces the reliability of the HES operation. Therefore, decreasing the corrosion rate of condensing HES at wall temperature below 110 °C to an acceptable level (about 0.2 mm/year) when undergoing WFE combustion will make it possible to reduce the exhaust gas temperature and, consequently, increase the efficiency of EGB and fuel saving during the operation of the ship power plant. The aim of the research is to assess improvements to the reliability, durability and efficient operation of condensing HES in marine EGB undergoing WFE combustion in a diesel engine based on experimental studies of the LTC process. A special experimental setup was developed for investigation. The use of WFE with a decreased wall temperature of HES below 80 to 70 °C would improve the reliability of the EGB along the accepted service life, increase the lifetime of the HES metal by almost six times as well as the overhaul period, and reduce the cost of repairing condensing HES. Furthermore, due to the reducing corrosion rate under WFE combustion, the application of low-temperature condensing HES makes it possible to enhance the efficiency of deeper exhaust gas heat utilization and provide sustainable efficient operation of a diesel engine plant on the whole at a safe thermal and environmentally friendly level. Full article