Search

为提升燃料的综合燃烧品质和性能，进一步降低有害物质排放和缓解温室效应，以燃烧动力学和化学反应机制作为理论基础，采用Chemkin软件将生物柴油替代物和氨气充分融合，模拟并计算氨气掺混比例分别为0、5%、10%、15%、20%的5组燃料在均质压燃发动机模式下燃烧和排放指标的数值，对比分析得到不同掺混比例对发动机燃烧和排放的影响和变化规律。结果表明：随着氨气掺混比例增加，燃料的点火滞燃期有所缩短，缸内燃烧最高温度升高，排温降低；排放方面，NOx的排放升高，CO2、CO和总碳氢化合物（THC）的排放均明显降低；生物柴油掺混氨气的最佳比例为20%，此时发动机功率下降12百分点，NO的单位功率排放升高了0.003 kW-1，而CO2和THC的单位功率排放分别降低了0.01 kW-1和0.001 3 kW-1。综上，生物柴油掺混氨气后改善了燃烧性能，降低了排放量，具有良好的应用前景 In order to improve the comprehensive combustion quality and performance of the fuel, further reduce the emission of harmful substances and mitigate the greenhouse effect, based on the theoretical basis of combustion kinetics and chemical reaction mechanism, the Chemkin software was used to fully integrate the mechanism of biodiesel substitute and ammonia gas, simulate and calculate the combustion and emission values of 5 groups of fuels with the ammonia gas molar ratio of 0, 5%, 10%, 15% and 20% respectively in homogeneous charge compression ignition engine mode. The effects and change rule of different mixing ratio on engine combustion and emission were compared and analysed. The results showed that with the increase of ammonia gas ratio, the ignition delay period of fuel was shortened, the maximum combustion temperature in the cylinder increased, and the exhaust temperature decreased. In terms of emission, NOx emission increased, while CO2, CO and total hydrocarbon (THC) emissions decreased significantly. The optimal ratio of biodiesel blended with ammonia gas was 20%, and under this condition, the engine power decreased by 12 percentage, and the unit power emission ratio of NO increased by 0.003 kW-1, while the unit power emission ratios of CO2 and THC decreased significantly, which were 0.01 kW-1 and 0.001 3 kW-1 respectively. In conclusion, biodiesel blended with ammonia gas significantly improves combustion and reduces emissions, and has good application prospect.

An enhanced YOLOv8 algorithm is proposed in the following paper to address challenging issues encountered in ferrographic image target detection, such as the identification of complex-shaped wear particles, overlapping and intersecting wear particles, and small and edge-wear particles. This aim is achieved by integrating the main body network with the improved Deformable Convolutional Network v3 to enhance feature extraction capabilities. Additionally, the Dysample method is employed to optimize the upsampling technique in the neck network, resulting in a clearer fused feature image and improved precision for detecting small and edge-wear particles. In the head network, parameter sharing simplifies the detection head while enhancing convergence speed and precision through improvements made to the loss function. The experimental results of the present study demonstrate that compared to the original algorithm, this enhanced approach achieves an average precision improvement of 5.6% without compromising the detection speed (111.6FPS), therefore providing valuable support for online monitoring device software foundations. [ABSTRACT FROM AUTHOR]

To assist vessels in meeting the net-zero emission target set by the International Maritime Organization for 2050, this article investigates the emission and combustion characteristics of biodiesel–ammonia dual-fuel engines. This research investigates the impact of various ammonia mass ratios (AMRs, m%) at 0, 14.67%, 29.48%, 46.21%, 58.73%, and 82.72% on the combustion and emission performance of biodiesel–ammonia dual-fuel engines at fixed speed and load. The results show that the biodiesel–ammonia dual-fuel engine is capable of operating at a substantial AMR of 82.72%. In addition, as the AMR increased, the in-cylinder pressure and brake thermal efficiency decreased. The heat release rate peaked at 57.13% AMR. When compared to the only-biodiesel mode, NOx, CO2, and soot emissions are significantly reduced. CO2 and soot emissions decreased by 63.43% and 60%, respectively, at 82.72% AMR, while NOx emissions fell by 34.15% at 58.73% AMR. The emissions of N2O and unburned ammonia rose linearly as AMR increased. The increase in N2O did not counteract the substantial fall in CO2e. CO2e fell by 63.12% at 82.72% AMR, following a trend to similar CO2. [ABSTRACT FROM AUTHOR]

In the case of the journal-bearing system under a mixed or boundary lubrication regime, the deformation of the bearing, the flow of the lubricating medium, and the contact of the asperities should be taken into account. The lubrication problem at the journal-shaft interface is a complicated fluid–solid coupling problem. In this study, a new approach is proposed to analyze the dynamic fluid–solid coupling problem of journal bearings. The dynamic fluid–solid coupling problem is solved by the presented non-linear hybrid conjugate gradient method, which is based on the principle of pressure balance in the lubrication zone. One transient mixed lubrication model was developed to analyze the journal-bearing performance by considering the effects of skewness and kurtosis and the mass-conserving cavitation. According to the simulated results from the journal-bearing systems under the start-up condition, it can be found that the bearing performance is sensitive to the value of skewness or kurtosis and the degree of misalignment. Within a certain range, these cases with more negative skewness or lower kurtosis are conducive to decreasing friction loss and lift-off time. The developed model can be effectively used to track the performance of journal bearings. [ABSTRACT FROM AUTHOR]

A cylinder liner and piston ring running under starved lubrication near the top dead centre (TDC) and bottom dead centre (BDC) cause abnormal friction and wear during operation of a marine diesel engine. The method of laser texturing is proposed to improve the surface friction property under this condition. Spherical crown pits with different parameters were formed on the surface of samples by femtosecond laser processing. The BDC and TDC conditions of oil starvation were simulated in a reciprocating friction and wear experiment, and a numerical model of surface texture lubrication based on the Reynolds equation was established. The influence of the distribution density, diameter, and depth parameters of the texture on the surface properties was studied. In the BDC condition, compared with the untextured surface, the average coefficient of friction (COF) can be reduced by up to 24% and the average friction force can be reduced by up to 18%. In the TDC condition, the COF can be reduced by up to 19%, and the average friction force can be reduced by up to 18%. Therefore, the textures with various parameters should be arranged in different positions on the cylinder liner; more attention should be paid to the optimisation of diameter in the texture of the cylinder liner near the BDC, whereas more attention should be paid to the optimisation of distribution density in the texture of the cylinder liner near the TDC

BACKGROUND: High blood pressure has been suggested to accelerate vascular injury-induced neointimal formation and progression. However, little is known about the intricate relationships between vascular injury and hypertension in the context of arterial remodeling. METHODS: Single-cell RNA-sequencing analysis was used to depict the cell atlas of carotid arteries of Wistar Kyoto rats and spontaneously hypertensive rats with or without balloon injury. RESULTS: We found that hypertension significantly aggravated balloon injury-induced arterial stenosis. A total of 36 202 cells from carotid arteries with or without balloon injury were included in single-cell RNA-sequencing analysis. Cell composition analysis showed that vascular injury and hypertension independently induced distinct aortic cell phenotypic alterations including immune cells, endothelial cells (ECs), and smooth muscle cells. Specifically, our data showed that injury and hypertension-induced specific EC phenotypic alterations, and revealed a transition from functional ECs to hypermetabolic, and eventually dysfunctional ECs in hypertensive rats upon balloon injury. Importantly, our data also showed that vascular injury and hypertension-induced different smooth muscle cell phenotypic alterations, characterized by deferential expression of synthetic signatures. Interestingly, pathway analysis showed that dysregulated metabolic pathways were a common feature in monocytes/macrophages, ECs, and smooth muscle cells in response to injury and hypertension. Functionally, we demonstrate that inhibition of mitochondrial respiration significantly ameliorated injury-induced neointimal formation in spontaneously hypertensive rats. CONCLUSIONS: This study provides the cell landscape changes of the main aortic cell phenotypic alterations in response to injury and hypertension. Our findings suggest that targeting cellular mitochondrial respiration could be a novel therapeutic for patients with hypertension undergoing vascular angioplasty. [ABSTRACT FROM AUTHOR]

Under the axial excitation of the propeller, the axial movement of the crankshaft on the large marine diesel engine is obvious. In order to explore the effect of the axial movement on the lubrication of the main bearing supporting the crankshaft, a crankshaft-bearings system of a marine diesel engine was taken as the research object, and a mixed-lubrica-tion model of marine diesel engine main bearing was established by considering the axial motion caused by propeller axial excitation and diesel engine self--excitation and the asperity contact (dry friction) .The axial movement of the crankshaft was obtained by using finite element method. Combined with the dynamic method, the oil film pressure was obtained by solving the average Reynolds equation considering axial motion and surface roughness, and the asperity contact pressure was obtained based on the Creenwood--Tripp contact model. The results show that after taking into account the axial motion, the oil film peak pressure and oil film frictional power loss of the bearings are reduced, and the asperity contact pressure is increased. However, the asperity contact frictional power loss of some bearings increase and the others decrease among the 8 bearings. The influence of the axial motion on the asperity contact is significant, but the reasons are complicated. After taking into account the axial motion, the minimum oil film thickness, end leakage of bearing,journal center orbital path change little., the axil motion of the crankshaft must be considered to predict the mixed--lubrication of main bearings of the large marine diesel engine more comprehensively and more accurately. [ABSTRACT FROM AUTHOR]