Development of quantitative measuring technique to find critical flow conditions for preventing soot deposit accumulated in the diesel exhaust system using main muffler composed of three chambers

If a vehicle that meets emission regulations operates sufficiently for a long time under low speed and low load conditions, soot contained in the exhaust gas is accumulated on the inner surface of the exhaust system. This soot deposition problem occurs frequently in all diesel cars. However, when a vehicle is placed under the conditions of sudden start and sudden acceleration after city mode driving for a long time, the deposited soot is abruptly blown up with the soot produced during fuel combustion. In the present study, the main cause of the abrupt outburst of deposited soot is investigated to overcome this adverse phenomenon. First, we developed a method to quantify the amount of the exhausted soot particles (or the accumulated soot particles) by measuring the opacity that represents the contamination level of the exhaust gas due to soot particles. Using this measuring scheme for deposited soot, we found the critical conditions for engine speeds and load conditions at which soot particles are emitted into the air without accumulation in the exhaust system using main muffler composed of three chambers. In order to meet these critical conditions and thus to drastically reduce soot accumulation, the exhaust system using the main muffler applied in this study must be designed to ensure that the flow velocity of the exhaust gas is higher than 62 m/s when the back pressure at the exit of the turbocharger is under 0.08 bars.     

船舶管理信息系统研发

经校企双方多年合作,采用先进船舶管理理念和标准化代码、运用国际先进的船岸通讯技术开发出的船舶管理信息系统完全符合国际、国内船舶管理行业的业务要求,该系统的研发成功对我国航运界实现船舶信息化和数字化管理起到了积极作用．     

Instantaneous 2-D visualization of spray combustion and flame luminosity of GTL and GTL-biodiesel fuel blend under quiescent ambient conditions

An experimental study has been performed on spray combustion and two-dimensional soot concentration in diesel (ULSD), GTL and GTL-biodiesel fuel jets under high-pressure, high-temperature quiescent conditions. Instantaneous images of the fuel jets were obtained with a high-speed camera. It was confirmed that by blending GTL with 20% rapeseed biodiesel, certain fuel properties such as kinematic viscosity, density, surface tension, volatility, lower heating value and others may be designed and improved to be more like those of conventional diesel fuel but with considerable decrease in the amount of sulfur, PAH, cold filter plugging point, etc. The results showed that the spray tip penetration increased and the spray cone angle decreased when 20% biodiesel fuel was added to GTL fuel. Autoignition of the GTL-biodiesel blend occurred slightly earlier than that of diesel fuel. Experiments under high-pressure, high-temperature conditions showed that higher injection pressure induced a lower soot formation rate. The integrated flame luminosity, which serves as an indicator of soot concentration in the fuel jet, was slightly higher for the GTL-biodiesel blend than for pure GTL fuel due to the slightly higher sulfur content of pure biodiesel fuel.     

Forecasting bus ridership using a “Blended Approach”

Transportation - As sources of “Big Data” continue to grow, transportation planners and researchers seek to utilize these new resources. Given the current dependency on traditional...     

Happy today,satisfied tomorrow: emotion—satisfaction dynamics in a multi-week transit user smartphone survey

Transportation - Travel well-being encompasses three dimensions: cognitive satisfaction judgments, positive emotions, and negative emotions. Most previous literature on transit users focused either...     

走滑断层错动量大小对铁路隧道结构安全性影响的数值分析北大核心CSCD

走滑断层错动容易使穿越活动断裂带的隧道结构遭受严重的破坏。以某铁路隧道穿越某断裂带为工程背景,采用有限差分数值模拟手段,通过分析不同走滑断层错动量下隧道结构的位移、应力和应变,对隧道结构的安全性进行评判。研究表明:走滑断层错动时,除纵向位移外,随着错动量的增加,隧道结构位移越大,且走滑断层错动对在断层区和上盘区域的隧道结构影响最大;在走滑断层错动量>0.6 m后,隧道结构应力受错动量的影响较小,且隧道结构开始破坏,随着错动量增加,破坏范围增大。     

Disparities in access to opportunities across neighborhoods types: a case study from the Los Angeles region

This study investigates the disparities in access to various types of opportunities in ethnic neighborhoods, as compared to wealthy white neighborhoods (the reference). Focusing on the heterogeneity within ethnic neighborhoods, I distinguish between different types of neighborhoods based on their racial/ethnic makeup and median household income. The Los Angeles region provides an interesting empirical setting because of its racial diversity and its auto-centric spatial structure. The results show that the various types of ethnic neighborhoods differ not only in spatial patterns within the region but also in terms of relative access to opportunities. Nevertheless, I find that all types of the low-income ethnic neighborhoods have higher levels of access to jobs and non-work opportunities, except for access to parks/open spaces, than do the reference neighborhoods. This holds true regardless of accessibility measures and travel modes. However, the relative access to opportunities for middle-to-high-income ethnic neighborhoods varies by accessibility measure. Considering that each accessibility measure has its own set of meanings and planning implications, diverse measures should be taken into account for policy interventions. The present study also adds further evidence of modal disparities, which are much greater than spatial disparities, in access to opportunities.

     

水平小净距隧道中夹岩安全系数法研究与应用北大核心CSCD

中夹岩柱是小净距隧道围岩稳定控制的关键部位,判别中夹岩的安全性是工程设计和施工过程中的重难点。文章通过分析不同围岩级别、埋深情况下中夹岩的破坏模式,建立Ⅳ级围岩条件下水平小净距隧道中夹岩力学分析模型,并确定中夹岩破裂面位置。根据中夹岩上部滑块体形状的不同分为两种情况,通过边坡稳定性原理、极限平衡假设及普氏压力拱理论推导中夹岩上部滑块体的抗滑力、下滑力以及安全系数的计算公式,从而建立起评判中夹岩安全性的安全系数法,并结合数值模拟对其进行验证。将经验证后的安全系数法应用于某实际隧道工程,判断其中夹岩安全性,得出该隧道中夹岩破坏临界厚度为6 m,进而对6 m以下的中夹岩使用锚杆进行加固。     

Prediction analysis on propulsion shafting load based on grey system theory北大核心CSCD

[Objective]The propulsion shafting system is an important part of a ship, and the bearing load directly affects its operating state and service life. In this paper, bearing load under hull deformation is studied using grey system theory. [Method] First, according to the empirical formula of the relative displacement of each bearing caused by the deformation of the hull of a 57 000 DWT oil tanker, the relative displacement of each bearing is calculated and input into a finite element model, and the load value of each bearing is output. On this basis, grey relationship analysis of grey system theory is introduced to study the influence degree of stern bearing displacement on the load of each bearing, and the relative change of the load of each bearing caused by the displacement of the stern bearings is analyzed. A GM (1,1) prediction model is then established for the bearing load considering the bearing displacement conditions, and the hull deformation-fitting and prediction of each bearing load are made. [Results]The results show that grey relationship analysis can effectively reflect the influence of hull deformation on bearing load. The GM (1,1) prediction model has high accuracy and prediction errors less than 6.0%, and the model test indexes can represent the accuracy of the prediction. [Conclusion]Grey system theory is effective and practical in research on propulsion shaft load. It can accurately predict bearing load under bearing displacement, giving it certain reference value for research on bearing load under actual sailing conditions. © The Author(s) 2022.     

Modeling the effects of congestion on fuel economy for advanced power train vehicles

Fuel-speed curves (FSC) are used to account for the aggregate effects of congestion on fuel consumption in transportation scenario analysis. This paper presents plausible FSC for conventional internal combustion engine (ICE) vehicles and for advanced vehicles such as hybrid electric vehicles, fully electric vehicles (EVs), and fuel cell vehicles (FCVs) using a fuel consumption model with transient driving schedules and a set of 145 hypothetical vehicles. The FSC shapes show that advanced power train vehicles are expected to maintain fuel economy (FE) in congestion better than ICE vehicles, and FE can even improve for EV and FCV in freeway congestion. In order to implement these FSC for long-range scenario modeling, a bounded approach is presented which uses a single congestion sensitivity parameter. The results in this paper will assist analysis of the roles that vehicle technology and congestion mitigation can play in reducing fuel consumption and greenhouse gas emissions from motor vehicles.