Electrically Assisted Internal Combustion Engines: A Comparative Analysis

An electrically assisted internal combustion engine is obtained by combining a conventional engine and one or more electrical motors of considerably smaller size. A key feature of such an innovative vehicle hybridization approach is that the torque generated by electric machines is not transmitted to the wheels. The electric motors are, in fact, intended only to assist the internal combustion engine in low efficiency, low performance, or high polluting working conditions. They however, draw extra power and energy from the battery. This paper presents a tool to evaluate different possible solutions in terms of energy balance, efficiency, battery stress and battery ageing. The method, which is based on suitable mathematical models and specific analysis criteria is also exploited to compare eight different configurations of a C-segment vehicle, pointing out limits and capabilities of traditional 12?14 V systems.     

Development of hydrogen-compressed natural gas blend engine for heavy duty vehicles

Natural gas fuel, as an alternative energy source of transportation, has been used widely since it has an advantage of low emission levels. However, new technologies are required in order to meet the reinforced emission regulations. For this purpose, research into the development of hydrogen-compressed natural gas (HCNG) blend engine was carried out to evaluate its feasibility and emission characteristics. The Engine Research Department at the Korea Institute of Machinery and Materials carried out a large number of tests based on various parameter changes that could affect the performance and emission of HCNG engine in different operating conditions. An earlier stage of the research project focused on the lean combustion of a HCNG engine for heavy duty vehicles to meet the EURO-VI standards. An 11-L/6-cylinder CNG engine was used for the test. The effects of the excess air ratio change were assessed based on various content ratios of hydrogen in the natural gas fuel. In the later part of the HCNG research, a stoichiometric mixture operation was suggested to meet reinforced emission regulation without requiring a De-NOx system. Additionally, an exhaust gas recirculation (EGR) system was introduced for the purpose of improving thermal efficiency and durability. The optimal operating conditions were selected to achieve the best thermal efficiency to meet the required emission levels. In this paper, we demonstrate that a HCNG engine can achieve a significant decrease in NOx emissions, as compared to that of a CNG engine, while meeting the requirements of the EURO-VI standards during a transient mode cycle test. EGR can suppress the weakness of stoichiometric mixture combustion strategy, such as the deterioration of the durability and thermal efficiency, while the emission level can be lowered with the use of a three-way catalyst. The possibility of further reduction of emissions and CO2 with EGR was evaluated to access practical application of a HCNG engine in the field. From that evaluation, the HCNG engine with stoichiometric mixture operation for heavy duty vehicles was developed. The emission levels of HCNG engine were 50 % lower when compared to the EURO-VI standards with a greater than 10 % decrease in CO₂ compared to that of a natural gas engine.     

Grid convergence study in the resistance calculation of a trimaran

As a new type of hull form, trimaran has remarkable excellent performances and has drawn more and more attention. When the viscous CFD technology now available is applied to the research of resistance performance of trimaran, the spatial discretization would usually result in the grid error and uncertainty, and thus the considerable discrepancy between the numerical results and the experimental data. In order to ascertain how much the grid would affect the calculation, the grid convergence should be studied. A mathematical trimaran was chosen as an example, with the commercial code CFX for the simulation, VOF for surface treatment, and the grid study was carried out based on two different turbulence models. It was concluded that carrying out grid study is helpful in estimating the grid error and uncertainty, and indicating the direction of improving the credibility of the numerical calculation, and, in addition to grid errors and uncertainties, the turbulence modeling errors and uncertainties contribute to the simulation errors.     

A spatially explicit ecosystem model of seston depletion in dense mussel culture

A fully-coupled biological–physical–chemical model of a coastal ecosystem was constructed to examine the impact of suspended mussel culture on phytoplankton biomass in Tracadie Bay, Prince Edward Island, Canada. Due to the extent of mussel culture there, we hypothesised that shellfish filtration would control the concentration and distribution of phytoplankton and other suspended particles in the bay. Circulation was delineated with a tidally-driven 2D numerical model and used to drive an ecosystem model with a focus on pelagic components including phytoplankton production, nutrients, detritus, and mussels. The benthos were treated as a sink. Nutrients and seston were forced by tidal exchange and river input, with phytoplankton additionally forced by light. Boundary conditions of seston and nutrients were derived from field studies with an emphasis on the contrast between spring (high river nutrients, low temperature) and summer (low river inputs and high temperatures). Model output was used to map phytoplankton carbon over the bay for each season and in the presence of mussels and river nutrient input. Results indicate severe depletion effects of mussel culture on overall phytoplankton biomass, but no spatial pattern that can be attributed to grazing alone. Primary production generated by nutrient-rich river water created a mid-bay spike in phytoplankton that dominated the spatial pattern of chlorophyll-based carbon. Model results were validated with surveys from a towed sensor array (Acrobat) that confirmed the river influence and indicated bay-wide depletion of 29% between high and low water. Our model results indicate that the farm-scale depletion emphasised in previous studies cannot simply be extrapolated to seston limitation at the ecosystem level.     

船体表面矩形块优化敷设设计(英文)

Rectangular tiles can be laid on a ship’s hull for protection, but the sides of the tiles must be adjusted so adjacent tiles will conform to the curvature of the hull. A method for laying tiles along a reference line was proposed, and an allowable range of displacement for the four vertices of the tile was determined. Deformations of each tile on a specific reference line were then obtained. It was found that the least deformation was required when the tiles were laid parallel to a line with the least curvature. After calculating the mean curvature on the surface, the surface was divided into three layout areas. A set of discrete points following the least deformation of the principal curvatures was obtained. A NURBS interpolation curve was then plotted as the reference line for laying tiles. The optimum size of the tiles was obtained, given the allowable maximum deformation condition. This minimized the number of bolts and the amount of stuffing. A typical aft hull section was selected and divided into three layout areas based on the distribution of curvature. The optimum sizes of rectangular tiles were obtained for every layout area and they were then laid on the surface. In this way the layout of the rectangular tiles could be plotted.     

Getting by with a little help from my friends…and family: immigrants and carpooling

While much of the scholarly literature on immigrants’ travel focuses on transit use, the newest arrivals to the United States make over twelve times as many trips by carpool as by transit. Using the 2001 National Household Travel Survey and multinomial logit mode choice models, we examine the determinants of carpooling. In particular, we focus on the likelihood of carpooling among immigrants—carpooling both within and across households. After controlling for relevant determinants of carpooling, we find that immigrants are far more likely to form household carpools than native-born adults and also are more likely than the native-born to form external carpools (outside the household). Moreover, when faced with the options of carpooling and public transit, immigrants—even recent arrivals—appear to prefer carpools over transit more strongly than the native born.     

Long-term behavior of particulate matters at urban roadside and background locations in Seoul,Korea

The concentrations of particulate matter, PM_2.5, PM₁₀, and TSP at an urban roadside and an urban background station are analyzed. Data collected over a 10 year period are analyzed. The concentrations of the particulates measured at the urban site are systematically larger than at the background station. The mean PM values at the former also exhibit a slight fall over the decade unlike those at the background station. Overall, the particulate matters at both locations are in an intermediate range of global level, e.g., approximately two times lower than those in other Asian regions but higher than in Europe.     

The environmental effects of airline carbon emissions taxation in the US

This study investigates how air traffic emissions taxes may impact carbon emissions in the US. The magnitude of emissions savings in the US domestic airline industry that would result from lower demand for air travel as taxes are levied and air fares increase is estimated. At the same time, the air-automobile substitution effect is considered and it is argued that some air travelers may divert to automobiles, thus increasing automobile carbon emissions. Both the analysis of the aggregate US domestic airline industry and the study of a sample of US domestic route markets indicate that potentially sizeable increases in automobile traffic and related emissions may substantially reduce the environmental benefits of air travel carbon emissions taxes. In some instances, carbon emissions may even increase in short-haul markets. Sensitivity analyses are performed to demonstrate the robustness of these findings.     

A numerical approach to trajectory planning for yoyo movement

Based on nonlinear trajectory generation (NTG) software package, a general approach (i.e. numerical solution) to trajectory planning for yoyo motion is presented. For the real-time control of such periodical dynamic system, a critical problem is how to implement fast solving the optimal trajectory, so as to meet the real-time demand. However, traditional numerical solution methods are very time-consuming. In this paper, the optimization problem is solved by mapping the problem to a lower-dimension space. And combined with multithread programming technology, the computation time for solving the optimal trajectory is greatly reduced. Simulation results show that the numerical solution is identical to the analytic one, which demonstrates the correctness of the proposed method. The computation time of one cycle of yoyo simulation is about 10 ms, which shows that the proposed numerical method can be applied to the real-time control of yoyo playing.     

Causal linkages between highways and sector-level employment

While transport infrastructure investments have usually been viewed to have long-term impacts on employment, what is perhaps not immediately clear is the direction of causality. This paper has sought to disentangle the causal relationship between highway infrastructure and employment, using panel data for the 48 contiguous US states from 1984 to 1997. Of particular emphasis in this analysis is the sectoral differences in the causal and spatial effects of highway capacity expansions for employment growth in alternative sectors of the economy. The results indicate that lane-mile additions of own-state major highways could increase state employment growth in the services sector while reducing growth in manufacturing. However, the causal relationship is also found to work the other way around. That is, both the rapid growth in services employment and the slowdown in manufacturing jobs temporally lead to increases in roadway capacity of non-interstate major roads. Our analysis also shows that highway infrastructure could produce both positive and negative employment spillovers across states. We find that improvements in non-interstate major roads outside the state border are beneficial to the manufacturing sector which generally serves regional and national markets. For the services sector, however, employment gains from interstate highways in the same state may come at the expense of other states as there is clear evidence of negative employment spillovers from interstate lane-mile additions.