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排序方式: 共有563条查询结果,搜索用时 15 毫秒
321.
O. T. Lim 《International Journal of Automotive Technology》2014,15(4):535-541
The HCCI (Homogeneous Charge Compression Ignition) engine is an internal combustion engine under development, which is capable of providing both high diesel-like efficiency and very low NOx and particulate emissions. However, several technical issues must be resolved before the HCCI engine is ready for widespread application. One issue is that its operating range is limited by an excessive pressure rise rate which is caused by the excessive heat release from its selfaccelerated combustion reaction and the resulting engine knock in high-load conditions. The purpose of this study was to evaluate the potential of thermal and fuel stratification for reducing the pressure rise rate in HCCI engines. The NOx and CO concentrations in the exhaust gas were also evaluated to confirm combustion completeness and NOx emissions. The computational work was conducted using a multi-zone code with detailed chemical kinetics, including the effects of thermal and fuel stratification on the onset of ignition and the rate of combustion. The engine was fueled with dimethyl ether (DME) which has a unique two-stage heat release, and methane which has a one-stage heat release. 相似文献
322.
323.
In 1992, scientists at National Estuarine Research Reserve (NERR) sites proposed establishing a national coordinated monitoring program that would attempt to identify and track short-term variability and long-term changes in representative estuarine ecosystems and coastal watersheds. Known as the NERR System-Wide Monitoring Program (SWMP), it currently consists of monitoring water quality and atmospheric variables over a range of spatial and temporal scales. Additional monitoring of ecological resources and land-water use will follow in subsequent components of the program. Water quality monitoring at NERR sites includes measurements of pH, conductivity, temperature, dissolved oxygen, turbidity, and water level. The NERR sites use data loggers that record at 30-minute intervals and relay measurements to internal memory. Standardized protocols assure that sampling, processing, and data management techniques are comparable among sites. Statistical techniques are being used to identify periodicity in water quality variables. Periodic regression analysis indicated that diel periodicity in dissolved oxygen is a larger source of variation than tidal periodicity at sites with less tidal amplitude. Tidal periodicity, however, is more important at sites with a tidal amplitude greater than 1 m. This finding suggests that natural processes controlling dissolved oxygen levels differ among sites depending upon tidal amplitude. Water quality data from the NERR SWMP have also been used to investigate occurrence of hypoxia. Results from analysis of water quality at several reserves indicate that hypoxia occurs but that the percentage of time that dissolved oxygen was less than 28% saturation varied substantially among sites and between years. Most of the hypoxic events occurred in summer but were also observed in winter and fall when low dissolved oxygen is usually not considered a problem. Without continuous monitoring by the NERR SWMP, many low dissolved oxygen events would have been missed, thus underestimating the duration and potential impact of this type of water quality variability. The NERR SWMP provides a unique opportunity to increase our understanding of how various environmental factors influence estuarine processes. Only by understanding how estuaries function and change naturally over time will we be able to predict how these systems respond to changes in climate and human-induced perturbations. 相似文献
324.
J. M. Hills D. Alcock T. Higham H. Kirkman M. Le Tissier C. Pagdilao 《Coastal management》2013,41(3):323-337
Development of awareness and capacity is a central component to the delivery of ICM and spans from local communities to national-level politicians. Education and training activities associated with ICM must be extremely varied to match both the existing capacity and role that the stakeholders play within the process of ICM. Consequently, there cannot be considered any effective “generic” ICM training; training must be tailored to match the requirements of target groups. The transfer and uptake of good-practice thus becomes an important aspect of quality enhancement in ICM capacity development. Six case studies from the Asia-Pacific region are presented that show diverse and innovative examples of good practice. A comparative analysis of these case studies is carried out in terms of institutional level of impact. In addition a generic systems-based evaluation framework is used to determine the extent to which the training impacts upon ICM implementation indicators. It is concluded that the exchange, transfer, and translation to local conditions of appropriate good practice in ICM capacity development can be an important element in enhancing the impact of ICM programs on the coastal environments and societies. Furthermore, there appears to be a positive link between the involvement of national/state/regional stakeholders in capacity-building initiatives and impacting a wider variety of indicators of ICM delivery. 相似文献
325.
Ever increasing demand for the petroleum is causing faster than expected oil shortages in the supply and demand balance around
the world and furthermore, many specialists in the field of oil production such as Association for the Study of Peak Oil and
World Energy Outlook are claiming that the petroleum is around the peak of its production (Figure 1). Such shortage made the
greatest impact on the gasoline price hikes at the gas pump and thus, this impact was felt by the consumers severely and became
the greatest motivation for automotive industries to strive to pioneer the researches for the next generation vehicle configurations
ranging from HEV, PHEV, Pure EV to FCHEV (collectively noted as xEV). While the great deal of researches has been carried
over the last few decades, it is still far from mass productions for consumer use except for the HEV mainly due to the high
cost involved with other types of xEV configurations. Therefore, it is critical to design the vehicle to maximize the use
of each component at its highest point regardless of any cost scenarios and it is clear that this optimization can only be
achieved through the accurate energy balance simulation for a specific target vehicle prior to the actual hardware implementation.
In this paper, it is our intention to introduce modified dynamic battery modeling scheme that would provide a more accurate
way of simulating the battery behavior when used in the vehicle energy simulation system. Starting from a typical battery
dynamic model to predict the voltage given an imposed current request, we have introduced a new scheme to establish the relationship
between the voltage and the power (rather than the current) requested by the vehicle simulation system. The proposed scheme
handles the power request from the vehicle simulator considering the dynamic battery characteristics and in turn, contributes
to the better estimation of the current integrated energy usage and battery SOC level in the given battery dynamic system
used in the vehicle energy simulation system. 相似文献
326.
Electro-hydraulic braking system for autonomous vehicles 总被引:4,自引:0,他引:4
V. Milanés C. González J. E. Naranjo E. Onieva T. De Pedro 《International Journal of Automotive Technology》2010,11(1):89-95
Reducing the number of traffic accidents is a declared target of most governments. Since dependence on driver reaction is the main cause of road accidents, it would be advisable to replace the human factor in some driving-related tasks with automated solutions. To automate a vehicle, it is necessary to control the actuators of a car, i.e., the steering wheel, accelerator, and brake. This paper presents the design and implementation of an electro-hydraulic braking system consisting of a pump and various valves, allowing the control computer to stop the car. It is assembled in conjunction with the original circuit for the sake of robustness and to permit the two systems to halt the car independently. This system was developed for installation in a commercial Citroën C3 Pluriel of the AUTOPIA program. Various tests were carried out to verify its correct operation, and an experiment showing the integration of the system into the longitudinal control of the car is described. 相似文献
327.
In this paper, a numerical procedure to estimate the performance of the high power pretensioner used in the seatbelt of a
passenger vehicle is presented. The data on the gas explosion pressure in a 10-cc volume and the data on the displacement
of the rack according to time were applied to the numerical procedure. The procedure was implemented using MATLAB. The testing
device, which met the automobile industry standards, was created. Experiments were carried out seven times under the same
conditions, and the mean values of the web retraction and belt load were used as the representative data. By comparing the
simulation results to the test results, the numerical procedure presented in this paper was verified. 相似文献
328.
A unique set of activity scheduling data is utilized in this paper to provide much needed empirical analysis of the sequence
in which activities are planned in everyday life. This is used to assess the validity of the assumption that activities are
planned in accordance to a fixed hierarchy of activity types: mandatory activities first (work/school), followed by joint maintenance, joint discretionary, allocated maintenance, and
individual discretionary activities. Such an assumption is typical of current generation activity and tour-based travel demand
models. However, the empirical results clearly do not support such assumptions. For instance, fewer than 50% of mandatory
activities were actually planned first in related out-of-home tours; remaining activity types also did not take any particular
precedence in the planning sequence. Given this, a search was made for the more salient attributes of activities (beyond activity
type) that would better predict how they are planned within tours. Several ordered response choice models for different tour
sizes were developed for this purpose, predicting the choice order of the 1st, 2nd, 3rd, etc. planned activity in the tour
as a function of activity type, activity characteristics (duration, frequency, travel time, and involved persons), and individual
characteristics. Activity duration played the most significant role in the models compared to any other single variable, wherein
longer duration activities tended to be planned much earlier in tours. This strongly suggests that the amount of time-use,
rather than the nature of the event as indicated by activity type, is a primary driver of within-tour planning order and offers
potential for a much improved and valid fit. 相似文献
329.
330.
T. Morita T. Matsukawa 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1995,24(4):401-412
A study on effective use of rear braking force to improve a brake performance and vehicle dynamics are carried out. On a ordinary condition, the rear braking force could be more increased to a conventional braking force distribution. Based on this thought, the brake performances are estimated. The results show the effects not only improve the brake performance but also reduce a pitching at braking and moderate a vehicle OS behavior in a turn during braking. These are verified by experimental test vehicle equipped with a rear braking force control system. 相似文献