Effect of a 2-stage injection strategy on the combustion and flame characteristics in a PCCI engine

Recently, to reduce environmental pollution and the waste of limited energy resources, there is an increasing requirement for higher engine efficiency and lower levels of harmful emissions. A premixed charge compression ignition (PCCI) engine, which uses a 2-stage type injection, has drawn attention because this combustion system can simultaneously reduce the amount of NOx and PM exhausted from diesel engines. It is well known that the fuel injection timing and the spray angle in a PCCI engine affect the mixture formation and the combustion. To acquire two optimal injection timings, the combustion and emission characteristics of the PCCI engine were analyzed with various injection conditions. The flame visualization was performed to validate the result obtained from the engine test. This study reveals that the optimum injection timings are BTDC 60° for the first injection and ATDC 5° for the second injection. In addition, the injection ratio of 3 to 7 showed the best NOx and PM emission results.     

Relationship between occupant injury and the perturbation mark on the velocity indicator on a cluster panel

A perturbation mark is occasionally produced on the velocity indicator of the cluster panel of a vehicle during a vehicle collision. This mark can be used to estimate the velocity of the vehicle at the moment of the vehicle’s impact. In this study, the effect of the impact velocity and the deceleration of the vehicle on the perturbation mark were investigated, and an analysis of the driver’s injury was also conducted through a numerical pulse representation and computer simulations. Sled and pendulum tests were used to replicate the conditions that produce a perturbation mark on the velocity indicator of a cluster panel. It was verified that a higher peak acceleration is more likely than the impact velocity to cause a perturbation mark. According to the computer simulation results, a driver’s injury could be more severe at higher peak accelerations with a constant impact velocity. If a perturbation mark, which can be used to estimate the impact velocity, is found while investigating a vehicle accident, this mark reveals that the acceleration was higher than that listed in the related crash report. Therefore, the injuries of the occupants could be more serious than those expected at the reported impact velocity.     

A traffic flow simulator for network reliability assessment

This paper investigates the transportation network reliability based on the information provided by detectors installed on some links. A traffic flow simulator (TFS) model is formulated for assessing the network reliability (in terms of travel time reliability), in which the variation of perceived travel time error and the fluctuations of origin-destination (OD) demand are explicitly considered. On the basis of prior OD demand and partial updated detector data, the TFS can estimate the link flows for the whole network together with link/path travel times, and their variance and covariance. The travel time reliability by OD pair can also be assessed and the OD matrix can be updated simultaneously. A Monte Carlo based algorithm is developed to solve the TFS model. The application of the proposed TFS model is illustrated by a numerical example.     

A spatial decision support system for retail plan generation and impact assessment

Current geographic information systems typically offer limited analytical capabilities and lack the flexibility to support spatial decision making effectively. Spatial decision support systems aim to fill this gap. Following this approach, this paper describes an operational system for integrated land-use and transportation planning called Location Planner. The system integrates a wide variety of spatial models in a flexible and easy-to-use problem solving environment. Users are able to construct a model out of available components and use the model for impact analysis and optimization. Thus, in contrast to existing spatial decision support systems, the proposed system allows users to address a wide range of problems. The paper describes the architecture of the system and an illustrative application. Furthermore, the potentials of the system for land-use and transportation planning are discussed.     

Estimation of AADT from short period counts in hong kong — A comparison between neural network method and regression analysis

The average annual daily traffic (AADT) volumes can be estimated by using a short period count of less than twenty‐four hour duration. In this paper, the neural network method is adopted for the estimation of AADT from short period counts and for the determination of the most appropriate length of counts. A case study is carried out by analysing data at thirteen locations on trunk roads and primary roads in urban area of Hong Kong. The estimation accuracy is also compared with the one obtained by regression analysis approach. The results show that the neural network approach consistently performed better than the regression analysis approach.     

Some promising innovations in taxicab operations

Several shared-ride passenger transportation services which could be offered by taxicabs are currently prohibited in U.S. cities by state or local regulations. Although relaxation of these regulations has been advocated on numerous occasions, little regulatory change has occurred to date. Moreover, the taxicab industry has rarely been considered as a potential provider for publicly subsidized transportation services. This paper discusses several promising innovations in taxicab service provisions and subsidy mechanisms which have been implemented or proposed recently in U.S. cities. The paper argues for more well-designed experimentation with such innovations as a means of stimulating greater interest on the part of planners, policy-makers, regulators, and public transportation operators in broadening the role of taxicabs in urban transportation.     

PC-based sketch planning methods for transport and urban applications

Historically, computer models have grown in complexity, and consequently have become more difficult to use. At the same time there is a growing need for quick-response methods and techniques for broad-brush policy formulation and decision making. The personal computer and its attendant software offer new means for quantitative sketch planning. This paper illustrates two PC-based applications for quick-response exercises. These involve interactive mapping and data analysis methods for the appraisal and interpretation of transport data, and the development and use of eclectic models for systems analysis and scenario generation. The LAMM and DIAMONDS packages are described, and their use in data analysis is illustrated. The Trends Integrator Procedure (TIP) is used to formulate a simple but versatile model for investigation of developments in an urban retailing system. These packages all run on PC's and offer powerful and adaptive tools for improved transport planning.Nomenclature a _i a technical coefficient indicating the influence of the unique factor component (U _i ) for factor F _i - c _ij a technical coefficient relating the influence of factor F _i on factor F _j - F _i the relative change in the level of factor F _i - U _i the relative change in the unique factor component for F _i      

A study of economic indicators in rail freight traffic cycles 1950–76

This paper examines the characteristics of rail freight traffic cycles from 1950 to 1976. Both the NBER's statistical indicator approach and time series approach are used to identify the leading indicators of rail freight traffic cycles from a set of leading economic indicators published by the Department of Commerce. The concepts and empirical results obtained by these two procedures are compared and contrasted. The interesting findings are: (1) the composite index of 12 leading indicators performs very well as a qualitative and quantitative predictor and (2) the empirical results obtained by the NBER approach are, in general, consistent with those obtained by the time series approach.     

Generalised time and the problem of equity in transport studies

The generalised time expenditure on travel,g _t, may be defined asg _t =t +m/λ where t is the amount of time spent, m is the amount of money spent, and λ is the value of time. Generalised time is expressed in units of time, unlikeg _c, the generalised cost (g _c =m + λt), which measures the same quantities in units of money. Data on all trips from two studies are analysed to show that, as household income increases, the money spent per mile travelled increases, but the time spent per mile decreases. The use of generalised time gives a different picture of the relationship between income and the total time and money spent on travel to that given by the use of generalised cost. The choice between using generalised time and generalised cost in evaluation is fundamentally a choice between assuming that the marginal utility of time and that of money is constant. The procedures at present recommended by the Department of the Environment in U.K. have elements of both assumptions, with some loss of consistency. There are some a priori reasons for expecting constant marginal utility of time to be a more plausible assumption than constant marginal utility of money. Time is, by its nature, equitably and unalterably distributed, not subject to the accidents of inheritance, theft, chance, inflation, social system or government decree. Everybody starts off with 24 hours a day. Although the amount of “free” time varies, of course, it probably varies within a much smaller range than the amount of wealth, certainly for the employed population. In allocating time between various activities, the use of words likespend, save, waste, lose, gain, and so on is a reflection of how deeply rooted in language and thought is the concept of time as a fundamental currency. This approach is strengthened by recent developments in two areas where generalised cost has been found to be a useful tool of analysis — (a) in explaining and predicting the behaviour of travellers, and (b) in evaluating the social costs and benefits arising from transport projects. Only non-working time will be considered here. It is suggested that in some circumstances generalised time would allowbehaviourally correct relationships between non-working time and money to be used in evaluation. This paper — which is a revised version of “A Hypothesis of Constant Time Outlay on Travel” (Paper F29: Planning and Transport Research and Computation Ltd. Sussex, June 1973) — is based upon work carried out with the financial support of the Social Science Research Council.