燃油二次喷射对柴油机燃烧和性能的影响

在Ricardo Hydra单缸柴油机上,采用一次主喷射+一次后喷射的方法进行了5组燃烧对比试验。示功图和缸内燃烧分析表明,两次喷射有效地延长了等压加热过程,平均有效压力得到较大的提高,NOx排放有一定幅度的下降。     

燃油2次喷射对柴油机性能的影响研究

研究了主喷射提前角和后喷射提前角对Ricardo Hydra单缸柴油机动力性能及排放性能的影响.结果表明.当该柴油机主喷射提前角为11°、后喷射提前角为3°时,柴油机最高爆发压力与采用单喷射时最高爆发压力相差不大,但平均有效压力却提高明显;随着喷油提前角的后移,烟度排放增加,NOx排放减少,HC排放增加.分析了主喷射和后喷射时该柴油机燃烧过程.     

Modelling user satisfaction in public transport systems considering missing information

Collecting data to obtain insights into customer satisfaction with public transport services is very time-consuming and costly. Many factors such as service frequency, reliability and comfort during the trip have been found important drivers of customer satisfaction. Consequently, customer satisfaction surveys are quite lengthy, resulting in many interviews not being completed within the aboard time of the passengers/respondents. This paper questions as to whether it is possible to reduce the amount of information collected without a compromise on insights. To address this research question, we conduct a comparative analysis of different Ordered Probit models: one with a full list of attributes versus one with partial set of attributes. For the latter, missing information was imputed using three different methods that are based on modes, single imputations using predictive models and multiple imputation. Estimation results show that the partial model using the multiple imputation method behaves in a similar way to the model that is based on the full survey. This finding opens an opportunity to reduce interview time which is critical for most customer satisfaction surveys.

     

Towards an enriched framework of service evaluation for pedestrian and bicyclist infrastructure: acknowledging the power of users’ perceptions

Transportation - More and more cities worldwide are striving for sustainability and livability. Measuring the service or performance of local-scale spaces for pedestrians and bicyclists to better...     

Changes in dissolved silicate loads to the Baltic Sea — The effects of lakes and reservoirs

We tested the hypothesis that dissolved silicate (DSi) yields [kg km^− 2 yr^− 1] of 82 major watersheds of the Baltic Sea can be expressed as a function of the hydraulic load (HL) as a measure of water residence time and the total organic carbon (TOC) concentration, both variables potentially increasing the DSi yield. Most boreal rivers fitted a linear regression model using HL as an independent variable to explain the DSi yield. Rivers with high HL, i.e., shortest residence times, showed highest DSi yields up to 2300 kg km^− 2 yr^− 1. This is most likely caused by an excess supply of DSi, i.e., the geochemical sources prevail over biological sinks in these boreal watersheds. The DSi yield for regulated and unregulated larger rivers of the boreal watersheds constituting about 40% of the total water discharge and of the total DSi load to the Baltic Sea, respectively, can be expressed as: DSi yield = 190 + 49.5 HL[m yr^− 1] + 0.346 TOC [µM] (R² = 0.80). Since both HL and TOC concentrations have decreased after damming, the DSi yields have decreased significantly in the regulated boreal watersheds, for the River Luleälven we estimated more than 30%. The larger eutrophic watersheds draining cultivated landscape of the southern catchment of the Baltic Sea and representing about 50% of the annual water discharge to the Baltic Sea, deviated from this pattern and showed lower DSi yields between 60–580 kg km^− 2 yr^− 1. DSi yields showed saturation curve like relationship to HL and it appears that DSi is retained in the watersheds efficiently through biogenic silica (BSi) production and subsequent sedimentation along the entire river network. The relationship between HL and DSi yields for all larger cultivated watersheds was best fitted by a Freundlich isotherm (DSi = 115.7HL¹⁰⁹; R² = 0.73), because once lake and reservoir area exceeds 10% of the watershed area, minimum DSi yields were reached. To estimate an uperturbed DSi yield for the larger eutrophic southeastern watersheds is still difficult, since no unperturbed watersheds for comparison were available. However, a rough estimate indicate that the DSi flux from the cultivated watersheds to the Baltic Sea is nowadays only half the uperturbed flux. Overall, the riverine DSi loads to the Baltic Sea might have dropped with 30–40% during the last century.     

Understanding the Relationship Between Physical and Virtual Representations of Transit Agencies

Abstract

This study examines whether physical attributes of transit agencies, such as agency size, make a difference in how transit websites are designed, and how transit information is distributed. The objective of this study is to see if there is a relationship between physical and virtual representations of transit agencies. A rating instrument is developed for evaluating the quality of transit websites. Our findings suggest that transit agency size plays a key role in determining website quality: When the size of transit system is large, the information about the agency is too complex to be effectively presented on web pages. Thus, the quality of the large agencies’ websites is lower than medium-sized agencies. Instead, we find that large agencies attempt to design more user-friendly sites, and provide advanced information searching tools to compensate for low information quality. Policy implications for transit agencies are discussed.