Modern tendencies in the development of diesel engines include the operation of the system for injecting diesel fuel at pressures higher than 100 MPa. Knowing the characteristics of liquid fuels such as speed of sound, bulk modulus and density depending on pressure, is important for predicting the behavior of fuel injection systems for diesel engines and optimization of the same. The paper presents an original method and apparatus (device) for determining the speed of sound and density of fluids depending on the pressures. With this method, values of these characteristics for rapeseed oil, biodiesel and conventional diesel fuel at pressures up to 160 MPa are determined. The method is non-destructive, it can also be applied to higher pressures than 160 MPa, as well as other liquid fluids that are used at high pressure - hydraulic oil, for example

Abstract. Regarding the application of vegetable oil based fuels in diesel engines, it is necessary to fully examine and understand the processes which take place in fuel delivery systems, namely, the processes of injection, mixture formation and combustion as well as emission characteristics. The paper provides an analysis of fuel flow in high pressure tubes of the fuel injection system, with the aim of determining function K as a link between fuel flow velocity and fuel pressure, and observing the influence of certain physical characteristics of the fuel upon the given function. The analysis presents the speed of sound and density, as fuel characteristics which affect the K function. The paper determines the speed of sound, density and bulk modulus for four fuels (pure rapeseed oil RO, biodiesel B100, a mixture of biodiesel and diesel B50, and diesel D), and forms appropriate K functions for each fuel in the pressure range from the atmospheric one to 1600 bar.

Freight transport is a composite dynamic system that forms the unity of the infrastructure, vehicles, and personnel and which has its purpose or aim. Evaluating operation performance for freight transport systems is important for the government, companies, and users. This paper will use one of the most famous Multiple Criteria Decision-Making (MCDM) techniques to assess the operational performance of freight transport systems. At beginning, the authors will create the evaluation indicator system based on official data with four basic indicators and two sub-indicators for freight transport. These operational data/indicators represent the input of the chosen MCDM method. After that, the Analytic Hierarchy Process (AHP) method will use to calculate the indicator and sub-indicators weight and also will use to calculate the universal evaluate values and rankings of each transport mode performance. The Serbian freight transport system for the 2021st year will be selected as a case study for testing the AHP method within the MCDM approach; the associated suggestions to freight transport will also be given.

Transport is one of the largest emitters of harmful substances that affect air quality. Each combination of freight transport modes has a different volume and at the same time has a differentiated negative impact on air quality. That is why the European Union has been making special efforts for many years to create and implement strategies aimed at improving air quality. The main goal of this paper is to present a methodology that enables quantification and analysis of the impact of each freight transport mode combination on air quality using feed-forward neural networks. The developed model uses the parameters of the EU member states in the period from 2000 to 2014. In addition to the scientific and practical contribution, the development of the model provides a good basis for the universal platform formation in order to create and develop strategies, i.e. measures to improve air quality on a global level.

Transport causes significant external effects that have a very harmful impact on the environment, human health, but also the economy. The costs of these external effects are not borne directly by those who caused them, but by other road users (congestion, accidents) and society as a whole (environmental pollution costs). This results in making wrong decisions in the transport market, which further leads to an inefficient use of available resources and loss of social welfare. The purpose of this paper is a comparative analysis of negative external costs arising from freight road and rail transport. The main goal of the paper is to quantify the external costs caused by two different modes of freight transport, based on the characteristics of the transport vehicles and the characteristics of the goods being transported, as well as the length of the goods transport. The road and rail freight transport through Serbia will be chosen as the case study.

The paper presents a numerical simulation of a two-phase turbulent flow in pneumatic transport through straight horizontal channels with a square cross-section. The transport of solid particles of ash and flour is taken as the two-phase flow, while air is chosen for the transporting fluid. The motion of solid particles occurs due to the aerodynamic forces of the transporting fluid. The paper considers the motion of solid particles by taking into account the influence of vertical forces, which act on the transported solid particles. In flow modelling, the transported solid particles are reduced to spherical shapes. The stress model of turbulence is corrected by taking into account the influence of the induction of secondary flows of the second kind in the gas phase. The full Reynolds stress model is used to model the turbulence, with the application of the complete model for turbulent stresses and turbulent temperature fluxes. The paper presents the results of the numerical grid with the highest resolution above which the increase of the mesh density does not affect the obtained results. The diagrams of the positions of the transported solid particles are provided for crosssections normal and parallel to the flow direction.