This paper presents a mathematical model of piston-rings-cylinder sealing (TPC) of a combustion engine. The developed model is an itegrated model of gas flow through gaps in TPC unit, displacements and twisting motions of piston rings in ring grooves as well as generation of oil film between ring face surfaces and cylinder liner. Thermal deformations and wear of TPC unit elements as well as heat exchange between flowing gas and surrounding walls, were taken into account in the model. The paper contains descriptions of: assumptions used for developing the model, the model itself, its numerical solution as well as its computer application for carrying out simulation tests.

The paper presents some aspects of operation of municipal transport system in the city of Lublin (Poland). Organization of Lublin Municipal Transport Company was described, its efficiency and perspectives of development. Particular attention was paid to the rules of adjustment to the EU requirements, and to the influence of demographic and social factors. Infrastructure of public transport in Lublin was analyzed (busses, trolley‐busses, bus stations, fixed objects and bus stops), as well as configuration of bus and trolley‐bus lines. Some specific proposals were also put forward regarding development solutions: development plan of trolley‐bus traction, plan of inter‐connection bus station, development plan of bus traction, introduction of advanced IT solutions into the public transport management and natural gas (CNG) fuelling of the city busses. Keywords: urban transport, urban transport problems.

The paper presents a comparative analysis of the operational parameters, smoke emission and the content of toxic components in exhaust gases of a compression ignition engine fuelled with fossil diesel, commercially available biodiesel (fatty acid methyl ester) and their 50%/50% blend. The study was carried out using a diesel engine equipped with an in-line injection pump used in delivery vans. An indirect injection, considerably worn engine was chosen because such engines are very often fuelled with the less expensive biodiesel. Measurements were made on an engine operated at different rotational speeds under full load as well as using the European Stationary Cycle (ESC) test. Emissions of regulated and non-regulated compounds were measured with the use of the Fourier-Transform Infrared (FTIR) analytical system, which provided concentrations of 23 exhaust gas components. The results showed that the use of commercially available biodiesel instead of diesel fuel did not considerably reduce engine performance. However, increased fuel consumption was noted. The biggest differences between the fuels were observed in the case of smoke and CO emissions, which were substantially lower for the engine fuelled with biodiesel. The study indicated that the environmental effect of the fuel used was not only different for various toxic components but also depended on engine operating conditions.