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The article presents issues related to the assessment of concentrations of harmful substances in the exhaust gas cloud behind the vehicle. In the theoretical part, considerations about the harmfulness of exhaust gases and methods of detection of chemical compounds were made, and the issues of von Karman vortices and the Lambert-Beer law were referred to. The test object was a vehicle equipped with an SI engine meeting the Euro 3 standard. The drive unit had a capacity of 2.8 dm3, a rated power reaching 142 kW at 5500 rpm and a maximum torque of 280 Nm at 3500 rpm. The measurements of the dilution of the exhaust gas cloud behind the vehicle were made in stationary conditions (laboratory) and during actual operation in the Poznań agglomeration. In the research, technically advanced equipment from the PEMS group was used. In the analysis of the obtained results, detailed considerations were made regarding the influence of the location of the measuring probe in relation to the exhaust system. As can be seen from the obtained dependencies, the vehicle motion is favorable for the assessment of concentrations behind a moving object, because the ecological indicators at successive distances behind the exhaust system achieve better parameters in most points than in a stationary test.

The paper presents the investigations of exhaust emissions under actual operation of two rail vehicles: a track geometry vehicle and a clearance vehicle. The environmental assessment of this type of objects is difficult due to the necessity of adapting the measurement equipment and meeting the safety requirements during the tests (particularly regarding the distance from the overhead electrical lines). The authors have proposed and developed a unique research methodology, based on which a detailed exhaust emissions analysis (CO, HC, NOx, and PM) was carried out. The complex assessment included the unit and on-track exhaust emissions. In the analyses, the authors also included the operating conditions of the powertrains of the tested machinery. The obtained environmental indexes were referred to the homologation standards, according to which the vehicles were approved for operation. Due to the nature of operation of the tested vehicles, the authors carried out a comprehensive environmental assessment in the daily and annual approach as well as in the aspect of their operation as combined vehicles, which is a novel approach to the assessment of the environmental performance of this type of objects.

The exhaust emission standards in force in various parts of the world for off-road vehicles are becoming more and more stringent. Therefore, research on the compounds of harmful exhaust fumes emitted by vehicles of this category is constantly being researched and activities aimed at limiting them are constantly being carried out. The basic problem in terms of measuring exhaust emissions is the approval tests of traction vehicles, which are carried out on engine dynamome-ters. Therefore, it is impossible to obtain reliable results concerning their actual impact on the natural environment. It is therefore advisable to carry out the tests in real operation conditions, as is the case for road vehicles for which RDE (Real Driving Emissions) tests are carried out. The latest Stage V emission standards push for the introduction of this type of test, but no limit values for toxic exhaust gases have been established and no test guidelines have been defined for as-sessing actual emissions. This article describes the issues related to the legislative guidelines for non-road vehicles in force in Europe, as well as the measurement tools used, such as mobile equipment for measuring emissions of PEMS (Portable Emissions Measurement Systems) and newly developed emission gates.

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