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The test procedure for the pollutant emissions from light-duty vehicles is currently under verification carried out at the international level. For this purpose, GRPE (Groupe des rapporteurs sur la pollution et energie)-the body developing UNECE regulations proposals-has set up a task group WLTP (Worldwide harmonized Light vehicles Test Procedure) which is supposed to prepare a new GTR (Global Technical Regulation) relating to this procedure. The development of light-duty vehicles, leading to the reduction of pollutants emissions, caused the increase of the requirements for their test procedure. A large number of factors associated, inter alia, with the test equipment affects its accuracy, repeatability and reproducibility. In the ongoing analysis attention is paid even to factors, which affect test results in a relatively small way, and which have been overlooked yet. One of the problems to which attention is paid is the impact of pollutant concentration in the dilution air in the CVS (constant volume sampler) system on test results. The CVS principle is accepted as the standard method to determine light-duty vehicle exhaust emissions on chassis dynamometer test cells worldwide. It was introduced in the early 1970s. One of its drawbacks is that it introduces an error resulting from the fact that the contractual DF dilution factor, rather than the actual dilution ratio DR, is used for the correction of concentration measurement results. The article discusses this error for different type of engines used in light-duty vehicles and different pollutants subject to measurements.

Currently produced diesel engines of different manufacturers, used for the same applications, have comparable specific fuel consumption. Therefore, the laboratories measuring fuel consumption, especially in comparative tests, require the use of more accurate methods of measurement. The Environmental Protection Centre of Motor Transport Institute has recently implemented the fuel consumption measurement method using KMA Mobile flow meter produced by AVL company. This device allows to carry out measurements by both volumetric and mass method, thanks to builtin device for measuring the fuel density. Due to some customers requirements the laboratory began with preparations for obtaining accreditation of the Polish Centre of Accreditation for the procedure of measuring fuel consumption by volumetric and mass method. One of the requirements of the Polish Centre for Accreditation is carrying out the validation of the new method. It can be done by comparing the results obtained with new method with the results of the method already validated. The validated method is described in the regulation. This is the carbon balance method described in UN-ECE Regulations No. 101. The calculation of fuel consumption according to this method is based on a measurement of pollutants emissions of carbon dioxide (CO2), carbon monoxide (CO) and hydrocarbons (THC). This paper describes the fuel consumptions measuring procedure using two methods: mass method using a AVL KMA Mobile flow meter and carbon balance method using the AVL AMA i60 analyzers. To verify measurement results additionally there was fuel consumption measured with using a scale, as a difference of the external fuel tank mass change, from which the vehicle was fuelled during the tests

Operation of vehicles equipped with combustion engines is a source of pollution. That is why the emissions from this source are restricted. The emissions reduction system consists of several steps, whose basic component is a typeapproval of vehicle in terms of emissions level and admission to the registration of vehicles that meets the requirements for emissions. It is assumed, that the gradual reduction of emissions limits will improve the emission properties of the vehicles, and gradual withdrawal of used vehicles, will reduce of emissions growth. The basis for issuing opinions on a vehicle's exhaust emissions is the measurement of emissions performed in the laboratory on a chassis dynamometer in reproducible conditions of preparing the vehicle for testing, test replication, fuel for the engine, and the procedure for collecting the exhaust gas analysis. Motor Transport Institute conducts the type approval tests, as well as the research on emissions from vehicles in the real traffic conditions, which are used to determine the actual emission from the vehicle population. Emission tests for applications, that go beyond the application of type approval show, that there are vehicles whose emissions in operation is substantially different from the emissions measured during type approval. It is a natural phenomenon in the case of used vehicles and vehicles with engine malfunctions or exhaust aftertreatment system defect. However, there are vehicles whose emissions under specific operating traffic conditions are significantly different from the values obtained in the course of type approval tests, despite the good properties of emission measured under the conditions provided by the type-approval procedure. The article discusses the results of the emissions from vehicles, obtained in the tests used to determine the emission factors for vehicles used in real traffic conditions, thus taking into account emissions from vehicles, made under different conditions than the type approval tests, which show that, in terms of driving cycles, which are not covered by the emission test procedure, can multiply and exceed the approved values.. This is particularly true for modern diesel engines.