Measurement of car engines exhaust pollutants emissions is very important because of their harmful effects on the environment. This article presents the assessment of repeatability of the passenger car engine exhaust pollutants emission research results obtained in the conditions of a chassis dynamometer. The research was conducted in a climate chamber, enabling the temperature conditions to be determined from − 20 to + 30 °C. The emission of CO, CH₄, CO₂, NO_X, THC, and NMHC was subjected to the analysis. The aim of the research is to draw attention to the accuracy of the pollutant emission research results in driving cycles, and the comparison of pollutant emission results and their repeatability obtained in successive NEDC cycles under cold and hot start conditions. The results of the analysis show that, in the case of a small number of measurements, the results repeatability analysis is necessary for a proper interpretation of the pollutant emission results on the basis of the mean value. According to the authors’ judgment, it is beneficial to determine the coefficient of variation for a more complete assessment of exhaust emission result repeatability obtained from a small number of measurements. This parameter is rarely presented by the authors of papers on exhaust components emission research.

Road transport is the main source of pollution to the environment in urban areas; therefore, there is a need to accurately estimate the amount of exhaust gases emitted by motor vehicles. The development of systems for measuring emissions of exhaust gases caused the exit from stationary chassis dynamometers to real road test. This paper presents an analysis of emission data from the PEMS system for real driving cycles of various types of vehicles, complying with EURO2-EURO6 standards, fueled with petrol, LPG, and diesel in urban, rural, and motorway areas as well as detailing roundabouts. The results show that in the range of roundabouts, there is an increased emission of harmful exhaust components, such as CO₂, THC, CO, and NOx. Due to the specific traffic conditions that prevail at the roundabout (acceleration, braking, acceleration to a certain speed), the methodology for creating an exhaust emission model for this type of objects has been proposed. Statistical analysis of the received boosted regression tree models based on the coefficient of regression, root mean square error, and mean absolute error and based on the visual assessment of the results show that the obtained models are well represented by real data. The obtained results of emission calculations on roundabouts may be used to identify areas of increased emission of harmful exhaust components, as well as an introduction to prepare new roundabout design guidelines concerning emission data.

The problem of global warming and the related climate change requires solutions to reduce greenhouse gas emissions, in particular CO₂. As a result, newly manufactured cars consume less fuel and emit lower amounts of CO₂. In terms of exhaust emissions and fuel consumption, old cars are significantly inferior to the more recent models. In Poland, for instance, the average age of passenger cars is approximately 13 years. Therefore, apart from developing new solutions in the cars produced today, it is important to focus on measures that enable the reduction in CO₂ emissions in older vehicles. These methods include the adaptation of used cars to run on gaseous fuels. Natural gas is a hydrocarbon fuel that is particularly preferred in terms of CO₂ emissions. The article presents the results of research of carbon oxides emission (CO, CO₂) in the exhaust gas of a passenger car fueled by petrol and natural gas. The emissions were measured under the conditions of the New European Driving Cycle (NEDC) test and in real road tests. The test results confirm that compared to petrol, a CNG vehicle allows for a significant reduction in CO₂ and CO emissions in a car that is several years old, especially in urban traffic conditions.

Until now, passenger cars before getting permission to sell were tested in the laboratory conditions in order to determine the amount of harmful gas compounds emission and average fuel consumption. However, studies have shown that, during real driving, emission results significantly differ from those obtained in the laboratory. For this purpose, in the European Union was created a new procedure for conducting of driving cycle WLTP (World Harmonized Light-Duty Procedure) taking into account road test (Real-Driving Emissions, RDE). The article presents selected results of pollutant emissions research using the HORIBA OBS 2200 road analysis system. The results show that emission in real traffic conditions can lead to exceeding vehicle emission standards. The largest exceeded emission limits occurred for the urban and motorway parts, while the smallest ones for the rural part. In relation to EURO 5, the limits for THC (exceeding by 9%) and CO (exceeding by 49%) were not included in the emission limit.

Among the fundamental factors affecting the emissions of internal combustion engines is the resistance to motion acting on the car. This is an important factor to be taken into account when testing cars in conditions simulated on a chassis dynamometer. The dependence of the driving resistance function on vehicle speed is determined on the basis of various methods, the most frequently used of which is the so-called alternative method specified in procedures for the type approval of motor vehicles with respect to the emission of pollutants in exhaust gases. The values adopted in accordance with the alternative method differ from the actual resistance acting on the car in road conditions. This is one of the reasons why the emission of pollutants and the fuel consumption of an engine in real road conditions differs from the values given by the car manufacturer, including the emission limits specified in the standards. This paper presents an evaluation of the influence of driving resistance on the energy demand and emission of pollutants in the exhaust gases by sample passenger car with SI engine fuelled by petrol and LPG.