## 5 Results and Discussion  
Table 2 lists the statistical characteristics of the investigated processes. The largest coefficient of variation was found for engine control and vehicle velocity and fuel consumption mass intensity. The smallest coefficient of variation was found for nitrogen oxides and carbon monoxide emission intensities and the particle number intensity. The ratio of the range to the standard deviation was definitely largest for particle number intensity, carbon monoxide emission intensity and engine control, as well as for nitrogen oxides and hydrocarbon emission intensity. The largest kurtosis values were observed for emission intensity of hydrocarbons as well as particle number intensity. The smallest negative kurtosis occurred for torque, engine rotational speed and vehicle velocity. Processes with positive kurtosis had leptokurtic distributions, while those with negative kurtosis had platykurtic distributions [27]. The largest skewness was found for particle number intensity, and the smallest was found for relative torque. The distributions of all the investigated processes were right-sided asymmetric [27]. Table 3 presents the linear correlation coefficients between the standardized processes investigated in this study. The strongest correlation was found, understandably, between relative torque and relative useful power, as well as between engine rotational speed and relative useful power (these values had a linear relation). There was a strong correlation between rotational speed and torque and between carbon dioxide emission intensity and fuel consumption mass intensity. There was also a strong correlation, which is also justified, between engine control and relative torque and relative useful power. A strong correlation was also found between emission intensities of hydrocarbons and carbon dioxide, as well as nitrogen oxides. The smallest correlation coefficient values were observed for processes such as particle number intensity and the other processes investigated. In the case of engine control and relative torque and relative useful power, the values of the correlation coefficient with the process of particle number intensity were found to be negative. The correlation coefficient was also negative for the rotational speed and carbon monoxide emission intensity. The interpretation of the results of correlation studies between processes is not always simple and unambiguous. The effect of increasing engine control is an increase in the fuel dose to the cylinders and, consequently, in torque and effective power. An increase in the fuel dose is accompanied by an increase in the size of solid particles, and although the emission of solid particles (i.e., mass) increases, the number of solid particles (i.e., quantity) decreases. Figure 5 shows the probability density of the standardized processes representing engine operating states. For the vehicle velocity process, small values are expected to occur the most frequently. The probability density for engine control and for rotational speed, torque and effective power was distinctly different. The maximum probability density value for engine control occurred for medium values, while for engine rotational speed, torque and effective power the maximum of the probability density occurred for small values. Relatively large values of engine control resulted from frequent acceleration of the vehicle in the test, while at a low driving velocity and during braking there were low values of engine rotational speed, torque and effective power. Figure 6 shows the probability density of the standardized processes representing the emission intensity of the selected pollutants: carbon monoxide, carbon dioxide, nitrogen oxides and hydrocarbons, as well as particle number intensity and fuel consumption mass intensity. In the case of the exhaust emission intensity values, the particle number intensity and the fuel consumption mass intensity, the occurrence of probability density maxima for small values was noted, as expected.