# Analysis of Biodiesel Influence on Unregulated Gaseous Emissions of Diesel Motor Vehicles
## 3 Results and Discussion
### The Regulated Emissions  
The regulated emissions that are analyzed in this article include: HC, CO and NOx. The obtained results are shown in Figures 3-5.  
It is evident from the analysis presented in Figure 3 that combustion of the fuel with a portion of biodiesel reduces the HC emissions under all conditions due to the oxygen, which is contained in biodiesel; thus, it increases the fuel combustion efficiency [12].  
Figure 4: Experimental fuels and the CO emissions.  
Figure 3: Experimental fuels and the HC emissions.  
It can be stated, according to the measured data, that the profile of HC emissions reaches its maximum at the average engine speed of 1920 rpm in the case of medium engine loading and for both types of fuels (100% diesel fuel and biodiesel). However, it should be also mentioned that in the case of low engine loading levels and at the engine speed of 1280 rpm, the HC emissions increased with higher engine loading; thereby, the HC emissions were reduced at high engine loading levels and at the engine speed of 2560 rpm. A similar situation was also recorded at engine speeds of 1920 rpm and 1280 rpm. In this case, the HC emissions increased if the engine loading raised from 20% to 40%. Higher fuel consumption causes also a higher amount of HC emissions. At the same time, the rising engine loading generates increased temperatures of the burned gas in the cylinder as well as increased temperature of the exhaust gases. In this way, there is also a reduced volume of the unburned fuel components. The HC emissions are lower at higher engine speeds thanks to the improved oxidation of HC due to the high level of the exhaust gas temperatures.  
Analogous to the HC emissions, we can say that a higher amount of biodiesel reduces the CO emissions, according to Figure 4.  
It can be stated, according to the obtained results, that an increase in the CO emissions is essential in the operational modes 11 and 12, namely due to the higher value of the fuel/air ratio, which is necessary at a high engine loading level. At the same time, the CO emissions rise with the increasing engine speed. It is visible from Figure 4 that the addition of biodiesel to the standard diesel fuel causes an increase in \(\mathrm{NO_{X}}\) emissions. The generation of \(\mathrm{NO_{X}}\) emissions is a function of the local oxygen concentration, combustion temperature and ignition delay [10]. The engine operational mode has a significant influence on the combustion process temperature and thus it can significantly affect the amount of generated \(\mathrm{NO_{X}}\) emissions. A higher engine speed at lower engine loading reduces \(\mathrm{NO_{X}}\) emissions. On the other hand, higher engine loading requires a higher amount of the injected fuel, which causes higher combustion temperature and, finally, an increase in \(\mathrm{NO_{X}}\) emissions.  
Figure 6 illustrates the particulate matter (PM) emissions in the operational modes 3, 6, 7, 8, 12. The PM emissions are reduced in the case of a larger volume of biodiesel in the fuel mixture during the operational modes 6, 7, 8, 12. The reason for this reduction consists in the following factors: the absence of aromatic content in biodiesel and the presence of oxygen in biodiesel, which improves the oxidation of the carbon particles.  
Figure 5: Experimental fuels and the \(\mathrm{NO_{X}}\) emissions.  
The PM emissions increase with higher engine loading due to a larger amount of the injected fuel. Another relevant factor for the increase in PM emissions is the higher engine speed level, which causes a decrease in the volumetric efficiency [13]. The reduced volumetric efficiency means the higher AFR value, which leads to the production of PM emissions.