# Analysis of Biodiesel Influence on Unregulated Gaseous Emissions of Diesel Motor Vehicles
## 3 Results and Discussion
### The Unregulated Emissions  
The emissions of acetaldehyde and formaldehyde (Figures 7 and 8) grow with the increasing portion of biodiesel in the fuel mixture. This dependence is caused mainly due to the fact that short-chain chemicals, which are contained in the biodiesel produced from the home waste oil, are able to create the shortest carbonyl chain during the combustion process, i.e., acetaldehyde and formaldehyde [14].  
Figure 6: Experimental fuels and the PM emissions.  
Figure 7: Experimental fuels and the formaldehyde emissions.  
At the same time, the operational or working conditions also have a major impact on these emissions. An increase in formaldehydee emissions was recorded within the interval from low to middle engine loading level. A decrease in this kind of emissions was monitored in the range from middle to high engine loading level and for all the tested fuels, according to Figure 7, at the engine speed 1920 rpm. The developed trend concerning acetaldehyde emissions is very similar, as seen in Figure 8. A higher volume of carbonyl emissions in the case of low engine loading level is caused due to increased fuel consumption. A reduction in these emissions at high engine loading level is a positive consequence of the rising combustion temperature as well as the exhaust gas temperature. Higher engine speed reduces acetaldehyde and formaldehyde emissions thanks to higher combustion temperatures.  
The unsaturated alkenes, i.e., propene, ethene and 1,3-butadiene, are the chemical precursors of diesel soot. 1,3-butadiene is one of the most harmful substances that pollutes air with regard to its carcinogenic impact [15].  
It is possible to say, according to the measured results presented in Figures 9-11, that the emissions of 1,3-butadiene grow with the increasing amount of biodiesel.  
Emissions of the three above-described toxic substances are reduced in the case of increased engine loading, but their concentration rises during the operational modes 11 and 12 [16].  
Taking into consideration the emissions of benzene, xylene and toluene (BXT), a phenomenon that just the unburned fuel molecules generate these kind of gaseous emissions is observed. Table 5 documents the influence of biodiesel on the BXT emissions in the operational modes 5, 9 and 11 within the 13-regime experimental test cycle at the engine speed 1920 rpm. Benzene emissions grow when the content of biodiesel in the fuel is higher, whereby this relation is valid in the case of every engine loading level. However, the emissions of xylene and toluene are reduced if the volume of biodiesel is increased [16].  
Figure 8: Experimental fuels and the acetaldehyde emissions.  
The total amount of BXT emissions is based on the measured data and is summarized in Table 5. The global volume of BXT emissions is lower if the engine loading increases, at the engine speed of 1920 rpm, because the higher temperature of the combustion process (due to higher level of engine loading) improves the oxidation process of the BXT emissions. The analogous results were obtained using another two engine speed levels: 1280 rpm and 2560 rpm. However, no relevant influence of the engine speed on BXT emissions was monitored.  
Figure 10: Experimental fuels and the propene emissions.  
Figure 9: Experimental fuels and the 1,3-butadiene emissions.