**3. Results and Discussion**

### *3.1. Influence of Various Fuel Mixtures on Output Characteristics*

The average values of the measured data for various fuel mixtures are given on Figures 2–7. More than 100 measuring cycles were performed in order to reduce in this way an influence of random changes during the experiment [24–26]. It is visible from Figures 4 and 7 that the value of pressure inside the cylinder decreased with higher engine operational loading in the case of increasing proportion of biodiesel in the experimental fuel. The curves, which describe the intensity of heat generation, are various in the operational regime utilizing the ULSDF and the biodiesel fuel mixture. The pressure value inside the cylinder grew more rapidly for the fuel mixture biodiesel–ULSDF compared to the clean ULSDF. The cetane number that belonged to the biodiesel and also the value of flame speed were higher in comparison with ULSDF. The speed of heat release was reduced with the increasing amount of biodiesel in the tested fuel mixtures and the ignition delay decreased if the volume of the biodiesel in the tested fuel was higher.

**Figure 2.** The dependence of fuels on the heat release rate and cylinder pressure (1000 rpm/30%).

**Figure 3.** The dependence of fuels on the heat release rate and cylinder pressure (1000 rpm/60%).

**Figure 4.** The dependence of fuels on the heat release rate and cylinder pressure (1000 rpm/90%).

**Figure 5.** The dependence of fuels on the heat release rate and cylinder pressure (1500 rpm/30%).

**Figure 6.** The dependence of fuels on the heat release rate and cylinder pressure (1500 rpm/60%).

**Figure 7.** The dependence of fuels on the heat release rate and cylinder pressure (1500 rpm/90%).

### *3.2. Influence of Fuel Mixture Compositions on NOX Emissions*

The NOX emissions, which belong among the most polluting substances, consist of the following components: the nitric oxide (NO), the nitrogen dioxide (NO2) and the dinitrogen monoxide (N2O). The most relevant are the NO emissions, because their amount is more than 60 percent. The portion of the NO2 emissions is less than 40 percent and volume of the N2O is negligible. It is evident, from the Figures 8 and 9, that a higher amount of biodiesel in the fuel mixture significantly affects formation of the NOX pollutants. Higher content of biodiesel in the tested fuel mixtures minimized the NOX emissions. It is possible to mention a fact as an illustrative example that operation of the tested engine in the ULSDF fuel mode at low engine speed and low operational loading generated approximately 145 ppm of the NOX gaseous emissions, whereby in the case of pure biodiesel it was only 100 ppm (Figure 8).

**Figure 8.** The dependence of testing fuels on the NOX emissions (1000 rpm).

**Figure 9.** The dependence of testing fuels on the NOX emissions (1500 rpm).

Higher levels of the engine operational loading and engine speed caused an increased amount of the NOX emissions in the case of all testing fuels. (i.e. up to 850 ppm for ULSDF and 750 ppm for biodiesel) (Figure 9). At the same time, the exhaust gas temperature increased with higher engine speed values and with higher engine operational loading. This fact had a major impact on growth of the NOX emissions.

### *3.3. Influence of Fuel Mixture Compositions on NO Emissions and NO2 Emissions*

The Figures 10 and 11 illustrate the influence of various fuel mixtures on the NO emissions and NO2 emissions. It is interesting that as the engine load increased, the volume of the NO emissions was higher. At the same time, however, these emissions were minimized with increasing amount of biodiesel in the tested fuels. Higher engine loading and higher portions of biodiesel in the tested fuel mixtures minimized the gaseous NO2 emissions.

**Figure 10.** The dependence of testing fuels on the NO emissions (1500 rpm).

**Figure 11.** The dependence of testing fuels on the NO2 emissions (1500 rpm).
