## 4 Results and Discussion
If considering the lower heating value of the fuels, the energy released per cycle is higher when using B20 than using diesel fuel for R1 and lower for R2, which involves a longer combustion duration for R1 and a shorter one for R2. Concerning the influence of the rate of injection shape on combustion duration, comparable results have been reported in [14; 18; 20] when using diesel fuel. Figure 6: Initial combustion phase variation by different shapes of ROI. Figure 7: Combustion duration variation by different shapes of ROI. In Figure 8 are displayed the values of peak in-cylinder temperature versus the ROI shape. The maximum values are obtained for the TR1 shape with an increase of 7% for diesel fuel, 6.7% for B20 on R1 and, respectively, 7.6% for diesel fuel, 6.2% for B20 on R2 relative to the reference TH shape. The minimum values are reached for the reference shape that was used for the model calibration. The shapes which promote the premixed combustion determine higher peak in-cylinder temperatures contrary to the TH and BO2 shapes, which develop the diffusive combustion. The values obtained when using diesel fuel are constantly greater than those achieved when using B20 due to the lower heating value, which is higher for diesel fuel than for B20 (41.87 MJ/kg compared to 40.59 MJ/kg). Similar results regarding the influence of the rate of injection shape on the peak in-cylinder temperature when using diesel fuel were reported in [14; 15; 22]. Figure 9 shows the dependence of peak in-cylinder pressure values on the ROI shape. The minimum values are reached for the BO2 shape with decreases of 3.1% for both fuels on the R1 operating condition, respectively 8.6% for diesel fuel and 5% for B20 on R2 because most of the fuel is late injected, at the beginning of the expansion stroke. For the R1 condition, the highest values are obtained with the RT shape presenting increases of  
Figure 8: Peak in-cylinder temperature variation by different shapes of ROI. Figure 9: Peak in-cylinder pressure variation by different shapes of ROI. 16.3% for diesel fuel and 16.5% for B20. For the R2 condition, such maximal values are obtained with the TR1 shape showing increases of 14.5% for diesel fuel and 16.6% for B20. The maximum values are reached for these shapes, because the fuel amount is rapidly injected at the end of the compression stroke compared to the other shapes. Comparable results on the peak in-cylinder pressure for diesel fuel were reported in [7; 15; 18; 20; 21; 23] for biodiesel usage. The increase in thermal efficiency when using triangular shapes is also reported in [18]. It is known that the peak in-cylinder pressure rise rate has a strong influence on the engine noise. Figure 10 exhibits the values of this parameter relative to the ROI shape. For the same reason mentioned in the comments of Figure 9, the minimum values of peak pressure rise rate are obtained by using the BO2 shape with reductions of 38.4% for diesel fuel and 39.2% for B20 on the R1 condition, respectively of 42.7% for diesel fuel and 42.4% for B20 on the R2 condition. The maximum values are achieved on the R1 when using the RT shape displaying increases of 50.8% for diesel fuel and 48.6% for B20, while on the R2 by using the BO1 shape, the increases are 49% for diesel fuel and, respectively, 51.2% for B20. Similar conclusions regarding the influence of the rate of injection shape on peak pressure rise rate when using diesel fuel were reported in [18]. It was emphasized that triangular rate-shape injections give higher in-cylinder pressure rise rates as compared to ramp rate-shape injections and, furthermore, the injection rate shaping causes combustion phasing to occur. In Figure 11 are displayed the values of brake power versus the ROI shape. It can be noticed that, for the R1 operating condition, all the triangular shapes offer maximum performance in respect to the reference TH shape with an average increase of 3% for diesel fuel and B20.