## 8 Results and Discussion  
In this section the results from the ORC simulations are presented, analyzing how efficiently the integrated system operated and where room for improvement could be identified. Lastly, the exact figures of the vehicle's fuel consumption are shown, respectively, for each of the three different driving cycles and constitute the deciding factor for the selection of the optimum hybrid profile for the integrated powertrain. Several aspects that control the efficiency of the ORC system and how this system is combined with the IC engine to provide more power to the wheels are analyzed in this section. It is worth stating at this stage that the global assumptions considered for the ORC configuration of the HEV powertrain, namely, that even though the backpressure caused by the ORC's evaporator placed in the exhaust pipe, and also all of the extra weight imposed by ORC components to the vehicle system, deteriorate the overall performance and the fuel consumption of the vehicle to some extent. In this early evaluation study of ORC WHR systems for HEVs, it has been assumed that the effects of these are negligible, but should be borne in mind by the reader when considering the results. The main target set for the results of the ORC analysis is that the maximum efficiency of the turbine and the pump does not have a percentage difference of higher than 15%. Moreover, the power output of the turbine is critical, as it is added to the power output of the IC engine to provide the total power of the powertrain, so it is required to be as high as possible. Another parameter that is tested in this analysis is the pressure rise in the pump which indicates the degree to which the pump ensures the successful provision of the required pressure level throughout the entire cycle. Finally, this section concludes with the presentation of the new BSFC map of the upgraded powertrain (with ORC). The distribution of the turbine and pump efficiency is illustrated in Figure 5a,b, respectively, over the tested engine load and speed range. In the figures it can be observed how the efficiencies of these two components fluctuate with engine speed and the BMEP, as well as how the contours of constant efficiency are formed inside the plot. The maximum value of turbine efficiency is 61% and it is obtained at part-load, while the maximum efficiency of the pump is 72% at higher BMEP values and engine speeds. Great effort was expended to reach the highest efficiencies of these two components and resulted in an efficiency improvement of almost 10% from the initial model. Figure 5c represents the allocation of the turbine power output over the tested range of engine loads and speeds. It can be observed that the maximum power is obtained at full load and high engine speeds because the exhaust gases have greater temperature and mass flow at these speeds. The plot shows that the maximum power output that the turbine produces is almost 5 kW at high engine speed and load. At part-load (around the median of 6 bar) and lower engine speeds the turbine can produce typical values of around 2.5 kW. These values may seem small at first sight, but they proved to be high enough to cause a decrease in BSFC of almost 7% under the same operating conditions. Figure 5: Schematic view of the engine system model in GT-Power code: (**a**) turbine efficiency distribution; (**b**) pump efficiency distribution; (**c**) turbine power distribution; (**d**) EVAPORATOR energy rate; (**e**) Pump pressure rise; (**f**) BSFC percentage reduction distribution; (**g**) ORC efficiency distribution; and (**h**) fuel consumption per driving cycle. Figure 5d,e provides information about the evaporator energy rate and the pump pressure rise, respectively. Figure 5f illustrates the BSFC reduction contour plot superimposed on the engine map. It can be interpreted from the plot that the BSFC percentage reduction differs for different engine loads and speeds with the maximum values of the reduction being obtained at the lower BMEP values, reaching a maximum 12% decrease.