bsfc reduction (%)

this cycle, the heat absorbed by the R245fa in the beginning of  the

evaporation process is  the  heat  released  by the non-recirculated

Reference configurations 311 e 357 e

exhaust gases energy, the high temperature cycle condenser, intercooler, cooling water and the aftercooler, as shown in bottom graph in Fig。 7。 In this case, the heat sources have temperatures between 195 ○C and 80 ○C。 The evaporation temperature must be lower than the temperature of cooling water to allow heat transfer

between  this  heat  source  and  the  working  fluid  cycle。  Thus, as

C。 all heat sources:

water Rankine cycle

C。 all heat sources: binary cycle

C。 high temp。 heat sources: water Rankine cycle

342 10。0% 868 8。8%

370 19。0% 938 16。0%

357 14。7% 729 8。5%

shown in Fig。 7, evaporation temperature is fixed in 71 ○C in the R245fa cycle and this fluid enters in the expansion machine from saturated steam conditions。 The heat transfer of each source is represented in the temperature vs transferred heat diagram in the top right side of Fig。 7, showing the critical point (pinch-point) in the low temperature vaporizer (PP2)。 The design criteria used at PP2 is the same that was used at PP1。 The condensation tempera- ture in the low temperature cycle is fixed at 50 ○C to ensure the cooling of the condenser with the atmosphere at 40  ○C。

The binary cycle has a significant effect on the total power compared to the Reference engine system。 The binary cycle produces a mechanical power of 59 kW (35 kW in the Top Rankine Cycle plus 24 kW in the Bottom Organic Rankine Cycle)。 Clearly, 59 kW, which is about 19% of effective power, can be stated as an ideal figure since only external irreversibilities have been considered during binary cycle analysis。 In addition, as in the previous configuration, one of the problems is an important increase of the dissipated heat in the heat exchangers, since the heat transferred was increased to almost 170% by the two thermodynamic cycles。 (938 kW in binary cycle configuration vs 357 kW in the reference configuration)。

6。Configuration with high temperature heat sources

In the previous solutions, many heat sources with different temperature ranges have been considered。 That solution provided a considerable increase in total engine efficiency, but it must deal with important technical difficulties due to the heat control system of all the heat transfer processes and the low temperature of some sources。 Consequently, a configuration with only high temperature heat sources, therefore using less heat sources, has been also investigated in order to obtain a more realistic technical solution。 The EGR cooler, exhaust gases and aftercooler are the best suitable sources for recovering heat taking into account their high temperatures。 Different working fluids and different cycles have been studied using the maximum output power as a goal。 The result of these studies gives a water Rankine cycle as the best option, since it is possible to reach a superheat temperature of 500 ○C。

The same iterative-parametric study, done previously, has been carried out in this case, with the same objective as for the config- uration with all heat sources。 Fig。 8 shows the main variables of this parametric study。 The water cycle has been optimized and this cycle has a 143 ○C vaporization temperature, a superheating temperature up to 485 ○C and regeneration。 The condensation temperature is 50 ○C due to the heat transfer and the pinch-point criteria。 The right striped area indicates the Rankine cycles in which the expansion ratio is higher than  25。