Fig。 1。   Reference  configuration  engine  scheme。

The objective of this first part of the paper is to evaluate the different  theoretical  bottoming  cycle  configurations  applied   as a waste heat recovery system。 The amount of heat dissipated by the cooling system of an installed engine represents a heat source in a bottoming cycle。 The two-stage HDD engine used on this study

is described in the experimental setup section。 The engine is tested in order to validate a model that reproduces real working condi- tions。 This model is used to calculate the waste heat sources。 The model will be also used to perform further studies with different combinations of turbocharger and bottoming cycle system in the second part of the paper。 In the study of the engine energy, all possible residual heat sources are analyzed separately considering their potential use in the different cycle configurations。 This aspect is the main uniqueness of the work。 To consider all possible sources of engine heat involves a highly complex work due to the variety of types of these sources。 The adjustment of the heat exchange between these sources and the Rankine cycle vaporizer implies many restrictions that must be considered thus adding difficulty to the study。 However, and due to the complexity of the final solution, the analysis of how all these heat sources can be used represents a study of possible maximum energy recovering (minimum external irreversibilities), which is the objective of this paper。

Finally, two basic engine configurations with bottoming cycles are compared to analyze the global efficiency increase of the engine。

2。Experimental setup and IC engine  model

The engine studied in this article is a 12 L two-stage HDD engine [12]。 Fig。 1 shows the scheme of the engine。 The selection of a two- stage engine for this work has been done in order to keep maximum dynamic capabilities of the resulting configuration once coupled with the bottoming cycle system; transients of this engine, without a bottoming cycle, have been experimentally analyzed in [12]。

The engine model has been fitted using experimental data at full load conditions with different engine speeds。 Some of these steady points are given in Table 1。

The steady point used in the present study is 1800 rpm with full load conditions。 The main reason for this selection is that this point has the highest available residual thermal sources。 Consequently, it is considered the ideal point to assess the maximum usable energy in the engine。

The 1D gas-dynamics code used to model the engine is devel- oped at “CMT-Motores Térmicos” and called OpenWAM™   [13,14]。

Fig。  2。   Energy  scheme  reference  engine configuration。

Table 2Residual  heat sources properties。

Mass flow (kg/s) Inlet temperature (○C) Outlet temperature (○ C) Cp

(kJ/kg K) Available heat (kW)

Intercooler 0。44 127 53 1。0 35

Aftercooler 0。44 172 49 1。0 57

Exhaust gas 0。45 330