EGR cooler 0。20 509 222 1。1 66

Cooling water 9。80 85 80 4。1 205

Total 517

The model calculates the engine behaviour solving the unsteady equations of mass, momentum and energy conservation by means of finite differences scheme [15] in the ducts and a filling and emptying model in the cylinders [16,17]。 The resolution scheme used in this model is a two step Lax & Wendroff scheme。 The heat transfer model is developed from [18,19] and fully described in [20]。 The friction model is described in  [14]。论文网

In addition, OpenWAM™ is able to reproduce the turbocharger performance based on the measured characteristics of the turbo- charger。 It is also capable of extrapolating operating conditions that differ from those included in the turbine maps, since the engines usually work within these points   [21,22]。

Recovery Energy (kW)

Fig。 3。 Schematic representation of waste heat temperature and working fluid temperature for a  typical  heat  recovery system。

R245fa Output Power (kW) R245fa Efficiency Cycle ( )

Evaporation Temperature (ºC)

Fig。 4。 Plots of output power and cycle efficiency varying evaporator and superheater temperature (condensation temperature 50 ○ C)。

Table 3

Cycle factor of optimum point for each working fluid considered。

The heat exchangers model is equivalent to that of two cham- bers and a pipe bundle in-between [23,24] where the air is cooled by a coolant fluid。

A 5% minimum error range in all parameters has been used to fit the engine model to the measured data in the investigated oper- ating points。

3。Study of the engine waste energy sources

The selected engine steady point has been modelled with OpenWAM™ to study the possible waste heat sources in the engine。 Afterwards, in order to analyze these waste heat sources, their fluid mass flows, temperatures, specific heats, and powers obtained by this model have been selected as input variables in the study of the engine waste energy sources。 The main waste heat sources are:

Fig。 5。 (Top) Temperature heat sources vs transferred heat in a single cycle with all the waste heat sources。 (Bottom) Energy scheme with the highest power output configuration。

-The exhaust gas heat energy。

-The EGR cooler。

-The intercooler, where the Low Pressure compressor outlet air is cooled。

-The aftercooler, where the High Pressure compressor outlet air is cooled also。

-Engine block cooling  water。

Fig。 2 shows the engine energy flows from the combustion of fuel to the dissipation of the waste heat sources to the atmosphere at 40 ○C。 Table 2 details the values of mass flow, temperature, specific heat and power in these sources。

The main difficulty when using these energy sources in Rankine cycles is their low temperature。 Rankine cycle efficiency depends on the heat source temperature value: the higher the source temperature, the better the efficiency of the Rankine cycle。 Exergy studies of Diesel engines analyze this phenomenon; however, the present work does not cover this topic as they have already been published  in previous  works [25e27]。