To further reduce fuel consumption and CO2 emissions of heavy-duty
vehicles, recovering waste heat from the engine’s exhaust gases is a promising
method. By means of an Organic Rankine Cycle (ORC), the thermal energy of the
exhaust gases is converted into useable energy to support the powertrain. The
integration of such a waste heat recovery (WHR) system into the powertrain as
well as the transient operation presents several challenges: The interactions
between the WHR system and the powertrain have to be analyzed, and their effect
on fuel consumption has to be quantified in order to provide reliable
fuel-saving potentials.
In this article, a co-simulation model that couples the cooling system, the
combustion engine, the vehicle’s longitudinal dynamics including the control
system, and the WHR system is presented. The latter uses a turbine generator to
supply electrical energy to a 48 V board net connected to an electric motor that
is used to both support the powertrain and to recuperate the brake energy (mild
hybrid concept).
The presented study uses three route profiles for the detailed investigation of
the ORC’s efficiencies, the comparison of two mild hybrid control strategies,
and the optimization of both the 48 V battery capacity and the electrical engine
power. Furthermore, the effect of the increased counter-pressure in the
combustion engine’s exhaust path and the additional cooling load caused by the
ORC’s condenser are analyzed. A 3% to 4% of fuel-saving potential is possible
with the presented WHR system, depending on the ambient temperature, the total
vehicle weight, and the route profile.
