Abstract
Even in nowadays engines which can reach 45% of efficiency a high amount of energy is released as heat to the ambient. The increase in oil prices compels manufacturers to focus on new solutions to improve fuel efficiency of truck powertrain such as Waste Heat Recovery Systems (WHRS). Over last few years a lot of studies have proven that there are a lot of hurdles (cooling margin, expansion machines, …) for a perfect match of such a system on a vehicle. The objective of this study is to define an optimal WHRS for a heavy duty vehicle. The results presented hereafter are obtained thanks to steady state modeling. Two kinds of simulations will be used for this study. Simple thermodynamic simulations for the comparison of several fluids then a more complex model will be presented in the second part. This part will be more focused on the expansion machine and Rankine cycle arrangement choice thanks to the evaluation of fuel economy for each concept. The fuel savings will be determined by reducing real driving cycle to a relevant number of steady state operating points weighting by their fraction of operating type over the cycle
In the first part a comparison of the net output power (Shaft Power minus Pump consumption) and the cycle efficiency is done for several fluids in order to choose the best one from a performance and environmental point of view. On the second part the fuel economy in percentage is evaluated for different concept in order to determine the best system architecture answering to our integration constraints (heat rejection, cold sink, packaging …). New or often forgiven constraints will be presented in this section. The optimization of a waste heat recovery system under vehicle constraint is rarely done. This analysis presents what are the limitations to take in account for having a perfect match between a Rankine cycle and a heavy duty vehicle.
This paper showed the importance of the application when designing WHRS. It yields to a better understanding when it comes to a vehicle integration of a Rankine cycle in a truck. The consideration of these limitations allow to maximize the WHRS output therefore of the fuel economy.
KEYWORDS Heat Recovery, Thermodynamic, Modeling, Trucks