Integration of a Piston Expander for Exhaust Heat Recovery in a Long Haul Truck

Abstract

Nearly 30 percent of the fuel energy in an internal combustion engine is lost as waste heat in the form of hot exhaust gases. Nowadays it seems clear that the heavy duty manufacturers will implement bottoming Rankine cycles to recover the exhaust heat on their long haul trucks in the 2020s as an answer to future stringent regulations and the still increasing customer pressure for reductions in operating costs.

The Exoès Company has developed a swashplate expander working with ethanol or refrigerant vapors for Rankine cycles that would provide 3 to 5 % fuel economy on heavy duties. The design of a swashplate piston expander has been carried out. A prototype has been built as well as a test bench that can reproduce the hot source and cold sink available in a truck. The performance tests of the prototype took place in 2015. A refined 1D Matlab physical model has been coded and calibrated to point out the different efficiency losses. A first feedback loop improved the general prototype design to increase efficiency, lower the weight and better the packaging so that the prototype is ready to be integrated and tested in a demonstration truck.

In this paper, we present the expander technology, the test results, the expander model and its calibration. The performances of the expander will be assessed as well as the detailed losses repartition. The choices made for the integration in the vehicle will be detailed. To conclude the paper, a dynamic simulation on a driving cycle will explain how the expander optimization is done.

Nomenclature, Subscripts and Abbreviations

h

specific enthalpy [J.kg−1 ]

Ṁ

flow [kg/s]

P

pressure [bar]

s

specific entropy [ J.T−1.kg−1 ]

T

temperature [K]

$\dot{W}$

work [kW]

η

efficiency

$\rho$

density [kg.m3]

HCV

heavy commercial vehicle

OCR

Oil Circulating Rate (%mass)

ICE

internal combustion engine

RC

Rankine cycle

WHR

waste heat recovery

in

relative to the expander inlet

is

isentropic

out

relative to the expander outlet

oil

relative to lubricant