Performance Analysis of Volumetric Expanders in Heavy-Duty Truck Waste Heat Recovery 2019-01-2266
With increasing demands to reduce fuel consumption and CO2 emissions, it is necessary to recover waste heat from modern Heavy Duty (HD) truck engines. Organic Rankine Cycle (ORC) has been acknowledged as one of the most effective systems for Waste Heat Recovery (WHR) due to its simplicity, reliability and improved overall efficiency. The expander and working fluid used in ORC WHR greatly impact the overall performance of an integrated engine and WHR system. This paper presents the effects of volumetric expanders on the ORC WHR system of a long haulage HD truck engine at a steady-state engine operating point chosen from a real-time road data. Performance of a long haulage HD truck engine is analyzed, based on the choice of three volumetric expanders for its WHR system, using their actual performance values. The expanders are: an oil-free open-drive scroll, a hermetic scroll and an axial piston expander with working fluids R123, R245fa and ethanol, respectively. Performance of the engine that accommodates the WHR system, with each expander and working fluid combination, is assessed based on the overall system efficiency that can be achieved through heat recovery from the engine exhaust. This simulation study is carried out using validated 0D models of the scroll expanders and performance data of the piston expander, adopted from literature, and a 1D system model of a long haulage HD truck engine encompassing a WHR system. Under the given conditions, the open-drive scroll expander (R123) leads to a higher system efficiency of 6.3% at an optimum expander speed of 3400 rpm with an estimated fuel saving of 3.6% in the vehicle under study. The hermetic scroll expander (R245fa) exhibits potential performance at higher rotational speeds; it leads to 5.4% system efficiency at 5000 rpm and 3% fuel-saving. The axial piston expander (ethanol) results in a consistent performance over a wide range of expander speeds. The effect of sizing a volumetric expander in improving the overall system efficiency is also investigated. This study provides insights on the suitability of volumetric expanders in HD truck WHR.