Direct and Indirect Exhaust Heat Recovery from Turbocharged Heavy-Duty Engine

AW Abstract Waste Heat Recovery (WHR) is one of the most viable opportunities to reduce fuel consumption and CO2 emissions from internal combustion engines in the transportation sector. Hybrid thermal and electrical propulsion systems appear particularly interesting because of the presence of an electric battery that simplifies the management of the electrical energy produced by the recovery system. The different technologies proposed for WHR can be categorized into direct and indirect ones, if the working fluid operating inside the recovery system is the exhaust gas itself or a different one whose sequence of trans- formations follows a thermodynamic cycle. In this paper, a turbocharged diesel engine (F1C Iveco) equipped with a Variable Geometry Turbine (VGT) has been tested to assess the energy recoverable from the exhaust gases both for direct and indirect recovery. A direct technology based on an auxil- iary turbine placed in the exhaust pipe (turbo-compounding) has been considered and compared with an Organic Rankine cycle (ORC)-based recovery unit fed by the exhaust gases. ITntroduction he raising global awareness on climate change, and more in general, of environmental problems related to human behaviors, resource consumption and waste management, produced many international and national regulations and political commitments in order to reduce the anthropic pressure on the environment. The transportation sector is one of the most important since it involves the increasing need for people moving and freight supply. The transition path in this sector is not so easy to achieve, although very stringent directives have been set, like the ban on new gasoline and diesel engines by 2035, approved by the EU under the Green Deal package, with the purpose of decarbonizing transport [1]. However, it is still dominated by internal combustion engines (ICEs) fed by conventional fuels [2] and an eventual fast transition is out of the technological possibility. Averagely, the specific fuel consumption for a light-duty vehicle is about 6.7 L/100 km of A model-based comparison between the two technologies has been assessed in this paper. The input data were the result of an experimental campaign done on the exhaust gases of the F1C Iveco operated on a high-speed dynamometer test bench. Data on exhaust gas properties, turbocharger equi- librium and engine performances were collected for a wide range of engine operating conditions. Concerning the ORC-based power unit, the model uses the significant research experience done on the sector that set up the most relevant machine performances (expander and pump effi- ciency, engine backpressure produced, pinch points at the two heat exchangers) so giving the model high reliability. Preliminary data on a turbo-compounding system operated on the same engine were also measured so resolving the most important uncertainties of the recovery unit (engine back- pressure produced, turbine and electrical generator effi- ciency, matching between the turbocharging unit). A prelim- inary assessment of the overall potential recovery when both technologies were present has been done, focusing the attention on heavy-duty engines.