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Figure 1. Test bed setup using vehicle frame.

Optimizing waste heat recovery for long-haul trucks

A waste heat recovery (WHR) system for a long-haul truck application was examined via simulation, test bench, and public road vehicle testing as part of a joint project between CNH Industrial and AVL, with the goal of developing a cost-effective mechanical WHR system for an Iveco Stralis Euro VI truck. The WHR system uses exhaust recuperation only and employs up to 110 kW of exhaust waste heat for the organic Rankine cycle (ORC) in a typical European driving cycle.

For on-road truck application, several waste heat sources were available for the ORC at different temperature levels. Based on thermodynamic calculations, production costs, and complexity, along with total cost of ownership evaluation, the decision was made to focus on the high-temperature sources from the vehicle cooling system for the ORC. This enabled a high overall ORC efficiency with a minimum number of heat exchangers.

Based on the temperature levels available in the long-haul truck application and component availability, ethanol was considered to be the best choice for operating fluid due to the highest power output enabling the highest overall efficiency of the complete combustion engine and WHR system. Selection of the EGR (exhaust gas recirculation) heat source was evaluated in terms of costs and benefits, as well as diagnostics implications and safety aspects. For the public road testing efforts beginning in 2015, the use of exhaust heat recuperation only was chosen.

The Euro VI Cursor II engine from FPT was selected for testing. The combustion engine and all the WHR components were instrumented and integrated on an Iveco Stralis vehicle frame to conduct test bench activities. The test bed setup of the WHR system is shown in Figure 1. After initial operation and controller optimization, the complete system was optimized for stationary and transient operation, focusing on typical European real-life driving cycles.

After successfully optimizing the WHR system on the test bed, the WHR system was integrated in the vehicle, as depicted in Figure 2. Vehicle tests were performed on public roads in Austria with the target of testing and calibrating the WHR system for a wide range of relevant operating conditions.

Simulation models supported the WHR development throughout the project, from the paper phase until final testing on the public roads. They provided useful input for working fluid selection, component sizing, control strategies development, and prediction of fuel consumption results under several operating conditions.

The vehicle testing and simulation showed the following results:

• 2.5% BSFC reduction for a European real-life cycle with 108 kW

• 3.1% BSFC reduction for a U.S. real-life cycle with 143 kW

• 3.4% BSFC reduction for a RMC with 182 kW

• Up to 6.5 g/kW·h BSFC reduction in the engine map.

All results were obtained with WHR prototype stage 2015 parts. The 3.4% brake specific fuel consumption (BSFC) reduction for the ramped-modal cycle (RMC) fits well to the EPA technology assessment claiming a 3.6% fuel consumption reduction potential for WHR in 2020.

Up to 3.5% BSFC reduction for the European real-life cycle is assumed as the parts mature toward series production. With this assumption, a BSFC reduction above 4% is expected for the higher powered U.S. cycles.

The research also included a possible technology roadmap containing WHR as a central part to achieve a future CARB BSFC target value of approximately 172 g/kW·h. WHR combined with other thermodynamics measures—including advanced turbocharger technologies, alternative EGR concepts, optimal compact combustion along with friction optimization—can possibly make this happen.

This article is based on SAE technical paper 2016-01-8057 authored by Michael Glensvig, Heimo Schreier, Mauro Tizianel, and Helmut Theissl of AVL List GmbH; Peter Krähenbühl and Fabio Cococcetta of FPT Motorenforschung AG; and Ivan Calaon of Iveco. The paper will be presented at the 2016 SAE Commercial Vehicle Engineering Congress.

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