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10:30   Session 6A: Automotive Chair: Christos Markides 10:30 20 mins Cost to benefit ratio of an exhaust heat recovery system on a long haul truck Rémi Daccord 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, together with its partners, developed a demonstration truck to prove the fuel savings achieved by such a technology. After a feasibility study, it has been chosen to use a mixture based on ethanol as a working fluid, as it has successfully passed through the criteria of performances, friendly to environment, compatible with materials (corrosion under control) and easy accommodation into the truck (safety and space requirements). The Exoès piston expander has been integrated on the engine power-take-off to inject torque on the truck driveline. After a period of test in an engine test cell, the system has been mounted on a real truck and driven on test tracks and open roads. A final fuel saving assessment was carried out on a roller test bench. In this paper, we detail the ORC system business case in order to conclude on the potential of this technology to be implemented in mass production. 10:50 20 mins Thermodynamic potential of Rankine and flash cycles for waste heat recovery in a heavy duty diesel engine Jelmer Rijpkema, Karin Munch, Sven Andersson Abstract: In heavy duty Diesel engines more than 50% of the fuel energy is not converted to brake power, but is lost as heat. One promising way to recapture a portion of this heat and convert it to power is by using thermodynamic power cycles. Using the heavy duty Diesel engine as the waste heat source, this paper evaluates and compares the thermodynamic potential of different working fluids in four power cycles: the Rankine cycle (RC), the transcritical Rankine cycle (TRC), the trilateral flash cycle (TFC) and the single flash cycle (SFC). To establish the heat input into the cycle, operating conditions from an actual heavy duty Diesel engine are used as boundary conditions for the cycle heat source. A GT-Power model of the engine was previously developed and experimentally validated for the stationary points in the European Stationary Cycle (ESC). An energy analysis of this engine revealed that it has four heat sources with the potential for waste heat recovery: the charge air cooler (CAC), the coolant flow, the exhaust gas recirculation cooler (EGRC), and the exhaust flow. Using fixed heat input conditions determined by the selected engine operating mode, the TFC performed best for the CAC with a net power increase of around 2 kW, while the RC performed best for the coolant flow, with a net power increase of 5 kW. For the EGRC, ethanol performed especially well with both the RC and TRC, leading to an 8 kW net power increase. When using the exhaust as heat source, all four cycles provided a power output of around 5 kW with some variation depending on the working fluid. This study shows that for most cases, considering the different heat sources, the choice of cycle has a larger impact on the cycle performance than the choice of working fluid. 11:10 20 mins Feasibility study of ice bottoming ORC with water/eg mixture as working fluid Davide Ziviani, Donghun Kim, Swami N. Subramanian, James E. Braun, Eckhard Groll Abstract: To achieve the U.S. Department of Energy’s brake thermal efficiency (BTE) goal for Heavy Duty Diesel Engine (HDDE) technologies, Waste Heat Recovery (WHR) by means of Organic Rankine Cycle (ORC) systems has been selected as a suitable solution. The current relatively high return on investment period of such technology needs to be improved by significant cost reductions to realize benefits on WHR for mobile applications. The performance of the ORC system under dynamic loads relies on the choice of the working fluid, the efficiency of its components (mainly expander) as well as the control strategy that optimizes the operation. A novel ORC architecture is proposed that uses the engine coolant as the working fluid. A fraction of the liquid phase engine coolant, i.e., mixture of water and ethylene glycol, is employed as working fluid through the ORC to recover waste heat from EGR (Exhaust Gas Recirculation) and part of the tail pipe exhaust gases. At the inlet of the expander, the mixture has mixed-phase conditions and a fixed volume ratio expander is employed to generate power output that can be fed directly to the engine crankshaft. Heat rejection is accomplished through the spare capacity of the engine radiator, which avoids the need for a separate condenser. To evaluate the feasibility of such system architecture, a thermodynamic steady-state cycle model has been developed to predict the potential increase of BTE under different engine loads as well as to understand the ORC performance. Parametric studies are carried out by varying the system pressure ratio, the internal volume ratio of the expander and the mixture quality at the expander inlet. Furthermore, a comparison with alternative working fluids is also presented. 11:30 20 mins Performances of an ORC power unit for waste heat recovery on heavy duty engine Davide Di Battista, Federica Bettoja, Roberto Cipollone Abstract: Reciprocating internal combustion engines (ICE) are still the most used in the sector of the on-the-road transportation, both for passengers and freight. CO2 reduction is the actual technological driver, considering the worldwide greenhouse reduction targets committed by most governments. In the near future (2020) these targets will have a significant reduction with respect to the today’s goals pushing the research towards more effective technologies. In ICE more than one third of the fuel energy used is rejected to the environment as thermal waste through the exhaust gases. Therefore, a greater fuel economy could be achieved, if this energy was recovered and converted into useful mechanical or electrical power. For heavy duty vehicles, which run for hundreds of thousands miles at relatively steady conditions, this recovery appears very worthy of attention. In this paper, an ORC-based power unit was tested on a heavy duty diesel engine. Firstly, experimental data has been treated in order to assess key differences between theoretical predictions and measured performances. Energetic and exergetic analyses has been carried out in order to assess the real performances of the ORC unit. The most critical aspects are certainly represented by the expander machine in mechanical power range of 2-5 kW. A single stage impulse axial turbine has been tested in this work, complete with an electric variable speed generator and an AC/DC converter. The tests demonstrated that the energy conversion chain is not negligible at all and an overall net efficiency of the power unit was around 2-3 %, with a mechanical power production equal to 2/2.5 kW and a thermal power recovered of about 55 kW. The analysis has been completed considering the engine and the ORC unit as a unique system: the influence of the exhaust backpressure increase on the fuel consumption of the internal combustion engine have been evaluated and compared to the power recovered by the ORC unit. In this regard, the effects of two different heat exchanger technologies were studied and a brake specific fuel consumption increase of about 1.5 % have been demonstrated in the best case. Even though these performances appear acceptable, the development of technologies for the expansion with higher efficiency is still an open question and calls for deeper theoretical and experimental evidences. 11:50 20 mins Combination of ORC system and electrified auxiliaries on a long haul truck equiped with 48 volt board net Oliver Dingel, Tobias Toepfer, Jan Treutler Abstract: The increase of efficiency has always been a main goal in the development of a truck powertrain as it has direct impact upon the fuel costs, which are a dominant part of the operating expenses of a long haul commercial vehicle. In addition, upcoming CO2-legislations put additional pressure on implementing efficiency enhancing technologies. The introduction of an ORC system is one further promising step towards better fuel consumption. Electrification of auxiliary components based on a 48 Volt board net is another opportunity that is currently in discussion. This paper shows in how far synergies can be derived from the combination of both technologies. The results were achieved with a vehicle model that includes detailed modelling of cooling system, auxiliary drives, board net and ORC system. The ORC model was validated based on engine dyno measurements. The ORC system uses ethanol as working fluid and includes a heat exchanger integrated into the exhaust gas aftertreatment box and an EGR heat exchanger replacing the series EGR cooler. A single cylinder piston expander generates mechanical work. Both heat exchangers and the piston expander are prototypes designed and manufactured by IAV. The piston expander was designed with the intention of a mechanical coupling to the Power Take Off (PTO) device of the engine. The impact of this configuration in a real life truck cycle was evaluated first. Auxiliaries such as water pump, air compressor and air conditioning compressor are normally mechanically coupled to the engine for instance by a belt drive. In the first part of the project a efficiency gain was investigated by adding a decoupling device such as a visco coupling . In addition to this, the combination with the mechanical coupled ORC system was evaluated taking into regard the general increase of load to the cooling system in order to reject the heat from the condenser to the ambient. These results had been the reference for the variants with electrified auxiliaries. For the future, it is expected that trucks will take over the 48 Volt board net from passenger cars. This facilitates additional flexibility by electrification of auxiliaries and predictive control strategies, but will also lead to an increased demand of electric power. This electric power could be provided by a generator or by an ORC system coupled to an electric generator. The impact of electrified water pump, air compressor and air conditioning compressor in combination with a belt driven 48 Volt generator on fuel consumption was evaluated and compared to the mechanical decoupled auxiliaries. In the next step the 48 Volt generator was coupled to the ORC expander. These results were compared also to those of the corresponding mechanical variants. It could be shown that the mechanical and the electrified variants show a similar potential to reduce fuel consumption. By optimising the operating strategy of the electrical system, using predictive control strategies and including additional electrified components such as E-booster a further improvement of powertrain efficiency is expected. 12:10 20 mins Design, modelling, and contrl of a waste heat recovery unit for heavy-duty truck engines Stefano Trabucchi, Carlo De Servi, Francesco Casella, Piero Colonna Abstract: This paper presents a feasibility study on a waste heat recovery system for heavy-duty truck engines based on organic Rankine cycle (ORC) technology. The elements of novelty of the work are: i) the proposed plant configuration, and ii) the feasibility study that encompasses the preliminary whole design workflow of the system, namely, from the thermodynamic cycle optimization and the components preliminary design, to dynamic modelling and the preliminary design of a PI-based control system. The conceived ORC turbogenerator employs hexamethyldisiloxane (MM) as working fluid and achieves a maximum rated mechanical power of approximately 5 kW at the design point, corresponding to a truck cruise speed and a Diesel engine power output of 85 km/h and 100 kW respectively. Regarding the dynamic performance, the higher response time of the ORC unit compared to that of the Diesel engine makes the adoption of an advanced control system necessary. In particular, the simulation of a PI-based control system shows that it becomes impossible to prevent the thermal decomposition of the working fluid when the engine operates continuously at high power levels. This case study demonstrates the importance for automotive ORC applications of performing the investigation of dynamic performance and control design already in the early design phase.