14:00
Session 4C: Waste heat (2)
Chair: Christoph Wieland
14:00
20 mins
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Exhaust Waste Heat Recovery for Intercity Bus Climatisation Using Rankine Technology with Focus on Topology Design
Maximilian Hebeler, Philipp Ebeling, Wilhelm Tegethoff, Jürgen Köhler
Abstract: In times of increasing energy prices and decreasing CO2-emission limits it becomes compulsive to improve energy efficiency. This does not only account for the sector of passenger cars but also for public and commercial passenger transportation, like intercity busses, which transport often more than 30 passengers. For short distance intercity busses one way of achieving this goal is to electrify the powertrain, since the needed range can be covered with current battery technologies. For long-range intercity busses with travel distances up to 1000 km or even further it is still more feasible to use an internal combustion engine (ICE). However, as a rule of thumb one third of the supplied chemical energy is converted into mechanical work, one third is rejected via the cooling system and one third is rejected as hot exhaust gas into the environment. That last portion of energy still comprises an unused exergetic potential. In order to use that exergetic potential a Waste Heat Recovery (WHR) system can be applied, e.g. an Organic Rankine Cycle. This system can be used for either reducing the engine load mechanically or by driving auxiliary loads e.g. the alternator or the refrigerant compressor, and thereby reduce fuel consumption. The compressor of the Air-Conditioning (AC) System of an intercity bus uses up to 15 kW of additional mechanical power from the engine, which reduces the effective work output for vehicle traction. For the period of a long haul journey that power input accounts for around 8 % of the overall diesel fuel consumption. Therefore, combining the waste heat recovery and air-conditioning system is a promising method for reducing primary energy usage. Still, it is a challenge to combine these two systems efficiently, since there are many possible topologies to consider.
In this work, three topologies for air-conditioning using exhaust waste heat are presented. The first topology uses direct mechanical coupling between WHR system, ICE and AC system. The second topology uses an indirect thermal coupling, where the AC condenser is used as a preheater for the WHR system. The third topology is based on a combined Organic Rankine Cycle and Vapor Compression Cycle (ORVC), where AC and WHR are using the same working fluid and share the condenser.
The focus of this work is on simulating the presented three topologies with respect to transient exergetic potential as well as optimal operating strategies. The goal of that topology comparison is to preevaluate, respectively analyze benefits and drawbacks of those configurations for further research. In addition, it is discussed if hybridization of components or subsystems can enhance system performance. The simulations are based on real life driving cycles such as journeys from Hannover to Munich and real life weather data.
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14:20
20 mins
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Pump Development for an Exhaust Heat Recovery Box on Heavy Duty Trucks
Frédéric Albergucci, Stéphane Watts, Antoine Darmedru, Jory Pouponnot, 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 developed several components for an organic Rankine system packaged in a box and installed in a truck tractor close to the exhaust pipe. This paper is focusing on the pump development results.
We developed a pump prototype and a dedicated test rig in order to assess its performance and to perform endurance tests. The key challenges for such a product development are to keep a good volumetric efficiency with high pressure difference between outlet and inlet around 30bars and with corrosive and low viscosity fluids such as ethanol, pumped in saturated liquid state at quite low flows. Leakage path are then critical to the pump efficiency as well as the electric actuator design to match the pump torque and speed requirements with high efficiency. Another challenge is to maintain this leakage rate under control in time despite wear. The choices made for the pump architecture and materials will be presented as well as test results. The road map for the necessary technical improvements will displayed.
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14:40
20 mins
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Experimental Study of Small Scale and High Expansion Ratio ORC for Recovering High Temperature Waste Heat
Antti Uusitalo, Teemu Turunen-Saaresti, Juha Honkatukia, Radheesh Dhanasegaran
Abstract: In the recent times, the use and development of small-scale (about 10 kW) ORC systems has received an increasing interest in different applications. In this study, a small-scale ORC system having high operational temperature of close to 300 oC was investigated experimentally. The studied ORC system has a high-speed turbogenerator (rotational speed of 30 000 rpm) including a supersonic radial inflow turbine, a permanent magnet generator and a barske type feed pump assembled on a single shaft. The experimental system uses high molecular weight siloxane MDM as the working fluid. The ORC system under study was designed to be able to operate at high operational temperatures that can be found for example in high temperature exhaust gas heat recovery and in small-scale biomass or biogas applications. The operation of the whole ORC system and especially the operation of the turbogenerator was studied in detail under different operating conditions with varying heat loads and with varying turbogenerator rotational speeds. The experimental results were compared against the results obtained from the numerical ORC cycle model for validating and comparing the numerical and experimental results.
Based on the results, the technical potential of using high rotational speed and supersonic turbomachinery in small-scale and high expansion ratio ORC applications was confirmed experimentally. The paper describes and discusses the main advantages and specific operational characteristcs of the studied ORC system as well as discusses the key aspects for further reducing losses in ORC systems adopting small-scale and high rotational speed turbomachinery.
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15:00
20 mins
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Characterization of Organic Rankine Cycle System for Waste Heat Recovery from Heavy Duty Engine Coolant and Exhaust
Sandhya Thantla, Jonas Aspfors, Jens Fridh, Anders Christiansen Erlandsson
Abstract: To meet the strict legislations on the carbon-dioxide emissions, Organic Rankine Cycle (ORC) Waste Heat Recovery (WHR) technology is being extensively studied and applied in long haulage Heavy-Duty (HD) truck engines. It is necessary to maximize heat recovery from the HD engines to achieve the objective of reducing fuel consumption and improving efficiency. Volumetric expanders are being considered to be reliable technologies for ORC WHR systems in HD commercial vehicles.
The focus of this paper is to characterize the ORC WHR system of a HD truck engine encompassing a volumetric expander, for the boundary conditions imposed by the engine coolant and the exhaust gas of the HD engine. Based on the quality of heat rejected from the engine at some chosen engine operating points, a study on changing the volume ratio and displacement volume of the expander is presented in this paper. Different WHR configurations integrated with the engine exhaust, engine coolant or both the exhaust and coolant as the heat sources are studied using the 1D simulation tool GT-suite. A Scroll-type volumetric expander is represented in the 1D model through maps of expander effectiveness and volumetric efficiency derived from a semi-empirical model of the expander.
The main objective of this work is to achieve overall system efficiency using different configurations of the engine and WHR system, and expander sizing. By investigating with unconventional engine coolant temperatures as the heat source for WHR, an optimum engine coolant temperature is proposed based on the overall system performance when using the Scroll expander with R245fa as the working fluid. The optimum expander size and the number of expanders required for improved system efficiency is also determined and compared based on the subjected boundary conditions.
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15:20
20 mins
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Assessment of Rankine Waste Heat Recovery Potential on Heavy Duty Trucks Using Direct Condensation
Galuppo Galuppo, Thomas Reiche, Vincent Lemort, Pascal Dufour, Madiha Nadri
Abstract: Upcoming regulations on CO2 emissions for the heavy duty truck industry [1] and increasing fuel prizes lead the truck manufacturers to adopt new solutions to reduce fuel consumption. The organic Rankine cycle (ORC) is a promising technology to achieve such a goal. Rankine cycle waste heat recovery on heavy duty trucks has been studied in the last decade focusing on fluid selection [2], modelling [3], control and component [4] development. Cost, integration and uptime are also considered as important aspects for a future series production. The objective of this study is to evaluate the performance of a Rankine system by means of road cycle simulations on a complete truck simulation environment (Exhaust after treatment system, as well as cooling system and the energy management of the mild-hybrid driveline are modeled). The Rankine uses exhaust gas flow as heat source, direct condensation radiator as condenser and volumetric expansion machine; selected working fluids for this study are ethanol and cyclopentane. Dynamic equations used for the modelling of the Rankine components are provided and a particular attention is dedicated to the model of the condenser and fan. In order to ensure the complete condensation of the working fluid two controllers are implemented to track a setpoint on subcooling at the outlet of the condenser by acting on the fan speed and condensation pressure. Results show that ethanol is more suitable than cyclopentane using direct condensation and the limitation of the fan power demand can lead to an increase of the Rankine net power.
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