- Email: [email protected]
EG Mixture as Working Fluid
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www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia IV International Seminar on ORC Power Systems, ORC2017 13-15 September 2017, Milano, Italy IV IV International International Seminar Seminar on on ORC ORC Power Power Systems, Systems, ORC2017 ORC2017 13-15 September 2017, Milano, Study of ICE Bottoming ORC with 13-15 September 2017, Milano, Italy ItalyWater/EG Mixture as
Feasibility Working Fluid Feasibility ICE with Water/EG Mixture Feasibility Study Study ofInternational ICE Bottoming Bottoming ORC with Water/EG Mixture as as The 15thof SymposiumORC on District Heating and Cooling a,∗ a b a Fluid Davide Ziviani , Donghun KimWorking , Swami Nathan Working FluidaSubramanian , James E. Braun , Eckhard A. Grollthe Assessing the feasibility of using heat demand-outdoor a,∗ a b a Davide Ziviani Kim Nathan Subramanian ,, James E. Braun a,∗, Donghun a , Swami a, Ray W. Herrick Laboratories, Purdue University 177 S Russell Street, West Lafayette, IN,b47907-2099, USA Davide Ziviani , Donghun Kim , Swami Nathan Subramanian James E. Braun , a temperature function for a long-term district heat demand forecast Eckhard A. Groll a Eaton Corporate Research & Technology, 26201A. Northwestern Eckhard Groll Hwy, Southfield, MI, 48076, USA a
b
a Ray a Ray
W. Herrick Laboratories, Purdue University 177 S Russell Street, West Lafayette, IN, 47907-2099, USA W. Herrick Laboratories, Purdue University 177 S Russell Street, West Lafayette, IN, 47907-2099, USA
a,b,c a & Technology,a26201 NorthwesternbHwy, Southfield, MI, 48076, c USA c b Eaton Research I. Andrić *, A. Pina , P. Ferrão 26201 , J. Fournier ., B.Southfield, Lacarrière , O. b Eaton Corporate Corporate Research & Technology, Northwestern Hwy, MI, 48076, USALe Corre
Abstract a
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b
Veolia Recherche & Innovation, 291 Avenue(BTE) Dreyfous 78520Duty Limay, France To achieve thec U.S. Department of Energys brake thermal efficiency goalDaniel, for Heavy Diesel Engine (HDDE) technoloAbstract Département Systèmes Énergétiques et Environnement IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France solution. gies, Waste Heat Recovery (WHR) by means of Organic Rankine Cycle (ORC) systems has been selected as a suitable Abstract The current relatively high return on investment period of such technology needs to be improved by significant cost reductions to To achieve the U.S. Department of Energys brake thermal efficiency (BTE) goal for Heavy Duty Diesel Engine (HDDE) technoloTo achieve the U.S. Department of Energys brake The thermal efficiencyof(BTE) goalsystem for Heavy Duty Dieselloads Engine (HDDE) technolorealize benefits on WHR for mobile applications. performance the ORC under dynamic relies on the choice of gies, Waste Heat Recovery (WHR) by means of Organic Rankine Cycle (ORC) systems has been selected as a suitable solution. gies, Waste Heat (WHR) bycomponents means of Organic Rankine Cycle (ORC) systems hasstrategy been selected as a suitable solution. the working fluid,Recovery the high efficiency (mainly expander) as well as the control that optimizes operation. The current relatively returnofonitsinvestment period of such technology needs to be improved by significant costthe reductions to Abstract The current relatively high return on investment period of such technology needs to be improved by significant cost reductions to A novelbenefits ORC architecture proposed that uses The the engine coolant working particular, a fraction engine realize on WHR forismobile applications. performance of as thethe ORC systemfluid. underIndynamic loads relies onof thethe choice of realize benefits ona WHR forofmobile applications. The performance of as theworking ORC system under dynamic loads relies on the heat choice of coolant, which is mixture water and ethylene glycol, is employed fluid through the ORC to recover waste from the working fluid, networks the efficiency its components (mainly expander) well thethe control optimizes operation.the District heating are of commonly addressed in the literatureas oneas of most strategy effectivethat solutions forthe decreasing the working fluid, efficiency of its part components (mainly expander) asas well asinlet the of control strategy that optimizes operation. EGR (Exhaust Gasthe Recirculation) and the tail exhaust gases. At the the expander, the mixture hasthe mixed-phase A novel ORCgas architecture isfrom proposed thatofuses the pipe engine coolant as the working fluid. In particular, areturned fraction of the engine greenhouse emissions the building sector. These systems require high investments which are through the heat A novel ORC architecture is proposed that uses the engine coolant as the working fluid. In particular, a fraction of the engine conditions and aisfixed volume ratio expander is employed generate power outputfluid thatthrough can be fed the engine coolant, which a mixture of water and ethylene glycol, istoemployed as working the directly ORC toto recover wastecrankshaft. heat from sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, coolant, which is a mixture of water and ethylene glycol, is employed as working fluid through the ORC to recover waste heat from Heat accomplished through theofspare capacity of the engine which avoids the need for a separate condenser. EGR rejection (Exhaust is Gas Recirculation) and part the tail pipe exhaust gases. radiator, At the inlet of the expander, the mixture has mixed-phase prolonging the investment return period. EGR (Exhaust Gas Recirculation) and part of the tail pipe exhaust gases. At the inlet of the expander, the mixture has mixed-phase To evaluateand theafeasibility of such architecture, thermodynamic has been developed to predict conditions fixed volume ratio system expander is employeda to generate powersteady-state output that cycle can bemodel fed directly to the engine crankshaft. conditions a fixed volume isengine employed output that can be performance. fed directly tofunction the engine The mainand scope of this paperratio is toexpander assess the feasibility ofasgenerate using the heat demand –the outdoor temperature for crankshaft. heat demand the potential of BTE under different loadsto wellengine aspower to understand ORC are Heat rejectionincrease is accomplished through the spare capacity of the radiator, which avoids the need forParametric a separate studies condenser. Heat rejection isdistrict accomplished throughlocated theratio, spare capacity ofvolume the engine which avoids themixture needdistrict forquality a separate forecast. ofsystem Alvalade, in the Lisbon (Portugal), wasradiator, used a case study. The is consisted of 665 carried out The by the internal ratio of the as expander and the at thecondenser. expander To evaluate thevarying feasibility of suchpressure system architecture, a thermodynamic steady-state cycle model has been developed to predict To evaluate that the feasibility of such system architecture, a thermodynamic steady-state cycle (low, modelmedium, has beenhigh) developed to predict buildings vary in both construction period and typology. Three weather scenarios and three district inlet. the potential increase of BTE under different engine loads as well as to understand the ORC performance. Parametric studies are the potential increase of BTE under different engine loads as well as to understand the ORC performance. Parametric studies are renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were c 2017out ThebyAuthors. Elsevierratio, Ltd. the internal volume ratio of the expander and the mixture quality at the expander carried varying Published the systembypressure carried out by varying the system pressure ratio, the internal volume ratio of the expander and the mixture quality at the expander compared with results from a dynamic heat demand model,of previously developed and validated by the authors. Peer-review under responsibility of the scientific committee the IV International Seminar on ORC Power Systems. inlet. inlet. results showed that when only weatherLtd. change is considered, the margin of error could be acceptable for some applications cThe 2017 The Authors. Published by Elsevier c(the 2017 The Authors. by Elsevier Ltd. WastePublished Heat Recovery; Heady-Duty Diesel Water-Ethylene Glycol mixture; However, after introducing renovation Keywords: error in annual demand was lower than forEngine; all of weather considered). © 2017 TheORC; Authors. Published by Elsevier Ltd.20% Peer-review under responsibility of the scientific committee the IVscenarios International Seminar on ORC Power Systems. Peer-review under responsibility of scientific committee ofofthe on Systems. Peer-review under responsibility ofthe theup scientific committee the IVInternational International Seminar onORC ORCPower Power Systems. considered). scenarios, the error value increased to 59.5% (depending onIV the weather andSeminar renovation scenarios combination The valueORC; of slope increased on average withinWater-Ethylene the range of Glycol 3.8% mixture; up to 8% per decade, that corresponds to the Wastecoefficient Heat Recovery; Heady-Duty Diesel Engine; Keywords: Keywords: ORC; Waste Heat Recovery; Heady-Duty Diesel Engine; Water-Ethylene Glycol mixture; decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and the accuracy of heat demand estimations. 1.improve Introduction
©It 2017 The known Authors.that Published Elsevier Ltd.Engines (HDDEs) reject a considerable amout of energy to the ambient. 1. Introduction is well Heavyby Duty Diesel 1.Peer-review Introduction under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and In order to meet the U.S. Department of Energy (DOE) break thermal efficiency (BTE) goals [1], waste heat recovery Cooling. It It is is well well known known that that Heavy Heavy Duty Duty Diesel Diesel Engines Engines (HDDEs) (HDDEs) reject reject aa considerable considerable amout amout of of energy energy to to the the ambient. ambient. In order to meet the U.S. Department of Energy (DOE) break thermal efficiency (BTE) goals [1], waste heat Forecast; Climate change InKeywords: order to Heat meetdemand; the U.S. Department of Energy (DOE) break thermal efficiency (BTE) goals [1], waste heat recovery recovery ∗
Corresponding author. Tel.: +1-765-418-2375; E-mail address: [email protected]
∗ Corresponding author. Tel.: +1-765-418-2375; ∗ Corresponding author. Tel.: +1-765-418-2375; c 2017 The Authors. Published by Elsevier Ltd. 1876-6102 E-mail address: [email protected] E-mail address: [email protected] Peer-review under responsibility of the scientific committee of the IV International Seminar on ORC Power Systems. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. c 2017 1876-6102 Authors. Published by Elsevier Ltd. of The 15th International Symposium on District Heating and Cooling. Peer-review underThe responsibility of the Scientific Committee c 2017 1876-6102 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the IV International Seminar on ORC Power Systems. 1876-6102 © 2017responsibility The Authors. Published ElsevierofLtd. Peer-review under of the scientificby committee the IV International Seminar on ORC Power Systems. Peer-review under responsibility of the scientific committee of the IV International Seminar on ORC Power Systems. 10.1016/j.egypro.2017.09.226
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(WHR) by means of an organic Rankine cycle (ORC) has been identified by U.S. engine manufacturers as a viable solution. During the recent years, research on ORC systems applied to passenger and commercial vehicles has seen a rapid growth as such power cycle combines maturity and cost-effectiveness. For example, Amicabile et al. [2] carried out a design optimization of an ORC integrated into a heavy-duty diesel engine by considering both subcritical and supercritical cycle architectures. Ethanol and pentane were identified as suitable working fluid both in terms of power output as well as costs. The ORC solutions proposed were costing averagely $15,000 for a class 8 line-haul truck [2]. However, only the Exhaust Gas Recirculation (ERG) cooler was considered as heat source. A more comprehensive study to exploit waste heat in both exhaust gases and the engine coolant has been done by Chen et al. [3]. A novel confluent cascade expansion (CCE) ORC system has been proposed to improve more conventional dual-loop ORCs. The new architecture running with cyclopentane allowed to generate up to 8% more net power compared to the conventional dual-loop ORC. The break specific fuel consumption (BSFC) was reduced from 185 g/(kWh) to 169.9 g/(kWh). Cost, complexity, environmental and safety issues are the major issues of ORC systems installed in vehicles. The return on investment period for the end customer is not highly attractive by using the current technology (3 to 4 years payback period). The successful commercialization of ORC systems is seeing a major impediment from OEMs. In this paper, an affordable ORC system is analyzed in order to obtain real benefits of WHR on the road and reduce the costs by 50% with a targeted pay-back period of 1.5 to 2 years. Nomenclature h specific enthalpy, J/kg m ˙ mass flow rate, kg/s p pressure, Pa Q˙ heat rate, W T temperature, ◦ C ˙ power, W W η efficiency, ∆T PPpinch point temperature difference, ◦ C effectiveness, -
2. ARC system description The novel ORC architecture proposed within the ARC project is based on using the engine coolant as the working fluid. The engine coolant is typically a water - Ethylene Glycol (EG) mixture with a mass fraction composition of [0.5-0.5]. As shown in Fig. 1, a small portion (usually <0.5% of total mass flow rate) of the engine coolant in liquid-phase is pressurized by means of a pump (state 1 to state 2) and used to recover waste heat from the exhaust gas recirculation (EGR) system (state 2 to state 3) and exhaust tail pipe (state 3 to state 4). While absorbing heat, the water/EG mixture becomes a wet binary mixture as it undergoes through partial evaporation. The high pressure two-phase water/EG mixture is then expanded through a fixed-volume ratio expander (state 4 to state 5), which is able to handle two-phase conditions. Heat rejection is accomplished through the engine radiator, avoiding the need for a separate condenser for the ARC system. However, limitations arise concerning the maximum heat rejection rate. To ensure normal operation of the truck engine, the following constraints are taken into account: • return temperature of engine coolant into the engine after EGR boiler; • maximum engine coolant temperature at expander inlet; • exhaust tail pipe boiler exit temperature. Such constraints are dictated by safety reasons, emission control and thermal stability of engine coolant.
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3
EGR HEX 3 EGR loop
2
Air in
Tail Pipe HEX
Exhaust
Filter
4
Exhaust to ambient
Fuel in
Water/EG Pump
Expander
Engine 5
1 Water/EG Loop
Radiator
Fig. 1. ARC system architecture for WHR from EGR and tail pipe exhaust gases.
Fig. 2. T-s thermodynamic plots for different concentrations of EG.
A thermodynamic cycle model is developed to analyze such cycle architecture and to demonstrate the feasibility of using the engine coolant as working fluid to reach similar fuel economy benefits as conventional ORCs.
2.1. Water-EG mixture thermophysical properties The working fluid is a binary mixture of water and ethylene glycol. Few studies have been found about the estimation of thermodynamic and transport properties of such mixture [4,5]. As the mixture phase-change is an important aspect to both recovery heat and generate power output, the vapor-liquid equilibrium (VLE) conditions need to be obtained. VLE diagrams (or temperature-concentration diagrams) are used to demonstrate the concentration shifts within the liquid and vapor phases, as described in Section 2.2. REFPROP [6] is used to retrieve the thermophysical properties of the water/EG mixture. Figure 2 shows T-s diagrams obtained for pure water, pure EG and a water-EG mixture with a EG mass fraction of 0.5 which has been selected for further analyses. To be noted is that the properties close to the critical point are not defined. However, in temperature and pressure ranges of interest for the cycle calculations, no converge issues have been experienced.
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Table 1. Assumptions and constraints of the thermodynamic cycle model. Parameter Mixture concentration (mass fraction) Twater−EG,max , ◦ C pmax , kPa Tail pipe HEX ∆T PP , ◦ C pcond , kPa Tail pipe HEX ∆T PP , ◦ C Minimum expander inlet quality, ηis,exp , ηis,pump , -
Value
Description
[0.5-0.5] 220-300 2000 5 variable 5 0.5 0.6-0.8 0.6
Engine coolant concentrations Issues with thermal stability above 200 ◦ C Expander limitations Design choice Related to radiator operating conditions Design choice Design choice Typical range for expanders [9] Design choice
2.2. Thermodynamic cycle model Based on the system architecture shown in Fig. 1, a steady-state cycle model has been developed to investigate the performance of the ARC. The heat inputs are determined from the engine operation. Furthermore, constraints on the maximum temperature of the coolant as well as recirculated exhaust gas temperature entering into the engine and tail pipe exhaust exit temperature are imposed to ensure safe operation of the engine as well as emission controls. The modeling assumptions and design constraints are listed in Tab. 1. The total heat rate available at the EGR can be quantified as: Q˙ EGR,in = EGR m ˙ EGR hEGR,in − hEGR,out
(1)
where hEGR,in and hEGR,out are the inlet and outlet enthalpies of the EGR and they are fixed by the engine operating conditions. A heat exchanger effectiveness is applied to obtain the heat recovered by the coolant. The heat rate available from the exhaust tail pipe, Q˙ TP,in , is defined analogously to Eq. 1. The effectiveness of the heat exchangers has been assumed to be 0.94. The heat rejected by the radiator is calculated by Q˙ cond = m ˙ water−EG ∆hradiator
(2)
Note that if the heat rejection limitations are applied, the exit temperature of the radiator is imposed. Both the pump and the positive displacement expander have been modeled by assuming a constant value of the isentropic efficiency. For the expander, the internal volume ratio is accounted for to estimate the specific work during the expansion process [7]. The cycle performance and the benefits of the ARC system are quantified by defining an ORC thermal efficiency and Break Power (BP) improvement as: ηORC,net =
BP =
˙ exp − W ˙ pump ˙ ORC,net W W = Q˙ tot,in Q˙ EGR,in + Q˙ TP,in
˙ ORC,net W ˙ engine W
(3)
(4)
The model has been implemented in EES (Engineering Equation Solver) [8] coupled with the REFPROP library. Parametric studies are conducted by varying the independent variables, i.e. pressure ratio, expander isentropic efficiency and expander inlet temperature. Furthermore, the quality of the water-EG mixture at the expander inlet is also a degree of freedom that depends on the high side pressure and mass flow rate for the given heat sources. The amount of EG that evaporates directly influences the work that can be extracted from the expander. It is important to point out that the mixture water-EG presents thermal stability issues at temperatures above 200 ◦ C. As development studies are ongoing to improve the working temperature range, parametric studies are carried out in the present work up to 300 ◦ C to understand the potential of adopting engine coolant as an ORC working fluid.
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Table 2. Nominal engine operating points considered for the analysis. Parameter ◦C
TEGR,in , TTP,in , ◦ C
#1
#2
#3
#4
#5
#6
#7
#8
358.4 272.4
464.2 326.4
543.0 354.7
611.0 389.1
437.1 298.4
513.2 328.5
654.9 415.2
428.3 296.2
Table 3. ARC model results for each engine operating condition. The results are obtained by fixing the condensing pressure at 150 kPa and a pressure ratio across the expander of 8. Parameter Expander inlet temperature, ◦ C Expander isentropic efficiency Net output power, kW ORC system efficiency, Total heat input, kW BP improvement, % Working fluid mass flow rate, g/s Expander specific volume ratio, Expander inlet mixture quality, Expander outlet mixture quality, Expander inlet EG concentration (vapor phase), Expander outlet EG concentration (vapor phase), -
#1
#2
#3
#4
#5
#6
#7
#8
216 0.6 1.948 0.0756 25.76 2.51 23.25 8.267 0.3694 0.4161 0.1773 0.1223
220 0.6 4.4019 0.0780 56.45 2.83 46.28 7.937 0.440 0.473 0.215 0.1605
221 0.6 7.0105 0.0789 88.91 3.01 71.709 7.873 0.457 0.487 0.225 0.171
221 0.6 10.2562 0.0791 129.71 3.37 104.91 7.73 0.457 0.487 0.225 0.171
220 0.6 6.0621 0.0791 76.66 3.23 62.009 7.8726 0.457 0.487 0.225 0.171
200 0.6 9.2816 0.0791 117.38 4.95 94.941 7.8726 0.457 0.487 0.225 0.171
200 0.6 14.0628 0.0791 177.844 5.00 143.847 7.8726 0.457 0.487 0.225 0.171
200 0.6 6.6174 0.0791 83.6866 3.46 67.6890 7.8726 0.457 0.487 0.225 296.2
Fig. 3. T-s thermodynamic plots of ARC system under engine operation # 2. The plot has been obtained with mixture concentration of [0.5-0.5] and evaporating and condensing pressures of 1600 kPa and 200 kPa, respectively.
3. Results and Discussion In order to evaluate the performance of the novel cycle architecture, several engine operating conditions have been identified. The engine parameters are not presented in this paper due to confidentiality. However, the inlet temperatures of EGR and tail pipe heat exchangers are reported in Tab. 2. The cycle model has been used to simulate all the operating points. As previously mentioned, a number of constraints have been taken into account while running the simulations. During the first case study, the maximum temperature of the water-EG mixture has been set equal to 220 ◦ C. At higher temperatures, the mixture tends to decompose and potentially compromise the engine performance. A pressure ratio of 8 is imposed across the expander due to the maximum pressure that the considered expander technology can safely support. The pump isentropic efficiency is set equal to 0.6, whereas the expander isentropic efficiency is in the range from 0.6 to 0.8. This range is representative of the majority of positive displacement expander performance [9]. This condition is named scenario 1. An example of a thermodynamic cycle plot is shown in Fig. 3. Engine condition #2 has been used to generate the plot. To be noted is that for a mixture composition of [0.5-0.5], the resulting cycle is a partial evaporating Rankine
Davide Ziviani et al. / Energy Procedia 129 (2017) 762–769 D. Ziviani et al. / Energy Procedia 00 (2017) 000–000
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(a)
767
(b)
Fig. 4. Parametric study of ARC system with maximum expander inlet temperature of 220 ◦ C with scenario 1: (a) BP improvements; (b) cycle thermodynamic efficiency.
(a)
(b)
Fig. 5. Parametric study of ARC system with scenario 2 (reduced or without tail pipe heat recovery): (a) BP improvements; (b) cycle thermodynamic efficiency. Only four engine operating conditions are shown.
cycle. The quality at the expander inlet represents a degree of freedom to be optimized, although the maximum temperature allowed for the mixture is fixed. At first, simulations are carried out for each engine operating conditions by maintaining the expander efficiency constant at 0.6. The main results are provided in Tab. 3. The cycle model is the exercised to evaluate the influence of the expander isentropic efficiency. The results of the parametric study are reported in Fig. 4. In particular, Fig. 4(a) shows the break power improvements for each operating conditions at two different expander isentropic efficiency values. To be noted is that when an isentropic efficiency of 0.6 is considered, the BP improvements are below 5% with the exception of engine operating conditions #6 and #7. Due to cycle constraints, the thermodynamic efficiency, reported in Fig. 4(b), presents limited variability. In this first analysis, no limitations have been imposed to the heat rejection rate at the condenser, i.e. an additional heat exchanger can be installed to handle the heat load at the condenser side. By introducing the heat rejection limits at the engine radiator, i.e. scenario 2, the BP improvement drops significantly, as shown in Fig. 5(a). However, the analysis seems to suggest that the cycle efficiency is less sensitive to the heat rejection limitations. This is partially due to the constraints imposed to the simulation, e.g., pressure ratio and maximum temperature. At this point, two constraints were relaxed to understand the potential of the ARC architecture. The maximum allowed temperature of water-EG mixture was raised up to 300 ◦ C and the maximum pressure ratio was set equal to
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(a)
7
(b)
Fig. 6. ARC system analysis with relaxed constrains on temperature and pressure values: (a) BP improvements; (b) cycle thermodynamic efficiency.
Fig. 7. Effect of varying the water-EG mixture concentration on expander specific work output at fixed expander inlet temperature of 220 ◦ C.
10. The calculation have been performed once again for all the engine operating conditions by keeping the expander isentropic efficiency fixed at 0.8. The results are shown in Fig. 6(a) and Fig. 6(b). The upper curve of Fig. 4(a) corresponding to an expander inlet temperature of 220 ◦ C, pressure ratio 8 and expander isentropic efficiency of 0.8 is taken as reference case. By increasing both the maximum temperature and pressure, the BP increased appreciably allowing engine conditions from #3 to #7 to reach or exceed the 5% target. A maximum BP improvement of 7.8% was achieved for engine condition #7 with a cycle thermodynamic efficiency of 0.124. It is interesting to observe the behavior of the mixture quality at the expander inlet. At 220 ◦ C and 1200 kPa, the mixture quality is approximately 0.44, while at 300 ◦ C and the same pressure, the mixture is superheated. The increased temperature upper limit leads to improve the expander specific work by up to 80%. In the current analysis the concentration of the water-EG mixture has been kept constant. However, it is interesting to evaluate the effect of increasing the water content. By maintaining an expander temperature limit of 220 ◦ C, the expander specific work output increases if the mass fraction of water increases, due to the fact that the quality of the mixture increases as well, as reported in Fig. 7. 4. Conclusions In this work, a novel organic Rankine cycle for waste heat recovery within heavy-duty trucks that employs a water - Ethylene Glycol mixture has been proposed. A thermodynamic cycle model has been developed to investigate the potential improvements on the engine brake thermal efficiency. Simulation results showed that engine coolant can
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potentially used as working fluid but its employment is heavily conditioned by engine operating conditions, high temperature limitations and expander performance. The maximum BP improvement obtained was 6.94% for engine operating point #7. Although the parametric studies showed some potential for the ARC architecture, additional work is needed to allow the system to work at higher temperatures and pressures to compete with traditional ORC configurations. Furthermore, as positive displacement expanders are considered in this work, the feasibility of using water-EG mixture in the liquid phase as lubricant should be evaluated. Acknowledgements This material is based upon work supported by the Department of Energy Vehicle Technologies Program under Award Number DE-EE0007286. The DOE/industry funded project is entitled ”Affordable Rankine Cycle (ARC) Waste Heat Recovery for Heavy Duty Trucks”. The Authors would like to acknowledge Brandon Rouse from PACCAR for his experimental work on the engine baseline data. The authors greatly appreciated the support of Dr. Eric Lemmon and Dr. Ian H. Bell from NIST addressing calculation of the thermophysical properties of water/EG mixtures. Finally, the authors would like to acknowledge Dr. Abhinav Krishna for his leadership and contributions during the first year of the project. Disclaimer This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. References [1] https://energy.gov/eere/vehicles/downloads/vehicle-technologies-office-merit-review-2016-affordable-rankine-cycle-arc (Accessed on March 6, 2017). ???? [2] Amicabile, S., Lee, J.I., Kum, D.. A comprehensive design methodology of organic Rankine cycles for the waste heat recovery of automotive heavy-duty diesel engines. Applied Thermal Engineering 2015;87:574–585. [3] Chen, T., Zhuge, W., Zhang, Y., Zhang, L.. A novel cascade organic Rankine cycle (ORC) system for waste heat recovery of truck diesel engines. Energy Conversion and Management 2017;138:210–223. [4] T., S., Teja, A.S.. Density, viscosity, and thermal conductivity of aqueous ethylene, diethylene, and triethylene glycol mixtures between 290 K and 450 K. J Chem eng Data 2003;48:198–202. [5] Dai, J., Wang, L., Sun, Y., wang, L., Sun, H.. Prediction of thermodynamic, transport and vapor-liquid equilibriuim properties of binary mixtures of ethylene glycol and water. Fluid Phase Equilibria 2011;301:137–144. [6] Lemmon, E.W., Bell, I.H., Huber, M.L., McLinden, M.O.. NIST Standard Reference Database 23: Reference Fluid Thermodynamic and Transport Properties-REFPROP, Version 9.1.1, National Institute of Standards and Technology. 2016. [7] Macchi, E., Astolfi, M., editors. Organic Rankine Cycle (ORC) Power Systems. Woodhead Publishing; 2016. Chapter 12 - Positive displacement expanders for Organic Rankine Cycle systems, Lemort, V., Legros, A., pp. 361-396. [8] Klein, S.. Engineering Equation Solver, F-Chart Software. . 2017. [9] Imran, M., Usman, M., B-S, P., Lee, D.H.. Volumetric expander for low grade heat and waste heat recovery applications. Renewable and Sustainable Energy Reviews 2016;57:1090–1109.
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www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia IV International Seminar on ORC Power Systems, ORC2017 13-15 September 2017, Milano, Italy IV IV International International Seminar Seminar on on ORC ORC Power Power Systems, Systems, ORC2017 ORC2017 13-15 September 2017, Milano, Study of ICE Bottoming ORC with 13-15 September 2017, Milano, Italy ItalyWater/EG Mixture as
Feasibility Working Fluid Feasibility ICE with Water/EG Mixture Feasibility Study Study ofInternational ICE Bottoming Bottoming ORC with Water/EG Mixture as as The 15thof SymposiumORC on District Heating and Cooling a,∗ a b a Fluid Davide Ziviani , Donghun KimWorking , Swami Nathan Working FluidaSubramanian , James E. Braun , Eckhard A. Grollthe Assessing the feasibility of using heat demand-outdoor a,∗ a b a Davide Ziviani Kim Nathan Subramanian ,, James E. Braun a,∗, Donghun a , Swami a, Ray W. Herrick Laboratories, Purdue University 177 S Russell Street, West Lafayette, IN,b47907-2099, USA Davide Ziviani , Donghun Kim , Swami Nathan Subramanian James E. Braun , a temperature function for a long-term district heat demand forecast Eckhard A. Groll a Eaton Corporate Research & Technology, 26201A. Northwestern Eckhard Groll Hwy, Southfield, MI, 48076, USA a
b
a Ray a Ray
W. Herrick Laboratories, Purdue University 177 S Russell Street, West Lafayette, IN, 47907-2099, USA W. Herrick Laboratories, Purdue University 177 S Russell Street, West Lafayette, IN, 47907-2099, USA
a,b,c a & Technology,a26201 NorthwesternbHwy, Southfield, MI, 48076, c USA c b Eaton Research I. Andrić *, A. Pina , P. Ferrão 26201 , J. Fournier ., B.Southfield, Lacarrière , O. b Eaton Corporate Corporate Research & Technology, Northwestern Hwy, MI, 48076, USALe Corre
Abstract a
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b
Veolia Recherche & Innovation, 291 Avenue(BTE) Dreyfous 78520Duty Limay, France To achieve thec U.S. Department of Energys brake thermal efficiency goalDaniel, for Heavy Diesel Engine (HDDE) technoloAbstract Département Systèmes Énergétiques et Environnement IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France solution. gies, Waste Heat Recovery (WHR) by means of Organic Rankine Cycle (ORC) systems has been selected as a suitable Abstract The current relatively high return on investment period of such technology needs to be improved by significant cost reductions to To achieve the U.S. Department of Energys brake thermal efficiency (BTE) goal for Heavy Duty Diesel Engine (HDDE) technoloTo achieve the U.S. Department of Energys brake The thermal efficiencyof(BTE) goalsystem for Heavy Duty Dieselloads Engine (HDDE) technolorealize benefits on WHR for mobile applications. performance the ORC under dynamic relies on the choice of gies, Waste Heat Recovery (WHR) by means of Organic Rankine Cycle (ORC) systems has been selected as a suitable solution. gies, Waste Heat (WHR) bycomponents means of Organic Rankine Cycle (ORC) systems hasstrategy been selected as a suitable solution. the working fluid,Recovery the high efficiency (mainly expander) as well as the control that optimizes operation. The current relatively returnofonitsinvestment period of such technology needs to be improved by significant costthe reductions to Abstract The current relatively high return on investment period of such technology needs to be improved by significant cost reductions to A novelbenefits ORC architecture proposed that uses The the engine coolant working particular, a fraction engine realize on WHR forismobile applications. performance of as thethe ORC systemfluid. underIndynamic loads relies onof thethe choice of realize benefits ona WHR forofmobile applications. The performance of as theworking ORC system under dynamic loads relies on the heat choice of coolant, which is mixture water and ethylene glycol, is employed fluid through the ORC to recover waste from the working fluid, networks the efficiency its components (mainly expander) well thethe control optimizes operation.the District heating are of commonly addressed in the literatureas oneas of most strategy effectivethat solutions forthe decreasing the working fluid, efficiency of its part components (mainly expander) asas well asinlet the of control strategy that optimizes operation. EGR (Exhaust Gasthe Recirculation) and the tail exhaust gases. At the the expander, the mixture hasthe mixed-phase A novel ORCgas architecture isfrom proposed thatofuses the pipe engine coolant as the working fluid. In particular, areturned fraction of the engine greenhouse emissions the building sector. These systems require high investments which are through the heat A novel ORC architecture is proposed that uses the engine coolant as the working fluid. In particular, a fraction of the engine conditions and aisfixed volume ratio expander is employed generate power outputfluid thatthrough can be fed the engine coolant, which a mixture of water and ethylene glycol, istoemployed as working the directly ORC toto recover wastecrankshaft. heat from sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, coolant, which is a mixture of water and ethylene glycol, is employed as working fluid through the ORC to recover waste heat from Heat accomplished through theofspare capacity of the engine which avoids the need for a separate condenser. EGR rejection (Exhaust is Gas Recirculation) and part the tail pipe exhaust gases. radiator, At the inlet of the expander, the mixture has mixed-phase prolonging the investment return period. EGR (Exhaust Gas Recirculation) and part of the tail pipe exhaust gases. At the inlet of the expander, the mixture has mixed-phase To evaluateand theafeasibility of such architecture, thermodynamic has been developed to predict conditions fixed volume ratio system expander is employeda to generate powersteady-state output that cycle can bemodel fed directly to the engine crankshaft. conditions a fixed volume isengine employed output that can be performance. fed directly tofunction the engine The mainand scope of this paperratio is toexpander assess the feasibility ofasgenerate using the heat demand –the outdoor temperature for crankshaft. heat demand the potential of BTE under different loadsto wellengine aspower to understand ORC are Heat rejectionincrease is accomplished through the spare capacity of the radiator, which avoids the need forParametric a separate studies condenser. Heat rejection isdistrict accomplished throughlocated theratio, spare capacity ofvolume the engine which avoids themixture needdistrict forquality a separate forecast. ofsystem Alvalade, in the Lisbon (Portugal), wasradiator, used a case study. The is consisted of 665 carried out The by the internal ratio of the as expander and the at thecondenser. expander To evaluate thevarying feasibility of suchpressure system architecture, a thermodynamic steady-state cycle model has been developed to predict To evaluate that the feasibility of such system architecture, a thermodynamic steady-state cycle (low, modelmedium, has beenhigh) developed to predict buildings vary in both construction period and typology. Three weather scenarios and three district inlet. the potential increase of BTE under different engine loads as well as to understand the ORC performance. Parametric studies are the potential increase of BTE under different engine loads as well as to understand the ORC performance. Parametric studies are renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were c 2017out ThebyAuthors. Elsevierratio, Ltd. the internal volume ratio of the expander and the mixture quality at the expander carried varying Published the systembypressure carried out by varying the system pressure ratio, the internal volume ratio of the expander and the mixture quality at the expander compared with results from a dynamic heat demand model,of previously developed and validated by the authors. Peer-review under responsibility of the scientific committee the IV International Seminar on ORC Power Systems. inlet. inlet. results showed that when only weatherLtd. change is considered, the margin of error could be acceptable for some applications cThe 2017 The Authors. Published by Elsevier c(the 2017 The Authors. by Elsevier Ltd. WastePublished Heat Recovery; Heady-Duty Diesel Water-Ethylene Glycol mixture; However, after introducing renovation Keywords: error in annual demand was lower than forEngine; all of weather considered). © 2017 TheORC; Authors. Published by Elsevier Ltd.20% Peer-review under responsibility of the scientific committee the IVscenarios International Seminar on ORC Power Systems. Peer-review under responsibility of scientific committee ofofthe on Systems. Peer-review under responsibility ofthe theup scientific committee the IVInternational International Seminar onORC ORCPower Power Systems. considered). scenarios, the error value increased to 59.5% (depending onIV the weather andSeminar renovation scenarios combination The valueORC; of slope increased on average withinWater-Ethylene the range of Glycol 3.8% mixture; up to 8% per decade, that corresponds to the Wastecoefficient Heat Recovery; Heady-Duty Diesel Engine; Keywords: Keywords: ORC; Waste Heat Recovery; Heady-Duty Diesel Engine; Water-Ethylene Glycol mixture; decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and the accuracy of heat demand estimations. 1.improve Introduction
©It 2017 The known Authors.that Published Elsevier Ltd.Engines (HDDEs) reject a considerable amout of energy to the ambient. 1. Introduction is well Heavyby Duty Diesel 1.Peer-review Introduction under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and In order to meet the U.S. Department of Energy (DOE) break thermal efficiency (BTE) goals [1], waste heat recovery Cooling. It It is is well well known known that that Heavy Heavy Duty Duty Diesel Diesel Engines Engines (HDDEs) (HDDEs) reject reject aa considerable considerable amout amout of of energy energy to to the the ambient. ambient. In order to meet the U.S. Department of Energy (DOE) break thermal efficiency (BTE) goals [1], waste heat Forecast; Climate change InKeywords: order to Heat meetdemand; the U.S. Department of Energy (DOE) break thermal efficiency (BTE) goals [1], waste heat recovery recovery ∗
Corresponding author. Tel.: +1-765-418-2375; E-mail address: [email protected]
∗ Corresponding author. Tel.: +1-765-418-2375; ∗ Corresponding author. Tel.: +1-765-418-2375; c 2017 The Authors. Published by Elsevier Ltd. 1876-6102 E-mail address: [email protected] E-mail address: [email protected] Peer-review under responsibility of the scientific committee of the IV International Seminar on ORC Power Systems. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. c 2017 1876-6102 Authors. Published by Elsevier Ltd. of The 15th International Symposium on District Heating and Cooling. Peer-review underThe responsibility of the Scientific Committee c 2017 1876-6102 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the IV International Seminar on ORC Power Systems. 1876-6102 © 2017responsibility The Authors. Published ElsevierofLtd. Peer-review under of the scientificby committee the IV International Seminar on ORC Power Systems. Peer-review under responsibility of the scientific committee of the IV International Seminar on ORC Power Systems. 10.1016/j.egypro.2017.09.226
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(WHR) by means of an organic Rankine cycle (ORC) has been identified by U.S. engine manufacturers as a viable solution. During the recent years, research on ORC systems applied to passenger and commercial vehicles has seen a rapid growth as such power cycle combines maturity and cost-effectiveness. For example, Amicabile et al. [2] carried out a design optimization of an ORC integrated into a heavy-duty diesel engine by considering both subcritical and supercritical cycle architectures. Ethanol and pentane were identified as suitable working fluid both in terms of power output as well as costs. The ORC solutions proposed were costing averagely $15,000 for a class 8 line-haul truck [2]. However, only the Exhaust Gas Recirculation (ERG) cooler was considered as heat source. A more comprehensive study to exploit waste heat in both exhaust gases and the engine coolant has been done by Chen et al. [3]. A novel confluent cascade expansion (CCE) ORC system has been proposed to improve more conventional dual-loop ORCs. The new architecture running with cyclopentane allowed to generate up to 8% more net power compared to the conventional dual-loop ORC. The break specific fuel consumption (BSFC) was reduced from 185 g/(kWh) to 169.9 g/(kWh). Cost, complexity, environmental and safety issues are the major issues of ORC systems installed in vehicles. The return on investment period for the end customer is not highly attractive by using the current technology (3 to 4 years payback period). The successful commercialization of ORC systems is seeing a major impediment from OEMs. In this paper, an affordable ORC system is analyzed in order to obtain real benefits of WHR on the road and reduce the costs by 50% with a targeted pay-back period of 1.5 to 2 years. Nomenclature h specific enthalpy, J/kg m ˙ mass flow rate, kg/s p pressure, Pa Q˙ heat rate, W T temperature, ◦ C ˙ power, W W η efficiency, ∆T PPpinch point temperature difference, ◦ C effectiveness, -
2. ARC system description The novel ORC architecture proposed within the ARC project is based on using the engine coolant as the working fluid. The engine coolant is typically a water - Ethylene Glycol (EG) mixture with a mass fraction composition of [0.5-0.5]. As shown in Fig. 1, a small portion (usually <0.5% of total mass flow rate) of the engine coolant in liquid-phase is pressurized by means of a pump (state 1 to state 2) and used to recover waste heat from the exhaust gas recirculation (EGR) system (state 2 to state 3) and exhaust tail pipe (state 3 to state 4). While absorbing heat, the water/EG mixture becomes a wet binary mixture as it undergoes through partial evaporation. The high pressure two-phase water/EG mixture is then expanded through a fixed-volume ratio expander (state 4 to state 5), which is able to handle two-phase conditions. Heat rejection is accomplished through the engine radiator, avoiding the need for a separate condenser for the ARC system. However, limitations arise concerning the maximum heat rejection rate. To ensure normal operation of the truck engine, the following constraints are taken into account: • return temperature of engine coolant into the engine after EGR boiler; • maximum engine coolant temperature at expander inlet; • exhaust tail pipe boiler exit temperature. Such constraints are dictated by safety reasons, emission control and thermal stability of engine coolant.
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3
EGR HEX 3 EGR loop
2
Air in
Tail Pipe HEX
Exhaust
Filter
4
Exhaust to ambient
Fuel in
Water/EG Pump
Expander
Engine 5
1 Water/EG Loop
Radiator
Fig. 1. ARC system architecture for WHR from EGR and tail pipe exhaust gases.
Fig. 2. T-s thermodynamic plots for different concentrations of EG.
A thermodynamic cycle model is developed to analyze such cycle architecture and to demonstrate the feasibility of using the engine coolant as working fluid to reach similar fuel economy benefits as conventional ORCs.
2.1. Water-EG mixture thermophysical properties The working fluid is a binary mixture of water and ethylene glycol. Few studies have been found about the estimation of thermodynamic and transport properties of such mixture [4,5]. As the mixture phase-change is an important aspect to both recovery heat and generate power output, the vapor-liquid equilibrium (VLE) conditions need to be obtained. VLE diagrams (or temperature-concentration diagrams) are used to demonstrate the concentration shifts within the liquid and vapor phases, as described in Section 2.2. REFPROP [6] is used to retrieve the thermophysical properties of the water/EG mixture. Figure 2 shows T-s diagrams obtained for pure water, pure EG and a water-EG mixture with a EG mass fraction of 0.5 which has been selected for further analyses. To be noted is that the properties close to the critical point are not defined. However, in temperature and pressure ranges of interest for the cycle calculations, no converge issues have been experienced.
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Table 1. Assumptions and constraints of the thermodynamic cycle model. Parameter Mixture concentration (mass fraction) Twater−EG,max , ◦ C pmax , kPa Tail pipe HEX ∆T PP , ◦ C pcond , kPa Tail pipe HEX ∆T PP , ◦ C Minimum expander inlet quality, ηis,exp , ηis,pump , -
Value
Description
[0.5-0.5] 220-300 2000 5 variable 5 0.5 0.6-0.8 0.6
Engine coolant concentrations Issues with thermal stability above 200 ◦ C Expander limitations Design choice Related to radiator operating conditions Design choice Design choice Typical range for expanders [9] Design choice
2.2. Thermodynamic cycle model Based on the system architecture shown in Fig. 1, a steady-state cycle model has been developed to investigate the performance of the ARC. The heat inputs are determined from the engine operation. Furthermore, constraints on the maximum temperature of the coolant as well as recirculated exhaust gas temperature entering into the engine and tail pipe exhaust exit temperature are imposed to ensure safe operation of the engine as well as emission controls. The modeling assumptions and design constraints are listed in Tab. 1. The total heat rate available at the EGR can be quantified as: Q˙ EGR,in = EGR m ˙ EGR hEGR,in − hEGR,out
(1)
where hEGR,in and hEGR,out are the inlet and outlet enthalpies of the EGR and they are fixed by the engine operating conditions. A heat exchanger effectiveness is applied to obtain the heat recovered by the coolant. The heat rate available from the exhaust tail pipe, Q˙ TP,in , is defined analogously to Eq. 1. The effectiveness of the heat exchangers has been assumed to be 0.94. The heat rejected by the radiator is calculated by Q˙ cond = m ˙ water−EG ∆hradiator
(2)
Note that if the heat rejection limitations are applied, the exit temperature of the radiator is imposed. Both the pump and the positive displacement expander have been modeled by assuming a constant value of the isentropic efficiency. For the expander, the internal volume ratio is accounted for to estimate the specific work during the expansion process [7]. The cycle performance and the benefits of the ARC system are quantified by defining an ORC thermal efficiency and Break Power (BP) improvement as: ηORC,net =
BP =
˙ exp − W ˙ pump ˙ ORC,net W W = Q˙ tot,in Q˙ EGR,in + Q˙ TP,in
˙ ORC,net W ˙ engine W
(3)
(4)
The model has been implemented in EES (Engineering Equation Solver) [8] coupled with the REFPROP library. Parametric studies are conducted by varying the independent variables, i.e. pressure ratio, expander isentropic efficiency and expander inlet temperature. Furthermore, the quality of the water-EG mixture at the expander inlet is also a degree of freedom that depends on the high side pressure and mass flow rate for the given heat sources. The amount of EG that evaporates directly influences the work that can be extracted from the expander. It is important to point out that the mixture water-EG presents thermal stability issues at temperatures above 200 ◦ C. As development studies are ongoing to improve the working temperature range, parametric studies are carried out in the present work up to 300 ◦ C to understand the potential of adopting engine coolant as an ORC working fluid.
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Table 2. Nominal engine operating points considered for the analysis. Parameter ◦C
TEGR,in , TTP,in , ◦ C
#1
#2
#3
#4
#5
#6
#7
#8
358.4 272.4
464.2 326.4
543.0 354.7
611.0 389.1
437.1 298.4
513.2 328.5
654.9 415.2
428.3 296.2
Table 3. ARC model results for each engine operating condition. The results are obtained by fixing the condensing pressure at 150 kPa and a pressure ratio across the expander of 8. Parameter Expander inlet temperature, ◦ C Expander isentropic efficiency Net output power, kW ORC system efficiency, Total heat input, kW BP improvement, % Working fluid mass flow rate, g/s Expander specific volume ratio, Expander inlet mixture quality, Expander outlet mixture quality, Expander inlet EG concentration (vapor phase), Expander outlet EG concentration (vapor phase), -
#1
#2
#3
#4
#5
#6
#7
#8
216 0.6 1.948 0.0756 25.76 2.51 23.25 8.267 0.3694 0.4161 0.1773 0.1223
220 0.6 4.4019 0.0780 56.45 2.83 46.28 7.937 0.440 0.473 0.215 0.1605
221 0.6 7.0105 0.0789 88.91 3.01 71.709 7.873 0.457 0.487 0.225 0.171
221 0.6 10.2562 0.0791 129.71 3.37 104.91 7.73 0.457 0.487 0.225 0.171
220 0.6 6.0621 0.0791 76.66 3.23 62.009 7.8726 0.457 0.487 0.225 0.171
200 0.6 9.2816 0.0791 117.38 4.95 94.941 7.8726 0.457 0.487 0.225 0.171
200 0.6 14.0628 0.0791 177.844 5.00 143.847 7.8726 0.457 0.487 0.225 0.171
200 0.6 6.6174 0.0791 83.6866 3.46 67.6890 7.8726 0.457 0.487 0.225 296.2
Fig. 3. T-s thermodynamic plots of ARC system under engine operation # 2. The plot has been obtained with mixture concentration of [0.5-0.5] and evaporating and condensing pressures of 1600 kPa and 200 kPa, respectively.
3. Results and Discussion In order to evaluate the performance of the novel cycle architecture, several engine operating conditions have been identified. The engine parameters are not presented in this paper due to confidentiality. However, the inlet temperatures of EGR and tail pipe heat exchangers are reported in Tab. 2. The cycle model has been used to simulate all the operating points. As previously mentioned, a number of constraints have been taken into account while running the simulations. During the first case study, the maximum temperature of the water-EG mixture has been set equal to 220 ◦ C. At higher temperatures, the mixture tends to decompose and potentially compromise the engine performance. A pressure ratio of 8 is imposed across the expander due to the maximum pressure that the considered expander technology can safely support. The pump isentropic efficiency is set equal to 0.6, whereas the expander isentropic efficiency is in the range from 0.6 to 0.8. This range is representative of the majority of positive displacement expander performance [9]. This condition is named scenario 1. An example of a thermodynamic cycle plot is shown in Fig. 3. Engine condition #2 has been used to generate the plot. To be noted is that for a mixture composition of [0.5-0.5], the resulting cycle is a partial evaporating Rankine
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(a)
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(b)
Fig. 4. Parametric study of ARC system with maximum expander inlet temperature of 220 ◦ C with scenario 1: (a) BP improvements; (b) cycle thermodynamic efficiency.
(a)
(b)
Fig. 5. Parametric study of ARC system with scenario 2 (reduced or without tail pipe heat recovery): (a) BP improvements; (b) cycle thermodynamic efficiency. Only four engine operating conditions are shown.
cycle. The quality at the expander inlet represents a degree of freedom to be optimized, although the maximum temperature allowed for the mixture is fixed. At first, simulations are carried out for each engine operating conditions by maintaining the expander efficiency constant at 0.6. The main results are provided in Tab. 3. The cycle model is the exercised to evaluate the influence of the expander isentropic efficiency. The results of the parametric study are reported in Fig. 4. In particular, Fig. 4(a) shows the break power improvements for each operating conditions at two different expander isentropic efficiency values. To be noted is that when an isentropic efficiency of 0.6 is considered, the BP improvements are below 5% with the exception of engine operating conditions #6 and #7. Due to cycle constraints, the thermodynamic efficiency, reported in Fig. 4(b), presents limited variability. In this first analysis, no limitations have been imposed to the heat rejection rate at the condenser, i.e. an additional heat exchanger can be installed to handle the heat load at the condenser side. By introducing the heat rejection limits at the engine radiator, i.e. scenario 2, the BP improvement drops significantly, as shown in Fig. 5(a). However, the analysis seems to suggest that the cycle efficiency is less sensitive to the heat rejection limitations. This is partially due to the constraints imposed to the simulation, e.g., pressure ratio and maximum temperature. At this point, two constraints were relaxed to understand the potential of the ARC architecture. The maximum allowed temperature of water-EG mixture was raised up to 300 ◦ C and the maximum pressure ratio was set equal to
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(a)
7
(b)
Fig. 6. ARC system analysis with relaxed constrains on temperature and pressure values: (a) BP improvements; (b) cycle thermodynamic efficiency.
Fig. 7. Effect of varying the water-EG mixture concentration on expander specific work output at fixed expander inlet temperature of 220 ◦ C.
10. The calculation have been performed once again for all the engine operating conditions by keeping the expander isentropic efficiency fixed at 0.8. The results are shown in Fig. 6(a) and Fig. 6(b). The upper curve of Fig. 4(a) corresponding to an expander inlet temperature of 220 ◦ C, pressure ratio 8 and expander isentropic efficiency of 0.8 is taken as reference case. By increasing both the maximum temperature and pressure, the BP increased appreciably allowing engine conditions from #3 to #7 to reach or exceed the 5% target. A maximum BP improvement of 7.8% was achieved for engine condition #7 with a cycle thermodynamic efficiency of 0.124. It is interesting to observe the behavior of the mixture quality at the expander inlet. At 220 ◦ C and 1200 kPa, the mixture quality is approximately 0.44, while at 300 ◦ C and the same pressure, the mixture is superheated. The increased temperature upper limit leads to improve the expander specific work by up to 80%. In the current analysis the concentration of the water-EG mixture has been kept constant. However, it is interesting to evaluate the effect of increasing the water content. By maintaining an expander temperature limit of 220 ◦ C, the expander specific work output increases if the mass fraction of water increases, due to the fact that the quality of the mixture increases as well, as reported in Fig. 7. 4. Conclusions In this work, a novel organic Rankine cycle for waste heat recovery within heavy-duty trucks that employs a water - Ethylene Glycol mixture has been proposed. A thermodynamic cycle model has been developed to investigate the potential improvements on the engine brake thermal efficiency. Simulation results showed that engine coolant can
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potentially used as working fluid but its employment is heavily conditioned by engine operating conditions, high temperature limitations and expander performance. The maximum BP improvement obtained was 6.94% for engine operating point #7. Although the parametric studies showed some potential for the ARC architecture, additional work is needed to allow the system to work at higher temperatures and pressures to compete with traditional ORC configurations. Furthermore, as positive displacement expanders are considered in this work, the feasibility of using water-EG mixture in the liquid phase as lubricant should be evaluated. Acknowledgements This material is based upon work supported by the Department of Energy Vehicle Technologies Program under Award Number DE-EE0007286. The DOE/industry funded project is entitled ”Affordable Rankine Cycle (ARC) Waste Heat Recovery for Heavy Duty Trucks”. The Authors would like to acknowledge Brandon Rouse from PACCAR for his experimental work on the engine baseline data. The authors greatly appreciated the support of Dr. Eric Lemmon and Dr. Ian H. Bell from NIST addressing calculation of the thermophysical properties of water/EG mixtures. Finally, the authors would like to acknowledge Dr. Abhinav Krishna for his leadership and contributions during the first year of the project. Disclaimer This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. References [1] https://energy.gov/eere/vehicles/downloads/vehicle-technologies-office-merit-review-2016-affordable-rankine-cycle-arc (Accessed on March 6, 2017). ???? [2] Amicabile, S., Lee, J.I., Kum, D.. A comprehensive design methodology of organic Rankine cycles for the waste heat recovery of automotive heavy-duty diesel engines. Applied Thermal Engineering 2015;87:574–585. [3] Chen, T., Zhuge, W., Zhang, Y., Zhang, L.. A novel cascade organic Rankine cycle (ORC) system for waste heat recovery of truck diesel engines. Energy Conversion and Management 2017;138:210–223. [4] T., S., Teja, A.S.. Density, viscosity, and thermal conductivity of aqueous ethylene, diethylene, and triethylene glycol mixtures between 290 K and 450 K. J Chem eng Data 2003;48:198–202. [5] Dai, J., Wang, L., Sun, Y., wang, L., Sun, H.. Prediction of thermodynamic, transport and vapor-liquid equilibriuim properties of binary mixtures of ethylene glycol and water. Fluid Phase Equilibria 2011;301:137–144. [6] Lemmon, E.W., Bell, I.H., Huber, M.L., McLinden, M.O.. NIST Standard Reference Database 23: Reference Fluid Thermodynamic and Transport Properties-REFPROP, Version 9.1.1, National Institute of Standards and Technology. 2016. [7] Macchi, E., Astolfi, M., editors. Organic Rankine Cycle (ORC) Power Systems. Woodhead Publishing; 2016. Chapter 12 - Positive displacement expanders for Organic Rankine Cycle systems, Lemort, V., Legros, A., pp. 361-396. [8] Klein, S.. Engineering Equation Solver, F-Chart Software. . 2017. [9] Imran, M., Usman, M., B-S, P., Lee, D.H.. Volumetric expander for low grade heat and waste heat recovery applications. Renewable and Sustainable Energy Reviews 2016;57:1090–1109.