A review of modified Organic Rankine cycles (ORCs) for internal combustion engine waste heat recovery (ICE-WHR)

A review of modified Organic Rankine cycles (ORCs) for internal combustion engine waste heat recovery (ICE-WHR)

Renewable and Sustainable Energy Reviews 92 (2018) 95–110 Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal...

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Renewable and Sustainable Energy Reviews 92 (2018) 95–110

Contents lists available at ScienceDirect

Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser

A review of modified Organic Rankine cycles (ORCs) for internal combustion engine waste heat recovery (ICE-WHR)

T



Lingfeng Shia,1, Gequn Shua,1, Hua Tiana, , Shuai Dengb a b

State Key Laboratory of Engines, Tianjin University, 92 Weijin Road, Nankai District, Tianjin 300072, China Key Laboratory of Efficient Utilization of Low and Medium Grade Energy (Tianjin University), Ministry of Education of China, Tianjin 300350, China

A R T I C LE I N FO

A B S T R A C T

Keywords: Internal combustion engine (ICE) Waste heat recovery (WHR) Organic Rankine cycle (ORC) Exhaust gas

Organic Rankine cycle (ORC) is considered as a rational solution to convert thermal energy of low and moderate temperature heat sources into mechanical work, which currently attracts more and more attention as an effective way for internal combustion engine waste heat recovery (ICE-WHR). Traditional design methods for low-temperature ORCs do not adapt to ICE-WHR suitably due to the specific large-gradient temperature drop characteristics of engine waste heats, and corresponding low-temperature organic fluids meeting with thermal matching and thermal decomposition issues for high-temperature exhaust gas recovery. Hence, there have been a great amount of studies focusing on modified ORCs to achieve a better performance from the aspects of cycle and fluid during the past decade, mainly in 2010s. In this paper, relevant researches of these modified ORCs were reviewed and divided into four parts to approach the ideal cycle, which was defined as the best matching cycle to engine waste heats. From paths of fluid and cycle, high-temperature ORCs (HT-ORCs), mixture ORCs (MORCs), ORCs combining with extra loops and dual loop ORCs (DORCs) were summarized. The method of temperature-entropy (t-s) map was applied to provide the approaching degree from modified ORCs to the ideal cycle. The study provides valuable information for stakeholders interested in ORC technologies and gives policymakers perspectives regarding different ORC options for ICE-WHR.

1. Introduction Internal combustion engines (ICEs) are the main consumers of fossil fuel as primary power sources widely applied in vehicles, industrial machineries, agricultural machineries and stationary power units [1]. To save fuel and reduce CO2 emissions, increasing total efficiency of engine has become a durable topic attracting wide research since last century. Many techniques have been implemented to achieve improvements in engine efficiency, such as homogeneous charge compression ignition (HCCI) [2], turbochargers [3], variable valve timing (VVT) [4], and hybrid powertrains [5–7]. While, above half of fuel energy is still lost as waste heats through exhaust gas and engine coolant mainly [8,9]. Therefore, waste heat recovery (WHR) technology becomes promising and potential to achieve a considerable increase of engine efficiency currently. With extra power generation, various thermodynamic cycles are used for ICE-WHR, such as Organic Rankine Cycle (ORC), Kalina Cycle and Steam Rankine Cycle [10]. Compared with Kalina Cycle's complex system structure, Steam Rankine Cycle's complex turbines, their high operating pressure and risk of erosion, ORC has the advantages of ⁎

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simple structure, high reliability and easy maintenance, which uses organic working fluids with low boiling temperatures [11]. Therefore, ORC is more suitable for using low and moderate energy (e.g. engine coolant and exhaust gas) than Kalina Cycle and Steam Rankine Cycle. The earliest attempt of ORC for ICE-WHR began in 1970s by Thermo Electron Corporation and Mack Trucks [12–14]. Fluorinol-85 (85% tetrafluoroethanol and 15% water) and Fluorinol-50 (50% tetrafluoroethanol and 50% water) were selected as working fluid successively. The test results for Mack 676 diesel engine demonstrated 13% increase in maximum power output under the largest torque condition. In this century, large organizations such as Cummins [15], AVL [16,17] and BMW [18–20] started related research and projects. The report of Cummins [15] in 2014 showed the “Super Truck” program sponsored by the Department of Energy had made much progress. The test results on road by an ORC system installed on a diesel engine showed that the brake efficiency of diesel engine was increased from 47.5% to over 51%. The ORC played a significant role in the energy-saving technologies of engine, which was also forecasted to possessing the greatest potential of increasing engine efficiency in the 2013 Argonne National Laboratory's report [21].

Corresponding author. E-mail address: [email protected] (H. Tian). These authors contributed equally to this work and should be considered co-first authors.

https://doi.org/10.1016/j.rser.2018.04.023 Received 17 November 2017; Received in revised form 14 January 2018; Accepted 12 April 2018 1364-0321/ © 2018 Elsevier Ltd. All rights reserved.

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Nomenclature BSFC EPC s t W

trans transcritical cycle CNG compressed natural gas B-ORC basic ORC CCE-ORC confluent cascade expansion ORC DORC dual-loop ORC EGR exhaust gas recirculation HCCI homogeneous charge compression ignition HT-ORC high-temperature ORC HT-Loop ORC high-temperature loop ORC in the DORC system ICE internal combustion engine IHX internal heat exchanger LT-Loop ORC low-temperature loop ORC in the DORC system M-ORC mixture ORC ORC Organic Rankine cycle TEG thermoelectric generator VVT variable valve timing WHR waste heat recovery

brake specific fuel consumption, (g/kW.h) electricity production cost ($/kW.h) specific entropy (kJ/(kg K)) temperature (°C) power work (kW)

Greek letters η

efficiency

Subscripts ex net th

exergy net output thermal

Abbreviations sub

subcritical cycle

ORCs.

Due to the rapid development, reviews of ORC for ICE-WHR have existed since 2011 to summarize achievement and guide direction. In the reviews of mainstream WHR technologies for ICE [10,22–26], ORC, generally classified as a power generation technology, was usually compared with thermoelectric generator (TEG) and turbocharger. High conversion efficiency was the biggest advantage of ORC. There were also reviews specially summarizing the ORC development for ICE-WHR. Wang et al. [27] overviewed the relevant researches about the possible system designs and thermodynamic principles to achieve high efficiency of ORCs, and selection of working fluids to maintain necessary system performance. The review line from the whole to local included three parts: system structure, expander and working fluid. Among the three, the expander should be the most key issue and challenge for ORC systems. Apart from three parts similar with Wang et al. [27], the review structure of Zhou et al. [28] added another section to summarize the implementation of ORC to passenger vehicles in a rough chronological order. There were some research groups and vehicle manufacturers (e.g. Toyota, Honda, BMW, etc.) who investigated ORC applications to passenger vehicles, showing an increasing potential of it. Sprouse III et al. [29] conducted another review line basing on the development history of ORC for ICE-WHR from 1973 to 2011. The historical review indicated that no configuration and fluid was optimal for various waste heat sources, so a new thermodynamic analysis must be conducted firstly when targeting specific source. Therefore, the relatively mature ORCs in other WHR fields, mainly low-temperature ORCs, could not adapt to ICE-WHR directly since engine waste heats appear the large-gradient temperature drop characteristic. Moreover, when the low-temperature ORCs with traditional organic fluids were transferred to high-temperature exhaust gas recovery, they would meet with heat matching and thermal decomposition issues definitely, thus the energy-efficiency would be deceased and even with an unhealthy operation. In order to solve such challenges, there have been abundant modified ORCs investigated to adapt to ICEWHR, especially in 2010s. An effective review is necessary to summarize these modified ORCs that have appeared in recent years. This paper provided a detailed review of modified ORCs to indicate various solutions of matching large-gradient temperature drop characteristic of engine waste heats. To describe the marching mechanism in an organized way, the modified ORCs would be divided into several parts to approach an ideal cycle, which was defined as the optimal matching cycle to engine waste heats. The method of temperature-entropy (t-s) map was used to present the approaching degree of modified

2. Ideal cycle for ICE-WHR It is well known that ideal Carnot cycle as the most ideal cycle between constant heat and cold source is a rectangle-shaped in temperature-entropy (t-s) map as shown in Fig. 1. The heat absorption and heat release process are a kind of typical constant-temperature process. When the temperature of heat absorption and heat release approach that of heat source and cold source, respectively, the cycle efficiency can reach to the maximum value theoretically. From another perspective, the size of the area circled by the cycle decides the level of cycle efficiency. Certainly, it cannot realize such an ideal Carnot cycle for a real ORC. The shape style should change and depends on the concrete characteristic of heat and cold sources. Hence, the rectangle shape is not applicable to the real ORC for ICE-WHR. For developing a highefficiency ORC for ICE-WHR, it is significant to comprehend an ideal cycle belonging to ICE-WHR. The characteristics of engine waste heats would be introduced below prior establishing the ideal cycle for ICEWHR. As evaluated on a diesel engine, limited fuel combusting energy can be converted into effective power output, and the remainder is mostly wasted as residual heat via the exhaust gas, engine coolant, exhaust gas recirculation and intake air [30]. For a typical turbocharged gasoline engine, exhaust gas, engine coolant and charge air are the main carriers

Fig. 1. Schematic t-s map of ideal Carnot cycle. 96

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choice was also concluded by the selection research by Jung et al. [39] and Yang et al. [40]. The above follows that R245fa is unquestionably a popular fluid among the numerous fluids, which attracted much attention. Usman et al. [41] simulated an R245fa-based ORC installation on light duty vehicle and accessed the positive and negative aspects by ORC installation. The cycle efficiency of ORC itself is 10.89%, but when considering the negative impacts of added back pressure, added weight and off design operation of ORC, the net efficiency of ORC reduced to 5.82%. An experimental investigation on R245fa-based ORC by Zhao et al. [42] showed an increase of 0.66% on the engine thermal efficiency and an decrease of 3.61 g/(kW h) on the Brake Specific Fuel Consumption (BSFC) of 258 kW engine. Studies on R245fa-based ORC for ICE-WHR were also conducted as comparisons with R123 [43–45], water [46,47] and R600 [48]. Besides, R123 [49], R113 [50], R134a [51], and R12 [52] were also studied as the working fluids for single recovery of exhaust gas. Except the researches on subcritical form of B-ORCs, transcritical configuration becomes another choice with higher operating pressure but well matching with exhaust gas. Hence better thermal and exergy efficiencies are obtained by the transcritical configuration [53]. The fluids comparison result of transcritical configuration by Yang et al. [43,54] showed that R1234yf possessed good thermodynamic and economic performance due to its low critical pressure, which leaded low system pressure and hence reduced purchased cost of equipment. Engine coolant is another valuable waste heat with similar amount of thermal energy versus exhaust gas. Engine coolant is a low-grade waste heat and leads to low thermal efficiency being used as single heat source of ORCs. Hence, only few researches on single recovery of engine coolant could be found [55,56]. A reasonable and potential solution is to use engine coolant as a preheat source of ORC on the base of exhaust gas recovery, which has been adopted a usual configuration for ICEWHR [56–61]. Boretti [58] studied a R245fa-based ORC aiming at exhaust gas and engine coolant of a 1.8 L naturally aspirated gasoline engine, and acquired an increase in thermal efficiency of engine by 6.4% and 2.8%, individually. But the increase could reach up to 8.2% when the exhaust gas and the engine coolant were made from a combined recovery. Ma et al. [60] analyzed two different ORC configurations to recover waste heat from exhaust gas and engine coolant simultaneously. The first was part of engine coolant to preheat fluids and full of exhaust gas to evaporate fluids, and the second was full of engine coolant to preheat fluids and exhaust gas to further heat the fluid. The results presented that the first system had 3–4% higher improvement for ICE than the second did, especially under part-load conditions of engine. Yang et al. [59] used scavenge air cooling water to first preheat engine coolant (cylinder cooling water) to next preheat a R1234yf-based trancritical ORC for a marine diesel engine. This solution obtained 2.96% lower levelized energy cost (LEC) and 21.6% lower CO2 reduction than common

of waste heats [8]. Among these engine waste heats of diesel engines or gasoline engines, exhaust gas and engine coolant carry similar amount of thermal energy and account for most energy proportion of fuel combusting energy together which can even reach to above 50%. Engine coolant is a kind of low-grade waste heat with temperature below 100 °C,sometimes being used as a preheat source if ORC system required. While, exhaust gas is a kind of high-grade waste heat with temperature reaching up to above 500 °C for diesel engine and above 700 °C for gasoline engine [31], hence it becomes the main recovery object in ICE-WHR researches. With the lower temperature limit (about 120 °C) for exhaust gas recovery due to acid dew point [31–33], a largegradient temperature drop from above 500 °C to the acid dew point temperature occurs to achieve complete recovery of exhaust gas. The red line in Fig. 2 shows the large-gradient temperature drop characteristic of exhaust gas. This paper would display some schematic t-s maps for a clearer illustration of each cycle. The temperature values and cycle shapes on the t-s maps are schematic and qualitative, which, do not depend on a specific cycle. Based on it, a t-s map of ideal cycle for ICE-WHR is conducted and shown in Fig. 2. The exhaust gas with large-gradient temperature drop characteristic behaves an oblique long line which is different from that in Fig. 1 as a constant temperature heat source. The engine coolant and cold source are supposed to slight change in ICEWHR process. The ideal cycle shape is sandwiched between the heat and the cold sources additionally considering temperature difference of heat transfer process. This similar triangle shape is exactly the specific t-s shape of ideal cycle for ICE-WHR, which is different from that of other WHR fields because of the large-gradient characteristic. It prompts that real cycle of ICE-WHR should be close to this similar triangle shape to achieve a high cycle efficiency and large output, which is the target track of the ORCs review below. 3. Basic ORCs (B-ORCs) for ICE-WHR Basic ORCs (B-ORCs) in this paper are considered as single loop ORCs with working fluids of halogenated hydrocarbon refrigerants (e.g. R123, R245fa, R134a, etc.). Due to low boiling point of working fluids, the B-ORCs have generally applied to low temperature heat, such as geothermy, solar, and industrial waste heat, hence are also usually called as low-temperature ORCs. Fig. 3 schematically shows a typical BORC in a form of subcritical superheating cycle when considering the thermal decomposition temperature of most low-temperature organic fluids. Researches on B-ORCs focus on fluids selection and cycles adopted as transcritical or preheated configurations. The fluids selection is an attractive research hotspot of basic subcritical ORCs for ICE-WHR, and concentrates on the single recovery of exhaust gas. Energy and exergy analysis basing on the first and the second laws of thermodynamics respectively, and technical economic analysis form the main methodologies to evaluate performance of working fluids. Shu et al. [34] summarized a Multi-Approach Evaluation System (MA-ES) that covered the three main aspects of typical ORC performance and provided a general method for ORC assessment. By this method, a case study was conducted for subcritical and transcritical ORCs, and its results was presented as Fig. 4(a) and (b), respectively. The performance of the transcritical cycle was much better than that of subcritical cycle for a certain fluid. R123 and R245fa showed excellent performance in three evaluation aspects of ORC system. The comparison results of energy and exergy analysis by Zhu et al. [35] indicated that ethanol and R113 performed better in the whole exhaust temperature range than water, R245fa and R123 for exhaust recovery. Tian et al. [36] indicated R141b, R123 and R245fa obtained better economic performance with a total 20 working fluids comparison for exhaust recovery of a duty diesel engine. Zhang's group compared fluids performance on the base of energy analysis [37] and economic analysis [38] successively, and concluded that R245fa was the best choice for ICE-WHR application if considering environment impact. The same

Fig. 2. Schematic t-s map of ideal cycle for ICE-WHR. 97

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condition due to the limitation of low thermal decomposition temperature. Still, there has potential of improvement from the t-s map shown as the blank area between exhaust gas and the B-ORCs in Fig. 3. Therefore, various modified ORCs were conducted to further increase the cycle and approach the ideal ORC of ICE-WHR in the 2010s as well. As shown in Fig. 6, the modified ORCs are classified into two paths. From fluid aspect, it can draw the heating line to the blank field by employing special fluids; and from cycle aspect, it can add new cycle part into the blank field. 4. Modified ORCs from fluid aspect Two solutions are mainly considered to fill the blank area between exhaust gas and working fluids in t-s maps from fluid aspect. The first is to adopt another type of pure fluids having a lower limitation of thermal decomposition temperature versus to low-temperature organic fluids, so called high-temperature organic fluids, mainly including alkanes, aromatics, siloxanes and alcohols. The second is to adopt mixture fluids to improve the temperature matching not only at evaporating process, but also at condensing process.

Fig. 3. Schematic t-s map of basic ORCs (B-ORCs) for ICE-WHR.

preheat cycle that combined exhaust gas and engine coolant. Another research by Yang et al. [61] compared ORC performance by combined recovery of exhaust gas and engine coolant with five working fluids: R152a, R245fa, R600a, R1234yf and R1234ze. With a thermo-economic optimization, R1234yf performed the best in the optimal economic evaluation, followed by R1234ze, R152a, and R600a orderly. Kim et al. [57] paid attention to the limit utilization rate of engine coolant in an ORC. Only 40% of the waste heat from the engine coolant was utilized at most, which could also be found in the research by Vaja et al. [62] and Shu et al. [63]. Hence, Kim et al. [57] proposed a novel ORC configuration with one or two regenerators basing on the preheat cycle, and obtained about 90% utilization rate of both exhaust gas and engine coolant. While, Shu et al. [63,64]adopted CO2 as working fluid to achieve both high utilization rates (above 90%, Fig. 5(a)) of exhaust gas and engine coolant only by single configuration. As shown in Fig. 5(b),the peak region of supercritical CO2's specific heat capacity is located in the temperature region of engine coolant, hence greatly increases the heat absorption from engine coolant. This is why the CO2based cycle is more suitable and efficient than ORCs for combined recovery of exhaust gas and engine coolant. When the preheated CO2 cycle continued to add with a regenerator, the performance would further improved in power output increase and cooling load reduction [65,66]. However, high pressure issue becomes a challenge for application of the CO2-based cycle at present. Through the above review, the B-ORCs achieve a fast development for ICE-WHR in the 2010s. Still, the thermal matching between exhaust gas and low-temperature organic fluids cannot reach to a desired

4.1. High-temperature ORCs (HT-ORCs) Table 1 lists critical property and category of frequent high-temperature organic fluids dividing into alkanes, aromatics and siloxanes and alcohols. Most high-temperature fluids are dry or isentropic type and possess high critical temperature. Dry or isentropic fluids do not need superheating, hence preventing impingement of liquid droplets on expander blades. High critical temperature characteristic leads to well thermal matching between fluids and exhaust gas, as presented in Fig. 7. A schematic t-s map of high-temperature ORCs (HT-ORCs) is described as Fig. 8. The shape of HT-ORCs covers more area of the ideal cycle than that of the B-ORCs due to a higher operating temperature. A better thermal matching can achieve and hence result in a higher efficiency of cycle. Table 2 lists the main research information of HT-ORCs for ICE-WHR. The results of comparison investigation with B-ORCs proved the better thermodynamic performance of HT-ORCs in the open literatures of ICE-WHR. Michos et al. [79] illustrated a detailed selection process of working fluids for a heavy duty diesel power generator of marine. Based on environmental consideration, the start point amount of fluids was 25 before screen containing most of common fluids, such as alkanes, aromatics, alcohols, siloxanes, and halogenated hydrocarbon

Fig. 4. Evaluations of ORC systems by MA-ES (a) subcritical cycle (b) transcritical cycle [34]. (Pnet, net power output; η1st, efficiency based on the first law of thermodynamics; η2nd, efficiency based on the second law of thermodynamics; As, heat transfer area per net power; EPC, electricity production cost; DPP, depreciated payback period.). 98

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Fig. 5. Comparison of utilization ability between R123 and CO2: (a) utilization rate; (b) heat recovery capacity [63]. (PR-CTRC: CO2-based transcritical Rankine cycle with preheater and regenerator; PR-ToRC: CO2-based transcritical Rankine cycle with preheater and regenerator Ug, utilization rate of exhaust gas; Uec, utilization rate of engine coolant; Cp, specific heat capacity; T1, inlet temperature of the preheater; T2, outlet temperature of the preheater.).

Fig. 6. Block diagram of modified ORCs solutions.

refrigerants. Finally, only six high-temperature fluids (n-hexane, n-octane, acetone, toluene, ethanol, MDM) remained by the following rules: lower ‘Health Hazard’ level than 2, lower ‘Flammability Hazard’ level than 3, lower freezing temperature than −30 °C, higher condensation pressure than 1 bar, higher condensation and evaporation and temperature than 50 °C, lower evaporation pressure than 30 bar and higher critical temperature than 200 °C. Zhang et al. [77] conducted a theoretical research of a bottoming ORC for ICE-WHR by the Monte Carlo simulation method. Two groups of working fluids were selected: hydrocarbons (benzene, toluene, cyclohexane, isohexane, hexane and pentane) and common refrigerants (R123, R245fa, R245ca and R134a).

Fig. 7. Temperature matching with different critical temperature of organic fluids.

The results are presented in Fig. 9 and indicated that the hydrocarbons had larger net power output, higher thermal efficiency, and higher exergy efficiency than the common refrigerants at various load of ICE between 70% and 100%. The simulation results in a ship operating condition by Baldi et al. [80] showed that benzene and cyclohexane as

Table 1 Property of frequent high-temperature organic fluids. Name

Critical pressure (bar)

Critical temperature (°C)

Category

Alkanes Ethane Propane Isobutane N-butane Neopentane Isopentane N-pentane Cyclopentane Isohexane N-hexane Cyclohexane N-heptane N-octane N-nonane N-decane N-dodecane

48.7 41.8 36.4 37.9 31.6 33.7 33.6 45.2 30.4 30.6 40.7 27.3 25 22.7 21 17.9

32 96 135 152 160 187 196 238 225 235 280 267 296 321 345 382

wet wet isentropic isentropic dry dry dry isentropic dry dry dry dry dry dry dry dry

99

Name

Critical pressure (bar)

Critical temperature (°C)

Category

Aromatics Benzene Toluene

48.8 41.3

298 319

isentropic isentropic

Siloxanes MM MDM MD2M MD3M MD4M D4 D5 D6

19.1 14.4 12.2 9.3 8.8 13.1 11.6 9.5

245 291 326 354 380 312 346 371

dry dry dry dry dry dry dry dry

Alcohols Methanol Ethanol

81 40.6

240 241

wet wet

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with methanol. Grelet et al. [76] indicated that ethanol was considered suitable for a mobile application because of its high net power output. Dolz's group [73,74,81,82] conducted a series studies on a small-scale ethanol-based ORC for a gasoline engine by using a swash-plate expander, including cycle parameters optimization, exergy analysis and experimental investigation. The experimental results showed that maximum isentropic and volumetric efficiency of the swash-plate expander got 38.5% and 38.2% respectively, and cycle achieved a maximum 79% Carnot cycle efficiency, 19% ideal Rankine cycle efficiency and 6% real cycle efficiency [73]. As HT-ORCs are suitable for high-grade waste heat and B-ORCs have been proved in low temperature field, the former for high-grade exhaust gas and the latter for low-grade engine coolant as double-ORCs parallel combined system attracted the researches’ attention [71,75,78]. For a 93.0 kW HCCI engine [75], R123-based ORC and nheptane-based ORC aimed at the recovery of exhaust gas and engine coolant, obtained 9.4 kW and 6.3 kW power output, respectively. The engine's thermal efficiency increased from 39.4% to 45.0% by the two bottoming ORCs. And for 996 kW marine diesel engine [71], R245fa and benzene were selected for the recovery of exhaust gas and engine coolant respectively. 10.3 kW net power output and 5.2% thermal efficiency were obtained by the R245fa-based ORC, 90.8 kW and 21.3% were obtained by the benzene-based ORC, then totally 10.2% increase was gained for engine thermal efficiency. Compared with the two separated system, a cyclohexane-based preheating ORC was presented, and 99.7 kW net power output was obtained, only 1.4% lower than the former. But 34.5% reduction of capital cost would be gained by preheating ORC. Hence two separate ORCs would be a questionable solution because double of complexity increase of system. From the previous researches, HT-ORCs have desirable thermodynamic properties, especially for alkanes and aromatics. But the flammability and toxicity are their neckbottle problems. The ASHRAE refrigerant safety classification is a good indicator of danger level for fluids. Good sealing and excellent ventilation must be two satisfied conditions for HT-ORCs in practical application. Besides, mixtures based on these flammable fluids and retardant may be good alternatives

Fig. 8. Schematic t-s map of high-temperature ORC (HT-ORC) for ICE-WHR.

working fluids of ORC got the most saving fuel yearly of the ship, followed by toluene, MDM and MM. R245fa and R236ea performed worse than the five high-temperature fluids. Investigations on selection of high-temperature fluids are also available in open literatures. Shu et al. [68] studied the energy and exergy performance of HT-ORCs for a diesel engine with ten alkanes as working fluids. The results pointed out cyclohexane and cyclopentane were the most suitable fluids, which obtained relatively high power output and low irreversibility, and also reasonable condensing pressure. The significant and positive rule between molecular complexity of alkanes and turbine size parameter, turbine volume flow ratio were also investigated to indicate the possibility of a simple turbine application. But when cyclohexane was compared with aromatics (benzene and toluene) in the thermodynamic investigation of Neto et al. [72], it performed lower first law and second law efficiency. Toluene also got higher net power output than methanol in the research by Benedikt [70], but the desirable choice of authors was methanol with stable performance when fitting for changes in temperature or pressure. While, ethanol was the more common alcohols for ICE-WHR compared

Table 2 Review of HT-ORCs for ICE-WHR. Year [Sources]

Engine type/ power (kW)

Exhaust temp. (°C)

ORC conf.

Working fluids

Performance

2010 [67]

diesel engine (8900)

346

trans (IHX)

MM

2014 [68]

diesel engine (235.8)

519

sub

2015 [69]

diesel engine (200–2000)

146–439

trans (IHX)

cyclohexanea, cyclopentanea, decane, nonane, octane, heptane, hexane, isohexane, pentane, isopentane n-decanea, n-dentane, n-hexane, n-heptane, noctane, n-nonane

For two engines, Wnet = 1603 kW; ηth = 21.5% Max. Wnet = 162.03 kW (cyclopentane);

2015 [70]

diesel engine (235.8)

519

sub

methanola, toluene, solkatherm

2015 [71] 2016 [72]

diesel engine (996) diesel engine (830)

275–300 473.2

sub sub

2015 [73] 2016 [74] 2016 [75]

gasoline engine (12.9–44.8) gasoline engine (93.05) diesel engine (/)

429–673

sub

cyclohexanea, benzene toluene, nonane, decane toluenea, acetone, benzene, byclohexane, heptane, hexane, octane ethanol

/

sub

n-heptane

Max. Wnet = 362 kW (n-decane) Max. ηth = 31.7% (n-nonane); Max. ηex = 64.1% (n-nonane) Max. ηth = 24.1% (Methanol); Methanol was more stable than Toluene and had higher average thermal efficiency. Max. Wnet = 99.7 kW (cyclohexane) Max. Wnet = 162.03 kW (toluene) EPS = 12362.23 R$/kW Experimental data: 0.21–1.83 kW power; 3.7% engine efficiency increase. Max. Wnet = 9.412 kW (only by exhaust gas)

212.5–581.0

diesel engine (180–250) dual-fuel engine (17,550) /

448–458

sub (IHX) sub

acetonea, ethanola, D4, ethylene, glycol, MD2M, MDM, MM, et al. benzenea, pentane, isohexane, hexane, cyclohexane, toluene, et al. n-pentanea, n-hexane

Acetone and ethanol show good performance at mid and high engine load; Hydrocarbons show more net power output than refrigerants (R134a, R245fa, R245ca and R123). Max. Wnet = 162.03 kW (n-pentane)

acetonea, n-hexane, n-octane, toluene, ethanol, MDM

ORCs reducing 17.7–19.7 g/kWh BSFC (9.1–10.2%).

2016 [76] 2016 [77] 2016 [78] 2017 [79]

a

373 466.8–484.5

sub (IHX) sub (IHX)

Optimal fluid indicated in the references or the ones with best output performance. 100

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Fig. 9. Variations of ORC performances versus sink temperature [77].

WHR field, alkanes, aromatics and siloxanes are the usual choices as the major composition of mixtures, which play the role of maintaining good thermodynamic property. Retardants are the other composition of mixtures to ensure acceptable flammability, which are mainly classified into two sorts: non-flammable refrigerants (e.g. R123, R11) and inert nature fluids (e.g. CO2). Shu et al. [88] investigated the group performance of hydrocarbon (cyclopentane, cyclohexane and benzene) and retardant (R123, R11) for diesel exhaust’ WHR based on energy end exergy analysis. As shown in Fig. 11(a) and (b), the results showed that thermal efficiency and exergy efficiency of all the groups firstly increased and then decreased with an increase in the mass fraction of retardants. Different optimal ratios existed for different mixtures and gradually approached the side of fewer retardants with an increase in evaporation temperature. The group of benzene/R11 (0.7/0.3) was the promising one to show the best performance. A similar investigation of blending cyclohexane with retardant (R11, R141b) was conducted by

to solve this safety issue, which would be illustrated in Section 4.2. 4.2. Mixture ORCs (M-ORCs) Mixture fluids are usually supposed to be binary or ternary zeotropic mixtures in ORC applications. From the thermodynamic perspective, mixture fluids can match the temperature profile of heat and cold sources by non-isothermal phase change. As shown in Fig. 10, more area is filled into the region ideal cycle by mixture ORCs (MORCs) compared with the B-ORCs, not only occurring between fluids and heat sources, but also at the cold side. Hence, M-ORCs are supposed as one solution to approach the ideal cycle. Panesar [83] aimed at exhaust gas recovery of diesel engine and conducted a fluids comparison study between two pure fluids, toluene and hexamethyldisiloxane (MM), and their mixtures types, T80 (80% toluene and 20% MM by mass) and MM80 (80% MM and 20% MM by mass). Compared with pure fluids, the two mixtures dealt well with irreversibility loss of phase-change process, had greater temperature and pressure difference for fixed expansion volume by higher density, and finally obtained 20–25% improvement in thermal efficiency, net power output but 5–18% lower electricity production cost (EPC). A comparison study between a mixture of isopentane/R245fa in a 0.7/0.3 mol fraction and pure R245fa as working fluid of regenerative ORC was conducted by Zhang et al. [84] for a diesel engine’ WHR. More net power output, higher exergy efficiency, lower optimum evaporating pressure and exergy destruction rate were provided by isopentane/R245fa than R245fa. This group also attempted several kinds of ternary mixtures for ICE-WHR [85–87], whose main components were low-temperature fluids. From another perspective mentioned in Section 4.1, high-temperature fluids possess good thermodynamic property but are usually flammable, hence mixtures of flammable high-temperature fluids and retardant might be suitable alternatives to solve the safety issue. In ICE-

Fig. 10. Schematic t-s map of mixture ORC (M-ORC) for ICE-WHR. 101

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Fig. 11. Efficiency variation with mass fraction of retardants: (a) thermal efficiency; (b) exergy efficiency. [88].

fraction of retardants should keep staying outside of flammable zone as shown in Fig. 12. Hence it is significant to gain upper and lower flammability of mixtures, for which Shu et al. [91–93] proposed theorybased models to make a prediction and achieve an accurate verification with experimental data. Therefore, it is necessary to conduct a combined study of thermodynamic analysis and flammability evaluation in the investigation of M-ORCs.

Song et al. [89] for a larger scale engine, but additional with engine coolant preheating. Cyclohexane/R141b (0.5/0.5) was optimal group and obtained 13.3% higher net power output than pure cyclohexane. Moreover, higher utilization rate of engine coolant by mixtures than pure fluids was concluded in this research. The thermodynamic and economic analysis was given by Tian et al. [90] for the transcritical configuration of M-ORCs with siloxanes (D4, MDM, MD2M) and R123. Among all the groups, D4/R123 (0.3/0.7) owned the highest net power output the highest thermal efficiency, as well as the highest exergy efficiency and the lowest exergy destruction. But MD2M/R123 (0.35/ 0.65) obtained the best economic performance with the smallest EPC of 0.603 $/kW h. As analyzed on the above researches, the mass fraction of retardants is a significant parameter impacting on the thermodynamic performance of M-ORCs. For direct reference, Table 3 lists the optimal mixtures and corresponding mass fraction of components in the main MORCs researches. Moreover, the mass fraction of retardants also determines the flammability of mixtures. Fig. 12 describes the flammable and nonflammable zone with the mass fraction of retardants as X-axle and mixture concentration in the air as the Y-axle. The composition

5. Modified ORCs from cycle aspect From cycle aspect, two solutions are classified to fill the blank area between exhaust gas and B-ORCs. The first is to add extra loops on the base of B-ORCs. The extra loops play a role of reducing temperature of exhaust gas so as to make it suitable for B-ORCs. The second is to adopt dual-loop ORCs (DORCs), including a high-temperature loop ORC (HTLoop ORC) to utilize high-grade exhaust gas and a low–temperature loop ORC (LT-Loop ORC) to utilize the residual heat of exhaust gas, engine coolant, the residual heat of the HT-Loop ORC and other engine low-grade waste heats.

Table 3 Optimal mixtures and mass fraction of M-ORCs for ICE-WHR. Year [Sources]

Engine type/ Power (kW)

Exhaust temp. (°C)

ORC conf.

Fluids pair (mass fraction)

Optimal pair (mass fraction)

2013 [85]

diesel engine (~280)

~546

sub

R125/propane/R22 (0.38/ 0.02/0.6)

2014 [88]

diesel engine (/)

519

sub (IHX)

2014 2014 2015 2015

diesel engine (~279) diesel engine (~280), CNG engine (1100) diesel engine (996)

/ /

sub sub (IHX)

R22/R152a (0.25/0.75), Propylene/R22/R152a (0.03/0.94/0.03), R125/propane/R22 (0.38/0.02/0.6), R32/R125/R134a (0.1/0.7/0.2), R22/R152a/R124 (0.53/0.13/0.34), R32/R125/R134a (0.15/0.15/0.7), R22/R124/R142b (0.65/0.25/0.1), R22/R124/R142b (0.6/0.25/0.15) cyclopentane/ R11, cyclohexane/ R11, benzene/ R11, cyclopentane/ R123, cyclohexane/ R123, benzene/ R123 (all mass fraction: 0–1) Isopentane/R245fa (0.7/0.3) (mol fraction) R134a/R124/R600 (0.59/0.395/0.015)

300

sub (IHX)

2016 [83]

diesel engine (316)

420

sub (IHX)

2017 [90]

diesel engine (243)

445

trans-sub DORC

[84] [86], [87] [89]

cyclohexane/R141b (0.8/0.2 0.7/0.3 0.6/0.4 0.5/0.5), cyclohexane/R11 (0.8/0.2 0.7/0.3 0.6/0.4 0.5/0.5) toluene/MM (0.8/0.2) toluene/MM (0.2/0.8) toluene/MM (0.8/0.2) toluene/MM (0.2/0.8) D4/R123 (0.3–0.7/0.7–0.3), MDM/R123 (0.3–0.7/0.7–0.3), MD2M/R123 (0.41–0.65/0.59–0.35)

* Optimal mixtures indicated in the references or the ones with best output performance. 102

benzene /R11 (0.7/0.3)

Isopentane/R245fa (0.7/0.3) R134a/R124/R600 (0.59/ 0.395/0.015) cyclohexane/R141b (0.5/ 0.5) toluene/MM (0.2/0.8)

D4/R123 (0.3/0.7)

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Fig. 12. Flammable and nonflammable zone for the flammable mixtures: (a) schematic diagram; (b) experimental and predicted diagram of propane/C3H8. (y, mass fraction of retardant).

ranging from 23.6% to 28.3% was obtained by the biomass-fuelled plants with different setups. However, in spite of the usefulness displayed above, the way of medium circuit has significant disadvantage from thermodynamic aspect. As shown in Fig. 13, the medium circuit certainly produces no effective work area in the t-s map, which is just a process for positive reduction of heat source grade without any power output. Both energy loss and exergy loss are produced during heat conduction. Shu et al. [100] compared a B-ORC combined with thermal oil circuit for WHR of a large gas engine, with steam Rankine cycle, two-stage ORC and HTORC in the thermodynamic and economic aspects. Evaluation results indicated that the B-ORC combined with thermal oil circuit obtained the lowest power output and the highest EPC. Yu et al. [97] conducted a theoretical simulation of an a R245fa-based ORC system combined with a thermal-oil circuit for WHR of diesel engine. The thermal-oil circuit only made heat transfer with exhaust gas, and engine coolant was used as the preheat source before thermal-oil heating the fluid. As revealed in the energy distribution diagram (Fig. 15), this system only obtained approximately 75% and 9.5% utilization rate of exhaust gas and engine coolant respectively under the most engine conditions. The second method is to cool exhaust gas firstly by other WHR systems, and then to lead the cooled exhaust gas to drive the B-ORCs safely. Different from thermal oil circuit, the first step of this method can generate extra power. Actually, this method has been mentioned in Section 4.2 [71,75,78,90], which makes the exhaust gas flow into HTORC and B-ORC successively. The HT-ORC undertakes the exhaust gas with high temperature. In this part, another WHR system, thermoelectric generator (TEG), takes this role. The exhaust gas firstly goes

5.1. Combined with extra loops (medium circuit or thermoelectric generator) For reducing the temperature of heat source contacting with organic fluids, the first method is heat conduction. By employing a heat transfer medium circuit, heat from the high-temperature exhaust gas converts to the relatively low temperature medium,whose t-s expression is shown in Fig. 13 and typical system structure is shown in Fig. 14. Generally, thermal oil is used as the heat-conducting medium between high-temperature exhaust gas and B-ORCs, which makes heat source from above 500 °C reducing to about 200 °C, which is a safe temperature for BORCs. Except thermal oil, water is also a medium choice but is used fewer [94]. Moreover, thermal oil shows great inertia against variation of heat sources and simple adaptability to load changes, which is just suitable for unstable operating condition of engine and has been proved by an experimental investigation of Shu et al. [95]. A R123 ORC combined with thermal-oil circuit was employed for WHR of a 240 kW diesel engine. During all the various engine condition with exhaust gas temperature from 200 °C and 480 °C, the temperature of thermal oil was from 81 °C and 222.5 °C, which prevented the thermal decomposition of R123. And it was promising to conclude from the response test that the system with thermal oil circuit was able to keep generating power when the engine condition changed vastly even shut down. Vaja [96] also displayed the significance of a medium circuit, which was not only for safety but also to stabilize the transient operation of the ORC system. Integration of multiple heat sources is another useful aspect of adding the medium circuit. Generally, more than one engine are set in a power plant where engines provide powers. The scheme of ‘one ORC for one engine’ is not desirable for these engines’ WHR, because it means more complexity and more cost. Using one thermal oil circuit provides a chance to collect all waste heats of these engines then drives only one ORC system. This solution keeps the ORC operating continually when only part of engines work. An economic calculation by Gewald et al. [98] showed a great difference between the system with or without waste heats integration of multiple heat sources by thermal oil circuit. 23.67 €/MW.h specific costs of electricity generation was for the only one ORC system integrated by thermal oil circuit, extremely lower than that of 9 units ORC system, which reached up to approximately 80 €/ MWh. The reason for the much higher costs of the 9 units ORC system was that, multiple manufacture, installation and connection to the grid of the 9 units was needed. The thermal oil circuit can be also used for integrating engine waste heats with other heat source. Kalina [99] conducted a thermal oil circuit to collect exhaust gas heat of a gas engine and raw gas heat of a downdraft gasifier, then to drive the bottoming ORC system. The total electricity generation efficiency

Fig. 13. Schematic t-s map of B-ORCs combined with oil cycle for ICE-WHR. 103

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Fig. 14. Schematic diagram of basic ORC combined with thermal oil cycle for ICE-WHR [97].

20.86 kW to 23.60 kW. However, it played an important role in practice to run the accessories such as boost pump and fans in engines. As compared with other combined system such as dual-loop ORC and Brayton-ORC [104], TEG–ORC system showed worse thermodynamic performance, namely lower output power, thermal efficiency and exergy efficiency, but reduced size/economic parameters. At present, low thermal-power conversion efficiency and expensive cost are the main restrains of TEG [105–107]. Thus, the TEG-ORC system has not attracted much attention so far, but this situation would change if thermoelectric material achieves breakthroughs. Although the exhaust gas can be cooled down by the addition with medium circuit or TEG system, but sacrifices the highest grade of heat source with no or little power output. It is a way to make heat source adapt to bottoming system, which reduces the potential area of ideal cycle in t-s maps. Still, making bottoming system adapt to heat source is more reasonable to approach the ideal cycle, like the HT-ORCs and MORCs in previous section, and the cascaded ORCs in next section. Fig. 15. Energy distribution of the diesel engine and the engine-ORC combined system [97]. (DE, diesel engine).

5.2. Dual-loop ORCs (DORCs) Fig. 18 displays the structure of typical and simple dual-loop ORC (DORC) for ICE-WHR. The HT-Loop ORC utilizes waste heat of exhaust

through a TEG system firstly, and then drives the B-ORCs. Fig. 16 describes a symbolic process of the TEG-ORC, which is not tenable in the t-s map actually and just for intuitionistic display of TEG-ORC combined system. Miller et al. [101] firstly proposed the TEG-ORC combined system to utilize high-grade thermal energy of engines and industrial waste heat. The schematic diagram of TEG-ORC is shown in Fig. 17. The TEG system generated electric power by the temperature difference between the high temperature exhaust gas and low temperature working fluid. After some temperature reduction in TEG system, the exhaust gas flowed into the ORC. The TEG system not only generated power by itself, but also transferred energy to preheat the ORC system by its cool side. On the base, Shu et al. [102,103] conducted investigations of similar TEG-ORC system with more complete mathematical models. The results showed that exhaust gas was cooled down by TEG system from 792 K to about 500 K, with 2.44–3.59 kW electric power output during this process under typical conditions. But power output of TEG was much smaller than that of ORC ranging from

Fig. 16. Schematic t-s map of basic ORC combined with TEG for ICE-WHR. 104

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choice for transcritical and subcritical configuration, respectively [109,110]. Among these pairs, toluene and R143a based trans-trans DORC achieved the highest net power output of 42.46 kW [109]. DORC presented good combined capability of different grate waste heats with both high utilization rate of exhaust gas and engine coolant [108], which was achieved difficultly by a single-loop ORC mentioned in Section 3. An experimental investigation of water/R123 DORC was conducted by Shu's group [112], which is rare for DORCs research at present. Test results estimated that the DORC system could gain 5.6% power improvement than basic diesel engine, and 3.2% power improvement than thermal oil/R123 ORC system. In other similar research, cyclohexane/R236fa [113] RC318/R1234yf [114] R1233zd/ R1234yf [115] and R245fa/R134a [116] were the desirable pairs of high/low loop working fluids. On the base of typical DORC, Chen at al. [117] proposed a confluent cascade expansion ORC system (CCE-ORC) to achieve a simpler structure, a smaller volume and higher efficiency. The system structure is shown in Fig. 20. The same working fluid was used in HT-Loop ORC and LT-Loop ORC. The working fluid after HTLoop turbine and that after LT-Loop evaporator came together, and then flowed into the LT-Loop turbine. Compared with the cyclopentane/R245fa conventional DORC, 7.94% more net power output and 18% smaller volume were obtained by the CCE-ORC with cyclopentane as working fluid. As shown in Fig. 21, the mixing process in the CCE-ORC system produced only about 1.2 kW exergy loss, while the intermediate heat exchanger in the DORC system caused about 4 kW exergy loss, Hence, thermal efficiency of CCE-ORC system (11.67%) was slightly higher than that of the DORC system (11.39%). DORCs are also adopted to combined use of more waste heats of engines, including waste heat of exhaust gas recirculation (EGR) and charge air except exhaust gas and engine coolant. Shu et al. did an integrated utilization of exhaust gas, engine coolant, EGR and charge air by DORC for a diesel engine, which is present in Fig. 22 [118,119]. According to the grade of waste heats, the working fluids after pumping was heated by the high-temperature charge air, engine coolant, lowtemperature charge air, residual heat of HT-Loop ORC, residual heat of exhaust gas and EGR in sequence. Multi-approach evaluations were conducted for the DORC and this methodology was ever introduced in Ref. [34]. From the fluids selection results of the HT-Loop and the LTLoop, toluene/R143a was the best pair from the thermodynamic evaluations (e.g. net power output results shown in Fig. 23) [118] and economic evaluations [119]. More optimization work at configuration design, downsizing and investment reduction of components should be required due to unacceptable economic performance of present design. Moreover, a simpler system was proposed by Zhang’ group [120–123] with LT-Loop ORC only utilizing charge air, engine coolant, residual heat of HT-Loop ORC. Similarly, much analysis was conducted from thermodynamic and economic aspects for it, mainly concentrating at the parameters analysis with the fixed working fluids. From the thermodynamic perspective, DORCs have advantages of

Fig. 17. Schematic diagram of basic ORC combined with TEG for ICE-WHR [101].

Fig. 18. Schematic diagram of typical dual-loop ORC (DORC) for WHR of exhaust gas and engine coolant.

gas, and the LT-Loop ORC utilizes the residual heat of exhaust gas, engine coolant, and the residual heat of the HT-Loop ORC. It abides by the rules of “according to the quality of energy”, with HT-Loop ORC for high-grade waste heat, LT-Loop for low-grade waste heats. As shown in Fig. 19, a satisfactory result is obtained by DORC that, the area of ideal cycle is almost filled by the DORC. There are four configurations of DORC according to the types of HT-Loop ORC and LT-Loop ORC: subcritical–subcritical (sub-sub) DORC, subcritical–transcritical (sub-trans) DORC, transcritical–subcritical (trans-sub) DORC, and transcritical–transcritical (trans-trans) DORC. The selection of cycle configurations and corresponding working fluids are the focus of DORCs research. Table 4 lists the main research information of DORCs for ICE-WHR. For combining recovery of exhaust gas and engine coolant by DORCs, Shu's group did a systematic research on selection of cycle configurations and working fluids for a 235.8 kW heavy-duty diesel engine, both at HT-Loop ORC and LT-Loop ORC aspects [108–111]. The Results showed that R143a and R1234yf performed the best as the working fluid of transcritical and subcritical LT-Loop ORC, respectively [108,111]. And for the HT-Loop ORC, toluene and water were the best

Fig. 19. Schematic t-s map of dual-loop ORCs (DORCs) for ICE-WHR. 105

106

diesel engine258.9 kW

CNG engine 210 kW CNG engine 210 kW

2017 [117]

2017 [115] 2017 [123]

exhaust gas, engine coolant exhaust gas, engine coolant, charge air

exhaust gas, EGR, engine coolant, charge air exhaust gas, engine coolant

exhaust gas, EGR, engine coolant, charge air

exhaust gas, engine coolant,

exhaust gas, engine coolant, exhaust gas, engine coolant

exhaust gas, engine coolant,

exhaust gas, engine coolant, charge air exhaust gas, engine coolant, charge air exhaust gas, engine coolant, charge air exhaust gas, engine coolant

exhaust gas, engine coolant,

exhaust gas, engine coolant

exhaust gas, engine coolant exhaust gas

Recovery objects

Optimal fluid with the best thermodynamic performance.

diesel engine 243 kW

2016 [119]

a

diesel engine 243 kW

diesel engine235.8 kW

2014 [108]

2016 [118]

diesel engine 105 kW

2014 [122]

diesel engine 235.8 kW

diesel engine 247 kW

2014 [121]

2016 [114]

diesel engine 105 kW

2013 [120]

diesel engine996 kW diesel engine760kW

diesel engine 235.8 kW

2013 [111]

2015 [113] 2016 [126]

diesel engine 235.8 kW

2013 [110]

diesel engine235.8 kW

gasoline engine 130 kW diesel engine 68.52 MW

2012 [116] 2013 [125]

2014 [109]

Engine type / power

Year [Source]

Table 4 Review of DORCs for ICE-WHR.

trans (IHX) sub

sub

trans (IHX)

trans (IHX)

sub

sub sub

trans (IHX)

sub

sub

sub (IHX)

sub

sub

trans/sub (IHX)

sub trans

HT-Loop configuration

sub (IHX) sub

sub

trans

trans

sub

sub trans

trans (IHX)

sub

sub

sub

sub

sub/ trans

trans (IHX)

sub sub

LT-Loop configuration

mixtures(RC318/R1234yf, butane/R1234yf, RC318/R245fa), butane, RC318, R1234yf, R245fa R143aa, R125, R218, R41

R143aa, R125, R218, R41 cyclopentana, R134a , butane , R245fa , R1233zd-e , pentane R1234yfa, R134a, R143a, ethanol R245fa

toluene , decane, cyclohexane, D4

toluenea, decane, cyclohexane, D4 cyclopentana, R134a , butane , R245fa , R1233zd-e , pentane R1233zda, R245fa,toluene, water R245fa

a

R245faa, R123, R236fa R143a

cyclohexanea, benzene and toluene watera, R123, R245fa, ethanol, R141b

water

R143a

Wnet = 29 kW ηex = 38.62% ηth = 11.67% Wnet = 32.2 kW Wnet = 23.62 kW ηth = 10.17%

Wnet = 33.9 kW ηth = 9.9% ηex = 39.1% EPC = 0.27 $/kW.h

Wnet = 36.77 kW ηex = 55.05% Wnet = 42.46 kW ηex = 51.92% ηth = 12.77% Wnet = 111.2 kW Wnet = 96.92 kW ηth = 14.13% ηex = 64.04% Wnet = 34.0 kW

R1234yfa, R124, R134a, R245fa, R600, R600a

R134a

Wnet = 27.85 kW ηth = 5.4% Wnet = 21.12 kW

Wnet = 35.96 kW Wnet = 2.07 MW ηth = 10.93% ηex = 58.77% Wnet = 39.67 kW ηex = 42.98% Wnet = 39.91 kW ηex = 48.42% Wnet = 18.89 kW

Performance

R245fa

toluenea, MM, D4, MDM, cyclohexane, n-decane

water

R245fa

R245fa

R245fa

R143aa, R125, R218(trans); R124, R134a, R245fa, R600, R600a, R1234yf(Sub); R134a

R143a

watera, siloxane water

R134a R1234yf

LT-Loop fluid

R245fa water

HT-Loop fluid

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suitable for stationary engines. Moreover, to find further safe and highefficiency high-temperature working fluid is another significant point for the DORCs. Thus, detailed economic analysis and rigorous working fluid selection should be specially considered in a concrete application. Meanwhile, against such a complex system with a large amount of parameters, effective optimization of DORC is necessary. In previous DORC research, the Genetic Algorithm is a frequently used method for multi-objective and multi-parameter optimization [123,124]. 6. Future research discussion Over the past decade, substantial progress has been made in fluid and configuration aspects of modified ORCs, such as HT-ORCs, M-ORCs, DORC, etc., which has greatly expanded ability of ORCs for ICE-WHR, also provides a reference for other fields of multiple heat sources and large-gradient heat sources. While, potential and challenge remain, research is needed in several areas. From fluid aspect, investigation of new organic fluids with environmental, safe, stable properties, and good thermophysical characteristic is an eternal topic. Besides, specific fluids selection for automotive application would be an attractive research point, which requires the fluids giving consideration to miniaturization potential and substantial thermodynamic performance simultaneously. For example, CO2 and CO2-based mixture organic fluids present the potential in the aspect in recent years. Relatively, further modification and innovation from configuration aspect shows less potential. The DORCs have excavated considerable efficiency improvement, and been represented as the most proximate way closing to ideal cycle of ICE-WHR among the modified ORCs. While, as their configurations are complicated, DORCs are more suitable for stationary engines. Therefore, research on multiple energy generation combined with the DORCs shows valuable prospect for stationary engines (e.g. CNG stationary power units).

Fig. 20. Schematic diagram of CCE-ORC system [117].

7. Conclusions In this comprehensive review, relevant modified ORCs for ICE-WHR were analyzed from cycle and fluid aspects. The ideal cycle for ICEWHR was defined as the optimal matching cycle with engine waste heats, which displayed as a triangle shape in t-s map. On the base, modified ORCs were divided into four parts to approach the ideal cycle: namely HT-ORCs and M-ORCs from the fluid aspect, B-ORCs combined with extra loops and DORCs from the cycle aspect. The HT-ORCs and M-ORCs can achieve better thermodynamic performance with a better thermal matching compared with the B-ORCs; the ORCs combined with thermal oil circuit takes the advantages of

Fig. 21. Exergy loss comparison between the CCE-ORC system and the DORC system [117].

higher net power, higher thermal and energy efficiency, which are represented as the most proximate way closing to ideal cycle of ICE-WHR. However, the system complexity is the main problem, leading higher difficulty of arrangement and operation, and more cost, which is more

Fig. 22. Schematic diagram of dual-loop ORC (DORC) for WHR of exhaust gas EGR, charge air and engine coolant [118,119]. 107

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Fig. 23. Fluids comparison for the DORC: (a) HT-Loop; (b) LT-Loop [118]. (EIP, expander inlet pressure).

great transient performance when engine condition changes vastly; the TEG-ORCs cool down exhaust gas to adapt for the B-ORCs with extra electric power output; the DORCs can achieve integrated recovery of multiple engine waste heats, which are the most proximate way closing to ideal cycle for ICE-WHR in the t-s map. The modified ORCs provide various solutions with various effects. In the future, more research is needed in the future, such as specific fluids selection for automotive application that gives consideration to miniaturization potential and substantial thermodynamic performance simultaneously, and research on multiple energy generation combined with DORCs for stationary engines.

[13] [14] [15]

[16] [17]

[18]

Acknowledgements

[19]

The authors would like to acknowledge the National Natural Science Foundation of China (No. 51676133 and No. 51636005) for grants and supports.

[20]

References

[21] [22]

[1] Alagumalai A. Internal combustion engines: progress and prospects. Renew Sustain Energy Rev 2014;38:561–71. [2] Yao M, Zheng Z, Liu H. Progress and recent trends in homogeneous charge compression ignition (HCCI) engines. Prog Energy Combust Sci 2009;35:398–437. [3] Feneley AJ, Pesiridis A, Andwari AM. Variable geometry turbocharger technologies for exhaust energy recovery and Boosting‐a review. Renew Sustain Energy Rev 2016;71:959–75. [4] Murata Y, Kusaka J, Odaka M, Daisho Y, Kawano D, Suzuki H, et al. Emissions suppression mechanism of premixed diesel combustion with variable valve timing. Int J Engine Res 2007;8:415–28. [5] Liu T, Hu X, Li S, Cao D. Reinforcement learning optimized look-ahead energy management of a parallel hybrid electric vehicle. IEEE/ASME Trans Mechatron 2017:1. [6] Hu X, Jiang J, Bo E, Cao D. Advanced power-source integration in hybrid electric vehicles: multicriteria optimization approach. IEEE Trans Ind Electron 2015;62:7847–58. [7] Martinez CM, Hu X, Cao D, Velenis E, Gao B, Wellers M. Energy management in plug-in hybrid electric vehicles: recent progress and a connected vehicles perspective. IEEE Trans Veh Technol 2017;66:4534–49. [8] Fu J, Liu J, Feng R, Yang Y, Wang L, Wang Y. Energy and exergy analysis on gasoline engine based on mapping characteristics experiment. Appl Energy 2013;102:622–30. [9] Payri F, Olmeda P, Martín J, Carreño R. Experimental analysis of the global energy balance in a DI diesel engine. Appl Therm Eng 2015;89:545–57. [10] Singh DV, Pedersen E. A review of waste heat recovery technologies for maritime applications. Energ Convers Manag 2016;111:315–28. [11] Bao J, Zhao L. A review of working fluid and expander selections for organic Rankine cycle. Renew Sustain Energy Rev 2013;24:325–42. [12] Morgan D, Patel P, Doyle E, Raymond R, Sakhuja R, Barber K. Laboratory test

[23]

[24]

[25]

[26]

[27] [28]

[29] [30]

[31]

108

results, low emission ranking-cycle engine with organic-based working fluid and reciprocating expander for automobiles. Intersociety Energy Conversion Engineering Conference; 1973. Patel PS, Doyle EF. Compounding the truck diesel engine with an organic Rankinecycle system. Diesel Trucks 1976. Doyle E, Dinanno L, Kramer S. Installation of a diesel-Organic Rankine compound engine in a class 8 truck for a single-vehicle test. Soc Automot Eng Prepr 1979. Delgado O, Nic L. The US SuperTruck program: Expediting the development of advanced heavy-duty vehicle efficiency technologies. The International Council on Clean Transportation; June 2014. C-70 C-71 C-73 C-75 C-76 C-77 C-78 C-79. Teng H. Waste heat recovery concept to reduce fuel consumption and heat rejection from a diesel engine. Sae Int J Commer Veh 2010;3:60–8. Teng H, Klaver J, Park T, Hunter GL, Velde BVD. A Rankine cycle system for recovering waste heat from HD diesel engines - Experimental results. Eur J Plant Pathol 2011;1:1–11. Ringler J, Seifert M, Guyotot V, Hübner W. Rankine cycle for waste heat recovery of IC engines. Sae Int J Engines 2009;2:67–76. Horst TA, Rottengruber HS, Seifert M, Ringler J. Dynamic heat exchanger model for performance prediction and control system design of automotive waste heat recovery systems. Appl Energy 2013;105:293–303. Horst TA, Tegethoff W, Eilts P, Koehler J. Prediction of dynamic Rankine Cycle waste heat recovery performance and fuel saving potential in passenger car applications considering interactions with vehicles' energy management. Energ Convers Manag 2014;78:438–51. Plotkin S, Stephens T, Mcmanus W. Vehicle technology deployment pathways: an examination of timing and investment constraints. Transp Energy Futures 2013. Arnaud L, Ludovic G, Mouad D, Hamid Z, Vincent L. Comparison and impact of waste heat recovery technologies on passenger car fuel consumption in a normalized driving cycle. Energies 2014;7:5273–90. Gabriel-Buenaventura A, Azzopardi B. Energy recovery systems for retrofitting in internal combustion engine vehicles: a review of techniques. Renew Sustain Energy Rev 2015;41:955–64. Liang X, Wang X, Shu G, Wei H, Tian H, Wang X. A review and selection of engine waste heat recovery technologies using analytic hierarchy process and grey relational analysis. Int J Energy Res 2015;39:453–71. Saidur R, Rezaei M, Muzammil WK, Hassan MH, Paria S, Hasanuzzaman M. Technologies to recover exhaust heat from internal combustion engines. Renew Sustain Energy Rev 2012;16:5649–59. Karvonen M, Kapoor R, Uusitalo A, Ojanen V. Technology competition in the internal combustion engine waste heat recovery: a patent landscape analysis. J Clean Prod 2016;112:3735–43. Wang T, Zhang Y, Peng Z, Shu G. A review of researches on thermal exhaust heat recovery with Rankine cycle. Renew Sustain Energy Rev 2011;15:2862–71. Zhou F, Joshi SN, Rhote-Vaney R, Dede EM. A review and future application of Rankine cycle to passenger vehicles for waste heat recovery. Renew Sustain Energy Rev 2016:75. Iii CS, Depcik C. Review of organic Rankine cycles for internal combustion engine exhaust waste heat recovery. Appl Therm Eng 2013;51:711–22. Teng H, Regner G, Cowland C. Waste heat recovery of heavy-duty diesel engines by organic rankine cycle part II: working fluids for WHR-ORC. Sae Tech Pap 2007;1:1–13. Wang T, Zhang Y, Zhang J, Peng Z, Shu G. Comparisons of system benefits and thermo-economics for exhaust energy recovery applied on a heavy-duty diesel engine and a light-duty vehicle gasoline engine. Energy Convers Manag 2014;84:97–107.

Renewable and Sustainable Energy Reviews 92 (2018) 95–110

L. Shi et al.

Rankine Cycles (ORCs). Energy 2010;35:1084–93. [63] Shu G, Shi L, Tian H, Li X, Huang G, Chang L. An improved CO 2 -based transcritical Rankine cycle (CTRC) used for engine waste heat recovery. Appl Energ 2016;176:171–82. [64] Shi L, Shu G, Tian H, Huang G, Chang L, Chen T, et al. Ideal point design and operation of CO 2 -based transcritical rankine cycle (CTRC) system based on high utilization of engine's waste heats. Energies 2017;10:1692. [65] Shi L, Shu G, Tian H, Huang G, Chen T, Li X, et al. Experimental comparison between four CO2-based transcritical Rankine cycle (CTRC) systems for engine waste heat recovery. Energy Convers Manag 2017;150:159–71. [66] Shu G, Shi L, Tian H, Deng S, Li X, Chang L. Configurations selection maps of CO 2 -based transcritical Rankine cycle (CTRC) for thermal energy management of engine waste heat. Appl Energy 2016;186:423–35. [67] Bombarda P, Invernizzi CM, Pietra C. Heat recovery from Diesel engines: a thermodynamic comparison between Kalina and ORC cycles. Appl Therm Eng 2010;30:212–9. [68] Shu G, Li X, Tian H, Liang X, Wei H, Wang X. Alkanes as working fluids for hightemperature exhaust heat recovery of diesel engine using organic Rankine cycle. Appl Energy 2014;119:204–17. [69] Chen Y, Han D, Pu W, He W. Comparative analysis of a bottoming transcritical ORC and a Kalina cycle for engine exhaust heat recovery. Energy Convers Manag 2015;89:764–74. [70] Kölsch B, Radulovic J. Utilisation of diesel engine waste heat by Organic Rankine Cycle. Appl Therm Eng 2015;78:437–48. [71] Song J, Song Y, Gu CW. Thermodynamic analysis and performance optimization of an Organic Rankine Cycle (ORC) waste heat recovery system for marine diesel engines. Energy 2015;82:976–85. [72] Neto RDO, Sotomonte CAR, Coronado CJR, Nascimento MAR. Technical and economic analyses of waste heat energy recovery from internal combustion engines by the Organic Rankine Cycle. Energy Convers Manag 2016;129:168–79. [73] Galindo J, Ruiz S, Dolz V, Royo-Pascual L, Haller R, Nicolas B, et al. Experimental and thermodynamic analysis of a bottoming Organic Rankine Cycle (ORC) of gasoline engine using swash-plate expander. Energy Convers Manag 2015;103:519–32. [74] Galindo J, Climent H, Dolz V, Royo-Pascual L. Multi-objective optimization of a bottoming Organic Rankine Cycle (ORC) of gasoline engine using swash-plate expander. Energy Convers Manag 2016;126:1054–65. [75] Khaljani M, Saray RK, Bahlouli K. Evaluation of a combined cycle based on an HCCI (Homogenous Charge Compression Ignition) engine heat recovery employing two organic Rankine cycles. Energy 2016;107:748–60. [76] Grelet V, Reiche T, Lemort V, Nadri M, Dufour P. Transient performance evaluation of waste heat recovery rankine cycle based system for heavy duty trucks. Appl Energ 2016;165:878–92. [77] Zhang T, Zhu T, An W, Song X, Liu L, Liu H. Unsteady analysis of a bottoming Organic Rankine Cycle for exhaust heat recovery from an Internal Combustion Engine using Monte Carlo simulation. Energy Convers Manag 2016;124:357–68. [78] Sung T, Kim KC. Thermodynamic analysis of a novel dual-loop organic Rankine cycle for engine waste heat and LNG cold. Appl Therm Eng 2016;100:1031–41. [79] Michos CN, Lion S, Vlaskos I, Taccani R. Analysis of the backpressure effect of an Organic Rankine Cycle (ORC) evaporator on the exhaust line of a turbocharged heavy duty diesel power generator for marine applications. Energy Convers Manag 2017;132:347–60. [80] Baldi F, Larsen U, Gabrielii C. Comparison of different procedures for the optimisation of a combined Diesel engine and organic Rankine cycle system based on ship operational profile. Ocean Eng 2015;110:85–93. [81] Galindo J, Ruiz S, Dolz V, Royo-Pascual L. Advanced exergy analysis for a bottoming organic rankine cycle coupled to an internal combustion engine. Energy Convers Manag 2016;126:217–27. [82] Torregrosa A, Galindo J, Dolz V, Royo-Pascual L, Haller R, Melis J. Dynamic tests and adaptive control of a bottoming organic Rankine cycle of IC engine using swash-plate expander. Energy Convers Manag 2016;126:168–76. [83] Panesar AS. An innovative organic Rankine cycle approach for high temperature applications. Energy 2016;115:1436–50. [84] Zhang J, Zhang H, Yang K, Yang F, Wang Z, Zhao G, et al. Performance analysis of regenerative organic Rankine cycle (RORC) using the pure working fluid and the zeotropic mixture over the whole operating range of a diesel engine. Energy Convers Manag 2014;84:282–94. [85] Yang K, Zhang H, Wang Z, Zhang J, Yang F, Wang E, et al. Study of zeotropic mixtures of ORC (organic Rankine cycle) under engine various operating conditions. Energy 2013;58:494–510. [86] Song S, Zhang H, Lou Z, Yang F, Yang K, Wang H, et al. Performance analysis of exhaust waste heat recovery system for stationary CNG engine based on organic Rankine cycle. Appl Therm Eng 2015;76:301–9. [87] Yang K, Zhang H, Song S, Yang F, Liu H, Zhao G, et al. Effects of degree of superheat on the running performance of an Organic Rankine Cycle (ORC) waste heat recovery system for diesel engines under various operating conditions. Energies 2014;7:2123–45. [88] Shu G, Gao Y, Tian H, Wei H, Liang X. Study of mixtures based on hydrocarbons used in ORC (Organic Rankine Cycle) for engine waste heat recovery. Energy 2014;74:428–38. [89] Song J, Gu CW. Analysis of ORC (Organic Rankine Cycle) systems with pure hydrocarbons and mixtures of hydrocarbon and retardant for engine waste heat recovery. Appl Therm Eng 2015;89:693–702. [90] Tian H, Chang L, Gao Y, Shu G, Zhao M, Yan N. Thermo-economic analysis of zeotropic mixtures based on siloxanes for engine waste heat recovery using a dualloop organic Rankine cycle (DORC). Energy Convers Manag 2017;136:11–26.

[32] Zarenezhad B, Aminian A. A multi-layer feed forward neural network model for accurate prediction of flue gas sulfuric acid dew points in process industries. Appl Therm Eng 2010;30:692–6. [33] Bahadori A. Estimation of combustion flue gas acid dew point during heat recovery and efficiency gain. Appl Therm Eng 2011;31:1457–62. [34] Shu G, Yu G, Tian H, Wei H, Liang X. A Multi-Approach Evaluation System (MAES) of Organic Rankine Cycles (ORC) used in waste heat utilization. Appl Energy 2014;132:325–38. [35] Zhu S, Deng K, Qu S. Energy and exergy analyses of a bottoming Rankine cycle for engine exhaust heat recovery. Energy 2013;58:448–57. [36] Tian H, Shu G, Wei H, Liang X, Liu L. Fluids and parameters optimization for the organic Rankine cycles (ORCs) used inexhaust heat recovery of Internal Combustion Engine (ICE). Energy 2012;47:125–36. [37] Wang EH, Zhang HG, Fan BY, Ouyang MG, Zhao Y, Mu QH. Study of working fluid selection of organic Rankine cycle (ORC) for engine waste heat recovery. Energy 2011;36:3406–18. [38] Yang F, Zhang H, Song S, Bei C, Wang H, Wang E, et al. Thermoeconomic multiobjective optimization of an organic Rankine cycle for exhaust waste heat recovery of a diesel engine. Energy 2015;93:2208–28. [39] Jung D, Park S, Min K. Selection of appropriate working fluids for Rankine cycles used for recovery of heat from exhaust gases of ICE in heavy-duty series hybrid electric vehicles. Appl Therm Eng 2015;81:338–45. [40] Yang MH, Yeh RH. Thermodynamic and economic performances optimization of an organic Rankine cycle system utilizing exhaust gas of a large marine diesel engine. Appl Energy 2015;149:1–12. [41] Usman M, Imran M, Yang Y, Park BS. Impact of organic Rankine cycle system installation on light duty vehicle considering both positive and negative aspects. Energy Convers Manag 2016;112:382–94. [42] Zhao M, Wei M, Song P, Liu Z, Tian G. Performance evaluation of a diesel engine integrated with ORC system. Appl Therm Eng 2016:115. [43] Yang MH, Yeh RH. Economic research of the transcritical Rankine cycle systems to recover waste heat from the marine medium-speed diesel engine. Appl Therm Eng 2016;114:1343–54. [44] Xie H, Yang C. Dynamic behavior of Rankine cycle system for waste heat recovery of heavy duty diesel engines under driving cycle. Appl Energy 2013;112:130–41. [45] Shu G, Zhao M, Tian H, Huo Y, Zhu W. Experimental comparison of R123 and R245fa as working fluids for waste heat recovery from heavy-duty diesel engine. Energy 2016;115:756–69. [46] Domingues A, Santos H, Costa M. Analysis of vehicle exhaust waste heat recovery potential using a Rankine cycle. Energy 2013;49:71–85. [47] Katsanos CO, Hountalas DT, Pariotis EG. Thermodynamic analysis of a Rankine cycle applied on a diesel truck engine using steam and organic medium. Energy Convers Manag 2012;60:68–76. [48] Sciubba E, Tocci L, Toro C. Thermodynamic analysis of a Rankine dual loop waste thermal energy recovery system. Energy Convers Manag 2016;122:109–18. [49] Zhang YQ, Wu YT, Xia GD, Ma CF, Ji WN, Liu SW, et al. Development and experimental study on organic Rankine cycle system with single-screw expander for waste heat recovery from exhaust of diesel engine. Energy 2014;77:499–508. [50] Srinivasan KK, Mago PJ, Krishnan SR. Analysis of exhaust waste heat recovery from a dual fuel low temperature combustion engine using an Organic Rankine Cycle. Energy 2010;35:2387–99. [51] Shi R, He T, Peng J, Zhang Y, Zhuge W. System design and control for waste heat recovery of automotive engines based on Organic Rankine Cycle. Energy 2016;102:276–86. [52] Yue C, Han D, Pu W. Analysis of the integrated characteristics of the CPS (combined power system) of a bottoming organic Rankine cycle and a diesel engine. Energy 2014;72:739–51. [53] Yağlı H, Koç Y, Koç A, Görgülü A, Tandiroğlu A. Parametric optimization and exergetic analysis comparison of subcritical and supercritical organic Rankine cycle (ORC) for biogas fuelled combined heat and power (CHP) engine exhaust gas waste heat. Energy 2016;111:923–32. [54] Yang MH, Lund H, Kaiser MJ. Optimizations of the waste heat recovery system for a large marine diesel engine based on transcritical Rankine cycle. Energy 2016;113:1109–24. [55] Peris B, Navarro-Esbrí J, Molés F. Bottoming organic Rankine cycle configurations to increase Internal Combustion Engines power output from cooling water waste heat recovery. Appl Therm Eng 2013;61:364–71. [56] Yang MH, Yeh RH. Analyzing the optimization of an organic Rankine cycle system for recovering waste heat from a large marine engine containing a cooling water system. Energy Convers Manag 2014;88:999–1010. [57] Kim YM, Dong GS, Chang GK, Cho GB. Single-loop organic Rankine cycles for engine waste heat recovery using both low- and high-temperature heat sources. Energy 2016;96:482–94. [58] Boretti A. Recovery of exhaust and coolant heat with R245fa organic Rankine cycles in a hybrid passenger car with a naturally aspirated gasoline engine. Appl Therm Eng 2012;36:73–7. [59] Yang MH. Thermal and economic analyses of a compact waste heat recovering system for the marine diesel engine using transcritical Rankine cycle. Energy Convers Manag 2015;106:1082–96. [60] Ma J, Liu L, Zhu T, Zhang T. Cascade utilization of exhaust gas and jacket water waste heat from an Internal Combustion Engine by a single loop Organic Rankine Cycle system. Appl Therm Eng 2016;107:218–26. [61] Yang MH, Yeh RH. Thermo-economic optimization of an organic Rankine cycle system for large marine diesel engine waste heat recovery. Energy 2015;82:256–68. [62] Vaja I, Gambarotta A. Internal Combustion Engine (ICE) bottoming with Organic

109

Renewable and Sustainable Energy Reviews 92 (2018) 95–110

L. Shi et al.

[110] Shu G, Liu L, Tian H, Wei H, Liang Y. Analysis of regenerative dual-loop organic Rankine cycles (DORCs) used in engine waste heat recovery. Energy Convers Manag 2013;76:234–43. [111] Shu G, Liu L, Tian H, Wei H, Xu X. Performance comparison and working fluid analysis of subcritical and transcritical dual-loop organic Rankine cycle (DORC) used in engine waste heat recovery. Energy Convers Manag 2013;74:35–43. [112] Yu G, Shu G, Tian H, Huo Y, Zhu W. Experimental investigations on a cascaded steam-/organic-Rankine-cycle (RC/ORC) system for waste heat recovery (WHR) from diesel engine. Energy Convers Manag 2016;129:43–51. [113] Song J, Gu CW. Parametric analysis of a dual loop Organic Rankine Cycle (ORC) system for engine waste heat recovery. Energy Convers Manag 2015;105:995–1005. [114] Zhou Y, Wu Y, Li F, Yu L. Performance analysis of zeotropic mixtures for the dualloop system combined with internal combustion engine. Energy Convers Manag 2016;118:406–14. [115] Wang E, Yu Z, Zhang H, Yang F. A regenerative supercritical-subcritical dual-loop organic Rankine cycle system for energy recovery from the waste heat of internal combustion engines. Appl Energy 2017;190:574–90. [116] Wang EH, Zhang HG, Zhao Y, Fan BY, Wu YT, Mu QH. Performance analysis of a novel system combining a dual loop organic Rankine cycle (ORC) with a gasoline engine. Energy 2012;43:385–95. [117] 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 Convers Manag 2017;138:210–23. [118] Shu G, Yu G, Tian H, Wei H, Liang X, Huang Z. Multi-approach evaluations of a cascade-Organic Rankine Cycle (C-ORC) system driven by diesel engine waste heat: part A – Thermodynamic evaluations. Energy Convers Manag 2016;108:579–95. [119] Yu G, Shu G, Tian H, Wei H, Liang X. Multi-approach evaluations of a cascadeOrganic Rankine Cycle (C-ORC) system driven by diesel engine waste heat: part Btechno-economic evaluations. Energy Convers Manag 2016;108:596–608. [120] Zhang HG, Wang EH, Fan BY. A performance analysis of a novel system of a dual loop bottoming organic Rankine cycle (ORC) with a light-duty diesel engine. Appl Energy 2013;102:1504–13. [121] Yang F, Dong X, Zhang H, Wang Z, Yang K, Zhang J, et al. Performance analysis of waste heat recovery with a dual loop organic Rankine cycle (ORC) system for diesel engine under various operating conditions. Energy Convers Manag 2014;80:243–55. [122] Wang EH, Zhang HG, Fan BY, Ouyang MG, Yang FY, Yang K, et al. Parametric analysis of a dual-loop ORC system for waste heat recovery of a diesel engine. Appl Therm Eng 2014;67:168–78. [123] Yang F, Zhang H, Yu Z, Wang E, Meng F, Liu H, et al. Parametric optimization and heat transfer analysis of a dual loop ORC (organic Rankine cycle) system for CNG engine waste heat recovery. Energy 2016:118. [124] Nazari N, Heidarnejad P, Porkhial S. Multi-objective optimization of a combined steam-organic Rankine cycle based on exergy and exergo-economic analysis for waste heat recovery application. Energy Convers Manag 2016;127:366–79. [125] Choi BC, Kim YM. Thermodynamic analysis of a dual loop heat recovery system with trilateral cycle applied to exhaust gases of internal combustion engine for propulsion of the 6800 TEU container ship. Energy 2013;58:404–16. [126] Huang H, Zhu J, Yan B. Comparison of the performance of two different Dual-loop organic Rankine cycles (DORC) with nanofluid for engine waste heat recovery. Energy Convers Manag 2016;126:99–109.

[91] Shu G, Long B, Tian H, Wei H, Liang X. Flame temperature theory-based model for evaluation of the flammable zones of hydrocarbon-air-CO2 mixtures. J Hazard Mater 2015;294:137–44. [92] Shu G, Long B, Hua T, Wei H, Liang X. Evaluating upper flammability limit of low hydrocarbon diluted with an inert gas using threshold temperature. Chem Eng Sci 2015;138:810–3. [93] Tian H, Wu M, Shu G, Liu Y, Wang X. Experimental and theoretical study of flammability limits of hydrocarbon–CO 2 mixture. Int J Hydrog Energy 2017:42. [94] Wang X, Tian H, Shu G. Part-load performance prediction and operation strategy design of organic rankine cycles with a medium cycle used for recovering waste heat from gaseous fuel engines. Energies 2016;9:527. [95] Shu G, Zhao M, Tian H, Wei H, Liang X, Huo Y, et al. Experimental investigation on thermal OS/ORC (Oil Storage/Organic Rankine Cycle) system for waste heat recovery from diesel engine. Energy 2016;107:693–706. [96] Vaja I. Definition of an object oriented library for the dynamic simulation of advanced energy systems: methodologies, tools and application to combined ICEORC power plants. Università Di Parma Dipartimento Di Ingegneria Industriale; 2009. [97] Yu G, Shu G, Tian H, Wei H, Liu L. Simulation and thermodynamic analysis of a bottoming Organic Rankine Cycle (ORC) of diesel engine (DE). Energy 2013;51:281–90. [98] Gewald D, Siokos K, Karellas S, Spliethoff H. Waste heat recovery from a landfill gas-fired power plant. Renew Sustain Energy Rev 2012;16:1779–89. [99] Kalina J. Integrated biomass gasification combined cycle distributed generation plant with reciprocating gas engine and ORC. Appl Therm Eng 2011;31:2829–40. [100] Shu G, Wang X, Tian H. Theoretical analysis and comparison of rankine cycle and different organic rankine cycles as waste heat recovery system for a large gaseous fuel internal combustion engine. Appl Therm Eng 2016;108:525–37. [101] Miller EW, Hendricks TJ, Peterson RB. Modeling energy recovery using thermoelectric conversion integrated with an organic rankine bottoming cycle. J Electron Mater 2009;38:1206–13. [102] Shu G, Zhao J, Tian H, Liang X, Wei H. Parametric and exergetic analysis of waste heat recovery system based on thermoelectric generator and organic rankine cycle utilizing R123. Energy 2012;45:806–16. [103] Shu G, Zhao J, Tian H, Wei H, Liang X, Yu G. et al. Theoretical Analysis of Engine Waste Heat Recovery by the Combined Thermo-Generator and Organic Rankine Cycle System. SAE2012 World Congress & Exhibition; 2012. [104] Zhang C, Shu G, Tian H, Wei H, Liang X. Comparative study of alternative ORCbased combined power systems to exploit high temperature waste heat. Energy Convers Manag 2015;89:541–54. [105] Meng F, Chen L, Sun F, Yang B. Thermoelectric power generation driven by blast furnace slag flushing water. Energy 2014;66:965–72. [106] Shen ZG, Wu SY, Xiao L, Yin G. Theoretical modeling of thermoelectric generator with particular emphasis on the effect of side surface heat transfer. Energy 2016;95:367–79. [107] Su S, Liu T, Wang J, Chen J. Evaluation of temperature-dependent thermoelectric performances based on PbTe 1−y I y and PbTe: Na/Ag 2 Te materials. Energy 2014;70:79–85. [108] Shu G, Liu L, Tian H, Wei H, Yu G. Parametric and working fluid analysis of a dualloop organic Rankine cycle (DORC) used in engine waste heat recovery. Appl Energy 2014;113:1188–98. [109] Tian H, Liu L, Shu G, Wei H, Liang X. Theoretical research on working fluid selection for a high-temperature regenerative transcritical dual-loop engine organic Rankine cycle. Energy Convers Manag 2014;86:764–73.

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