Search

The present work focused on modeling the nitrogen oxides (NOX) generation characteristics based on the interpretable machine learning algorithm for an in-service coal-fired power plant. Computation...

The majority of the energy in the fuel burned in the internal combustion engines is lost in the form of waste heat. To address this issue, waste heat recovery technology has been proposed to increase the overall efficiency of engine. This paper investigates a heat driven cooling system based on a supercritical CO2 (S-CO2) power cycle integrated with a transcritical CO2 (T-CO2) refrigeration cycle, aiming to provide an alternative to the absorption cooling system. The combined system is proposed to produce cooling for food preservation on a refrigerated truck by waste heat recovery of engine. In this system, the S-CO2 absorbs heat from the exhaust gas and the generated power in the expander is used to drive the compressors in both S-CO2 power cycle and T-CO2 refrigeration cycle. Unlike the bulky absorption cooling system, both power plant and vapour compression refrigerator can be scaled down to a few kilo Watts, opening the possibility for developing small-scale waste heat driven cooling system that can be widely applied for waste heat recovery from IC engines of truck, ship and train. A new layout sharing a common cooler is also studied. The results suggest that the concept of S-CO2/T-CO2 combined cycle sharing a common cooler has comparable performance and it is thermodynamically feasible. The heat contained in exhaust gas is sufficient for the S-CO2/T-CO2 combined system to provide enough cooling for refrigerated truck cabinet whose surface area is more than 105 m2.

In order to ensure uniform distribution of dry evaporator under various operating conditions, two novel distributors based on the distribution concept of ``flow pattern setting & critical distribution'' are proposed. The theoretical analysis and structure design of rectifying nozzle type critical distributor (RD) based on the distribution principle of ``swirling setting & critical distribution'' are carried out. And the mechanism of swirling setting and critical flow of gas-liquid two-phase refrigerant is expounded. The flow pattern setting is to adjust the up-flow non-uniform and asymmetrical flow pattern to ideal annular flow by rectifying elements, to overcome the influence of up-flow flow state on distribution characteristics. The critical distribution is to make the two-phase flow reach the local sound velocity by sonic nozzle, to overcome the influence of the non-uniform heat transfer of each branch of the downflow on distribution characteristics, and solve the influence of inconsistent resistance of each breach, pressure wave oscillation and other unfavorable factors on the heat transfer performance of the dry evaporator. Based on the results of theoretical analysis, the RD is designed, and tested on the performance test system of dry evaporator. The experimental research results show that the distribution effect of RD is the best. The cooling capacity of the dry evaporator with the RD is increased by 22.7% or more, compared with Venturi distributor. The results show that the use of RD restrain the problem of gas-liquid two phase refrigerant mal-distribution in dry evaporator.

The power conversion efficiencies of organic solar cells (OSCs) have reached over 19%. However, the combination of high efficiency and long-term stability is still a major conundrum of commercialization. Here a Y6-analogue and a 2,2′-bithiophene unit are utilized to construct a series of oligomer acceptors to investigate the effect of molecular size and packing properties on photovoltaic performance. By altering the molecular chain length, we modify the thermal properties, crystallization behaviours and molecular packing and achieve an optimal microstructure and a more stable morphology in blend films. A combination of efficiencies over 15% and an extrapolated T80 lifetime over 25,000 h, which equates to an average lifetime exceeding 16 years in Guangzhou, is achieved for binary OSCs based on an oligomer acceptor. This work emphasizes the importance of oligomeric strategy in tuning molecular packing behaviours and blend morphology, leading to development of novel non-fullerene acceptors for stable and efficient OSCs.

Objectives Carbapenem-resistant Acinetobacter baumannii (CRAB) has become a worldwide issue. This study aimed to characterise the epidemiology and genetic relationships of A. baumannii isolates in Guangdong Province, China. Methods CRAB isolates were collected from five municipal hospitals from June–December 2017. The 16S–23S rRNA intergenic spacer region was used for confirmation of strain identity. Antimicrobial susceptibility testing and the CarbAcineto NP test were performed to analyse the resistance spectrum and carbapenemase production of the isolates. PCR-based assays were used to detect β-lactamase genes and related mobile genetic elements. Genetic diversity among the isolates was analysed by enterobacterial repetitive intergenic consensus (ERIC)-PCR, multilocus sequence typing (MLST) and multiplex PCR. Results A total of 122 isolates were confirmed as A. baumannii; all were resistant to the tested antibiotics except for tigecycline and colistin. The CarbAcineto NP test showed that 93.4% of the isolates produced a carbapenemase. blaOXA-23-like and extended-spectrum β-lactamase-encoding genes were found by PCR in 94.3% and 91.8% of the isolates, respectively. Furthermore, the genetic environment of blaOXA-23-like was mainly associated with transposons Tn2008 (46.1%), Tn2006 (27.0%) and Tn2009 (20.9%). MLST identified six existing sequence types (STs) and three novel STs, of which ST195 (35.7%) and ST208 (32.1%) were the most common, belonging to clonal group 92 and European clone II. Conclusion This study suggests that co-production of β-lactamases was the major resistance mechanism of CRAB isolates. Dissemination of blaOXA-23-like may be facilitated by transposable elements. ST195 and ST208 were the predominant epidemic types of A. baumannii in Guangdong Province.

The performance of thermodynamic cycle strongly depends on the properties of working fluids. A gas-fuelled hot water system based on coupling of an organic Rankine cycle and an air source heat pump cycle (ORC-ASHP) was investigated in this paper. This system is integrated with a gas burner to provide heat for ORC. The power generated in ORC is used to drive the air source heat pump cycle. Comparisons on the system performance are presented for seven different organic working fluids, with emphasis on the effect of thermodynamic properties of the working fluids. In terms of fuel-to-heat efficiency, benzene, toluene and cyclohexane have better performance for the high temperature heat source. The results indicate that working fluids presenting higher decomposition temperatures shows a higher fuel-to-heat-efficiency. When benzene is used as working fluids, the fuel-to-heat efficiency reaches 161.7% and 139.47% to provide 50 °C and 65 °C hot water respectively.

Laser-induced breakdown spectroscopy (LIBS) was applied for the characterization of the methane-air laminar diffusion flame, revealing the spatial distribution of its composition. From the measurement, it was found that distribution of the atomic and ionic N emissions produced by the flame had obvious differences, which were mainly distributed in the air area and flame area, respectively. A comparison of the LIBS spectra of air, methane gas, and methane-air laminar diffusion flame showed that the atomic N emissions were mainly produced by the excitation of N2, and the ionic N emissions were more related to the N-containing combustion products. In addition, the correlation between typical emissions and the flame temperature measured by thermocouple was estimated to show that the tendency of the changes in temperature can be characterized by C2 emission intensities. This work provides a new method for real-time online flame temperature measurement, and also provides a reference for revealing the formation process and conversion pathway of each component in the flame.

Organic Rankine cycle (ORC) has become a promising energy harvesting technique to recover thermal energy from low-grade heat sources. In this study, a lab-scale ORC system has been designed, constructed, and tested to investigate the potential of utilizing the heat from hot water, which is used to simulate the jacket water of internal combustion engines. The ORC system employs an oil-free scroll expander with R245fa as working fluid. A wide range of operating conditions has been studied by adjusting the pump frequency, the load and the mass flow rate of cooling water. Effect of the superheat degree at the expander inlet was investigated and the results showed that the ORC system presented better performance with superheat of 0. It is concluded that the system should be controlled to maintain the least possible superheat degree to obtain higher power output and better efficiency. The maximum electric power output and the maximum thermal efficiency are 0.61 kW and 4.09%, respectively, when the heat source is 96.8°C. The power consumed by the pump ranges from 0.07 to 0.18 kW, which accounts for 22 to 39% of the power output of ORC.

In organic solar cells, interfacial materials play essential roles in charge extraction, transportation, and collection. Currently, highly efficient and thickness-insensitive interfacial materials are urgently needed in printable large area module devices. Herein, water/alcohol-soluble conjugated polyelectrolyte PFNBT-Br, with medium bandgap based on benzothiadiazole, are doped by two alkali metal sodium salts, NaH

The efficiency of distributed energy systems can be significantly increased through waste heat recovery from industry or power generation. The technologies used for this process are typically dependent on the quality and temperature grades of waste heat. To maximize the efficiency of cascade heat utilization, it is important to optimize the choice of waste heat recovery technologies and their operation. In this paper, a detailed mixed integer linear programming optimization model is proposed for waste heat recovery in a district-scale microgrid. The model can distinguish waste heat quality for planning and operation optimization of distributed energy systems. Heat utilization technologies are formulated in this developed model and categorized in different temperature grades. The developed model is validated using four typical cases under different settings of system operation and business models. It is found that the optimization model, by distinguishing waste heat temperature, can increase energy cost savings by around 5%, compared to models that do not consider waste heat temperature grades. Additionally, the results indicate that the developed model can provide more realistic configuration and technologies dispatch.

Cogeneration system based on cascade utilization of heat has been proved to be a promising technology to enhance energy conversion efficiency. An electricity-cooling cogeneration system (ECCS) based on coupling of a steam Rankine cycle (SRC) and an absorption refrigeration system (ARS) is proposed to recover the waste heat of marine engine to meet the electricity and cooling demand aboard. The SRC absorbed heat from the exhaust gas of engine to generate electricity, and the ARS makes use of the condensation heat of SRC to provide cooling needed on ship. Electricity output, cooling capacity, equivalent electricity output, exergy efficiency, and equivalent thermal efficiency are adopted to evaluate the performance of ECCS. The simulation results indicate that recovering the expansion work in the absorption refrigeration cycle is an effective way to increase electricity output at the cost of decreasing cooling capacity. The equivalent electricity output of the WHR system is 5223 kW, accounting for 7.61% of the rated power output of the marine engine.

Huge thermal losses through the exhaust system of the refrigerated truck offer an opportunity for lowering fuel consumption by using waste heat recovery system. To meet the demand of mixed load of refrigerated truck, a basic cycle integrating the supercritical CO2 cycle and dual-temperature refrigeration cycle (BSRC) is proposed and evaluated from the thermodynamic and economic perspective. Besides, a two-phase ejector is introduced into the BSRC to improve cycle performance (defined as SRCE). The proposed cycles can conveniently change operation modes in response to different forms of energy demand, including combined power generation, refrigeration and freezing (mode 1), refrigeration and freezing (mode 2), power generation (mode 3). Detailed parametric analysis and performance comparison between the BSRC and the SRCE are conducted. Thereafter, multi-objective optimization is employed to obtain the optimal operating condition. Comparison results show that the SRCE presents superiority than BSRC owing to pressure lift provided by the ejector. Besides, the advantage of employing ejector is more pronounced under mode 2 than under mode 1. The SRCE can provide an extra power of 28.19 kW under mode 1 when the basic need for freezing and refrigeration (1.635 kW) is satisfied, accounting for 11.23% of the engine power output. And the exergy efficiency and sum unit cost of product of the SRCE are 57.186% and 13.78 $/GJ, respectively. Compared with the BSRC, the exergy efficiency and sum unit cost of product of the SRCE under mode 2 are respectively increased by 15.92% and decreased by 14.85%. While under mode 3, the SRCE can be regarded as a typical regenerative SCO2 cycle, which can provide considerable net power output of 28.362 kW.

This paper proposes solutions to address the issues of traditional refrigerant substitution and the compatibility between secondary fluid and indirect refrigeration system. By using heat balance test method, the performance of three new different secondary fluids, LM-1, LM-4, LM-8, is compared with ethylene glycol at different flow rates. The secondary fluid with the best performance and its optimal working parameters are obtained. Furthermore, the Reynolds and Prandtl numbers corresponding to the optimal working parameters are derived, which provides theoretical basis for the design of intermediate heat exchanger in indirect refrigeration systems. The test results show that in the cold storage temperature of −18 °C, compared to the aqueous solution of ethylene glycol, the coefficient of performance (COPc) of LM-8, LM-1, and LM-4 is higher by 12.3%, 3.9%, and 1.7%, respectively. When the cold storage temperature of is 0 °C, compared to that of ethylene glycol solution, the COPc of LM-1 and LM-8 increases by 9.3% and 6.1%, respectively, while the COPc of LM-4 decreases by 0.9%. Therefore, these three secondary fluids can be used as potential alternatives for ethylene glycol, but LM-1 has a low flash point and certain risk, so it is not recommended to use. LM-8 exhibits the best performance, but the price is more expensive. The LM-4 is less expensive and has the closest performance to ethylene glycol. In the existing systems, considering cost and safety, LM-4 secondary fluid can be used to directly replace ethylene glycol.

Volatile matter content is one of the important characteristics of coal, which would inevitably influence the laser-coal interaction process. In this work, the coal samples with different volatile matter contents were carried out by laser induced breakdown spectroscopy (LIBS) in argon atmosphere. The temporal and spatial evolution of spectra was captured along with the plasma evolution to investigate the mechanism of the volatile matter effects. The results showed that the spectral emissions for the species that abundant in volatile matter were intense at the plasma front, which indicated that the volatile matter vaporized preferentially as laser irradiating and pushed toward the upper part of the plasma. The distribution characteristics of the atomic carbon emission and ionic calcium emission of different coals demonstrated that the amount of vaporization increased with the volatile content. The more abundant dissociated volatile matter in the plasma plume benefited the generation of molecular carbon (CN and C2) formed by several pathways, resulting in an enhancement on the corresponding emissions. Moreover, effects of volatile content on ablation process contributed to the difference in plasma structure and composition, which would be magnified during the plasma expansion and fluctuation process, contributing to greatly diverse plasma morphology and parameter distribution. Consequently, a conceptual laser-coal interaction model was proposed based on the comprehensive analysis of the measurements to describe the initiation and propagation of the effects of volatile matter on coal plasma.

An experimental study was conducted on the optimal charge of carbon dioxide in water–water heat pump systems (WWHPSs) with and without an internal heat exchanger (IHX). An appropriate carbon dioxide charge standard was obtained from the experimental results. All tests were conducted with the inlet and outlet water temperatures set to 12°C and 7°C in the evaporator, respectively and 20°C and 55°C in the gas cooler, respectively. During the tests, the evaporation temperature was 0°C. The coefficient of performance of cooling (COPc) and coefficient of performance of heating (COPh) increased by 8.3% and 0.7% in the WWHPS with an IHX compared with the WWHPS without an IHX. Under the test conditions, the optimal carbon dioxide charges with and without an IHX were found to be 2.0 kg and 2.25 kg, respectively. The test results show that the optimal carbon dioxide charge decreases by 11.1% when an IHX is included in the WWHPS.

This study presents a comparative analysis of thermodynamic performance of cascade refrigeration systems (CRSs) for refrigerant couples R41/R404A and R23/R404A to discover whether R41 is a suitable substitute for R23. The discharge temperature, input power of the compressor, coefficient of performance (COP), exergy loss (X) and exergy efficiency (η) are chosen as the objective functions. The operating parameters considered in this paper include condensing temperature, evaporating temperature, superheating temperature and subcooling temperature in both high-temperature cycle (HTC) and low-temperature cycle (LTC). The results indicate that an optimum condenser temperature exists for LTC (T4opt) at which COP acquires maximum value. Under the same operation condition, the input power of R41/R404A CRS is lower than that of R23/R404A CRS, and COPopt is higher than that of R23/R404A CRS. The maximum exergy efficiency of R41/R404A and R23/R404A CRSs are 44.38% and 42.98% respectively. The theoretical analysis indicates that R41/R404A is a more potential refrigerant couple than R23/R404A in CRS.

Heating sector is one of the key emitters of greenhouse gas, and thus innovations are needed to improve the energy efficiency of heating technologies. In this paper, a recently proposed gas fuelled heat pump system that integrates an Organic Rankine Cycle (ORC) with an air-sourced heat pump (ASHP) has been further investigated. The heat produced by the gas burner is used to drive an ORC power system to produce mechanical power, which is then directly used to drive a vapour compression heat pump. Two different designs of the combined system were modelled, and their performances were compared and analysed. In the first design, the cold water is firstly heated in the heat pump condenser and then further heated in the ORC condenser to achieve the required final temperature. In the second design, the water is firstly heated in the ORC condenser and then further heated in the heat pump condenser. The results showed that the first design can achieve better overall fuel-to-heat efficiency. Using Aspen Plus, a dynamic model has then been developed to study the optimal control strategies for this design when ambient air temperature changes. The results revealed that, for the ambient temperature ranging from 7 ˚C to 15 ˚C, increasing air mass flow rate is sufficient to maintain the overall system performance. While when ambient temperature is below 7 ˚C, more heat is required from the gas burner that would reduce the fuel-to-heat efficiency.

In this paper, a heat driven cooling system that essentially integrated an organic Rankine cycle power plant with a vapour compression cycle refrigerator was investigated, aiming to provide an alternative to absorption refrigeration systems. The organic Rankine cycle (ORC) subsystem recovered energy from the exhaust gases of internal combustion engines to produce mechanical power. Through a transmission unit, the produced mechanical power was directly used to drive the compressor of the vapour compression cycle system to produce a refrigeration effect. Unlike the bulky vapour absorption cooling system, both the ORC power plant and vapour compression refrigerator could be scaled down to a few kilowatts, opening the possibility for developing a small-scale waste heat-driven cooling system that can be widely applied for waste heat recovery from large internal combustion engines of refrigerated ships, lorries, and trains. In this paper, a model was firstly established to simulate the proposed concept, on the basis of which it was optimized to identify the optimum operation condition. The results showed that the proposed concept is very promising for the development of heat-driven cooling systems for recovering waste heat from internal combustion engines&rsquo, exhaust gas.

Data center is an essential part of modern life that is predicted to increase both in capacity and size over the coming years. This sector consumes a significant proportion of electricity for its operation and for the essential cooling facilities. This consumption is expected to rise with increasing demands which can result in more CO2 emission. Waste heat is an inevitable by-product of DC operation with a potential of being sustainable, low cost and environmentally friendly heat source. In this paper, we proposed a novel system that integrates three thermodynamic cycles including an ORC, a HP and a Gas burner. The aim of this system is to provide cooling for the DC as well as to utilize the rejected heat to supply hot water for central heating. The results show that this system can maintain the indoor room temperature between 18-25 oC by absorbing 12 kW of heat to increase water temperature from 50 to 80 oC. In addition, the system can achieve an overall fuel-to-heat efficiency of 141.8%. Therefore, utilizing such system can have a great potential of improving DC performance as well as providing usable energy by waste heat recovery.

Waste heat recovery has been considered as an attractive technique to improve the overall energy utilization efficiency of internal combustion (IC) engines. In this paper, as distinct from most past research work, a thermally driven refrigeration system based on combined organic Rankine and vapour compression cycles is proposed to recover the IC engines’ waste heat contained in the cooling water. Based on the proposed concept, a lab-scale prototype has been designed and constructed using off-the-shelf components to prove the feasibility of producing refrigeration for ships and refrigerated lorries. In this prototype, the power generated by the Organic Rankine cycle (ORC) is used to drive the compressor of a Vapour Compression Cycle (VCC) through a belt transmission mechanism. Pentafluoropropane (R245fa) and Tetrafluoroethane (R134a) are used as the working fluids for ORC and VCC systems, respectively. An electrical water heater is used to simulate the cooling jacket, while a cooling enclosure is used to simulate the cooling load. With the hot water at a temperature around 95 °C, the system produces around 1.8 kW refrigeration effect at −4 °C, leading to an overall heat-to-cooling efficiency of 0.18, which is defined as the ratio of the cooling capacity of the refrigerator to the heat input to the ORC power plant. The system performance could be significantly improved if optimal components could be utilized.

An engine waste heat driven combined power and refrigeration system, comprised of a regenerative supercritical CO2 Brayton cycle (RSCBC) and an ejector expansion refrigeration cycle (EERC), is proposed. In this system, the RSCBC is adopted as the topping cycle to generate power by recovering the high-temperature waste heat of engine. Meanwhile, the power is utilized by the compressor in the EERC. Such a waste heat recovery system can not only decrease the specific fuel consumption, but also provide refrigeration for refrigerated trucks to realize food preservation. Energy and exergy analysis are conducted on the RSCBC/EERC. The performance of four zeotropic mixtures used in EERC and different mixture compositions are compared. Moreover, the effects of several significant operating parameters are discussed in detail, including turbine inlet pressure and temperature, compressor inlet pressure and temperature, pressure drop in the ejector, evaporating temperature, and condensing temperature. To investigate the influence of the installation of the RSCBC/EERC system, weight estimation analysis is conducted. The results show that the refrigerating capacity and COPcomb of the system with R32/CO2 (0.9/0.1) are up to 225.5 kW and 2.05, respectively. And the equivalent power loss due to the additional weight is estimated to be 5.21 kW. In general, the RSCBC/EERC has proven its application potential in recovering waste heat to provide refrigeration through thermodynamic analysis.

Supercritical carbon dioxide cascade waste heat recovery has proven to be a promising alternative for energy conversion applications. In this paper, four different CO2 Brayton-based dual-loop cycles are integrated to the dual-fuel engine respectively to recover the engine waste heat, including regenerative supercritical CO2 Brayton cycle/organic Rankine cycle (RSCBC/ORC), regenerative supercritical CO2 Brayton cycle/supercritical CO2 Brayton cycle (RSCBC/SCBC), supercritical CO2 recompression Brayton cycle/organic Rankine cycle (SCRBC/ORC), and supercritical CO2 recompression Brayton cycle/supercritical CO2 Brayton cycle (SCRBC/SCBC). Comprehensive parametric analysis and comparison were carried out. When the engine was operated at 1100 rpm and cycle fuel injection quantity of 14.1 mg, the SCRBC/ORC combined system presents the best performance when cyclohexane is used as the working fluid for the ORC, followed by the RSCBC/ORC, RSCBC/SCBC, and SCRBC/SCBC. The energy efficiency of the whole system is increased by 7.03% with the SCRBC/ORC, compared with the condition that engine without waste heat recovery.

This paper provides a literature review of the cascade refrigeration system (CRS). It is an important system that can achieve an evaporating temperature as low as −170 °C and broadens the refrigeration temperature range of conventional systems. In this paper, several research options such as various designs of CRS, studies on refrigerants, and optimization works on the systems are discussed. Moreover, the influence of parameters on system performance, the economic analysis, and applications are defined, followed by conclusions and suggestions for future studies.

In this paper, a R744 Partial Cascaded Two-stage Compression Refrigeration System (R744-PC-TCS) was proposed and evaluated in terms of coefficient of performance (COP) and seasonal energy efficiency ratio (SEER) when it operated in five typical climate representative cities in China. R134a and CO2 are used as refrigerants in this study. The results show that the SEER of the supermarket refrigeration system in the severe cold zone and the mild zone is higher than that of the other climate zones. The performance of the R134a Two-stage Compression Refrigeration System (R134a-TCS) performs better than the R744 Two-stage Compression Refrigeration System (R744-TCS). However, both COP and SEER of the CO2 system can be improved significantly by adding a parallel compressor, as well as using the single-stage vapor compression partial cascade cycle for subcooling under the practical working conditions (such as R744-PC-TCS). The greatest improvement of R744-PC-TCS can be achieved in the areas with poor climatic conditions, in which COP increases by 48.9% at an ambient temperature of 39 °C, and SEER increases by the maximum of 21.5% in hot summer and warm winter zones, compared with that of R744-TCS. Compared with R134a system, the R744-PC-TCS basically achieves the comparable or even higher energy efficiency. It can be concluded that the proposed R744-PC-TCS has a great potential to replace the existing R134a refrigeration system for the supermarket refrigeration application.

To discuss the application feasibility of CO2 two-stage compression refrigeration system with parallel compression and solar absorption partial cascade refrigeration system (CTRS + PC + PCRS), a CO2 two-stage compression refrigeration system was proposed for the purpose of commercial supermarket application. Some important parameters, including coefficient of performance (COP), energy saving share (ESS), and partial seasonal energy efficiency ratio (PSEER) are taken as the objective functions to make comparisions among basic CO2 two-stage compression refrigeration system (BCTRS), CO2 two-stage compression refrigeration system with parallel compression (CTRS + PC) and CTRS + PC + PCRS. China's five typical climate representative cities (Beijing, Harbin, Wuhan, Guangzhou, Chengdu) are considered in this study. The results indicated that the COP of CTRS + PC + PCRS increased by 47.28% and 14.28% in Harbin area, compared with BCTRS and CTRS + PC, respectively. When operating under subcritical and transcritical conditions, the maximum COP of CTRS + PC + PCRS increased by 31.71% (Wuhan) and 47.28% (Harbin) respectively compared with the BCTRS, and increased by 12.27% (Harbin) and 7.78% (Wuhan) respectively compared with the CTRS + PC. The ESS and PSEER were introduced to evaluate the energy-saving effect of the solar partial cascade system (PCRS) and the performance of the composite system, and the maximum ESS is 0.19 (Beijing). Compared with the BCTRS and the CTRS + PC, the PSEER is increased by 22.54% and 2.81%, respectively. The research results in this paper provide a theoretical basis for the application of CO2 two-stage compression refrigeration system in the application of commercial supermarket.

In this paper, we propose a novel gas-fuelled hot water system based on combined power and heat pump cycles. The proposed system essentially integrates a premixed gas burner, an organic Rankine cycle (ORC) power plant, and an air source heat pump for supplying hot water. An ORC power plant generates mechanical power from the thermal energy produced from the combustion of natural gas in the burner. Subsequently, the generated power directly drives a vapour compression cycle heat pump. Cold tap water is heated by three heat exchangers in series to gradually increase its temperature. It is preheated in the condenser of the heat pump, then heated in the condenser of the ORC power plant, and finally further heated by the flue gas exiting from the burner in a post heater. The flue gas exiting the post heater will be mixed with ambient air to further extract its residual heat in the evaporator of the heat pump. A comprehensive numerical analysis has been presented in this paper, and the results show that the proposed system can achieve an overall fuel-to-heat efficiency up to 147% when the cold water is heated from 10 to 65 °C and the ambient air temperature is in the range of −5 to 5 °C. The research results demonstrated that the proposed technology has a great potential for domestic hot water applications.

This study presents a performance analysis of a novel electricity–cooling cogeneration system (ECCS) which combines a Rankine cycle (RC) with an absorption refrigeration cycle (ARC) to recover the exhaust heat of marine engine aboard ships. The RC is to provide electricity using water as the working fluid and the ARC is to provide cooling capacity needed aboard ships using a binary solution of ammonia–water as the working pair. Several performance parameters, including electricity output of Rankine cycle, cooling capacity, coefficient of performance (COP) of absorption refrigeration cycle and exergy efficiency, are analyzed and optimized. The simulation results indicate that compared with basic Rankine cycle, higher exergy efficiency can be realized by ECCS due to the extra cooling energy generated by the ARC, especially at a low condensing temperature of Rankine cycle. When the condensing temperature is 323 K and the superheat is 100 K, the exergy efficiency of the cogeneration system increases by 84%.

In the present study, the impact of exhaust gas recirculation (EGR) rates, from 0% to 15%, and compression ratio (CR) of 8, 9, and 10 on the combustion characteristics and emission performance of 2-methylfuran (MF) and gasoline were studied. Experiments were carried out on a Ricardo E6 single-cylinder sparkignition (SI) research engine, under stoichiometric conditions, MF could produce higher cylinder pressure, knocking intensity, combustion temperature, and nitrogen oxides (NOx) emissions than gasoline at higher CRs. However, an appropriate level of cool EGR improved the combustion and emissions, particularly through knock suppression and reduced NOx emissions. When the cooled EGR rate reached 15%, the NOx emissions from the gasoline at a compression ratio of 10 was reduced by about 20.6 g/kW h (>72.5%) compared with 0% EGR. With a low EGR rate, there was only a slight improvement in the indicated thermal efficiency; however, when the EGR reaches 15%, the MF results in 31.2% higher indicated thermal efficiency when compared to gasoline with a CR of 10. This work further advances the knowledge of how to improve the overall performance of MF as an alternative fuel for internal combustion engines. 2014 Elsevier Ltd. All rights reserved.

To reduce the cyclic variation is an effective way to improve the fuel economy and combustion of spark ignition engines. In this paper, the effect of exhaust gas recirculation (EGR), compression ratio and boost pressure on cyclic variation was investigated by means of both experiments and simulation for a port fuel injection (PFI) engine. The mechanisms of these effects were analyzed by computational fluid dynamics (CFD) tools. A Ricardo E6 PFI engine was used as the experimental prototype. The experiments were performed with six EGR ratios, three compression ratios and two boost pressures for a given equivalence ratios. The experiments were operated with the same parameters as that of the simulation. Results showed that the simulation work agree well with the experiment. Both simulation and experiment results showed that an increase of EGR ratio will increase cyclic variation for its lower laminar flame speed. However, the combination of EGR with either an appropriate compression ratio or boost pressure can achieve a relatively low cyclic variation.

Organic Rankine cycle (ORC) systems are a promising solution for improving internal combustion engine efficiencies, however, conflicts between the pressure drops in the heat exchangers, overall thermodynamic performance and economic viability are acute in this space-constrained application. This paper focuses on the interaction of the heat exchanger pressure drop (HEPD) and the thermo-economic performance of ORC systems in engine waste-heat recovery applications. An iterative procedure is included in the thermo-economic analysis of such systems that quantifies the HEPD in each case, and uses this information to revise the cycle and to resize the components until convergence. The newly proposed approach is compared with conventional methods in which the heat exchangers are sized after thermodynamic cycle modelling and the pressure drops through them are ignored, in order to understand and quantify the effects of the HEPD on ORC system design and working fluid selection. Results demonstrate that neglecting the HEPD leads to significant overestimations of both the thermodynamic and the economic performance of ORC systems, which for some indicators can be as high as >80% in some cases, and that this can be effectively avoided with the improved approach that accounts for the HEPD. In such space-limited applications, the heat exchangers can be designed with a smaller cross-section in order to achieve a better compromise between packaging volume, heat transfer and ORC net power output. Furthermore, we identify differences in working fluid selection that arise from the fact that different working fluids give rise to different levels of HEPD. The optimized thermo-economic approach proposed here improves the accuracy and reliability of conventional early-stage engineering design and assessments, which can be extended to other similar thermal systems (i.e., CO2 cycle, Brayton cycle, etc.) that involve heat exchangers integration in similar applications.

Supercritical carbon dioxide Brayton cycle is considered one of the most promising systems for waste heat recovery of engines because of its compactness and high energy efficiency. To further improve the fuel utilization ratio and solve the difficulties of waste heat recovery of high temperature exhaust gas, a regenerative supercritical carbon dioxide Brayton cycle/organic Rankine cycle dual loop is proposed for cascade utilization of exhaust heat from a dual-fuel engine. The regenerative supercritical carbon dioxide Brayton cycle of the proposed system is powered by the waste heat contained in the exhaust gas. The working fluid in the organic Rankine cycle is pre-heated by CO2 exiting the regenerator and then further heated by the residual heat of the exhaust gas. The flow rates of the working fluids in both sub cycles are adjusted to match the waste heat recovery system to respond to the changing conditions of the dual-fuel engine. The results revealed that the maximum net power output of this system is up to 40.88 kW, thus improving the dual-fuel engine power output by 6.78%. Therefore, such a regenerative supercritical carbon dioxide Brayton cycle/organic Rankine cycle dual loop system design enables the thorough recovery of high temperature exhaust heat, leading to higher energy efficiency and lower fuel consumption of the engine.

In this paper, an electricity–cooling cogeneration system based on Rankine–absorption refrigeration combined cycle is proposed to recover the waste heat of the engine coolant and exhaust gas to generate electricity and cooling onboard ships. Water is selected as the working fluid of the Rankine cycle (RC), and a binary solution of ammonia–water is used as the working fluid of the absorption refrigeration cycle. The working fluid of RC is preheated by the engine coolant and then evaporated and superheated by the exhaust gas. The absorption cycle is powered by the heat of steam at the turbine outlet. Electricity output, cooling capacity, total exergy output, primary energy ratio (PER) and exergy efficiency are chosen as the objective functions. Results show that the amount of additional cooling output is up to 18 MW. Exergy output reaches the maximum 4.65 MW at the vaporization pressure of 300 kPa. The study reveals that the electricity–cooling cogeneration system has improved the exergy efficiency significantly: 5–12% increase compared with the basic Rankine cycle only. Primary energy ratio (PER) decreases as the vaporization pressure increases, varying from 0.47 to 0.40.