[en] Highlights: • Engine geometrical configuration was modified based on bowl radius and displacement. • The best engine performance indices associated with D3 and R1 structures. • Increasing the bowl radius and outward bowl displacement increases ignition delay. • The best configuration for uniform air/fuel mixture, TKE, and temperature is found. - Abstract: The simulation was carried out based on 1.8 L Ford diesel engine and the geometrical modification in structure of piston were considered in terms of bowl movement and the bowl size in four equal increments. Two major conflicting parameters in combustion and engine efficiency were taken into account and visualized in contour plots as the bowl geometry was varied: (1) the air/fuel mixing process demonstrated by Homogeneity Factor and equivalence ratio, (2) combustion initiation and work delivery by heat release rate, pressure curves, and indicated thermal efficiency. A new version of Coherent Flame Model’s sub-model (ECFM-3Z) was adopted during the calculations to shed light into the combustion chemistry and reaction rate in detail. It was found that the bowl displacement toward the cylinder wall, increases the mixture uniformity (higher HF) thus higher pressure and heat release rate peak were obtained with the penalty of combustion delay which substantially reduces the effective in-cylinder pressure. Furthermore, it was demonstrated that smaller bowl size induces better squish and vortex formation in the chamber, although lesser spray penetration and flame quenching owing to the spray-wall impingement reduces ignition delay

[en] Highlights: • NLPQL algorithm with Latin hypercube and multi-objective GA were applied on engine. • NLPQL converge to the best solution at RunID41, MOGA introduces at RunID84. • Deeper, more encircled design gives the lowest NOx, greater radius and deeper bowl the highest IMEP. • The maximum IMEP and minimum ISFC obtained with NLPQL, the lowest NOx with MOGA. - Abstract: This study is concerned with the application of two major kinds of optimization algorithms on the baseline diesel engine in the class of evolutionary and non-evolutionary algorithms. The multi-objective genetic algorithm and non-linear programming by quadratic Lagrangian (NLPQL) method have completely different functions in optimizing and finding the global optimal design. The design variables are injection angle, half spray cone angle, inner distance of the bowl wall, and the bowl radius, while the objectives include NOx emission, spray droplet diameter, indicated mean effective pressure (IMEP), and indicated specific fuel consumption (ISFC). The restrictions were set on the objectives to distinguish between feasible designs and infeasible designs to sort those cases that cannot fulfill the demands of diesel engine designers and emission control measures. It is found that a design with deeper bowl and more encircled shape (higher swirl motion) is more suitable for NO_x emission control, whereas designs with a bigger bowl radius, and closer inner wall distance of the bowl (Di) may lead to higher engine efficiency indices. Moreover, it was revealed that the NLPQL could rapidly search for the best design at Run ID 41 compared to genetic algorithm, which is able to find the global optima at last runs (ID 84). Both techniques introduce almost the same geometrical shape of the combustion chamber with a negligible contrast in the injection system.

[en] Highlights: • A new thermodynamic cogeneration system is proposed. • Energy and exergy analysis of the considered cycle were performed. • An enhancement of 2.6% in exergy efficiency compared to that of baseline cycle. - Abstract: Among Rankine cycles (simple, reheat and regeneration), regeneration organic Rankine cycle demonstrates higher efficiencies compared to other cases. Consequently, in the present work a regeneration organic Rankine cycle has been utilized to recuperate gas turbine’s heat using heat recovery steam generator. At first, this cogeneration system was subjected to energy and exergy analysis and the obtained results were compared with that of investigated cogeneration found in literature (a cogeneration system in which a reheat organic Rankine cycle for heat recuperation of gas turbine cycle was used with the aid of heat recovery steam generator). Results indicated that the first and second thermodynamic efficiencies in present cycle utilizing regeneration cycle instead of reheat cycle has increased 2.62% and 2.6%, respectively. In addition, the effect of thermodynamic parameters such as combustion chamber’s inlet temperature, gas turbine inlet temperature, evaporator and condenser temperature on the energetic and exergetic efficiencies of gas turbine-heat recovery steam generator cycle and gas turbine-heat recovery steam generator cycle with regeneration organic Rankine cycle was surveyed. Besides, parametric analysis shows that as gas turbine and combustion chamber inlet temperatures increase, energetic and exergetic efficiencies tend to increase. Moreover, once condenser and evaporator temperature raise, a slight decrement in energetic and exergetic efficiency is expected.

[en] Highlights: • A new configuration of power plant for Sabalan wellheads data is proposed. • Energy, exergy and exergoeconomic analyses are done. • A transcritical CO₂ and KCS11 is used to produce power from geothermal brines. • An algorithm for Pinch point analysis for heat exchangers is demonstrated. • Maximum net output power and minimum power specific cost have been improved. -- Abstract: A new integrated cycle based on different real temperatures and pressures on Sabalan geothermal power plant, located in Iran, has been proposed and thermodynamic and exergoeconomic analyses are performed. The Kalina and Transcritical Rankine cycles are used as bottoming cycles and an algorithm are applied to find the exact location of the pinch points in heat exchangers. Also, a parametric study carried out to reveal the effects on the thermodynamic and exergoeconomic performance of the integrated cycle of such important parameters as separator 1 pressure, separator 2 pressure, pinch point temperature difference in the evaporators, higher pressure of the Kalina cycle and the ratio of the Transcritical cycle higher pressure to the critical pressure. Finally, the proposed cycle performance is optimized from the thermodynamic and exergoeconomic viewpoints. The results show that for the integrated geothermal power plant, the power generation, thermal efficiency, exergy efficiency and power specific cost rate are calculated to be 19,448 kW, 16.63%, 63.78%, and 4.521 $/GJ, respectively, which indicate that the proposed cycle has improved thermodynamically and exergoeconomically compared to previous studies.

[en] Highlights: • A three-dimensional model of a two-stage ATEG is established. • Thermodynamic and exergoeconomic performance of the two-stage ATEG is investigated. • The comparison of results for different geometrical parameters is conducted. • Two-stage ATEG leads to better energy and exergy performance. • The single-stage ATEG performs more economical than the two-stage ATEG. -- Abstract: A three-dimensional simulation of a two-stage annular thermoelectric generator is conducted to investigate the thermodynamic and the exergoeconomic performance of the thermoelectric device. The simulations are carried out considering the influence of Thomson effect and temperature-dependent material properties of thermoelectric legs to improve the precision of the study. The effect of two geometrical parameters, the height ratio of thermoelectric stages and angle ratio of legs as well as the influence of heat source temperature on the energy, exergy and economic performance of two-stage ATEG is studied. Results indicate that for a range of heat source temperatures, the output power, conversion efficiency and exergy efficiency of two-stage ATEG are higher compared to single-stage ATEGs based on the low-temperature and high-temperature materials. Moreover, the exergoeconomic study reveals that the single-stage ATEG performs more economical than the two-stage ATEG in all of the studied heat source temperatures. The amount of heat source temperature has a direct influence in determining the proper height ratio to reach the maximum thermodynamic and exergoeconomic efficiencies. Also, it is found that the angle ratio of 1 leads to better energy and exergy performance and least unit cost of output power.

[en] Highlights: • A geothermal based system is presented in order to produce hydrogen and distilled water. • A Dual fluid ORC is employed to harvest the thermal energy into power. • A PEM electrolyzer and an RO desalination unit are employed to produce hydrogen and water, respectively. • Exergy analysis is used to find the highest irreversibility source of the presented system. • Exergy based economic analysis is adopted to estimate the cost of produced hydrogen and water. - Abstract: Exergy and Exergoeconomic analysis are carried out for a new hydrogen and distilled water producing system. The presented cogeneration system is the combination of geothermal driven dual fluid organic Rankine cycle (ORC), proton exchange membrane (PEM) electrolyzer and reverse osmosis (RO) desalination unit. In fact, hot geothermal water is the system input energy, which turns into power and runs the PEM electrolyzer and RO unit. Exergy analysis revealed that the ORC has the highest exergy destruction among the all main units and causes 59% of the total exergy destruction. Also, within the ORC, low pressure evaporator has the highest exergy destruction compared with other components. An increase in the geothermal water temperature resulted in a reduction in system overall exergy efficiency. Furthermore, exergoeconomic analysis showed that 56% of the total investment cost refers to the ORC. Based on the exergoeconomic analysis and considering the unit exergy cost of 1.3 $/GJ for geothermal hot water, produced hydrogen and distilled water have costs of 4.257 $/kg and 32.73 cent/m³, respectively. Moreover, the annual payback period of 5.6 years indicates that the presented system can be of interest from the viewpoint of initial investment.

[en] Highlights: • Experimental study on Mn₂O₃ nanoparticle addition in ethanol and gasoline is investigated. • The blend of gasoline-10%ethanol-20ppmMn₂O₃ shows 19.56% increase of BP. • The BSFC of engine is reduced 22.81% with ethanol addition, 38.89% decrease with 20 ppm nano-additive. • Mn₂O₃ nanoparticle decreases UHC significantly due to catalytic impact of additives and micro-explosion. -- Abstract: The present study deals with application of ethanol and manganese oxide nano-particle at different ratios to gasoline-fueled SI EF7 engine. The blends are prepared in three emulsions namely gasoline-10%ethanol, gasoline-10%ethanol-10ppmMn₂O₃, and gasoline-10%ethanol-20ppmMn₂O₃. In order to prevent the amalgamation of nanoparticles and sedimentation during the test, the ultrasonic cleaner device is utilized to ensure the homogeneity of the composition. To measure the engine power, a 190 kW eddy current dynamometer is coupled and for determination of engine out exhaust gas, AVL gas analyzer is used. The results indicate that ethanol addition by 10% lead to 2.6% increase in brake power (BP), but interestingly 10 ppm Mn₂O₃ nano-additive raise the BP to 14.38% and 20 ppm nano-additive led to 19.56% increase of BP. With regard to emissions, ethanol presence in the blend reduces CO and UHC and raises the NOx and CO₂ because the abundant oxygen bonds in ethanol help oxidation process. The best blend in terms of UHC and BSFC reduction is gasoline-10%ethanol-20ppmMn₂O₃. The results also revealed that the peak of CO and UHC occurs at 75 N.m since at 75 N.m the inlet valve is actuated and the excess air is inducted to cylinder.

[en] Highlights: • Different configurations of TEM were tested in this research. • 6-Jointed TEM provided around 100% higher COP in the same power input. • A comprehensive sensitivity analysis was carried out for 6-jointed mode. • Perforation technique was employed to further enhance the COP. • Spring wire was used to further improve the COP of the cooler. -- Abstract: Although individual commercial thermoelectric module has been widely investigated and its cooling behavior is clear, jointed thermoelectric modules show completely different cooling behavior and higher coefficient of performance (without the change of input electrical power) which requires further study. At the first step of this research, cooling characteristics of 2-jointed, 4-jointed and 6-jointed thermoelectric modules are experimentally evaluated and discussed under the same range of input electrical power. In the same total input electrical power, 6-jointed TEM (thermoelectric module) provided around 100% higher COP (coefficient of performance) than the 2-jointed TEM which was significant. Cooling behavior of different-number jointed TEM (in the same input power) are analyzed and discussed in this paper. In the second step of this research, the COP of 6-jointed TEM cooler (selected from the first step) has been increased again by proposition of two new techniques based on the modification of the popular rectangular-fin heat sink. Attempts are made to further enhance the COP of the system by two methods including “perforating technique” and “spring wire technique” through a Peltier air cooler which have not been proposed before. In the same electrical power input, perforating technique enhanced the thermal performance of the Peltier air cooler around 50% (totally 150% compared to the 2-jointed TEM with simple heat-sink) and the use of spring-wire between the fins of heat-sink improved the COP around 130% (totally 230% compared to the 2-jointed TEM with simple heat-sink). Exact explanation of the quality/quantity and improvement reasons of each technique are described in this paper for different working conditions of the cooler.

[en] Highlights: • A novel numerical method is proposed in order to analyze pinch point characteristics. • The different combinations of the binary mixture and pure fluid are used. • To converge the answers, a method similar to the bisection is used. • Heat exchangers are considered to be counter-flow. • The calculations are performed in EES software by writing an internal procedure. -- Abstract: A novel numerical method is proposed in order to analyze pinch point (PP) characteristics in the heat exchangers such as evaporator, condenser, regenerator, preheater and so on. The different combinations of the binary mixture and pure fluid are used as hot and cold streams. In addition, using the correlation between isobaric specific heat and temperature, an extra algorithm is presented in order to calculate the temperature of fluids like commercial oils with respect to dimensionless enthalpy. In this work after a comprehensive interpretation of the presented method, a parametric study is carried out for the selected commercial oils (e.g. Therminol-66), ammonia and water as pure fluids and ammonia-water mixture as a binary mixture. The effects of parameters like ammonia mass fraction in the solution and PP temperature difference on the PP characteristics such as PP position, mass flow ratio and average temperature difference between hot and cold streams are studied afterwards. This novel method is used for all heat transfer processes in heat exchangers including binary mixtures or pure fluid as one or even both of the hot and cold streams.

[en] Highlights: • Exergy gained and exergy given-out by cold/hot water are discussed for coiled tubes. • NTU-dimensionless exergy charts are presented. • An exergetic sensitivity analysis is provided for coiled tubes. • A new empirical correlation was proposed to predict the dimensionless exergy loss. Frictional and thermal characteristics in helically coiled tubes have been abundantly probed in the recent decade. Nonetheless, exergy analysis has not been conducted impressively. Particularly, no empirical correlation has been provided for exergetic parameters of coiled-tubes. Hence, the aim of this research is developing a new empirical correlation to evaluate the non-dimensional exergy destruction of fluid flow through the helical tubes. Exergy gained by cold fluid (coil side), exergy given-out by hot fluid (shell-side), total exergy destruction, NTU and non-dimensional exergy destruction are investigated. Coiled tube is adjusted inside a cylindrical shell and then two fluid streams are flowed toward the both shell-tube side and coiled-tube side. Each side has its own exergetic specifications which are separately calculated and discussed. Finally, an empirical correlation is provided for total non-dimension exergy loss as a function of Number of Thermal Units (NTU).