First-law Efficiency Research Articles

Semi-Closed Oxy-Combustion Combined Cycles for Combined Heat and Power Applications

Abstract This study focuses on the design and comparison of three utility-scale combined heat and power (CHP) cycles with carbon capture and storage (CCS): (i) a CHP semi-closed oxy-combustion combined cycle (SCOC-CC), (ii) a CHP natural gas combined cycle (NGCC) with postcombustion CCS, and (iii) a CHP NGCC with postcombustion CCS and supplementary firing. Performance evaluations are conducted at the design point and partial load (gas turbine at 30%) for different exports of high-temperature pressurized steam. The comparison is extended against two reference separate production systems with CCS, one based on postcombustion technologies, and another based on oxy-combustion. Simulations of the H-class gas turbines are performed using gas steam (GS), a specific in-house validated software, while the heat recovery steam cycle is modeled using Thermoflex. The CO2 capture processes employ validated models in Aspen Plus. The results highlight the suitability of the SCOC-CC for CHP applications, demonstrating superior performance and flexibility compared to CHP postcombustion technologies at both nominal and minimum loads. The SCOC cycle achieves a maximum first-law efficiency of 65.95%, outperforming CCS technologies that generate electricity and heat separately and enabling fuel savings up to 9.2%.

Study and Analysis thermal performance of Taza gas power plant in Kirkuk –Iraq

In this research, the concept of energy balance was implemented in one of the gas turbine electricity generation units in Iraq (Kirkuk - Taza) K1. The design operating data is taken and compared with the data calculated in the computer model used by Engineering Equation Solutions (EES), and the validity of the model used was confirmed. The results indicate the release of a large amount of thermal energy into the atmosphere due to the open Brayton cycle, as energy losses amounted to 60% of the energy input. The results based on the data of the first unit of the station demonstrated that the theoretical efficiency of the unit is a function of the two variables, which are the temperature of the air entering the compressor and the Turbine inlet temperature: Increasing the compressor inlet temperature leads to a decrease in net power output and first-law efficiency and an increase in the specific fuel consumption rate. Increasing the turbine inlet temperature to 1°C leads to an improvement in both net power output and first-law efficiency by (0.24MW, and 0.04) %), respectively. The results also showed that cooling the air entering the compressor for 1°C leads to improving power output and first law efficiency by (0.72MW, and 0.12%), respectively, and reduces specific fuel consumption by 7.8kg/MWh.

Energy and exergy analysis of photovoltaic systems integrated with pulsating heat pipe and hybrid nanofluids

Solar energy is harnessed from solar radiation and converted into various forms of energy, primarily electricity. It is a crucial part of the renewable energy landscape due to its abundance, sustainability, and potential to reduce greenhouse gas emissions. Photovoltaic (PV) panels have become a critical component in the transition toward sustainable energy; however, the efficiency and longevity of PV systems are significantly influenced by their operating temperature. Excessive heat can reduce the efficiency of PV cells and accelerate material degradation. Pulsating heat pipes (PHPs), with their excellent thermal management capabilities, present a promising solution to these challenges. This paper comprehensively investigates the effect of incorporating a three-dimensional PHP into PV systems, using working fluids with varying thermal properties, namely water, graphene oxide (GO) nanofluid with three different concentrations (0.2, 0.4, and 0.8 g/L) and their mixture with nano-encapsulated phase change material (Nano PCM), forming a hybrid nanofluid, at a concentration of 5 g/L. The collected data are analyzed from energy and exergy perspectives. The findings show that using Nano PCM in the nanofluid-based PV system (at the highest concentration) produces 22.3 Wh/day, increasing the system’s electrical power output by approximately 12 % compared to a PV panel with no cooling system. It outperforms the other systems studied, with the highest overall exergy efficiency of 35.4 %. The results also indicate an average improvement in first-law efficiency. Additionally, the study shows varying levelized costs of energy (LCOE) for the system cooled with different coolants.

Experimental demonstration of a dispatchable power-to-power high temperature latent heat storage system

The development of electricity storage solutions is crucial to support the integration of variable renewable electricity sources in electricity systems. This study experimentally characterizes a state-of-the-art full-scale electrical thermal energy storage (ETES) system in outdoor conditions. The system integrates a 600 kWhth high-temperature latent heat storage module and a 13 kWe Stirling engine. The heat storage module uses an 88Al12Si metallic alloy as the phase change material to store electricity converted to thermal energy by a resistive heater in charging mode. The Stirling engine uses hydrogen as the working fluid for re-electrification (discharging). The system uses liquid sodium as the heat transfer fluid between the latent heat storage module and both the charging (electrical heater) and discharging (engine) sub-systems. Over the characterization period, the ETES prototype produced stable electricity at an average rate of 10.5 ± 1 kW for 13 consecutive hours daily with overall and power block first-law efficiencies of 23 % and 25 %, respectively. The effective storage utilization ratio varied between 0.58 and 0.94 depending on the discharge parameters. The response time was <5 s for output power regulation. The results highlight the potential of this latent heat thermal energy storage system to satisfy long-duration electricity storage applications and therefore contribute to the stabilization of electricity grids.

Thermoeconomic analysis of a novel cogeneration system for cascade recovery of waste heat from exhaust flue gases

In low-grade waste heat recovery scenarios, an absorption refrigeration cycle (ARC) or organic Rankine cycle (ORC) can be used because of its widespread acceptance in combined cooling and power applications. This paper introduces a cogeneration configuration employing a cascade waste-heat recovery architecture (including an ARC, ORC, and intermediate heating loop) to harness waste heat from the flue gas of a gas turbine (GT). The results demonstrated that the first-law efficiency and total power generation were largely influenced by the ARC, whereas the second-law efficiency and total available energy were primarily affected by the ORC. When the ARC generation temperature difference and ORC evaporation temperature were adjusted, the first- and second-law efficiencies exhibited divergent trends, suggesting the absence of a unified strategy to enhance both efficiencies simultaneously in the current system. The system achieved its highest first-law efficiency of 54.84 % and maximum total power generation of 1866.10 kW at an ORC evaporation temperature of 145 °C and a heat-source inlet temperature of 160 °C. Furthermore, at an ORC evaporation temperature of 150 °C and a heat-source inlet temperature of 200 °C, the system reached its highest second-law efficiency of 34.57 % and maximum total available energy of 1233.3 kW. The case study revealed that the GT system (including air compressor, air preheater, combustion chamber, and gas turbine) accounted for the highest level of irreversibility, comprising 74 % of the overall system. Specifically, the combustion chamber in the GT system produced a significant irreversibility due to chemical reactions. Compared with traditional combined cooling and power systems, the proposed system can increase the first-law efficiency and lower the unit energy cost of the output.

H2/CO production via high temperature electrolysis of H2O/CO2 coupling with solar spectral splitting at a tunable cut-off wavelength

Solar driven CO2/H2O splitting is a promising path for large-scale and long-term solar energy conversion and storage. In this work, a thermodynamic model of solar driven high-temperature CO2/H2O electrolysis was established, with the full solar spectrum split at a tunable cut-off wavelength for meeting the electrical and thermal energy demands of the process at a high efficiency. Compared with the system without spectral splitting, the solar-to-H2 efficiency can be significantly improved from 36.0 % to 45.5 % by introducing spectral splitting. Besides, the optimal electrolysis temperature can be largely lowered, from 1623 K to 1323 K due to the significant reduction of the solar radiation input for electricity generation. The exergy efficiency of CO2 electrolysis was shown to be higher than that of H2O electrolysis due to the higher molar exergy of CO compared to H2, although the first-law efficiency of H2O electrolysis is higher at Tele < ∼1200 K. A high concentration ratio of the solar-thermal process can lead to both high solar-to-fuel efficiency and high optimal electrolysis temperature because of the reduction of reradiation loss. The electrolysis temperature and the use of excessive CO2/H2O were shown to have an important effect on both the efficiency and the optimal cut-off wavelength because they are closely related with the thermal and electrical energy demands of the whole process. The optimal cut-off wavelength can be as low as 540 nm at electrolysis temperature of 1873 K (Tele = 1873 K) and excessive H2O coefficient of 6 (r = 6), and increases to the working limit of the photovoltaic material (900 nm in this work) as the electrolysis temperature and excessive coefficient decrease to Tele < 1023 K and r < 2.

Surrogate-Assisted Multi-Objective Optimisation of Transcritical Carbon Dioxide Scroll Expander Flank Clearance Based on Computational Fluid Dynamics

Transcritical carbon dioxide waste heat recovery systems and the construction of scroll expanders have recently been hot topics. The flank clearance, located between the orbiting and fixed scroll, has a vital impact on the scroll expander performance. This paper estimates the effect of the flank clearance on the expander’s thermodynamic performance (first-law efficiency) based on computational fluid dynamics (CFD) simulations. The manufacturing cost of different flank clearances is also considered to enhance the feasibility of the machinery design. The computational cost for different flank clearance cases is significantly reduced with a surrogate-assisted multi-objective optimisation algorithm (SAMOA), which also supports modelling the trade-off relationship between manufacturing cost and machinery efficiency. The results indicated that an increasing flank clearance negatively affects the first-law thermal efficiency. The efficiency decreased from 87.41% to 44.83% moving from 20 to 200 μm flank clearances. The SAMOA successfully reduced the computational cost of the dynamic mesh CFD model from 90 h to 15 s with 0.6% discrepancy. The final Pareto solutions presented a clear trade-off relationship between the first-law efficiency and manufacturing cost and promised a diversity of optimum solutions. The “knee points” for the relationship were 25, 55, and 127 μm, which provided flexible clearance choices based on the importance of either machinery efficiency or manufacturing cost.

Exergy Analysis and Off-Design Modeling of a Solar-Driven Supercritical CO2 Recompression Brayton Cycle

The latest generation of concentrated solar power (CSP) systems uses supercritical carbon dioxide (s-CO2) as the working fluid in a high-performance recompression Brayton cycle (RcBC), whose off-design performance under different environmental conditions has yet to be fully explored. This study presents a model developed using the Engineering Equation Solver (EES) and System Advisor Model (SAM) to evaluate the operation of two solar-driven s-CO2 RcBCs over a year, considering meteorological conditions in northern Chile. Under design conditions, the power plant outputs a net power of 25 MW with a first-law efficiency of 48.3%. An exergy analysis reveals that the high-temperature recuperator contributes the most to the exergy destruction under nominal conditions. However, the yearly simulation shows that the gas cooler’s exergy destruction increases at high ambient temperatures, as does the turbine’s during off-design operation. The proposed cycle widens the operational range, offering a higher flexibility and synergistic turndown strategy by throttling the mass flow. The proposed cycle’s seasonal first-law efficiency of 39% outweighs the literature cycle’s 29%. When coupled to a thermal energy storage system, the proposed cycle’s capacity factor could reach 93.45%, compared to the value 76.45% reported for the cycle configuration taken from the literature.

Techno-economic analysis of large-scale green hydrogen production and storage

Producing clean energy and minimising energy waste are essential to achieve the United Nations sustainable development goals such as Sustainable Development Goal 7 and 13. This research analyses the techno-economic potential of waste heat recovery from multi-MW scale green hydrogen production. A 10 MW proton exchange membrane electrolysis process is modelled with a heat recovery system coupled with an organic Rankine cycle (ORC) to drive the mechanical compression of hydrogen. The technical results demonstrate that when implementing waste heat recovery coupled with an ORC, the first-law efficiency of electrolyser increases from 71.4% to 98%. The ORC can generate sufficient power to drive the hydrogen's compression from the outlet pressure at the electrolyser 30 bar, up to 200 bar. An economic analysis is conducted to calculate the levelised cost of hydrogen (LCOH) of system and assess the feasibility of implementing waste heat recovery coupled with ORC. The results reveal that electricity prices dominate the LCOH. When electricity prices are low (e.g., dedicated offshore wind electricity), the LCOH is higher when implementing heat recovery. The additional capital expenditure and operating expenditure associated with the ORC increases the LCOH and these additional costs outweigh the savings generated by not purchasing electricity for compression. On the other hand, heat recovery and ORC become attractive and feasible when grid electricity prices are higher.

Thermodynamic and Exergo-economic Analyses of Waste Heat Recovery of a Two-shaft Turbofan Engine Using Supercritical Carbon Dioxide Brayton Cycle

In this study, first-law, second-law, and exergo-economic investigations are accomplished to recover the waste heat of a two-shaft turbofan engine applying a supercritical carbon dioxide Brayton cycle. The efficacy of different operating parameters including the inlet temperature of the turbine, the pressure ratio of the compressor, and Mach number on the performance of the proposed system in terms of energy and exergy performance, exergy destruction rate, and annual levelized cost of investment have been examined. The results indicate that the energy performance of the cycle is specified as 42.94%, the second-law performance of the cycle is calculated as 85.88% and the whole power generation amount of the system is achieved to be 9806 kW. Also, the results display that among the various components of the proposed system, the maximum amount of exergy destruction occurred in the low-pressure compressor, the fan, and the mixer. It is found that by increasing the inlet temperature of the high-pressure turbine, the first-law efficiency and the second-law efficiency of the proposed cycle decrease while the total cost rate and exergy destruction rate increase. Moreover, it is inferred that the thermodynamic efficiency of the system rises when the pressure ratio of the compressor and Mach number increase. The outcomes also demonstrate that concerning the capital costs and exergy destruction costs of components, the highest amount is obtained for high-pressure turbine and recuperator, which are 326.3 $/h and 358.4 $/h, respectively.

Performance analysis of a large TES system connected to a district heating network in Northern Italy

The addition of storage capacity to district heating systems increases flexibility and expands the range of usable heat sources. Despite their apparently simple nature, thermal energy storage (TES) tanks display a wide range of performances due to different construction and operation choices, as proven by numerous literature studies. However, most of the investigations focus on domestic-size tanks of few cubic metres or, on the other hand, very large seasonal storages of hundreds of thousands of cubic metres. In this work, the performances of a 5000 m3 TES recently introduced in a district heating network in Brescia, Italy, are experimentally analysed using temperature and flow rate measurements acquired over two months in the heating season. First-law efficiencies, exergy, and stratification parameters are calculated and discussed. Energy and exergy efficiencies computed for all examined cycles are above 90%, in line with literature values for smaller and larger TESs. The thermocline profile is generally stable through the cycle unless anomalous events occur, and its average thickness is below 4% of the water height. The combined analysis of single-point indicators, thermocline profiles, and qualitative temperature heatmaps shows that short partial charge/discharge events followed by long stand-by periods negatively affect performances. Stratification efficiency and stratification number give further time-dependent information on the vertical distribution of temperatures in the TES. Heat losses towards the outside are also estimated and discussed in the light of integrative measurements performed on other TESs with similar characteristics, showing that particular care must be paid to the top, where dissipation could be increased by evaporation phenomena if the water surface is not protected.

Performance analysis of vortex tube-thermoelectric system in gas stations

At natural gas pressure reducing stations, gas first enters a water bath heater to boost its temperature slightly, and after leaving the heater, it enters the throttle valve to reduce its pressure. This method has two major drawbacks, which are the consumption of natural gas in the heater and the excessive loss of exergy in the throttle valve. The pressure of natural gas can be reduced by using a vortex tube and converting it into hot and cold currents, and then generating electricity by directing these currents to thermoelectric generators (TEGs). Investigation of energy, exergy and environmental performance of the hybrid vortex tube-TEG system and optimization of its performance for the working condition of Kermanshah pressure reducing station is the subject of the present study. The cold mass fraction (CF) and efficiency of vortex tube are considered as decision variables. Moreover, annual average first-law efficiency (ηI-TEG), annual average second-law efficiency (ηII-TEG) and annual total electric power generated by the TEGs (Pout) are considered as optimization target functions. The results of genetic algorithm based three-objective optimization revealed that the specifications of the optimal system are: vortex tube efficiency = 0.36967, CF=0.95598, ηI-TEG=0.03442, ηII-TEG=0.04544, Pout=42770.58 kW and amount of CO2 mitigation per annum = 8.55 tons.

Energy and exergy analysis and multi-objective optimization of using combined vortex tube-photovoltaic/thermal system in city gate stations

The goal of this study is to investigate the possibility of replacing the water bath heater and pressure relief valve with a hybrid vortex tube-photovoltaic/thermal system in pressure reduction stations like city gate stations. By using this system, both the natural gas pressure can be reduced to the desired level (from 5-7 MPa to 1.5–2 MPa) and electricity can be generated. The effect of cold mass fraction of vortex tube (0.01–0.1), air mass flow rate (0.569–5.69 kg/s) as well as the length (1–10 m), width (0.5–5 m) and depth (0.1–0.5 m) of the photovoltaic/thermal system on the energy and exergy performance of the hybrid vortex tube-photovoltaic/thermal system is investigated. Then, the genetic algorithm based two-objective optimization is used to find the appropriate value of these parameters to maximize the annual average first-law efficiency (ηI) and second-law efficiency (ηII) of the hybrid system. It was found that the ηI and ηII of the optimal system are respectively 74.05% and 19.46%. Moreover, it was observed that the use of optimal system causes a reduction in the CO2 emission by 27.7-tons per year.

Detailed transient assessment of a small-scale concentrated solar power plant based on the organic Rankine cycle

• New procedures for modeling the components of solar-ORC power plant are proposed. • A routine for optimizing the turbine geometry and evaluating its performance is used. • The power plant results are obtained by coupling the accurate components models. • A power plant continuously supplying electricity to remote communities is designed. • The low ODP and GWP refrigerant R1233zd(E) provided the best performance. Motivated by environmental issues and the needs of communities that live far from the electricity grid, this work presents an innovative methodology for modeling a small-scale concentrated solar power plant based on the organic Rankine cycle. An integrated simulation tool, which consists of accurate computational routines of the energy storage tank, parabolic trough collector, plate heat exchanger, finned air-cooled condenser, and inward-flow radial turbine, is developed. The components are modeled according to distributed models and the mean line method for the turbine in homemade codes to account for local property changes. The transient power plant performance is assessed by employing solar irradiation data of three locations that present mean direct normal irradiation rates of 6306, 4712, and 3220 Wh/m 2 .day. The following working fluids were considered: a low GWP and ODP refrigerant (R1233zd(E)), a natural one (R600a), and a high GWP fluid that is currently employed for such applications (R245fa). The smallest configuration that led to annual uninterrupted power production is a 565-m 2 collector and a 90-m 3 storage tank. The R1233zd(E) refrigerant presented the best overall performance by providing about 2% and 30% higher turbine power output, 3% and 29% higher turbine efficiency, and 4% and 36% higher ORC first-law efficiency than R245fa and R600a, respectively. The designed solar power plant generated 48.396 MWh/year of electricity and 80.621 MWh/year of cogeneration energy with R1233zd(E), which is enough to provide electricity and sanitary hot water to about 33 and 64 houses, respectively.

Thermodynamic Assessment of a Solar-Driven Integrated Membrane Reactor for Ethanol Steam Reforming.

To efficiently convert and utilize intermittent solar energy, a novel solar-driven ethanol steam reforming (ESR) system integrated with a membrane reactor is proposed. It has the potential to convert low-grade solar thermal energy into high energy level chemical energy. Driven by chemical potential, hydrogen permeation membranes (HPM) can separate the generated hydrogen and shift the ESR equilibrium forward to increase conversion and thermodynamic efficiency. The thermodynamic and environmental performances are analyzed via numerical simulation under a reaction temperature range of 100–400 °C with permeate pressures of 0.01–0.75 bar. The highest theoretical conversion rate is 98.3% at 100 °C and 0.01 bar, while the highest first-law efficiency, solar-to-fuel efficiency, and exergy efficiency are 82.3%, 45.3%, and 70.4% at 215 °C and 0.20 bar. The standard coal saving rate (SCSR) and carbon dioxide reduction rate (CDRR) are maximums of 101 g·m−2·h−1 and 247 g·m−2·h−1 at 200 °C and 0.20 bar with a hydrogen generation rate of 22.4 mol·m−2·h−1. This study illustrates the feasibility of solar-driven ESR integrated with a membrane reactor and distinguishes a novel approach for distributed hydrogen generation and solar energy utilization and upgradation.

Novel design for tri-generation cycle with Parabolic Trough Collector: An exergy-economic analysis

In this work, a new design for the tri-generation cycle with solar energy resources using Therminol 66 in its parabolic thermal solar collectors has been proposed. The solar collectors absorb the solar energy and pass that to the Organic Rankine Cycle (ORC) with n-octane, n-pentane, n-hexane, and n-heptane working fluids. Besides, the energy loss of the evaporator of the organic Rankine cycle has been used for producing thermal load and that of condenser has been utilized for the cooling load generation. In this research, the main innovation is the use of an organic Rankin cycle condenser as the energy source of the absorption refrigeration cycle. Also, the effect of different fluids such as n-octane, n-heptane, n-pentane, and n-hexane on the operation of the whole system has been investigated. The validation of the results has been carried out which showed acceptable agreement and confirms the accuracy of the proposed model. The power coefficient and exergy factor of the cycle have been obtained as 32.72 and 23.83%, respectively. Furthermore, the highest exergy destruction of the proposed tri-generation system occurs in the steam generator, the generator of the absorption refrigeration cycle, and turbine of organic Rankine cycle by 14742 KW, 3974 KW and 3374 KW with the exergy destruction percentage of 54%, 15%, and 12%, respectively. In the economic aspect of the proposed system, the highest cost is for the evaporator of the absorption refrigerator system with 69.71 dollars per hour and the second and third highest cost are for HRSG and the turbine with 32.4 and 30.33 dollars per hour which have 41%, 19% and 18% of the total cost of the proposed system, respectively. Also, the results show that the most costs of waste are for the generator, turbine, and SHX heat exchanger which waste 6.639, 5.586 and 4.22 dollars per hour with 34%, 29%, and 22% of the total cost of waste, respectively. Moreover, it can be seen that by increasing the temperature of the solar collector from 200° to 500°, the first-law efficiency decreases from 37.6% to 28.6%, the second-law efficiency decreases from 40.15% to 17.29% and the total cost decreases from 4.78 to 4.77 dollars per Gigajoule.

A Comparison of Different Approaches to Estimate the Efficiency of Wells Turbines

AbstractWells turbines are among the most interesting power takeoff devices used in oscillating water column (OWC) systems for the conversion of ocean-wave energy into electrical energy. Several configurations have been studied during the last decades, both experimentally and numerically. Different methodologies have been proposed to estimate the efficiency of this turbine, as well as different approaches to evaluate the intermediate quantities required. Recent works have evaluated the so-called second-law efficiency of a Wells turbine, and compared it to the more often used first-law efficiency. In this study, theoretical analyses and numerical simulations have been used to demonstrate how these two efficiency measures should lead to equivalent values, given the low pressure ratio of the machine. In numerical simulations, small discrepancies can exist, but they are due to the difficulty of ensuring entropy conservation on complex three-dimensional meshes. The efficiencies of different rotor geometries are analyzed based on the proposed measures, and the main sources of loss are identified.

Heat-driven direct reverse osmosis for high-performance and robust ad hoc seawater desalination

This work presents an approach to using a low-grade thermal energy source to power seawater desalination at high performance ratios and with minimal complexity - important requirements for a system that can generate potable water off the grid. In the proposed process - called heat-driven direct reverse osmosis (HDRO) - heat is transferred to a piston containing a saturated working fluid, which in turn directly applies pressure to a feed water reservoir connected in series with a standard reverse osmosis membrane assembly. Presented here are the underlying operating principles and thermodynamics for a generalized HDRO device, including criteria for selecting a working fluid and the definition of several key performance metrics. An idealized HDRO device is analyzed and a theoretical upper bound on performance is computed. At low recovery ratios, a lossless device using ethanol as a working fluid can achieve a performance ratio of up to 49, with a first-law efficiency 5.7%, indicating the significant potential for using this approach for small-scale, thermally driven desalination.

A multigeneration system of combined cooling, heating, and power (CCHP) for low-temperature geothermal system by using air cooling

A new definition of the energy, exergy, economic and environmental model (3,4E-Chaiyat models) was used to evaluate cascade air-cooled multigeneration from a single-stage organic Rankine cycle of 10 kWe, a single-stage absorption chiller of 15 kW, and a drying room of 20 kW, respectively. From the study results, a first-law efficiency of 17.23% was found to be higher than a second-law efficiency of 15.13%. According to a life cycle assessment (LCA), a single score of the energy model of approximately 0.0250Pt was lower than that of the exergy model of approximately 0.1223Pt. In the 3E model, a levelized energy cost per life cycle assessment (LEnCA) was approximately 0.0017 USD⋅Pt/kWh2 for an investment cost of 159,729 USD. At the same time, in the 4E model, a levelized exergy cost per life cycle assessment (LExCA) was approximately 0.0414 USD⋅Pt/kWh2, which was lower than that of the water-cooled multigeneration system (approximately 0.0442 USD⋅Pt/kWh2). Thus, the suitable cooling type for the cascade geothermal-multigeneration system used in San Kamphaeng, Thailand, is the air-cooled type.

Identification of factors affecting exergy destruction and engine efficiency of various classes of fuel

The fuels of internal combustion (IC) engines are gradually becoming diverse. However, differences in physicochemical properties among fuels result in different efficiency potentials. In this work, the factors affecting exergy destruction and engine efficiency of various classes of fuel were identified based on the first- and second-law of thermodynamics. The results demonstrate that exergy destruction fraction (fEx_D) shows strongly positive correlation to the ratio of fuel chemical exergy (LExV) to lower heating value (LHV) (ε) and dimensionless entropy change (αS), and the first-law efficiency has strongly positive correlation to the product ratio of specific-heat during combustion (γc). Specifically, small molecule fuels have lower first-law efficiency than large ones, while the second-law efficiency of hydrocarbons are higher than that of oxygenates due to their lower exergy destruction losses. However, the lower exergy destruction does not always lead to improved second-law efficiency, but increased exhaust exergy. With increasing air or EGR dilution, both the first- and second-law efficiency increase, but the increased exergy destruction results in the reduced exhaust exergy. As a result, it is more important and reasonable to design or reform fuel for increasing the thermal efficiency, rather than reducing the exergy destruction of IC engines.