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In the present study, environmental impact analysis is used for the optimization to an actual heat engine. Four new thermoenvironmental evaluation criteria called as thermoenvironmental function, ecological based thermoenvironmental function, ecologicoenvironmental function and finite time exergoenvironmental criteria are developed and compared with the each other. Ecologicoenvironmental function is used to determine environmental impact at the maximum ecological function. It is defined as the most suitable criteria for an actual heat engine. Because, it has lower irreversibilities compared with others, its work output is equal to 90% of the maximum work and 60% energy efficiency at the optimum point and exergy destruction is lower than others at the optimum point. [ABSTRACT FROM AUTHOR]

Highlights: [•] Dimensionless equation that links COP, entropy rate variation and heat exchange. [•] Maximum COP as function of parameter controlling thermal exchanges. [•] Application at irreversible vapor compression refrigerator based on literature data. [•] Results show the analysis is useful in diagnostic and designing of refrigerators. [Copyright &y& Elsevier]

Abstract: An analysis on the influence of the recuperator effectiveness in a multi-step solar-driven Brayton engine is presented. The solar collector model includes heat losses from convection and radiation. The Brayton engine includes an arbitrary number of turbines and compressors, regeneration, and several realistic irreversibility sources. It is stated that the combination of both systems makes the evolution of the overall efficiency with the effectiveness of the regenerator not trivial. Such behavior is associated to the losses arising from the coupling of the working fluid with the collector and the surroundings. The overall efficiency admits a simultaneous optimization in regards to the pressure and temperature ratios. When the system is designed to work close to the optimum values of those parameters an increase in the effectiveness of the recuperator is always associated with an increase in the overall optimum efficiency. This holds for configurations from the simplest solarized Brayton up to arrangements with several turbines and compressors. [Copyright &y& Elsevier]

Abstract: We present a general model for a multi-step regenerative irreversible Brayton cycle on thermodynamic basis. The model incorporates an arbitrary number or turbines and compressors with reheating and intercooling intermediate processes. We consider several internal and external irreversibility sources that include losses in the non-isentropic turbines and compressors, pressure drops in the heat input and heat release, irreversibilities in the regenerative heat exchanger, heat-leak through the plant to the ambient and non-ideal couplings with the external constant-temperature heat reservoirs. The general equations for power output and efficiency depend on a reasonable low number of parameters, with a clear physical meaning, that account for cycle design and geometry, and for the characterization of irreversibilities. From this general model several results found in the literature could be considered as particular or limit cases. Moreover, we explicitly compare our theoretical results with computer simulation results in the literature for particular plant arrangements where the number of turbines and compressors is not the same. Also, we analyze the maximum power and maximum efficiency working regimes in terms of internal and external irreversibilities. [Copyright &y& Elsevier]

Abstract: During the last decades there has been an increasing interest in the low heat rejection (LHR) diesel engine. In an LHR engine, an increased level of temperatures inside the cylinder is achieved, resulting from the insulation applied to the walls. The steady-state, LHR engine operation has been studied so far by applying either first- or second-law balances. Only a few works, however, have treated this subject during the very important transient operation with the results limited to the engine speed response. To this aim an experimentally validated transient diesel engine simulation code has been expanded so as to include the second-law balance. Two common insulators for the engine in hand, i.e. silicon nitride and plasma spray zirconia are studied and their effect is compared to the nominal non-insulated operation from the first- and second-law perspective. It is revealed that after a step increase in load, the second-law values unlike the first-law ones are heavily impacted by the insulation scheme applied. Combustion and total engine irreversibilities decrease significantly (up to 23% for the cases examined) with increasing insulation. Unfortunately, this decrease is not transformed into an increase in the mechanical work but rather increases the potential for extra work recovery owing to the higher availability content of the exhaust gas. [Copyright &y& Elsevier]