The purpose of this article is to evaluate four different gas turbine cogeneration cycles which are basic, absorption cooling, air heating and air fuel heating cogeneration cycles by using the most important six evaluation criteria for different excess air coefficient, different compression rates, and different compressor inlet air temperatures. These six evaluation criteria are electrical heat ratio, exergy efficiency, incremental heat rate, artificial thermal efficiency, fuel energy saving ratio, and specific fuel consumption. It is seen that the air-fuel heating cogeneration cycle is the most efficient among the cycles examined for a certain compressor compression ratio, followed by the air heating, basic, and absorption cooling cycles.
Cryogenics has an important influence on industry and science. In this study, optimum working conditions are obtained by applying exergy analysis and local optimization methods to two- and three-stage vapor compression cascade cryogenic cycle. The first and second laws of thermodynamics, exergy analysis, and local optimization methods are applied to the two- and three-stage cascade cryogenic cycle. By considering the needs and demands, it is possible to create new cycles by adding new devices and/or new stages to these cycles. The results of the optimum operating conditions are obtained for the two- and three-stage vapor compression cascade cryogenic cycle. It is seen that to achieve high COP values and high efficiency; it is necessary to reduce the compression ratio of the compressor as much as the fluid allows. For the two-stage cycle, the minimum total work required for cryogenic cooling is around P 7 = 2,400 kPa. The COP value is 0.30 between P 7 = 2,400 and 2,800 kPa, and the maximum exergy efficiency is obtained around 0.235. It is seen operating the first-stage compressor at high pressures increases the total losses of the entire cycle from 7,500 to 18,550 kW. The increase in total exergy losses is around 247%, and operating the first-stage compressor at high pressures increases the exergy efficiency of the entire cycle. The increase in total exergy efficiency is around 160%. When the second-stage compressor is operated at low pressure, the COP value increases by 2%, the exergy efficiency increases by 20%, and the exergy losses decrease by around 40%.
The electrical energy consumption is increasing in our country and in the world. The electrical energy and heat energy are primary energies and has a vital role on industry and our lives. The production of these two energies in different cycles leads to energy loss and low efficiency. With the production of both in the same cycle, the efficiency increases a lot, and the energy losses and emission values decrease a lot. By installing cogeneration system to produce electrical and heat energy, the energy consumption costs can be reduced importantly. The cycle in which the fuel and the air entering into combustion chamber is heated by the heat taken from the exhaust gases at the outlet of the gas turbine is analyzed by using exergy analysis method and, first and second laws of thermodynamics. The heat energy remained in the exhaust gases are used to produce in steam production, after some heat energy is consumed to heat the air and the fuel, in this cycle. The performance analysis of the devices that make up the cycle such as turbine, recuperator compressor, combustion chamber, and heat exchanger and for the whole cycle and were obtained and discussed. Exergy efficiency, exergy losses and other performance parameters of the devices were obtained and discussed.
Internal combustion engines use generally fossil fuel products. World resources of it is limited. Renewable alternative energy sources are getting important solution for energy demand. Hazelnut oil ethyl ester is obtained from raw hazelnut and mixed with diesel oil in certain proportions to use in a four-stroke direct injected single cylinder diesel engine. In this study the effects of the mixture of diesel oil with hazelnut oil ethyl ester on the engine performance and exhaust gas emissions are investigated for the first time in literature. The fuel injection system is regulated to use the mixture in the engine for the investigation. The results show that, the mixture with 25% ethyl ester extracted from hazelnut oil can be used as an alternative fuel without any change or regulation of the diesel engine.
Aircraft engines such as gas turbines and detonation engines have very important attention by the researchers in the last decades. However, using detonation engines for producing electrical and heat power was not researched efficiently. In this study, gas turbine and pulse detonation engines cogeneration systems were analyzed and compared by using first and second laws of thermodynamics and exergy analysis method. Three different cycles, namely, basic gas turbine, Zeldovich–von Neumann–Döring (ZND) detonation engine and steam injected regenerative ZND detonation engine cogeneration systems were investigated. The performance analyses and the advantage of these three cycles were obtained and discussed. The performance analyses were done for different compression ratios (r), and the combustion outlet temperatures and pressures, exergy efficiencies, specific fuel consumption, electrical efficiency, exergy fuel consumption, electrical heat rates and other performance parameters of the three cycles were obtained and discussed. It is found that gas turbine cogeneration systems have some advantages and disadvantages in some conditions than ZND cycle. The steam injected regenerative ZND detonation engine cogeneration systems can compete with the Brayton cycle cogeneration systems.
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