Stirling engines work with all kinds of heat sources thanks to the external heat supply. It has many advantages over internal combustion engines, especially in terms of noise emissions and pollutant emissions. Since the first Stirling engine invented by Robert Stirling, development work continues on it. Considering the problems caused by fossil fuels, Stirling engines are promising in the recovery of solar energy, geothermal energy and waste heat. As a result of the studies carried out from the past to the present, many Stirling engine types, cylinder configurations and drive mechanisms have been designed. In this study, the importance, advantages-disadvantages, usage areas and working principles of Stirling engines are explained. The Stirling cycle has been analyzed in detail. Carnot cycle and Ericsson cycle are mentioned and these three cycles are compared with each other in terms of work and efficiency. Stirling engine classifications, cylinder configurations and drive mechanisms are explained in detail. The design differences, operating characteristics, technological details and structural features of these configurations are examined. The advantages and disadvantages of all these different structures in terms of design, production, cost, power, efficiency, friction, wear, sealing, weight, dead volume, noise and number of parts are stated.

With the increase in global energy demand, air pollution becoming uncontrollable does not fall off the agenda. It is inevitable to use and spread of renewable energy sources to make energy production cleaner, more reliable and sustainable. In studies for this purpose, the use of fuel cell systems comes to the forefront thanks to its many advantages. The use of hybrid systems is becoming more common day by day in order to minimize the efficiency losses that may occur in the energy production, use and waste management process, to ensure energy reliability and to prevent systemic problems. In this study, hybrid systems created with fuel cells are discussed in detail, and examined under three main headings: hybrid systems created with renewable energy sources, created with storage devices, and created for energy recovery. It has been observed that the main purpose of hybrid systems created with renewable energy sources is to ensure energy reliability. In addition, the electrical energy required for the electrolysis of hydrogen used as fuel in fuel cells can be provided by photovoltaic panels or wind turbines, thus eliminating fuel storage and transportation problems. In hybrid systems created with storage devices, it is aimed to prevent instantaneous interruptions in the system by meeting the instantaneous power needed by the system and successful results have been achieved. In the hybrid systems created for energy recovery, it has been seen that it is possible to recover the heat and unburned fuel energy released from the fuel cell with thermophotovoltaic cells, gas turbines and heat exchangers.

The performance of active suspension systems is directly related to the mechanical design and control of the system. The stable operation of the controller improves driving comfort and handling. The quarter car model is frequently used in the analysis of suspension systems due to its simple structure. In this study, Matlab Simulink software was used in the modeling, control and simulation of the quarter car active suspension model. System performance was investigated for four different road profiles with PID and fuzzy logic control methods. Two of the road profiles used are in the form of impact signals consisting of pits and bumps. The other two road profiles are random road disturbances with high frequency. The effects of active and passive suspension systems on driving comfort are compared by taking into account the control methods used. As a result of the study, it has been determined that the fuzzy logic controller gives better results in pulse signals consisting of bumps and pits, and the PID controller gives better results in high-frequency random road disturbances. In addition, with the use of fuzzy logic control method in the active suspension system, a significant decrease in the actuator force has occurred. This result is very interesting in terms of minimizing energy, reducing actuator sizes and reducing costs.

Nowadays, researchers are making intense efforts to develop biomass-based industrial products. This study developed low-metallic and asbestos-free samples based on Cortaderia selloana (12–15% and 18% ratios), a natural species, to contribute to the brake pad field. The developed samples’ friction coefficient and wear rate experiments were carried out on a brake pad test device with a load of 1 MPa and a disk rotation speed of 6 m/s, according to the TS555 standard. Scanning electron microscopy and electron-dispersive x-ray analysis were performed on the worn surfaces of the samples. According to the results obtained, the wear rate increased while the average friction coefficient decreased in the brake pad samples using 18% Cortaderia selloana content in the sample content. In scanning electron microscopy analysis, primary and secondary plateau formations were observed on the worn surfaces of all samples. At the same time, samples containing 15% and 18% Cortaderia selloana also showed signs of abrasive wear. High friction coefficient and low wear rate are expected for brake pads to be used in automobiles. In general, the friction of brake pads must be within the range, and it is always necessary to balance the friction to avoid driver discomfort. However, except for some racing applications, a high coefficient of friction is only sometimes desirable, which can cause rotor wear problems. As a result of this research, a consistent friction coefficient and low wear rate for the brake pads with the brake pad sample containing 12% Cortaderia selloana.