نشریه تحقیقات موتور
پیاپی 71 (تابستان 1402)

The Stirling engine is a combustion engine that converts mechanical work into electricity. Stirling engine needs a working fluid to work and usually, air, helium, hydrogen, nitrogen, etc. are used. Among the mentioned operating fluids, only air is free, but unfortunately, it has lower power and efficiency compared to other working fluids. It is expected that the desired power and efficiency can be obtained at a lower cost by combining two working fluids such as air and helium. However, to check this issue, it is needed to analyze the sensitivity of different input parameters on the outputs. Therefore, in this study, the non-ideal thermodynamic model was investigated, and the results of the presented model were validated by experiments, and then with the help of Design Expert software, 1260 designs were considered. Finally, the effect of changes in input parameters such as the speed, gas injection pressure, temperature, and helium percentage on outputs such as power, efficiency, heat loss, and cost were investigated. It was found that the cost was only a function of the gas injection pressure and the percentage of the fluid composition. Moreover, the results showed that with the increase of the temperature, pressure, speed, and percentage of helium, the power increased by 189%, 178%, 82%, and 54%, respectively. With increasing the temperature, speed, and pressure, efficiency increased by 42%, decreased by 23%, and decreased by 17%, respectively. With the increase in the temperature, speed, and pressure, the heat loss increased by 85%, 71%, and 357%, respectively.

Due to the complex geometry and loading conditions, exhaust manifolds are the most challenging components among all parts of internal combustion engines. They must withstand severe cyclic thermo-mechanical loading throughout their lifetime. Thus, simulation and analysis of fatigue cracks are essential. In this paper, low cycle fatigue (LCF) life analysis of the exhaust manifold is performed by using the finite element method and ABAQUS software to predict the temperature and stresses and then LCF life by using Smith-Watson-Topper theory and FE-SAFE software. Mechanical properties of silicon-molybdenum ductile cast irons obtained by LCF tests at different temperatures. The combination of the Chaboche nonlinear isotropic-kinematic hardening model with viscous stress law is used to consider the effect of viscosity. The results of finite element analysis (FEA) showed that the maximum temperature and stress values in the exhaust manifold are 757.7 °C and 395.2 MPa and the position is at the confluence region. According to the fatigue life analysis results, neglecting the elastoviscoplastic effect caused an estimation of 619 cycles or about 5.7% higher than the limit. Therefore, it is necessary to consider the elastoviscoplastic effect in the analysis of the low cycle fatigue life of the exhaust manifold. The results of the fatigue life analysis showed that the minimum LCF life of the exhaust manifold occurs in the confluence area. Thermo-mechanical analysis and LCF life results are compared with experimentally damaged exhaust manifolds to evaluate the results appropriately. It has been shown that the critical identified area match well with the area of failure in the experimental sample.

The importance of the effect of geographic climate on the performance parameters of cars requires comprehensive studies and research in this field, especially in Iran, where the diversity of climatic conditions is clearly evident. The factor scores of each of the influential components in determining the climate divide Iran into four climatic categories, which are: (1) dry, (2) humid with heavy rainfall, (3) semi-humid, semi-dry and (4) humid with little rainfall. Therefore, in this research, the effect of geographic climate on the characteristics of statistical data and driving cycle has been investigated. For this purpose, four cities of Arak (semi-arid to semi-humid), Tehran (dry), Ahvaz (humid with low rainfall) and Rasht (humid with high rainfall) were selected as representatives of their climate. Then, by reducing the dimensions of the data from 12 to 2 statistical data characteristics, using PCA analysis, and then by clustering the data using the chemical mean method, and extracting the driving cycles of each city under different climatic conditions, the effect of the geographic climate on the characteristics of the statistical data and the driving cycles of the case was investigated, and also the data of the city of Rasht on rainy and non-rainy days were separated and analyzed, and in the results of the investigations, it was observed that climatic conditions can have significant effects on the average driving speed (about 21 percent), travel time ( about 18 percent) as well as average travel speed (about 22 percent) and car stopping percentage (about 84.4 percent). As a result, it can be said that geographical climate is one of the most influential factors on driving cycles.

In this research, an experimental analysis of the effect of using aluminum oxide nanofluid (Al2O3) in improving the heat transfer of the engine radiator (XU7) with complete cooling system equipment was done. Tests in three pure water conditions; water and ethylene glycol (60:40) and finally with aluminum oxide nanofluid (Al2O3) with volume fractions of 1% and 2% and flow rates of 10, 21, and 32 liters per minute, in two slow and fast cycles. The cooling fan is done. The results showed that increasing the volume fraction of nanoparticles to the base fluid increases the heat transfer coefficient up to a flow rate of 21 liters per minute, and after that this coefficient decreases. By adding 2 percent by volume of nanoparticles to the base fluid at high fan speed, for flow rates of 10, 21, and 32 Lit/min, respectively, we see an approximate increase of 3%, 20%, and 16% in the displacement heat transfer coefficient compared to the base fluid. The pressure drop of the radiator with a volume fraction of 1 and 2% compared to the base fluid at a constant flow rate of 30 liters per minute was calculated as 22% and 40.8%, respectively.

Cast-in liner cylinder block, a crankcase with an integrated cast iron cylinder into the cylinder block, is an efficient and useful design in reducing the weight of the engine, reducing the time and cost of machining, and eliminating the environmental emission caused by the use of cast iron. The purpose of this article is to investigate the issues and challenges in the manufacturing process of this product. The most important issue in making an appropriated product is the bonding strength between the cast iron cylinder and the aluminum body, which is responsible for heat transfer between these two components. In this article, only the mechanical strength between the cast iron cylinder and the aluminum body is discussed. To achieve this goal, measures have been devised including the use of different coating methods, coating with different materials, and using different patterns such as grooves and porous casting surface (as cast) on the external surface of the cylinder to create a reliable and mechanical connection against the incoming forces caused by the piston movements and the difference is in the expansion of aluminum and cast iron components during engine operation. This study shows how a cylinder with a porous outer surface coated with zinc by melt immersion method produces a better bond quality than other tested designs concerning the bonding force of 320 N which is higher than other samples, also considering the Penetration liquid test determined that the thickness and length of cracks observed in the sample coated with zinc element is less than others.