نشریه تحقیقات موتور
پیاپی 61 (زمستان 1399)

In this article, an intelligent system is introduced in order to detection and classification of some common mechanical faults of an engine alternator based on the frequency analysis of vibration signals. For this purpose, firstly the vibration signals of an alternator under four conditions, including healthy, bearing corrosion, cracked rotor and unbalanced excited shaft, were captured by an accelerometer. Time-domain signals were then transformed into frequency-domain with the aid of FFT. At the next step, power spectral density (PSD) method was used for the secondary frequency signal processing level. Afterward, in data mining step, twelve statistical features were extracted from the PSD values of the signals, which were fed as the input data into the ANN classifier to detect and classify the alternator faults. The results indicate that the proposed method has the capable of detecting the different alternator faults with an accuracy higher than 92%.

The effect of the temperature on exhaust manifold modal analysis was investigated in this study. For doing this, Solidworks software was used to model the exhaust manifolds. Then the modal analysis was performed to get the natural frequencies in Abaqus software.  Finally, the modal analysis that considers temperature effect was done. The study of structural dynamics is essential for understanding and evaluating the performance of any engineering product. The determination of the dynamic characteristics of automotive structures has become an extremely important issue in the automobile industry. Modal Analysis is currently one of the key technologies in structural dynamics analysis. The temperature-dependent of material parameters was considered in order to increase the accuracy of finite element analysis (FEA) results. The results of FEA proved a very good agreement between temperature distribution and thermal analysis results, carried out in references. The frequency and vibration mode between cold modal and thermal modal’s was compared. The results showed that temperature has a great influence on the exhaust manifold mode and it is very valuable to product design. The results of the modal analysis proved that the maximum strain energy density and total strain energy exist in the confluence area. The results of the finite element analysis correspond with the experimental tests, carried out in references, and illustrate the exhaust manifold cracked in this region. The obtained FEA results show that gas pressure is effective on the modal analysis and must be considered in the modal analysis of exhaust manifold.

The effect of perimeter fins on the thermal stress and low cycle fatigue life (LCF) of exhaust manifolds was investigated. For doing this, Solidworks software was used to model the exhaust manifolds. Three Perimeter fins with 4 mm thickness was attached to the modified exhaust manifolds outlet section. Then ANSYS Workbench software was used to determine stress and fatigue life based on Morrow and Smith-Watson-Topper (SWT) approaches. Finally, the improvement of the low cycle fatigue life was studied. The temperature-dependent of material parameters was considered in order to increase the accuracy of LCF life results. The results of finite element analysis (FEA) uncovered the fact that perimeter fins reduce the temperature distribution in the exhaust manifolds about 32.54°C. As a result, the exhaust manifolds tolerates lower temperature and fatigue life will increase. The results of thermo-mechanical analysis indicated that the stress in the modified exhaust manifolds decreased approximately 22MPa for the sake of depletion of temperature gradient which can lead to higher fatigue lifetime. The results of LCF showed that the number of cycles of failure for modified exhaust manifold is approximately 55% higher than the results obtained from the original exhaust manifolds.

In this research study, alumina nanoparticles (80 and 120 ppm) were prepared and added as additive to the diesel fuel. Effect of these blended fuels was investigated on the performance and exhaust emission of six cylinders, four-stroke diesel engine and the results were compared with the neat diesel fuel. Experimental results reveal that by using of nano-fuels and increase of nanoparticles concentration at diesel fuel increased engine performance variables including engine power and torque output up to 2% and brake specific fuel consumption (BSFC) was decreased 6.01% compared to the neat diesel fuel. Also results proved by increase of nanoparticles concentration at diesel fuel CO and HC emission decreased 13.1% and 23.4% compared to pure diesel fuel respectively. Moreover, CO2 and NOx emission increased 29.5% and 33.3% compared to pure diesel fuel respectively. Therefore, the results showed that alumina nanoparticle additives in diesel fuel increased engine performance and reduced exhaust emission of diesel engine and it can be used as an alternative and environmentally friendly fuel in CI engines.

In this paper, the influence of equivalence ratio on combustion characteristics have been examined by considering 16 different operating conditions. The fuel used in this research is gasoline and the ignition takes place in two stages. The first stage of combustion is due to low temperature reaction heat release (LTRHR), and the second stage is related to the high temperature reaction heat release (HTRHR). The three-dimensional computational fluid dynamics (3D-CFD) with chemical kinetics has been chosen as the numerical method. In all of the studied operating conditions, the 3D-CFD simulations were able to see the combustion properly and the increase of maximum pressure and maximum rate of heat release (ROHR max) with the rise of the equivalence ratio was properly observed. Also, by increasing the equivalence ratio, 3D-CFD model show advanced maximum pressure and ROHRmax but mistakenly predicted the start of LTRHR more delayed, while the HTRHR was properly predicted.

Choosing the appropriate concept for the engine components and systems is one of the essential issues that influence directly on the cost and functional characteristics of the product. For selecting the right concept for an engine component, it is necessary to take different contradictory factors into account.  Parameters like functional aspects, durability, cost of production and assembly issues are commonly of interest for selecting the best concepts. In this research, concept evaluation and choosing the best concept for an engine component was investigated using multi-criteria decision-making techniques. The purpose of this study is to investigate the problem of selecting the appropriate cam bearing frame concept from available four concepts based on 10 measurement indicators. For this purpose, this research is intended to use the DEMATLE-ANP-TOPSIS compilation method for modeling and solving the problem. At the beginning, using the DEMATEL method, the relationship between multi criteria is determined and afterwards ANP method determined the weight of the criteria. Finally, the TOPSIS method was used to rank the options. The results, for the selected case indicated that the two-piece ladder frame (concept 4) is the preferred option.

Engine downsizing has been considered as a promising approach for reducing CO2 emitted from internal combustion engines, since the long term goal of International Energy Agency was published in 2011.  By engine downsizing, the engine dimensions would decline while the performance is preserved. So, the fuel consumption and engine emission decrease as well as power to weight ratio increases. In this study, the Iranian national engine EF7 is considered as the target of downsizing and three conceptual designs for downsizing are propose: 3-cylinder gasoline turbocharged (EF7α), 3-cylinder CNG turbocharged (EF7β) and 3-cylinder CNG turbocharged with improved compression ratio (EF7γ). The performance of each concept is investigated and compared with the base engine employing a hybrid-structured engine simulation tool involving a 1D model for engine components and a thermodynamic two-zone model for combustion process. The model is validated with experimental data for base engine. Indeed, the performance of the gasoline-fueled version of downsized engine EF7α is estimated close to the base engine. Shifting the fuel to CNG (EF7β) would lead to lower and poor performance of engine, especially in low load regions. Modification of spark timing would somehow solve the problem however deficiency in lower engine speeds still remains. Employing anti-knock index as the main advantage of CNG as a fuel for spark ignition engine, the third concept (EF7γ) is introduced by improving the compression ratio. Results show that a 3-cylinder CNG fueled turbocharged engine with improved compression ratio would be a good choice for EF7 downsizing.