نشریه تحقیقات موتور
پیاپی 30 (بهار 1392)

In this research، vibration control of national engine (EF7) using active mounts is studied for two different mounting layouts. The first layout is based on the current engine mounting of national engine (system of three passive mounts)، but the hydraulic mount is substituted by an active mount. The other mounting layout contains 4 mounts، 2 of which are active ones and the others are passive mounts. In order to simulate the dynamic behavior of the engine، a 6-degree-of-freedom، one-way-coupled model is hired. In addition، a proper dynamic model for active mount with electromagnetic actuator is chosen. In order to reduce transmitted force to the chassis through the mounting system، a feed-forward adaptive control method، FXLMS (Filtered-x Least Mean Squares) is employed which is one of the widely used methods in cancellation of acoustical and vibrational noises. Considering the characteristics of the transmitted force to the chassis، this method is used in a specific algorithm called narrow-band algorithm to cancel dominant harmonic frequency of the unwanted vibrations of the engine.

In many industrial processes، heat exchangers play the important role of the cooling function. The effective heat transfer rate in a specific process strongly depends on the heat exchanger design. The most popular type of heat exchangers commonly used in the automotive industry، is called «radiator». In engines، radiators play the important role of the cooling process. The present study is devoted to develop a mathematical model for the simulation of the vehicle radiator by utilizing the genetic algorithm method. Beside available experimental/analytical studies for studying the behavior of heat exchangers، an analytical model to predict and simulate their performance is of great worth. In the present study، we are going to use results of experimental data to obtain a general correlation، which can simulate the performance of heat exchangers. In this regard، a program is written to develop a mathematical model applying experimental data as inputs. The model is based on thermodynamic and heat transfer calculations and calculates cooling rate in each time step with deviation of 1. 68%.

In the present article، the thermal analysis of the cylinder and the piston in four-cylinder engines، made of functionally graded materials (FGMs)، has been performed by using the super element method. The objective of using FGMs in the cylinder and the piston is to increase their performance. FGMs include a combination of ceramics and metals. Inside the cylinder، the ceramic is considered and outside the cylinder، there is the metal. On the top area of the piston، it is consumed that there is the ceramic and on the bottom، there is the metal. This combination causes a better wear property (according to proper wear characteristics of the ceramic) and also makes a thermal barrier system (according to low heat transfer properties of the ceramic). The wear benefit is inside the cylinder and the thermal barrier benefit is on the top area of the piston. Obtained results indicate that there is a good agreement between finite element and super elements methods. However، the number of super elements is so lower than the number of finite elements with the same accuracy in results. In addition، the power value، which is related to material properties of FGMs، has no significant effect on the temperature distribution and the temperature gradient.

A typical dynamometer drive shaft was damaged during its working condition. This failure was repeated in four cases. In the present article، a failure analysis of a dynamometer drive shaft has been performed. To analyze the failure، the material investigation was carried out by scanning electron microscopy (SEM) images. Additionally، the micro-structure of the failed coupling shaft was photographed، the hardness was measured and compared to properties of the original material. Besides، the fatigue lifetime was calculated based on the high cycle fatigue (HCF) regime and the fatigue endurance limit by simulating the misalignment in a finite element (FE) model. The possibility of torsional vibrations and the occurrence of the resonance condition were also studied. Finally، vibration-monitoring practices were done to compare the vibration amplitudes to an acceptable criterion. SEM images showed cleavage marks under fatigue loadings. These marks indicated the brittle behavior of the material. The micro-structure together with the hardness of the alloy was satisfied. Based on numerical results، the fatigue lifetime of the coupling was likely to terminate according to the misalignment increase، as a cause of the failure. The other cause could be the resonance and the shaft critical speed، which was calculated below the idle speed of engines.

Pressure control valve (PCV) is implemented in internal combustion engine to regulate crankcase pressure. In this study، the performance of a diaphragm PCV valve is investigated numerically and experimentally. Firstly، numerical simulation is carried out using commercial code to predict the flow and pressure distribution inside the valve. Furthermore، downstream and upstream pressure of the valve is measured in a laboratory test rig. Finally، displacement and oscillation of the diaphragm are measured by a high speed laser displacement sensor. Comparison of experimental and numerical results show that proposed method is capable to properly predict performance curve of the valve.

In this research, a new exhaust manifold and its cooling jackets is first designed for the integrated exhaust manifold into cylinder head (IEMCH) for a turbocharged engine. Then, the gas exchange and flow analysis is carried out numerically to evaluate the proper conditions for the exhaust gas and the coolant stream respectively. Finally, the entire engine parts are thermally analyzed to assure their acceptable temperature. The obtained results are compared to the base engine conditions, indicating that the new engine with IEMCH may well satisfy all its thermal limitations.