نشریه تحقیقات موتور
پیاپی 36 (پاییز 1393)

Pistons are always exposed to scuffing fault in an internal combustion engine. This fault can seriously damage piston and cylinder so that engine performance decreases drastically. The objective of this research is to investigate the effects of piston scuffing fault on the engine vibration in order to the usage of vibrations for detecting this fault. To this end، horizontal and vertical vibration signals of the engine were captured for healthy condition and scuffed piston and cylinder state. In this research، time-domain، frequency-domain and time-frequency domain analyses were used for the engine vibrations. In time-domain analysis، two parameters of root mean square and impulse factor were extracted from the vibration signals. Fast Fourier transform and short-time Fourier transform were employed for frequency-domain and time-frequency domain analyses، respectively. Moreover، two features of mean and energy were used in time-frequency domain analysis. The results showed that the piston scuffing fault generates significant vibrations in horizontal and vertical directions of the engine. Also based on the obtained results، the piston scuffing fault produced substantial vibrations in the frequency band of 2 to 6 kHz in the horizontal direction، whereas for the vertical vibrations of the engine، the frequency band of 4 to 6 kHz was affected. The obtained results demonstrated that the engine vibrations are capable of identifying the pistion scuffing fault، and can be used for its detection in engine.

Due to the important and large contribution of rail transport and the high costs of machinery and equipment used in this section، the use of modern maintenance and repair methods is an inevitable necessity. The present study has been done experimentally in cooperation with “Bafgh locomotive repair factories complex” and has been defined due to its specific need. In this study the vibration analysis capabilities in order to find the cracked liner of Alstom diesel locomotives، operating in Iran’s railroads، have been discussed. The goal is that by mounting accelerometer sensors on the outer wall of locomotive engine and processing and analysis of collected signals، the faulty liner could be identified. Due to the non-stationary nature of collected signals، Short Time Fourier Transform and Wavelet Transform have been adopted for processing of these signals. The results show that both of these transforms are efficient in distinguishing the faulty and normal liners and can be an appropriate alternative to the current traditional methods. Among the benefits of replacement of this method with current methods، repair time reduction، running costs reduction، engine down time period in repairs section reduction، efficiency increment and timely and reliable detection can be named. In case of lack of timely diagnosis and completion of crack، irreparable damages will come. Sometimes the damage is so that the engine is completely outdated. This was the main motivation of the present study.

In an internal combustion engine، the temperature of the exhaust valve and its seat becomes extremely high as high temperature gases exit the engine. In order to avoid damage of the exhaust valve، the rate of the heat transferred from it should be under control. As the significant amount of the heat transfers when the exhaust valve is in contact with its seat، the estimation of thermal contact conductance and the identification of the parameters which have influence upon it are one of the most considerable challenges in the design of an internal combustion engine. In this paper، the thermal contact conductance is estimated by using the temperatures measured at several points within the exhaust valve and its seat. The linear extrapolation and inverse methods are applied. The results show that the thermal contact conductance increases as the contact pressure rises. In addition، a numerical simulation of the problem is performed by using a commercial software package. The thermal contact conductance obtained by inverse method is utilized as an input to the analysis. The temperatures obtained at thermocouple locations are compared with measured temperatures in order to validate the inverse solution and to investigate the accuracy of the numerical solution using the software. The error associated with numerical solution is larger than those due to two other methods. Generally، numerical results cover the measured temperatures and are acceptable.

In this research work، mechnanism of SiC insertation into A106 steel surface and composite layer formation studied. This layers formed using TIG arc welding process. Therefore، silicon carbide particles with different volume percentages were applied on the steel surface by changing the current density، melting and mixing process. Composite layer microstructures studied using optical microscopy، scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) spot analysis. The results showed that surface layers have the dendritic structure with silicon carbides particles into ferite phase. Micro hardness tests results showed increasing of surface hardness about 650 to 1200 VHN compare to uncoated samples about 200 VHN. Studing of composite layers wear behavior showed significant improvements with added silicon carbide reinforcement. The dominant wear mechanism of uncoated samples were delamination wear and surface oxidation. But، results showed that coated samples had a mixture of delamination wear، surface oxidation and adhesive wear.

Investigation of 3-D flow behavior into Internal Combustion Engines is always of designers’ interests. Due to refine designs، using CFD models makes designs towards a real evaluation. A 3-D CFD model was developed to study effects of early intake valve opening on the flow field characteristics in the intake manifold of a domestically-produced spark-ignited gasoline 1. 5 liter، 4-cylinders engine، TIBA (manufactured by MEGA motor Co.). The performance of the model was validated against experimental results of the engine obtained from the flow bench of the company. Investigation of EIVO/EIVC strategies has been done first time in Iran with 3D simulation for the National Engine. The results of implementing these strategies on valve events show that the average of intake manifold pressure has direct relation with the amount of throttle opening. Also the average of intake manifold pressure has reverse relation with engine speed. In addition، with considering of early intake valve opening (EIVO) and early intake valve closing (EIVC)، the volumetric efficiency will be increased in higher engine speed.

In this research، an intelligent and automatic procedure is introduced for diagnosis of some common faults of timing belt bases on its vibration signals. For this goal، vibration signals were gained in different faulty conditions of timing belt. In data mining step، six features namely، standard deviation، kurtosis، skewness، impulse factor، shape factor and crest factor were extracted from vibration signals aim to better monitoring of signals behavior. After extracting the fault characteristics، Artificial Neural Network (ANN) classifier was used for intelligent detection of faulty belts. The ANN was trained with 60 percent of signals and was tested with other signals. The results show the faulty belts have a turbulence vibration and impulsive behavior. Also، ANN classifier detected and classified the timing belts faults with 90 percent accuracy. The results show which the use of vibration signals for small faults detection of timing belt was effective aim to prevent its complete rupture. The results demonstrate the combination of data mining and artificial intelligence techniques is a powerful and successful procedure for precision timing belt troubleshooting.