نشریه تحقیقات موتور
پیاپی 19 (تابستان 1389)

Frictional damage in bearing is the leading cause of shutdown for industrial machineries including car engines. Early detection of this kind of damage may reduce maintenance costs and prevent unpredicted shutdown. Recently, researchers have been interested in using acoustic emission method, due to its high sensitivity, for condition monitoring of working machineries. In this study, the friction process is simulated by an experimental setup and its acoustic emissions have been analyzed to recognize which mechanisms affecton the acoustic emission signals. The results show that the signal waveforms varies greatly with initiation of damage in the frictional surfaces hence, damage process can be detected as early as it begins. In addition, the parameters affecting on friction, such as surface material, moving speed, frictional force, and lack of lubricant have sensible effect on the emission signals, so that, the frictional condition can be evaluated by monitoring and analyzing the signal waveforms.

Every industrial company will confront unforeseen and high expenses if there is not a plan for machinery maintenance. In such cases, spare part expenses and outcome decrease due to machinery stop are two main obstacles which hinder a company’s progress. Today, condition monitoring technology via oil analysis has been known as an effective method in determining abnormal wear or faults in instruments and mechanical systems. In this study, condition monitoring via oil analysis as a aintenance procedure as well as a method for applying this way in an affective CM plan have been introduced. Thus, wear pattern in diesel engine has been studied. A logical relation among engine state and wear particles such as Fe, Al, Cr, Pb, Cu, Si, Vis40, PQ, TBN and water contamination in oil analysis report will be drawn. As a sample, oil analysis reports of a Benz 2628 vehicle have been analyzed. Recognizing the logical relation between oil analysis report and engine part failures can be written in the form of fuzzy rules such as an expert knowledge.Finally, diesel engine failures will be predicted by this fuzzy program.

At this study combustion process of biodiesel and diesel blending was simulated with a thermodynamic model in a direct injection diesel engine. Different mixtures of biodiesel and diesel (B00, B20, B40, B60, B80 and B100) examined at maximum torque revolution and at full load on engine. Heat release rate simulated via double wieb’s function and heat transfer rate via experimental woschni model. Specific heats of biodiesel compounds (ethyl stearate, ethyl palmitate, ethyl oleate and ethyl linoleate) are determinedat confine of temperature of combustion chamber by means of quantum chemistry calculations and using the Gaussian 98 and Gaussian 03 softwares. Theoretical and experimental results for heat release rate and heat transfer rate was compared and was observed a good agreement between its.

There is a main problem that the noise generated in air intake system may be disgusting. Statistical energy analysis is a suitable method for acoustical - vibration analysis of structures in high frequency range. In this paper, the air intake system of an engine compartment is modeled using SEA. The transmission loss through the intake duct is calculated with importing CAD model and creating subsystems at high frequency range. In order to verify the results, a simple model of double walled cylindrical shell is modeled in Auto- SEA, and the results are compared with those of analytical ones. In addition, comparing the results of fully modeled of intake systems with experimental data available shows a good accuracy of results especially in high frequency range. Furthermore, the influence of inserting porous material is studied. Finally, the influence of some other parameters such as the thickness of the porous layers on the transmission loss of thesystem is investigated.

This study, investigate on the effects of piston cooling jet on the amount pollutant oil drops in engine blow-by using empirical methods. Considering that crankcase gases returned to the engine, always some oil drops are carried into the engine and increase the pollution. The tests are down using EF7 engine in motoring condition. Temperature and pressure of oil and water are controlled using external sensors and actuators. Results indicate that produced oil droplets increase with increasing engine speed. Also, the drops size decrease with increasing engine speed and oil flow rate. According to the test results, the amount of produced oil drops in the crankcase in 4000 rpm is at least 0.25 gram/Hr. This value is important according to EU5 pollutant regulation. To measure the drops glass micro fiber with different retention value are used and weigh with 0.001 gram precision. Also the best arrangement for the estimate the changing of droplet size has been investigated.

DI diesel engine is widely used in different automobile and industrial usages. With tightening of Diesel emission regulations and tending to making high efficiency engines, it is essential to understand these engines better because of the improving of engine design to reduce emissions and to improve performance of engine. One of the factors that play a significant role for engine performance obtaining treatment of combustion isinjection pressure. CFD codes programs have been used recently to simulate I.C. engines.This study investigates theoretically the effects of injection pressure on exhaust emissions and performance in a four cylinder DI diesel engine that has been equipped with turbocharger by AVL-FIRE. In order to validating the results, first, the engine is simulated and after that the results are compared with experimental results and then,injection pressure is changed. In this study, injection pressure is changed between 250bar and 1000bar while fuel consumption is kept fix. At the end, with changing duration and time injection, optimized point is recognized. The results show that by increasing the injection pressure, NOx emission is severely increased and PM emission is decreased about 50% and also the efficiency of engine is increased about 12%.

Heat transfer in the engine should be simulated to have a good estimation of emperature distribution in the engine and therefore control thermal stresses and the engine performance. Heat transfer simulation is obtainable through accurate modeling of cooling passages of the engine. Subcooled boiling is usually occurred in the cooling passages. Ignoring this phenomenon in the modeling procedure results in a considerableerror in estimation of heat transfer coefficient at the wall. In the present study numerical models for simulation of heat transfer in cooling passages of combustion engines are introduced and evaluated. The models, appropriate for simulation of each stage, are then explained and their precision will be calculated. In this study the method of principal convective heat transfer is introduced by exerting some modifications on the empirical correlation of Foster-Zuber. The proposed method in this study results in a significant zecrease in amount of calculations and therefore increases the rate of calculation of heat transfer and thermal stresses. One of the significance of this model is consideration of boiling effects in the heat transfer coefficient.The proposed model is employed for simulation of heat transfer in cooling passages of the “EF7”engine to calculate heat transfer coefficient and boiling zones and then proved to have a good precision.