نشریه تحقیقات موتور
پیاپی 28 (پاییز 1391)

In the present study, effects of different percentages of ethanol as a gasoline additive on high temperature oxidation behavior of cylinder head and valve alloys were investigated. A single-cylinder four-stroke engine was used to simulate the hot chamber of cylinder environment. Samples were located within the exhaust pipe and were deposited with ethanol blended gasoline combustion gases under certain operating cycles. Then in order to evaluate the oxide layer, the cross-section of samples were observed by scanning electron microscopy (SEM) and to determine the amount of oxygen, the surface of samples were analyzed by energy dispersive X-ray (EDX) technique. The obtained results exhibited that, thickness of oxide film was increased by increasing of the ethanol percentages and engine operating cycles. The most porous film was belonged to steel in 15% ethanol-containing fuel with 60 operating cycles. Metal loss in steel specimens was significantly more due to linear behavior of steel oxidation.

As for spray-guided direct injection gaseous fueled engines, a few time is available for mixture preparation, exact determination of the gaseous jet characteristics emanating from the injector is very important. The main purpose of the present work is investigation of the effects of pressure and density ratios on the multi hole gaseous jet tip axial and radial penetration lengths and its velocity. For this, ultra high speed Schlieren imaging of the transient jet with high spatial and temporal resolution was utilized. jet images were analyzed using digital image processing method and the jet characteristics were extracted using an in house software which worked based on edge detection approach. Results revealed that regarding to the velocity curves, formation of the multi-hole gaseous jet is comprised of three stages of: emergence of the individual plumes, merging and penetration of the main spray. It was also found that changing the chamber gas density wouldn’t alter the maximum and minimum times in velocity curves and decreasing the density ratio of the injection gas to chamber gas would decrease axial penetration and jet tip velocity and increase jet spreading angle.

Spark plug condition is an effective parameter on the combustion quality of a spark-ignition (SI) engine. If the condition of spark plug becomes abnormal, engine’s pollution and efficiency will be affected. In the present paper, a procedure is proposed based on vibration analysis for spark plug fault detection. The vibration signals of a SI engine were collected by an accelerometer under two spark plug conditions, namely, normal and abnormal. In order to remove the noises from the signals, wavelet denoising technique was used. Then feature extraction method by statistical parameters was applied to obtain fault-indicating information. In this work, seven feature parameters were employed in the feature extraction stage, namely, maximum, mean, standard deviation, variance, Skewness, Kurtosis and impulse factor. Neural network (NN) was trained with seven neurons in input layer. After constructing the optimum structure, the network’s performance was tested. The results showed that a high level of efficiency was gained in spark plug fault detection. So it can be mentioned that the proposed approach can reliably be used for fault identification in engine spark plug.

Internal combustion engines are used as stationary engines in factories and power plants for a long time. In recent years, the demand for environmental protection and the use of alternative fuels have excited the product market to the power generation systems using heavy duty gas engines. This research activity investigates the effect of piston bowl depth on the performance and emissions of gas engines. Towards this purpose, 3D computational fluid dynamic is used to simulate the cycle engine. By implementing the equations of combustion, turbulence and pollution, close cycle of engine is simulated and the results are presented as graphs and contours. Firstly, results are validated with experimental data and the by simulating of three different pistons, their pressure and temperature inside the cylinder and their amount of emissions are compared.The results show that combustion chamber which creates best mixing and optimum turbulence has the best performance and releases lower emissions.

The objective of this article is to simulate the thermal and mechanical behavior of the diesel engine cylinder head. This finite element analysis was performed in the ABAQUS software. Thus، to identify the material behavior، results of low cycle fatigue tests at various temperatures (stress- mechanical strain hysteresis curve at the mid-life cycle) were used and material constants of the two-layer elastic-viscoplastic model were extracted. Fatigue tests were performed in the strain-controlled tensile-compressive condition on the aluminum-silicon-magnesium alloy (A356. 0). Then، by using these material constants at 25، 200 and 250°C، thermal and mechanical stresses of the cylinder head were calculated. The validation result illustrated that the elastic-viscoplastic model has a proper accuracy to predict the hysteresis behavior of the aluminum alloy. Finite elements results showed the location of cracking between valves. In addition، the calculated viscous strain cannot be eliminated، although it is less than the plastic strain.