نشریه تحقیقات موتور
پیاپی 53 (زمستان 1397)

Engine oil is one of most important parameters in internal combustion engine that plays effective role in component wear. One of the ways to optimize the performance of the IC engines is online monitoring of wear particle in engine oil. There are different ways to identifying these particles, most of which are offline. Nowadays online oil monitoring sensors are quickly developed. In this study two online inductive sensors have been designed and tested to optimize and compare these sensors. Sensor No. 1 has two triggers and two sensing coils, and sensor No. 2 has two triggers and one sensing coil. After determining the optimal input variables, the sensors were tested. The outputs of each of the sensors were examined and compared. By detecting the best power of detecting each sensors, an optimal sensor with higher sensitivity was determined. Sensor No. 1 has lower pressure drop and sensitivity than sensor number two. In sensor No. 2, the fluid is faster due to the smaller diameter of the duct, which increases the accuracy and sensitivity of this sensor.

The piston ring which prepares mechanical sealing of a combustion chamber, should have significant abrasion resistance and less friction loss, using appropriate ring coating. The coating widely used is CrN, because of its good abrasion resistance at room temperature. However, it suffers from some shortcomings, such as high abrasion rate at temperatures above 200°C and lack of self-lubricating property. Although the abrasion behavior of various coatings has been widely investigated, a comprehensive comparing procedure is required to demonstrate the advantages of each coating. In this study, the effects of different Nano-coatings applied to the piston rings of the TU5 IC engine is investigated. The AVL software was used to create hydrodynamic lubrication model and solve numerically the related equations, such as Reynolds and friction loss and the parameters such as friction loss, abrasion, blow-by and oil film thickness were investigated. The results demonstrate that using the Nano-coating reduced friction loss and abrasion by 30 percent and 83 percent, respectively, and the mechanical sealing were improved by 79 percent.

Boiling heat transfer always has been proposed as a solution for enhancing heat transfer between the fluid and solid surfaces. Subcooled flow boiling is one of the mechanisms that occur in Internal Combustion Engine water jacket in which high amounts of heat is transferred. In this research, it has been tried to simulate subcooled flow boiling in a geometry similar to coolant channel inside the internal combustion engine using commercial software. The geometry, based on experimental studies, was considered as a channel with a rectangular cross-section and a hot spot on the channel lower surface, this geometry is the innovative part of this study. The models required for simulating the subcooled flow boiling were extracted from literature and implemented in the commercial software. The obtained results, after validation, applied in the final geometry. The results showed that with increasing the velocity, roughness effects are reduced, and numerical values get close to the experimental values. Also, with the surface temperature passing through the saturation temperature, the heat transfer rate was significantly increased by this mechanism.

Increasing the power (torque) of nowadays engines, along with reduction of fuel consumption and dimensions of them, cause to the use of turbocharged systems. Since turbo chargers are exposed to the exhaust hot gases and have a high operating speed, it is necessary to utilize high technology design and special materials with high cost. The temperature of the exhaust system with gasoline fuel sometimes reaches 950 degrees Celsius, and the change of operating points causes to its thermal fatigue. Hence, the thermal evaluation is one of the basic design activity for manufacturing and testing of turbo charger and its related parts, such as the turbo gasket. In this paper, a new method for evaluating the temperature of a gasket of a four-cylinder gasoline engine is presented. In this method, the temperature of the closest points to gasket is measured at the turbo housing and the exhaust manifold flange, and finally the temperature of the gasket is estimated using them. The results show that in this study, the maximum temperature of the gaskets is about 807 degrees Celsius, which is consistent with the results of analyzes and other turbo charger temperature measurements. Since the access to turbo charger gasket and direct measurements of its temperature is difficult or impossible, the proposed method can be useful in evaluating the temperature of the turbo charger gasket. Then, the measured temperature in the test of durability of thermal-mechanical fatigue was used and the obtained result was evaluated. The failure of gasket in this type of test could indicate the accuracy of the temperature.

Oil analysis is one of the main methods for monitoring the status of internal combustion engines and oils to ensure the lubricant's protective performance and engine health. This paper investigate oil condition monitoring in gasoline engine using oil dielectric coefficient measurement. At first capacitive sensor pectinate type is designed and manufactured that engine oil can pass through the sensor with high resolution and accuracy for engine monitoring application. Results show that up to 1.5% water pollution in oil, dielectric coefficient and θ is increased linearly. More water pollution increase dielectric coefficient exponentially. Due to investigate oil oxidation in controllable real condition, this sensor and another industrial quality sensor is evaluated in engine durability test. Although oil dielectric coefficient is increased with oil oxidation but also θ is constant permanently. Monitoring the result of dielectric behavior of engine oil in new design sensor is similar to industrial quality sensor. In addition interaction effect of water pollution and oil oxidation is studied. Results indicate that this sensor is capable of detecting water pollution and oxidation in engine oil.

Improvement and optimization of the Powertrain mounting system are one of the ways to improve the performance NVH cars. The study aims to find the optimal stiffness coefficients for each mount in three directions. The natural frequencies of the system remain steady and stay away from the excitation frequencies, so that the system does not a resonance. It was also, using the decoupling vibration mode theory the kinetic energy matrix was optimized. Powertrain as a rigid model with 6 degrees of freedom, and the engine mounts in the Kelvin-Voight model. To optimize the genetic algorithm in MATLAB software was used. By inventing a reverse method, using the proposed natural frequencies, we calculated the allowable range for the stiffness coefficients. Using this method compared to the conventional methods for determining the range of stiffness in the optimization algorithm, the results show that the natural frequency range is 17.2%, system decoupling modes 7% and in some of the modes 14%, objective function 7.5% improved. By using this method and using optimized stiffness coefficients, the decoupling of system modes 54% relative to non-optimal state improved.