جستجوی مقالات مرتبط با کلیدواژه "موتور" در نشریات گروه "مکانیک"

The cylinder-piston reciprocating mechanism has been one of the most dominant designs since the invention of internal combustion engines. By reducing friction between the cylinder and piston of the engine, the reciprocating movement of the piston can be made possible, easily. The pressure inside the cylinder during the compression and expansion strokes is much higher than in the crankcase. Due to the movement of the piston inside the cylinder and its temperature change during the engine operation, a clearance needs to be between them. The clearance creates some crevices between the cylinder chamber and the crankcase. By placing the open-mouthed elastic rings in their special grooves on the piston, some serious flowing obstacles are created. However, in addition to the loss of work, the friction between the rings and cylinder can cause the relative motion of the rings in their grooves during the reciprocating movement of the piston and change the blowby geometry, so the ring friction forces are important. In the present work, an accurate experimental method is proposed and used to measure the friction of a ring with a cylinder applying a mass-pulley-string set, equipped with a displacement measurement sensor. After the experimental-analytical estimation of pulley-resistant torques, to extract the friction force of the ring, the friction force was measured and calculated in two states piston without ring and piston with ring. The results showed that the friction force of a compression ring was 2.87 N and although the piston under vertical movement had no noticeable lateral load, it was observed that its friction force was about 77% of the compression ring friction.

The jet pump thrust system is one of the types of marine propulsion systems that creates the thrust force based on the momentum difference method. The jet pump is primarily designed for underwater vehicles. The jet pump propulsion system has been widely used due to its stealth and excellent performance, but due to its secrecy and complexity, few details have been published. The behavior of this propulsion system is similar to axial flow pumps. The main components of jet pump thrust system include duct, motor, stator, hub and boss. The motor is installed on the hub with a specific number of blades and the stator is attached to the hub from the root side and to the inner surface of the duct from the tip side.Jet pumps are classified into four categories according to the placement of the motor and stator inside the duct as well as the rotation mechanism: pre-rotation, post-rotation, driving ring and double anisotropy. The pre-rotation type has less noise and efficiency than the post-rotation type and is considered a type of ultra-silent propulsion system. Considering the numerous advantages of using nuclear propulsion in submarines and other marine vehicles, the jet pump seems to be a suitable candidate for marine propulsion systems with nuclear propulsion, considering the acoustic advantages as well as the limitations of the phenomenon of xenon poisoning and power reduction in nuclear reactors. arrives. In this research, an attempt is made to introduce this type of engine and examine its advantages.

Today, due to the increasing weight of cars, the addition of turbochargers to internal combustion engines increases performance and at the same time, produces high noise in the range of 72 dB to 154 dB when the engine is running at high speeds and during the initial acceleration. To reduce the negative effects of these noises and increase the comfort of the car occupants, various methods such as including finite element analysis and numerical analysis of compressor blades to optimize pressure drop coefficients (ratio of turbine input to compressor output), sound pads and acoustic materials around engine parts including turbocharger parts and air manifold, are used. The purpose of this article is to express and classify the research done in the field of reducing annoying noises resulting from the operation of the car engine and turbocharger.

The purpose of this paper is to optimize the gearbox conversion ratios of vehicles and the gearbox gear ratios are calculated in such a way that the engine provides the maximum possible traction, thus providing the maximum slope force with respect to the stability condition. First, the gearbox conversion ratios are determined by considering the type of vehicle and the appropriate calculation method. Then the gear conversion ratios are changed so that, considering the stability condition, the traction force diagram in the gears is as close as possible to the ideal traction force diagram and the uncovered parts are less in the ideal traction force diagram and the actual middle gear diagram. This is done for a two-stage gearbox with two intermediate axles, which is located in the transmission line with a diesel engine. The obtained results show that with the optimization of the gearbox, the rate of improvement of traction force in the maximum case is 17.5%, slope 16.3%, acceleration 17.2% and torque 13.5% in 3rd gear. Comparisons made for validation with a base vehicle also show a good agreement between the base vehicle and the vehicle in this study.

This article describes the advanced design of the car engine at IPCO. Product development models including model V, gateway and network are described first. In the following, in order to introducing engine production to readers, some of the literature and subsystems of the engine are briefly presented. There are also different levels of engine development programs, either low, medium, high, or completely new products. Depending on the level of development, the development of the engine takes 4 to 48 months. Members of the development team and components influencing engine development are also introduced. By these premises, a product development model from the beginning, the conceptual development phase, to mass production with its details is described. At the end, by combining V and Gateway models, the details of the IPCO product development model are outlined. In fact, the result of this article is to systematize the engine development process in Iran and the Iran Khodro complex. As such structure has not existed in Iran so far, IPCO, as a domestic innovative engineering company in the design and production of engines, has described the model used by researchers and industry leaders in field.

In piston engines, as the engine speed increases, the combustion cycle time decreases. Reducing the engine combustion cycle time, the opportunity for complete fuel combustion is reduced. As a result, in order to complete the fuel combustion, at high engine speeds, the spark plug must ignite sooner. Now that the natural gas flame is slower than gasoline, this problem is becoming more noticeable. As a result, the spark ignition timing should be increased further in CNG fuel mode than in the case of gasoline combustion. This leads to an increase in negative work during the compression phase, resulting in reduced cycle efficiency. Researchers have suggested adding hydrogen to improve natural gas combustion (HCNG). By adding hydrogen, the flammability properties of natural gas are improved. In this study, using Hydrogen generator, hydrogen and oxygen (HHO) gas is produced and consumed water by electrolysis method. The gas (HHO) produced together with the gas (CNG) is combined with the air entering the engine. Then the effect of gas (HHO-CNG) on the parameters of efficiency, power and pollution has been investigated. The results show that the thermal efficiency increases with the addition of HHO. Under these conditions, CO and UHC levels have decreased. This reduces contamination and increases efficiency due to reduced need for spark plug advance and complete fuel combustion.

Recent developments in automotive industry tend reseachers to design engines of lower volumes and higher efficiencies. Volume reduction enhances the generated heat per volume which in turn requires effective cooling methods to avoid thermal stresses on the engine walls. Nowadays nanofluids are extensively welcomed and employed as effective working fluids with efficient cooling potentials. Boiling phenomenon, by providing more amounts of heat transfer in comparison with single-phase, provides conditions for size reduction. In the present study effects of adding nanoparticles to the pure water as the cooling working fluid in the radiator is assessed. The employed nanoparticle is TiO2. A 3D model of engine with the cooling passages is simulated by CFD both for the pure fluid (water) and nanofluid. It will be shown employing 1 vol% TiO2 nanofluid improves cooling heat transfer up to 37% in comparison with the pure water. Keywords: Boiling mode heat transfe, Nanofluid, Engine, Cooling passages.

Clearances between cylinder and piston, and pressure difference between top and bottom of piston causes a flow through the crevices termed blowby. This phenomenon results in cylinder pressure and temperature drops; some unburned mixture remains in the crevices leading to inconvenient usage of the mixture in firing cycle and reduction in engine performance. In the current work a thermodynamic blowby simulation code validated in motoring condition has been used to study and predict the blowby of XU7JP/L3 engine in terms of engine speed and engine working life. Some geometrical measurements of cylinder-piston-ring pack were performed in two engine operations, 70000km and 200000km, to apply the code after required corrections. The obtained results showed that the values of the blowby geometry increased with enhancement of engine life and engine temperature. Increasing engine life enhanced cylinder leakage significantly so the leaking value of 200000km reached to 4 times greater than that for new engine life. Also the mass lost through second compression ring at 70000km and 200000km working durations increased to about 7 and 15 times of that for new engine one, respectively.

Since spark ignition engines has a large portion in emission production, recognition of the engine emissions when engine work at high compression ratios and different conditions with gasoline and natural gas could be useful to compare engine exhaust emissions in gasoline and natural gas fuel case and find the lowest emissions production condition. In the current work, an engine was set at 9 and 10 compression ratio for gasoline and natural gas fuel case. It warmed up with fuel injection at full load, three engine speeds, at certain spark advance and four equivalence ratios. Then in each engine speed and equivalence ratio, spark advance (according to the crank angle) was changed on non-knock domain with two degree per step and external results were recorded. External data included HC and CO emissions, relative air-fuel ratio (l), also internal air-flow and external torque. It was observed that the decrease of representative equivalence ratio causes the reduction of HC and CO. At equal representative equivalence ratio the amount of HC in gasoline fuel case is more than natural gas fuel case and overall increasing was estimated more than three times. Engine speed change causes variation in the amount of HC while it has no impact in the amount of CO.

In this study, a number of tests are conducted on a four-cylinder spark ignition engine with natural gas and the cycle to cycle variations of peak pressure max P and peak pressure angle Pmax  in the engine are analyzed for nine different equivalence ratios. By using multi scale entropy technique, it is shown that the complexity of peak pressure and peak pressure angle depends on the equivalence ratio variations. Thereby, a limitation is found for optimum equivalence ratios that can be used for controlling the combustion process and improving engine performance.

In the direct gas injection engine, the mixture formation and the combustion rate are affected by the geometry of injector holes (the diameter, angles, K-factor) and discharge the coefficient of the exit nozzle. This paper presents a new method to determine the diameter and the nozzle exit angle, based on silicone molding of the injector exit nozzle, using image processing techniques. The actual fuel mass flow rate was measured through experiments, which were done with a designed experimental set-up. Tests have been done in an optical constant volume chamber, where the ambient gas was pressurized air, limited between 5 to 15 bar and the injection gas was compressed natural gas (CNG) at two different pressures, 30 and 40 bar. Discharge coefficients have been calculated for different ambient and injection pressures, considering values of actual and ideal mass flow rates. Results verified the present approach for determining the diameter and the nozzle exit angle. Moreover, results showed that there was a direct relationship between the actual mass flow rate and the discharge coefficient with ambient and the injection pressure.

Piston and connecting rod are the most sensitive moving mechanical parts in engine which must have very special features. In this article, because of importance of the breaking down of piston and connecting rod in high-round marine engines, we are trying by using the performed investigation and our different experiences and also those of mechanics of sea areas, so give an analytical reasons for the failure of these two parts and give an technical suggestion for improving and increasing the long life these two parts and consequently the long life of the engine.

This study discusses about the ceramic-metal joint. Alumina and copper samples with the Ag-Cu-Sn-Zr nano filler at 1050°C of the temperature and 20 minutes of the holding time had been jointed in the furnace. The cross-cutting and the microscopic examination of the sample showed that the sample was joined by the filler with the active zirconium. It was absolutely spotless and the joint region was continuous. The active zirconium reacted with the surface of the ceramic and helped it being metallized. Thus، the difference of the coefficient expansion between the metal and the ceramic and also thermal stresses reduced، and there was no crack. The shear strength of the joint was measured as 18. 37 (MPa).

For spark ignition engines, the fuel-air mixture preparation process and injection timing mechanism are known to have a significant influence on engine performance and exhaust emissions. Injection timing mechanism is effective on fuel mixture preparation and fuel vaporization and also HC production. In this paper,a model of a 4 cylinder multi-point fuel injection engine was prepared using a fluid dynamic code. By this code one-dimensional, unsteady, multiphase flow in the intake port has been modeled to study the mixture formation process in the intake port for 2600 and 6000 rpm in part load and full load condition. Accuracy of model was verified using experimental results of engine testing and it shows good agreement between the model and the real engine According to the present investigation, a key point was found to design optimum injection timing for different engine velocities and loads

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.

Homogenous charge compression ignition (HCCI) engines are being actively developed worldwide as they can have efficiencies close to that of diesel engines, with low levels of oxides of nitrogen as we particulate matter emissions. There are challenges associated with the successful operation of HCCI engines particularly with combustion phasing controls. Thus, auto-ignition models are proposed to be used in engine control systems. Hu and Keck model, Shell model, and Knock integral method are selected. Two equations in Knock integral method are proposed for the prediction of start of ignition of the first- and second-stage combustion. The comparison of average differences in auto-ignition delay between the models, experimental data and time calculation indicates that Knock integral model has the highest accuracy as well as shorter time.