نشریه تحقیقات موتور
پیاپی 54 (بهار 1398)

This research proposes the effect of temperature variation in the Prandtl number on the power, the efficiency and the heat loss of the Gama-type Stirling engine. It should be noted that the Prandtl number included the viscosity, the thermal conductivity coefficient and the specific heat at constant pressures of the working fluid, which the temperature dependency of such first two thermo-dynamics properties were studied in this article. For this objective, a thermo-dynamics code based on the non-ideal-adiabatic method was firstly written to consider losses, including the engine pressure drop and the regenerator heat loss. In the second stage, such code was validated by experimental data. Then, results at 8 bar of the pressure, 970 rpm of the speed for three working fluids of air, helium and hydrogen were obtained within the hot source temperature of 350-750°C and for two conditions of constant Prandtl number and variable Prandtl number with the temperature. Obtained results demonstrated that the variation value for the power, the efficiency and the heat loss was less than 12%, 6% and 5% for air, helium and hydrogen, respectively, where the maximum change was observed in the engine power. Finally, using the regression analysis, the sensitivity value of the variation percentage of the Stirling engine performance was determined for three working fluids and under two conditions of constant and variable Prandtl number.

High pressure amount of fuel in new generation diesel engines’ injector equipped with multiple and small nozzle holes has created significant improvement in the outgoing spray behavior and engine performance. On the other hand, poor fuel quality and injector nozzle embedded in high temperature combustion chamber form fundamental deposits on the nozzle leading to fuel spray inappropriate behavior. Regarding the engine functional characteristics close correlation with fuel outlet spray behavior, in this study, the destructive effects of the fuel flow interaction with injectors nozzle sediment have been analyzed in terms of injector different operating time. The deposition process of injectors is carried out with standard fuel under specified experimental circumstances. Non-destructive electron microscopy methods have been used to analyze the sediment characteristics formed on the injectors nozzle. In order to analyze the outlet fuel spray characteristics, the spray evolution images of injectors with different operating time are processed by the code provided in MATLAB software at different pressures of the constant volume chamber and fuel injection. The imaging process was carried out in a constant volume chamber with a high speed camera. the injector deposits intensification increases the fuel injection delay and deteriorates the injector outlet spray behavior. The spray deposit destructive effects are alleviated through increasing the fuel injection pressure.

In this study, the effect of creation swirly flow and needle lift profile change on the behavior of the diesel fuel spray considered. To this end, two phase flow inside the diesel injector was simulated using the CFD. Solid works software has been used for geometry creation and AVL-Fire software has been used for meshing and simulating. Firstly, the liquid flow and spray characteristics of the cylindrical and conical nozzles with the same needle lift are investigated numerically. Numerical results of this step show that the conical nozzle has a longer penetration length than cylindrical nozzle, but Sauter mean diameter of these two nozzles are almost the same. In the second step, in order to increase the spray cone angle and improving atomization quality, spiral rifling like guides used in conical nozzle and needle lift profile had been changed. Numerical results of this step show that these new nozzles have more spray cone angle and less penetration length and sauter mean diameter than nozzles simulated in the first step. Thus the fuel spray characteristics can be controlled by creation of swirly flow and changing the nozzle geometry and needle lift profile. Numerical results and experimental data validated from previous researches.

When the mass flow rate through the compressor is reduced at a constant pressure ratio, mass flow rate will drop to an extent that the complete reversal of flow and surge occurs. Recently many research focuses on turbocharger surge, however, there are not enough investigation on the effect of surge on the performance of the turbocharger. The aim of the paper is to investigate the effect of repetitive surge condition on the performance of gasoline engine turbocharger. An experimental investigation has been performed on the turbocharger test cell for 3 different shaft speeds. Turbine and compressor power and efficiency have been investigated while turbocharger was performed in the surge zone. After 4 times repetition of the test procedure, turbocharger failure occurred. Results show that at 180000 rpm and minimum flow, the pressure ratio of compressor decreased by 7 percent after repetitive surge condition. Moreover, turbocharger failure analysis has been performed for the turbocharger which is repeatedly in the surge zone. Investigation shows that there the reason for failure was excessive axial clearance which caused high-temperature signs on the thrust bearing.

HCCI operating window has two distinct boundaries of knock at higher load region and misfiring/partial burning at lower load region. Moreover, there is no conventional direct way of controlling combustion timing in an HCCI engine. In this research, experimental study were carried out to investigate the effect of thermal and charge stratification on expansion of the operating range of a natural gas HCCI engine. To achieve this aim, a single-cylinder natural gas HCCI engine was used to characterize the effect of key operating conditions, including λ/EGR combination, reformer gas and glow plug tip temperature. The results reveal that increasing EGR ratio because of diluent effect on mixture; move the operation region towards rich boundary. So, it allows for more power. Reformer gas expands operating range toward lean mixtures and increases acceptable points in these region. The glow plug due to the disruption of homogeneous temperature inside the combustion chamber advances the start of combustion and increases the ignition duration.

The using of wet clutches and hydraulic control devices causes a smoothly torque transfer. In this study, a wet clutch was simulated in Simulink MATLAB software. Firstly the mechanical section of the clutch was modeled and then the hydraulic section was simulated with the addition of electric flow control valve and inlet and outlet of oil flow.  Finally, the effects of oil flow rate, electric signal of flow control valve and controller on the clutch performance were investigated. The results showed that it can reach a higher hydraulic pressure level by the addition of a flow control valve with electrical signal. The results showed that the proportional controller causes a sharp rise in torque (220 N.m) during the transmission, which can be reduced by the addition of derivative term to the system. The results also showed that using the dual mode controller can reduce response time of the system near zero and the clutch output velocity variations occurred in 0.1 sec, although the torque value will be a little more than a single-state controller in the dual controller mode.