نشریه تحقیقات موتور
پیاپی 70 (بهار 1402)

One of the main factors influencing the fatigue of the components is the torsional vibration of the transmission system. These vibrations are mainly caused by periodic changes in the gas pressure inside the cylinder and the inertial forces due to the reciprocating motion of the crank and slider mechanism. Furthermore, in order to decrease fuel consumption, the new engines have been downsized. Consequently, due to the fewer number of power strokes, the vibration has increased. One way to reduce these vibrations is to use a dual mass flywheel (DMF). In this research, inertia torque and gas pressure torque of a three-cylinder engine are obtained. Then the equations of torsional vibrations in the time domain are solved. It is shown that angular velocity fluctuations in the secondary mass is reduced. Also, according to the torsional vibration model of two degrees of freedom, frequency responses under sinusoidal excitation are calculated. The results show that in the case of using DMF, the resonance is kept away from the working range of the engine. Finally, A parametric study is performed on design parameters and the effects of varying design parameters on oscillation amplitude of the angular velocity of the secondary mass are analyzed.

Dynamic analysis and modal analysis of high speed rotors are a vital step in the design and development stages of rotating machines. Turbomachine rotor consists of disks of various shapes, shafts whose diameters change depending on their longitudinal position, and bearings situated at various positions. The vibrations of the rotor in the operating conditions can cause catastrophic failure of the parts or even the whole turbomachine. In this paper, lateral vibrations of a turbocharger rotor in non-rotating and rotating conditions are analyzed numerically using a finite element model based on Timoshenko beam elements. The Campbell diagram, critical speeds, operational deflection shapes and unbalance response of the rotor are the results of numerical dynamic analysis in the operating conditions. Also, the ambient modal testing of the rotor in non-rotating conditions is performed using frequency domain decomposition (FDD) method. In the modal testing, the laser doppler vibrometer and piezoelectric accelerometers are used simultaneously in order to exactly measure the vibrations. The good agreements between the numerical and experimental results show the accuracy of analyses.

In this paper, while examining the use of fuel cells in vehicles and past research, modeling of vehicles equipped with fuel cells with GT-SUITE software has been performed. In this modeling, various details have been considered and the specifications of a model vehicle have been used. In the following, the effect of effective parameters on the performance of the polymer membrane fuel cell is investigated. The simulation conditions are obtained by considering the existence of battery management system. The obtained results showed that with increasing the number of fuel cells and the surface area of the fuel cells, the output power of the fuel cell increases. Also, according to the simulation performed, with increasing the thickness of the fuel cells, the output power of the fuel cell remains constant. Although some results have been qualitatively predictable, it is important to know the impact of these parameters on the design. Then, the effect of load transfer coefficient and mass transfer coefficient of fuel cell mass was investigated. The results show the sensitivity of each parameter on the performance of the fuel cell and it was found that the effect of the parameters of the number of fuel cells and the surface area of the fuel cells is more pronounced than other parameters. Also, in these simulations the effect of changes made on the average temperature of the fuel cell was evaluated.

In this study, AL2O3+H2O nanofluid was used in a laboratory setting to test the thermal performance of the M13NI engine. AL2O3 nanoparticles were employed in this experiment along with base fluids made of water and ethylene glycol. We employed 20 nm nanoparticles with volume fractions of 1 to 2%. The outcomes demonstrated that the AL2O3 nanofluid made in the first 22 days was stable after being added SDBS sulphate. Additionally, the zeta potential, which was calculated to be 37.7 mv, shows the stability of the nanofluid. The heat transmission and pressure drop rose as the volume fraction of nanoparticles increased, while the merit parameter fell (ratio of heat transfer to pump power). At 1150 RPM and 1% volume fraction of nanoparticles in the water-based fluid, it was found that the heat dissipated increased by 7.2 and 13.1% in comparison to the mixture of water+ethylene glycol and pure water, respectively. When the volume proportion of nanoparticles in the base fluid increases, the radiator's outlet temperature decreases, resulting in a greater difference between the inlet and outlet temperatures and a faster rate of heat transfer. By utilizing nanofluid, it is possible to lower the radiator's size and the volume of the cooling system, so reducing the volume of circulating water and the engine's wasted power.

In diesel engines, for reasons such as increasing power and efficiency, reducing volume, reducing weight and increasing combustion quality, it is very common to employ a turbocharger. One of the most common problems in diesel engines is the absorption of soot particles in the turbocharger outlet, which clogged after a while. The blocked filter prevent to exhaust the gases with required flow rate, as a result, the back pressure and temperature of exhaust gases increase. This factor causes the turbocharger to be located near the unstable operating range and these factors expected to change the vibration behavior of this set. In this study, by creating several levels of soot particle clogging at 2500 and 3200 RPM, the turbocharger vibration signal was stored. Using this non-destructive method, more accurate data obtained to perform active Regeneration than the conventional method. Employing fast Fourier transform on stored time signal and filtering expected range of the signal, the turbocharger operating frequencies were determined and by extracting the frequency domain characteristics and comparing them, it observed that the power spectrum density and spectral flux had a resolution of approx. It has 4 times more than other features in indexing this event. In addition, as the engine speed increases, the soot filter clogging has a greater effect on the vibration behavior of the turbocharger.

Reactivity-Controlled Compression Ignition (RCCI) is one of the attractive low-temperature combustion strategies because of its high efficiency, reduced fuel consumption, and good potential in reducing emissions. This type of combustion has gained attention in recent years due to global concerns regarding environmental degradation, strict emission regulations, reduction of oil reserves, and rising fossil fuel prices. In this research, an RCCI engine, with a fuel mixture of diesel and gasoline, simulated with the aid of computational fluid dynamics coupled with chemical kinetics. The AVL FIRE software employed for the simulations. The aim was to investigate the impacts of changing the diesel fuel injection timing on combustion and emissions. In this regard, the effects of changing the diesel fuel injection timing in the range of 20 to 40° bTDC on the in-cylinder pressure, heat release rate, combustion phase, and the amount of carbon monoxide, carbon dioxide, nitrogen oxides, and unburned hydrocarbons emissions investigated at a constant engine speed of 1150 rpm. One of the most important results of this study is the reduction of NOX emissions by advancing fuel injection timing to 40° bTDC. Furthermore, with the advancement of diesel fuel injection timing, the combustion starts earlier. By raising the injection duration, the maximum in-cylinder pressure decreases, and the start of combustion delayed. As the fuel injection advances from 20 to 30° bTDC, the produced carbon monoxide decreases, and a further advancement from 30 to 40° bTDC, raises the amount of this pollutant. It is worth noting that the amount of CO2 greenhouse gas has an almost negative relationship with carbon monoxide production.