نشریه تحقیقات موتور
پیاپی 52 (پاییز 1397)

Valvetrain is one of the major sources of noise and vibration in IC engines. The importance of cam surface quality parameters is highlighted in the valve train mechanisms with direct sliding contact between cam and tappet. In this paper, the influence of surface quality parameters on high frequency noise producing is investigated. The roughness and waviness of some intake and exhaust camshafts with diverse surface qualities were measured and then were mounted on a four cylinder gasoline engine to measure the noise level of valvetrain mechanism through NVH analysis. Furthermore, the characteristics of the unusual sound which is considered as an annoying noise were determined also, the camshaft Surface topology was inspected by a Scanning electron microscope (SEM). The results show that the nonconformities in surface parameters such as roughness and waviness are the main factors that lead to producing high frequency annoying noise and therefore must be carefully considered by designer.

One of the most efficient methods to reduce emissions and fuel costs of SI engines in petrol case, is the use of combined gasoline and NG. The ability of an engine is usually expressed with maximum power and maximum torque output of full-load state, but the operating time of the engines with full-load is less than that of part-load time. Therefore, studying the performance of the engine with a new mixed fuel (dual-fuel) requires studies under full-load and part-load. In the present work, dual gasoline-NG fuel with equal mass ratio together with single original fuel modes in full-load and a few part-load at 1800 rpm, 10.12 compression-ratio and almost stoichiometric equivalence-ratio have been taken into consideration in a SI single-cylinder research engine. In each load with a certain fuel, the spark advance was changed with 2°CAbTDC step and from obtained output and in-cylinder results, the optimum spark timing was determined for that mode and load. The results at optimum advance showed that increasing engine load, the exhaust gas temperature almost linearly for G100 and G0 but nonlinearly for G50 enhanced. Also, in full-load, the HC of the G100 appeared to be noticeably larger than those of G50 and G0. Decreasing engine-load for G100, HC amount reduced, while those for G50 and G0 increased. By changing the load, CO content for G50 and G0 fuels changed slightly, whilst that for G100 changed significantly. These observations emphasize a serious attention to dual fuel study mode in part-loads.

In this paper, a non-destructive eddy current test system was designed to evaluate the surface hardness of the carbonitrided steel parts. For this purpose, various samples of the tappet were used after the surface hardening and grinding operations as control samples and, if necessary, were subjected to destructive and non-destructive tests. Microstructural studies were performed with a microscope equipped with an image processing and micro and microprocessor based on the Vickers method as destructive tests. Statistical methods were used to identify the critical point for eddy current test position. Then, using a non-destructive eddy current test device, the microstructure and hardness of the good and bad part were evaluated at different frequencies at the critical point. The apparent resistance of the coil (impedance) was used as the eddy current response. Using regression analysis (R2), the frequency was chosen to evaluate the components. The results of this study showed that, using the eddy current method, carbonitrided parts can be identified and separated on the basis of the microstructure and the thickness of the hardened layer in a non-destructive manner. It was also found that the best separation of these samples is obtained at a frequency of 80 kHz.

The development of spray is one of the important factors effecting the combustion of PFI engines. This research was carried out in order to investigate some of the spray characteristics from PFI injector. In this study, the injector flux was investigated by a mass method and equations for it were presented. The results showed that in the pressure interval (2 to 6 bar), the relation of flux with pressure is a quadratic polynomial. The linearity of the injector was investigated and the results of experiments and equations with the manufacturer's nominal value were less than the difference of 2%. Use the Shillerin Imaging method to get the geometry of the spray. Tip penetration depth was followed as a geometric characteristic. The images were processed by image processing in MATLAB software. Investigations showed changes in penetration depth with pressure injections. At a Certain time after the injection began, the depth of penetration increased with pressure. Also, the effect of injector angle on the depth of penetration of the spray was followed by a finding that a certain trend could not be proposed for it, but in some cases, the angle change would change the depth of penetration by 15 mm then vertical position.

In this article, the isothermal low-cycle fatigue continuum damage in the engine piston aluminum alloy has been evaluated at different temperatures. For this objective, experimental data of low-cycle fatigue tests on standard specimens were used at 280, 350 and 425°C. Based on the continuum damage mechanics method, the fatigue damage was calculated during cyclic loading. Obtained results, including the predicted low-cycle fatigue lifetime of the piston aluminum alloy, indicated that based the maximum value of the relative error and the average error, a proper agreement was achieved, compared to the experimental fatigue lifetime. Applying the continuum damage mechanics approach in each temperature level in a separately condition, reduced significantly the relative error. Then, properties of the engine piston aluminum-silicon alloy based on the continuum damage mechanics model were obtained versus the temperature, under cyclic loadings. Finally, different damage parameter were defined and their results were compared to results of the continuum damage mechanics technique and the superior parameter was defined and selected.

In marine diesel engine, main bearing bolts (M18×1.5) withstand large tensile and cyclic loads to keep the crank shaft, bearing whit acceptable clearance and precision clamping force at high crank speed like 3100 rpm. In this research, the relationship between torque and clamp force, the friction coefficient, the effect of number of tightening and bearing conditions on the new manufactured bolt (with and without coating) and the original bolt were studied and compared. Also, the experimental results show that the new bolt designed and manufacture at maximum level of bolts standard (DIN 898 class 12.9). The process of manufacturing of new bolt was cold forging and heat treatment method after thread rolled. In order to determine the behavior and compering the performance of the new and original bolt, the tightening torque and clamping force were measured according to clamping process using a digital torque-wrench and load cell. Finally, the coefficients of friction were calculated using Motoch relationship for a bolt with and without coating in several stages of tightening. In addition, the amount of k constant (Torque coefficient) estimated. Also the bearing clearance measured with the micrometer. The results showed that about 10% of the tightening torque was converted to the clamping force, and the new bolt had the same functional condition with the original bolt.  Also, the value of the diameter deviations of the bearing caps was acceptable.