نشریه تحقیقات موتور
پیاپی 23 (تابستان 1390)

Experimental investigation on the pumping loss and pressure oscillations in the crankcase Abstract:During the crankshaft rotation, as the pistons fall, the gas in crankcase compresses and its pressure rises because the crankcase is generally closed vessel. Pumping losses inside reciprocating engine is obviously undesirable power reducing parasite. However, precise investigation about deviation of crankcase pressure would be helpful for finding efficient method of oil separation from blow by gases. In this study, a experimental test rig and a thermodynamic model was used to estimate, crankcase pumping loss, pressure deviation, and horizontal ventilation of crankcase gas. Numerical simulation was validated by results of experimental tests which carried out for 4 stroke spark ignition engine. Crankcase pressure was measured by a piezoelectric sensor with 80 kHz frequency. Numerical simulation and experimental results had good agreement especially at low engine speed. By increasing engine speed, variation of numerical and experimental results increased due to effect of crankshaft rotation on the effective area. In addition, effects of window area between liners of crankcase were investigated. Results showed that, decreasing windows area caused higher amount of pumping loss. At low engine speed, frequency of crankcase pressure was two times of engine frequency, but at higher engine speed, frequencies were equal. Moreover, increasing engine speed caused more fluctuation of pressure amplitude. Keywords: Pumping loss, ventilation window, crankcase pressure, one dimensional simulation

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

The biodiesel fuel is produced from vegetable oils and adipose tissue. Biodiesel with diesel fuel are used in internal combustion engines in different ratios. Noise and vibration generated by combustion engines have detrimental effects on users. This is more acute in diesel engines. A few researches of vibration biodiesel blends exist in the world. Therefore, in this study, the vibrations of different blends biodiesel with diesel fuel on a four-stroke diesel engine Perkins 1006-6 were evaluated. The experiments were performed in two conditions, before and after the service engine. Artificial neural networks were used for modeling of the vibrations. Because neural networks methods have more benefits than many of the usual definite statistical methods. Results showed that the vibration values decrease considerably after the service engine. Fuel blend, was significantly affected on vibration values. It was fixed that diesel engine with B40 and B20 fuel blends have the lowest vibration and B15 and B30 fuel blends had the highest vibrations. The results demonstrated that there is a good match between roots-mean- squares acceleration values and neural networks,and the error rate approximately is close to zero in most patterns. Comparing the results of the neural network simulation and experimental results showed that neural networks are a powerful tool for the modeling of vibration in the engine.

Regarding environmental pollution of internal combustion engines and depletion of fossil fuels resources, compressed natural gas has been considered as an alternative to gasoline in vehicle applications. As supplementary fuel for spark-ignition engines, CNG has some advantages over gasoline, such as higher octane number and reduction of CO2, CO and UHC emissions. In this paper, a quasi-dimensional thermodynamic predictive model used to simulate the working cycle of a 4-stroke spark ignition engine fueled with gasoline,CNG, and their mixture for variable mass CNG fraction. The model predicts the performance parameters such as power, ISFC and environmental emissions including CO2, CO, UHC and NO. The results obtained from the present study have been compared with the experimental data. The experiments have been done on a bi-fuel CNG-gasoline engine for gasoline, CNG and the dual fuel operations. The results for pressure traces and performance parameters of the engine showed a good agreement with corresponding experimental data.

Porous media (PM) has interesting advantages compared with free flame combustion due to the higher burning rates, the increased power range, the extension of the lean flammability limits, and the low emissionsof pollutants. Future internal combustion (IC) engines should have had minimum emissions level under possible lowest fuel consumption permitted in a wide range of speed, loads and having good transient response. These parameters strongly depend on mixture formation and combustion process which are difficult to be controlled in a conventional engine. This may be achieved by realization of homogeneous combustion process in engine. This paper deal with the simulation of direct injection IC engine equipped with a chemically inert PM, with cylindrical geometry to homogenize and stabilize the combustion of engine. A 3D numerical model for PM engine is presented in this study based on a modified version of the KIVA-3V code.Due to lack of any published data about PM engine, numerical combustion wave propagation in a porous medium are compared with experimental data of methane-air mixture under filtration in packed bed and very good agreement is seen. Methane as a fuel is injected directly inside hot PM that is assumed, mounted in cylinder head. Lean mixture is formed and volumetric combustion occurs in PM. Mixture formation,pressure and temperature distribution in both phases of PM and in-cylinder fluid with the production of pollutants CO and NO and also effect of injection time, in the closed part of the cycle are studied.

Most of mechanical components of automobile engine and structures applied in powerhouses, petrochemical and aviation industries are subjected to different kinds of cyclic loadings, such as low cycle fatigue (LCF) stresses at high temperatures. Thermo-mechanical fatigue is the dominant cause of fracture in these components.Therefore, investigation of different thermo-mechanical fatigue life assessment methods of these components is very necessary. When a component is subjected to high temperature thermal cycles and mechanical strain cycles simultaneously, the thermo-mechanical fatigue process leads to micromechanical damage and final fracture of the component.In this study a precise procedure for the Thermo-mechanical fatigue life assessment of hot diesel engine components is investigated. In high cycle fatigue assessment, the effect of mean stress is considered using Haigh diagram. Different LCF life assessment methods have been used to investigate LCF life and their results are compared to each other. Almost all of the engine components are subjected to proportional or non-proportional multiaxial loadings. The non-proportional loading leads to an additional cyclic hardening in the material. Critical plane LCF theories are appropriate for consideration of the additional cyclic hardening effect on the fatigue life reduction of the component. Effect of high cycle fatigue on low cycle fatigue life reduction is also studied. Finally, the discussed thermo-mechanical fatigue life assessment process is used to estimate thermo-mechanical fatigue life of a diesel engine piston.

A dynamic-thermodynamic model of stirling engine is presented to study some of optimization factors on engine thermal efficiency and output power. The optimization factors have been assumed as heater and cooler heat transfer areas, regenerator solid mass amount and its heat transfer area and fluid pressure drop. To study these factors, the model takes into account non-ideal heat transfer, non-uniform pressure distribution and time dependant temperature variation in any stirling engine gas chambers. Calibration parameters also have been defined so that the model should be calibrated via a test result data or simulation data, afterward it can predict the engine behavior while changing the optimization factors.Geometrical dimensions and test results at nominal gas pressure for ST500 stirling engine was used in order to calibrate the model. To ensure the prediction accuracy, comparisons were accomplished between model output and motor test results for different gas pressures. Finally the optimization factors of the model were varied separately, model outputs were compared and the most important factor in improving the thermal efficiency and work output was selected. The determined optimization factor was applied to the engine and the thermal efficiency and output power was measured. The engine test results were compared to the model prediction and to previous engine state.