نشریه تحقیقات موتور
پیاپی 45 (زمستان 1395)

Heat transfer is one of an important issue in the design of internal combustion engines, because it has a direct influence on performance, efficiency and emissions of the engine. Investigation of heat transfer in IC engines needs consider to boiling phenomena in water jacket, because sub-cooled boiling in hot spot of engine increases heat transfer rate. In this paper, coupled heat-transfer simulation of cooling jacket, block and cylinder head with AVL-Fire software was carried out. First, validation with experimental data of boiling in cylindrical passage using two correlations BDL and Chen was down, which results showed in operating temperature of an engine two correlations have similar results, but Chen correlation has better results. Therefore, Chen correlation for computational fluid dynamics of national engine was used. Results of velocity, pressure and heat transfer coefficient in water jacket and temperature distribution in block and cylinder head were achieved. Finally, effect of precise cooling with geometry modification near exhaust valve seat and spark plug, on temperature distribution in water jacket, block and cylinder head have been investigated.

This research work is directed toward determining the thermal stresses in a Ni-Resist cast iron commercial exhaust manifold of a turbo-charged gasoline engine. At first, based on a fluid-structure interaction (FSI) method, the steady state temperature distributions in the exhaust gas as well as in the exhaust manifold set are determined, using a CFD model. The thermal B.C.’s previously estimated by conducting a motor temperature detection test. Next, to conduct a thermal stress analysis, a full FEM model for the manifold set has been generated in the Abaqus software, and the mechanical B.C.’s are imposed in that. Also, the temperature distribution resulted from the thermal analysis imputed to the nonlinear FEM model as a predefined temperature field. Also, the range of temperature variations in the manifold is defined for the software material property module, so that Abaqus computes the material properties and stresses in each point according to the local temperature. Finally, executing the FEM model, the thermal stress distributions are computed. The numerical results show that the thermal stresses have the most critical values at the confluence region of the manifold, and maximum shear stresses occur around the bolted joints.

Performance optimization of diesel engines is the subject of most researchers in the field of internal combustion engine in recent decades. One of the the most effective ways toward optimizing the performance of heating systems is exergy analysis. In this study, energy and exergy concepts are applied to evaluate the performance of a compression ignition engine with premixed gasoline fuel at various loads and constant speed. To reach proper performance of diesel engine with premixed fuel, in addition to first and second-law efficiencies, exhaust emission characteristics are reviewed. The results of this study indicated that greater portion of exergy transfer was due to the irreversibility, averaged 50% while at high loads exergy destruction rate decreased to %5 by using premixed gasoline fuel. Also, energy and exergy losses through exhaust emissions with premixed fuel will be reduced to about %8.5 and %16/5 (averaged on all engine loads), respectively. The use of premixed fuel gasoline can increase energy and exergy efficiency (maximum 8% at high loads) at all loads while NOX pollutants will be reduced. It was also found that both HC and CO emissions with premixed gasoline fuel will be increased at all loads.

The idea of using porous media in internal combustion engines is developed to achieve charge homogenization in recent decade. In this paper, the macroscopic characteristics of high pressure diesel spray has been studied in interaction with porous media. Spray penetration length has been obtained numerically in both free spray and porous media (PM) presence in a constant volume chamber under different ambient pressure conditions. Four empirical correlations in the literature has been compared to predict the spray pressure drop through the PM and obtained the viscous and inertia loss coefficients in the Forchheimer equation and then the most accurate correlation will be introduced based on the experimental results. The numerical results predict correctly the length of the spray penetration after passing through porous media. Although these correlations were developed for water in low Reynolds flows but the result indicates that the correlations can be used in high Reynolds streams and expanded scope of its applications.

Increased exhaust emissions and fuel consumption from internal combustion engines is a significant challenge in large cities. One of the most effective way to reduce pollutant emissions in combustion process, is providing the required conditions for homogeneous combustion. Using the porous medium for homogeneous combustion in internal combustion engines has important advantages such as decreasing air pollutions (HC, CO), decreasing the specific fuel consumption and increasing the specific fuel consumption. This paper presents the effect of using the porous medium in the intake manifold of a a four-Stroke Honda motorcycle engine with direct fuel distribution. Emissions, specific fuel consumption, engine torque and output power were measured and compared by the performance of the conventional engine. The results show that using the porous medium reduces production (HC,CO) and specific fuel consumption up to 70% and 27% respectively.

Power increase, efficiency improve and reduce of fuel consumption of internal combustion engines is a great technological interest. For this reason, turbochargers are widely used in the internal combustions engines nowadays. So, studying of the performance of turbochargers is focused in automotive industries. In the present paper, the effect of blades angle of a turbocharger compressor on its performance is studied numerically. First, the impeller geometry and volute geometry of Garrett T25 turbocharger compressor is acquired using 3D scanning, then it is modeled in CFX Ansys software. The results show that the performance of compressor is slightly changed when the blade angle is changed at the layer of hub inlet. On the other hand, the transferred energy to fluid is considerably increased when the blade angle is increased at the shroud. For the mass flow rate of 0.122 kg/s, the efficiency and total pressure ratio are increased up to 1.67 and 1.7 percent respectively when the blade angle is increased 9 degree at the shroud in comparison to the default compressor. The maximum impact on compressor performance is caused due to changing the angle of the outlet of blade. For mass flow rate of 0.124 kg/s, isentropic efficiency and total pressure ratio is increased 1.12 and 3.43 percents respectively when this angle is decreased 9 degree in comparison to the default compressor. Finally, a new impeller was designed in order to have maximum efficiency and maximum total pressure ratio using the acquired results. The results of the final compressor show a shifted of mass flow range in comparison to the main compressor. For the same mass flow rate, The mean values of isentropic efficiency and total pressure ratio of the final compressor are increased 6.52 and 6.65 percents respectively, while the input power is increased 6.19 percent related to the default compressor.