Modeling in Engineering
Year:2011 | Volume:9 | Issue:25|Papers Count:8

Temperature of spark plug can effect on spark plug lifetime and combustion quality. The electrode erosion and gap growth are consequences of temperature rise. The temperature of spark plug should be maintained in allowable range to increase its lifetime.Utilization of materials that have better heat transfer is one of the useful methods to decrease electrode temperature. So, high heat transfer ability of copper can be effective. Considering dependence of erosion of nickel electrodes on temperature, it is required to study the effect of copper core on reduction of temperature in electrodes. In the present study, the effect of copper core on electrode temperature is studied by two types of spark plugs that have the same heat range. According to the results, utilization of copper core resulted in reduction of electrode temperature. So that electrode temperature was decreased by 115 oC, while engine operates by CNG at 2500 rpm under full load conditions. The difference decreases as engine speed increases at full load conditions until it reaches 90 oC at 6000 rpm. Therefore, copper core will lead to 10-15% decrease in ground electrode temperature that can decline electrode erosion by two times.

In this study, the rate of heat transfer between engine and vehicle body room in steady state has been investigated using analytical methods and the concept of net radiation heat transfer and energy-balance equation at the boundaries. Also, the net radiation heat transfer, percent reduction in heat transfer, temperature and emissivity were calculated while there are one, two and three radiation shields with temperature- dependent emissivity. The findings reveal that one radiation shield with lower emissivity can reduce the net heat transfer even better than two radiation shields with higher emissivity. Also, an optimized combination of two and three radiation shields is obtained with different materials.

In this paper, high speed Schlieren method was employed for measurement of geometrical characteristics of transient gaseous jet. Axial jet penetration and its angle versus time were calculated in pressure ratios of 2, 3 and 4 and three different nozzle diameters of 0.4, 0.5 and 0.6 mm using digital image processing method by analyzing of the Schlieren images of transient helium direct injection jet. For finding the edges of Schlieren images, Gaussian filter was applied to images. The J2715 SAE standard was used as a criterion for angle determination. Equivalent diameter was used for nondimensional analysis of the penetration. Experimental results proved linear dependency of non-dimensional penetration to nondimensional time with slope of 2.3-2.9. Angle measurement showed that jet angle would decrease after time passing from start of the injection and reaches a constant value at the end of injection. The turbulent stochastic behavior of the jet arise need for repeating the experiments until achieving acceptable results.

In this article, the model of a radiator filled with nanofluid and variations in flow pattern and the heat transfer of mixed convection through it is investigated.Al2O3-water nanofluid is used as heat transfer fluid and dynamic viscosity and thermal conductivity according to new models of variable properties are dependent to the diameter of nanoparticles, concentration of nanoparticles, temperature and so on. The right wall of cavity is cold and other walls are adiabatic. Finite volume method is used for the numerical solution of the equations of continuity, momentum and energy, and these equations have been resolved using a FORTRAN computer code. The effect of the Richardson number, solid volume fraction of nanoparticle, height of heated obstacle and its position within radiator on fluid flow and heat transfer are studied. The results are present in streamlines and isotherms contours and also in Nusselt number plots. Results show that increasing solid volume fraction and decreasing Ri number leads to heat transfer increases.

This paper presents energy and exergy analysis of the power generation system of a 2700 kW marine diesel engine. The power generation system is consisted of diesel engine, turbocharger, high and low temperature water cooling system, and heat exchangers. Compressed air is passed through the compressor and is cooled using an intercooler by high and low temperature cooling system. In addition, oil temperature is lowered in the oil heat exchanger via the low temperature cooling system.Implementation of exergy analysis leads to identifying critical points with maximum entropy generation. Outcomes of this research can be used in order to improve performance characteristics of the system. Obtained results showed that the exergy destruction in diesel engine is 41.9% of inlet fuel’s exergy and 86.9% of the total exergy of the system. Although 18% of heat dissipation occurs at the intercooler and oil heat exchanger, they waste less than 1.8% of inlet fuel’s exergy. While the turbocharger plays no role in the energy balance of the system, it dissipates 4.5% of inlet fuel’s exergy.

In this article, turbulent flow in a cycle of internal combustion engine has been analyzed by OpenFOAM software. The cycle consists of suction, compression, expansion and exhaust. A two dimensional geometry has been used and moving boundaries in valves and piston have been simulated by using dynamic mesh.Three types of changing topology have been used which consist of add or removal layers of cells for simulation of moving piston, sliding mesh for simulation of valves and attach or detach boundaries for simulation of intake and exhaust ports. The k- estandard model has been used for turbulent flow and the problem has been solved for two rotational speeds 1500 and 3000 rpm, respectively. The contours of pressure and vector plots of velocity are presented. Asymmetry of flow in exhaust port at the end of the cycle is evident. Also swirl increases due to increasing of rotational speed. Using dynamic mesh has caused achieving of flow’s details. So, numerical simulation could replace difficult experimental methods.

Internal Combustion Engines (ICE) are heat engines in which heat transfer plays an important role in their performance and efficiency. In an ICE, the cooling system is responsible for removing additional heat from the engine. The cooling system of an ICE consists of many parts that water jacket of the cylinder block and cylinder head of the engine is one of them. In this paper, the effect of redesigning of coolant inlet and outlet location on the temperature distribution of the engine body, engine coolant and water pump power is investigated. Both hydraulic and thermal governing equations are solved numerically. After simulation and validation of the coolant flow in the water jacket, some changes in location of coolant inlet are considered. The obtained results showed that both the pressure gradient and flow rate of the coolant will reduce when the new inlet locations are used. It was showed that reduction of the pressure gradient and flow rate decreased input power of the water pump and consequently increased output power of the engine. The proposed idea in this paper can be used in intelligent cooling systems of the internal combustion engines.