فصلنامه مدل سازی در مهندسی
پیاپی 25 (تابستان 1390)

Temperature of spark plug can effect on the lifetime and combustion quality. The electrode erosion and gap growth are consequence of temperature rise. The temperature of spark plug should maintain in allowable range to increase of 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 cupper can be effective. Considering dependence of erosion of nickel electrodes to temperature، it is required to study effect of cupper core on decrease of temperature in electrodes. In the present effect of cupper core on electrode temperature is studied by two types of spark plugs that have same heat range. According to results، utilization of cupper core resulted to decrease of electrode temperature. So that electrode temperature is decreased 115 °C while engine operates by CNG at 2500 rpm under full load conditions. The difference decreases as engine speed increases at full load conditions until reaches 90 °C at 6000 rpm. Therefore cupper core will lead to 10-15% decrease in ground electrode temperature that can decline electrode erosion 2 times.

In this study، has been investigated the rate of heat transfer between engine and vehicle body room in steady state using analytical methods and the concept of net radiation heat transfer and energybalance equation at the boundaries. Also، calculated the net radiation heat transfer،percentage reduction in heat transfer، temperature and emissivity 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، Is obtained an optimized for combination of two and three radiation shields with different materials.

In this paper high speed Schlieren method was employed for measurement of the 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 diameter of 0. 4، 0. 5 and 0. 6. using digital image processing method by analyzing of the Schlieren images of transient helium direct injection jet. For finding edges of Schlieren images the Gaussian filter was applied to images. The J2715 SAE standard was used as a criterion for angle determination. Equivalent diameter was used for non-dimensional analysis of the penetration. Experimental results prove linear dependency of non-dimensional penetration to non-dimensional 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 to a constant value at the end of injection. The turbulent stochastic behavior of the jet arise need for repeating the experiments until achieving to 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 show 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 that the cycle consists of: suction،compression،expansion and exhaust. A two dimensional geometry has been used and moving boundries in valves and piston has been simulated by using the dynamic mesh. Three types of changing topology have been used that they consists of add or removal layers of cells for simulation of moving piston and sliding mesh for simulation of valves and attach or detach boundries for simulation of intake and exhaust ports. The k- standard model has been used for the turbulent flow and the Problem has been solved for two rotational speed 1500 and 3000 respectively. The contours of pressure and vector plots of velocity is showed. Asymmetry of flow in exhaust port at the end of the cycle is evident. Also swirl increases due to increasing of rotational speed. Using the dynamic mesh has caused achieving of flow’s details. So the numerical simulation could replace the difficult experimental methods.

Internal Combustion Engines (ICE) are heat engines that heat transfer plays important role in their performance and efficiency. In an IC Engine، the cooling system is responsible to remove additional heat from the engine. The cooling system of an ICE consist 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 equation is solved numerically. After the simulation and validation of the coolant flow in the water jacket، some changes in location of coolant inlet are considered. The obtained results show that both the pressure gradient and the flow rate of the coolant will reduce when the new inlet locations are used. It was showed that، the reduction of the pressure gradient and the flow rate، decreased the input power of the water pump and consequently increased the output power of the engine. The proposed idea in this paper can be used in the intelligent cooling systems of the internal combustion engines.