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A simple theoretical analysis was carried out in order to clarify the general characteristics of pressure loss in exhaust gas flow induced when exhaust gas passes through a catalyst, which is generally used for the purification of exhaust gas emitted from automobile engines. Namely, Darcy's friction factor was applied to an equation, which is well known in the field of fluid dynamics, to determine the pressure drop of fluid flowing in a flow path. Using this friction factor, the air pressure difference between the upstream and downstream of the catalyst was calculated using the hydraulic diameter of the catalyst cell, the Reynolds number based on the hydraulic diameter of the catalyst cell, the length of the catalyst, and the density and velocity of the air flowing in the catalyst cell. Here, the flow of air is a laminar flow, which is assumed to be in the steady state, and the cross-sectional shapes of the catalyst cells examined are square, circle and equilateral triangle.

Investigations were conducted on a quasi quantitative analysis method for exhaust manifold stiffness and deformation that is useful when designing exhaust manifolds for in-line 4-cylinder engines. This method analyzes the exhaust manifold as a combination of beams, making it possible to obtain the effects of the dimensions and shapes of major parts of exhaust manifold on stiffness and deformation. These results clarified the effects of various exhaust manifold shape characteristics (aspect ratio, branch ratio, offset ratio) on non-dimensional stiffness, and also the effects of aspect ratio on the non-dimensional warping quantity. In addition, the effects of each of the aspect ratio, collective part different angle, branch ratio and offset ratio on non-dimensional stiffness and deformation when the dimensions and shape of each exhaust manifold part are changed could also be clarified by obtaining the degree of effects of each factor.

The objective of the study was to confirm whether or not it is possible to use the restraint ratio as an evaluation parameter for the thermal fatigue durability of the exhaust manifold. The study revealed that there was a conformity between the thermal fatigue observed in the material experiment and the restraint ratio. The ratio, under certain temperatures, is an effective tool in estimating the thermal fatigue durability of the manifold. An analysis was carried out by regarding the local restraint condition of the exhaust manifold as a spring system. This provided a method where the restraint ratio was reproduced for the manifold under engine operation temperatures of up to 300°C. As a result, the actual restraint ratio can be obtained by performing a relatively simple process. Since the restraint ratios that were calculated correlate with those that were actually measured, quantitative evaluation of thermal fatigue durability using the restraint ratio was found to be possible.