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To understand the mechanism of the combustion by torch flame jet in a gas engine with pre-chamber and also to obtain the strategy of improving thermal efficiency by optimizing the structure of pre-chamber including the diameter and number of orifices, the combustion process was investigated by three dimensional numerical simulations and experiments of a single cylinder natural gas engine. As a result, the configuration of orifices was found to affect the combustion performance strongly. With the same orifice diameter of 1.5mm, thermal efficiency with 7 orifices in pre-chamber was higher than that with 4 orifices in pre-chamber, mainly due to the reduction of heat loss by decreasing the impingement of torch flame on the cylinder linear. Better thermal efficiency was achieved in this case because the flame propagated area increases rapidly while the flame jets do not impinge on the cylinder wall intensively.

In CFD (Computational Fluid Dynamics) verification of vehicle aerodynamics, detailed velocity measurements are required. The conventional 2D-PIV (Two Dimensional Particle Image Velocimetry) needs at least twice the number of operations to measure the three components of velocity ( u,v,w ), thus it is difficult to set up precise measurement positions. Furthermore, there are some areas where measurements are rendered impossible due to the relative position of the object and the optical system. That is why the acquisition of detailed velocity data around a vehicle has not yet been attained. In this study, a detailed velocity measurement was conducted using a 3D-PIV measurement system. The measurement target was a quarter scale SAE standard vehicle model. The wind tunnel system which was also designed for a quarter scale car model was utilized. It consisted of a moving belt and a boundary suction system.

Recently, rider comfort at highway driving has become an important issue in the performance improvement of motorcycles. Comfort includes windbreak, pressure on the rider, wind noise, visibility, and steering characteristics. However, most of these factors cannot be analyzed conventionally. Therefore we used CFD (Computational Fluid Dynamics) to examine the rider’s airflow environment. The environment of a rider on a motorcycle is an open space, very different from the passenger environment in an automobile. There are many airflow paths in a motorcycle with a cowl and a windscreen; thus, airflow behavior is constituted with a delicate balance. Though wind tunnel tests can give us an outline of airflow, CFD is a useful way to visualize the airflow of the rider’s environment and clarify the details. As the results, a lot of helpful knowledge was obtained for the development of new motorcycles.

This paper describes the evaluation of flow characteristics inside a model engine cylinder using particle image velocimetry (PIV), laser Doppler anemometry (LDA), and numerical simulation by Partial Cells in Cartesian coordinate (PCC) method. The main goal of the study is to clarify the differences in the velocity characteristics obtained by these methods. The model engine head has a four-valve system. Single- and dual- valve opening conditions of the model engine head were tested by a steady flow test rig. The flow structures were completely different for these valve opening conditions. The mean velocities and their distributions obtained by the three methods show satisfactory agreement. However, there were differences in the turbulence intensities under several conditions and measuring positions. Taylor's hypothesis in the integral length scale of turbulence was also compared with single LDA and PIV measurements.

To achieve power output and cooling performance in motorcycle air-cooled engines equivalent to those in water-cooled engines, an engine utilizing air-flow generated by the moving motorcycle and a new oil-cooling system for an air-cooled engine was studied. The engine temperature distribution was obtained based on a CFD (Computational Fluid Dynamics) analysis of cooling-air/oil behavior using an inline four-cylinder 900cm3 engine. As a result of this study, engine temperature was sufficiently decreased and the difference in temperature among cylinders was reduced; the engine was tested in a prototype motorcycle.

In the development of an air-cooled engine, cooling air flow was analyzed by CFD. Cooling performance of the engine is necessary for precise temperature control. However, stable radiation is difficult for motorcycles because of the effects of driving wind. Cooling fins are thin and complicated; therefore plenty of time and effort is necessary to create a boundary fitted mesh. In addition, since low Reynolds (Re) number areas coexists with high Re number areas in a calculation domain, applications of the wall function are limited. Therefore, we employ the Partial Cells in Cartesian coordinate method, which expresses complex shapes according to turbulence boundary conditions in the Cartesian coordinate. Analysis results show good agreement with test results in a wind tunnel. Furthermore, useful knowledge in engine development was obtained by examination of local heat transfer coefficients calculated by Karman's analogy.

Recently, utilization of CFD (Computational Fluid Dynamics) at the initial stage of motorcycle development is increasing the importance and is becoming indispensable to environment matters. This paper describes a CFD system, which was developed based on PCC (Partial Cells in Cartesian coordinate) method CFD code. The code does not require the mesh generation at each computation. The merit of this system is a full automation after the solid modeling by a 3D-CAD system, such as geometry data transferring, starting of processes, and mailing the results. Moreover, an example of a combination between CFD and DOE (the design of experiment) will be explained. It is an application of an exhaust muffler design of motorcycles. In the past, the decision concerning to the power output during an exhaust muffler design could be done by only a few skilled engineers, but the decision became possible to designers who use this system.

For passenger vehicles with direct injection (DI) diesel engines, it is desirable for the engine to have high speed and high power output performance comparable to that of gasoline engines, yet maintaining its good fuel economy. Accordingly, we examine a dual inlet port system, which operates both valves simultaneously at high engine speed to improve the volumetric efficiency but operates only one valve at low engine speed to obtain the optimum swirl ratio (SR). The swirl ratio with two valve operation (SR1+2) is affected by SR and the mean effective valve area (Zm) of each valve. Therefore, with experimental technique, it is difficult to find port configurations which are optimum for both high and low engine speeds simultaneously. We have employed a predictive method to obtain the optimum configurations. This paper describes how to derive the predictive equation of SR1+2 from the SR and Zm of each valve for the optimum intake system design.