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The rapid progress of industrialization and urbanization due to economic growth and concentration of social function in the urban areas have made the urban environment worse and worse. In most of urban cities, it has become more and more distinct that the increase of energy consumption is causing environmental problems including the temperature rise in the urban atmosphere(urban warming), and air pollution[1]. The present paper reports the results of field observation and three-dimensional simulation of urban warming in Tokyo metropolitan area. The three-dimensional governing equations in an urban atmospheric boundary layer were formulated by virtue of vorticity-velocity vector potential method. A particular attention was focused on the representation of a buoyancy term in equation of motion in the vertical direction, thereby describing the crossover and stratification effects near the ground surface.

A variable swirl inlet system with swirl control subport was developed with consideration of how to control the angular momentum of inlet flow into the cylinder. The effects of swirl on direct injection diesel engine performance and emissions are investigated with this variable swirl system. Basically, lower swirl level reduces the amount of initial stage burning, which is related to NOx emission, maximum cylinder pressure and rate of cylinder pressure rise, over the entire range of engine speed and load. As a result, in high speed range or partial load range, low swirl level simultaneously gives better BSFC and lower NOx level. An intercooled turbocharged engine with this variable swirl inlet system gave higher low-speed torque, higher brake horse power and better cold startability by selection of optimum swirl level for each engine condition.