石田 正弘

蒸気タービンの低負荷運転における低圧最終動翼内逆流現象の三次元数値解析 : 流体工学,流体機械

Reverse flow which occurs in a low pressure steam turbine rotor under the low load operation was analyzed by the three-dimensional turbulent flow computation. The computed flow angles at the inlet and exit of the rotor agreed well with the experimental results in the scale-model turbine and also with the results based on the quasi 3-D inviscid flow analysis. It is clearly shown that the spiral-type vortex appears due to the reverse flow at the rotor root, and in addition, the leading-edge separation occurs on the pressure surface over the rotor blade height, especially a large separation occurs at the root side due to a high incidence angle. The present study suggests that the unstable flow might be caused by the spiral-type vortex and the leading-edge separation under lower load operations.

2領域モデルによるディーゼル燃焼解析 : 第2報,燃焼域空気過剰率の検討

The excess air ratio of the burned zone, Ad, which was estimated by two-zone model analysis, was compared with the excess air ratio of the modeled steady-state fuel spray and diffusion flame. There was little correlation between λd and the averaged excess air ratio in the cylinder λm, and λd was mainly dominated by the characteristics of fuel spray and ignition delay. The excess air ratio during the premixed combustion period minimally influenced upon the NO formation fraction if the premixed combustion fraction was less than 50%. The major factors of NOx reduction were investigated using the two-zone model. As a result, it was made clear that a large NOx reduction due to timing retard was mainly caused by both a decrease of combustion temperature and a large decrease in combustion pressure on the expansion stroke, and a small NOx reduction with the decreased nozzle hole diameter was caused by a decrease of combustion pressure based on the decrease of the heat release rate in the premixed combustion.

遠心羽根車の羽根先端すきまに基づく二次流れ : 続報,二次流れとすべり係数の関係

The velocity distributions measured at the exit of two different types of unshrouded centrifugal impellers respectively under four different tip clearance conditions were reexamined with respect to the shroud wall surface. By increasing the tip clearance, the hub-to-shroud velocity distribution was hardly changed at the exit of the radial blade impeller, by contrast, the relative flow angle was reduced significantly and monotonously in the backward-leaning blade impeller. The change in input power due to the tip clearance was clearly related to the change of flow pattern at the exit of the impeller due to the secondary flow, which must be induced by the component, normal to the blade, of the shear force to support the fluid in the clearance space against the pressure gradient in the meriodional plane without blades.

高速ディーゼル機関の燃焼と排気に関する研究 : 第2報, 水添加乳化油の燃焼と振動・騒音

This paper deals with quantitatively the influence of water emulsified fuel on combustion, engine vibration and noise, and the effect of ignition improver on the reduction of vibration and noise. The main conclusions obtained are as follows : (1) With an increase in the water addition rate, ignition delays and the maximum pressure rise rate increases. As a result, engine vibration and noise increase, in proportion to the pressure rise rate. (2) An increase in ignition delay with the addition of water is closely related to the heat quantity required to evaporate water in the fuel spray under a high temperature and high pressure condition. (3) Increases in engine vibration and noise due to the addition of water can be reduced by adding a small amount of ignition improver without aggravating engine performance.

高速ディーゼル機関の燃焼と排気に関する研究 : 第1報, 排気NOxの低減

The authors have been conducting studies on the reduction of exhaust emissions using a high speed diesel engine with a bore of 110 mm and a maximum speed of 2 500 rpm. By applying composite countermeasures consisting of five items ; 1) timing retard, 2) optimization of fuel injection system, 3) water-in-oil type emulsified duel, 4) application of ignition improver and 5) an increase in air flow quantity, an exhaust NOx level about a half of the original was attained while retaining the original low levels of fuel consumption, smoke density and engine noise. Especially, in combustion tests on water-in-oil type emulsified fuel, it is clearly demonstrated that not only exhaust NOx but also smoke density are significantly reduced due to an increase in the excess air ratio of the fuel spray.

Compressor Performance Influenced by Distribution of Tip Clearance of Centrifugal Impeller

The tip-clearance effects of centrifugal impellers are usually related to the clearance/bladewidth ratio at the impeller exit, and the relationship has been experimentally examined. In some cases the clearance was changed by the axial movement of the shroud casing relative to the impeller, and as a result the radial clearance in the inducer was hardly changed. If the tip clearance is changed uniformly along the shroud, the effects of tip clearance must be larger than predicted based on those experiments. In the case of a centrifugal compressor with 6 : 1 pressure ratio, the decrement of impeller efficiency due to tip clearance is theoretically examined for five types of clearance-distribution along the shroud, and significant influences of the radial clerance in the inducer are demonstrated.