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The purpose of this study was to find factors to improve the performance of louvered fins through visualization of air flow in the louvered portion of the fins. As part of this study, three dimensional enlarged models were used to visualize and examine the basic flow in the fins. Also, more complicated flows induced by bend configuration (or inclination of fins), which are caused by large fin pitch, have been visualized and examined. The latter flow pattern could not be observed in two dimensional models.

The hunting phenomenon which occurs at the lean air-fuel ratio and under light load conditions was studied in the previous paper and it was disclosed that this was not “mechanical hunting” and the fuel flow delay into the cylinder had a dominant effect on this “lean hunting”. This paper describes first, the experiments which demonstrate that such a fuel flow delay can occur by changing the throttle position sinusoidally in various periods, and that Pmax (the maximum pressure in the cylinder) responds quite differently according to the magnitude of the air-fuel ratio; secondly, the effects of ignition energy and ignition timing on the lean hunting were also studied.

A quite interesting self-excited oscillation phenomenon in engine speed, which may not be explained with the classical theory of mechanical hunting, is studied experimentally. The effects of the various engine operating variables on the phenomenon are examined using a four cycle single cylinder gasoline engine with an inertia governor. It was found that the phenomenon occurs when engines are operated at a lean air fuel ratio under light load conditions, and that the hunting phenomenon is ascrlbable to the temporary shift in air fuel ratio from the steady state value. This shift in air fuel ratio occurs due to the fuel flow delay into the cylinder caused by the fact that the fuel flow into the cylinder cannot follow the movement of the throttle valve.