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In this paper, visualization by means of the Schlieren method was accomplished in a two dimensional flow channel model of a CNG engine mixer. From the visualization results:(1)Mixing in the region of the venturi tube and throttle valve was influenced by the throttle opening and by the distance of the nozzle and valve, and in addition in this region natural gas behavior shows many different flow patterns.(2)The mixing (diffusion) characteristics clarified the relationship between the throttle opening and two natural gas flows; high velocity flow near the channel wall and swirl flow under the throttle valve.(3)The concept of gas and air mixing being affected by the dimensions of the main elements (main nozzle, venturi tube, throttle valve, their relative relationships and auxiliary air) of the CNG mixer were clearly shown. Premixing of natural gas and air in a CNG engine vehicle is said to be inadequate because it adversely influences the engine combustion and emission characteristics.

Methanol is considered to be an alternative fuel which saves crude oil. However, methanol-fueled engines have the technical problem of poor cold startability. An ultrasonic atomizer facilitates the atomization of methanol fuel under low-temperature conditions. This paper studies the effect of the methanol-gasoline blend ratio and flash boiling on spray evaporation characteristics when the ultrasonic atomizer is used. Spray plumes were observed with an image-converter-type high-speed camera at 10,000 frames per second. Fuel was sprayed under low atmospheric pressure at the boiling point of methanol. The experimental results of the spray observation show that the methanol-gasoline blend ratio affects the spray shape,especially the cone angle, because of the change of fuel evaporation characteristics. The methanol spray characteristics when an ultrasonic atomizer is used as shown in this paper are useful data for low temperature conditions also.

In order to study air flow distribution to individual cylinders of an SI engine at transient conditions, a new small-sized high-response air flow meter was investigated and developed to measure instantaneous air flow rates. The experiments were performed with changes in initial throttle opening, throttle movement angle and period, and crank-angle at the opening of the throttle valve and related engine speeds. Air flow rates for individual cylinders of a four cylinder engine were measured during acceleration. The relative rising rate was used for estimation of air distribution values, namely, the ratio of the initial amount of increased air flow rate of to the air flow rate for each cylinder. Air flow begins to increase from the second induction stroke from throttle opening. The variations of crank-angle at throttle opening influences the rate of increase. The effect of transient conditions on air flow rate distribution was researched.