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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.

This paper has two purposes: the first is to study the air flow behavior in the MPI type engine manifold by means of flow visualization; the second purpose is the verification of the air flow characteristics described in SAE paper No.950066 (1)using the results of that paper. The tuft grid method was adopted for air visualization. The MPI type engine manifold used in this study (common chamber) has dimensions of 332 × 79 × 74mm. The amount of the tuft is 630 points. Two directions(yz and xz planes, respectively) of the tuft were instantaneously photographed at every 20 degrees of crank angle and the composed direction was calculated. The experimental conditions are 1) steady air flow, 2) transient flow, 3) the inlet pipe position and 4) ram pipe locations.

The objective of this experimental study is to clarify the air flow rate characteristics of an MPI gasoline engine intake-manifold at transient conditions. A new high-response air flow meter was investigated and developed for the study which can simultaneously measure the air flow rate of all four cylinders. The influence of transient conditions to air flow rate distribution to each cylinder were researched and verified with regard to the geometry of the ram pipe length and location, and intake air pipe location for the air distributor. The transient conditions were examined by varying the following: initial throttle opening, throttle operating opening, throttle operating period, and engine speed and crank angle at starting to open the throttle valve. A comparison was also made with a “Siamese” type manifold.

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.

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.

The good relationship between the spray condition in the intake manifold and the combustion characteristics is required. Firstly by this report it was tried the visualization and observation of spray of gasoline injection. It was mainly photographed when injection just began and the spray impinged on a intake valve. The photographs of fuel spray were taken by a image converter type high speed camera. The characteristics of the fuel spray injected in early injection period is influenced with fuel pressure and flow rate of fuel. The atomizing phenomenon of tip fuel of spray could be visualized. The atomizing process in early injection period are differ from that in stady-state spray. And the picture of spray at impingement on the intake valve was shown too. The atomizing condition on the valve surface could be observed visually.