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This paper presents the fuel atomization effect of a fuel supply system on the lean burn characteristics of a spark-ignition engine and its mechanism. The fuel supply system can realize extremely different two state of atomization, i.e., wall-film of fuel flow and ultra-fine spray (less than 7 um S.M.D. by Malvern measurement). For the first step of the study, the atomization effect is examined under steady operation; several operating parameters including cyclic variability are expressed against the A/F over the wide range of operating condition. Within the operation limits, the fuel atomization does not affect any parameters, while it gives pretty much influence on the lean operation limit. Furthermore, this influencing behavior strongly depends on the throttle valve position and its opening.

By using an inside visible carburettor, effects of high voltage application to the injected fuel on its behaviour and engine performances are investigated. At first five electrode arrangements around the venturi are examined to clearify the charging mechanism on the injected fuel and its effect on the fuel atomization. The experimental results show that when induced charging, corona charging and electrostatic force are effectively applied to the injected fuel, its atomization is remarkably improved. The diameter of fuel droplets monotonously decreases with increase of applied voltage and the effect is more distinct when the induced air velocity is low. Firing engine test is also carried out and it is revealed that when the throttle valve opening is large, the application of voltage considerably spreads the combustible range toward leaner side. Cyclic variation is reduced and startability is improved by the charge under the severe operating condition.