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Two ways to attain low emission diesel combustion, which are capable of meeting future regulations, are the so-called two-stage “rich and lean” combustion and ‘lean” diesel combustion. To actually achieve these types of combustion, homogeneous lean air-fuel mixture formation is very important In this study, two methods of producing a desirable air-fuel mixture axe investigated experimentally by observing fuel sprays from several unique injection nozzles in a high-pressure vessel. One was a slit shaped hole nozzle, which might result in increased air entrainment into the spray because of the larger surface area. The other was impinging flow nozzle, which generated a more homogeneous mixture by its high turbulence. It was observed that with the slit shaped hole nozzle, the cross-sectional shape of the spray was unexpectedly circular, which was attributed to a greater dispersion of the spray perpendicular to the lengthwise slit axis.

The effects of a multi-hole nozzle with throttle construction (NTC) on combustion and emissions were investigated at high pressure fuel injection conditions. The throttle area was larger than the total injector hole area, therefore its fuel flow quantity was about the same as the standard nozzle under steady flow conditions. But the initial fuel injection rate was lower under unsteady flow conditions and smoke emissions were improved with the NTC. It is postulated that these effects were due to fuel flow turbulence inside the nozzle during the time of needle valve lift.