Laser-induced plasma generation and evolution in a transient spray.

Nobuyuki Kawahara,Eiji Tomita,Kazuya Tsuboi

doi:10.1364/oe.22.000a44

Abstract

The behaviors of laser-induced plasma and fuel spray were investigated by visualizing images with an ultra-high-speed camera. Time-series images of laser-induced plasma in a transient spray were visualized using a high-speed color camera. The effects of a shockwave generated from the laser-induced plasma on the evaporated spray behavior were investigated. The interaction between a single droplet and the laser-induced plasma was investigated using a single droplet levitated by an ultrasonic levitator. Two main conclusions were drawn from these experiments: (1) the fuel droplets in the spray were dispersed by the shockwave generated from the laser-induced plasma; and (2) the plasma position may have shifted due to breakdown of the droplet surface and the lens effect of droplets.

Highlights

IntroductionIn order to reduce global CO2 emissions, biomass fuel, such as ethanol, methanol, MTBE (methyl tertiary-butyl ether), ETBE (ethyl tertiary-butyl ether), have been focused as an attractive alternative fuel instead of gasoline in an SI engine [1-3]
In order to reduce global CO2 emissions, biomass fuel, such as ethanol, methanol, MTBE, ETBE, have been focused as an attractive alternative fuel instead of gasoline in an SI engine [1-3]
(3) There is a possibility that the plasma position is moved by the breakdown at the droplet surface and the lens effect of droplets

Summary

Introduction

In order to reduce global CO2 emissions, biomass fuel, such as ethanol, methanol, MTBE (methyl tertiary-butyl ether), ETBE (ethyl tertiary-butyl ether), have been focused as an attractive alternative fuel instead of gasoline in an SI engine [1-3]. High enthalpy of vaporization of ethanol affects the vaporization of ethanol-blended gasoline, and forms thicker liquid film around intake valves, cylinder wall and piston top [4] These liquid films can form leaner mixture inside engine cylinder at the early stage of compression stroke. In this case, spray-guided DISI (Direct Injection Spark Ignition) system is effective in a spark-ignition engine with ethanol or ethanol-blended gasoline. Ignition by a spark-plug traditionally used, is difficult to change its position and interference of the spark-plug to the fuel spray makes the combustion instability To improve such problems, laser-induced plasma ignition attracts attention. The behaviours of laser-induced plasma and fuel spray were investigated by visualizing images with ultra-high-speed cameras. Interaction between a single droplet and laser-induced plasma is investigated using levitated single droplet by the ultrasoniclevitator [9]

Experimental Apparatus

Laser-Induced Breakdown Spectroscopy

Ignitability of laser-ignited ethanol spray flame

Interaction between laser-induced plasma and fuel spray

Conclusions