Published 12 issues per year
ISSN Print: 1044-5110
ISSN Online: 1936-2684
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SPARK-IGNITED SPHERICAL FLAMES PROPAGATING IN A SUSPENDED DROPLET CLOUD
ABSTRACT
A droplet suspension of liquid fuel produced by an ultrasonic atomizer was ignited using an electric spark. The Sauter mean diameter (SMD) of the droplet suspension was 57μm to 66 μm for fuel injection rates of 2.13 cm3/min to 4.44 cm3/min, respectively. The droplet distribution for any fuel injection rate included a negligible amount of droplets smaller than 20 μm or larger than 100 μm in diameter. The flame ball propagating outward was monitored by observing light emission from OH- and C2-radical bands using photomultipliers, a highly sensitive CCD camera, and a high-speed camera. Thereby, the mechanism of flame propagation and the complicated structure of spray flames were observed. It was found that a nonluminous flame was propagating continuously through a gas-phase mixture, followed by luminous flamelets, such that a number of small-scale droplet clusters with luminous emissions appeared randomly and discontinuously behind the flame front propagating in a premixed combustion mode. This result shows that the group structure of spray flames is not simple.
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