http://deepblue.lib.umich.edu/bitstream/handle/2027.42/28407/0000182.pdf?sequence=1

Asymptotic Analysis of the Shock Wave Ignition of Dust Particles

A shock-tube ignition study of a Utah coal

This paper presents the description of a pneumatically‐operated particle ejector and its performance under atmospheric ambient conditions. The ejected 100‐μ particles are observed to remain an aggregate for approximately 10 ms prior to dispersion. The particles move at the initial velocity for a short initial period. This observation can be verified by a mathematical analysis. The instant of time at which the particles leave the ejector can be determined within approximately 1 ms.

Small solid‐particle ejector

To investigate the ignition delay of dust particles in hot stagnant oxygen gas. reflected shock waves have been created in a horizontal shock tube. By using a newly designed air injector, very well-distributed cloud formation of various dusts could be obtained. The proper hot stagnant gas conditions were generated by placing a reflector 1.5 cm behind the air injector. The post-reflected shock gas temperature of 1200-1600 K could be obtained by reflecting the incident shock waves in the range of Mach number 2.8-3.3. Experimentally the ignition delay was defined as the time interval between the arrival of a reflected shock wave at dusts and the detection of visible light. Measured ignition delays of various dusts investigated were located lower than 1 msec under the given conditions. These values are one order higher than those measured in the incident shock wave conditions where a strong gas flow around particles enchances the ignition of particles.

On Ignition of Dust Particles in Hot Stagnant Oxygen Gas

Temperature histories of coal particles in shock-heated air up to 2200 K are measured using the two-wavelength pyrometry. A very small amount (less than 10) of coal particles of various sizes (40,100, and 200 μm) is subjected to simultaneous heating, so that the resulting temperature history may represent that of a single particle. The results show that the initial particle temperature rise is extremely high and that the particle temperature is in general higher than the surrounding gas temperature.

Temperature measurement of coal particles in shock-heated air

The objective of this study is to obtain the ignition delay for Pittsburgh seam coal particles shock heated in air to various temperatures and I atmosphere pressure. The ignition delay for coal particles of 19 μ and 41 μ was determined in a 7.62 cm shock tube. The gas temperature behind the reflected shock wave, T 5, was calculated from the measured incident shock-wave speed. Plots or the ignition dealy vs. T 5indicate the existence of a minimum gas temperature for ignition. The effect of particle size on the ignition delay is small for the particle size range used.

Suresh Pillay

Papers

Ignition Delay of Coal Particles in Shock-Heated Air