Synchronised
droplet size measurements for coal-water slurry sprays
generated
from a high-pressure diesel injection system
K. D. KIHM, D P TERRACINA, S E PAYNE and J A CATON
An
experimental study has investigated intermittent sprays
of coal-water slurry (CWS) fuel injected from an electronically
controlled accumulator injector system. A laser diffraction
particle-analysing (LDPA) technique was used to measure
the Sauter mean diameter (SMD) near the spray-tip region.
To ensure accurate synchronisation of the measurement
with the intermittent sprays, a synchronisation technique
was developed that uses the light extinction signal
as a trigger for initiating the data-taking. This technique
allowed measurement of SMDs near the spray tip, where
the light-extinction level was low and the data were
free from the multi-scattering bias. Coal-water slurry
fuel with 50% coal loading in mass containing 5 gm mass
median diameter coal particulate was considered. The
studies involved injection pressures ranging from 28
to 110 MPa, nozzle orifice diameters of 0.2 and 0.4
mm, and four axial measurement locations from 60 to
120 mm from the nozzle orifice. Measurements were made
for pressurised (2.0 MPa g) and for atmospheric chamber
conditions. The spray SMD showed a rise with the distance
of the axial measurement location and with the ambient
gas density, and a fall with rising injection pressure.
An experimental correlation of the Sauter mean diameter
with the injection conditions was determined as SMD
= 0.279  P-0.702 a0.285 x1.521, showing satisfactory agreement with the
measured SMD data. The results were also compared with
previous SMD correlations that were available only for
diesel-fuel sprays.
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Spray-tip droplet
SMDs of intermittent high-pressure spays of diesel fuel
compared with coal-water slurry sprays
K.
D. Kihm, D P
Terracina and J. A, Caton
An
experimental study investigated droplet-size characteristics
near the spray tip of intermittent sprays of diesel
fuel from an electronically controlled accumulator injection
system. A modified laser-diffraction particle-analysing
technique (Malvern 2600C system) optically synchronized
the data taken with the spray penetration. so that the
Sauter Mean Diameter (SMD) could be measured at low
obscurations without multi-scattering bias. Measurements
were made at axial locations 60, 80, 100 and 120 mm
downstream of the injector orifices with 0.2 and 0.4
mm diameter orifices. Injection pressures studied were
28, 56 and 83 MPa g, and measurements took place in
both pressurised (2.07MPa g) and unpressurised
chamber conditions. The spray-tip SMD increased with
ambient gas density and axial measurement location,
and fell inversely with injection pressure. Dependence
of SMD on nozzle orifice diameter was negligible for
fully developed sprays. A regression equation for the
SMD(?) was found as SMD=1.402 P -0.461 a0.1588x0.8977 where  P is MPa gauge,  a is
the ambient gas density in kg m-3
, and x is the axial measurement location in mm. These
results show characteristics consistent with previous
studies where coal-water slurry was the atomised liquid.
Quantitatively, under identical injection conditions
the droplet SMDs of diesel sprays were always smaller
than those of coal-water slurry. Parametric comparisons
for the two types of injected fuels are presented.
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Effect of Coal
Particle Size on Coal-Water Slurry (CWS) Atomization
S.
Y. Son and K.
D. Kihm
To
determine the effect of coal particle size on coal-water
slurry (CWS) atomization, Sauter mean diameters (SMD)
of spray droplets have been measured for various slurries
containing three different coal particle sizes (32-45
µm, 45-63 µm, and 63-90 µm). The test
sprays are generated by a sonic air jet blasting onto
the cross-injecting CWS mixture. The diffraction particle
analyzing technique (the Malvern 2600D system) measures
spray SMDs nonintrusively. The results show persistently
that the spray droplet SMDs of the CWS containing smaller
coal particles are larger than the SMDs of the CWS containing
larger coal particles. This finding is consistent with
the fact that the former exhibits larger viscosity than
the latter. In addition, the internal capillary holding
force between the particles and water increases with
decreasing particle sues because of their smaller radii
of curvature and larger total surface area. The increased
holding forces of smaller coal particles enhance their
resistance against the external airbfast and make the
atomization difficult. However, smaller spray SMDs of
the CWS containing larger coal particles are attributed
to both their lower viscosity and their lower capillary
holding forces, and thereby weaker resistance against
the external airblast.
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