Environmental Engineering Reference
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very low speed. Subsequently, compression waves are generated in front of the
combustion array due to the expansion of combustion products, affording a two
wave, three-zone structure composed of precursor compression wave front and
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flame and precursor compression
wave both transmit outward spherically. When they
flame array front. Since this is a spark ignition,
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finally reach the wall, the
motion of precursor compression wave is blocked, thus the turbulence intensity of
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field near the wall will increase suddenly to generate a recirculation zone,
which can dramatically deform the
ow
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flame surface. In the form of re
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ection wave, the
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flame surface can quickly pass through the unburned area below the ignition head,
and then
flow toward the three-phase suspension clouds of nitromethane/aluminum/
air as planar wave.
It was found that an attenuated transmission wave can be formed when the
combustion compression plane wave generated by propylene oxide precursor enters
the area of three-phase suspension mixture of nitromethane/aluminum/air. After the
departure of transmission wave, the droplets and nitromethane aluminum
fl
ake
particles are effectively compressed, which would further atomize nitromethane
droplets until evaporation. At this stage, aluminum
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flakes will undergo melting and
vaporization on the surface, resulting in the combustion of mixture in the form of
gas phase reaction. Subsequently, combustion products can either expand or
compress surrounding media to produce compression waves, which can be
strengthened via integrating with chemical reactions.
Therefore,
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the pressure in the area distant
from the ignition end 2.45
-
6.65 m should increase due to the formation of compression wave; however, it should
do so slowly. At 6.65 m, the pressure is only 0.85 Mpa; when the compression wave
approaches 8.05 m, the pressure jumps to 1.32 MPa, at which the compressive wave
has been adequately enhanced. When the wave reaches 9.45 m area, the pressure is
1.65 Mpa with a speed of 1.35 km/s. At this moment, the reaction compression
process is complete and the transition process starts. Afterward, the combustion
process gradually moves from the slow reaction compression stage into the transition
process, and the combustion speed is suddenly increased from 1.35 to 2.13 km/s. The
rapid expansion of combustion products results in the reduction of reaction zone
pressure from 1.65 to 1.12 MPa, marking the end of transition process. Subsequently,
the combustion process enters the rapid reaction shock stage. Due to enhanced
integration between chemical reactions and shock waves, the reaction has been
substantially accelerated, while the pressure in the combustion tube will be gradually
increased. At the measuring point of 21.35 m, the peak overpressure reaches its
maximum of 3.85MPa, and the detonation wave velocity is 1.94 km/s, suggesting the
occurrence of detonation overvoltage status. Subsequently, the detonation wave
velocity seems to be gradually stabilized, so that
flame front can catch up on the
detonation wave front, affording a stable detonation process.
As shown in Table 7.10 , the peak explosion overpressure reaches its maximum
of 3.85 MPa at 21.35 m (aspect ratio L/D = 107), exhibiting typical detonation
characteristics. Meanwhile, under the same experimental conditions, the blasting
experiments of the three-phase mixtures of isopropyl nitrate/aluminum/air and
ether/aluminum/air were carried out with equivalent ratio. The results obtained
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