Schlieren photographs

PLATE 6 The turbulent environment in whieh eombustion, a chemical process, takes place is dramatized by this Schlieren photograph of a propane diffusion flame. Courtesy, Norman A. Chigier, Carnegie Mellon University... 

Figure 3.2.1 shows flame kernels of the schlieren photograph taken by a high-speed camera. These photographs can be compared with the calculated temperature distribution in Figure 3.2.4. As can be seen, both of them bear a close resemblance. From this result, the authors firmly believe that the numerical simulation is a significant tool for grasping the mechanism of spark ignition. Of course, the experimental work should also be of importance to verify the results obtained by numerical simulations. In this work, the authors mainly introduce the results of numerical simulations that have been obtained xmtil then in their laboratory.

Schlieren photograph of flame kernels by a high-speed camera. Time is given from the onset of spark discharge in microseconds. Spark electrode diameter 0.2 mm spark gap width 1mm. 

Instantaneous schlieren photographs of turbulent Bunsen burner flames at P = 0.1 MPa (left) and P = l.OMPa (right). The flow at U = 2.0m/s is made turbulent, thanks to a perforated plate with hole diameter d = 2.0mm. The burner exit diameter is 20mm. (Reprinted from Frank, J.H., Kalt, P.A., and Bilger, R.W., Combust. Flame, 116, 220, 1999. With permission. Figure 9, p. 238, copyright Elsevier editions.)... 

Figure 8.4.9 shows the time sequence of schlieren photographs of DDT in very rough channel. If is clearly seen... 

Time sequences of schlieren photographs showing DDT in very rough tube stoichiometric H2/O2 mixture at 100 torr 2 ps between frames. 

Figure 8.4.10 shows two time sequences of schlieren photographs of quasi-detonation. In Figure 8.4.10a, detonation reinitiation occurs at the Mach stem on the bottom wall. However, prior to complete reinitiation of the decoupled wave by the upward-growing detonation, reflection and, subsequently, diffraction of the detonation occur again by encountering another obstacle. In the sixth frame of Figure 8.4.10a, the curved, diffracted, and reflected shock with a reaction zone close behind is clearly evident. However, as this cylindrical... 

Schmidt, E., Steinicke, H., and Neubert, U., Flame and schlieren photographs of the combustion of gas-air mixtures in tubes. TDI-Forschungsheft, 431, Ausgabe B., Band 17, Deutscher Ingenieur-Yerlag, Dusseldorf, 1951. 

Far from being difficult to explain, the appearance of a shock is hard to prevent in view of the chemically reactive nature of the medium in which the wave is advancing. Heat released in the combustion makes the gaseous products expand,and they push against the unburned mixture ahead of the wave front. Thus they set up a pressure wave of velocity (pr), called a precompression or "precursor wave, which has been observed in schlieren photographs and streak camera records. The flame now advances into a mixture, still unburnt but "processed by precompression and heating which increases the reactivity, in a third region between the other two ... 

Figure 3.6. Schlieren photographs showing the changes in thickness of the diffusion boundary layer and the behavior of buoyancy-driven convection shown in relation to bulk supersaturation [1], [2]. The figure shows the (111) faceofaBa(N03)2 crystal from an aqueous solution. In region I, only the thickness of the diffusion boundary layer increases in region II, we see unstable lateral convection (HA) and intermittently rising plumes (IIB) and in region III we see steady buoyancy-driven convection.

The multi-spark schlieren photographs obtd by Collins (Ref) have proved most valuable for their qualitative insight into the general behavior of the cylindrical blast wave. The results of this investigation show that cylindrical expins can be satisfactorily generated and adapted to laboratory observation study... 

Fia. 133. Series of schlieren photographs of blood serum (Tiselius)... 

FIGURE 42 Short durations in Schlieren photographs of open turbulent flames [after Fox and Weinberg, Proc. Roy. Soc., London, A 268,222 (1962)]. 

Figure 1. Ultracentrifuge Schlieren photographs of sedimentation behavior of highly purified rat skin collagen and its mildly gelatinized product at corresponding times...

Figure 3. Schlieren photographs of silica sol S4 taken during ultracentrifugation at 1100 rpm after (a) 3.5 min, (b) 5.5 min, and (c) 7.5 min. The vertical lines toward the left side of the photographs indicate the air-solution meniscus sedimentation is from left to right.

A determination of the critical exponent 8 has been made for the liquid-liquid system, n-decane-fifi dichloroethyl ether (chlorex). Utilizing schlieren photographs of the system in an ultracentrifuge at a temperature slightly below the critical solution point, the density gradient was obtained as a function of radius. These gradients, used in conjunction with sedimentation theory, provided a means for calculating values for the exponent 8. The values thus obtained are consistent with accepted values for the exponents / and y in two-fluid systems. They are, however, smaller than those found for pure fluids. 

Figure 1. Actual Schlieren photograph of interace for n-decane-chlorex (/3,f3 dichloroethyl ether). Liquid-liquid interface is double line to left of center. The other two vertical lines are the pure decane reference and mixture vapor-liquid...

When a dependence of the local burning velocity on the turbulence field is induced in the computations, a much more rapid burning will occur in the shear layers. The computer generated movie shown in Figure 7 corresponds very closely to the actual high speed schlieren photographs of flame acceleration through a baffle obstacle (25). 

Figure 2. Time-resolved Schlieren photographs of a constant volume combustion chamber at k atm. pressure. The vertical dimension of each frame is 0.3 cm.

Schlieren photographs of the spark kernel and the developing flame were obtained using a conventional arrangement. A flash-lamp-pumped dye laser was used to furnish a 1 ys light pulse (X 600 nm) to illuminate the interior of the combustion bomb. 

Figure 2. Schlieren photographs of a stoichiometric flame passing the sampling cone.

Our spark is undoubtedly rapid enough (2 ys duration) to produce this same effect because we can observe a shock wave due to the spark in our schlieren photographs. In addition, the cone can cause a boundary layer to be formed which adds to the amount of unburned mixture which can flow into the electrode region. Experiments involving electrodeless ignition, such as by a laser spark, would be useful in verifying whether this phenomenon occurs. 

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