Schlieren photography

Schlieren picture of upward propagating rich limit propane flame with superimposed direct photography. 

Quenching process of a flat hmit flame, propagating downward from the open end of the tube in mixture with 2.20% CjHg observed by schlieren system with superimposed direct photography. Square tube 125 mm x 125 mm x 500mm. Time interval between frames 0.3 s. 

If the flame.is not sufficiently luminous, "visible photography cannot be used, but the "Schlieren and "Shadow" methods are applied (See Vol 2, pp Cl6 C17)... 

C) M. Kusakahe Y. Mizushima, "Study of Explosion by Schlieren Photography , Ibid,... 

Spark photography with shadowgraph, schlieren and interferometer techniques (such as described in. Vol 2 of Encycl, under CAMERAS) showed that density is uniform in zones I-TP-M and I-TP-R, but not in the zone R-TP-M, which includes the Mach region. The Mach shock M appears to be followed by rarefaction. Above the slipstream there is an angular variation of density so that, if measured at points farther and farther behind R, the density first rises to a maximum and then falls again For more detailed description of Mach waves etc, see Refs 2a, 3, 4, 5, 6, 7 and 8 Refs 1) Anon, "Military Explosives , TM9-1910 (1955), PP 74-5 2) Dunkle s... 

In his supplement to Syllabus, Dunkle remarked (Ref 22, p lid) that schlieren photography of deton waves in 40/60 C2H2/O2 initially at 1/4 atm showed a wavy pattern of criss-crossing dark diffuse lines behind the front. Fay Opel (Ref 17) calculated that if these lines are a weak wake of Mach waves in supersonic flow, the flow of the burnt gases with respect to the front is Mach 1.14 rather than Mach 1.00 as in a C-J process. However, at this pressure the reaction is complete within a fraction of a millimeter behind the front, and the flow could very well accelerate to Mach 1.14 with density decrease below the C-J value. Fay Opel traced the effect to the boundary layer. 

P.W. Holder R. J. North, Schlieren Methods, Natl Physical Laboratory Notes on Appl Science, No 31, HMSO, London, 1963 The bibliography on image dissection in high-speed photography by J,S. Courtney-Pratt... 

Direct Photography. Photography by reflected light to distinguish it from Shadow, Schlieren and other methods which are described in Vol 2, pp C13 to C19 under CAMERAS, HIGHSPEED PHOTOGRAPHIC... 

Thus, the beginning of the luminous zone cannot be correct, because the mixture has undergone great changes before it reaches that point. Schlieren photography yields a flame surface with a temperature close to that of the unburned gas, so it is a desirable method of observation (1, 10, 37, Ifi, 50). 

CC)Spark Cinematography. See Stationary Film with Multiple Spark Camera DD)Spark Photography. When it is required to have a source of light of brief duration (below 1 microsec) an elec spark in air (or in inert gas) is used. Sparks may be used in "Shadow , Schlieren and "Interferometric techniques... 

Schlieren photography gives simply the density gradient (dp/dx) or (— 1 / T ) (dT/dx), which has the greatest value about the inflection point of the temperature curve it also corresponds more closely to the ignition temperature. This surface... 

For analytical convenience the relations developed up to this point have been derived in terms of linear velocities and with respect to the shock front. In practice, it is difficult to measure directly such properties of the shocked gas as v, Pg, and Tg. It is feasible, however, to measure the velocity U of the shock front and when necessary to convert from velocities with respect to the shock front to corresponding velocities in the laboratory-coordinate system. There are a number of satisfactory methods for measuring 17, e.g., schlieren photography and piezoelectric detection. 

Keller, J.O., Saito, K., and Kishunoto, K., An experimental investigation of a pulse combustor— Flow visualization by Schlieren photography. Fall Meeting of the Western States Section of the Combustion Institute, Stanford, CA, 1984, pp. 1-10. 

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