A study of the structure of gaseous detonation waves using Rayleigh scattering

An experimental program has been conducted to develop a diagnostic technique for the study of oblique detonation waves in combustible gas mixtures. The need for multi-point, non-intrusive measurements led to the use of laser-based Rayleigh scattering to determine density. In the development of the technique, it was used to study normal detonation waves and to obtain two-dimensional density images surrounding the wave front. The detonations were generated in mixtures of H$\sb2$, O$\sb2$ and Ar with (O$\sb2$) / (Ar) held at 0.21/0.79, equivalence ratios varying between 0.6 and 1.4 and initial pressures set between.272 and.578 atm. The fourth harmonic of a Nd:YAG laser provided a pulsed sheet of UV laser light which cut through the detonation wave front as it traversed the test section to generate the Rayleigh scattering. An intensified CID camera was used to acquire and image the resulting signals. Schlieren images were acquired simultaneously for comparison. Cellular structure was clearly visible in the images and cell sizes have been correlated with detonation parameters for comparison with measurements and analyses by earlier investigators. The progression of wave front structure could be understood by observing images which were each acquired from different runs and at random times in the wave front development. Rayleigh signal ratios comparing reactant and product densities were quantified at various locations within the wave front. They were compared with calculated values based on shock theory and equilibrium analysis and were found to be in good agreement.