Coherent Anti-Stokes Raman (CARS) temperature measurements in a propellant flame

Abstract

This paper presents the results of an experimental investigation of the flame structure of hydrazinium nitroformate (HNF) at pressures of 0.06 and 0.13 MPa. Laser diagnostics, including laser Doppler anemometry (LDA) and coherent anti-Stokes Raman spectroscopy (CARS), has been used to obtain the velocity and temperature profiles above the burning surface of an HNF pellet. Great effort has been made to measure velocity and temperature in the flame regions close to the burning surface (primary reaction zone and nonluminous zone). As a by-product of the LDA and CARS measurements, we found that these regions contain a dispersed phase with aerosols and gaseous reactants being irregularly released from bubbles formed at the foam layer. Aerosols with size larger than approximately 0.1–0.2 μm have been found in the region between the foam layer and the primary reaction zone. At larger distances from the surface, the aerosols shrink to a size below 0.1 μm until they are fully consumed in the beginning of the brightly luminous flame. It appears that at a fixed location above the surface one intermittently finds final products or gaseous reactants with the balance between the two shifting toward the hot products with increasing distance from the surface.