Concentration Of Heat Release Research Articles

The Structure of the Auto-Ignition Region of Turbulent Dilute Methanol Sprays Issuing in a Vitiated Co-flow

This paper presents planar imaging of laser induced fluorescence (LIF) from key reactive species in the auto-ignition region of dilute turbulent spray flames of methanol. High-speed (5 kHz) LIF-OH imaging as well as low speed (10 Hz) imaging of joint LIF-OH-CH2O is performed. The product of the OH and CH2O signals is used as a qualitative indicator of local heat release. The burner is kept intentionally simple to facilitate computations and the spray is formed upstream of the jet exit plane and carried with air or nitrogen into a hot co-flowing stream of vitiated combustion products. The studied flames are all lifted but differ in the shape of their leading edge and heat release zones. Similarities with auto-ignition of gaseous fuels, as well as differences, are noted here. Formaldehyde is detected earlier than OH implying that the former is a key precursor in the initiation of auto-ignition. Growing kernels of OH that are advected from upstream, close in on the jet centreline and ignite the main flame. The existence of double reaction zones in some flames may be due to ignitable mixtures formed subsequent to local evaporation of droplets and subsequent mixing. When air is used as spray carrier, reaction zones broaden with distance, possibly due to increased partial premixing and regions of intense heat release occur near the flame centreline further downstream. With nitrogen as carrier, the flame maintains a nominal diffusion-like structure with reaction zones of uniform width and substantially less concentration of heat release on the flame centreline.

Flow features of shock-induced combustion around projectile traveling at hypervelocities

The shock-induced combustion with periodic unsteadiness around a projectile fired into hypersonic flows is numerically studied. The mechanism of periodic unsteadiness is clarified using an x-t diagram of the flow variable on the stagnation streamline. The frequencies of the periodic unsteadiness obtained quantitatively agree with the experimental observations. The key parameters which are responsible in triggering the instability and in determining the frequency of the periodic unsteadiness are discussed by using the time integration of the species equations. The result indicates that the key parameters are induction time, heat release, and concentration of the heat release. The induction time is a key parameter for the frequency of the unsteadiness. The concentration of heat release is important for the unsteadiness itself. Total energy creating the compression waves depends on the amount of heat release itself. All of these features are recognized in a simple zero-dimensional analysis.