Forced Low-Frequency Spray Characteristics of a Generic Airblast Swirl Diffusion Burner

Abstract

The low-frequency response of the spray from a generic airblast diffusion burner with a design typical of an engine system has been investigated as part of an experimental study to describe the combustion oscillations of aeroengine combustors called rumble. The atomization process was separated from the complex instability mechanism of rumble by using sinusoidal forcing of the air mass flow rate without combustion. Pressure drop across the burner and the velocity on the burner exit were found to follow the steady Bernoulli equation. Phase-locked particle image velocimetry measurements of the forced velocity field of the burner show quasisteady behavior of the air flow field. The phase-locked spray characteristics were measured for different fuel flow rates. Here again quasi-steady behavior of the atomization process was observed. With combustion, the phase-locked Mie-scattering intensity of the spray cone was found to follow the spray behavior measured in the noncombusting tests. These findings lead to the conclusion that the unsteady droplet Sauter mean diameter mean and amplitude of the airblast atomizer can be calculated using the steady-state atomization correlations with the unsteady burner air velocity.

Model for Acoustic Induced Aluminum Combustion Fluctuations in Solid Rocket Motors

“…To better understand aluminum droplet-driven combustion instabilities, it is interesting to make a parallel with liquid-fueled systems, for which dynamic stability can also be altered by the droplet vaporization process [2,29]. In hydrocarbon fuel spray systems, acoustic oscillations may 1) modify the droplet size distribution at the injector inlet [30,31], 2) segregate large from small droplets during their transport in the pulsed flow [32], and 3) reduce the droplet evaporation time due to the additional drag on the droplets from the pulsed flow [19,27,33]. Each of these mechanisms alters the flame dynamics.…”

Spray Characteristics of Alternative Aviation Fuel Blends

“…The performance of a combustor depends on the droplet size produced by the nozzle atomizer and the way in which the air mixes with the droplets [8][9][10][11][12]. Spray formation at a nozzle is dominated by different mechanisms, depending on the relative velocity and the properties of the liquid and the ambient gas [13,14].…”

Flame Spectra of a Turbulent Liquid-Fueled Swirl-Stabilized Lean-Direct Injection Combustor

“…There are fewer opportunities for the KelvinHelmholtz shear-layer mode to continuously grow and for the wakelike absolutely unstable mode to form. Several researchers have observed almost no variations in the flame structure in swirling combustion during both self-excited combustion instability and forced flame responses with air modulations [23,24]. Even for sharpedged nonswirling combustors, large vortex shedding does not occur unless air forcing is applied around the preferential frequencies of the shear-layer dynamics and the forcing amplitude exceeds certain thresholds [25].…”