A Joint Experimental and Large Eddy Simulation Characterization of the Liquid Fuel Spray in a Swirl Injector

Abstract

The quality of liquid fuel spray injection determines to a large extent the performance of aeroengine combustors. The present investigation focuses on the detailed characterization of the liquid fuel spray in a test rig targeted at aeroengine applications. The liquid fuel is injected as a hollow cone by a simplex atomizer and the injector comprises a radial swirler. Two features of the droplet distribution are less commonly found. First, the distributions of droplet diameters exhibit nonaxisymmetric patterns, which are investigated for three types of swirlers. Second, it is found that the size-conditioned velocity distributions feature a single wide peak for small droplets and become bimodal for the largest droplets, with a first peak at low velocities, and a second one at higher velocities. The analysis is complemented with Large Eddy Simulations and Lagrangian Particle Tracking. The spray interacts with the lateral injector surface and requires a droplet-wall interaction model for the liquid film. Simulations do not retrieve the lack of rotational symmetry that is found experimentally indicating that this is not linked to the nature of the swirling flow. This is also consistent with further experiments with a different atomizer confirming that this is due to imperfections in the atomizer geometry. Another result is that certain swirler designs are more robust to atomizer imperfections. Simulations accounting for the liquid film yield a bimodal distribution for the droplets' axial velocity distribution which is not obtained without this model indicating that it is important to represent the droplet-wall interaction.

Experiments on symmetry breaking of azimuthal combustion instabilities and their analysis combining acoustic energy balance and flame describing functions

“…The backplane comprises 16 regularly spaced injection units, which deliver liquid fuel, heptane in the present experiments, as a hollow cone spray of droplets mixed with air (Vignat et al. 2021). The air mass flow rate is controlled through two Bronkhorst EL-FLOW mass flow meters and the fuel mass flow rate through a Bronkhorst CORI-FLOW mass flow rate controller.…”

“…The MICCA-spray annular combustion chamber, shown in figure 1, is formed by two quartz walls of the same length, l = 400 mm, of outer diameter 300 mm for the inner cylinder and inner diameter 400 mm for the outer quartz cylinder. The backplane comprises 16 regularly spaced injection units, which deliver liquid fuel, heptane in the present experiments, as a hollow cone spray of droplets mixed with air (Vignat et al 2021). The air mass flow rate is controlled through two Bronkhorst EL-FLOW mass flow meters and the fuel mass flow rate through a Bronkhorst CORI-FLOW mass flow rate controller.…”

“…Injectors' characteristics: swirl number (S N ), pressure drop ( p) and pressure drop coefficient (σ ), obtained from measurements under cold conditions for an air mass flow rate of 2.3 g s −1(Vignat et al 2021).…”