The Effect of Fuel Density on Mixing Profiles in a DACRS Type Premixer: Experiments and Simulation

Abstract

A combined experimental and computational study was conducted to investigate the effect of fuel density variations on mixing from a double annular counter-rotating swirl (DACRS) nozzle operated at atmospheric pressure under non-reacting conditions using either helium (He) or a mixture of He and CO2 as fuel simulants. A small probe traversed through the flow collecting gas samples that were sent to gas analyzers measuring the concentration profiles. The resulting measurements are then used to validate the computational fluid dynamics (CFD) model. A commercial CFD code (CFX 10) with a Reynolds averaged Navier-Stokes (RANS) formulation was used to simulate the experiment. Multiple turbulence closures, such as standard and realizable k-ε and SSG Reynolds stress model were evaluated. Additionally, several geometrical considerations, such as modeling a 72° sector versus a full 360°, were tested. While at high fuel-to-air momentum flux ratios (J) the fuel simulant concentration profiles were outward-peaked, and at low J the profiles were center-peaked. An analysis of the experimental results clearly indicate the momentum flux ratio is the most influential parameter controlling mixing in a DACRS nozzle. The simulations produced quantitative agreement with the experimental measurements using the realizable k-ε turbulence closure and only modeling a 72° sector of the nozzle. The complexity of the studied problem required a considerable refinement of the grid to produce an accurate and grid independent solution. The validated model may now be used to explore the design space for optimization of a nozzle for utilization in a syngas application.

Structure and Lean Extinction of Premixed Flames Stabilized on Conductive Perforated Plates

“…Both central and pilot jets are further surrounded by a large-diameter coflow of H 2 –air combustion products to prevent the quenching and dilution effects of ambient-air entrainment from affecting the central combustion process. Such configuration of a LPM central jet piloted by a stoichiometric annular flame mimics LPM gas-turbine combustors utilizing dual annular counter-rotating swirlers (DACRS) premixers, − but without the complications of swirl and flow recirculation. Two-dimensional Rayleigh–PLIF (OH) and LDV measurements were conducted to demonstrate that the PPJB design provides efficient stabilization for flames with intense shearing and significant finite-rate chemistry, such as the conditions encountered in highly turbulent LPM combustion systems.…”

Fuel Flexibility in LM2500 and LM6000 Dry Low Emission Engines

“…Fuel composition influences autoignition, flashback, and flameholding by changing chemical kinetic time scales, the speciation of intermediate reactants and radicals, and the relative rates of mass and thermal diffusion [5]. In addition, changes in fuel jet momentum ratio relative to the surrounding air stream modify jet penetration and fuel-air mixing [6]. Flashback is thought to occur most frequently in boundary layers where flow velocities are lowest; however, vortex breakdown in highly swirling flow fields can also result in flame propagation into the mixing duct if axial velocities drop below the turbulent flame speed.…”