A universal non-dimensional formula that describes the blow-out stability limit of gaseous jet diffusion flames in still air has been found experimentally. Its validity has been established over a wide range of parameters that affect the blow-out limit. Its extrapolation to cases where the burner exit flow is choked suggests that for a given gas there is a critical burner diameter above which a stable flame can exist at any flow rate.

Blow-Out Stability of Gaseous Jet Diffusion Flames. Part I: In Still Air

Ignition and combustion performance of a scramjet combustor with a fuel injection strut was experimentally investigated with Mach 2.5 vitiated air. Five strut models with different leading-edge geometry were tested without fuel injection to select the less flow-disturbing configuration. The nonreacting flowfields were also investigated by computation with a two-dimensional Navier—Stokes code. Using the selected strut, combustion and ignition tests were conducted. A pitot pressure and gas composition survey was carried out to deduce mixing and combustion efficiencies. It was found that mixing and combustion with a less flow-disturbing strut was considerably worse than those with a more flow-disturbing strut. Autoignition and forced ignition with plasma torches were tested for hydrogen. Ignition characteristics of parallel and perpendicular injection were quite different. The plasma igniters could successfully ignite both parallel and perpendicular fuel jets without a noticeable time delay between both sides of the strut.

Ignition and Combustion Performance of Scramjet Combustors with Fuel Injection Struts

1.

The standoff distance of the stabilization ring of the base of a lifted flame increases along the surface of maximum velocity fluctuations, causing it to stand off from the surface of stoichiometric composition in the direction of lean fuel mixtures and finally resulting in extinction.




2.

There is a limiting value of the injection nozzle diameter (determined by the fuel composition, ambient pressure, fuel temperature, and ambient temperature), above which absolute stability of the lifted flame is ensured for any velocities.




3.

A stability model has been proposed, along with analytical relations, making it possible to determine the domain of flame instability for subsonic and supersonic fuel streams discharging into a stationary surrounding air space.

Stability of submerged diffusion flames in subsonic and underexpanded supersonic gas-fuel streams

The combustors using supersonic combustion are characterized by two fundamental problems: 


the stabilization of the flame in a supersonic air flow,


the maximum combustion efficiency.

Flame Stabilization in a Supersonic Combustor

The effect of swirl on the performance of a flare stack was experimentally investigated as a passive control technique for combustion in a cross-flow. The burner comprised a circular fuel nozzle with a co-annular airflow, swirled by a concentric vane swirler, with a crosswind of air at the flare tip. It was found that the flames issuing from swirl-vane flare tip were shorter and had wider flame stability limits than the flames issuing from a circular flare tip. Recirculation zones in the wake region of the flare stack were found to persist at relatively higher momentum ratios between the fuel jet and the crosswind. This enhancement was accompanied by an increase in the mixing/combustion efficiency.

V. A. Yasakov

Papers

Stability of a diffusion flame in single and mixed jets