Spray combustors

Stephens, J.R., S. Acharya, and E. J. Gutmark. 1997. Controlled swirl-stabilized spray combustor. AlAA Paper No. 97-0464. 

Measurements from synthetic fuel spray flames and laboratory droplet reactors indicated the extent to which fuel properties and combustion conditions influenced particulate yields. A series of seven fuels were tested in a 21 kW spray combustor for total particulate by gravimetric sampling and soot by Bacharach smoke number. Variations in total particulate were dominated by the tendency of the fuel to form ceno-spheres while smoke number correlated with the C H ratio of the fuel. The laboratory droplet studies were performed in a gas flame supported reaction environment. These results confirmed the correlation between soot yield and C H ratio. In addition, two distinct forms of disruptive droplet combustion were observed. 

The quantitative results contained in Figure 3 are quite instructive. For example, if a cloud containing only 10 particles were to bum in a QS-individual flame mode, it would have to have a mean interparticle separation of about 7000 Rp. By comparison, droplets in a spray combustor typically have interparticle separations of (10-100 )Rp, implying that QS clouds with particle spacings of practical interest would never bum in the individual flame mode. This results from the remarkable eflBciency of such cloud particles in preventing oxidizer penetration by diffusion into the cloud. 

While it is tempting, it would be premature to apply these equations and findings directly to more complex spray combustor situations. Apart from obvious differences in overall geometry, in practical sprays three effects are superimposed transients associated with oxidizer entrained in the fuel injector region, droplet-size-dependent relative motion between the fuel droplets and the surrounding gas, and oxidizer and product transport by turbulence and convection. Rather, our present QS and future transient studies of the behavior of quiescent fuel droplet clouds should be viewed as necessary first steps in the qualitative and quantitative theoretical understanding of fuel droplet sprays. Future work should be concerned not only with the conditions under which theoretical group combustion occurs in fuel sprays but also with the implications of such cooperative phenomena for combustion eflBciency in volume-limited systems, and pollutant emissions. 

While complicated by such additional phenomena as turbulence, droplet slip, etc., qualitatively similar phenomena shouM occur locally in fuel droplet sprays of practical interest. Our hope is mat the insights gained in the present theoretical treatment of quiescent fuel droplet arrays ultimately prove useful in the understanding and mathematical modeling/optimal design of practical spray combustors. 

The present research deals with the control of an industrial gas-turbine spray combustor with multiple swirlers and distributed fuel injection for rapid mixing and stabilization [1]. The research focuses on investigating the mixing patterns and flame structure in a multiple-swirl stabilized combustor and develops control strategies for improved performance [2]. It is performed in collaboration with Delavan Gas Turbine Products, a division of Goodrich Aerospace. The research... 

For more details see Gutmark, E. J., G. Li, and S. Abrjiham. Cheiracteristics cmd control of a multiswirl spray combustor. Chapter 10 (Section 1) in this book, pp. 97-110. (Editor s remark.)... 

Figure 15.1 Coaxial jet spray combustor 1 — primary and secondary fuel lines 2 — primary speaker 3 — secondary speaker 4 — inlet section 5 — combustion section p — primary fuel nozzle s — secondary fuel nozzle and m — fuel-modulation nozzle.

Active control studies on a swirl-stabilized spray combustor are presented. Significant improvements with model-based control over traditional time-delay control is demonstrated in the present work. These improvements are particularly noted with acoustic modulation. Future work in this area is directed toward using a proportional drive spray injector where the full amplitude/phase information from the model-based controller can be exploited. 

Campos-Delgado, D. U., K. Zhou, D. Allgood, and S. Acharya. 2003. Active control of a swirl-stabilized spray combustor using model-based controllers. Combustion Science Technology 175(l) 27-53. 

Gas sparged chemical reactors are designed and used in many different geometries. These reactors are usually continuous in gas, and batch or continuous in liquid. Some of the geometries in use are bubble columns, pipe and static mixer reactors, stirred vessels, packed columns, tray columns, spray columns, jet loop reactors, and venturi ejector reactors. Design equations for each geometry are based on correlations and simpUfying assumptions, such as uniform kLa in the stirred vessel. Other gas-Uquid reactors include spray columns and spray combustors. 

Reactions most commonly occur in the liquid phase in gas-liquid reactors. The most likely exception to this is spray combustors in which the reactions occur in the gas phase after or as the liquid droplets vaporize. Usually, in chemical reactors one reactant is transferred from the gas phase to the liquid phase, where the chemical reactions occur, as in chlorinations, oxidations, and hydrogenations. 

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