Swirl combustor, modulated

Potential Application of a Modulated Swirl Combustor to Clean Combustion of Liquid Fuel... 

The modulated swirl combustor decribed here (2) represents a step in this direction when operated with propane or hquid kerosene. It exhibits a very distinct change in flow pattern and potentially can satisfy pollution legislation over a wide operating range of heat release rates, as required, for example, in an aircraft gas turbine engine combustor. 

Modulated Swirl Combustor. The design of the modulated swirl combustor evolved from swirl burners tested by the authors at SheflBeld University and Institute of Flame Research Foundation (IFRF), Ijmuiden (3,4,5,9,10), The modulated swirl combustor (Figure 2) consists essentially of a cyUndrical chamber 1.8 diameters long with an outlet consisting of a contraction followed by a short wide-angle diffuser. Air could be... 

Figure 2, Schematic of the modulated swirl combustor Details of the modulated swirl combustor are as follows ...

It is therefore evident that a detailed experimental analysis of the spray flame is necessary for its theoretical characterization. The aerodynamic changes achieved within the modulated swirl combustor, in which it is demonstrated that blue flame combustion of oil can be achieved using this combustor and a Sonicore atomizing nozzle, clearly show the strong effect of flow aerodynamics upon the spray combustion process. 

Figure 7. Flame photographs obtained from the modulated swirl combustor using propane as the fuel showing no-ring and ring modes of combustion...

The different type of combustion processes obtained from this experimental modulated swirl combustor therefore help in understanding and analyzing the complex flow behavior observed in certain type of industrial flames (13). 

Propane Fuel—Results and Discussion. Onuma (12) showed that in a kerosene spray flame, there is no evidence of droplet burning. The vapor cloud formed by evaporation of the droplets bums like a turbulent diffusion flame. A close relationship between kerosene spray flame and gaseous diffusion flames (using propane as the fuel) was provided. The results reported in this section are those obtained from the modulated swirl combustor using propane as the fuel. 

Figure 8, Stability limits of the modulated swirl combustor. Total air flow = 1070 LI min, equally distributed in the four points of inlets.

Figure 9. Boundaries of the internal recirculation region in the modulated swirl combustor—propane fuel...

Kerosene Fuel—Results and Discussion. Liquid kerosene was burned in the above modulated swirl combustor using a Sonicore atomizing nozzle. As expected the flame could be modulated to obtain a bright yellow, highly radiative flame or a clean blue flame as shown in Figure 12. Total air flow was the same, and the bum-out was complete by about 1 diameter downstream of the burner exit in both cases. Radial distribu-... 

The modulated swirl combustor presented here has generally stable and acceptable basic characteristics, but in addition, it has two modes of... 

Figure 12, Flame photographs of the kersosene-air flame using sonicore atomizer and the modulated swirl combustor, (a) Bright yellow, highly radiative flame (b) clean, blue flame.

Active combustion control in a swirl-stabilized combustor is being investigated to reduce combustion instabilities and to control mixing in order to enhance certain key performance metrics (pattern factor, emissions, and volumetric release). For instability control, it has been demonstrated that experimental model-based controllers can provide substantially greater reductions in pressure oscillations relative to time-delay controllers. Phase-locked CH measurements are presented to provide improved understanding of the heat-release dynamics. It has also been shown that active modulation of dilution air jets can be utilized to control the heat-release and temperature distributions. 

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. 

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