https://orcid.org/0000-0002-7737-6087
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ABSTRACT
This paper presents experimental studies on flame height, thermal and emission characteristics of Inverse Jet Diffusion Flame (IJDF) using a circumferentially arranged fuel port (CAFP) burner by following two different protocols, namely, Protocol I and Protocol II. Experiments are carried out to investigate the effect of momentum flux ratio (MFR) on flame height and base flame height characteristics for a fixed air jet velocity, by varying fuel jet velocity (Protocol I) and by varying air jet velocity for a fixed fuel jet velocity (Protocol II). For both Protocols, there is a decrease in flame height with MFR due to the deterioration of fuel-air mixing process. Two separate semi-empirical correlations between normalized flame height and MFR are proposed for Protocol I and II, respectively. The center-line temperature characteristics indicate a faster air-fuel mixing at higher MFR for both Protocols. Moreover, Froude number is used to delineate the buoyancy and momentum-controlled regimes in IJDF. A constant temperature plateau is defined to identify the suitability of burner for industrial heating applications and is found to be higher for 32-port burner than that of the 12- port inverse jet diffusion flame burner due to enhanced air-fuel mixing along the jet central axis. Moreover, at lower MFR, emission index (EI) of NO remains independent of both the Protocols, whereas at higher MFR, the variation depends on the type of Protocol due to a larger variation of Froude number. On the other hand, the variation of CO emission index is almost independent of Protocol I and II. The experimental results show that the present 32 port burner design outperforms the emission characteristics of 12-port burner for an overall equivalence ratio less than 1.63. Two semi-empirical correlations for EINO and EICO, respectively, are developed as a function of overall equivalence ratio and MFR, which can be used for design and development of CAFP IJDF burner.
Nomenclature
| CAFP | = | Circumferentially arranged fuel port |
| CoA | = | Co-axial |
| ds | = | Effective Jet diameter |
| D | = | Twice the center-to-center distance between air-fuel ports |
| Da | = | Air jet diameter |
| Df | = | Fuel jet diameter |
| Go | = | Combined momentum flux |
| Hb | = | Base flame height |
| EI | = | Emission Index |
| Hf | = | Flame height |
| IJDF | = | Inverse jet diffusion flame |
| lt | = | Distance from burner rim to attain maximum center-line flame temperature |
| MFR | = | Momentum flux ratio |
| MWi | = | Molecular weight of ith species |
| MWF | = | Molecular weight of fuel species |
| NJDF | = | Normal jet diffusion flame |
| Fr | = | Froude number |
| Tc, max | = | Maximum center-line temperature |
| Va | = | Average air jet velocity |
| Ve | = | Relative jet velocity between average air-fuel jet velocity |
| Vf | = | Average fuel jet velocity |
Greek symbols
| ρa | = | Density of air |
| ρf | = | Density of fuel |
| ϕ | = | Overall equivalence ratio |