Development of distributed combustion index from a swirl-assisted burner

Colorless Distributed Combustion is a combustion technique to reduce pollutants emission, reduce noise, enhance flame stability, promote a uniform thermal field distribution in the flame, and mitigate combustion instability. To achieve these conditions, hot reactive gases must be entrained into the oxidizer to reduce the oxygen concentration, which slows down the reaction rate to broaden and homogenize the reaction front. This paper focuses on the development of a distributed combustion index that will predict transition to favorable distributed combustion conditions over a range of conditions. Distributed conditions were achieved by adding either N2 or CO2 dilution to the oxidizer stream to simulate hot gas entrainment. The index developed here is for either N2 or CO2 dilution and focuses on the effects of heat release intensity, equivalence ratio, and mixture preheat temperature. The results show heat release intensities in the range of 5.72–9.53 MW/m3-atm to have minimal effect on the oxygen concentration corresponding to transition to distributed combustion. In contrast, equivalence ratio and preheat temperature provided strong effects on this transition. Decrease in equivalence ratio from 0.9 to 0.6 required increased oxygen concentration for transition to distributed conditions by some 4% with N2 as the diluent and only 3% with CO2 as the diluent. Increase in mixture preheat temperature from 300 to 700 K decreased oxygen concentration transition requirements by some 3% with N2 and 2% for CO2. Emission levels obtained showed ultra-low NO and CO under favorable distributed combustion condition. The distributed combustion index development presented here is aimed to help guide in the design and development of novel next generation of advanced colorless distributed combustors with much reduced further experimentation.