Temporally Resolved Two-Dimensional Spectroscopic Study on the Effect of Highly Preheated and Low Oxygen Concentration Air on Combustion

2015

Applied Energy

h i g h l i g h t sExamined the role of entrainment on distributed combustion under different conditions. N 2 and CO 2 are used to simulate entrained combustion gases from within the combustor. Local equivalence ratio distribution obtained through OH ⁄ and CH ⁄ chemiluminescence. NO chemiluminescence significantly reduced under distributed combustion conditions. Reaction distribution demonstrated at 15% O 2 and lower, with almost invisible flame. a b s t r a c tHigh intensity colorless distributed combustion (CDC) provides high efficiency combustion with stable operation and ultra-low emissions. The role of internal entrainment of hot reactive gases requires further investigation in order to obtain minimum requirements for distributed combustion. In this paper, the impact of internal entrainment of reactive gases on the flame behavior and structure is investigated with focus on fostering distributed combustion. A mixture of nitrogen and carbon dioxide was introduced to the air stream prior to mixing with the fuel to simulate the recirculated product gases from within the combustor. Increase dilution with nitrogen or carbon dioxide increased the reaction zone volume to result in uniform distribution of CH ⁄ and OH ⁄ chemiluminescence signal and uniform equivalence ratio (measured optically). These conditions replaced the normally present blue flame with a uniform almost invisible faint bluish flame. The increased entrainment also decreased NO chemiluminescence significantly for the same amounts of fuel burned. The chemiluminescence data suggested that lowering oxygen concentration from 21% to 15% resulted in improved distributed combustion conditions with the reaction volume occupying most of the combustor. These conditions provide the minimum entrainment requirement and reduction of oxygen concentration for achieving distributed combustion. Results obtained at different equivalence ratios and entrained gas temperatures showed similar behavior at oxygen concentration of 15%. The reaction distribution was further enhanced at lower oxygen concentration ($11%) with further reduction in pollutants emissions.

Section: Introductionmentioning

confidence: 92%

Internal entrainment effects on high intensity distributed combustion using non-intrusive diagnostics

2015

Applied Energy

“…In another investigation, the flame temperature have been measured, showing that the reaction is much more distributed at 4% oxygen concentration as compared to 21% oxygen in air. This was demonstrated with and without air preheats prior to combustion [10] with experiments performed at those two oxygen concentration.…”

Section: Introductionmentioning

confidence: 94%

Impact of internal entrainment on high intensity distributed combustion

2015

Applied Energy

h i g h l i g h t sExamined the role of entrainment on Distributed Combustion under different conditions. N 2 and CO 2 are used to simulate entrained combustion gases from within the combustor. Low O 2 concentration in the mixture prior to ignition fostered distributed reaction. Reaction distribution demonstrated at 15% O 2 and lower, with almost invisible flame. 80-90% NO reduction demonstrated at oxygen concentration of 15% in the mixture. a b s t r a c tColorless Distributed Combustion (CDC) has shown ultra-low emissions and enhanced performance of simulated gas turbine combustors. To achieve distributed combustion, the flowfield must be tailored for desirable mixture preparation within the combustor prior to mixture ignition. Though CDC have been extensively studied using a variety of geometries, heat release intensities, and fuels, the role of internally recirculated hot reactive gases needs to be further investigated and quantified to obtain the minimum requirement of internal entrainment for achieving distributed reaction condition. In this paper, the impact of internal entrainment of product gases on flame structure and behavior is investigated with focus on fostering distributed combustion and to provide guidelines for seeking distributed combustion. To simulate the recirculated gases from within the combustor, a mixture of nitrogen and carbon dioxide is introduced to the air stream prior to mixing with fuel and combustion. Increase in the amounts of nitrogen and carbon dioxide (simulating increased recirculation) increased the reaction volume to occupy larger volume with an overall enhanced and uniform distribution as revealed from the OH ⁄ chemiluminescence intensity. At the same time, the bluish flame is replaced with a more uniform almost invisible bluish flame. The increased recirculation also decreased the NO emission significantly for the same amount of fuel burned. Lowering oxygen concentration from 21% to 15% (due to increased recirculation) resulted in 80-90% reduction in NO with no impact on CO emission with sub PPM NO emission achieved at an equivalence ratio of 0.7. The same trend was demonstrated for a range of recirculated gases temperature. The reaction distribution was significantly enhanced with ultra-low emissions for oxygen concentration lower than 16% setting a minimum recirculation requirement for distributed combustion.

“…In another investigation, the flame temperatures have been measured, showing that the reaction is much more distributed at 4% oxygen concentration as compared to 21% oxygen in air. This was demonstrated with and without air preheats prior to combustion [10], however, experiments were only performed at those two oxygen concentrations.…”

Section: Introductionmentioning

confidence: 97%

Internal Entrainment Effects on Distributed Combustion

Volume 4: 20th Design for Manufacturing and the Life Cycle Conference; 9th International Conference on Micro- And Nanosystems

2015

Colorless Distributed Combustion (CDC) has been shown to provide ultra-low emissions and enhanced combustion performance of high intensity gas turbine combustors in terms of efficiency and stability. To achieve distributed combustion, the flowfield needs to be carefully tailored for adequate mixing between reactants and hot reactive species from within the combustor to result in high temperature low oxygen concentration environment prior to ignition. Such distributed reactions result in uniform thermal field and also eliminates any hot spots for mitigating NOx emission. Though Distributed Combustion have been extensively studied using a variety of geometries, injection velocities, heat release intensities, and fuels, the role of hot reactive internally recirculated gases requires further examination. In this paper, the impact of internal entrainment of reactive gases on flame structure and behavior is investigated with focus on fostering distributed combustion and providing guidelines for designing high intensity combustors operating in distributed combustion mode. A mixture of nitrogen and carbon dioxide, used to simulate the recirculated gases, is introduced to the air stream prior to mixing with the fuel and subsequent combustion. Increase in the amounts of nitrogen and carbon dioxide (simulating increased entrainment), led to volume distributed reaction over a larger volume in the combustor with enhanced and uniform distribution of the OH* chemiluminescence intensity. At the same time, the bluish flame stabilized by the swirler is replaced with a more uniform almost invisible bluish flame. The increased recirculation also reflected on the pollutants emission, where NO emissions were significantly decreased for the same amount of fuel burned. Lowering oxygen concentration from 21% to 15% (due to increased entrainment) resulted in 80∼90% reduction in NO with no impact on CO emission with sub PPM NO emission achieved at an equivalence ratio of 0.7. The same trend was seen at higher diluents injection temperature as well, with significant pollutants emission reduction down to an oxygen concentration of 10%.