Thermal field investigation under distributed combustion conditions

Abstract

Distributed Combustion has demonstrated significant performance gains, especially on combustion efficiency and near zero pollutants emission. Controlled mixture preparation between air, fuel and internal hot reactive gases prior to mixture ignition is a critical 10 requirement to achieve distributed combustion condition. Though distributed combustion have been extensively studied using a variety of geometries, heat loads and intensities, and fuels, limited information is available on the role of hot reactive gas entrainment and the resultant thermal field uniformity. In this paper, the impact of internal entrainment of hot reactive gases on thermal field uniformity and pollutants emission is investigated. A 15 mixture of nitrogen and carbon dioxide was introduced to the fresh air stream prior to mixing with the fuel and its subsequent combustion to simulate the product gases from within the combustor. Increase in the amounts of nitrogen and carbon dioxide (simulating increased entrainment) significantly reduced pollutants emission, enhanced thermal field uniformity, and increased the reaction volume to occupy larger portion of the combustor. This was evident through spatial temperature measurements in the combustor along with the enhanced distribution of the flame visible signature and OH* chemiluminescence signal. The temperature data demonstrated that lowering oxygen concentration from 21% to 15%, through increased entrainment, promoted distributed combustion conditions with lower overall temperature rise throughout the combustor. In addition, the peak temperature regions associated with swirl burners disappeared, eliminating most of the hot spots in the combustor. The enhanced thermal field uniformity and reduced temperature variation provided ultra-low emissions, demonstrating the impact of enhanced thermal flowfield uniformity on emissions. Experiments performed at different equivalence ratios and entrained gas temperatures demonstrated similar behavior of thermal field uniformity and ultra-low emissions.

On the flame–flow interaction under distributed combustion conditions

“…As the combustor transitioned from swirl flame to distributed combustion, the combustion noise was significantly reduced. The main frequency for this swirl flame was found to be ~500Hz and its harmonics [13]. The signal at this frequency disappeared upon transitioning to CDC with no other frequency detected.…”

“…Figure 8 shows the velocity profile and velocity fluctuations under the reacting confined N 2 /CO 2 diluted condition (case 5). It is to be noted that this flowfield represents distributed combustion as the oxygen concentration in the reactants fell below 15% [12,13]. The first thing to notice is that the central recirculation zone was strengthened further (as seen from the increased negative axial velocity, compared to that shown in Fig.…”

“…This investigation revealed that the reduction in emission is from oxygen concentration reduction rather than dilution of the gases. This was confirmed by performing experiments with no dilution, increased air and fuel flow rates, air dilution (lower equivalence ratio) and N 2 -CO 2 dilution (lower oxygen concentration) conditions [13]. Reynold"s number was kept constant for the latter three investigations to eliminate velocity change effects.…”

Organi̇k Atiklarin Fermantasyonu Sonucu Elde Edi̇len Bi̇yogazlarin Yanma Karakteri̇sti̇kleri̇ni̇n İncelenmesi̇

“…Buradaki temel neden de, biyogaz bünyesinde bulunan CO2'nin, yanıcı bileşeni daha fazla olan biyogazın reaksiyon hızını daha fazla yavaşlattığı, başka bir deyişle alevsiz yanma (dağıtılmış yanma) şartlarına daha fazla yaklaştırdığı sonucu ile açıklanabilir. Benzer sonuçlar, alevsiz ya da dağıtılmış yanma üzerinde yapılmış ve literatürde bulunan bazı çalışmalarda da tespit edilmiştir [16,17]. Yanma odası çıkışına doğru ise sıcaklık seviyeleri 800 K dolaylarında seyretmiştir.…”

Fuel property effects on distributed combustion

“…Lowering oxygen concentration demonstrated lower emission as compared to adding more air. In addition, distributed combustion was only evident in the lower oxygen concentration case while air dilution showed a consistent swirl structure [13]. In this paper, the impact of fuel type on the conditions at which distributed combustion zone is achieved is investigated.…”