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가스터빈용 희박 예혼합 연소기 내부에 와류 발생기(vortex generator)를 장착하여 그에 따른 연료/공기혼합 및 NOx 배출 특성 변화를 조사하였다. 이를 위해 수치해석적 방법을 채택하여 연소기내 유동특성, 연료/공기 혼합도, 배기가스(NOx), 화염형상을 분석하였다. 와류 발생기를 장착한 경우, 연소기 내부에서 와류 발생기에 의한 나사산 형상으로 인해 와류가 형성되며 이는 연소기 전면부까지 유지되었다. 또한 연소기 내부 면적 차로 인해 압력섭동이 발생하였다. 이와 더불어 연소기 전면부 기준 상류지역의 연료와 공기의 혼합도가 증가됨으로서 연료 과농지역이 감소하게 되며 이로 인해 전반적인 NOx 발생량의 감소 효과를 볼 수 있었다. 화염 형상의 변화로부터 와류 발생기의 영향으로 선회수는 다소 감소할 것으로 예상되며, 이는 와류 발생기로 인한 유속의 반복적 증감에 의한 결과라고 판단된다.
This paper shows a general development process for aircraft gas turbine combustors. As a first step for developing the preliminary combustor design program, several combustor sizing methodologies using reference area concepts are reviewed. There are three ways to determine the reference area; 1) combustion efficiency approach, 2) pressure loss approach, 3) velocity assumption approach. The current study shows the comparisons of the calculated results of combustor reference values from the pressure loss and velocity assumption approaches. Further works are required to add iterative steps in the program using more reasonable values of pressure loss and velocities, and to evaluate the sizing results using data for actual combustor performance and sizes.
Leading edge statistics are obtained by direct numerical simulation(DNS) of freely propagating incompressible and stagnating compressible turbulent premixed flames. Conditional averages of velocities in terms of reaction progress variable, c, and local flame surface density, Σf, are defined and compared through the flame brush. It holds asymptotically that 〈u〉f = 〈Sd〉f and 〈u〉u - 〈u〉b = Dt/Lω with the characteristic length scale of c variation, Lω. It also holds that 〈u〉b = 〈u〉f for a freely propagating flame under no mean strain rate. The turbulent burning velocity, ST, is determined by the conditional statistics at the leading edge under large activation energy.
In the Shell coal gasification process, the syngas produced in a gasifier passes through a syngas cooler for steam production and temperature control for gas cleaning. Fly slag present in the syngas may cause major operational problems such as erosion, slagging, and corrosion, especially in the upper part of the syngas cooler(gas reversal chamber, GRC). This study investigates the flow, heat transfer and particle behaviors in the GRC for a 300 MWe IGCC process using computational fluid dynamics. Three operational loads of 100%, 75% and 50% were considered. The gas and particle flows directly impinged on the wall opposite to the syngas inlet, which may lead to erosion of the membrane wall. The heat transfer to the wall was mainly by convection which was larger on the side wall at the inlet level due to the expansion of the cross-section. In the evaporator below the GRC, the particles were concentrated more on the outer channels, which needs to be considered for alleviation of fouling and blockage.
In order not to release Landfill gas (LFG) having a high global warming potential into the atmosphere and to burn in an internal combustion engine for power generation, a study was conducted to measure and calculate flame speed under turbocharged and lean burn conditions of spark ignition engine. By changing the ratio between methane and carbon dioxide, which are the main components of LFG, experiments were conducted to measure the flame speed using a constant volume combustion chamber. Also comparative analysis was performed with data obtained using CHEMKIN library with GRI 3.0 mechanisms. In addition, using the data obtained through numerical analysis the correlations were derived to calculate the flame speed as a function of equivalence ratio. This study concludes that the overall trend of LFG flame speed is in good agreement between the experimental and calculated results. Using the correlated equation derived from the results of this study, it is possible to estimate the flame speed of LFG under turbocharged and lean burn of spark ignition engine
Authors’ previous works on thermoacoustic(TA) model development showed good results in predicting combustion instability characteristics in a gas turbine combustor. However, they also suggested there were some limitations in growth rate estimation, which might be related with over-simplification of flame structure. As a first trial for improving the model accuracy, the current paper introduces the modified TA model considering the actual flame location in the combustor. The combustor is divided into the unburned and the burned area before and after the flame location, and then acoustic equations are re-organized. The modified TA model results show a better accuracy in predicting the growth rate of instabilities comparing with the previous results. However, obtained results still overestimate the conditions where the combustor goes unstable. Further researches considering heat release distribution through flames are required.
Numerical study is conducted to understand the effects of additional H2O on downstream interaction in CO-O2 counterflow premixed flames. Adding 1% H2O to fuel side for freely-propagating premixed flame with CO-O2 mixture increases laminar burning velocity from 5.3 cm/s to 81.8 cm/s in a way that the main oxidation reaction is changed from CO + 0.5O2 → CO2 to CO + OH → CO2 + H. When global strain rate reaches 23.5 s-1 for interacting CO-O2 premixed flames, the flames cannot be sustained. While for (0.1% H2O + CO)-O2 premixed flames, the flame is extinguished at 2687 s-1. Because the fuel Lewis number and effective one are larger than unity, downstream interaction are mainly through chemical one. For lean-lean (rich-rich) flames, the production of O (H) radical is vigorous, resulting in the formation of OH via H2O + O → OH + OH (H2O + H → OH + H2). These different chemical situations can influence downstream interactions in various flame configurations. Such interesting aspects in chemical interactions are presented and discussed in detail
Numerical study is conducted to grasp the flame structure and NO emissions for a wide range of oxy-fuel combustion (covering from air blown combustion to pure oxygen combustion) and for various mole fractions of recirculated CO₂ in CH₄-O₂/N₂/CO₂ counterflow diffusion flames. Special concern is given to the difference of the flame structure and NO emissions between air blown combustion and oxy-fuel combustion w/o recirculated CO₂ and is also focused on chemical effects of recirculated CO₂. Air blown combustion and oxy-fuel combustion w/o recirculated CO₂ are shown to be considerably different in the flame structure and NO emissions. Modified fuel oxidation reaction pathways in oxygen-enriched combustion are provided in detail compared to those in air blown combustion w/o recirculated CO₂. The formation and destruction of NO through Fenimore and thermal mechanisms are also compared for air blown combustion and oxyegn-enriched combustion w/o recirculated CO₂, and the role of the recirculated CO₂ and its chemical effects are discussed. Importantly contributing reaction steps to the formation and destruction of NO are also estimated in oxygen-enriched combustion in comparison to air blown combustion ..
Environmental regulations are being reinforced for the solution of environmental pollution, that are global issues. Exhaust gas regulations of off-road engines also demand stepwise reduction emission from beginning of Tier 4 interim(2013). Characteristically, Tier 4 regulation apply the NRTC mode which is a transient cycle. And technical studies using NRTC mode are uncommon. In this study, for satisfy the Tier 4 final regulation on the NRTC mode, experimental study was conducted using a 3.4 L off-road engine. Fuel injection timing and injector hole number are chosen as parameters for investigation of combustion and exhaust gas characteristics on off-road diesel engine.