火焰稳定器对直喷式燃烧室污染物生成影响的研究

研究了不同火焰稳定器对直接喷射式燃烧室燃烧和污染物排放的影响.实验中所用的火焰稳定器为30°、45°和60°旋流角的旋流器和三种开孔率不同的多孔板.采用Testo360燃气测试仪测量不同工况条件下相应的燃烧室出口温度,以及NOx和CO生成量.通过对采用不同火焰稳定器燃烧室所得到的燃烧与排放性能的分析比较,得到了多孔板的开孔率和旋流器的旋流角度对污染物排放的影响结果.     

微型燃气轮机燃油燃烧室燃烧特性的模化试验研究

基于模化试验方法,对设计的100kW级微型燃气轮机燃油燃烧室在额定工况下的性能以及在保持微型燃气轮机燃烧室出口排气温度不变的情况下,改变进口空气温度对燃烧室燃烧特性的影响进行了研究。结果表明,燃烧室燃烧效率达到99%以上,总压恢复系数达到94.5%,出口温度最大不均匀度低于20%,NOx排放指标低于9g/kg,火焰筒壁面温度分布均匀。此外,随着燃烧室进口温度的升高,燃烧效率增大,出口温度最大不均匀度减少,CO和UHC的排放指标明显降低,但总压恢复系数有所降低,NOx排放指标有所升高。     

火焰筒扩张角与旋流匹配对燃烧特性的影响

为研究旋流器流量分配对干式低排放(Dry Low Emission,DLE)燃烧室燃烧特性的影响规律,针对单头部中心分级旋流燃烧室,以天然气作为燃料,在保持旋流数不变的前提下开展两级旋流器不同空气分配比例下的试验测试和数值模拟,获得不同结构参数条件下燃烧室的综合燃烧性能以及污染物排放等变化规律。研究表明：随主燃级/预燃级旋流器流量比增大,燃烧室中心回流区变小、回流区长度变短;预燃级局部当量比的增大造成燃烧室出口CO排放增加,主燃区燃烧加剧,热力型NOx排放也增加;同时,燃烧室中心高温区域向燃烧室出口方向扩张,出口温度分布均匀性变差。     

基于反扩散火焰的低NOx旋流燃烧器数值模拟

采用非预混稳态小火焰模型（Steady Flamelet Model,SFM）耦合110步甲烷燃烧简化机理和Realizable k-ε模型对反扩散-旋流低氮燃烧器进行模拟,对比分析了不同旋流角度（30°,45°和60°）及过量空气系数（1.05,110,115和1.20）下燃烧时燃烧室内各截面轴向速度分布、中心截面温度及NOx质量浓度分布。详细研究了燃烧室内天然气与空气的燃烧特性及NOx的排放规律。模拟结果表明：随着旋流叶片角度逐渐增大,燃烧室内回流作用逐渐增强,导致火焰长度变短、燃烧室内最高温度及出口NO质量浓度逐渐降低;在旋流叶片角度为60°时,出口NO质量浓度仅为114 mg/m3;随着过量空气系数逐渐增大,火焰末端温度逐渐提高,导致燃烧室出口NO排放量逐渐增大;在过量空气系数为1.2时,出口NO质量浓度达到294 mg/m3,相比于过量空气系数为1.05时,其NO排放量增加153%。     

空气分级燃烧降低NOX排放技术的研究

利用Fluent数值模拟软件分析了空气分级对高温低氧空气燃烧污染物排放的影响.应用空气分级燃烧技术的燃烧器不仅使燃烧室内具有较高的温度水平,温度场均匀,燃烧效率高,而且NOx的生成量也较低,可以达到节约燃料和降低污染物的综合效果.计算结果分析表明:分级燃烧的二次空气配比对燃烧室内的NOx排放有较大影响.当一次空气占40%左右时,NOx排放最少.     

配风比对微型燃气轮机燃烧室燃烧性能影响的数值模拟

以采用燃料和空气预混燃烧方式的微型燃气轮机燃烧室为研究对象,根据设计参数对燃烧室进行建模和模拟计算,模拟不同工况下预混燃料在燃烧室内经过湍流流动并发生燃烧化学反应的过程,进而得到燃烧室内的热态流场、温度分布以及出口烟气中污染物的排放量.结果 表明:在总过量空气系数为3.01的情况下,随着旋流器进口当量比的增大以及助燃风质量流量比例的升高,预混火焰的锋面温度有所升高,出口NOx质量浓度与出口温度分布因子呈正相关.     

空气分级比对同轴分级燃烧室性能参数的影响

为掌握同轴分级燃烧室性能参数随空气分级比(主燃级空气流量的比值)的变化规律,以某同轴分级燃烧室为研究对象,数值分析了空气分级比对燃烧室的燃烧效率、总压损失、出口温度分布、污染物排放和绝热壁面最高温度的影响。结果表明：空气分级比主要会改变角涡位置的燃烧温度和高温烟气的停留时间;随着空气分级比的升高,燃烧室总压损失、出口温度分布系数、NO_x排放、绝热壁面最高温度逐渐升高,但燃烧效率、CO污染物排放、径向温度分布系数对空气分级比不敏感;在同轴分级燃烧室设计中,在保证燃烧稳定的前提下可采用较小的空气分级比以实现燃烧室高效、低阻、低污染燃烧。     

燃料热值对不同燃烧方式下燃气轮机燃烧特性的影响

针对燃气轮机运行过程中出现的燃烧不稳定和污染物排放高的问题,开展了燃料热值对不同燃烧方式下燃气轮机燃烧特性（燃烧稳定性和污染物排放影响规律）影响的研究。以某重型燃气轮机分管燃烧室为研究对象,在扩散燃烧和预混燃烧方式下,保持燃料流量、空气流量及大气温度等参数不变,仅改变燃料热值,采用数值仿真方法对燃烧室设计监测点处压力、燃烧室出口温度及污染物排放等数据进行分析。研究表明：在扩散燃烧方式下,热值较低时,燃烧室高频压力脉动较大,热值增加,燃烧室低频压力脉动先减小后增加;在预混燃烧方式下,热值增加,燃烧室高频压力脉动减小;在两种燃烧方式下,热值增加,燃烧室出口NO_x排放均增加,而热值变化对燃烧室出口CO的排放影响较小。     

旋流器间距及空气分配对富油/焠熄/贫油燃烧室温度和排放的影响

针对3种旋流器间距的富油/焠熄/贫油RQL燃烧室,保持燃料流量和总空气流量一定,通过改变头部空气占比,研究了不同旋流器间距下燃烧室温度分布及污染物排放变化,并对反应状态下燃烧室内流场信息进行了数值研究.结果表明:RQL燃烧室轴向温度的最低点处于焠熄孔上游,且随着焠熄空气占比的下降,轴向温度的最低点会向下游偏移.头部3个同向旋流器形成的涡结构在燃烧室出口仍然存在,进而导致出口温度分布的不均.旋流器间距S=2 D(D为旋流器出口直径)时NOx排放最低.旋流器间距S=1.7 D时CO排放高于另外两种结构.随着旋流器间距加大,燃烧室中氧气的分布更均匀,富燃区不完全燃烧生成的CO也能在更多区域得到氧化从而降低CO的排放.     

某航空发动机燃烧室天然气湿燃烧数值模拟研究

针对某型航空发动机燃烧室,探究将其改造为天然气湿燃烧低污染燃烧室的可行性。采用计算流体力学方法,研究了压力(1～2.33 MPa)、空气预热温度(510～790 K)及加湿比例(0～2.0)对温度分布、污染物排放的影响。通过Chemkin软件进行参数化计算,对全局当量比进行补偿,以确保燃烧室出口温度均达到设计值。计算结果表明:高压工况下,火焰向燃烧室出口方向延伸,导致出口径向温度分布恶化,其中,压力2.33 MPa时NO_x排放量是常压下的10倍;较高的空气预热温度将导致NO_x排放量增加,但同时可能有利于消除局部高温区;NO_x排放量随加湿比例的提高单调下降,但CO质量浓度表现出先降后增的趋势;无当量比补偿时NO_x质量浓度偏差最高达到90.7%;综合考虑NO_x和CO的排放特性,改造后燃烧室最佳燃料加湿比为1.5。     

Investigation of reverse flow distributed combustion for gas turbine application

In this paper reverse flow modes of colorless distributed combustion (CDC) have been investigated for application to gas turbine combustors. Rapid mixing between the injected fuel and hot oxidizer has been carefully explored for spontaneous ignition of the mixture to achieve distributed combustion reactions. Distributed reactions can be achieved in premixed, partially premixed or non-premixed modes of combustor operation with sufficient entrainment of burned gases and faster turbulent mixing between the reactants. In the present investigation reverse flow modes consisting of three configurations at thermal intensity of 28 MW/m³-atm and five configurations at thermal intensity of 57 MW/m³-atm have been investigated and these high thermal loadings represent characteristic gas turbine combustion conditions. In all the configurations the air injection port is positioned at the combustor exit end, whereas the location of fuel injection ports is changed to give different configurations. The results are presented on the exhaust emissions and radical emissions using experiments, and evaluation of flowfield using numerical simulations. Ultra-low NO_x emissions were found for both the premixed and non-premixed combustion modes investigated here. Cross-flow configuration, wherein the fuel is injected at high velocity cross stream to the air jet resulted in characteristics closest to premixed combustion mode. Change in fuel injection location resulted in changing the combustion characteristics from closer to diffusion mode to distributed regime. This feature is beneficial for part load operation where higher stability limit is desirable.     

Development of high intensity CDC combustor for gas turbine engines

Colorless distributed combustion (CDC) has been demonstrated to provide ultra-low emission of NOx and CO, improved pattern factor and reduced combustion noise in high intensity gas turbine combustors. The key feature to achieve CDC is the controlled flow distribution, reduce ignition delay, and high speed injection of air and fuel jets and their controlled mixing to promote distributed reaction zone in the entire combustion volume without any flame stabilizer. Large gas recirculation and high turbulent mixing rates are desirable to achieve distributed reactions thus avoiding hot spot zones in the flame. The high temperature air combustion (HiTAC) technology has been successfully demonstrated in industrial furnaces which inherently possess low heat release intensity. However, gas turbine combustors operate at high heat release intensity and this result in many challenges for combustor design, which include lower residence time, high flow velocity and difficulty to contain the flame within a given volume. The focus here is on colorless distributed combustion for stationary gas turbine applications. In the first part of investigation effect of fuel injection diameter and air injection diameter is investigated in detail to elucidate the effect fuel/air mixing and gas recirculation on characteristics of CDC at relatively lower heat release intensity of 5 MW/m³ atm. Based on favorable conditions at lower heat release intensity the effect of confinement size (reduction in combustor volume at same heat load) is investigated to examine heat release intensity up to 40 MW/m³ atm. Three confinement sizes with same length and different diameters resulting in heat release intensity of 20 MW/m³ atm, 30 MW/m³ atm and 40 MW/m³ atm have been investigated. Both non-premixed and premixed modes were examined for the range of heat release intensities. The heat load for the combustor was 25 kW with methane fuel. The air and fuel injection temperature was at normal 300 K. The combustor was operated at 1 atm pressure. The results were evaluated for flow field, fuel/air mixing and gas recirculation from numerical simulations and global flame images, and emissions of NO, CO from experiments. It was observed that the larger air injection diameter resulted in significantly higher levels of NO and CO whereas increase in fuel injection diameter had minimal effect on the NO and resulted in small increase of CO emissions. Increase in heat release intensity had minimal effect on NO emissions, however it resulted in significantly higher CO emissions. The premixed combustion mode resulted in ultra-low NO levels (<1 ppm) and NO emission as low as 5 ppm was obtained with the non-premixed flame mode.     

Hydrogen addition effects on methane-air colorless distributed combustion flames

In this investigation the role of hydrogen addition in a reverse flow configuration, consisting of both non-premixed and premixed combustion modes, have been examined for the CDC flames. In the non-premixed configuration the air injection port is positioned at combustor exit end while the fuel injection port is positioned on the side so that the fuel is injected in cross-flow with respect to air injection. The thermal intensity of the flames investigated is 85 MW/m³ atm to simulate high thermal intensity gas turbine combustion conditions. The results are presented on the global flame signatures, exhaust emissions, and radical emissions using experiments and flowfield using numerical simulations. Ultra low NO_x emissions are found for both the premixed and non-premixed combustion modes. Addition of hydrogen to methane fuel resulted in only a slight increase of NO emission, significant decrease of CO emission and extended the lean operational limit of the combustor.     

外二次风旋流数对燃烧室内湍流燃烧与NOx生成的影响

建立了采用分级进风方式的旋流燃烧室实验装置。在此实验装置上分别对天然气进行了湍流旋流燃烧的实验研究。在保持过量空气系数不变的条件下,测量了在不同外二次风旋流数下,燃烧室内烟气的时均温度场,O2,CO2,CO和NO浓度场的分布。由实验结果分析讨论了二次风旋流数对旋流燃烧室内湍流燃烧及NOx生成的影响。     

Swirling distributed combustion for clean energy conversion in gas turbine applications

Distributed combustion provides significant performance improvement of gas turbine combustors. Key features of distributed combustion includes uniform thermal field in the entire combustion chamber, thus avoiding hot-spot regions that promote NO_x emissions (from thermal NO_x) and significantly improved pattern factor. Rapid mixing between the injected fuel and hot oxidizer has been carefully explored for spontaneous ignition of the mixture to achieve distributed combustion reactions. Distributed reactions can be achieved in premixed, partially premixed or non-premixed modes of combustor operation with sufficient entrainment of hot and active species present in the flame and their rapid turbulent mixing with the reactants. Distributed combustion with swirl is investigated here for our quest to explore the beneficial aspects of such flows on clean combustion in simulated gas turbine combustion conditions. The goal is to develop high intensity combustor with ultra low emissions of NO and CO, and much improved pattern factor. Experimental results are reported from a cylindrical geometry combustor with different modes of fuel injection and gas exit stream location in the combustor. In all the configurations, air was injected tangentially to impart swirl to the flow inside the combustor. Ultra-low NO_x emissions were found for both the premixed and non-premixed combustion modes for the geometries investigated here. Swirling flow configuration, wherein the product gas exits axially resulted in characteristics closest to premixed combustion mode. Change in fuel injection location resulted in changing the combustion characteristics from traditional diffusion mode to distributed combustion regime. Results showed very low levels of NO (∼3 PPM) and CO (∼70 PPM) emissions even at rather high equivalence ratio of 0.7 at a high heat release intensity of 36 MW/m³-atm with non-premixed mode of combustion. Results are also reported on lean stability limit and OH^* chemiluminescence under both premixed and non-premixed conditions for determining the extent of distribution combustion conditions.     

Distributed swirl combustion for gas turbine application

Colorless distributed combustion (CDC) has been shown to provide significant improvement in gas turbine combustor performance. Colorless distributed combustion with swirl is investigated here to develop ultra-low emissions of NO and CO, and significantly improved pattern factor. Experimental investigations have been performed using a cylindrical geometry combustor with swirling air injection and axial hot gas exit stream from the combustor. Air was injected tangentially to impart swirl to the flow inside the combustor. The results obtained from the combustor have demonstrated very low levels of NO (∼3 PPM) and CO (∼70 PPM) emissions at an equivalence ratio of 0.7 and a high heat release intensity of 36 MW/m³-atm under non-premixed combustion. To further simulate gas turbine operating conditions, inlet air to the combustor was preheated to 600 K temperature and the combustor operated at 2 atm pressure. Results showed very low levels of CO (∼10 PPM) but the NO increased somewhat to ∼10 PPM at an equivalence ratio of 0.5 and heat release intensity of 22.5 MW/m³-atm under non-premixed combustion conditions. For premixed combustion, the combustor demonstrated low levels of both NO (5 PPM) and CO (8 PPM) at an equivalence ratio of 0.6 and a heat release intensity of 27 MW/m³-atm. Results are reported at different equivalence ratios on the emission of NO and CO, lean stability limit and OH^* chemiluminescence. These results suggest that further performance improvement can be achieved with improved fuel mixture preparation prior to the ignition of fuel at higher operational pressures using swirling combustor design for our quest to develop ultra low emission high intensity combustor for gas turbine application.     

Effect of flow field for colorless distributed combustion (CDC) for gas turbine combustion

Colorless distributed combustion (CDC) investigated here is focused on gas turbine combustion applications due to its significant benefits for, much reduced NOx emissions and noise reduction, and significantly improved pattern factor. CDC is characterized by distributed reaction zone of combustion which leads to uniform thermal field and avoidance of hot spot regions to provide significant improvement in pattern factor, lower sound levels and reduced NOx emission. Mixing between the combustion air and product gases to form hot and diluted oxidant prior to its mixing with the fuel is critical so that one must determine the most suitable mixing conditions to minimize the ignition delay. Spontaneous ignition of the fuel occurs to provide distributed reaction combustion conditions. The above requirements can be met with different configuration of fuel and air injections with carefully characterized flow field distribution within the combustion zone. This study examines four different sample configurations to achieve colorless distributed combustion conditions that reveal no visible color of the flame. They include a baseline diffusion flame configuration and three other configurations that provide conditions close to distributed combustion conditions. For all four modes same fuel and air injection diameters are used to examine the effect of flow field configuration on combustion characteristics. The results are compared from the four different configurations on flow field and fuel/air mixing using numerical simulations and with experiments using global flame signatures, exhaust emissions, acoustic signatures, and thermal field. Both numerical simulations and experiments are performed at a constant heat load of 25 kW, using methane as the fuel at atmospheric pressure using normal temperature air and fuel. Lower NOx and CO emissions, better thermal field uniformity, and lower acoustic levels have been observed when the flame approached CDC mode as compared to the baseline case of a diffusion flame. The reaction zone is observed to be uniformly distributed over the entire combustor volume when the visible flame signatures approached CDC mode.     

Effect of hydrogen-diesel fuel co-combustion on exhaust emissions with verification using an in–cylinder gas sampling technique

The paper presents an experimental investigation of hydrogen-diesel fuel co-combustion carried out on a naturally aspirated, direct injection diesel engine. The engine was supplied with a range of hydrogen-diesel fuel mixture proportions to study the effect of hydrogen addition (aspirated with the intake air) on combustion and exhaust emissions. The tests were performed at fixed diesel injection periods, with hydrogen added to vary the engine load between 0 and 6 bar IMEP. In addition, a novel in–cylinder gas sampling technique was employed to measure species concentrations in the engine cylinder at two in–cylinder locations and at various instants during the combustion process.     

Influence of biodiesel on engine combustion and emission characteristics

This paper discusses the influence of biodiesel on the engine combustion characteristics. The considered fuel is neat biodiesel from rapeseed oil. The considered engine is a bus diesel engine with injection M system. The engine characteristics are obtained by experiments and numerical simulation. The results obtained with biodiesel are compared to those obtained with mineral diesel under various operating regimes. In this way, the influences of biodiesel usage on the injection pressure, injection timing, ignition delay, in-cylinder gas pressure and temperature, heat release rate, exhaust gas temperatures, harmful emissions, specific fuel consumption, and on engine power are analyzed. Furthermore, the relationships among fuel properties, injection and combustion characteristics, harmful emissions, and other engine performance are determined. Special attention is given to possible explanations of higher NO_x emission in spite of lower in-cylinder gas temperature.