湍流预混对冲火焰结构及熄火特性试验研究

利用激光层析技术和数字图像处理技术对对冲方式下湍流预混火焰的结构及熄火特性进行了试验研究。采用PIV方法测量了冷态对冲面附近的速度场,获得了速度作为衡量流场对锋面燃烧影响的参数。在不同射流工况配置下（Reynolds数,全局应变率,燃料的化学混合当量,不对称动量）,观察到随着湍流对冲强度的提高,在高度皱褶的火焰锋面上存在非连续突触和空洞,这是局部熄火的表现,这些局部熄火点影响的扩展会导致火焰的整体熄火。此观点通过局部火焰锋面曲率的概率统计分析得到支持。另外,获得的在火焰熄火的极限条件下,对实际燃烧器的设计有指导意义。     

H_2O对CO在0.5%PdZrO_2/γ-Al_2O_3上催化燃烧特性的影响

以0.5%PdZrO_2/γ-Al_2O_3为催化剂,在所搭建的比例积分微分控制(PID)多功能实验装置上进行CO催化燃烧基础特性实验,分析了H_2O对CO转化率的影响,以及H_2O体积分数的变化对CO转化率和CO催化燃烧反应时间的影响.结果表明:H_2O的加入大幅提升了CO在催化剂上的起燃温度和燃尽温度,增大了CO催化燃烧反应所需的活化能,且随着H_2O体积分数的增大,CO起燃温度和燃尽温度逐步升高;CO转化率随H_2O体积分数的增加逐渐降低;CO反应稳定所需时间随H_2O体积分数的增大而增加;H_2O的存在降低了催化剂的活性,抑制了催化燃烧的进行.     

粉煤流化床燃烧中N_2O的生成特性

粉煤流化床 (PC- FB)是一项燃烧效率高 ,同时实现炉内脱硫 ,低 NOx 和 N2 O排放的新型高效、清洁煤燃烧技术。在一座 0 .3MW的试验台上 ,研究了其 N2 O生成与分布特性 ,包括床层温度 Tb、流化速度 U0 、二次风率 R2 ,PC- FB流化床燃烧区 (FBCZ)出口氧浓度 O 2 、钙硫比 (Ca/S)对 FBCZ出口 N2 O浓度的影响 ;以及各层二次风份额(R2 i% )及悬浮空间燃烧区 (FCZ)的温度分布与炉内 N2 O浓度分布的关系。     

超临界H2O/CO2混合工质的物性计算

准确计算H_2O/CO_2混合工质的热力特性是新型混合工质汽轮机设计及变工况计算的前提。介绍了EOS-CG模型的数学模型及热力特性的计算方法,并利用该模型、PR、GERG-2008模型对混合工质的物性进行了对比分析。对比分析结果表明,EOS-CG、GERG-2008模型对H_2O/CO_2混合工质的物性计算具有较高精度,可以满足混合工质汽轮机热力计算精度要求。     

预混式燃气燃烧器的熄火保护装置的设计

介绍了预混式燃气燃烧器熄火保护装置的设计过程,根据对单火孔预混式燃气燃烧器燃烧时在火焰不同位置火焰电阻的测试结果,讨论了火焰导电信号的变化规律和信号处理方法,在此基础上设计出信号转化电路和与控制电路的接口,使火焰导电检测成为熄火保护装置的可靠、灵敏的火焰检测部件。     

流化床O_2_CO_2燃烧_氧浓度对NO_x和N_2O的影响

循环流化床能实现高氧气浓度下的O2/CO2燃烧,进而减少燃烧室尺寸并降低再循环烟气量.本研究使用两种烟煤、一种褐煤,分别在15 kW循环流化床试验系统和0.15MW循环流化床试验系统上进行试验,研究了氧气浓度对NOx和N2O的影响.结果表明,3个煤种均在一次风氧气浓度44.3％ ～55.3％、二次风氧气浓度43.2％～ 60.2％下实现稳定燃烧.氧气浓度约50％燃烧时,煤中氮向NOx的转化率降低到空气气氛燃烧的19％ ～ 60％,煤中氮向N2O的转化率降低到空气气氛燃烧的20％ ～81％.     

13．把杀虫剂转变为CO2和H2O的新技术

磷对植物和动物两者的生命都是至关紧要的元素,但这种养分如果大量排放到湖或河里。会扰乱自然生态系统。(Pollution Engineering)2000年No．6报导,一种新的以树脂为基础的技术。提供一种可以代替池塘或洼地的治理这一常见祸害的方法。     

煤焦特性及其N_2O生成影响因素的实验研究

在流化床上进行了两种煤的热解及焦炭的燃烧实验,研究了煤种、粒径、热解条件对煤焦性质及Ｎ２Ｏ转化率的影响。研究结果表明：除粒径外,煤种和热解条件都对煤焦中Ｎ的Ｎ２Ｏ转化率有明显影响。     

O2/CO2气氛下痕量元素迁移特性试验研究

在管式炉上进行徐州烟煤的燃烧试验,采用电感耦合等离子体光谱质谱联用仪(ICP-MS)对燃烧剩余灰渣进行测定.研究了不同温度和不同燃烧气氛(空气气氛和O2/CO2气氛)下痕量元素的迁移特性.结果表明,煤燃烧过程中,痕量元素Cr、Mn、Ni、Zn、Cd、Pb在灰渣中富集,As挥发率达70%以上.随着温度的升高,大部分痕量元素在灰渣中的含量降低,Mn、Ni、Cr在灰渣中的含量相对比较稳定.O2/CO2气氛下,各元素随温度的变化趋势并未受到影响,但整体上O2/CO2气氛下各痕量元素在灰渣中的含量要大于空气气氛下的,随着温度的升高,O2/CO2气氛和空气气氛下痕量元素在灰渣中的含量越来越接近,说明燃烧气氛对痕量元素迁移的影响随温度升高而减弱.     

磁场对预混火焰特性的影响

通过对磁场影响预混火焰特性的研究，发现磁场的作用能够改变预混火焰的燃烧特性，使火焰的温度升高，同时火焰的直径也会增加，而火焰的高度有所降低．由此可使人们更精确地了解实际火灾过程中火焰的燃烧特性，掌握火灾的特点，为减灾和灭灾提供有益的参考．     

Thermal and chemical contributions of added H2O and CO2 to major flame structures and NO emission characteristics in H2/N2 laminar diffusion flame

Numerical simulation with detailed chemistry has been carried out to clearly discriminate the thermal and chemical contributions of added diluents (H₂O and CO₂) to major flame structures and NO emission characteristics in H₂/N₂ counterflow diffusion flame. The pertinence of GRI, Miller–Bowman, and their recent modified mechanisms are estimated for the combined fuel of H₂, CO₂, and N₂. A virtual species X, which displaces the individual CO₂ and H₂O in the fuel sides, is introduced to separate chemical effects from thermal effects. In the case of H₂O addition the chain branching reaction, H + O₂ → O + OH is considerably augmented in comparison with that in the case of CO₂ addition. It is also seen that there exists a chemically super‐adiabatic effect in flame temperature due to the breakdown of H₂O. The reaction path of CH₂O→CH₂OH→CH₃ and the C1‐branch reactions become predominant due to the breakdown of CO₂. In NO emission behaviour super‐equilibrium effects caused by the surplus chain carrier radicals due to the breakdown of added H₂O are more superior to the enhanced effects of prompt NO with the breakdown of added CO₂. Especially, it is noted that thermal NO emission is directly influenced by the chemical super‐equilibrium effects of chain carrier radicals in the case of H₂O addition. As a result the overall NO emission in the case of the addition of H₂O is higher than that in the case of CO₂ addition. Copyright © 2002 John Wiley & Sons, Ltd.     

Computed extinction limits and flame structures of H2/O2 counterflow diffusion flames with CO2 dilution

A narrowband radiation model is coupled to the OPPDIF program, which uses detailed chemical kinetics and thermal and transport properties to enable the study of one-dimensional counterflow H₂/O₂ diffusion flames with CO₂ as dilution gas over the entire range of flammable strain rates. The effects of carbon dioxide dilution, ambient pressure and inlet temperature of opposed jets on the extinction limits and flame structures are compared and discussed. The extinction limits are presented using maximum flame temperature and strain rate as coordinates. Both high-stretch blowoff and the low-stretch quenching limits are computed. When the CO₂ dilution percentage is higher, the flame is thinner and flame temperature is lower. The combustible range of strain rates is decreased with increasing CO₂ percentage due to the effects of CO₂ dilution, which is categorized as dilute effect, chemical effect and radiation effect. In addition, the flame temperature of low-stretch diffusion flame with radiation loss is substantially lower than that computed with the non-radiation model. This large temperature drop results from the combined effect of flame radiation and chemical kinetics. The extinction limits and flame temperature are increasing with increasing atmospheric pressure and temperature, but the flame thickness is decreased with the pressure. At higher pressure and temperature, the extinction limits are extended more on the high-stretch blowoff limits, indicating the influence of the ambient pressure and temperature on the chemical reaction.     

Effects of CO2 addition on flame structure in counterflow diffusion flame of H2/CO2/N2 fuel

Numerical analysis on flame structure in a counterflow diffusion flame has been conducted for understanding the effects of CO₂ addition to fuel, systematically varying initial concentration of CO₂ and axial velocity gradient. The effects of CO₂ addition to fuel side in a counterflow diffusion flame are globally divided into two categories: diluent effects due to the relative reduction in the concentrations of the reactive species, and direct chemical effects caused by the breakdown of CO₂ through the reactions of third‐body collision and thermal dissociation. The deflection of CO₂ mole fraction profile with mixture fraction clarifies that the converted CO quantity from CO₂ is not negligible at low axial velocity gradients. It is also known that the addition of CO₂ does not alter the basic skeleton of the H₂–O₂ reaction mechanism, but contributes to the formation and destruction of hydrocarbon products such as HCO. At high axial velocity gradients the CO converted reaction is suppressed and then CO₂ plays the role of a diluent at these conditions. Copyright © 2001 John Wiley & Sons, Ltd.     

Effect of steam addition on flame structure and NO formation in H2–O2–N2 diffusion flame

Numerical analysis is conducted to clarify chemical effects of added steam to either fuel‐ or oxidizer‐side on flame structure and NO emission behaviour with detailed chemistry in hydrogen–oxygen–nitrogen diffusion flames. An artificial species, which has the same thermodynamic, transport, and radiation properties to added H₂O, is introduced to feasibly isolate chemical effects of added H₂O. It is found that the reaction step (‐R23) is the starting point to induce chemical effects of added steam. Special concern is, thus, focused on the impact of OH radical on flame structure and NO emission behaviour. A strong dependency of the amount of steam addition on OH radical behaviour is clearly displayed, and this modifies flame structure sufficiently to produce higher flame temperature at more than a certain mole fraction of added steam in comparison to that diluted with artificial species. It is also shown that the reaction step (‐R23) is closely related to flame temperature and thereby the location of maximum flame temperature. The behaviour of NO emission index is shown to be greatly influenced by the competition between the reaction steps of (R63) and (R65) in addition to Zeldovich NO. It is, consequently, seen that the intermediate active species, HNO, affects NO emission behaviour remarkably. These results may be helpful to understand the role of recirculated steam in the combustion systems with flue gas recirculation to either fuel‐ or oxidizer‐side. Copyright © 2004 John Wiley & Sons, Ltd.     

Emission characteristics and axial flame temperature distribution of producer gas fired premixed burner

This paper presents the emission characteristics and axial flame temperature distribution of producer gas fired premixed burner. The producer gas fired premixed burner of 150 kW capacity was tested on open core throat less down draft gasifier system in the present study. A stable and uniform flame was observed with this burner. An instrumented test set up was developed to evaluate the performance of the burner. The conventional bluff body having blockage ratio of 0.65 was used for flame stabilization. With respect to maximum flame temperature, minimum pressure drop and minimum emissions, a swirl angle of 60° seems to be optimal. The experimental results also showed that the NO_x emissions are inversely proportional to swirl angle and CO emissions are independent of swirl angle. The minimum emission levels of CO and NO_x are observed to be 0.167% and 384 ppm respectively at the swirl angle of 45–60°. The experimental results showed that the maximum axial flame temperature distribution was achieved at A/F ratio of 1.0. The adiabatic flame temperature of 1653 °C was calculated theoretically at A/F ratio of 1.0. Experimental results are in tune with theoretical results. It was also concluded that the CO and UHC emissions decreases with increasing A/F ratio while NO_x emissions decreases on either side of A/F ratio of 1.0.     

Effect of gravity on laminar premixed gas combustion II: Ignition and extinction phenomena

Minimum ignition energies and flame radii as a function of time were measured for near-limit, limit, and sublimit fuel-lean methaneair mixtures burning at one-g and zero-g. Minimum ignition energy values were the same at one-g and zero-g except for mixtures very near the zero-g flammability limit and leaner, where the zero-g values were much higher than the one-g values. For sublimit mixtures at zero-g a previously unreported mode of unstable flame propagation was observed; this mode was characterized by a flame radius increasing in proportion to the square root of the time lapse from ignition, an energy release often orders of magnitude greater than the spark energy input, and sudden extinction. This mode of flame propagation was observed at all gas pressures tested but was more pronounced at higher pressures. All zero-g propagation was spherically symmetric except for a few unusual flame extinguishments at high pressures. The principal conclusions are that flame extinguishment at zero-g is caused by a flame-front instability and that gravitational forces have a stabilizing effect on upward flame propagation. The cause of the instability could not be determined; further experiments which might aid in determining the cause are suggested.     

Soot particle inception and O2 profiles in a premixed ethylene flame

We have found that soot particle inception in our premixed ethylene flame occurs in a region where the O₂ concentration is of the order of 1 % and that particle inception ceases as the O₂ mole fraction drops much lower. This relationship between soot formation and O₂ concentration is in qualitative agreement with shock tube results. The net specific surface growth rate is close to zero in the inception zone, a fact that is consistent with oxidation of soot by O₂.     

Study of the flue gas characteristics and gasification reaction of pulverized coal combustion in O2/CO2/H2O atmosphere

The impacts of O₂ and H₂O on the combustion characteristics of pulverized coal in O₂/CO₂/H₂O atmosphere were studied. The gasification reaction ratio was calculated from the components of flue gas. The competition exists between C-CO₂ and C-H₂O reactions under rich CO₂ atmosphere. At various H₂O concentrations, the differences were found in generation amounts of CO and H₂ in flue gas. At O₂ concentrations <10%, C-CO₂ reaction decreased while C-H₂O reaction increased with increasing H₂O concentration; while at O₂ concentration >30%, H₂O showed no obvious specific patterns of effects. The gasification ratio was reduced as coal ranks increase.