乙醇和二甲醚微射流火焰燃烧特性研究

采用实验及数值计算研究了乙醇和二甲醚微圆管射流火焰燃烧特性。通过实验观察到不同燃料流速下乙醇和二甲醚火焰都具有四种典型的火焰形态；使用平面激光诱导荧光测试系统获得了微射流火焰的OH基元分布，实验结果表明在较高流速下稳定燃烧的乙醇火焰比二甲醚火焰直径小，且略高于二甲醚火焰；采用考虑详细化学反应机理的数值计算对乙醇和二甲醚火焰进行了数值模拟，计算结果与实验现象吻合较好；利用一维非预混对冲火焰计算进一步研究了这两种燃料的化学反应路径，分析结果表明乙醇和二甲醚火焰的中间产物有显著差异，两种燃料化学反应特性的差异导致了不同的微火焰结构。     

乙醇和二甲醚微射流火焰燃烧特性研究

采用实验及数值计算研究了乙醇和二甲醚微圆管射流火焰燃烧特性。通过实验观察到不同燃料流速下乙醇和二甲醚火焰都具有四种典型的火焰形态;使用平面激光诱导荧光测试系统获得了微射流火焰的OH基元分布,实验结果表明在较高流速下稳定燃烧的乙醇火焰比二甲醚火焰直径小,且略高于二甲醚火焰;采用考虑详细化学反应机理的数值计算对乙醇和二甲醚火焰进行了数值模拟,计算结果与实验现象吻合较好;利用一维非预混对冲火焰计算进一步研究了这两种燃料的化学反应路径,分析结果表明乙醇和二甲醚火焰的中间产物有显著差异,两种燃料化学反应特性的差异导致了不同的微火焰结构。     

二甲醚生产前景看好

二甲醚简称甲醚，为最简单的脂肪醚，分子式为C２H６O。二甲醚是具有挥发性醚味的无色气体，燃烧时的火焰略带光亮，沸点为－２４．９℃，熔点为－１４１．５℃，自燃温度为３５０℃，在空气中的爆炸极限（体积比）为３．４５％～２６．７％。二甲醚在幅射或加热条件下会分解成甲烷、乙烷、甲醛等。二甲醚在制药、染料、农药等工业中有许多用途。可作杀虫剂、喷漆、涂膜和抛光剂、防锈剂等，高浓度的二甲醚可用作为麻醉剂，二甲醚也可作为特种燃料，当它混合在燃料中，可用作寒冷地区柴油发动机的抗冻燃料。并且二甲醚也可作为优良的萃取…     

微型定容燃烧腔内C2~C4烷烃/空气火焰传播

在直径35 mm、高度2 mm光学可视的定容燃烧腔内,实验研究了常温常压静止乙烷/空气、丙烷/空气和正丁烷/空气预混气在燃烧腔中心由电火花点燃后向外传播的火焰传播特性。结果表明：3种燃料空气混合气可形成火焰传播的当量比范围不同,范围由大到小排序为乙烷>丙烷>正丁烷;3种燃料均存在由光滑火焰面向褶皱火焰面转变的传播形态;在微型定容燃烧腔内,3种燃料的火焰传播速度均低于常规尺度下定容燃烧弹内火焰传播速度,且火焰传播速度随半径增加而减小;随着当量比增加,火焰锋面容易出现褶皱和断裂现象,在高当量比情况下,火焰传播会出现短暂停滞。     

微型定容燃烧腔内C_2～C_4烷烃/空气火焰传播

在直径35 mm、高度2 mm光学可视的定容燃烧腔内,实验研究了常温常压静止乙烷/空气、丙烷/空气和正丁烷/空气预混气在燃烧腔中心由电火花点燃后向外传播的火焰传播特性。结果表明:3种燃料空气混合气可形成火焰传播的当量比范围不同,范围由大到小排序为乙烷丙烷正丁烷;3种燃料均存在由光滑火焰面向褶皱火焰面转变的传播形态;在微型定容燃烧腔内,3种燃料的火焰传播速度均低于常规尺度下定容燃烧弹内火焰传播速度,且火焰传播速度随半径增加而减小;随着当量比增加,火焰锋面容易出现褶皱和断裂现象,在高当量比情况下,火焰传播会出现短暂停滞。     

强化锅炉燃烧的途径

强化锅炉燃烧的途径１．合理配风（１）一次风及时供给燃料燃烧所需要的风量可以保证燃料燃烧稳定。一般地讲，锅炉运行中控制空气过剩系数在１．１５～１．５之间。采用监测仪器和凭经验观察火焰颜色都可做到合理配风。即火焰呈麦黄色，表示配风量合适；火焰呈刺眼白色，...     

替代燃料二甲醚在梭式窑中的燃烧实验研究

在对二甲醚(DME)进行理论燃烧计算的基础上,开展了DME作为替代燃料应用于梭式窑的燃烧实验研究,观察了随燃料DME流量的增加,预混和非预混燃烧火焰的变化,研究了空气系数对垂直烟道处火焰的影响。在1.0m3梭式窑内进行DME与石油液化气(LPG)的对比实验,实测数据结果表明,由于DME烧成排烟热损失比LPG降低了7.79%,DME烧成热耗比LPG烧成热耗低8.85%,窑炉热效率提高9.6%。     

国内外二甲醚生产应用与市场前景分析

二甲醚(DME)又称甲醚，是一种无色易燃的气体或压缩液体，无毒，具有轻微醚香味，常压下沸点为-23．9℃，凝固点-140℃，20℃C时的蒸压为0．53MPa，自燃温度为350℃，在空气中的爆炸极限为3．45～26．7％(体积比)。溶于水及醇、乙醚、丙酮、氯仿等多种有机溶剂。易燃，在燃烧时火焰略带光亮。常温下二甲醚具有惰性，不易自     

层流预混火焰传播特性概述

理论研究层流预混火焰的传播可以更好地理解燃烧过程 ,为实际应用时有效地控制燃烧过程提供理论依据。本文对层流预混火焰特性及层流火焰传播速度进行归纳 ,对有化学反应和可压缩的层流边界层进行简单的理论分析 ,介绍了层流火焰传播的火焰焰锋结构及与层流火焰传播速度有关的预混气体物理化学参数的关系。     

循环流化床中石油焦与煤混合燃烧NO排放特性

在一座0．5MWt循环流化床热态试验台上进行了石油焦与煤混合燃烧试验，研究了烟气中NO的排放特性，对于石油焦与煤不同燃料配比，不同锅炉运行参数，如一次风率、过量空气系数、床温和Ca／S比等对烟气中NO排放浓度的影响规律进行了研究。试验表明对纯焦而言，其NO排放浓度较其他混合燃料要高得多，当燃料中焦煤比增大时，NO的排放浓度降低，对不同焦煤比的燃料，随一次风率增大，NO的排放量增加；随过量空气系数的增大，NO的排放浓度增大；随着运行床温的提高，NO排放浓度升高。     

Experimental study on the laminar flame speed of hydrogen/natural gas/air mixtures

Laminar flame speeds of hydrogen/natural gas/air mixtures have been measured over a full range of fuel compositions (0–100% volumetric fraction of H₂) and a wide range of equivalence ratio using Bunsen burner. High sensitivity scientific CCD camera is use to capture the image of laminar flame. The reaction zone area is employed to calculate the laminar flame speed. The initial temperature and pressure of fuel air mixtures are 293 K and 1 atm. The laminar flame speeds of hydrogen/air mixture and natural gas/air mixture reach their maximum values 2.933 and 0.374 m/s when equivalence ratios equal to 1.7 and 1.1, respectively. The laminar flame speeds of hydrogen/natural gas/air mixtures rise with the increase of volumetric fraction of hydrogen. Moreover, the increase in laminar flame speed as the volumetric fraction of hydrogen increases presents an exponential increasing trend versus volumetric fraction of hydrogen. Empirical formulas to calculate the laminar flame speeds of hydrogen, natural gas, and hydrogen/natural gas mixtures are also given. Using these formulas, the laminar flame speed at different hydrogen fractions and equivalence ratios can be calculated.     

Laminar flame speed measurements of dimethyl ether in air at pressures up to 10 atm

Laminar flame speed measurements of dimethyl ether/air mixtures were made at 1, 5, and 10 atm with equivalence ratios ranging from 0.7 to 1.6. All experiments were performed in a large cylindrical constant-volume bomb with optical access. A new method for converting flame images into flame radii was used. Results reported in other studies were investigated, and some explanations on the disparities found are presented. A full uncertainty analysis was performed combining precision errors from data scatter with predicted systematic errors. Uncertainties ranging between 4.2% and 8.6% were found depending on the equivalence ratio and initial pressure. Experimental results agreed well with some other spherical flame experiments and counterflow flame measurements, but were found to be much lower than PIV-based stagnation flame results. Also, two spherical flame studies deviated significantly both in magnitude and trend. Critical radii and Peclet numbers, defined by the onset of rapid flame acceleration, were recorded for all high-pressure experiments. Markstein lengths were measured and showed a decreasing trend with increasing equivalence ratio. Three different methods were used to define the laminar flame thickness, and large disparities were found between them. In this study, the modeled temperature gradient method for the definition of flame thickness is preferred over other methods. Modeling was performed with the latest version of a C3 chemical kinetics mechanism. Good agreement is seen between the experimental results and the model at all pressures. Emphasis is placed in this paper on reporting experimental uncertainties, calculated density ratios, flame temperatures, and flame radii ranges used for data analysis, and the results resolve some discrepancies seen in the literature for dimethyl ether flame speeds.     

Laminar burning velocities of three C3H6O isomers at atmospheric pressure

Laminar flames of three C₃H₆O isomers (propylene oxide, propionaldehyde and acetone), representative of cyclic ether, aldehyde and ketone species important as intermediates in oxygenated fuel combustion, have been studied experimentally and computationally. Most of these flames exhibited a non-linear dependency of flame speed upon stretch rate and two complementary independent techniques were adopted to provide the most reliable burning velocity data. Significant differences in burning velocity were noted for the three isomers: propylene oxide + air mixtures burned fastest, then propionaldehyde + air, with acetone + air flames being the slowest; the latter also required stronger ignition sources. Numerical modelling of these flames was based on the Konnov mechanism, enhanced with reactions specific to these oxygenated fuels. The chemical kinetics mechanism predicted flame velocities in qualitative rather than quantitative agreement with the measurements. Sensitivity analysis suggested that the calculated flame speeds had only a weak dependency upon parent fuel-specific reactions rates; however, consideration of possible break-up routes of the primary fuels has allowed identification of intermediate compounds, the chemistry of which requires a better definition.     

不同CO2浓度下负直流电场对C3H8/O2/Ar/CO2预混火焰的影响规律

为了揭示电场对火焰效应与火焰传播速率的关系,在定容燃烧弹上研究了常温常压下、负直流电场（U=0、-5、-10 kV）对当量燃空比f为1.0的C₃H₈/O₂/Ar/CO₂预混火焰影响规律随混合气中CO₂掺混浓度（混合气中CO₂体积分数分别为0、10%、15%、20%）的变化关系。实验结果表明：给定加载电压,随着CO₂掺混浓度的增大,C₃H₈/O₂/Ar/CO₂预混火焰传播速率降低,规范化火焰变形率与平均火焰传播速率变化率均增大。当U=-10 kV时,CO₂掺混浓度为0、10%、15%、20%时对应的平均火焰变形率分别为1.01、1.31、1.80、3.12,平均火焰传播速度变化率分别为10.87%、17.87%、19.16%和34.63%。研究结果表明负直流电场对C₃H₈/O₂/Ar/CO₂火焰传播的促进效应随着火焰传播速率的降低而显著增强。     

Autoignition mechanism of dimethyl ether–air mixtures in the presence of atomic iron

The search for reactive additives capable of reducing the combustibility of dimethyl ether is an important problem due to the widening use of ether as an alternative environmentally friendly motor fuel. This paper presents a numerical study of the autoignition chemistry of mixtures of dimethyl ether with air in the presence of atomic iron. Atomic iron, which is an effective inhibitor of premixed laminar hydrocarbon flames, was found to shorten the induction period. However, the additive affects only the first stage of the induction period. The mechanism of promotion of the low-temperature oxidation of dimethyl ether–air mixtures by atomic iron is the formation of hydroxyls in reactions involving iron compounds. Since the additive hardly changes the duration of the second stage of the induction period, it can be suggested that OH radicals play an insignificant role in the low-temperature oxidation of dimethyl ether at this stage.     

Numerical study on laminar flame speed of natural gas-carbon monoxide-air mixtures

Laminar flame speeds of natural gas-carbon monoxide-air mixtures are calculated by CHEMKIN II with GRI Mech-3.0 over a large range of fuel compositions, equivalence ratios, and initial temperatures. The calculated results of natural gas are compared with previous experimental results that show a good agreement. The calculated laminar flame speeds of natural gas-carbon monoxide-air mixtures show a nonmonotonic increasing trend with volumetric fraction of carbon monoxide and an increasing trend with the increase of initial temperature of mixtures. The maximum laminar flame speed of certain fuel blend reaches its biggest value when there is 92% volumetric fraction of carbon monoxide in fuel at different initial temperatures. Five stoichiometric natural gas-carbon monoxide-air mixtures are selected to study the detailed chemical structure of natural gas-carbon monoxide-air mixtures. The results show that at stoichiometric condition, the fuel blend with 80% volumetric fraction of carbon monoxide has the biggest laminar flame speed, and the C normalized total production rate of methane with 80% volumetric fraction of carbon monoxide is the largest of the five stoichiometric mixtures.     

Monte carlo computation of turbulent premixed methane-air ignition

A one-dimensional time dependent monte Carlo numerical computation of sparkignited premixed flames propagating in isotropic turbulence is described. The Monte Carlo method is a statistical fluid particle tracking method for modeling turbulence. The presumed method uses the probability distribution function (PDF) method in order to avoid full solution of the flow equations. The model simulates flame propagation in a homogenous, turbulent environment by prescribing Gaussian distributions of the PDFs of fluctuating velocity and fuel concentration. The current model is unique in that it does not require the modeling of complex chemistry or sophisticated, and costly, flow solvers. Solutions have been obtained for the early phase spark ignition of a lean gaseous mixture of methane-air in a turbulent, spherically-symmetric environment. The simple, yet robust, Monte Carlo method correctly predicts such trends as the increase in turbulent flame propagation speed with increasing turbulence intensity. Turbulent flame speeds are in good agreement with experimental and numerical values reported in the literature. An expression correlating the turbulent flame speed and the rate of speed fluctuations compares well with correlations of other researchers. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 3, pp. 8–14, May–June 1988.     

Experimental study on the laminar flame speed of hydrogen/carbon monoxide/air mixtures

Carbon monoxide and hydrogen are two important components in the syngas. In this study, the laminar flame speed of hydrogen/carbon monoxide fuel mixtures is measured over a large range of fuel compositions (0-100% volume fraction for hydrogen in the mixture) by using a Bunsen burner. The reaction zone area is used to calculate the laminar flame speed. The equivalence ratio covers from lean conditions to rich conditions. The experimental results show that by using the Bunsen flame, the laminar flame speed calculated with the reaction zone area is reliable. Based on the experimental results, empirical equations are derived which can be readily employed to calculate the laminar flame speeds of hydrogen, carbon monoxide, and hydrogen/carbon monoxide mixtures.     

二甲醚燃料汽车的研究和应用进展

从二甲醚燃料发动机的特性、二甲醚燃料的排放指标等方面论述了国外二甲醚燃料汽车的研发进程,介绍了国内在二甲醚燃料喷雾、燃料特性、发动机性能等方面的研究和应用。上海将成为国内首先推广二甲醚燃料汽车的城市。     

Flame propagation through an aluminum aerosuspension at reduced pressure

The rate of flame propagation through an aerosuspension of ASD-1 powdered aluminum is measured in the pressure range 0.1–0.05 MPa and at various component ratios corresponding to a fuel excess. Linear reduction in flame speed with reduction in pressure is observed. It is shown that the combustion of aluminum—air mixture is the most sensitive to pressure change. Spectrozonal cinerecording and optoelectronic image analysis are used to determine the temperature field in the flame front of an overenriched aerosuspension; the formation of eddy structures due to the hydrodynamic interaction of particle settling and the formation and propagation of a combustion surface is recorded. N. é. Nauman Moscow State Technical University. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 5, pp. 23–31, September–October, 1995.