Determination of laminar burning velocities for natural gas

Spherically expanding flames of natural gas-air mixtures have been employed to measure the laminar flame speeds, at the equivalence ratios from 0.6 to 1.4, initial pressures of 0.05, 0.1 and 0.15 MPa, and preheat temperatures from 300 to 400 K. Following Markstein theory, one then obtains the corresponding unstretched laminar burning velocity after omitting the effect of stretch imposed at the flame front. Over the ranges studied, the burning velocities are fit by a functional form u_l=u_l0(T_u/T_u0)^α_T(P_u/P_u0)^β_P, and the dependencies of α_T and β_P upon the equivalence ratio of mixture are also given. The effects of dilute gas on burning velocities have been studied at the equivalence ratios from 0.7 to 1.2, and the explicit formula of laminar burning velocities for dilute mixtures is achieved.     

Effects of gas temperature fluctuation on the NO release from pulverized coal particle during char combustion

The effects of gas temperature fluctuation on the NO release from pulverized coal particle during char combustion are investigated. The computed results show that the NO formation through the heterogeneous oxidation and reduction reactions is influenced by the gas temperature fluctuation for the particles with initial diameters of 10-50 μm. The gas temperature fluctuation leads to faster NO release from the particle. The heterogeneous NO formation during the char combustion is further enhanced by the increase in the fluctuation amplitude of gas temperature.     

Modeling the temperature in coal char particle during fluidized bed combustion

The temperatures of a coal char particle in hot bubbling fluidized bed (FB) were analyzed by a model of combustion. The unsteady model includes phenomena of heat and mass transfer through a porous char particle, as well as heterogeneous reaction at the interior char surface and homogeneous reaction in the pores. The parametric analysis of the model has shown that above 550 °C combustion occurs under the regime limited by diffusion. The experimental results of temperature measurements by thermocouple in the particle center during FB combustion at temperatures in the range 590-710 °C were compared with the model predictions. Two coals of different rank were used: lignite and brown coal, with particle size in the range 5-10 mm. The comparisons have shown that the model can adequately predict the histories of temperatures in char particles during combustion in FB. In the first order, the model predicts the influence of the particle size, coal rank (via porosity), and oxygen concentration in its surroundings.     

Numerical investigation of turbulent non-premixed combustion of a wood pyrolysis gas

A fully compressible database of turbulent non-premixed flames of a wood pyrolysis gas is developed by means of direct numerical simulation (DNS). A reduced kinetic mechanism is used to model the combustion of a pyrolysis gas-air mixture. The instantaneous flame surface density evolution equation based on the concept of a displacement speed is examined. The normal component of the displacement speed is nearly constant with respect to curvature, while the curvature-related component tries to restore the flame front to a planar shape. The strain-rate term is mainly a source as the flame is mostly extended. The normal displacement is responsible for both positive and negative contributions to the flame area. The displacement/curvature term is primarily a sink, since it is dominated by its curvature component. Effects of strain and curvature are analyzed by considering their correlations with reaction rates. Reaction rates are enhanced with increased positive strain rates owing to an increase in the flame surface area and to a decrease in curvature. The analyzed results aid in the development of turbulent combustion models. Finally, a new model for a mean variance of the scalar dissipation rate, based on a scale similarity approach, is proposed and examined. A comparison with DNS results shows that the proposed model provides a significant improvement over existing models. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 15–34, May–June, 2007.     

低燃速低燃温双基推进剂燃烧性能的调节

为调节低燃速燃温双基推进剂的燃烧性能(燃速及压强指数),探索铅、铜盐和碳黑等燃烧催化剂在该类推进剂中的催化效果,从理论燃温在900～1700K的低燃速双基推进剂中选出4种作为基础配方,分别加入不同种类的铅盐、铜盐及碳黑等燃烧催化剂,改变催化剂的加入量及搭配关系,进行了一系列试验研究。同时还研究了辅助增塑剂对推进剂燃烧性能的影响。结果表明,常规的铅、铜盐和碳黑等催化剂在低燃速低燃温推进剂中仍能发挥催化作用,作用效果与催化剂的品种及加入量相关,特别是使用复合催化剂时,对燃烧性能的调节更为有效。不同品种的辅助增塑剂对燃烧性能也有影响。     

Effect of the equivalence ratio on the effectiveness of inhibition of laminar premixed hydrogen-air and hydrocarbon-air flames by trimethylphosphate

This paper reports results of an experimental study and numerical simulation of the effect of the equivalence ratio (φ = 0.6–1.6) on the burning velocity of laminar, premixed atmospheric methane-air and propane-air flames without additives and with 0.06% trimethylphosphate (TMP). The effect of the equivalence ratio (φ = 0.7–4.5) on the burning velocity of hydrogen-air flames without additives and with 0.1% TMP was studied by simulation. The experimental and simulation results show that, in hydrocarbon flames doped with TMP, the inhibition effectiveness decreases sharply with a growth in φ from 1.2–1.3 to 1.4–1.6 and in hydrogen-air flames, the inhibition effectiveness increases with a rise in φ from 1.5 to 4.5. The reactions determining the dependence of the inhibition effectiveness on the equivalence ratio were found by analyzing the flame velocity sensitivity coefficients to changes in reaction rate constants. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 14–22, March–April, 2008.     

高渐增性发射药研究进展

列举出发射药燃烧渐增性判断的方法,阐述了燃速渐增性发射药、燃面渐增性发射药、变燃速发射药技术的实现方式。对这3种方式进行对比分析,表明变燃速发射药在燃烧渐增性实现上有较大的优势。     

预测生物质颗粒热解时热损失影响的分析模型(英文)

This paper presents the combined influence of heat-loss and radiation on the pyrolysis of biomass parti-cles by considering the structure of one-dimensional, laminar and steady state flame propagation in uniformly pre-mixed wood particles. The assumed flame structure consists of a broad preheat-vaporization zone where the rate of gas-phase chemical reaction is small, a thin reaction zone composed of three regions：gas, tar and char combustion where convection and the vaporization rate of the fuel particles are small, and a broad convection zone. The analy-sis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number is large and the equivalence ratio is larger than unity （i.e. u 1？ ≥ ）. The principal attention is made on the determination of a non-linear burning velocity correlation. Consequently, the impacts of radiation, heat loss and particle size as the de-termining factors on the flame temperature and burning velocity of biomass particles are declared in this research.     

Modeling of circulating fluidized beds systems for post‐combustion CO2 capture via temperature swing adsorption

The technology of circulating fluidized beds (CFBs) is applied to temperature swing adsorption (TSA) processes for post‐combustion CO₂ capture employing a commercial zeolite sorbent. Steady state operation is simulated through a one‐dimensional model, which combines binary adsorption with the CFB dynamics. Both single step and multi‐step arrangements are investigated. Extensive sensitivity analyses are performed varying the operating conditions, in order to assess the influence of the main operational parameters. The results reveal a neat superiority of multi‐step configurations over the standard one, in terms of both separation performance and efficiency. Compared to fixed‐bed TSA systems, CFB TSA features a high compactness degree. However, product purity levels are limited compared to the best performing fixed‐bed processes, and heat management within the system appears to be a major issue. As regards energy efficiency, CFB systems place themselves in between the most established absorption‐based technologies and the fixed‐bed TSA. © 2017 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 64: 1744–1759, 2018     

Problems in studying formation of smoke oxide particles in combustion of aluminized solid propellants

The present paper deals with properties of smoke oxide particles formed near the surface of burning aluminized solid propellants. The global physical picture of formation of this product is formulated. Based on this picture, it is demonstrated that smoke oxide particles are formed in two processes: combustion of non-agglomerating metal in the gas-phase layer above the surface and combustion of agglomerating metal in the surface layer of the propellant. Combustion mainly proceeds in the heterogeneous and gas-phase modes in these two cases, respectively. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 45–53, January–February, 2007. An erratum to this article is available at .     

Devolatilization and combustion of large coal particles in a fluidized bed

Devolatilization and combustion of large particles of Eastern Canadian coals (Evans and Minto), 5-50 mm dia., were studied in a bench-scale atmospheric fluidized bed reactor at 1023-1173 K with 0.5 mm sand particles as the bed material. The devolatilization time, mass loss history, changes in proximate volatiles content and C/H mass ratio, and temperature history at the centre of the particle during devolatilization were determined. The mass loss during devolatilization is correlated with the proximate volatiles content of the parent coal. The devolatilization time is correlated with the initial particle diameter by a power-law relation with an exponent of 1.54-1.64. The results show insignificant effect of superficial velocity on devolatilization.     

Evaluation of the effects of injection timing and rate-shape on diesel low temperature combustion using advanced CFD modeling

It is well known that injection strategies including the injection timing and the injection rate-shape play an important role in determining engine performance, especially pollutant emissions. But how the injection timing and the injection rate-shape quantitatively affect the performance of diesel low temperature combustion (LTC) is still not well understood. In this paper, the KIVA-CHEMKIN computational fluid dynamics (CFD) code with an improved spray model is used to simulate the spray and combustion processes of diesel LTC with early and late injection timings and seven different injection rate-shapes. The validation of the models is based on comparisons with laser diagnostic and in-cylinder pressure data under a low load operating condition. It is concluded that the use of early injection provides lower soot, HC and CO emissions but higher NOx emissions than the late injection. A rectangular-type (case1) and boot-type (case 4) injection rate-shape displays the potential to reduce the soot, HC and CO emissions compared the other generic rate-shapes considered.     

微波辅助溶液燃烧法制备MgAl_2O_4粉体

将硝酸镁、硝酸铝、尿素按物质的量比为1 2 6.66制得透明混合前驱液,用低温燃烧技术与微波加热技术相结合的方法制备了高纯度、低团聚的镁铝尖晶石(MgAl2O4)粉体。研究了燃烧反应过程中,微波输出功率(200、400、600、700 W)对Mg Al2O4粉体晶体结构、形貌及比表面积的影响。结果表明:微波高效加热方式导致燃烧反应瞬间产生大量气体,促进了Mg Al2O4超细颗粒的形成。同时,随着微波输出功率的增加,尿素氧化加速,利于MgAl2O4晶粒的生长发育。在微波功率700W,微波时间2 min的条件下,可制备结晶完整,粒度分布均匀(平均晶粒尺寸为56.03 nm)的Mg Al2O4粉体。     

Biodiesel engine performance and emissions in low temperature combustion

Engine performance and emission comparisons were made between the use of soy, Canola and yellow grease derived B100 biodiesel fuels and an ultra-low sulphur diesel fuel in the high load engine operating conditions. Compared to the diesel fuel engine-out emissions of nitrogen oxides (NO_x), a high-cetane number (CN) biodiesel fuel produced comparable NO_x while the biodiesel with a CN similar to the diesel fuel produced relatively higher NO_x at a fixed start of injection. The soot, carbon monoxide and un-burnt hydrocarbon emissions were generally lower for the biodiesel-fuelled engine. Exhaust gas recirculation (EGR) was then extensively applied to initiate low temperature combustion (LTC) mode at medium and low load conditions. An intake throttling valve was implemented to increase the differential pressure between the intake and exhaust in order to increase and enhance the EGR. Simultaneous reduction of NO_x and soot was achieved when the ignition delay was prolonged by more than 50% from the case with 0% EGR at low load conditions. Furthermore, a preliminary ignition delay correlation under the influence of EGR at steady-state conditions was developed. The correlation considered the fuel CN and oxygen concentrations in the intake air and fuel. The research intends to achieve simultaneous reductions of NO_x and soot emissions in modern production diesel engines when biodiesel is applied.     

烟气分析法测试燃煤SO_2释出量的研究

为了有效控制SO2的排放量,有必要研究不同温度下燃煤排放SO2含量的测试方法。介绍了烟气分析法用于测试燃煤可释出SO2含量时的试验方法,其中包括间歇式烟气分析法和连续式烟气分析法。通过分析烟气分析法的精确度及重现性,分析该方法的优缺点,并验证其可行性。结果表明:烟气分析法的精确度和重现性不佳,但是可以及时反映燃煤排放SO2的真实情况。因此在完善测试装置后,烟气分析法作为燃煤SO2的测试方法值得进一步深入研究。     

Some aspects of the effect of the porosity of the condensed phase on the combustion of nitrocellulose propellants

This paper considers the mechanisms involved in the effect of the unconnected porosity of the condensed phase of nitrocellulose propellants on the linear burning rate with a pressure rise. A model based on experimental data is proposed for the variation in the linear burning rate taking into account the compaction of the fuel cells resulting in a nonlinear dependence of the burning rate on pressure. The temperature coefficient of the linear burning rate is found to exhibit a nontrivial behavior under pressure rise conditions in various ranges of initial temperatures. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 58–63, September–October, 2008.     

褐煤燃烧阶段风量对指标气体的影响

以平庄瑞安褐煤为研究对象,通过热重试验确定褐煤燃烧阶段温度范围,利用管式炉程序升温系统进行煤样氧化自燃试验,得到风量分别为40、80、120、160和200 m L/min条件下的气体;为确定优选指标气体的关联度大小,采用灰色关联法对其进行分析。结果表明:褐煤燃烧阶段温度为247~433℃,408℃左右达到快速燃烧状态。当风量恒定时,CO_2/ΔO_2、CO/ΔO_2、C_2H-4与温度的关联度比CO、C_2H_6、C_2H_4/C_2H_6高。随风量不断增加,指标气体与温度的关联度:CO_2/ΔO_2最大,其次是CO/ΔO_2、C_2H_4和CO,C_2H_6和C_2H_4/C_2H_6最小。故可将CO_2/ΔO_2、CO/ΔO_2和C_2H_4作为主要指标,CO作为辅助指标用于预测煤矿井下封闭火区燃烧状态。     

富氧燃烧中气体辐射模型对燃烧与换热数值模拟的影响

富氧燃烧过程中,由于使用再循环烟气代替空气中N₂作为稀释剂,烟气中存在大量CO₂和H₂O。CO₂和H₂O作为非极性三原子分子,具有N₂没有的辐射能力,导致富氧燃烧中气体辐射特性发生变化。在数值模拟过程中,气体辐射模型是一个重要的子模型。前人提出多种修改后适用于富氧燃烧的气体辐射模型,但不同气体辐射模型在不同富氧燃烧工况数值模拟中的影响尚未有统一研究。为了研究不同炉型下,气体燃烧和煤粉燃烧中气体辐射模型对燃烧换热模拟结果的影响,通过编程,将一种考虑CO影响的气体辐射模型以及文献中的6种典型气体辐射模型耦合入数值模拟计算。结果表明,在气体富氧燃烧中,气体辐射模型影响了火焰结构。同时,燃烧温度分布有所变化,不同模型结果之间差别最高可到500 K。气体与壁面之间的辐射换热受到影响。气体辐射模型对炉膛中心火焰区域影响较大,而对非火焰区域影响较小。在煤粉富氧燃烧过程中,当有效辐射层厚度在0.3 m左右时,如在100 kW下行炉中,气体辐射模型对煤粉燃烧数值模拟结果几乎没有影响。这可能是由于颗粒辐射在辐射换热计算中占主导地位。而当有效辐射层厚度在16 m左右时,如1000 MW塔式炉中,气体辐射模型对炉内切圆燃烧火焰温度以及组分浓度影响较大,温度差别可到100 K左右。而气体辐射模型对炉膛中心模拟结果没有影响。     

Video-chromatic measurements of temperature fields during combustion of low-temperature solid propellants

A method for measuring temperature fields in luminous zones of burning nonmetal condensed substances (sooty flames) was implemented in the form of an automated information-measuring system which provides computer processing of digital video images with separation of the video signal into monochromatic components. The system was used to study the combustion of a low-temperature solid-propellant composition with a coolant. The statistical parameters of the temperature fields were estimated by stochastic modeling of video-recorded information, providing a better insight into the hotspot-pulsating combustion mechanism of such compositions. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 66–76, May–June, 2009.