A new reduced reaction mechanism of a surrogate fuel for kerosene

The introduction of detailed chemical reaction mechanisms for aviation fuels into complex multidimensional fluid dynamics problems is not practical at the present time. Simplified reaction mechanisms that have been thoroughly evaluated must be developed to address specific issues arising in realistic combustor configurations. A reduced chemical kinetic mechanism features 210 elemental reactions (including 92 reversible reactions and 26 irreversible reactions) and 50 species for the ignition and combustion of n‐decane was compiled and validated for a wide range of combustion regimes. Validations were performed using experimental measurements on a premixed flame of Jet‐A1, O₂ and N₂, stabilised at 1 atm on a flat‐flame burner, as well as from n‐decane shock‐tube ignition experiments. Numerical calculations were performed using this reduced mechanism and the detailed mechanism respectively for n‐decane surrogate fuel. The calculated values of ignition delay times at pressures of 12, 50 bar and equivalence ratio is 1.0, 2.0, respectively and the main reactants and main products mole fractions agree well with experimental data. The present study shows that this reduced mechanism for the n‐decane surrogate can be employed to predict premixed combustion of kerosene. © 2012 Canadian Society for Chemical Engineering     

An experimental study on the hypergolic ignition of hydrogen peroxide and ethanolamine

This paper presents the hypergolic ignition test results of a potential environmentally friendly liquid propellant consisting of hydrogen peroxide oxidizer (with a concentration of 85%) and ethanolamine fuel for use in rocket engines. Open cup drop tests were conducted to study the effect of amount of metal salt catalyst in fuel and the initial temperatures of fuel and oxidizer on the ignition delay time. To test the hypergolic ignition of bipropellant formulation in a real rocket engine environment, a pressure-fed liquid propellant rocket engine (LPRE) was designed and developed. During the tests it was found that the amount of catalyst and the initial temperature of the fuel had a significant effect on the ignition delay of hypergolic bipropellant. However, the oxidizer temperature seemed to have almost no affect on the ignition delay. There was also significant difference between the ignition delay times from open cup tests and those from rocket engine static firings.     

金属/AP颗粒混合物燃烧特性的光谱分析

为了使Al/AP双组元粉末火箭发动机密度比冲最大化,将燃烧室特征长度由2.31 m增至 12.62 m进行了Al/AP粉末火箭发动机点火测试.采用光谱仪、CCD 相机、CO2 激光点火器等对 Al/AP 混合物在 1.0132 5 × 105 Pa的氮气环境中的点火延迟、燃烧时间、燃烧平稳性等燃烧性能进行了研究.测量了Al颗粒的表观堆积密度.作为一种替代燃料,对镁颗粒也进行了研究.结果表明,增加燃烧室特征长度至 12.62 m 时,可以得到最大燃烧室压强振荡幅度±2 .43%的平稳燃烧性能.含粒径 1μm 铝粉的 Al/AP 混合物其燃烧过程的光强远大于含粒径10μm铝粉的样品,并且其在波长 568 nm 发射光谱的光子数强度超过了光谱仪检测上限(65 000 数).而含粒径10μm铝粉样品燃烧过程的568 nm发射光谱信号出现间断且其全程强度低于 19 036 数.粒径 10μm 铝粉点火延迟时间为粒径1μm铝粉点火延迟时间的3.65 倍,燃烧时间为3.03 倍以上,最大RAlO却比 1μm铝粉少 14.3%,密度低21 .3%,说明粒度小的铝粉具有更好的燃烧性能,但是其堆积密度也更低.虽然Mg/AP的理论比冲为Al/AP的95.6%,但是其堆积密度比粒径1μm铝粉高8%,其点火延迟时间比粒径10μm铝粉短 90.3%.火焰照片也表明镁粉可在很大程度上减少凝相沉积.     

Static Electric Sensitivity Characteristics of Zr/BaCrO4 Pyrolants

Zirconium (Zr) easily ignites in air atmosphere and generates high‐energy output. Therefore, it is used as a fuel for pyrolants. Barium chromate (BaCrO₄) dose not ignite in air, so it is one of safety materials and it is used as oxidizer. These materials are mixed with viton as coating material/agent, since viton is easily dissolved in acetone. The static electric sensitivity of only‐BaCrO₄‐coated material is lower than that of Zr‐coated one. The static electric energy, E, influences the chemical and the physical ignition delay times and they decrease with increasing E. The chemical ignition delay time decreases with increasing concentration of Zr. The chemical and physical ignition delay times of only‐BaCrO₄‐coated pyrolant are longer than those of both‐coated material and only‐Zr‐coated, so the pyrolant of only‐BaCrO₄‐coated pyrolant is the safer material.     

铝镁贫氧推进剂的点火性能

为研究镁铝富燃料固体推进剂组分对点火性能的影响,采用改进的靶线法燃速测试系统对多种含镁铝富燃料固体推进剂在常压和加压下进行了通电金属丝点火性能的对比实验。被测试推进剂的镁铝合金含量为20%～40%,或者同时含镁铝合金及硼,氧化剂含量为30%～53%。实验表明,在固定外界输入热源的情况下,推进剂的点火性能主要与氧化剂含量和粒度有关;金属的含量和种类也有一定的影响;催化剂对点火延迟时间影响很小;压强对此种点火方式几乎无影响。该点火延迟测试方法简单易行,并具有一定的可靠度,适于配方调试。     

铝–油酸/正庚烷基纳米浆体燃料液滴着火燃烧特性

采用液滴悬挂法研究了正庚烷液滴、油酸/正庚烷混合燃料液滴、含20wt%纳米铝粉的铝–油酸/正庚烷基纳米浆体燃料液滴在不同温度下(600~800℃)的着火燃烧特性。用高速摄像机观测液滴进入管式电阻炉后的着火燃烧过程,使用热电偶记录液滴周围的气相温度变化,同时通过对应的温度曲线计算液滴的着火延迟时间。结果表明,纳米铝粉和油酸的添加均能降低正庚烷液滴的着火延迟时间。随温度升高,正庚烷、油酸/正庚烷混合燃料、铝–油酸/正庚烷基纳米浆体燃料液滴的着火延迟时间显著降低,但变化趋势逐渐趋于平缓。铝–油酸/正庚烷基纳米浆体燃料液滴的着火延迟时间与环境温度满足阿累尼乌斯方程。与纯正庚烷、油酸/正庚烷混合液滴的燃烧过程相比,铝–油酸/正庚烷基浆体燃料液滴的燃烧过程有显著差异,其燃烧经历3个阶段：正庚烷稳定燃烧阶段、正庚烷微爆炸阶段和表面活性剂微爆炸阶段。铝–油酸/正庚烷基浆体燃料液滴燃烧时间延长,火焰熄灭后又复燃,且燃烧过程中发生剧烈的火焰形变和铝颗粒溅射现象,大部分铝以团聚体形式在第三阶段完成氧化还原反应。     

Optical Coal Particle Temperature Measurement under Oxy‐Fuel Conditions: Measurement Methodology and Initial Results

Coal combustion under oxy‐fuel conditions shows significant differences to combustion in air. Examinations on the single‐grain level give detailed insight into the combustion phenomena of ignition, volatile combustion, and char burnout and, therefore, provide the fundamentals for the development of large‐scale oxy‐fuel facilities. The combustion of a hard coal in a size fraction of d_p = 90–125 μm was investigated in a laminar flow reactor at a temperature of 1500 K. The gaseous fuel oxidizer contained 3 % O₂ by volume and CO₂ or N₂ as diluents. A third measurement in a CO₂‐rich atmosphere containing 9 % O₂ is also presented to show the influence of O₂ concentration. Particle temperatures were measured for three residence times with an imaging two‐color pyrometer.     

Properties of a Gas‐Generating Composition Related to the Particle Size of the Oxidizer

In general gas generators are defined as devices which produce force or power in the form of gas. In the present work we will focus on cold gas generators actuated by pyrotechnics. These gas generators are often applied for pressurizing or inflating systems in which high temperatures are not acceptable. Typical applications are: airbags, seat‐belt tensioners, fire extinguishers. Depending on the application, gas‐generating materials have to fulfil a series of requirements, such as good performance reproducibility, easy and reliable ignition, low explosion temperature, high yield of gas, low yield of condensed products, specific gas composition, and adequate burning rate and vivacity. In previous work a whole range of possibly suitable single compounds, such as sodium azide, double base propellant, azodicarbonamide, guanidine derivatives and azole derivatives were studied. These compounds – whether or not stoichiometrically mixed with an oxidizer (e.g. KNO₃, KClO₄ or NH₄NO₃) – were theoretically and experimentally examined in order to evaluate their combustion properties. The objective of this work is to experimentally investigate the influence of the particle size of an oxidizer on the combustion behavior of a gas‐generating pyrotechnic mixture. As an example a series of nitroguanidine (NQ) / potassium nitrate (KNO₃)‐mixtures with well‐defined KNO₃‐particle size fractions are selected. Raman spectroscopy is used to examine the constituent distribution within the bulk and thus the mixing efficiency. Closed vessel tests are used to experimentally compare ignition delay, burning rate, dynamic vivacity, and yield of gas. The composition of the combustion gases is examined through gas analysis. The experiments show that a decrease of the particle size of the KNO₃‐particles has a positive influence on the mixing efficiency and on the investigated combustion properties of a NQ/KNO₃‐composition. The combustion process of this mixture becomes better controllable when a small KNO₃‐particle size fraction is selected, but its combustion behavior is comparable to that of a NQ/KNO₃‐mixture containing a broad KNO₃‐particle size distribution.     

A comparative experimental study of the autoignition characteristics of alternative and conventional jet fuel/oxidizer mixtures

Autoignition characteristics of an alternative (non-petroleum) and two conventional jet fuels are investigated and compared using a heated rapid compression machine. The alternative jet fuel studied is known as “S-8”, which is a hydrocarbon mixture rich in C₇-C₁₈ linear and branched alkanes and is produced by Syntroleum via the Fischer-Tropsch process using synthesis gas derived from natural gas. Specifically, ignition delay times for S-8/oxidizer mixtures are measured at compressed charge pressures corresponding to 7, 15, and 30 bar, in the low-to-intermediate temperature region ranging from 615 to 933 K, and for equivalence ratios varying from 0.43 to 2.29. For the conditions investigated for S-8, two-stage ignition response is observed. The negative temperature coefficient (NTC) behavior of the ignition delay time, typical of higher order hydrocarbons, is also noted. Further, the dependences of both the first-stage and the overall ignition delays on parameters such as pressure, temperature, and mixture composition are reported. A comparison between the autoignition responses obtained using S-8 and two petroleum-derived jet fuels, Jet-A and JP-8, is also conducted to establish an understanding of the relative reactivity of the three jet fuels. It is found that under the same operating conditions, while the three jet fuels share the common features of two-stage ignition characteristics and a NTC trend for ignition delays over a similar temperature range, S-8 has the shortest overall ignition delay times, followed by Jet-A and JP-8. The difference in ignition propensity signifies the effect of fuel composition and structure on autoignition characteristics.     

Ignition and combustion of pyrotechnic compositions based on microsized and ultra-nanosized aluminum particles in a moist medium in a two-zone gas generator

This paper presents the results of an experimental study of the ignition and combustion of pyrotechnic compositions based on microsized and ultra-nanosized aluminum particles in a model two-zone gas generator using water as oxidizer. The flow of combustion products from the gas generator was video recorded, and the condensed products sampled behind the nozzle exit were studied by chemical and particle-size analyses. It was found that the replacement of microsized aluminum particles by ultra-nanosized particles in the samples led to a ≈17% decrease in the active aluminum content in the condensed phase, a 10–15% increase in the efficiency of the process in the gas generator (completeness of conversion of the pyrotechnic composition to combustion products), and a factor of about three decrease in the ignition delay.     

Role of Oxalic Acid in Promoting Ignition and Combustion of Boron: an Experimental and Theoretical Study

Boron is an attractive fuel for propellants and explosives because of its high energy density. However, its combustion is inhibited by the oxide layer that covers the particles. The use of oxalic acid as an additive was shown to promote boron oxidation. In this study, the thermodynamic model FactSage 6.2 and a laser ignition facility were used to investigate the effect of oxalic acid on the burning characteristics of boron particles. The results of the thermodynamic analyses show that oxalic acid can reduce B₂O₃(l) production during boron combustion. This enables removal of the the oxide film and promotes the burning of boron. However, only at high temperatures (>1500 K) H₂O(g) (produced from H₂C₂O₄) can react with B₂O₃ and remove the oxide film. The evolution of boron combustion flame takes place in three stages: ignition, stable combustion, and extinction; the bright yellow color in the flame indicates boron ignition, the bright white color indicates boron combustion, and the bright green color is interpreted as BO₂ emission. Addition of oxalic acid into boron powders can significantly promote boron ignition and combustion. The ignition delay time of the resulting mixture is reduced by 42.4 %, the combustion intensity is raised by 16.7 %, and the combustion efficiency of boron is increased by 21.5 percentage points. The mechanism of action of oxalic acid on enhancing the combustion of boron was studied by scanning electron microscopy.     

Theoretical Evaluation and Experimental Validation of Performance Parameters of New Hypergolic Liquid Fuel Blends with Red Fuming Nitric Acid as Oxidizer

A number of fuel blends based on 3‐carene, norbornadiene, furfuryl alcohol, ethylidene norbornene, and kerosene in different weight proportions have been developed as rocket fuels which exhibit synergistic hypergolic ignition with red fuming nitric acid (RFNA) as oxidizer with low ignition delays (IDs<40 ms). The optimum compositions of fuel blends were determined by measuring ID values of different blends at optimum O/F ratios. Eight selected fuel blends and one neat fuel (ethylidene norbornene) were theoretically evaluated for their performance parameters using NASA‐CEC‐71 software with RFNA as oxidizer at different O/F ratios and at chamber pressure of P_c, 2451.66 and 4903.33 (or 5197.52) kPa, keeping the exit pressure constant at 98.07 kPa. For experimental validation of performance parameters, static firing trials of these fuel blends with RFNA were carried out using 735.5 N thruster at 2451.66 kPa chamber pressure using doublet or triplet impinging stream type of injector. The experimental C* values were compared with theoretically determined C* values to predict combustion efficiencies which were found to be more than 95% in all the cases.     

带延迟点火部件的发射药点火性能试验研究

为了更好地研究发射药的点火性能,在基于密闭爆发器原理的点火性能测试装置基础上增加了一个延迟点火部件,构建了一个新型点火性能模拟试验装置,根据该装置建立了简单的火药分层点火过程模型,模拟并对比了高能太根-18/1、双芳-3-18/1及NR11-18/1三种发射药的点火性能。结果表明,NR11-18/1发射药较易点火,双芳-3-18/1发射药最难点火,点火时间分别为19和45ms。增加延迟点火部件后,可将点火药的燃烧和发射药的燃烧阶段有效区分,不仅有利于对比点火性能差异较小的发射药之间的区别,还有助于分析发射药低压段的燃烧速度。随着延迟点火部件长度的增加,点火时间也增长。     

Effect of Initial Oxide Layer on Ignition and Combustion of Boron Powder

Only few data exist for experimental studies on ignition and combustion of boron particles with initial oxide thickness. The oxidation, ignition and combustion characteristics including the onset temperatures, weight gain, apparent activation energy, emission spectra during combustion, and ignition delay time of crystalline boron powders with different initial oxide thickness (x₀) were studied by a laser ignition and thermogravimetric (TG) analyses. Simulations of the kinetics of oxide layer during boron ignition were conducted using a common model. The results indicated that the onset temperature was approximately 775 °C, independent of x₀. The total weight gain decreased with increasing x_0, whereas the weight gain at 775 °C did not change. The apparent activation energy was found to be insensitive to x₀ and had a constant value of about 210 kJ mol⁻¹. The intensity of the emission spectra gradually decreased while the ignition delay time increased with increasing x₀. Numerical simulation showed that the removal rate of oxide layer enhanced with increasing x₀. The experimental results revealed that the oxidation of boron powder was no diffusion‐controlled process at low temperatures. But the diffusion of oxygen could become important to the oxidation reaction at high temperatures     

Laser Ignition of Nano‐Composite Energetic Loose Powders

Laser ignition experiments were conducted to better understand parameters that influence ignition of energetic materials. A Nd:YAG laser (10 ms, 1.5 J, 3 mm spot diameter) was used to heat the top surface of an energetic powder composed of nanometric aluminum (Al) combined stoichiometrically with an oxidizer (copper oxide (CuO), iodine pentoxide (I₂O₅), polytetrafluoroethylene (C₂F₄), molybdenum trioxide (MoO₃) or iron oxide (Fe₂O₃)). Ignition delay time was calculated as the difference between first light of the laser’s flash lamp and the energetic material. Results show that laser energy required for ignition is dependent on pre‐ignition reactions, phase change/decomposition temperatures, confinement, and laser absorbance.     

Shock tube investigation of propane-air mixtures with a pilot diesel fuel or cotton methyl ester

The propane (or LPG) is one of the best candidates as an alternative fuel in dual-fuel engines which operate primarily on any type of gaseous fuel using pilot injection of diesel to achieve ignition. The ignition delay has received considerable attention in the published literature for various gaseous fuels using different dual-fuel engines which showed that the ignition delay in a dual-fuel engine is different from that in a diesel engine especially at low loads. In this research, the measurement of ignition delay of propane-air mixtures with a pilot diesel fuel or cotton methyl ester (CME) similar to mixtures used in dual-fuel engines have been performed in a shock tube. The operating conditions were the equivalence ratio ranging from 0.3 to 1.2, the initial pressure varied from 0.4 to 1.0 bar, the initial temperature varied from 423 to 673 K, the relative mass of pilot liquid fuel and the type of liquid fuel. The ignition-delay times were measured using a piezo-electric pressure transducer, charge amplifier, data acquisition card, PC computer and LabVIEW program. From the results, it is shown that, the minimum ignition-delay time for the dual-fuel combustion was observed at stoichiometric equivalence ratio for propane-air mixtures with a pilot diesel fuel or CME. Higher initial temperatures and pressures reduced the ignition delay. Also, the ignition delays of propane-air mixtures are affected by changes in pilot fuel quantities and properties.     

Investigation on the Reaction of Powdered Tin as a Metallic Fuel with Some Pyrotechnic Oxidizers

Thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC) have been used to examine the thermal behavior of Sn+KClO₃, Sn+KNO₃, and Sn+KClO₄ pyrotechnic systems and the results were compared with thermal characteristics of individual constituents. TG curves for tin powder, heated alone in air, showed a relatively slow oxidation above 570 °C. From thermal results the decomposition temperatures of KClO₃, KClO₄, and KNO₃, in nitrogen atmosphere, were measured at 472, 592 and 700 °C, respectively. For the Sn+KNO₃ pyrotechnic system, the tin oxidation was completed within the range of 480 to 500 °C. Replacing KNO₃ with KClO₄ led to an increase of thermal stability of the pyrotechnic mixture. Among above‐mentioned pyrotechnic mixtures, Sn+KClO₃ has the lowest ignition temperature at about 390 °C. The apparent activation energy (E), ΔG^#, ΔH^# and ΔS^# of the combustion processes were obtained from the DSC experiments. Based on these kinetic data and ignition temperatures, the relative reactivity of these mixtures was found to obey in the following order: Sn+KClO₃>Sn+KNO₃>Sn+KClO₄.     

Effects of octane number on autoignition and knocking phenomena in a stratified mixture

The effects of the fuel concentration gradient and the octane number on the autoignition and knocking phenomena in a stratified mixture were studied experimentally on a using a rapid compression machine using stratified mixtures of air and fuels n-heptane, iso-octane, n-hexane, and n-pentane with different octane numbers (0, 100, 25, and 62, respectively). In the chamber, the lower the vertical location, the richer the fuel concentration of the mixture. The mixture contains no gradient in the horizontal direction. The experimental results show that rapid spread of the flame is caused not by flame propagation but by sequential autoignition. Although ignition delays of a stratified mixture are not dependent on the fuel concentration gradient in the mixture, they are constant as long as mean equivalence ratio is the same, and they decrease with the decreasing mean equivalence ratio. In excess of certain gradient value, the knock intensity is smaller as the gradient becomes larger for all fuels tested regardless of their octane number. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 4, pp. 93–100, July–August, 2009.     

Laser Ignition of Pyrotechnics – Effects of Wavelength,Composition and Confinement

Ignition tests were carried out using three different laser systems and three different pyrotechnic compositions. Pyrotechnic materials investigated are: sulfur/charcoal/potassium nitrate based composition (gunpowder, GP), Shellac binder‐based boron/potassium nitrate composition (SR 44) and acaroid resin binder based magnesium/potassium nitrate composition (SR 371C). The laser sources were the multimode output from an Ar‐ion laser (λ=500 nm average), a high‐power commercial diode laser (λ=784 nm) and a small laser diode operating at around the same wavelength but controlled by a customized electronic circuitry. Lasers operating in the visible wavelength range provided more reproducible and quicker ignition than the infrared output from the diode lasers. It was found that unconfined gunpowder exhibits more reproducible ignition for both the visible and the infrared wavelengths compared to the other two compositions. The composition based on magnesium, SR 371C appeared to be very sensitive to laser intensity variations and gave erratic and therefore, irreproducible ignition delay times. The threshold laser energies to initiate reproducible ignition for the different wavelengths were measured and ignition maps were constructed. From these maps, the required laser power density for any value of the ignition delay time, i.e. laser energy density was determined. Tests were also conducted on gunpowder samples, partially confined in a modified pyrogen igniter capsule and a small laser diode. The diode was operated in single pulse mode using a current surge, which was much higher than the recommended value for CW operation. This provided ~1 W pulses at the end of a 1 mm diameter fiber optic cable and caused reproducible ignition in the semi‐confined pyrotechnic bed within the capsule. The threshold ignition energy under semi‐confined conditions was found to be substantially less than that required in the unconfined environment under similar experimental conditions.     

Mn+Sb2O3 Thermite/Intermetallic Delay Compositions

The binary Mn+Sb₂O₃ pyrotechnic composition was investigated for mining detonator time delay applications. EKVI thermodynamic modelling predicted two maxima in the adiabatic reaction temperature. The local maximum, at a manganese fuel content of ca. 36 wt‐%, corresponds to a pure thermite‐type redox reaction: 3 Mn+Sb₂O₃→3 MnO+2Sb. The overall maximum in the adiabatic reaction temperature (ca. 1640 K), at the fuel‐rich composition of 49 wt‐% Mn, is consistent with the reaction 5 Mn+Sb₂O₃→3 MnO+2 MnSb, i.e. a combination of the standard thermite with an additional exothermic intermetallic reaction. XRD analysis of combustion residues confirmed the formation of MnSb and Mn₂Sb for fuel‐rich compositions. Burn rates were measured using delay elements assembled into commercial detonators. The d₅₀ particle sizes were 23.4 and 0.92 μm for the Mn fuel and Sb₂O₃ oxidant powders, respectively. The delay elements comprised rolled lead tubes with a length of 44 mm and an outer diameter of 6.4 mm. The rolling action compacted the pyrotechnic compositions to 74 ± 2 % theoretical maximum density. The burning rate increased linearly from 4.2 to 9.4 mm s⁻¹ over the composition range 25–50 wt‐% Mn.