单滴燃料热壁蒸发、微爆与着火的实验研究

多组分燃料在热板的蒸发与着火规律与空间相比,具有一些新的特点,特别是乳化油的贴壁燃烧现象更有重要意义。本文通过实验将多组分与单组分的燃烧情况进行了对比研究。结果表明：（１）易挥发组分的着火延迟在较低的温度条件下长于不易挥发份,在较高温度时情况相反。混合物则居于其中;（２）对于含水的乳化油,燃烧与微爆发生先后同的外界条件有关,其着火过程极为迅速。（３）乳化油中易挥发燃料含量较高,环境温度也较高时,微爆滞后很明显。     

弱浮力下导线绝缘层着火先期特性的研究

本文在低压弱浮力环境中模拟了微重力过载电流时导线绝缘层的着火先期过程,研究了压力对绝缘层着火先期特性的影响。结果表明,2 A时,绝缘层的温升率和最终平衡温度随压力降低而不断增大,模拟出了微重力下绝缘层的温升特性;10 A时,随着压力降低,绝缘层存在三种破坏机制;在不同区域压力对着火延迟时间的影响不同。最后,提高环境氧气浓度修正了低压对化学反应速率的抑制。结果表明,当压力在一定范围内降低时,随着氧气浓度的提高,绝缘层的着火极限范围拓宽,着火延迟时间缩短,可以初步模拟微重力下绝缘层的着火先期过程。     

不同重力环境下辐射加热材料表面着火特性分析

研究外界辐射加热下，不同重力环境中热薄燃料的着火特性．探讨了重力、环境氧浓度、环境压力及外界辐射强度对着火的影响．结果表明，随着重力的变化，存在不同的着火机制．在微重力和在高的环境氧浓度中，材料的着火延迟时间变短．压力减小，着火延迟时间增大．随着辐射强度的增大，着火延迟时间变小．     

利用OH自由基特征发射谱测量正庚烷的点火延迟时间

在化学激波管中利用反射激波进行点火,采用OH自由基在306.4nm处特征发射谱线强度的急剧变化标志燃料的着火,由光谱单色仪、光电倍增管、压力传感器和示波器组成测量系统,测量了正庚烷/氧气的点火延迟时间,点火压力(1.0±0.1)和(0.75±0.05)atm,点火温度1 170～1 730K,当量比1.0,得到了在此实验条件下正庚烷/氧气点火延迟时间随温度变化的关系式。研究结果表明正庚烷/氧气点火延迟时间随温度的增加呈指数减小,点火压力为0.75atm时,随着点火温度的增加,点火延迟时间的变化率要小于1.0atm条件时。实验结果为建立正庚烷燃烧反应动力学模型,验证正庚烷燃烧反应机理提供了实验依据。     

乙烯着火延迟的激波管测量与分子碰撞理论分析

在75%和96%两个不同的稀释度下,测量了乙烯/氧气/氩气混合气的着火延迟时间,实验当量比为1,压力为1.3-3.0 atm,温度为1092-1743 K.实验结果表明,着火延迟时间的对数与温度倒数呈良好的线性关系,在两个稀释度下,着火延迟时间随着温度增加而减少.通过回归分析,得到了乙烯着火关联式.计算得乙烯着火延迟在96%稀释度时是75%稀释度的5倍.采用分子硬球碰撞模型,计算了不同稀释度下,乙烯与氧分子的碰撞次数,在96%稀释度下,乙烯与氧气分子碰撞次数为1.53×10²⁹/（s·cm³）,而在75%稀释度下,该碰撞次数增加为5.99×10³⁰/（s·cm³）,约为前者40倍,而着火延迟时间的差异在两条件下仅为5倍的关系,可能由于位阻因子的影响所致.     

单颗粒无烟煤着火特性典型影响因素研究

为理解不同典型参数对无烟煤着火特性的影响,本文建立了单颗粒煤粉着火模型。基于主要的总包非均相反应和气相反应及相应的对流和传热传质规律,模拟O_2/N_2燃烧方式下煤粉颗粒的着火过程,研究了不同的气流温度、O_2浓度、对流条件等关键因素对无烟煤颗粒着火的影响特征,结果表明气流温度增加时煤粉颗粒着火延迟时间在不同对流条件下普遍变短,且温度较高时着火延迟时间对对流强度变化的响应有所减弱;在相同气流温度和O_2浓度条件下,气流对流强度处于较低水平时,其变化对着火延迟时间的影响相对明显;当气流的温度和对流条件一定时,O_2浓度增加则着火延迟时间变短,但影响较小。模型得到文献数据的有效检验。     

进气加入CO2对直喷式柴油机燃烧的影响

在直喷式柴油机上研究了进气加入CO2气体对其燃烧特性以及发动机性能和排放品质的影响.研究结果表明,进气加入CO2,柴油机的混合气形成过程几乎不受CO2气体加入量的影响,主要反映在着火延迟期随着CO2加入量的增加而变长,燃烧持续期缩短,燃烧最高温度降低.同时导致柴油机的最大爆发压力和压力升高率降低,并且其出现的位置后移,充气效率下降,排气温度上升.加入CO2后,NOx排放有较大下降,HC、CO稍有增加,烟度受到的影响不大.     

激光触发伪火花开关的研究

通过等离子体建模仿真及物理实验结合的方式验证了激光触发伪火花开关的可行性。分别使用波长266 nm和532 nm的激光,对激光触发伪火花开关的最低激光触发能量、阳极着火延迟时间和时间跳动三项参数进行测试。在非聚焦模式下,仅调整激光能量,测得开关在波长266 nm激光触发下,最低触发能量为15 mJ,该触发能量下,阳极着火延迟时间约为340 ns,时间跳动约为40 ns;在波长532 nm激光触发下,最低触发能量为83 mJ,该触发能量下,阳极着火延迟时间约为420 ns,时间跳动约为60 ns。在维持实验平台不变的情况下,仅对入射激光进行聚焦,测得波长266 nm激光触发下,最低触发能量为4 mJ,当触发能量8 mJ时,阳极着火延迟时间190 ns,开关时间跳动小于1 ns;波长532 nm激光触发下,最低触发能量为6 mJ,当激光触发能量为8 mJ时,阳极着火延迟时间240 ns,开关时间跳动小于1 ns。     

直接数值模拟浓度和温度分层下庚烷的点火

使用二维直接数值模拟方法研究HCCI发动机条件下浓度和温度不均匀性对庚烷点火过程的影响。计算中考虑了详细的组分输运过程、活塞运动带来的气体压缩效应以及简化的庚烷化学动力学机理。二维直接数值模拟展示了燃料的负温度系数(NTC)特性对点火过程的影响,结果表明浓度分层增加使得第二阶段点火延迟时间缩短;温度分层增加,点火延迟时间增加,与具有单一阶段点火特性的燃料相反。之后使用相同DNS程序计算了一维算例,发现初始温度在NTC以内,并且温度与浓度不相关时,浓度分层对点火过程起主导作用,浓度高温度较低的区域先着火;初始温度在NTC以外,并且温度与浓度负相关时,存在一个最容易着火的区域:浓度和温度都较高的地方先点火。     

废气再循环和添加剂对高辛烷值燃料HCCI燃烧的影响

本文对废气再循环(EGR)和十六烷值改进荆-过氧化二叔丁基(DTBP)对高辛烷值燃料HCCI燃烧的影响进行了研究。实验结果表明:辛烷值为90的燃料(RON90)只能在高温高负荷下才能运行HCCI燃烧模式;在其中加入少量的DTBP后,RON90实现HCCI燃烧的工况范围向低温低负荷下大幅度拓展。加入添加剂后,低负荷性能改善的同时,浓混合气的着火时刻可以通过EGR将含添加剂燃料的着火时刻推迟到上止点附近,从而大幅度提高热效率,降低了燃料消耗率。     

Evolution of temperature of a droplet of liquid composite fuel interacting with heated airflow

The macroscopic patterns of a temperature change at the center of a droplet of three-component (coal, water, petroleum) composite liquid fuel (CLF) were studied using a low-inertia thermoelectric converter and system of high-speed (up to 10⁵ frames per second) video recording during the induction period at different heating intensity by the air flow with variable parameters: temperature of 670?870 K and motion velocity of 1?4 m/s. The studies were carried out for two groups of CLF compositions: fuel based on brown coal and coal cleaning rejects (filter cake). To assess the effect of liquid combustible component of CLF on characteristics of the ignition process, the corresponding composition of two-component coal-water fuel (CWF) was studied. The stages of inert heating of CLF and CWF droplets with characteristic size corresponding to radius of 0.75?1.5 mm, evaporation of moisture and liquid oil (for CLF), thermal decomposition of the organic part of coal, gas mixture ignition, and carbon burnout were identified. Regularities of changes in the temperature of CLF and CWF droplets at each of identified stages were identified for the cooccurrence of phase transitions and chemical reactions. Comparative analysis of the times of ignition delay and complete combustion of the droplets of examined fuel compositions was performed with varying droplet dimensions, temperatures, and oxidant flow velocity.     

催化着火的实验研究

本文就CH4-水蒸气以及正庚烷或正十二烷-水蒸气的催化重整反应对燃料与空气预混气的着大影响进行了几种不同工况的实验研究,并与纯燃料气（CH4气、正庚烷或正十二烷蒸气）和空气的预混气的着火进行对比．实验结果表明,在催化剂的作用下,烃类燃料气和水蒸气能在200～500℃的较低温度下进行重整反应,产生部分H2和CO。少量H2的存在大大降低了预混气的着火温度。若将这种催化剂用于柴油机汽缸壁,则可望使柴油机中的乳化油在汽缸壁上生成部分H2,因此可能在掺水量加大的条件下,仍然能实现汽缸中的正常燃烧,这不仅使乳化油在柴油机中的应用成为可能,而且将显著地改善柴油机的排放性能和节能效果．     

The influence of radiative-convective heat transfer on ignition of the drops of coal-water fuel

Simulation results are presented for thermal treatment and ignition of coal-water fuel drops under conditions of radiative-convective heating. The data demonstrate reasonbble compliance between theory and experiment for the integral parameter of ignition process — the delay time of ignition. The radiative component of heat transfer is significant for parameters and conditions of ignition. The increase in the fuel particle size makes this influence bigger. Prognostic potential was evaluated for differnet models of radiative heat tarnsfer. The delay time of ignition obtained from radiative heat transfer model “grey wall” is in good agreement with experimental data. Meanwhile, the method based on radiation diffusion approximation gives the simulation data for delay time much higher than experimental data. It is confirmed that while the process of inflammation of a coal-water particle, the key impotance belongs not to fuel-oxidizer reactions, but rather to a chain of heat treatment events, such as radiative-convective heating, water evaporation, and thermal decomposition of fuel.     

Ignition of a floating droplet of organic coal–water fuel

The results of experimental investigations are presented for the ignition of droplets (particles) of organic coal–water fuels (OCWFs) floating in a flow of an oxidizer using a special combustion chamber from high-temperature quartz glass. The temperature and the velocity of motion of the oxidizer vary in the ranges of 500–900 K and 0.5–3 m/s. The initial sizes (radii) of fuel droplets amounted to 0.3–1.5 mm. As the basic OCWF components, particles (of 80–100 µm in size) of brown coal “B2,” water, mazut, and waste castor and compressor oils are used. With use of the system of high-velocity video registration, the conditions providing for floating of OCWF particles without initiation of burning and with the subsequent steady ignition are established. Four modes of OCWF-droplet ignition with different trajectories of their motion in the combustion chamber are singled out. The times of the OCWF-ignition delay in dependence on the size of fuel particles and oxidizer temperatures are determined. The deviations of the OCWF-ignition-delay times obtained under conditions of suspension of a droplet on the thermocouple junction and while floating in the oxidizer flow are established.     

Ignition and combustion of a falling, single sodium droplet

Ignition and combustion of a single sodium droplet has been studied experimentally, by use of a falling droplet. It is found that the ignition delay time increases first gradually and then rapidly, with decreasing initial temperature and/or oxygen concentration, and reaches the limit of ignitability, because of the suppression of surface reaction in the ignition stage. It is also found that with decreasing droplet diameter, the ignition delay time first decreases gradually, because of the decrease in the droplet mass to be heated, and then increases steeply, because of the enhancement of heat loss from the droplet surface. As for the effect of the relative speed, it is found that the ignition delay time increases with increasing relative speed, because of the enhanced heat loss. Experimental comparisons with the analytical results have also been conducted to elucidate dominant parameters, and it is confirmed that a set of comprehensive parameters in the literature can be useful in correlating dominant parameters that influence the ignition delay and/or the limit of ignitability. Furthermore, the analysis has been extended to determine the critical size for the ignition and that for the minimum ignition delay time. Combustion behavior after the ignition has also been examined, and it is found that d²-law can hold for the sodium droplet combustion. In addition, it is found that the burning rate-constant without forced convection has nearly the same value as those for usual hydrocarbon droplets, while the sodium combustion in air is quite similar to that of the usual hydrocarbon fuel in an oxidizer-rich environment.     

Promotion of the self-ignition of fuel–air mixtures with mechanoactivated Al (Mg)–MoO<Subscript>3</Subscript> particles

The ignition delay times of heptane–air and diesel oil–air mixtures with and without additives of mechanoactivated Mg–MoO³, Al–MoO³, and Mg–fluoroplastic nanopowders are measured using a rapid-mixture-injection setup. At temperatures below a certain threshold value, the metal–MoO³ additives produce practically no effect on the ignition delay time, whereas at higher temperatures, these additives sharply reduce the ignition delay time, down to the resolution time of the experimental method. The promoting efficiency of the small heterogeneous additives tested is many times superior to that of the known homogeneous promoters. Magnesium–fluoroplastic additives are demonstrated to produce no promoting effect on the ignition of the fuel–air mixtures studied. The mechanism of the action of the heterogeneous additives on the gasphase self-ignition of fuels is discussed.     

多组份混合燃料滴着火规律的研究

1前言多组份燃料滴的着火研究有很重要的实际与理论意义。人们在实际中使用的传统液体燃料通常都是由多种分子结构、沸点等技术指标相差较大的组份混合而成的，另外，人们在实践中发现使用一些混合燃料如油一酒精，油一甲醇，重油一轻油以及油水乳化液等，可以改善蒸发过程，改善气相反应的化学特性。这就使得混合燃料具有改善内燃机工况及减少污染物排放的潜在优点。所以多组份燃料滴着火燃烧的研究更有意义。多种组份液滴的蒸发、着火比单组份液滴更为复杂，不同点主要集中在以下三个方面：（1）液滴内热量与组份的输运过程更为复杂；（2…     

Numerical investigation of pulverized coal particle group combustion using tabulated chemistry

The ignition and combustion of coal particle groups are investigated numerically in a laminar flow reactor. The Flamelet Generated Manifold method is extended to account for the complex mixture of gases being released during devolatilization, which is calculated with a competing two-step model. A second mixture fraction is introduced to include the mixing with the second methane fuel stream. The interactions of the gas phase with particles are modeled within a fully coupled Euler-Lagrange framework. To investigate the influence of particle groups on ignition and combustion, successively increasing densities of particle streams have been analyzed. The ignition delay time is increased significantly by higher particle densities. This delay is validated successfully with the available measurements. Moreover, the shape of the volatile flame was found to be strongly influenced by the particle number density inside the flame. A transition from spherical flames around single particles to a conical flame around the particle cloud could be found in numerical results as well as in experiments. As the primary mechanism for the substantial ignition delay and the formation of the flame, the increased heat transfer from the gas-phase to the particle group, resulting in lower gas-phase temperatures, was identified.