Prediction of micro-explosion delay of emulsified fuel droplets

Burning a water-in-oil emulsion enables reduction in solid and gaseous pollutants in comparison with neat oil. In the emulsion, Heavy Fuel-Oil and water lie in distinct phases, having a high difference in boiling point (up to 200 K). In an emulsion droplet injected and subsequently heated inside a flame, the internal water droplets are enclosed inside the emulsion and do not systematically vaporise at boiling point. They are known to reach a metastable state, breaking up at a temperature below the spinodal limit of water. From this moment, the surrounding Fuel-Oil is fragmented into numerous faster and smaller droplets by the suddenly expanding steam. This physical phenomenon is called “micro-explosion”. This work demonstrates a numerical modelisation of unsteady heat and mass transfer at the surface and inside of the emulsion droplet, and provides a prediction of its micro-explosion delay, using homogeneous nucleation hypothesis. This assumption of homogeneous nucleation for internal water droplets matches the use of a “drop tower” experimental facility. Finally, comparisons between predicted ranges for micro-explosion delays and experimental delays from literature are discussed, along with combustion parameters (ambient temperature, relative velocity) and combustible emulsion parameters. As a result, the experimental and numerical micro-explosion delays decrease with liquid or ambient temperature and relative velocity, and increase with water content and radius of emulsion droplet. Their low average deviation reveals the accuracy of the assumption of homogeneous nucleation in the considered situations.     

Study on the spray characteristics of methyl esters from waste cooking oil at elevated temperature

In Taiwan, millions of tons of waste cooking oil are produced each year, and less than 20% of it, about 150,000 ton/a, is reclaimed and reused. Most waste oil is flushed down the drain. Utilizing waste cooking oil to make biodiesel not only reduces engine exhaust gas pollution, but also replaces food-derived fuels, and reduces ecologic river pollution. This study employed two-stage transesterification to lower the high viscosity of waste oil, utilized emulsion to reduce the methyl ester NOx pollution, and used methanol to enhance the stability and viscosity of emulsified fuel. To further analyze spray characteristics of fuels, this experiment built a constant volume bomb under high temperature, used high speed photography to analyze spray tip penetration, spray angle, and the Sauter mean diameter (SMD) of fuel droplets, and compared the results with fossil diesel. The experimental results suggested that, two-stage transesterification can significantly lower waste oil viscosity to that which is close to fossil diesel viscosity. At a temperature above 300 °C, waste cooking oil methyl esters had a water content of 20%, spray droplet characteristics were significantly improved, and NOx emission dropped significantly. The optimal fuel ratio suggested in this experiment was waste cooking oil methyl ester 74.5%, methanol 5%, water 20%, and composite surfactant Span–Tween 0.5%.     

乳化燃料滴的蒸发与着火

本文研究了乳化燃料滴的着火现象，探讨了液相输运过程处于两种极限情况下着火延迟的变化规律。结果表明液相输运过程对乳化油的着火有决定作用。挂滴法的实验结果与凝固模型较接近，水分的加入使液滴表面温度，燃料浓度明显下降，从而使着火延迟时间变长。水分的加入对高沸点燃料着火的影响更为显著。     

乳化煤焦油作为锅炉燃料的初步研究

研究发现煤焦油在掺水乳化后具有良好的流动性、稳定性和燃烧特性。研究了煤焦油的性质及其乳化后的性质变化 ,尤其是粘度。并在工业燃油锅炉上进行燃烧试验 ,就锅炉效率及污染的排放与燃用重油进行对比 ,其结果表明乳化煤焦油代替重油作为燃料是可行的。     

Behaviour of a heavy fuel oil droplet on a hot surface

When heavy fuel oil sprayed in droplets burns in water heating boilers, there are cases when the zones of incomplete combustion are present. The volatile compounds and tar contained in the droplets burn out there and the carbon starts to accumulate on the pipes of the screen. Combustion of a fuel droplet on a solid surface is less investigated than that of the droplet falling down in hot air. In this work, the burnout of a droplet of a heavy fuel oil has been measured on a hot surface whose temperature varies in the interval from 400 to 700 °C. Times of evaporation of volatile compounds and burnout of the resulting carbon residue were measured. Changes of the form of the carbon residue depending on the surface temperature were recorded. Ceramic, quartz and stainless steel surfaces were used. The effect of surface roughness was additionally examined. In the case of a droplet of the heavy fuel oil dropped on a hot surface, heat transfer into the droplet is very sudden. The surface wetting condition is important, as it determines evaporation and boiling. Another difference from a freely falling droplet is oxidation of the pure coke because the oxygen diffusion is possible only from one side of the space.     

燃用乳化油柴油机排放特性的试验研究

本文建立在大量的试验基础上,对燃烧柴油加水乳化油和纯柴油作对比,在不同机型上测量其排气成分和烟度值,证明柴油机加水乳化油对于降低NOx和颗粒排放有明显的作用。     

乳化油在1135柴油机上的应用

乳化油作为一种代用燃料，既可以减少燃料消耗又可以控制排放，作者采用HLB值法筛选和复配乳化剂，在1135柴油机上进行了该乳化柴油的台架试验，结果表明该型乳化油与0＃柴油相比平均节同率不低于10％，主要排放物NOx、碳烟降低40％以上，同时排温和最高燃烧压力降低。还分析了影响乳化油燃烧效果的两个主要因素：含水率和喷油提前角。     

乳状液体系在油田中的应用综述

乳状液体系凭借其特殊的物理化学性能,在油田开发中得到广泛应用,形成了乳化钻井液、乳化酸、乳化压裂液、乳化稠油堵水剂、多重乳状液延缓交联、微乳液、乳化驱油等体系。其中,乳化钻井液体系具有井壁稳定性强、润滑性好和保护油层等优点。乳化酸适用于低渗透碳酸盐岩油气藏的深度酸化改造和强化增产作业,滤失量小,缓速性能好,能进入地层深部。乳化压裂液分为水包油型和油包水型两种,水包油型乳化压裂液具有比油包水型摩阻小、流变性便于调节、易返排等优点;油包水型乳化压裂液与油基冻胶压裂液相比,性价比高,适合于水敏性、低压、低渗储层的压裂改造,具有增黏能力强、黏度调节便利、高携砂、低滤失、低残渣等优点。乳化稠油堵水剂分为活性稠油堵水剂和水包稠油堵水剂,前者注入油井的堵剂为加有适量油包水乳化剂的高黏度稠油;后者是用水包油型乳化剂将稠油乳化在水中制成。乳状液可有效降低地层中的残余油含量,从而提高采收率。多重乳状液体系一般为W/O/W型,由于破乳时间较长,达到了延缓交联的目的;微乳液是指具有超低界面张力、热力学稳定的乳状液。三次采油中,在水中加入表面活性剂和部分高分子化合物,配成驱油溶液进行驱油,可显著提高原油采收率。     

乳化燃料油在船舶柴油机上的应用研究

为了实现乳化燃料油在船舶上的应用,研发了一套重油在线乳化装置,并在以G6300ZC18B型柴油机为动力的宁大6号运输船上进行实船试验.试验结果表明:当掺水率在16％-24％时,乳化质量好,可作为船舶燃料使用;乳化燃料油燃烧时,柴油机爆发压力在1 ～2 MPa间波动,排气温度平均下降12℃,冷却水出口温度略有下降,参数变化都处于正常范围内;平均节油率为9.7％,NOx、CO、碳烟排放平均分别降低19.6％、20％、35％.     

乳化柴油的应用研究

采用HLB值法进行筛选，复配出乳化效果和稳定性均较好的三种混合乳化剂。将乳化剂按1％、水20％掺入纯柴油，采用乳化剂在油中法，手工振荡制备出的油包水型乳化柴油，其稳定时间可达1个月。经过大量的台架试验表明：配制的乳化柴油与原纯柴油相比，平均节油率超过10％，主要排放物NOx降低超过10％、碳烟降低50％以上。     

废轮胎热解油特性及其燃烧应用

随着石油资源的日益枯竭及废轮胎数量的日益增多,利用废轮胎热解制取燃料油对缓解能源供应紧张局面,充分利用废弃资源都具有重要意义.废轮胎热解油具有热值高、灰分低、粘度低和残炭值低等优点,但也存在整体性能较柴油差的缺陷.与柴油混合作为发动机燃料使用的结果表明,废轮胎热解油可以作为重柴油使用;炉内燃烧试验表明.废轮胎热解油污染物排放量较柴油高.探索合适的废轮胎热解工艺,提高废轮胎热解油的品质,是将废轮胎热解油直接作为燃料油使用须研究的主要课题之一.     

稠油油泥混煤燃烧的掺混比例分析

稠油污水处理场的初沉池中,通常产生大量的高含水污泥,其主要是由原油、泥砂颗粒、水及少量化学药剂和部分工业杂质形成的混合物.稠油油泥成分复杂、处理难度大.对稠油油泥进行脱水并掺混一定比例的煤作为燃料,是一种有效的稠油油泥资源化利用和无害化处理方式.利用自制实验装置进行实验,考察了油泥、原煤掺混比例对燃烧烟气污染物和灰分中重金属含量的影响.结果表明:油泥与原煤按1∶3的掺混比例燃烧时的效果最佳,烟气中主要的污染物NOx、SO2以及CxHy平均含量为147 μL/L 、420μ L/L以及106μL/L,均符合国家排放标准;重金属Pb、Hg、Cr和非金属污染物As在稠油油泥燃烧后的灰分中的平均含量分别为2.75mg/kg、0.05mg/kg、91.5mg/kg和0.68mg/kg,也都符合国家排放标准.     

Performance and emission characteristics of a diesel engine operating on different water in diesel emulsion fuels: optimization using response surface methodology (RSM)

The nitrogen oxide (NO_x) release of diesel engines can be reduced using water in diesel emulsion fuel without any engine modification. In the present paper, different formulations of water in diesel emulsion fuels were prepared by ultrasonic irradiation. The water droplet size in the emulsion, polydisperisty index, and the stability of prepared fuel was examined, experimentally. Afterwards, the performance characteristics and exhaust emission of a single cylinder air-cooled diesel engine were investigated using different water in diesel emulsion fuels. The effect of water content (in the range of 5%–10% by volume), surfactant content (in the range of 0.5%–2% by volume), and hydrophilic-lipophilic balance (HLB) (in the range of 5–8) was examined using Box-Behnken design (BBD) as a subset of response surface methodology (RSM). Considering multi-objective optimization, the best formulation for the emulsion fuel was found to be 5% water, 2% surfactant, and HLB of 6.8. A comparison was made between the best emulsion fuel and the neat diesel fuel for engine performance and emission characteristics. A considerable decrease in the nitrogen oxide emission (–18.24%) was observed for the best emulsion fuel compared to neat diesel fuel.     

柴油乳化燃料的配制及应用

本文系统地介绍了柴油乳化燃料的配制设备、方法及其稳定性影响因素,其中阐明了除使用合适的乳化设备外,应用恰当的乳化方法,如混合膜生成法也可得到性能比较稳定的乳化燃料;利用配比合适的Ｓｐａｎ８０和Ｔｗｅｅｎ８０混合乳化剂可在油－水界面上形成络合物,使乳化液更趋稳定;乳化液两相密度差也是影响其稳定性的重要因素之一。文章最后对柴油乳化燃料的应用作了分类总结,指出柴油－甲醇(乙醇)－水复合乳化燃料和植物油燃料是代用燃料的今后发展趋势。     

柴油掺水乳化油雾化特性的研究

作者采用高速纹影摄影和同轴激光全息技术,在定容燃烧弹中,从宏观和微观两个角度研究了乳化油束的雾化特性.研究表明,乳化油的雾化特性比纯油好,特别是在高温环境下,乳化油束中发现了单个大油滴"伞状"破碎的雾化现象.作者认为,乳化油中的内相油—水界面的非连续性和高温时水分蒸发汽化对液滴产生的内部扰动,是改善乳化油雾化质量和发生"微爆"的主要因素.     

生物油/柴油乳化燃料的稳定性及理化性质

利用非离子表面活性剂复配,对热解生物油/柴油混合液进行一系列乳化实验,测量乳化油的密度、热值、pH值.以乳化油的稳定性为实验指标,研究乳化剂种类、乳化剂用量、生物油含量对乳化油稳定性的影响.实验结果表明:在乳化温度为40℃(水浴),乳化时间为30min的条件下,以2%用量的Span80和Tween80复配乳化剂乳化生物油含量为20%的生物油/柴油混合液效果最佳.另外,随着生物油含量的增加,乳化油密度逐渐增加,热值与pH值逐渐减小.     

生物质热解生物油与柴油乳化的试验研究

通过生物质热解生物油模型化合物与柴油乳化的研究确定了乳化剂合适的HLB范围,在该范围内稻壳热解生物油与柴油的乳化效果良好,同时研究了生物油贮存时间对乳化效果的影响。在柴油、乳化剂和生物油质量分数分别为92%、3%和5%,试验研究了不同种类生物质热解生物油与柴油的乳化性能,乳化燃料在热值上接近柴油,粘度符合国家轻柴油标准,具有商业应用的可能。最后通过生物油和柴油乳化的三组分相图分析了形成稳定乳液时三组分的相对含量变化。     

Factors affecting emissions from diesel fuel and water-in-diesel emulsion

The purpose of this research is to investigate the effect of addition of surfactant and water in diesel and to make an emulsified fuel considering the needs for vehicle performance and its cleanest possible operation. The total surfactant concentration in each of the diesel-water emulsion samples studied (span 20, span 80, tween 20, tween 80) is fixed at 1% w/w. The water content is variable at 5–15% w/w and the diesel content is varied from 84 to 94% w/w. Among all the tested nonionic surfactants, tween 80 is found to prominently reduce the carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx) emissions. Tween 20 reduced the NOx emission to a greater extent. Diesel emulsion with a fixed ratio of span 80 and tween 80 (1:1) efficiently reduced the overall emissions as compared to diesel alone. The developed diesel emulsion employed with nonionic surfactants clearly reduced the harmful engine emissions such as CO, HC, and NOx, signifying them as a future potential emulsifier in diesel fuel emulsion.     

Spray characteristics of emulsified castor biodiesel on engine emissions and deposit formation

Castor plants are a common wild poisonous plant in Asia, and especially a weed seen across Taiwan. Due to its high viscosity and water content, straight castor oil cannot be used as a fuel for DI engine. Transesterification and emulsion technologies have been utilized to improve the spray characteristics of castor oil. Without heat, the castor biodiesel (CBD) completes the transesterification reaction under ambient temperature. Gas chromatography indicates that the CBD yield rate is 97% or above. After long-term biodiesel generator test, the emulsified castor biodiesel (EBD) leads to the problem of engine deposition. Thus, this study aimed to investigate the EBD spray characteristics on DI engine emission and deposit formation. A constant-volume bomb was established to analyze the biodiesel spray characteristics under elevated temperature. A biofuel deposit simulator was developed to solve the EBD deposit problem. Thermal gravimetric analysis, Fourier transformation infrared spectroscopy, and scanning electron microscope were utilized to analyze the EBD deposit formation mechanisms. The experimental results indicated that biodiesel generator operated on EBD can improve the fossil diesel emissions. The high NO_X emission of CBD was solved by water-biodiesel emulsion technology. The biofuel deposit simulator provided some potential deposit control additives for EBD during the laboratory research stage. Without changing the engine structure, when the injection pressure was increased by 5–10%, the optimum combination was 82.8% of castor biodiesel, 15% of water, 2% of bioethanol, and 0.2% of composite surfactant Span-Tween.     

乳化重油含水量对锅炉NOx和SO2排放的影响

乳化重油是对节能和环保都具有重要意义的乳化状混合燃料，具有广泛的应用前景。本研究通过反应动力学模型计算了乳化重油燃烧过程中ＮＯＸ和ＳＯ２的形成规律，以及乳化重油含水量，炉膛空气过剩系数等因数对ＮＯＸ和ＳＯ２形成与排放的影响。