生物柴油的酯类组成和理化特性对燃烧温度的影响

利用色谱-质谱联用仪测量了生物柴油的酯类组成,分析了燃料的密度、运动粘度、元素组成、弹性模量、碘值、氧化安定性等理化特性对燃烧温度的影响.结果表明:生物柴油中含有大量的不饱和脂肪酸甲酯,主要是油酸甲酯、亚油酸甲酯和棕榈酸甲酯;生物柴油较大的密度、较高的含氧量和碘值、较大的弹性模量、含有较长的碳链、较差的氧化安定性、存在双键且双键位置偏向分子中间会导致燃烧温度升高,而较大的运动粘度会使燃烧温度降低.     

燃料理化特性对柴油机燃烧和排放影响

将燃料理化特性参数依次分离,研究不同燃料特性在宽广废气再循环(EGR)范围内对柴油机燃烧和排放的影响规律.结果表明:试验选用的国Ⅳ柴油燃料,成份的改变如芳烃和硫含量降低对燃烧和NO_x、THC、CO及碳烟排放影响作用很小.燃料沸点和黏度降低,预混放热峰值增大,碳烟排放降低;负荷增大后对碳烟降低作用减小.燃料沸点和黏度在中、低比例EGR率下对气体排放影响很小,在高比例EGR率下低沸点、低黏度燃料THC和CO排放较高.十六烷值是决定燃烧放热时刻的最重要参数,不同十六烷值燃料在高比例EGR率下对滞燃期影响更显著.十六烷值和含氧是降低碳烟两个决定性因素,孰重孰轻视燃料特性而定,不同十六烷值燃料的气体排放差异很小,只在低EGR率下随十六烷值降低,NO_x排放略有升高.正丁醇分子结构较甲醇、乙醇、丁酸甲酯和2,5-二甲基呋喃(DMF)能更有效降低碳烟.     

单酯类燃料组成与结构对燃料特性的影响

生物柴油是一种可再生的国产绿色替代能源，来自于植物油单酯衍生物。脂肪酸酯作为发动机燃料的可行性来自于其分子结构和较高的能量密度。燃料的热值主要取决于燃料中C、H、O等元素的质量分数。作为柴油的品质参数之一，十六烷值同样适用于替代燃料生物柴油。脂肪酸链中的不饱和键是导致CN下降的最重要因素。不饱和键的数目及位置对燃料特性参数CN、IV、低温流动性和氧化安定性等都具有重要的影响。     

燃料理化特性对柴油机低温燃烧过程及排放特性的影响

在一台单缸柴油机上,通过柴油掺混20%的正庚烷、正庚烷与异辛烷混合物以及异辛烷与40%正庚烷(体积分数),研究燃料组分、沸点和十六烷值等理化特性对柴油机传统燃烧和低温燃烧影响机理.结果表明,不同十六烷值燃料在高比例EGR下对滞燃期影响更显著;随掺混燃料十六烷值降低,碳烟排放降低;在20%掺混比下混合燃料沸点、黏度等物理特性和燃料组分等化学特性改变对燃烧和碳烟排放影响较小.与20%正庚烷掺混相比,低沸点、低黏度燃料在更高掺混比(40%)下对碳烟排放的降低作用变得明显.大比例EGR低温燃烧下,THC排放明显升高,其中甲烷占总碳氢比例达60%;NO2对整体NOx排放影响很小.在20%掺混比下,燃料理化特性的改变对THC、不同成分HC、CO和NOx排放影响很小;在40%正庚烷掺混比例下,芳香烃排放降低,NOx及NO2排放较柴油升高.     

加氢催化生物柴油对GCI发动机燃烧与排放影响

汽油压燃(GCI)发动机具有较高的热效率及较低的排放,但使用商用高辛烷值汽油存在低负荷工况下着火困难、燃烧稳定性差的难题.将高十六烷值的加氢催化生物柴油(HCB)按照不同体积比例添加到95号汽油中,通过一台共轨单缸柴油机,研究在小负荷工况下加氢催化生物柴油体积分数对发动机燃烧与排放特性的影响.结果表明:随着加氢催化生物柴油体积分数的增加,燃料的着火性能显著改善,有效降低燃烧爆压.同时,不同活性燃料的掺混比例应与运行工况匹配才能获得较为合适的燃烧相位,进而提高发动机性能.排放方面,掺混燃料在降低颗粒物排放方面有着巨大的潜力,随着生物柴油体积分数的增加,虽然颗粒物排放有所增加,但可以有效地降低CO及未燃碳氢化合物(UHC)排放.掺混燃料中生物柴油掺混比例对NO_x排放的影响在不同负荷下表现出不同的趋势.     

正丁醇燃料特性对柴油机低温燃烧影响的机理

在一台单缸柴油机上,将20%体积分数的正庚烷、异辛烷和正丁醇分别与柴油进行掺混燃烧,研究了正丁醇沸点、燃料组分、十六烷值和含氧特性等理化特性对柴油机低温燃烧(LTC)的影响机理.结果表明,十六烷值是影响LTC燃烧特性的主导参数,柴油+正庚烷和柴油+异辛烷的燃烧特性分别与纯柴油和柴油+正丁醇接近.碳烟排放上,柴油+正庚烷与纯柴油差别很小,表明在20%掺混条件下,物理特性和燃料组分对LTC碳烟排放影响较小;柴油+异辛烷的碳烟排放较纯柴油降低明显,表明十六烷值是影响LTC碳烟排放的重要因素;柴油+正丁醇的碳烟排放比柴油+异辛烷有较大降低,表明正丁醇含氧特性对改善LTC碳烟排放具有重要作用.燃料理化特性对NOx、CO和HC等气体污染物排放影响较小.     

生物柴油氧化安定性研究的新进展

作为石化柴油的替代燃料,生物柴油在世界范围内得到广泛应用。氧化安定性是生物柴油在贮存和使用过程中面临的技术难题之一,因此氧化安定性是生物柴油研究必须关注的重要质量指标。文章对生物柴油氧化安定性的影响因素、生物柴油氧化机理、生物柴油氧化安定性的标准评价方法的最新进展等方面作了综述,并对我国生物柴油氧化安定性的标准评价方法的建立提出了建议。     

生物柴油氧化改质对NOx和碳烟排放的影响

在一台共轨柴油机上,测量燃用氧化改质处理前后的生物柴油的排放污染物.通过气相.质谱联用仪,测量并分析改质前后油品组分变化.分析含氧燃料的热力NOx形成理论,提出了燃料化学结构决定柴油机排放污染物生成的观点.研究结果表明,生物柴油经氧化改质后,部分脂肪酸甲酯碳链中的双键被破坏,增加了环氧基或双羟基,含氧量和饱和度增加.改质处理抑制了生物柴油自身的氧化,避免了酸败和黏度增加.改质后生物柴油NOx和碳烟排放同时降低,改变了传统柴油机NOx和碳烟排放存在的互为消长关系.     

柴油燃料特性对重型柴油机燃烧和排放影响的试验

在一台电控高压共轨重型柴油机上,选择5种不同十六烷值(CN)柴油(CN为29、40、44、53和62)进行欧洲稳态测试循环(ESC)测试.结果表明:在25%,负荷下,燃烧放热始点随十六烷值降低而推迟,最大爆发压力和最大压升率明显增大;负荷增大后,十六烷值对放热始点影响变小,在75%,和100%,负荷下,只有CN为29的燃料放热时刻推迟,其余4种燃料缸内压力和放热规律受十六烷值影响很小.随十六烷值降低,有效燃油消耗率增大,但不同燃料有效热效率差异很小,因而低十六烷值燃料较高的燃油消耗是由其较低的热值造成的.随十六烷值降低,NO_x、soot、HC和CO排放增大,在小负荷工况,十六烷值变化对排放影响更显著.ESC十三工况加权结果表明,CN从62减到29,有效燃油消耗率增加5.6%,,NO_x排放增加23%,,soot排放增加300%,,HC和CO排放增加50%,.     

直喷式柴油机燃用不同燃料时的工作稳定性与燃烧特性

本文介绍了在一台直喷式柴油机上利用电火花助燃,燃用甲醇、乙醇、汽油等低十六烷值燃料的研究状况。详细分析与比较了发动机燃用上述三种燃料和柴油的着火特性、放热率、循环压力变动、NO_x排放、热效率等燃烧特性参数。     

Catalytic production of biodiesel from soy-bean oil, used frying oil and tallow

Three fatty materials, soy-bean oil, used frying oil and tallow, were transformed into two different types of biodiesel, by transesterification and amidation reactions with methanol and diethylamine respectively. The ignition properties of these types of biodiesel were evaluated calculating the cetane index of the transesterification products, and the blending cetane number of the amide biodiesel blended with conventional diesel. Amide biodiesel enhances the ignition properties of the petrochemical diesel fuel, and it could account for the 5% market share that should be secured to biofuels by 2005.     

Fuel properties of biodiesel from vegetable oils and oil mixtures. Influence of methyl esters distribution

In this work, the quality of biodiesel produced by basic transesterification from several vegetable oils (soybean, rapeseed, sunflower, high oleic sunflower, Cynara Cardunculus L., Brassica Carinata and Jatropha Curca) cultivated in Extremadura has been studied in detail. The influence of raw material composition on properties such as density, viscosity, cetane number, higher heating value, iodine and saponification values and cold filter plugging point has been verified. Other biodiesel properties such as acid value, water content and flash and combustion points were more dependent on characteristics of production process. Biodiesel produced by rapeseed, sunflower and high oleic sunflower oils transesterification have been biofuels with better properties according to Norm EN 14214. Finally, it has been tested that it is possible to use oils mixtures in biodiesel production in order to improve the biodiesel quality. In addition, with the same process conditions and knowing properties of biodiesel from pure oils; for biodiesel from oils mixtures, its methyl esters content, and therefore properties dependent this content can be predicted from a simple mathematical equation proposed in this work.     

Assessment of tree seed oil biodiesel: A comparative review based on biodiesel of a locally available tree seed

The present investigation is undertaken to investigate prospect of seeds of a locally available tree (koroch) for biodiesel production. The middle-size, evergreen koroch tree with spreading branches are available in Assam. The characteristics of koroch biodiesel and engine performance fueled by koroch biodiesel are also analyzed reviewing similar results available in the literature so as to ascertain its status. Twelve number of different tree seed oils, reported earlier, are considered for making the present comparative assessment. Though transesterification has been the common process for converting tree seed oil into biodiesel, as evidenced from the literature consulted in this study, but there have been variations of the chemical processes. Variations of the transesterification are attributed to (i) types of catalysis viz., acid (H₂SO₄) or base (KOH, NaOH, and NaOCH₃), (ii) reaction temperature, (iii) molar ratio, (iv) nature of reaction viz., single stage or multi-stage. The outputs of the reaction have also been found varying in terms of yield as well as quality. Quality of biodiesel, however, was found to influence by the nature of feedstock. The assessment of quality parameters was made either by ASTM D 6751 or EN 14214 standards. The major fuel properties such as calorific value, kinematic viscosity, cetane number and cloud point of the reference biodiesel (koroch biodiesel) are compared with the properties of five biodiesel obtained from non-edible tree seed (karanja, mahua, polonga, jatropha and rubber seed) and then ranked them in order of desirable property. No single biodiesel type could be found at top rank with reference to more than one property. With regards to viscosity, except rubber seed biodiesel, all other biodiesels (karanja, mahua, polonga, jatropha and koroch) fulfilled the ASTM D 6751 (1.9-6 cSt) as well as EN14214 (3.5-5) standards. Koroch biodiesel ranks 3rd, 3rd and 6th in case of kinematic viscosity, cetane number and calorific value amongst the biodiesel types considered for the present study. Cloud point of koroch, polanga, mahua, rubber, karanja and jatropha biodiesels are 4, 13.2, 5, 4, 12 and 4 °C. Further, properties of biodiesel were found to have influencing correlation with the fatty acid characteristics of the feedstock. Therefore, biodiesel with desirable properties could be expected form optimum mixing of different feedstock.Eleven number of different engine performance results pertaining to uses of biodiesel are also reviewed in this paper. Varying test conditions with reference to fuel types and blends, engine size and loading pattern are discussed. Engine performance results of koroch biodiesel were then compared with five similar tree-based biodiesel. It is observed that tree seed oil with more unsaturated fatty acids exhibits lower thermal efficiency compared to biodiesel having more saturated acids.     

车用典型生物燃料的组分及理化特性对比研究

基于特定的原材料和典型的制备工艺,选取废弃油脂生物柴油（WME）、麻风树果生物柴油（JME）和生物裂解燃油（PBF）作为典型的生物燃料,与在用的国Ⅴ标准0^# 石化柴油（PD）进行组分分子结构及组分含量的对比。GC-MS分析结果表明,生物柴油分子碳链长度集中于C₁₆ ~ C₁₈,且不饱和组分含量较高,生物裂解油组分分子碳链长度较为分散,短链组分明显增加,不饱和组分明显降低。四种燃料的理化特性对比分析结果表明,分子碳链长度及不饱和度对燃油的粘度、十六烷值（CN）以及热值等产生综合影响,三种典型生物燃料特别是生物裂解油对石化柴油有着良好的替代性。     

Characterization and transesterification of Iranian bitter almond oil for biodiesel production

In the present work the production of biodiesel using bitter almond oil (BAO) in a potassium hydroxide catalyzed transesterification reaction was investigated. The BAO was obtained from resources available in Iran and its physical and chemical properties including iodine value, acid value, density, kinematic viscosity, fatty acid composition and mean molecular weight were specified. The low acid value of BAO (0.24 mg KOH/g) indicated that the pretreatment of raw oil with acid was not required. The fatty acid content analysis confirmed that the contribution of unsaturated fatty acids in the BAO is high (84.7 wt.%). Effect of different parameters including methanol to oil molar ratio (3–11 mol/mol), potassium hydroxide concentration (0.1–1.7% w/w) and reaction temperature (30–70 °C) on the production of biodiesel were investigated. The results indicated that these parameters were important factors affecting the tranesterification reaction. The fuel properties of biodiesel including iodine value, acid value, density, kinematic viscosity, saponification value, cetane number, flash point, cloud point, pour point and distillation characteristics were measured. The properties were compared with those of petroleum diesel, EN 14214 and ASTM 6751 biodiesel standards and an acceptable agreement was observed.     

Correlation for the estimation of the cetane number of biodiesel fuels and implications on the iodine number

Some European experts on normalization of transport fuels have recently suggested the suppression of the cetane-number limitation from the European biodiesel norm when its final destination is blending with diesel fuel. Although this measure should not affect the range of oils used for biodiesel production (only few of them lead to biodiesel fuels with cetane numbers below this limit), the trend of cetane number to decrease with increasing unsaturation could reinforce the arguments to maintain the iodine-number limitation as an indirect limit for the cetane number.The iodine number has frequently been subjected to controversy because its stringent limitation in Europe prevents from using differently unsaturated fatty oils for biodiesel production. Some of the arguments in favour of extending or eliminating the iodine-number limitation in the norm are exposed here. Previously, a correlation for the estimation of the cetane number based on a literature review is proposed. From this correlation, a procedure is proposed for the estimation of the limiting effect of the current cetane-number limitation on the unsaturation degree of biodiesel fuels. Finally, the impact of the elimination of the cetane-number limitation on the use of different oils for biodiesel production is analyzed.     

Combustion performance and emission reduction characteristics of automotive DME engine system

This article is a condensed overview of a dimethyl ether (DME) fuel application for a compression ignition diesel engine. In this review article, the spray, atomization, combustion and exhaust emissions characteristics from a DME-fueled engine are described, as well as the fundamental fuel properties including the vapor pressure, kinematic viscosity, cetane number, and the bulk modulus. DME fuel exists as gas phase at atmospheric state and it must be pressurized to supply the liquid DME to fuel injection system. In addition, DME-fueled engine needs the modification of fuel supply and injection system because the low viscosity of DME caused the leakage. Different fuel properties such as low density, viscosity and higher vapor pressure compared to diesel fuel induced the shorter spray tip penetration, wider cone angle, and smaller droplet size than diesel fuel. The ignition of DME fuel in combustion chamber starts in advance compared to diesel or biodiesel fueled compression ignition engine due to higher cetane number than diesel and biodiesel fuels. In addition, DME combustion is soot-free since it has no carbon–carbon bonds, and has lower HC and CO emissions than that of diesel combustion. The NO_x emission from DME-fueled combustion can be reduced by the application of EGR (exhaust gas recirculation). This article also describes various technologies to reduce NO_x emission from DME-fueled engines, such as the multiple injection strategy and premixed combustion. Finally, the development trends of DME-fueled vehicle are described with various experimental results and discussion for fuel properties, spray atomization characteristics, combustion performance, and exhaust emissions characteristics of DME fuel.     

Effect of ethanol addition on the properties of Jatropha ethyl ester

Fossil fuels are available in limited quantity and may extinct in future. Moreover, pollutant emission from diesel engines affects the ecological systems. Biodiesel, derived from vegetable oil, is a renewable and green source of fuel. In this study, biodiesel produced from base catalyzed transesterification was blended with different diesel volumes. The diesel–biodiesel blends showed varied flash point (168–42°C), viscosity (4.34–3.31 mm²/s), density (0.872–0.8351 g/cm³), acid value (0.3–0.4 mg KOH/g), and cetane number (51.6–49.5). The results showed that alcohol addition helped in reducing viscosity and density of biodiesel by almost half. These provide explanation on engine performance, combustion, and emission characteristics.     

Methyl ester of peanut (Arachis hypogea L.) seed oil as a potential feedstock for biodiesel production

The peanut (Arachis hypogea L.) seed oil was extracted from the seeds of the peanut that grows in SE Anatolia of Turkey. Oil was obtained in 50 wt/wt.%, by solvent extraction. Peanut (A. hypogea L.) seed oil was investigated as an alternative feedstock for the production of a biodiesel fuel. Biodiesel was prepared from peanut by transesterification of the crude oil with methanol in the presence of NaOH as catalyst. A maximum oil to ester conversion was 89%. The viscosity of biodiesel oil is nearer to that of petroleum diesel and the calorific value is about 6% less than that of diesel. Peanut seed oil have about 8.3% less heating value than that of diesel oil due to the oxygen content in their molecules. The quality of biodiesel is most important for engine part of view and various standards have been specified to check the quality. The important properties of peanut oil and its methyl ester (biodiesel) such as density, kinematic viscosity, flash point, iodine number, neutralization number, pour point, cloud point, cetane number are found out and compared to those of no. 2 petroleum diesel, ASTM and EN biodiesel standards. The comparison shows that the methyl ester has relatively closer fuel properties to diesel than that of raw peanut seed oil.     

Optimized production and advanced assessment of biodiesel: A review

Biodiesel production is profitable only under special conditions. Technical challenges including methods to make the transesterification reaction more energy efficient and faster by using catalysts, controlling reaction conditions more efficiently in narrow range, or selection of appropriate feedstocks should be properly addressed to make biodiesel economical viable fuel. Cradle to grave assessment of biodiesel is provided in the present review article. Transesterification reaction variables that affect the purity and performance of biodiesel including quality of raw materials, molar ratio of alcohol to oil, type and concentration of used catalysts, concentration of free fatty acids, water content, temperature, and time required for the reaction are critically described to provide complete understanding and obtaining economical and optimal biodiesel yields. This article also provides a critical review of biodiesel properties such as density, viscosity, cetane number, cloud point, pour point, and flash point. The importance of analytical methods including gas chromatography, high‐performance liquid chromatography, nuclear magnetic resonance spectroscopy, infrared spectroscopy, and Raman spectroscopy is presented and highlighted here in a novel way. Finally, this review will provide complete understanding to readers about biodiesel.