生物柴油燃料特性参数对NO_x排放影响的分析

分析了生物柴油的燃料特性及脂肪酸组成结构,结合发动机燃烧生物柴油的试验,分析了燃料的十六烷值、密度、运动黏度、氧化安定性、不饱和双键的数量和位置等因素对NO_x排放的影响;运用FIRE软件分别模拟了生物柴油与柴油燃烧时的温度场、氧浓度场、黏度场以及十六烷值对滞燃期的影响规律。结果表明:生物燃料较低的十六烷值、较大的密度和运动黏度、较差的氧化安定性、存在双键且双键位置偏向脂肪链中间等,均会导致生物柴油NO_x排放升高。提出了降低NO_x排放的方法。     

生物柴油颗粒表面含氧官能团及氧化活性研究

为研究生物柴油颗粒物表面含氧官能团相对含量与氧化活性的关系,在电控高压共轨柴油机上进行台架试验并采集颗粒物,分别利用X射线光电子能谱仪(XPS)和热重分析仪(TGA)对柴油、大豆油甲酯、棕榈油甲酯和地沟油甲酯颗粒物进行分析.结果发现:颗粒物表面主要为C元素与O元素,生物柴油颗粒物表面O元素与C元素的摩尔质量比n(O)/n(C)比柴油颗粒高40.4%～48.9%.生物柴油颗粒表面含氧官能团相对含量高于柴油颗粒,其中C—OH官能团相对含量变化更为明显,而C=O官能团相对含量在1%左右.相比于柴油颗粒,大豆油甲酯、棕榈油甲酯和地沟油甲酯颗粒的无序化程度(sp3/sp2)分别增加了54.5%、59.1%和68.2%,表观活化能分别降低了22.4%、23.2%和26.6%.生物柴油颗粒的起燃温度Ti、燃尽温度Te和氧化速率峰值温度Tp更低,颗粒物表面含氧官能团相对含量、无序化程度和氧化活性均随着生物柴油氧质量分数增加而增大,随着碘值增加而减小.     

基于光谱分析的大豆油生物柴油氧化机理研究

根据游离基氧化的相关理论,利用红外光谱和紫外光谱分析了大豆油生物柴油中不饱和脂肪酸甲酯分子在氧化过程中的构型变化,提出了不饱和脂肪酸甲酯分子中的双键在氧化过程中会发生顺-反异构化,以及由于双键转移而生成共轭双键的观点。     

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。     

生物柴油氧化降解与动力学分析的研究进展及展望

作为石化柴油的替代燃料,生物柴油在世界范围内已得到广泛的应用。生物柴油的性能主要取决于混合脂肪酸甲酯的组成和结构,脂肪酸甲酯的不饱和结构极易发生氧化反应,在氧化降解过程中生成氢过氧化物,以及可溶性聚合物等二级氧化产物,这不仅影响生物柴油的质量,而且还会带来车辆引擎腐蚀、油路阻塞和引擎功率不稳定等问题。文章综述了生物柴油氧化安定性、氧化降解机制以及热动力学分析的研究进展等方面,并对生物柴油氧化降解特性方面今后应重点研究的方向进行了探讨。     

高效改良剂助燃生物柴油

近日,由中国农科院油料所研发的生物柴油品质改良技术与多功能高效改良剂通过了有关鉴定。目前,我国以废弃油脂为原料生产的生物柴油原料成份复杂,成品油普遍存在两大品质问题,一是含有大量易氧化的不饱和双键,既降低燃烧热值,又产生酸性物质腐蚀发动机金属部件,同时产生的氧化物不能充分燃烧,产生黑烟,污染环境;     

压燃发动机燃用不同原料生物柴油的燃烧与排放特性

利用KIVA3数值模拟研究柴油以及三种生物柴油(大豆油甲酯、棕榈油甲酯、麻疯油甲酯)对压燃发动机燃烧和排放性能的影响。数值计算结果表明:生物柴油在燃烧初始阶段与柴油燃烧特性基本一致,燃烧中后期,生物柴油的平均缸温低于柴油,其中麻疯油甲酯最为明显;生物柴油碳烟和CO生成量明显低于柴油。生物柴油虽然缸内氧含量比柴油高,但由于受缸温的影响,NOx排放比柴油低,而麻疯油甲酯在三种生物柴油中NOx排放最低。     

生物柴油多环芳香烃形成的动力学模型

通过对癸酸甲酯化学动力学氧化机理与多环芳香烃(PAHs)生成机理的分析,构建了由713个基元反应和125种组分组成的生物柴油PAHs计算模型.研究了激波管条件下,生物柴油/氧气/氩气燃烧过程中苯环的产生过程、主要反应路径及变化规律.结果表明,该模型可以预测生物柴油燃烧过程中间产物浓度的变化规律;丙炔基(C3H3)对于PAHs第1个苯环的形成作用明显,脱氢加乙炔(HACA)反应和苯环间环化反应是形成两环和多环PAHs的主要路径;随着生物柴油和氧气的化学当量比的减小,PAHs生成量减少.     

后喷射策略下生物柴油对发动机燃烧和排放影响的数值模拟

以正庚烷-癸酸甲酯(MD)-癸烯酸甲酯(MD9D)简化机理为基础,构建了生物柴油(大豆生物柴油SME)-柴油混合燃料燃烧化学反应动力学机理。在单次喷射和主-后喷射两种喷油方式下,将大豆生物柴油、纯柴油以30∶70和70∶30体积比掺混,将该化学反应机理与CFD计算软件耦合,研究后喷策略下生物柴油-柴油混合燃料的低温燃烧特性和排放特性。数值计算结果表明:随着SME掺混比例增加,缸内燃烧温度峰值逐渐降低,缸内燃烧放热主要受OH自由基与燃料的脱氢反应速率影响,反应速率随温度升高而增大;NO_x排放随掺混比例增加而逐渐降低,NO_x排放主要受温度影响;单次喷射下,掺混比例越高,碳烟排放量越低;后喷射下,碳烟生成量受C_2H_2影响,随掺混比例增加而逐渐降低,OH在碳烟氧化过程中起主要作用,碳烟最终排放量受掺混比例影响不大。     

花生油及其生物柴油的低温性能研究

对花生油及其制成的生物柴油的运动粘度随温度变化的规律及其低温性能进行了研究,并测定了花生油制成生物柴油后平均分子量的变化情况.结果表明:花生油制成生物柴油后,平均分子量降低,粘度显著降低,低温性能提高.     

Experimental study and empirical correlation development of fuel properties of waste cooking palm biodiesel and its diesel blends at elevated temperatures

In this experimental work, the density, dynamic viscosity and higher heating value of methyl ester based waste cooking palm-biodiesel oil (WMEPB) was investigated under varying temperature and blend ratio condition with No. 2 diesel fuel. The transesterified fatty acid methyl ester of palm vegetable oil collected from local food and beverage shops was used as neat biodiesel. Four different fuel blends (20%, 40%, 60% and 80% by volume mixing with base diesel) were studied along with base No. 2 diesel fuel and pure biodiesel. Tests for dynamic viscosity and density were performed in the temperature range 0–130 °C for each fuel sample whereas the higher heating values were determined at 25 °C room temperature condition. It is found that pure biodiesel has the highest density and dynamic viscosity at a given temperature whereas it exhibits lowest combustion heating value among the six fuels. Moreover, the density for each fuel sample decreases linearly with the increase in temperature. On the other hand, the dynamic viscosity decreases exponentially with the temperature for each fuel sample. In addition, based on the experimental results, regression correlations have been proposed for the density, dynamic viscosity, and higher heating value of the fuels. Subsequently, comprehensive error analyses of these proposed correlations were performed. In particular, the correlation for density and dynamic viscosity were respectively compared with Kay's mixing rule and Grunberg-Nissan mixing rule theory in order to validate their applicability. It is found that density correlations predicted within ±0.3% average error band. And, as high as 72.2% of the dynamic viscosity data were in the range of ±5% average error while the remaining data fell within ±10% error range. And finally, through a comparative study with the available fuel property results of fresh methyl ester palm biodiesel, it is found that available existing correlations derived from fresh palm biodiesel studies can not accurately predict the fuel properties of same waste biodiesel and its blends with diesel.     

Variations in the chemical composition and morphology of soot induced by the unsaturation degree of biodiesel and a biodiesel blend

This work is about the influence of the molecular structure of the fatty acid esters present in two neat biodiesel fuels and their blend (50% by volume) on particulate matter emission. Experiments were performed in a four-cylinder direct injection automotive diesel engine under carefully controlled operating conditions, so that the difference in performance and emissions were affected only by biodiesel fuels composition and properties. The results indicated that the composition and degree of unsaturation of the methyl ester present in biodiesel plays an important role in the chemical composition of particulate matter (PM) emitted. It was observed that linseed biodiesel (BL100) produces more PM and hydrocarbons (HC) than Palm biodiesel (BP100) as a consequence of more unsaturated compounds in its composition, which favor the soot precursor’s formation in the combustion zone. Thermogravimetric analysis (TGA) showed that the amount of volatile material in the soot from biodiesel fuels was slightly lower than that of diesel fuel, but not significant differences were observed among biodiesels. Similarly, the chemical characteristics of the hydrocarbons of volatile material present in the particulate matter (referred in the literature as SOF-soluble organic fraction), showed an increase in the aliphatic component as the unsaturation degree of the fatty acid methyl ester increased. Additionally, it is concluded that there are not significant nano-structural differences in the soot obtained from pure biodiesel fuels, even if they have very different degrees of unsaturation.     

Biodiesel production from inedible animal tallow and an experimental investigation of its use as alternative fuel in a direct injection diesel engine

In this study, a substitute fuel for diesel engines was produced from inedible animal tallow and its usability was investigated as pure biodiesel and its blends with petroleum diesel fuel in a diesel engine. Tallow methyl ester as biodiesel fuel was prepared by base-catalyzed transesterification of the fat with methanol in the presence of NaOH as catalyst. Fuel properties of methyl ester, diesel fuel and blends of them (5%, 20% and 50% by volume) were determined. Viscosity and density of fatty acid methyl ester have been found to meet ASTM D6751 and EN 14214 specifications. Viscosity and density of tallow methyl esters are found to be very close to that of diesel. The calorific value of biodiesel is found to be slightly lower than that of diesel. An experimental study was carried out in order to investigate of its usability as alternative fuel of tallow methyl ester in a direct injection diesel engine. It was observed that the addition of biodiesel to the diesel fuel decreases the effective efficiency of engine and increases the specific fuel consumption. This is due to the lower heating value of biodiesel compared to diesel fuel. However, the effective engine power was comparable by biodiesel compared with diesel fuel. Emissions of carbon monoxide (CO), oxides of nitrogen (NO_x), sulphur dioxide (SO₂) and smoke opacity were reduced around 15%, 38.5%, 72.7% and 56.8%, respectively, in case of tallow methyl esters (B100) compared to diesel fuel. Besides, the lowest CO, NO_x emissions and the highest exhaust temperature were obtained for B20 among all other fuels. The reductions in exhaust emissions made tallow methyl esters and its blends, especially B20 a suitable alternative fuel for diesel and thus could help in controlling air pollution. Based on this study, animal tallow methyl esters and its blends with petroleum diesel fuel can be used a substitute for diesel in direct injection diesel engines without any engine modification.     

Experimental and chemical kinetic modeling study of small methyl esters oxidation: Methyl (E)-2-butenoate and methyl butanoate

This study examines the effect of unsaturation on the combustion of fatty acid methyl esters (FAME). New experimental results were obtained for the oxidation of methyl (E)-2-butenoate (MC, unsaturated C₄ FAME) and methyl butanoate (MB, saturated C₄ FAME) in a jet-stirred reactor (JSR) at atmospheric pressure under dilute conditions over the temperature range 850-1400 K, and two equivalence ratios (Φ=0.375,0.75) with a residence time of 0.07 s. The results consist of concentration profiles of the reactants, stable intermediates, and final products, measured by probe sampling followed by on-line and off-line gas chromatography analyses. The oxidation of MC and MB in the JSR and under counterflow diffusion flame conditions was modeled using a new detailed chemical kinetic reaction mechanism (301 species and 1516 reactions) derived from previous schemes proposed in the literature. The laminar counterflow flame and JSR (for ?=1.13) experimental results used were from a previous study on the comparison of the combustion of both compounds. Sensitivity analyses and reaction path analyses, based on rates of reaction, were used to interpret the results. The data and the model show that MC has reaction pathways analogous to that of MB under the present conditions. The model of MC oxidation provides a better understanding of the effect of the ester function on combustion, and the effect of unsaturation on the combustion of fatty acid methyl ester compounds typically found in biodiesel.     

Effect of biodiesel unsaturated fatty acid on combustion characteristics of a DI compression ignition engine

Several research works have been carried out on biodiesel combustion, performance and emissions till today. But very few studies have been made about the chemistry of biodiesel that affects the diesel engine operation. Biodiesel is derived from vegetable oil or animal fats, which comprises of several fatty acids with different chain length and bonding. The present work focuses on the effect of biodiesel molecular weight, structure (Cis & Trans), and the number of double bonds on the diesel engine operation characteristics. Three types of biodiesel with different molecular weight and number of double bond were selected for the experimental studies. The biodiesels were prepared and analyzed for fuel properties according to the standards. A constant speed diesel engine, which develops 4.4 kW of power, was run with biodiesels and its performance was compared with diesel fuel. The results show that Linseed oil methyl ester with high linolenic (unsaturated fatty acid ester) does not suit best for diesel engine due to high oxides of nitrogen emission and low thermal efficiency.     

Biologically derived diesel fuel and NO formation: An experimental and chemical kinetic study, Part 1

Pyrolysis and oxidation experiments have been conducted on two representative biodiesel surrogate components, methyl octanoate (C9:0) and methyl trans-2-octenoate (C9:1), using the UIC High-Pressure Shock Tube (HPST). The nominal experimental pressures ranged from 27 atm to 53 atm and temperatures varied from 900 to 1450 K with nominal reaction times of 1.65 ms. Dilute reagent mixtures of ∼100 ppm of each fuel were prepared in bulk argon and shock heated to study the stable intermediates. The experimental data have been used to develop and validate a kinetic model for the pyrolysis and oxidation of saturated and unsaturated C₈ methyl esters. The developed model has also been coupled to an existing NO mechanism to predict prompt NO formation spanning the experimental temperature regime. It has been predicted that an increased amount of NO is formed from the unsaturated methyl ester, methyl trans-2-octenoate (C9:1) compared to the saturated methyl ester, methyl octanoate (C9:0) over the intermediate temperature range of 1050–1450 K.     

Review of biodiesel composition, properties, and specifications

Biodiesel is a renewable transportation fuel consisting of fatty acid methyl esters (FAME), generally produced by transesterification of vegetable oils and animal fats. In this review, the fatty acid (FA) profiles of 12 common biodiesel feedstocks were summarized. Considerable compositional variability exists across the range of feedstocks. For example, coconut, palm and tallow contain high amounts of saturated FA; while corn, rapeseed, safflower, soy, and sunflower are dominated by unsaturated FA. Much less information is available regarding the FA profiles of algal lipids that could serve as biodiesel feedstocks. However, some algal species contain considerably higher levels of poly-unsaturated FA than is typically found in vegetable oils.Differences in chemical and physical properties among biodiesel fuels can be explained largely by the fuels’ FA profiles. Two features that are especially influential are the size distribution and the degree of unsaturation within the FA structures. For the 12 biodiesel types reviewed here, it was shown that several fuel properties - including viscosity, specific gravity, cetane number, iodine value, and low temperature performance metrics - are highly correlated with the average unsaturation of the FAME profiles. Due to opposing effects of certain FAME structural features, it is not possible to define a single composition that is optimum with respect to all important fuel properties. However, to ensure satisfactory in-use performance with respect to low temperature operability and oxidative stability, biodiesel should contain relatively low concentrations of both long-chain saturated FAME and poly-unsaturated FAME.     

Performance, emission and combustion characteristics of biodiesel fuelled variable compression ratio engine

Experiments has been carried out to estimate the performance, emission and combustion characteristics of a single cylinder; four stroke variable compression ratio multi fuel engine fuelled with waste cooking oil methyl ester and its blends with standard diesel. Tests has been conducted using the fuel blends of 20%, 40%, 60% and 80% biodiesel with standard diesel, with an engine speed of 1500 rpm, fixed compression ratio 21 and at different loading conditions. The performance parameters elucidated includes brake thermal efficiency, specific fuel consumption, brake power, indicated mean effective pressure, mechanical efficiency and exhaust gas temperature. The exhaust gas emission is found to contain carbon monoxide, hydrocarbon, nitrogen oxides and carbon dioxide. The results of the experiment has been compared and analyzed with standard diesel and it confirms considerable improvement in the performance parameters as well as exhaust emissions. The blends when used as fuel results in the reduction of carbon monoxide, hydrocarbon, carbon dioxide at the expense of nitrogen oxides emissions. It has found that the combustion characteristics of waste cooking oil methyl ester and its diesel blends closely followed those of standard diesel.     

Influence of blending ratio on the physicochemical properties of safflower oil methyl ester-safflower oil,safflower oil methyl ester-diesel and safflower oil-diesel

In this study, the methyl ester production and characterization from safflower oil (SO) was examined. The seed were collected from Yozgat-Turkey and SO was obtained from safflower seeds using screw press. SO was transesterified with methanol and NaOH to obtain safflower oil methyl ester (SOME). SO and SOME show high amounts of linoleic acid of 62.29 and 61.17%, respectively. This result in better low temperature properties of SOME like cloud point (CP) of −5 °C, pour point (PP) of −14 °C, freezing point (FP) of −16 °C and cold filter plugging point (CFPP) of −9 °C. Cold flow properties of SOME demonstrate its operational viability during the cold weather conditions and also it exhibited excellent transportation safety with flash point of 171 °C. It has been found that fuel properties of SOME indicate that SO can be considered as a future biodiesel source. Furthermore, viscosity, density, higher heating value (HHV), flash point, water content, pH, copper strip corrosion, CP, PP, FP and CFPP of SOME-SO, SOME-Euro Diesel(ED) and SO-ED blends have been investigated and discussed in the light of biodiesel standards. The effects of temperature and fraction on density and viscosity of blends were studied and constants of these correlations vary depending on the type of blend.