用近红外光谱分析法测定汽油辛烷值

用近红外光谱技术测定汽油辛烷值,在高精度分光光度计上测得１２个汽油标准样品和４个未知样品的近红外区吸收光谱,建立多元统计分析模型,用逐步回归法和偏最小二乘法对模型进行校准,并将其用于未知样品的预估分析,辛烷值的分析精度达到≤±１．０。     

汽油替代物辛烷值正向建模及敏感性分析

基于辛烷值正向预测原理,本文发展了一种多项式混沌展开-全局敏感性分析(PCE-GSA)融合的高效燃烧参数分析方法,研究了初始温度、压力及汽油典型成分对辛烷值的影响规律。结果表明,采用PCE替代正向预测方案,可在保证预测精度的前提下,将建模需求的样本数量降低1～2个量级。在敏感性分析方面,初始热力学环境参数对辛烷值的Sobol敏感度随汽油种类、测试工况的不同而改变;相较于热力学环境,燃料成分的小范围扰动对辛烷值的影响不显著;乙醇的加入将明显地提升环境温度对汽油自燃特性的影响能力,同时进一步抑制了燃料成分对辛烷值的贡献度。     

结合小波变换与微分法改善近红外光谱分析精度

微分法可以有效消除光谱背景和基线漂移,同时会增加光谱噪音;小波变换具有很好的去噪功能,章将微分法和小波变换结合用于重整汽油辛烷值近红外光谱分析。考察了微分噪音对辛烷值分析精度的影响以及小波去噪对微分光谱的噪音扣除以及对辛烷值分析精度改善情况。结果表明,微分光谱可以扣除原始光谱的基线漂移,提高分析精度,同时增加光谱的噪音;噪音对分析精度影响很大。微分光谱经过小波去噪处理后信噪比增加,辛烷值分析精度得到改善。     

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。     

近红外稳健分析校正模型的建立(Ⅰ)--样品温度的影响

样品温度对近红外光谱分析模型稳健性有明显影响 ,消除其影响的三类方法包括光谱预处理、波长选择和温度补偿校正集。文章以重整汽油 /辛烷值 /苯含量为研究体系 ,考察了这三类方法对建立稳健分析模型的有效性 ,并详细研究了温度补偿校正集样品数量及性质分布对温度混合模型稳健性的影响规律。结果表明 ,仅通过光谱预处理方法难以消除温度对模型稳健性的影响 ;遗传算法波长选择和温度补偿校正集对消除温度影响是有效的 ,而后者更容易实现 ,但在实际应用中应考虑非线性问题     

基于互信息方法的燃油品质光谱分析模型构建与简化

近红外漫反射光谱和紫外吸收光谱分别用于燃油的辛烷值和单芳香族化合物含量的测定,偏最小二乘回归(partial least squares regression,PLSR)用于光谱多元校正模型的构建。基于互信息(mutual infor-mation,MI)理论的变量筛选方法用于模型优化以提高模型的预测精度,降低模型的复杂度。结果表明,MI-PLSR可以有效的提高燃油品质模型的预测精度,简化分析模型。辛烷值的预测均方根误差(root meansquare error of prediction,RMSEP)由0.288减小为0.111,预测相关系数R从0.985提高到0.998,建模变量由401减小为112;单芳香族化合物含量的RMSEP从0.753减小为0.478,R由0.996提高为0.998,建模变量由572缩减为37。说明振动光谱结合MI-PLSR方法可用于燃油品质检测,具有高效率低成本的特点。     

傅里叶变换近红外全谱回归分析的应用研究

文章以66个小麦样品为实验材料,其中33个为建模集,剩余33个为预测集,利用广义逆矩阵直接确定傅里叶变换近红外全谱分析回归模型中的回归系数,建立了用于蛋白质定量分析的近红外全谱回归模型。用此模型对预测集中的样品进行预测,结果与凯氏定氮法测定结果间的相关系数为r=0.979 9,平均相对误差为1.76%,表明由广义逆矩阵方法所建近红外全谱定量分析回归模型有较好的分析结果。所建模型不仅可用于对样品的实际分析,而且可根据回归模型中各个系数了解各个波长点处的光谱信息对模型预测值的贡献,从而可理解并解释傅里叶变换近红外全谱回归模型的物理学与化学意义。     

近红外光谱的甲醇汽油定量检测与分析方法

甲醇汽油因其辛烷值高、成本低等优势成为新型化石燃料替代物,其甲醇含量的精确检测是决定其品质的重要环节,甲醇汽油组分的精确定量检测与分析对于缓解我国传统石油资源短缺但需求量增多的现状具有重大的现实意义。甲醇汽油中甲醇检测的常规方法如酒醇仪测定法、速测盒测定法等,操作复杂,准确定性低。近红外光谱分析具有测量速度快、灵敏度高、可连续测量等诸多优点,在石油化工领域定性、定量分析中具有巨大应用潜力。为研究甲醇汽油近红外光谱无损定量检测方法,配制了0.5%～30%组分的甲醇汽油标准样品,设计了甲醇汽油近红外光谱数据采集系统并采集60个组分的甲醇汽油近红外光谱数据;利用移动平均平滑法、 S-G卷积平滑法(Savitzky-Golay)和多元散射校正(MSC)对甲醇汽油近红外光谱数据进行预处理分析,研究了BP人工神经网络(ANN)和主成分回归(PCR)模型的决定系数和均方根误差,对两种算法的结果和预测效果进行对比。结果显示：各模型的均方根误差均小于1%, SG平滑-主成分回归预测模型拟合度最好,其决定系数为0.998 98;基于SG卷积平滑算法和神经网络算法建立的模型预测值与真值偏差最小,其均方根误差...     

近红外光谱用于植物样品中水溶性氯离子含量的测定

基于离散小波变换(DWT)和最小二乘支持向量回归(LSSVR)方法,建立了近红外光谱测定植物样品中水溶性氯离子的回归校正模型。以烟草样品中水溶性氯离子含量的测定为研究对象,首先采用DWT对近红外光谱进行数据压缩和背景扣除,再用LSSVR建立氯离子的校正模型。结果表明,与偏最小二乘回归(PLSR)和传统的LSSVR方法相比,作者所建模型的预测准确性具有一定优势。     

虫草氨基酸的人工神经网络-近红外光谱快速测定方法

提出了用近红外漫反射光谱技术快速检测发酵冬虫夏草中氨基酸含量的新方法。采用比色法测定虫草菌粉中氨基酸含量。用BP神经网络建立了近红外光谱数据与氨基酸、精氨酸和总氨酸含量间的定量关联模型。通过比较不同的光谱预处理方法及光谱范围, 得到最优模型,即在7 501.7～6 097.8,5 453.7～4 246.5 cm-1区域内,近红外光谱的一阶微分光谱与其氨基酸含量之间建立模型。甘氨酸、精氨酸和总氨基酸的预测标准偏差分别为0.08,0.07和0.36,均优于主成分回归(PCR)和偏最小二乘回归(PLS)等线性模型的处理结果。结果表明,该方法是一种有效实用的非线性校正方法。为近红外光谱快速测定中药组分含量提供了一条新途径。     

Evaluating a novel gasoline surrogate containing isopentane using a rapid compression machine and an engine

Simple surrogate formulations for gasoline are useful for modelling purposes and for comparing experimental results using a carefully designed fuel. Simple three-component surrogates based on primary reference fuels (PRF) and Toluene (TPRF) are frequently used to match the antiknock properties of actual gasoline fuels through the RON and MON. However, using PRF or TPRFs to test or to calibrate gasoline engines is still challenging, with the main difficulty being the capabilities of PRF fuels to match the physical properties of the road fuel such density, volatility (DVPE) and the distillation curve. To overcome such issues, an alternative to TPRF is presented in this work with a focus on premium fuel (RON98 EN228). This alternative consists of replacing some or all of isooctane by isopentane. In the event of total replacement, a three-component “THIP” (Toluene, Heptane, IsoPentane) surrogate fuel is produced. The physical and combustion properties of isopentane makes it easier to create surrogates that can match the DVPE, RON, MON and distillation characteristics of a real fuel. Furthermore, the use of isopentane allows the definition of a wider range of surrogate fuel compositions that can replicate the RON and MON of a given fuel. Surrogate formulations were developed at Shell Global Solutions that matched the RON, MON and selected physical properties of a reference premium gasoline (RPG). A Rapid Compression Machine (RCM) in PCFC was used to demonstrate that those surrogates can reproduce the essential autoignition characteristics of the selected RPG. Two mechanisms were used to predict RCM data and showed reasonable agreement, opening some perspective for further investigations. Finally, an engine test performed at Ferrari test facilities demonstrated that simple surrogates containing isopentane can be used to closely match the knock-limited combustion phasing of an RPG. In this paper, it is demonstrated such surrogates have advantages compared to TPRFs in being able to match the properties of a real fuel and that the surrogate approach is consistent with RCM data and engine results.     

Estimation of the petroleum product knock rating by regression analysis of near-infrared absorption spectra

Spectroscopic measurements in the near-infrared region are suggested to determine the octane number of petroleum products. Statistical regression analysis of the absorption spectra of hydrocarbons is used for calculating the gasoline octane number and several other physicotechnical parameters of fuel. The knock rating of commercial gasoline was determined with a specially designed analyzer. Its working parameters and limiting capabilities in determining the octane number are discussed.     

A chemical kinetic interpretation of the octane appetite of modern gasoline engines

Fuel anti-knock quality is a critical property with respect to the effective design of next-generation spark-ignition engines which aim to have increased efficiency, and lower emissions. Increasing evidence in the literature supports the fact that the current regulatory measures of fuel anti-knock quality, the research octane number (RON), and motor octane number (MON), are becoming decreasingly relevant to commercial engines. Extrapolation and interpolation of the RON/MON scales to the thermodynamic conditions of modern engines is potentially valuable for the synergistic design of fuels and engines with greater efficiency. The K-value approach, which linearly weights the RON/MON scales based on the thermodynamic history of an engine, offers a convenient experimental method to do so, although complementary theoretical interpretations of K-value measurements are lacking in the literature.This work uses a phenomenological engine model with a detailed chemical kinetic model to predict and interpret known trends in the K-value with respect to engine intake temperature, pressure, and engine speed. The modelling results support experimental trends which show that the K-value increases with increasing intake temperature and engine speed, and decreases with increasing intake pressure. A chemical kinetic interpretation of trends in the K-value based on fundamental ignition behaviour is presented. The results show that combined experimental/theoretical approaches, which employ a knowledge of fundamental fuel data (gas phase kinetics, ignition delay times), can provide a reliable means to assess trends in the real-world performance of commercial fuels under the operating conditions of modern engines.     

Ignition delay measurements of four component model gasolines exploring the impacts of biofuels and aromatics

This study explores the impacts of combinations of biofuel (ethanol, isobutanol and 2-methyl furan) and aromatic (toluene) compounds in a four component fuel blend, at fixed research octane number (RON) on ignition delay measured in an advanced fuel ignition delay analyzer (AFIDA 2805). Ignition delay measurements were performed over a range of temperatures from 400 to 725 °C (673 to 998 K) and two chamber pressures of 10 and 20 bar. The four component mixtures are compared to primary reference fuels at RON values of 90 and 100. The ignition delay measurements show that as the aromatic and biofuel concentrations increased, two stage ignition behavior was suppressed, at both initial chamber pressures. But both RON 100 (isooctane) and RON 90 reference fuels showed two stage ignition behavior, as did fuel mixtures with low biofuel and aromatic content. RON 90 fuels showed stronger two stage ignition behavior than RON 100 fuels, as expected. Depending on the type of biofuel in the mixture, the ignition delay at low chamber temperatures could be far greater than for the reference fuels. In particular, for the RON 100 mixtures at either 10 or 20 bar initial chamber pressure, the ignition delay at 400 °C (673 K) for the high level blend of 2-methyl furan and toluene (30 vol% of each) exhibited an ignition delay that was 10 times longer than for neat isooctane. The results show the strong non-linear octane blending response of these three biofuel compounds, especially in concert with the kinetic antagonism that toluene is known to display in mixtures with isooctane. These results have implications for the formulation of biofuel mixtures for spark ignition and advanced compression ignition engines, where this non-linear octane blending response could be exploited to improve knock resistance, or modulate the autoignition process.     

Experimental and kinetic modeling study of combustion of gasoline, its surrogates and components in laminar non-premixed flows

Experimental and numerical studies are carried out to construct surrogates that can reproduce selected aspects of combustion of gasoline in non premixed flows. Experiments are carried out employing the counterflow configuration. Critical conditions of extinction and autoignition are measured. The fuels tested are n-heptane, iso-octane, methylcyclohexane, toluene, three surrogates made up of these components, called surrogate A, surrogate B, and surrogate C, two commercial gasoline with octane numbers (ON) of 87 and 91, and two mixtures of the primary reference fuels, n-heptane and iso-octane, called PRF 87 and PRF 91. The combustion characteristics of the commercial gasolines, ON 87 and ON 91, are found to be nearly the same. Surrogate A and surrogate C are found to reproduce critical conditions of extinction and autoignition of gasoline: surrogate C is slightly better than surrogate A. Numerical calculations are carried out using a semi-detailed chemical-kinetic mechanism. The calculated values of the critical conditions of extinction and autoignition of the components of the surrogates agree well with experimental data. The octane numbers of the mixtures PRF 87 and PRF 91 are the same as those for the gasoline tested here. Experimental and numerical studies show that the critical conditions of extinction and autoignition for these fuels are not the same as those for gasoline. This confirms the need to include at least aromatic compounds in the surrogate mixtures. The present study shows that the semi-detailed chemical-kinetic mechanism developed here is able to predict key aspects of combustion of gasoline in non premixed flows, although further kinetic work is needed to improve the combustion chemistry of aromatic species, in particular toluene.     

Increasing the octane number of gasoline using functionalized carbon nanotubes

The octane number is one of the characteristics of spark-ignition fuels such as gasoline. Octane number of fuels can be improved by addition of oxygenates such as ethanol, MTBE (methyl tert-butyl ether), TBF (tertiary butyl formate) and TBA (tertiary butyl alcohol) as well as their blends with gasoline that reduce the cost impact of fuels. Carbon nanotubes (CNTs) are as useful additives for increasing the octane number. Functionalized carbon nanotubes containing amide groups have a high reactivity and can react with many chemicals. These compounds can be solubilized in gasoline to increase the octane number. In this study, using octadecylamine and dodecylamine, CNTs were amidated and the amino-functionalized carbon nanotubes were added to gasoline. Research octane number analysis showed that these additives increase octane number of the desired samples. X-ray diffraction (XRD), Fourier transforms infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and thermal gravimetry analyses (TGA) were used for characterization of the prepared functionalized carbon nanotubes.     

An experimental and modeling study of tetramethyl ethylene pyrolysis with polycyclic aromatic hydrocarbon formation

Iso-olefins, in the C₅–C₈ range can potentially be blended with renewable gasoline fuels to increase their research octane number (RON) and octane sensitivity (S). RON and S increase with the degree of branching in iso-olefins and this is a desirable fuel anti-knock quality in modern spark-ignited direct-injection engines. However, these iso-olefins tend to form larger concentrations of aromatic species leading to the formation of polycyclic aromatic hydrocarbons (PAHs). Thus, it is important to understand the pyrolysis chemistry of these iso-olefins. In this study, a new detailed chemical kinetic mechanism is developed to describe the pyrolysis of tetramethyl ethylene (TME), a symmetric iso-olefin. The mechanism, which includes the formation of PAHs, is validated against species versus temperature (700–1160 K) measurements in a jet-stirred reactor at atmospheric pressure and in a single-pulse shock tube at a pressure of 5 bar in the temperature range 1150–1600 K. Synchrotron vacuum ultraviolet photoionization mass spectrometer (SVUV-PIMS) and gas chromatography (GC) systems were used to quantify the species in the jet-stirred reactor and in the single-pulse shock tube, respectively. The mechanism derives its base and PAH chemistry from the LLNL PAH sub-mechanism. The predictions are accurate for most of the species measured in both facilities. However, there is scope for mechanism improvement by understanding the consumption pathways for some of the intermediate species such as isoprene. The formation of 1, 2, and 3-ring aromatic species such as benzene, toluene, naphthalene and phenanthrene measured experimentally is analyzed using the chemical kinetic mechanism. It is found that the PAH formation chemistry for TME under pyrolysis conditions is driven by both propargyl addition reactions and the HACA mechanism.     

Determination of the octane number of a fuel by the IR spectroscopy method

The near-IR spectroscopy method of control of the octane number (o.n.) of a fuel is studied. An analysis is made of a device developed as an alternative of a measuring system based on a nonselective IR radiation source and of an analyzer based on a laser semiconductor diode. It is shown that the use of the methods of multicomponent regression analysis of spectral data allows measurement of the octane number with an accuracy of S ∼ 0.17 octane number units. The characteristics of the semiconductor laser-based analyzer are investigated and the parameters of radiators are discussed that provide the required sensitivity of the measuring system (up to 10⁻⁴ with respect to optical absorption) in controlling the octane number of a fucl. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 244–248, March–April, 2000.