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...     

航空替代燃料低温氧化实验与模型研究

在射流搅拌反应器中开展了常压航空煤油替代燃料的低温(500~1100 K)氧化实验研究。利用气相色谱和气质联用仪测得了34个物种的摩尔分数曲线。通过研究芳烃和正癸烷间的耦合作用阐述了替代燃料低温区负温度系数效应对燃料燃烧特性的影响,揭示了实际航空燃料的低温自动点火机理。建立包括975物种和5920反应的亚琛替代燃料的动力学模型,并利用该模型准确地预测实际燃料燃烧的点火延迟等。实验和模拟得到的结果有助于理解燃气轮机低温点火过程。     

利用同步辐射研究汽油及其混合物的火焰成分特征

本文利用同步辐射和分子束取样技术并结合飞行时间质谱仪,分别检测了加入MTBE前后的汽油在氧气中的燃烧产物.通过比较标准汽油与MTBE/汽油在火焰中的成分差异,以及几种典型燃烧产物的空间分布曲线,分析了MTBE对汽油的微观影响机理,为建立燃烧反应动力学模型提供了参考.     

正丙醚低温氧化特性的反应机理研究

醚类被认为是优质的直接燃料或燃料添加剂。为进一步揭示醚类的低温氧化反应机制,本文构建了包含详细机理的正丙醚燃烧反应动力学模型,并利用前人的高压氧化实验数据对模型进行了验证。相比于前人的模型,本文模型可以准确预测不同当量比条件下正丙醚的氧化特性。基于模型分析,本文揭示了不同温度下OH自由基的来源以及不同温度下正丙醚的氧化路径差异,为正丙醚的进一步研究提供了方向。     

640×512制冷探测器非线性响应分析

由于制冷探测器焦平面制作工艺的缺陷,使其各部分组分不会完全相同,从而导致焦平面在进行光电转换时各个位置的光电流大小存在差异.本文以国产640×512中波凝视型制冷热像仪整机研制项目为基础,通过对探测器接收红外辐射并转换为光电流的过程中主要参量与焦平面材料Hg1-xCdxTe中组分x的关系进行分析,推导出探测器焦平面光电流与组分x的关系模型.在探测器能够正常工作的宽温度范围内利用黑体面源对探测器进行照射,采集各个温度点下探测器输出数据,并对本探测器整体响应特性及单个像素点的响应特性进行分析.根据影响光电流的最主要的参量变化情况,提出了双指数曲线模型来描述实际响应数据,并通过大量的数据和图表分析,证明了该模型能够提高对探测器实际响应描述的精确程度,对实际的工程应用具有指导意义.     

拉曼光谱技术的汽油组分含量测定

为实现汽油中所含组分含量的快速测定,对93号、97号汽油,芳烃、烯烃、苯、甲醇、乙醇等几类物质,以及往汽油中添加几类物质后的410个汽油混合物进行拉曼光谱检测。将获取的原始拉曼光谱经过有效波段提取、平滑去噪、基线扣除、数据归一化等一系列预处理过程,最终提取出每个汽油混合样品光谱中所含的33个特征峰信息,依据现行的国标检测方法,以气相色谱法测定的汽油中各组分含量值为基础,结合化学计量学多重回归分析方法,建立了汽油组分含量测定模型。经过比较,使用多输出最小二乘支持向量回归机(MLS-SVR)建立的模型优于偏最小二乘(PLS)模型。MLS-SVR模型对汽油中芳烃、烯烃、苯、甲醇、乙醇测定精度均较好,预测均方根误差(RMSEP)分别为0.27%,0.30%,0.16%, 0.17%, 0.12%;相应的相关系数(r)为0.999 2,0.998 4,0.998 5,0.992 6,0.996 8。通过对未知混合汽油样品的测定,证明了该方法具有较好的推广预测精度,预测均方根误差不超过0.5%,能够满足工业中的测量需求。拉曼光谱结合多输出最小二乘支持向量机为汽油组分测定提供了一种高精确、快捷、方便的测定方法。     

采用核磁共振信息的FACE汽油替代燃料机理构建

提出了一种基于核磁共振分析所得的官能基团信息来构建替代燃料模型的新方法。根据核磁共振的光谱信息,定义了五种基本官能基团:烷烃CH_3基团、烷烃CH_2基团、环烷烃CH-CH_2基团、烯烃CH-CH_2基团和芳香烃C-CH基团,并通过匹配实际燃料的这些官能基团来构建FACE汽油替代燃料。选取正丁烷、正庚烷、异辛烷、甲苯、2,5二甲基己烷、甲基环己烷和1-己烯作为备选基础燃料,根据FACE F、FACE G、FACE I和FACE J四种目标燃料的官能基团信息选取合适的替代燃料组分,进而构建相应的替代燃料模型。将所获得的替代燃料机理用于模拟不同初始条件下激波管内的燃料氧化燃烧,模拟结果与实验数据的对比表明,所构建的替代燃料机理能较好地预测FACE汽油在不同温度、压力和当量比条件下的着火特性。     

二甲醚低温氧化及甲醛生成特性实验研究

在常压环境下对二甲醚的低温氧化特性做了实验研究,并在不同当量比下研究了预混气中甲醛的生成特性.实验结果表明,二甲醚在200℃左右开始缓慢发生氧化反应,在250~379℃时氧化反应最为剧烈,750℃时被完全氧化为CO2和水;在二甲醚低温氧化产物中,甲醛是其重要的组分,二甲醚在200~400℃温度环境下最容易氧化而产生甲醛...     

一种新型生物柴油替代燃料模型

为了分析实际生物柴油的燃烧特性,综合考虑了燃料的分子量、碳氢比、化学键能和十六烷值等特性,基于丁酸甲酯、醋酸乙酯、癸酸甲酯与正十二烷四种燃料,采用配平原子个数和十六烷值的方法构建了反映生物柴油基本燃烧特性的一种新的替代燃料模型。通过不同工况下模拟结果与实验数据的比较,对该方法的合理性进行了验证,结果表明该替代燃料模型能较好地预测生物柴油在不同压力、温度和当量比下的氧化过程。该机理构成方法为替代燃料机理的构建提供了新的思路。     

铜铁合金与金铁合金低温热电偶特性研究

本文以铜铁合金、金铁合金低温热电偶的分度实验为基础,对两种热电偶的分度特性、微观机理等进行了分析比较.并在微型气体制冷机二级冷头温度(10K)测定中进行了实际考核.给出了国产含铁0.13％的镍铬-铜铁热电偶(NiCr-Cu 0.13％Fe)4—273K的分度表.从理论和实验上肯定了在较广的温域使用铜铁合金低温热电偶与金铁合金具有相同优越的热电性能.     

Experimental and modelling study of gasoline surrogate mixtures oxidation in jet stirred reactor and shock tube

The oxidation of several mixtures of surrogate for gasoline was studied using a jet stirred reactor and a shock tube. One representative of each classes constituting gasoline was selected: iso-octane, toluene, 1-hexene and ethyl tert-butyl ether (ETBE). The experiments were carried out in the 800-1880 K temperature range, for two different initial pressures (0.2 and 1 MPa), with an initial fuel molar fraction of 0.001. The equivalence ratio varied from 0.5 to 1.5. Each hydrocarbon sub-mechanism was validated using shock tube data. The full mechanism describing the surrogate fuel oxidation is constituted of the sub-mechanisms for each fuel components and by adding interaction reactions between different hydrocarbon fragments. Good agreement between the experimental results and the computations was observed under JSR and shock tube conditions.     

Combustion and emission modelling of a direct-injection spark-ignition engine by combining flamelet models for premixed and diffusion flames

The combustion and emission production processes of a DISI (direct-injection spark-ignition) engine were modelled by combining flamelet models for premixed and diffusion flames. A new surrogate fuel was proposed to approximate the complicated composition of real gasoline. In contrast to simpler conventional models, the fuel was modelled as a ternary mixture of three hydrocarbons: iso-octane, n-heptane and toluene. Turbulent flame propagation in a partially premixed field was modelled by a premixed flamelet model. The mass fractions of the detailed composition of species in burnt gas were predicted by a diffusion flamelet model. For the pollutant formation modelling, a two-step oxidation of CO and H₂ was used to simulate the secondary diffusion flame. The extended Zeldovich mechanism was used to model NOx formation, while a phenomenological model was used to model soot formation. This model was initially applied to a simple geometry to investigate the fundamentals of the model's behaviour, after which three-dimensional computational fluid dynamic (CFD) simulations were performed in a realistic engine geometry.     

An experimental and kinetic modeling study of a four-component surrogate fuel for RP-3 kerosene

Detailed high-fidelity kinetic models of fuels are of great significance by providing guidance for the improvement of the combustion performance in engines and promising the reduction of design cycle of new concept combustors. However, the kinetic modeling works on Chinese RP-3 kerosene, the most widely used civil aviation fuel in China, are meager to date. In this study, a kinetic model, including a surrogate fuel and its combustion kinetic mechanism, were developed to describe the combustion of RP-3. Firstly, a surrogate comprised of components n-dodecane, 2,2,4,6,6-pentamethylheptane (PMH), n-butylcyclohexane and n-butylbenzene (22.82/31.30/19.19/26.69 mol%) was proposed based on the combustion property target matching method. These components are all within the typical molecular size (C10-C14) of jet fuels and thereby can potentially improve the ability of the surrogate in emulating the properties that depend on molecular size. Experiments were then carried out in a heated rapid compression machine and a heated shock tube to evaluate the performance of the surrogate in reproducing the combustion behavior of the target fuel over wide conditions. It is found that the surrogate can reproduce the autoignition characteristics of RP-3 very well. A chemical kinetic mechanism was developed to describe the oxidation of this surrogate. This mechanism was assembled using a published n-butylbenzene sub-mechanism and our previous sub-mechanisms for the other pure components, and was assessed against the present experimental data. The results showed that the simulations agreed well with the experimental data under the investigated conditions, demonstrating that the composition of the surrogate and its mechanism are appropriate to describe the combustion of RP-3. The first-stage ignition negative temperature coefficient behavior and the evolution of key radicals were investigated using the kinetic model.     

Ignition delay time measurements and modeling for gasoline at very high pressures

Ignition delay times (IDT) for high-octane-number gasolines and gasoline surrogates were measured at very high pressures behind reflected shock waves. Fuels tested include gasoline, gasoline with oxygenates, and two surrogate fuels, one dominated by iso-octane and one by toluene. RON/MON for the fuels varied from 101/94 to 106.5/91.5. Measurements were conducted in synthetic air at pressures from 30 to 250 atm, for temperatures from 700 to 1100 K, and equivalence ratios near 0.85. Results were compared with a recent gasoline mechanism of Mehl et al. (2017). IDT measurements of the iso-octane-dominated surrogate were very well reproduced by the model over the entire pressure and temperature range. IDT measurements for the toluene-dominated surrogate were also reproduced by the model to a lesser extent. By contrast, IDT measurements for the neat gasoline and gasoline with oxygenates, show excellent agreement with the trends of the Mehl et al. model only below 900 K. Above 900 K, the model returned IDT values for the two gasolines that were approximately 1.6× the measured values. Finally, we observed that IDT measurements for the toluene-dominated surrogate fuel and the two gasolines, near 70 atm and below 900 K, appeared to be shortened, possibly by non-homogeneous ignition or non-ideal gas processes. This dataset provides a critically needed set of IDT targets to test and refine boosted gasoline models at high pressures.     

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.     

On the importance of species selection for the formulation of fuel surrogates

Fuel surrogates are mixtures of simple compounds that emulate the combustion characteristics of more complex fuels, with the primary objective to enable detailed combustion modeling of very complex real fuels. Current efforts in surrogate development aim at optimizing the compositions of pure hydrocarbons to emulate multiple combustion related properties. In doing so, weights are assigned when defining optimization problem to reflect the importance of each property. In this study, we report on the relative importance of species selection and their weights on the overall performance of the optimized surrogate. Using experimental data of a reference jet fuel as target, we designed a study using a surrogate optimizer that imposes orthogonal perturbations on the surrogate components and weights and analyzed their impact on the optimized surrogate mixtures. Results from 3600 cases show that perturbations of surrogate components, rather than weights, induce far greater variability in the optimized composition and target property agreement. While the Derived Cetane Number (DCN) agreement shows a greater variability from the weight perturbation, the main reason for such high sensitivity is due to the wide range of values for pure component DCN of the individual components, which is also a result of the surrogate component selection. Further, the results show that the selection of surrogate components nearly predefines the overall shape of the distillation curves regardless of the weight values. The current study quantitatively supports the idea that appropriate selection of surrogate components that capture the physical and chemical characteristics of actual constituents of target fuel will increase the possibility of successful surrogate formulation and will mitigate the impact from arbitrary weight assignment.     

Simulation-driven formulation of transportation fuel surrogates

An alternative way to formulate transportation fuel surrogates using model predictions of gas-phase combustion targets is explored and compared to conventional approaches. Given a selection of individual fuel components, a multi-component chemical mechanism describing their oxidation kinetics, and a database of experimental measurements for key combustion quantities such as ignition delay times and laminar burning velocities, the optimal fractional amount of each fuel is determined as the one yielding the smallest error between experiments and model predictions. Using a previously studied three-component jet fuel surrogate containing n-dodecane, methyl-cyclohexane, and m-xylene as a case study, this article investigates in a systematic manner how the surrogate composition affects model predictions for ignition delay time and laminar burning velocities over a wide range of temperature, pressure and stoichiometry conditions, and compares the results to existing surrogate formulation techniques, providing new insights on how to define surrogates for simulation purposes. Finally, an optimisation algorithm is described to accelerate the identification of optimal surrogate compositions in this context.     

Autoignition of gasoline and its surrogates in a rapid compression machine

The analysis and interpretation of the combustion chemistry is greatly simplified by using simple mixtures of pure components, referred to as surrogates, in lieu of fully-blended transportation fuels, such as gasoline. Recognizing that the ability to model autoignition chemistry is critical to understanding the operation of Homogeneous Charged Compression Ignition engines, this work is an attempt to experimentally and computationally assess the autoignition responses of research grade gasoline and two of its proposed surrogates reported in the literature using a rapid compression machine (RCM), for the low-to-intermediate temperature range and at high pressures. The first surrogate studied is a three-component mixture of iso-octane, n-heptane, and toluene. The second is a four-component mixture that includes an olefin (2-pentene), in addition to the ones noted above. Ignition delay times of stoichiometric mixtures, for gasoline and the two surrogates in air, are measured using an RCM for pressures of 20 and 40 bar, and in the temperature range of 650–900 K. The four-component surrogate is found to emulate the ignition delay times of gasoline more closely when compared to the three-component surrogate. Additionally, the experimental data are compared against the computed results from a recently developed surrogate model for gasoline combustion. A good agreement between the experimental and computed results is observed, while discrepancies are also identified and discussed.     

Impact of preferential vaporization on combustion chamber deposit generation from a gasoline surrogate: A parametric study

The effect of injection pressure and impingement-surface temperature on combustion chamber deposit (CCD) inside a constant volume combustion chamber (CVCC) was studied. The CVCC was modified to capture the main characteristics of the spray-wall and film–flame interaction observed in gasoline direct injection (GDI) engines. The measurements were performed at three different injection pressures (30, 100, and 200 bar) and four wall temperatures (353, 393, 433, and 473 K) using a gasoline surrogate (S01) with four components (hexane, isooctane, toluene, 1-methylnaphthalene), under a global equivalence ratio of one. High speed Schlieren measurements and Mie scattering were used to characterize the spray–wall interaction. Moreover, the influence of the vapor distribution of the heavy and light fractions of a second non-fluorescent surrogate (S02, with similar vaporization behavior and composition to S01) doped with p-difluorobenzene (pDFB) and 1-Methylnaphtalene (1-MN) was analyzed around the impingement region. The fluorescent signal of the traces made it possible to study indirectly the effect of preferential vaporization on the CCD generation. Finally, the CCD build-up rate was determined by a gravimetric method. It was found that regardless of the injection pressure, the maximum production of CCD took place at a wall temperature of 393 K, and that an additional increase in the temperature reduced the build-up rate of CCD. The higher retention of heavy fraction on the impingement region at 353 and 393 K, identified by fluorescence, could not explain by itself the higher production of CCD outside the impingement region.     

From electronic structure to model application of key reactions for gasoline/alcohol combustion: Hydrogen-atom abstraction by CH3OȮ radicals

Hydrogen atom abstraction by methyl peroxy (CH₃OȮ) radicals can play an important role in gasoline/ethanol interacting chemistry for fuels that produce high concentrations of methyl radicals. Detailed kinetic reactions for hydrogen atom abstraction by CH₃OȮ radicals from the components of FGF-LLNL (a gasoline surrogate) including cyclopentane, toluene, 1-hexene, n-heptane, and isooctane have been systematically studied in this work. The M06–2X/6–311++G(d,p) level of theory was used to obtain the optimized structure and vibrational frequency for all stationary points and the low-frequency torsional modes. The 1-D hindered rotor treatment for low-frequency torsional modes was treated at M06–2X/6–31G level of theory. The UCCSD(T)-F12a/cc-pVDZ-F12 and QCISD(T)/CBS level of theory were used to calculate single point energies for all species. High pressure limiting rate constants for all hydrogen atom abstraction channels were performed using conventional transition state theory with unsymmetric tunneling corrections. Individual rate constants are reported in the temperature range from 298.15 to 2000 K. Our computed results show that the abstraction of allylic hydrogen atoms from 1-hexene is the fastest at low temperatures. When the temperature increases, the hydrogen atom abstraction reaction channel at the primary alkyl site gradually becomes dominant. Thermodynamics properties for all stable species and high-pressure limiting rate constants for each reaction pathway obtained in this work were incorporated into the latest gasoline surrogate/ethanol model to investigate the influence of the rate constants calculated here on model predicted ignition delay times.