Advanced Methodology for the Detection of Smoke Point Heights in

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Advanced Methodology for the Detection of Smoke Point Heights in Hydrocarbon Flames Barbara Graziano, Tamara Ottenwälder, Daniel Manderfeld, Stefan Pischinger, and Gerd Grünefeld Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03584 • Publication Date (Web): 04 Feb 2018 Downloaded from http://pubs.acs.org on February 12, 2018

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Advanced Methodology for the Detection of Smoke Point Heights in Hydrocarbon Flames Barbara Graziano,*† Tamara Ottenwälder,† Daniel Manderfeld,†§ Stefan Pischinger,† Gerd Grünefeld‡ †

Institute for Combustion Engines, RWTH Aachen University, Forckenbeckstraße 4, 52074 Aachen Germany ‡

Institute of Technical Thermodynamics, RWTH Aachen University, Schinkelstraße 8, 52062 Aachen, Germany

KEYWORDS: Soot, Smoke Point, Image processing, Threshold Sooting Index, Hydrocarbons. *Author to whom correspondence should be addressed. Telephone: (+49) 241 80 48123. Fax: (+49) 241 80-926 30. E-mail: [email protected]. §

now at STEAG Energy Services GmbH, Rüttenscheider Straße 1-3, 45128 Essen, Germany

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Abstract

The American Society for Testing and Materials (ASTM) D1322 assesses the sooting tendency of fuels using smoke points. Recently, the fuel uptake rate measurement with threshold imaging (FURTI) method has improved the smoke point determination. Herein, a precise and accurate detection of smoke point heights is investigated when tests are conducted with the FURTI method. First order gradients of the soot luminosity, recorded with a charge-coupled device camera, are used to detect the flame height. The analysis of several iso-octane / toluene calibration blends shows a significant diminution in the height experimental error in comparison to the ASTM D1322 standard, ranging from a minimum of 67% to a maximum of 86%. A low flame height bias, ranging from 1% to 5%, and a negligible sensitivity to the fuel sample composition is present when additional hydrocarbons are analyzed, owing to a high measuring accuracy and a robust height detection method.


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1. Introduction The solid fraction of the particulate matter (soot) produced during the combustion of fossil fuels is a harmful pollutant for humans and the environment.1 In Diesel engines soot emissions remain a major concern, since particles surviving the filter regeneration represent a harmful pollutant for humans’ respiratory organs.2 Moreover, soot deposits reduce the anti-wear properties of the engine oil.3,4 Thus, the realization of cleaner propulsion systems is important from both a technological and an environmental perspective. In this regard, the experimental characterization of the sooting tendency of a fuel is crucial. Rapid screening of the sooting propensity of aviation fuels is performed with the American Society for Testing and Materials (ASTM) D1322 standard for smoke point (SP) tests.5 The Threshold Sooting Index (TSI)6 establishes a soot rating based on SPs as eqs. 1 and 2 introduce: TSI = a (

Mw )+b hSP

TSII = a' (

(1)

Mw ) + b' ̇VSP

(2)

where Mw is the fuel molecular weight in g/mol, hSP is the SP height of the flame in cm, V̇ SP is the volumetric fuel flow rate at the SP in cm3/s, (a, b) and (a′, b′) are apparatus dependent constants. The TSI metric allows to normalize different data sets to a common scale, ranging from 0 to 100. Both formulations are equivalent and in agreement with Roper’s model from 19777. Successively, in 1985 Olson and co-workers 8 analyzed the sooting tendency of 42 fuels in a wick-fed burner and proposed the following expression: Mw TSIII = a'' ( ) + b'' mSP ̇

(3)


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where mSP ̇ is the critical fuel mass consumption rate at the SP in g/s and (a′′, b′′) are apparatus dependent constants. This last formulation is equivalent to the previous two, since the volumetric flow rate is related to the mass flow rate by the molar density. The simplicity of the TSI metric is not its only advantage. It obeys to a linear blending rule that was firstly introduced by Gill and Olson in 19849; hence, the TSI of a mixture (TSImix ) is defined as: n

TSImix = ∑ xk TSIk

(4)

k=1

where xk is the mole fraction of the k component of a mixture composed of n fuels and TSIk represents its sooting tendency. Olson et al.8 observed a correlation between the SP height and the maximum soot volumetric fraction for several hydrocarbons and directly linked the TSI with the soot production of a fuel. Another advantage of the SP test is its validity for a wide variety of hydrocarbon fuels that allows for the formulation of surrogates. Interesting surrogates for aviation fuels were tested in binary-10,11 or ternary- blends12 to derive tailored fuel compositions featuring a low sooting propensity. Fuels for internal combustion engines were also analyzed in the same way.13−17 However, a relatively low experimental repeatability and high bias were observed for both high and low sooting fuels, when the tests were conducted with the standard ASTM D1322 procedure. This latter aspect is in agreement with former works,6,8 where paraffinic (i.e., low sooting fuels) and aromatic compounds (i.e., high sooting fuels) exhibited the highest TSI errors. Recently, Mensch et al.10 analyzed the sooting tendency of binary hydrocarbon mixtures. Their results exhibited an increase in the TSI bias with increasing content of the high sooting fuel in the mixture. This is linked to the limited measuring range of the ASTM D1322 setup.5 The wick-fed lamp covers flame heights from 0 to 5 cm, which are measured with the help of a yardstick placed on the backside of the combustion chamber. The metric yardstick 4 ACS Paragon Plus Environment

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has a resolution of 1 mm, which limits the by-eye detection of high sooting flames below 1 cm. Low sooting fuels (e.g., saturated hydrocarbons and oxygenated fuels), featuring a SP height above 5 cm, cannot directly be measured and require blending with other fuels. This introduces additional errors in the experimental determination of the SP height. In the past years, attempts were made to improve the SP measurements accuracy and repeatability. In 2006 the Yield Sooting Index (YSI) was introduced by McEnally and Pfefferle.18 The authors derived a quantitative soot rating method, accurately measuring the maximum soot volumetric fraction of several aromatics in a nitrogen-diluted laminar diffusion methane flame by means of laser induced incandescence. The YSI proved to be a more accurate metric than the TSI, featuring an experimental error of only 3%. In 2008 Crossley et al.19 introduced the Micropyrolysis Index (MPI) as proportional to the amount of carbon deposited onto an alumina bed during fuel injection. The carbon deposits were inserted into a temperature programmable oxidation system to be quantified. The comparison of MPI and TSI showed good agreement only when analyzing low sooting fuels. Both MPI and YSI guarantee high experimental accuracy but have the drawbacks of requiring costly instrumentation and detailed technical skills to master the experimental procedure. In the same year as the introduction of the MPI, an Automated Smoke Point SP10 test was patented by Reminiac and Pestiaux.20 The system adopts the standard ASTM D1322 setup, which is coupled with a charge-coupled device (CCD) camera and allows an automated flame height measurement. The light intensity is analyzed to detect the SP as the point of highest sensitivity to the decrease in the Feret diameter, while reducing the fuel uptake rate. Since the patent presents only a single calibration blend compared with the ASTM D1322 norm, additional investigations are needed to rate this method in detail. 5 ACS Paragon Plus Environment

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In 2013 Watson et al.21 introduced the fuel uptake rate measurement with threshold imaging (FURTI) method. The SP was defined as the first inflection point displayed by the flame height when plotted over the fuel uptake rate. The authors used the wick sheath and burner of the ASTM D1322 SP lamp, but removed it from the combustion chamber and placed it directly on an analytical balance. Fuel uptake rate measurements of 1 min duration were performed, while the flame evolution was simultaneously recorded by a web-cam. Watson and co-workers adopted the TSIII definition presented in eq. 2 and compared their experimental results with a previous literature work8 on the basis of the ASTM D1322 calibration blends.5 Their results generally exhibited half the experimental error. Although this latest attempt to improve the SP determination delivered a robust characterization of the SP, it relied on a subjective choice of a fixed light intensity threshold “best representing the observed flame structure”.21 Overall, the FURTI method represents the most promising method in literature, being capable of reducing the TSI experimental bias while ensuring simplicity in experimental setup and providing a clear definition of the SP condition. However, as in literature the wider TSI database is based on SP heights (see eq. 1) and not on critical fuel uptake rates, attention should be given to detect the SP height with precision and accuracy. The present article focuses on the development of a novel methodology for the automatic determination of the flame morphology during fuel uptake rate measurements. This research goal is pursued by analyzing first order intensity gradients of the soot luminosity recorded by a CCD camera, while keeping the experimental apparatus as compliant as possible with the ASTM D1322 setup.


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2. Materials and Methods In the current study the ASTM D1322 wick-fed lamp was used to conduct SP tests. The flame morphological evolution during uptake rates was analyzed according to the FURTI method, introduced by Watson and co-workers.21 Differently from the FURTI setup, where only the ASTM D1322 candle body and the burner gallery were adopted to conduct the experiments, the standard wick-fed lamp was used to perform the SP tests. This choice was made to achieve a higher comparability with previous works in literature. Particular care was given to achieve a high accuracy in the measurement. This was attained by substituting the commercially available webcam with a CCD camera to record soot luminosity. A maximum resolution of 0.0745 mm/pixel was achieved, which is higher than the 0.2 mm/pixel detected by the webcam adopted by Watson et al.21 and the 1 mm of the ASTM D1322 setup.5 Soot luminosity was preferred to the natural broadband luminosity to rule out the influence of the emission of other combustion species on the flame height calculation. The radiation of chemically excited hydroxyl radicals (OH*) was also recorded simultaneously for combustion diagnosis purposes. Since the SP determination was based on the soot luminosity analysis, for sake of brevity the analysis of the OH* radiation is omitted herein. Figure 1 presents the experimental setup under examination. The components are numbered and each part is listed in Tab 1. The ASTM D1322 wick-fed lamp was placed on a Sartorius LP6200s analytical balance, with a resolution of 0.01 g and maximum capacity of 6200 g. The position of the lamp on the balance was fixed with the help of reference marks. The laboratory scale was interfaced with a PC by means of a software provided by the manufacturer, which processed the analytical balance signal and saved continuous weight readings with a 1 Hz output frequency. An in-house developed algorithm written in MATLAB was used to perform linear regression analysis and assess the fuel uptake rates for each measuring point, as also performed by Watson and co-workers.21 To 7 ACS Paragon Plus Environment

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avoid the light reflection during the measurements, the inner surfaces of the SP wick-fed lamp were painted with a commercially available black opaque varnish, resistant towards high temperatures. The lamp gallery gleam of the combustion chamber was reduced via bluing and the yardstick was removed from the back-side of the combustion chamber. The CCD cameras were mounted on aluminum profiles for structural framing with a relative angle of 90°. The light beam of the flame was analyzed with regards to soot and OH* simultaneously, owing to a coated quartz glass. For the CCD, an OG570 long-pass filter, which prevented the passage of light below the wavelength of 570 nm, was adopted to capture soot luminosity as described elsewhere.22−24 Details of the CCD camera settings can be found in Tab. 2. Here, the optical equipment maximum mm/pixel resolution and the global measuring error are listed. The optical equipment and the analytical balance were activated with an external trigger and operated with a 1 Hz recording frequency. Air environmental boundary conditions were monitored during the measurements with regards to pressure, temperature and humidity. In the experimental assembly represented in Fig. 1, an aluminum and an acrylic glass box are depicted. The aluminum box was adopted in accordance with the ASTM D1322 norm to avoid drafts affecting the flame stability.5 The acrylic glass box was introduced to avoid the air flow influence on the balance measuring performance, since the experiments were conducted under a ventilation hood. 2.1 Experimental procedure The SP tests were conducted strictly following the ASTM D1322 norm5, with regards to apparatus calibration, warm-up and handling of the wick-fed lamp and cotton wicks during and after the measurements. After the warm-up procedure, the flame height was set to a specific starting value. The starting flame height was chosen to allow up to 40 measuring points to be conducted with 20 mL of fuel sample. Each measuring point lasted 120 s, where light intensity and fuel mass consumption were 8 ACS Paragon Plus Environment

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recorded. The fuel uptake rate variations were realized by increasing the wick surface area exposed to air. This procedure was standardized by adopting the pitch of the outer thread of the wick-fed burner, which featured an overall angular pitch of 9° and allowed for different uptake rate variations (viz., 4.5°, 9° and 18°). Table 3 summarizes the experimental procedure for the iso-octane/toluene calibration blends. The measurements aimed to capture the transition from a non-sooting flame with a well-defined round flame tip to a sooting one, with a sharp flame tip. The blends in Tab. 3 were measured nine times, as done by Watson et al.21 to enable a direct comparison of the measuring error and experimental reproducibility. The fuel uptake rate corresponded to the slope of the regression line obtained by plotting the mass over the time as done by the pioneers of the FURTI method.21 The fuels exhibiting a SP height not falling within the apparatus measuring range, such as saturated hydrocarbons and aromatic fuels, where measured in a base blend (BB) consisting of 35 vol% toluene and 65 vol% nheptane as also done elsewhere,13,14 to obtain a diesel surrogate fuel with a carbon (C) mass fraction of 87% and an hydrogen (H) mass fraction of 13%. The ternary blends were prepared with pipettes that had a resolution of 0.05 mL and therefore an accuracy of ± 0.025%. 2.2 Image post-processing during smoke point measurements Before describing the image post-processing method in detail, a few considerations need to be made concerning the drawbacks of using a fixed intensity threshold method to perform the image postprocessing. Figure 2 presents a flame of iso-octane processed in black and white colors for different fixed light intensity thresholds. Here, the influence of the intensity threshold on the flame morphology is evident. With decreasing threshold values, the area of elevated intensities above the flame has higher intensity counts than the threshold and is therefore considered as being part of the flame. This causes single white pixels, termed herein “flying pixels”, to appear above the flame area and makes a precise 9 ACS Paragon Plus Environment

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flame edge detection difficult. Moreover, the occurrence of these discontinuities in the flame intensity counts is greatly sensitive to the fixed threshold value, as shown in Fig. 3. Here, an iso-octane raw image at the SP is presented on the left-hand side and is followed, moving from the left to the right, by pictures processed at different intensity thresholds. An increase in the threshold value introduces a deviation in the flame height calculation that reaches a maximum of 9%. Hence, the adoption of a fixed intensity threshold significantly affects the flame detection and the height calculation. In light of the above considerations an intensity gradient approach was preferred to perform the image post-processing. The averaged intensity arrays (I̅) - obtained by applying an arithmetic mean to the 120 images recorded at each measuring point - were used to develop an algorithm to automatically detect the flame height. The image averaging is a well-known data reduction technique that allows ruling out small frame fluctuations and gathering a precise representation of the flame.25 First order gradients were derived from the ensemble-averaged intensity distributions and approximated by means of central finite difference coefficients;26 this approach was inspired by the methods presented by Jähne.27 The numerical gradients were calculated along i- and j-dimension, using a built-in MATLAB function named “gradient”. This function returned the numerical gradient array for each dimension. The array dimensions i and j represented the number of pixels along each image direction. The gradient array for the i-dimension, corresponding to the longitudinal flame direction, is introduced in eq. 5: ∆Ii̅ = 1, j=1 ∆i ∆I̅ = ⋮ ∆i ∆Ii̅ =imax , j=1 [ ∆i

⋯ ⋱ ⋯

̅ j=j ∆Ii=1, max ̅ ∆Ii=i

∆i ⋮

(5)

max , j=jmax

∆i

]

where the elements of the gradient array ∆I̅⁄∆i along the 𝑖-dimension are calculated by means of a symmetric difference quotient. Equation 7 defines this quotient:


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̅ ̅ ∆I̅i,j Ii+1,j -Ii-1,j = ∆i 2

(6)

The calculation for the 𝑗-dimension, which corresponds to the horizontal flame direction, is analogous as shown in eq. 7: ̅ ∆Ii=1,j=1 ∆j ∆I̅ = ⋮ ∆j ̅ ∆Ii=imax ,j=1 [ ∆j

⋯ ⋱ ⋯

̅ ∆Ii=1,j=j max ̅ ∆Ii=i

∆j ⋮

(7)

max ,j=jmax

∆j

]

where the elements of the gradient array ∆I̅⁄∆𝐣 along the j-dimension are calculated as described above. The discretization of the intensity array to integer values by the camera read-out system, in combination with the central finite difference coefficients calculation described in eq. 6, resulted in a minimum discretization size of 0.5 counts/pixel. At the extreme values of the array dimensions (i.e., i = 1, j = 1, i = imax and j = jmax ) the numerical gradient was defined as the difference to the next inner value, because the second supporting point for the calculation of the central finite difference coefficients was missing. Figure 4 presents exemplary images for the horizontal- and vertical-gradient arrays for iso-octane at a low and high flame height. Hence, the variation of the intensity gradients during a measurement is shown. A gray-scale color map with white to black representing strongly positive to strongly negative gradients is chosen. Here, it is easy to observe that flame and background are easily distinguishable, especially at lower heights and that the edges become more blurry with increasing flame size. The vertical-gradients are more useful than the horizontal ones, when trying to determine the tip of the flame. This is due to the absence of a change in the algebraic sign of the vertical gradient in the flame tip region. Hence, the i-direction gradients were chosen to realize the automatic flame height detection. To detect the edge of the flame, the vertical gradient array ∆I̅⁄∆i was analyzed column-wise. The 11 ACS Paragon Plus Environment

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column vectors that were closest to the longitudinal symmetry axis of the flame were investigated to automatically recognize the flame tip. For every column vector, belonging safely to the flame area, the entry of a first increase above the signal scattering corresponded to the flame edge. Figure 5 displays an evolution of intensity (left-hand side y-axis) and gradient intensity distribution (right-hand side y-axis) for a column at the horizontal flame center of a soot image. This location was chosen since the highest flame position was always observed there. The first substantial gradient increase (iterating from top to bottom) in the plot was considered as the start of the flame region. Due to noise and image averaging, it was necessary to rule out the signal scattering, while keeping the gradient value as low as possible to avoid an underestimation of the flame height. In this regard, the minimum discretization size of 0.5 counts/pixel was chosen. As shown in Fig. 5, the scattering of the gradient usually ranged from -1 to 1 counts/pixel, with some rare occurrences of 1.5 counts/pixel. Therefore, two conditions were considered relevant for the automatic recognition of the flame’s edge: (1) Entry under investigation above or equal to 1.5 counts/pixel; (2) Three out of four subsequent entries have to be above or equal to 1.5 counts/pixel. A value of 1.5 counts/pixel was chosen because it was the smallest possible increase from a value of 1 counts/pixel. A similar procedure was applied in the field of digital images processing by Jähne.27 This procedure was repeated for the 50 columns adjacent to the flame center in each direction. Figure 6 presents the flame tip edge detection according to this procedure on both gradient and raw intensity images. The aforementioned post-processing methodology was set on the basis of best practice, after having investigated the evolution of the intensity gradients around the flame tip for all fuels under analysis. The flame height was determined based on the highest position of the detected contour. To obtain the height, a conversion factor from pixels to mm was performed by means of a targeting procedure. A target device of known dimensions (1 cm grid size) was adopted to record an image prior to each 12 ACS Paragon Plus Environment

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experiment. The error introduced by the algorithm for the flame height calculation was set to be 2.5 pixels. This error accounted for the intensities array averaging bias and an average error observed during the experimental tests inherent to the targeting procedure. The procedure described above yielded robust results for all fuels when the flame heights varied from a non-sooting condition to the SP. However, in the case of fuels exhibiting significant flame flickering in the SP region, the discrete gradient approach yielded in few occurrences to an underestimation of the flame height. Thus, a reverse engineering approach was developed to overcome this problem. A built-in MATLAB smoothing function - based on a fifth order polynomial - was used to fit the discretized gradient vector. This procedure could no longer distinguish flame and background intensities on the basis of a reference discrete gradient (DG) value. To find the value of the smoothed gradient (SG) function best matching the DG until the SP, a sensitivity analysis was performed on all fuels under discussion. Figure 7 shows that a value of SG 1.5 accurately captures the original DG curve and matches the flame height at the SP (dashed horizontal line). Another advantage of the introduction of the SG was to negate the best-practice rules for the flame edge detection, since it switched from a discrete derivative function to a continuous one. Thus, it was adopted to process all fuels analyzed in this study. 3. Results In this section the detection of SP heights is firstly presented. Secondly, the determination of the TSI is given with a discussion concerning the error introduced by the experimental constants. Thirdly, the experimental TSI results are shown and the TSI linear blending rule is analyzed. 3.1 Determination of smoke point heights Figure 8 presents the evolution of the flame height over the fuel uptake rate for two out of the five iso-octane/toluene calibration blends. The top diagram (a) depicts the evolution of the flame height of 13 ACS Paragon Plus Environment

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iso- octane (2,2,4-trimethylpentane), while the bottom figure (b) shows a blend consisting of 90 vol% iso-octane and 10 vol% toluene. The flame height is obtained with the soot luminosity images which were recorded with the CCD camera. For both the flame height and the fuel uptake rate the experimental bias is presented in the form of error bars, which are difficult to be distinguished from the scatter points due to their small magnitude. The SP condition is marked with dashed lines. Equation 8 summarizes the error calculation for the flame height (σm,h-global) and eq. 9 the fuel uptake rate determination (σm,uptake-global ): σm,h-global = √σm,h 2 + ϵCCD 2 + ϵh,algo 2

(8)

σm,uptake-global = √σm,uptake 2 + σm,d 2 + σm,e 2

(9)

where: − m indicates a measuring point; − 𝜎 is the standard deviation evaluated over nine measurements; − ϵCCD is the systematic error introduced by the CCD camera resolution; − ϵh,algo is the systematic error introduced by the flame height calculation; − σm,d and σm,e are the deviations introduced by the regression line ym -dxm -e used to compute the fuel uptake rate. Equations 10 and 11 show the error related to the slope and intercept of a regression line, respectively. The error relative to the regression line is introduced in eq. 12, where E indicates the square root of the quantity obtained dividing the sum of the squares of the deviations from the best-fit line, by the number of data points p beyond the minimum required to fit the regression line.


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σm,d = E√

σm,e = E√

p

(10)

p ∑ x2m -(∑ xm )2

∑ x2m p ∑ x2m -(∑ xm )2

(11)

with: E =√

∑(ym -dxm -e)

2

(12)

p-2

The results exhibit linearity until the SP is reached. Afterwards, an inflection point is displayed as noticed also elsewhere.21 The plots show the first two flame regimes that can be observed while adopting the FURTI method: the linear increase in flame height with fuel uptake rate of non-sooting flames and the SP region characterized by a stronger dependence of the height on the fuel uptake rate. Since the flame stability decreases after the SP, due to a weak flickering, the experimental error increases which is in agreement with previous works.11,21 The uptake rate error is generally higher than the one displayed by the flame height and, in case of the iso-octane 90 vol% / toluene 10 vol% blend, the uptake rate error is significantly larger. As observed by Watson and co-workers,21 this is due to the wick height control performed with the sheath that gets affected by the cotton ‘burr’ at the wick top. Looking at Fig. 8−b the addition of 10 vol% toluene in iso-octane reduces its SP height from about 39 mm to 23 mm, due to the increased blend aromaticity. To compare the results of this work with the ASTM D1322 standard, the measurements of the isooctane/toluene calibration blends were firstly conducted following the standard procedure, 5 then according to the FURTI method.21 In the first case only three measurements were conducted per blend as stated in the ASTM D1322 standard,5 while in the second one nine times as done by Watson et al.21


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Table 4 compares the results obtained with the different methods. The reference values of the SP height measured according the ASTM D1322 norm are reported before and after the scaling procedure included in the standard. The scaled SP values are marked with the superscript ‘s’. This enables a comparison between the raw SP heights obtained with both procedures. This work’s results obtained with the ASTM D1322 standard are comparable with the normed values after the scaling procedure (the scaling factor was computed using the iso-octane and the iso-octane 90 vol% / toluene 10 vol% blend). Furthermore, the results are in agreement with the values found in literature. Looking at the first-column from the right-hand side, the SP heights obtained with the novel FURTI method are listed. These agree with the unscaled SP height values derived with the ASTM D1322 norm but exhibit a significantly lower experimental error. An error of ± 0.5 mm is found for all calibration blends with the exception of the iso-octane 90 vol% / toluene 10 vol% blend. This blend shows a higher experimental bias which was also found by Watson et al.,21 due to the reason previously discussed (i.e., cotton ‘burr’ at the wick top mentioned in the presentation of the results in Fig. 8-b). The results obtained with the novel methodology reduce the experimental error in the flame height calculation, yielding a relative error reduction from a minimum of 67% to a maximum of 86% in comparison to the unscaled values obtained according to the norm. Figure 9 presents the unscaled values obtained according to the ASTM D1322 norm with the results obtained with the novel methodology for the SP determination based on the FURTI approach. An excellent agreement between the data sets is observable, confirming the validity of the FURTI method to also determine SP heights. Here, the regression line indicates an underestimation of the SP height values obtained with the proposed method in comparison to the ASTM D1322 norm. Several factors are of relevance for the overall reduction in experimental error obtained with the novel methodology. Firstly, the adoption of the inflection point to define the SP allows for a high experimental 16 ACS Paragon Plus Environment

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repeatability.21 Secondly, the objective image post-processing approach that does not rely on a fixed light intensity threshold improves the repeatability of the height calculation. This last aspect in combination with the soot intensity recorded with a high accuracy CCD camera diminishes the experimental error. The reduction of the experimental bias in the SP height determination is important, especially when considering that the majority of works in literature adopt the TSII formulation.6,8,10,13,14,28 To prove a comparability of the results with the original FURTI method, Fig. 10 presents a regression analysis between the uptake rates obtained in this work and the ones published by Watson and co-workers.21 The correlation displayed in the plot shows that both methodologies are comparable. Here, the regression line indicates an underestimation of the uptake rate values in comparison to the original FURTI method. This can be attributed to different wick-fed lamp setups (e.g., this work uses the original ASTM D1322 lamp, whereas Watson et al.21 use only the candle body of the ASTM D1322 burner) and analytical balances used. Hence, it is impossible to decouple in which extent each effect plays a role on the determination of the fuel uptake rates. 3.2 Threshold Sooting Index determination The TSI determination implies the adoption of two apparatus-dependent constants. In literature, two main methods are found for the calculation of those constants. A first approach was introduced by Calcote and Manos6 and derives the constants by setting the Mw /hSP of two fuels equal to two TSI values, which can be arbitrarily chosen in a scale ranging from 0 (assigned to ethane) to 100 (assigned to naphthalene). In this study two fuels were chosen among the neat hydrocarbons tested. A TSI of 3.5 was assigned to cyclohexane and 15 to decalin, considering the normalized TSI rating scale published by Olson et al.8 that agreed with the ranges of the abovementioned scaling procedure. Solving a two


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equation linear system, as presented in eqs. 13 and 14, the constants a and b were determined to be 2.47 mol g−1mm−1 and -0.78, respectively. {

3.5 = a(Mw,cyclohexane /hSP,cyclohexane ) + b 15 = a(Mw,decalin /hSP,decalin ) + b

(13−14)

The simplicity of the above method has the drawback to introduce an arbitrary choice of two compounds to solve eqs. 13 and 14. This directly affects the error introduced by the experimental constants on the TSI determination. An accurate choice of the compounds can lead to low errors even if the experimental database features an averaged experimental bias higher than the one of the two specific compounds. For this reason, Olson and co-workers8 suggested another possibility to obtain the apparatusdependent constants by performing a linear regression analysis between a set of Mw /hSP and the corresponding TSI values from another normalized database. For sake of clarity, the experimental constants obtained by this regression process are termed a* and b* from now on. Figure 11 shows the correlation between this work hSP and the TSI values published by Olson et al.8 The experimental results indicate a good agreement with literature, exhibiting a squared correlation coefficient (R2) of 98.4%. With the two pairs of constants (a, b) and (a*, b*), TSI values for the reference blends were derived and compared with literature in Tab. 5. The TSI error was evaluated including the deviations introduced by the apparatus dependent constants according to eqs. 11 and 12. The TSI error is presented in eq. 15:

σTSI =

Mw 2 σa 2 σm,h-global 2 ) (( ) + ( ) ) + σ2b hSP a hSP

√a2 (

(15)

Where σa and σb are the deviations introduced by the experimental constants. These were computed in case of (a, b) using the standard rules for the error propagation as also done elsewhere,21 while in case of (a*, b*) the error introduced by the regression line was computed as explained in eqs. 10−12. 18 ACS Paragon Plus Environment

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The errors introduced by the constants yielded in case of (a, b) to a σa of 0.06 and a σb of 0.1, while in case of (a*, b*) to a σa* of 0.1 and a σb* of 1.75. Thus, considerably higher errors are present when a larger number of experimental data is used for the normalization procedure. The absence of an arbitrary choice of two reference compounds to perform the scaling, allowed to best capture the deviations between different data sets and should be preferred. This aspect is evident in the absolute experimental errors listed in Tab. 5. The comparison of the TSI with the TSIII from literature shows a good agreement, since both TSI values were obtained with the (a, b) constants. Here, this work’s results present slightly lower TSI bias. Differently, the TSIs calculated with the (a*, b*) constants - due to higher inherent errors of the experimental constants - feature higher bias in comparison to the literature values obtained with the (a, b) constants, generally. Table 6 presents the experimental database derived in this work. It consists of several hydrocarbon classes including aromatic, cyclic and paraffinic hydrocarbons. Few compounds were measured neat (viz., European standard EN590 diesel,29 cyclohexane, cyclohexene, decalin and iso-octane) since they fitted the measuring range of the wick-fed lamp, while the majority of the fuels were blended with the BB. Only n-heptane was blended with toluene, since the BB was obtained by mixing these two fuels. Looking at the absolute experimental errors of the flame height listed in Tab. 6 the low bias discussed for the calibration fuels are featured also by the other compounds. Additionally, the error exhibits a low sensitivity to the fuel type, ranging from a minimum of 1% to a maximum of 5% for the SP heights. This aspect is important considering the continuing interest in surrogates for fossil-derived fuels. While generally aromatic hydrocarbons and their blends exhibited high experimental errors in literature,30,16,8,10 here the same magnitude of errors is observed among the different hydrocarbon classes, independently from their blend composition.


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3.3 Validation of the linear blending rule for TSI and extrapolation of SP heights for neat compounds Figure 12 presents the ternary-blends tested in this work. The y-axis indicates the TSImix and the xaxis the molar fraction of the BB in the mixture. Each blend is distinguished by the symbol style and a horizontal dashed line is plotted to indicate the TSI of the BB. An excellent linearity is present for all the blends analyzed, as confirmed by the trend lines approaching the BB reference line. All the aromatic and cyclic hydrocarbons have increasing sooting tendencies when added to the BB. Since the trend lines do not cross each other, the following ranking can be derived. 1-Methylnaphthalene exhibits the highest sooting tendency, followed by naphthalene, toluene, benzene and cyclopentene. All ringstructured molecules do not exert a dilution effect on the BB aromatic content and contribute to the increase in sooting tendency of the mixture. n-Octane, being the only representative of paraffinic molecules, introduces a dilution effect on the BB sooting tendency that is proportional to the amount of this fuel in the mixture. The paraffinic functional groups of n-octane dilute the toluene content of the mixture and reduce its TSI. The TSIs of the fuels, which were blended with the BB, were extrapolated according to a procedure that can also be found elsewhere.32 The Mw /hSP values were plotted versus the molar fraction of the BB and the resulting trend line was used to extrapolate the SP height of the neat compound, as shown for n-octane in Fig. 13. The extrapolated TSI values are given in Tab. 7, together with results of the regression analysis and the relative 95% prediction intervals (PI95). The correlation coefficients of the regression exhibit an excellent agreement, showing the validity of the linear blending rule for the TSI metric. Thanks to the extrapolation procedure, a global soot rating scale was established, as shown in Fig. 14. Here, the fuels are presented in bar charts in order of increasing sooting tendencies. In agreement with the general trends observed in the literature,6,8,10,12 the sooting tendency increases with 20 ACS Paragon Plus Environment

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the carbon unsaturation level (i.e., paraffinic < iso-paraffinic < cyclic < aromatic hydrocarbons) as is evident by the comparison of molecules like tetralin, decalin and naphthalene or cyclohexane and cyclohexene. Additionally, for fuels of the same hydrocarbon class, the sooting tendency increases by raising C/H ratio, as can be seen when comparing n-heptane with n-octane or benzene with naphthalene. An interesting comparison to be made is between cyclopentene and cyclohexene. This C5 cyclic compound has almost double the TSI of cyclohexene. This is in agreement with previous works.6,8,33 Gomez et al.33 explained this behavior as follows. Initially, during the fuel pyrolysis, cyclopentene is dehydrogenated to cyclopentadiene, which forms highly conjugated species and greatly contributes to soot precursor formation. On the contrary, cyclohexene pyrolizes primarily to ethane and butadiene that are both non-cyclic molecules. A comparison of the results discussed above with literature follows in Fig. 15. Here, the TSIs listed in Tab. 7 obtained with the (a*, b*) experimental constants are compared with reference values (TSIref), which were calculated by averaging results found in previous literature sources8,10,21,38,39 as also done elsewhere.6,8 The regression line in Fig. 15 exhibits a correlation coefficient of 99%, confirming that the proposed methodology strongly agrees with previous works in literature. Table 8 lists the data sets used to derive the TSIref. The values suggested by Olson and co-workers8 are the results of the normalization that the authors conducted on their experimental results with previous works.28,30,34−37 Hence, they represent the starting values herein. Additionally, recent works10,21,38,39 are also considered. Few literature works allow a direct comparison in terms of absolute error;21 thus, a standard deviation from the mean value was computed for the fuels featuring TSIref based on at least three literature instances. Generally, the TSIs obtained in this work with the experimental constants (a*, b*) are higher than the values from the previous literature sources. This is, as previously shown (see Tab. 5), due to the regression method adopted to compute the experimental 21 ACS Paragon Plus Environment

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constants (a*, b*). To clearly demonstrate this point, Tab.8 also includes the TSIs computed with the (a, b) constants. Here, the TSI values show a better agreement with the reference database since the same method for the determination of the (a, b) constants is used. Among all fuels, the TSI obtained for toluene and tetralin feature the highest absolute deviations from the TSIref values. Since both compounds have a high standard deviation of the TSIref and this indicates a high level of uncertainty in the reference value itself, it is difficult to comment on the nature of such deviations. 4. Conclusions This work presents a novel methodology for the determination of SP heights based on the FURTI method. Here, the standard ASTM D1322 wick-fed lamp is used and the flame height is measured by means of a CCD camera recording soot luminosity. First order gradients of the light intensity arrays are used to detect the flame height without the need for a fixed intensity threshold value based on best practice. The novel methodology was compared with the ASTM D1322 standard using a set of reference calibration iso-octane/toluene blends. The comparison showed: o Good agreement between the smoke point heights and the values by the ASTM D1322 norm. o Significant reduction of the experimental bias in the SP height in comparison to the norm, ranging from a minimum of 67% to a maximum of 86%. o Experimental bias less sensitive to the blending proportion of the calibration blends. o Validity of the FURTI method also in the determination of the TSI on the basis of smoke point height measurements. A comparison between the two existing methods to derive the experimental constants for the TSI was performed. The analysis outlined that the choice of the TSI normalization method significantly affects the TSI error. The novel methodology was also tested against several hydrocarbon classes, measured neat or blended with a mixture consisting of 65 vol% n-heptane and 35 vol% toluene. The 22 ACS Paragon Plus Environment

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analysis showed comparable results with previous works in literature, ensuring a low SP height bias that ranged from a minimum of 1% to a maximum of 5 % as well as a low sensitivity to the fuel sample composition. The results verified the validity of the linear blending rule and allowed the analysis of sooting tendency on a molecular level basis. Future work should focus on testing this methodology also with ternary blends including oxygenated hydrocarbons. The excellent linearity exhibited by the hydrocarbon mixtures together with the novel flame height morphological detection will enable the soot rating with high measurement precision and accuracy of fuels which reach the SP outside the apparatus measuring range. Next, the image post processing approach could be extended to the synergic analysis of vertical and horizontal first order light intensity gradients in order to implement an automated morphological detection of the flame. 5. Acknowledgments This work was performed as part of the Cluster of Excellence ‘‘Tailor-Made Fuels from Biomass’’, which is funded by the Excellence Initiative by the German Federal and State Governments to promote Science and Research at German Universities. 6. Nomenclature Abbreviations ASTM

American Society for Testing and H Materials

Hydrogen

BB

Base blend

MPI

Micropyrolysis Index

C

Carbon

OH*

Excited hydroxyl radical

CCD

Charge-coupled device

SG

Smoothed gradient

DG

Discrete gradient

TSI

Threshold Sooting Index

FURTI Fuel uptake rate measurement with YSI threshold imaging

Yield Sooting Index


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Symbols a

TSI experimental constant

ṁ

Mass flow rate

b

TSI experimental constant

Mw

Molecular weight

d

Angular coefficient of a regression line

R

Correlation coefficient

e

Intercept of a regression line

V̇

Volumetric flow rate

E

Error introduced by a regression line

x

Molar fraction

I̅

Averaged intensity array

ϵ

Measuring accuracy

i

Longitudinal flame direction

Δ

Gradient

j

Radial flame direction

Subscripts and superscripts (repetition of abbreviations/symbols avoided) algo

Image processing algorithm

min

Minimum

e

Intercept of a regression line

mix

Mixture

f

Flame

n

Total fuels in a mixture

h

Flame height

p

Number of minimum points in a fit-line

k

Component of a fuel mixture

s

Scaled

m

Measuring point

I, II

Different TSI formulation

max

Maximum

′, ′′, * Different method for the calculation of the TSI experimental constants

5. References (1) Penner, J. E.; Lister, D. H.; Griggs, D. J.; Dokken, D. J.; McFarland, M. IPCC Special Report Aviation and the Global Atmosphere; Technical report, Intergovernmental Panel on Climate Change (IPCC), 1999. (2) Working Group on the Evaluation of Carcinogenic Risks to Humans, Diesel and gasoline engine exhausts and some nitroarenes; Technical report, International Agency for Research on Cancer (IARC), Lyon, FR, 2013. 24 ACS Paragon Plus Environment

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(3) Liu, C.; Nemoto, S.; Ogano, S. Effect of Soot Properties in Diesel Engine Oils on Frictional Characteristics, Tribol. Trans., 2003, 46 (1), 12–18. (4) George, S.; Balla, S.; Gautam, M. Effect of diesel soot contaminated oil on engine wear, Wear, 2007, 262 (9–10), 1113–1122. (5) ASTM D1322-08, Standard Test Method for Smoke Point of Kerosine and Aviation Turbine Fuel, American Society for Testing and Materials (ASTM): West Conshohocken, PA, 1997. (6) Calcote, H. F.; Manos, D. M. Effect of molecular structure on incipient soot formation, Combust. Flame, 1983, 49 (1–3), 289–304. (7) Roper, F. G. The prediction of laminar jet diffusion flame sizes: Part I. Theoretical model, Combust. Flame, 1977, 29, 219–226. (8) Olson, B.; Pickens, J. C.; Gill, R. J. The effects of molecular structure on soot formation II. Diffusion flames, Combust. Flame, 1985, 62 (1), 43–60. (9) Gill, R. J.; Olson D. B. Estimation of Soot Thresholds for Fuel Mixtures, Combust. Sci. Technol., 1984, 40 (5–6), 307–315. (10) Mensch, A.; Santoro, R. J.; Litzinger, T. A.; Lee, S. Y. Sooting characteristics of surrogates for jet fuels, Combust. Flame, 2010, 157 (6), 1097–1105. (11) Botero, M. L.; Mosbach, S.; Akroyd, J. Kraft, M.; Sooting tendency of surrogates for the aromatic fractions of diesel and gasoline in a wick-fed diffusion flame, Fuel, 2015, 153, 31–39. (12) Yang, Y.; Boehman, A. L.; Santoro, R. J. A study of jet fuel sooting tendency using the threshold sooting index (TSI) model, Combust. Flame, 2007, 149 (1–2), 191–205. 25 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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(13) Pepiot-Desjardins, P.; Pitsch, H.; Malhotra, R.; Kirby, S. R.; Boehman, A. L. Structural group analysis for soot reduction tendency of oxygenated fuels, Combust. Flame, 2008, 154 (1–2), 191–205. (14) Barrientos, E. J.; Lapuerta, M.; Boehman, A. L. Group additivity in soot formation for the example of C-5 oxygenated hydrocarbon fuels, Combust. Flame, 2013, 160 (8), 1484–1498. (15). Botero, M. L.; Mosbach, S.; Kraft, M. Sooting tendency of paraffin components of diesel and gasoline in diffusion flames, Fuel, 2014, 126, 8–15. (16) Jiao, Q.; Anderson, J. E.; Wallington, T. J.; Kurtz, E. M. Smoke Point Measurements of DieselRange Hydrocarbon–Oxygenate Blends Using a Novel Approach for Fuel Blend Selection, Energy Fuels, 2015, 29 (11), 7641–7649. (17) Barrientos, E. J.; Anderson, J. E.; Matti Maricq, M.; Boehman, A. L. Particulate matter indices using fuel smoke point for vehicle emissions with gasoline, ethanol blends, and butanol blends, Combust. Flame, 2016, 167, 308–319. (18) McEnally, C. S.; Pfefferle, L. D. Improved sooting tendency measurements for aromatic hydrocarbons and their implications for naphthalene formation pathways, Combust. Flame, 2007, 148 (4), 210–222. (19) Crossley, S. P.; Alvarez, W. E.; Resasco, D. E. Novel micropyrolysis index (MPI) to estimate the sooting tendency of fuels, Energy Fuels, 2008, 22 (4), 2455–2464. (20) Reminiac, M.; Pestiaux, P. Method and Device for Determining the Smoke Point of Hydrocarbons, US Patent App. 11/722,770, 2008.


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(21) Watson, R. J.; Botero, M. L.; Ness, C. J.; Morgan, N. M.; Kraft, M. An improved methodology for determining threshold sooting indices from smoke point lamps, Fuel, 2013, 111, 120–130. (22) Jakob, M.; Hülser, T.; Janssen, A.; Adomeit, P.; Pischinger, S.; Grünefeld, G. Simultaneous high-speed visualization of soot luminosity and OH* chemiluminescence of alternative-fuel combustion in a HSDI diesel engine under realistic operating conditions, Combust. Flame, 2012, 159 (7), 2516–2529. (23) Hülser, T.; Jakob, M.; Grünefeld, G.; Adomeit, P.; Pischinger, S.; Klein, D. Optical investigation of fuel and in-cylinder air-swirl effects in a high-speed direct-injection engine,“ Int. J. Engine Res., 2015, 16 (6), 716–737. (24) Smooke, M.; Long, M.; Connelly, B.; Colket, M.; Hall, R. Soot formation in laminar diffusion flames, Combust. Flame, 2005, 143 (4), 613–628. (25) Hernandez, R.; Ballester, J. Flame imaging as a diagnostic tool for industrial combustion, Combust. Flame, 2008, 155(3), 509–528. (26) Fornberg, B. Generation of finite difference formulas on arbitrarily spaced grid, Math. Comput., 1998, 51 (184), 699–706. . (27) Jähne, B. Digital image processing, Springer: Berlin, GE, 1991. (28) Clarke, A.; Hunter, T. G.; Garner, F. H. The Tendency to Smoke of Organic Subastances on Burning , Part I, J. Inst. Pet. Technolo.,1946, 32, 627–642. (29) Technical Commitee CEN/TC 19, Automotive fuels-Diesel-Requirements and test methods, European Commitee for Standardization: Brussels, BE, 1999. 27 ACS Paragon Plus Environment

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(30) Pischinger, S. Alternative Vehicles Propulsion Systems: 4th Edition, Institute for Combustion Engines (VKA) RWTH Aachen University, Aachen, 2015. (31) Hunt, R. A. Relation of Smoke Point to Molecular Structure, Ind. Eng. Chem., 1953, 45 (3), 602–606. (32) Haas, F. M.; Qin, A.; Dryer, F. L. “Virtual” Smoke Point Determination of Alternative Aviation Kerosenes

by

Threshold

Sooting

Index

(TSI)

Methods,

Proceeding

of

the 50th

AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Cleveland, OH, USA, Jul 28–30, 2014, American Institute for Aeronautics and Astronautics (AIAA): Reston, VA, 2014. (33) Gomez, A.; Sidebotham G.; Glassman, I. Sooting behavior in temperature-controlled laminar diffusion flames, Combust. Flame, 1984, 58 (1), 45–57. (34) Minchin, S. T. Luminous stationary flames: The quantitative relationship between flame dimensions at the sooting point and chemical composition, with special reference to petroleum hydrocarbons, J. Inst. Pet.Technolo., 1931, 17 (1), 102–120. (35) Shalla, R. L.; McDonald, G. E. Variation in Smoking Tendency Among Hydrocarbons of Low Moleuclar Weight, Ind. Eng. Chem., 1953, 45 (7), 1407–1500. (36) Van Treuren, K. W. Sooting characteristics of liquid pool diffusion flames, Ph.D. Dissertation, Princeton University, Princeton, NJ, 1978. (37) Schug, K. P.; Maheimer-Timnat, Y.; Yaccarino, P.; Glassman, I. Sooting Behavior of Gaseous Hydrocarbon Diffusion Flames and the Influence of Additives," Combust. Sci. Technol., 1980, 22 (5– 6), 235–250.


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(38) Ladommatos, N.; Rubenstein, P.; Bennett, P. Some effects of molecular structure of single hydrocarbons on sooting tendency, Fuel, 1996, 75 (2), 114–124. (39) Barrientos, E. J.; Boehman, A. L. Examination of the sooting tendency of three-ring aromatic hydrocarbons and their saturated counterparts, Energy Fuels, 2010, 24 (6), 3479–3487.


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Figures

8 3 1

4 7

11 10

2

5

9 6 6 Figure 1. CAD rendering of the SP test experimental setup.

Threshold: 255

Threshold: 250

Threshold: 245

Threshold: 240

Continuous flame shape

First appearance of “flying pixels”

Increase in “flying pixel”

“Flying pixel” part of the flame

(a)

(b)

(c)

(d)

Figure 2. Influence of intensity count thresholds on the morphology of an iso-octane flame.


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44.17 / mm

43.21 / mm

42.02 / mm

40.61 / mm

Figure 3. Influence of intensity threshold value on the height of an iso-octane flame: from the raw image on the left-hand side a reduction in height is progressively shown by increasing threshold values (i.e., 10, 15, 50 and 150 moving from the left to the right-hand side).

∆̅ ∆

∆̅ ∆i

∆̅ ∆

∆̅ ∆i

Array index 𝑖 -direction

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Array index 𝑗 -direction Figure 4. iso-Octane soot images post-processed with first order intensity gradients.


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4 3 1.5 2 1 0 -1 -2 100 200 300 400 Vertical position / pixel

0

Vertical gradient / (counts/pixel)

600 500 400 300 200 100 0

Vertical position

Intensity / counts

Center horizontal position

Figure 5. Intensity and gradient intensity distributions at flame center location for an exemplary iso-

Flame height / mm

octane soot image (bottom part of the flame cut to fit the plot dimensions).

Flame height / mm

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Distance to center / mm (a)

Distance to center / mm (b)

Figure 6. Soot vertical gradient image (a) and raw soot image (b) of an iso-octane flame: flame edge indicated with a solid line.


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Figure 7. Comparison of DG and SG functions during uptake rate variations of an iso-octane flame (i.e., an uptake rate variation defines a measuring point): sensitivity analysis to match the DG of 1.5 best capturing the flame evolution until the SP.


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(a)

(b)

Figure 8. Flame height over fuel uptake rate for (a) iso-octane and (b) iso-octane 90 vol% / toluene 10 vol%: SP values marked with dashed lines and absolute errors represented with error bars.


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Figure 9. SP flame heights of the calibration blends: comparison of this work’s results obtained according to the ASTM D1322 norm5 with the novel SP detection methodology applied to the FURTI approach.21

Figure 10. Uptake rate measurements at the SP of the calibration blends: comparison of this work’s results against literature.21


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Figure 11. Determination of the TSI experimental constants via regression analysis: this work against the literature data published by Olson et al. 8 (fuels analyzed: cyclohexane, cyclopentene, cyclohexene, heptane, octane, iso-octane, decalin, benzene, toluene, tetralin, 1-methylnaphtalene and naphthalene).


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Figure 12. Hydrocarbons ternary blends tested in this work: error bars indicate absolute errors.


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Figure 13. Trend line used to extrapolate the neat Mw/hSP value of n-octane.

Figure 14. Soot rating scale of the hydrocarbon fuels tested: error bars representing the absolute experimental error (i.e., cyclohexane, iso-octane, cyclohexene, cyclopentene, decalin and diesel) in case of neat fuels and the PI95 corresponding to the extrapolated neat value in case of fuels tested in blends.


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Figure 15. Comparison of the TSIs obtained in this work with the (a*, b*) constants with the reference literature database: values listed in Tab. 8.


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Tables Table 1. Components of the SP test experimental setup. Part N° Description 1

ASTM D1322 SP wick-fed lamp

2

Sartorius LP6200s analytical balance

3

CCD camera

4

High-pass filter

5

CCD camera

6

Low-pass filters combination

7

Beam splitter

8

Aluminum box

9

Acrylic glass box

10

Aluminum flat rail system

11

Aluminum structural profile

Table 2. Optical equipment specifications and settings.

Long-pass filter

SCHOTT OG570

CCD camera resolution / pixel

1024 x 1286

Flame height resolution / (mm/pixel)

maximum

0.0745

CCD camera exposure time / µs

48

CCD camera recording interval / Hz

1


Page 41 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 3. Fuel uptake rate variation strategy when executing SP tests for the calibration blends. Iso-octane Toluene Starting flame height Fuel uptake variation strategy vol%

vol%

mm

Before SP

SP and beyond

100

0

20

18° x 10

9° x 25

95

5

18

18° x 8

9° x 12

90

10

17

9° x 10

4.5° x 10

80

20

12

9° x 7

4.5° x 10

60

40

10

4.5° x 15

4.5° x 10

Table 4. Comparison of this work reference blends with literature. SP detection method

ASTM D1322

Calibration blends

Norma

FURTI method Watson al.b

This work

IsoToluene hSP octane

hSP s

vol%

vol%

mm

mm

mm ±

100

0

42.8

44.4

95

5

35.4

90

10

80 60 a

hSP

et Watson et This work al.b

hSP mm

Uptake rate

±

µg/s

39.4 1.50 38.7

1.40

34.1

30.3 3.80 30.7

30.2

29.2

20

22.7

40

14.7

Uptake rate ±

µg/s

hSP ±

mm

±

1832 106 1497 40

38.6

0.49

4.30

1335 36

1125 61

30.1

0.52

25.9 3.50 24.0

3.50

1098 61

877

59

23.3

0.85

22.6

20.1 2.30 18.1

2.20

753

37

762

67

18.3

0.54

16.0

14.2 1.80 11.2

1.20

525

52

492

32

12.7

0.48

ASTM D1322 standard ref 5.

b

Data from ref 21.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 46

Table 5. TSI determination for the calibration blends: comparison of the different methods to derive the experimental constants - each blend tested nine times.

TSIII a

TSI formulation

TSI

Constants

(a, b)b

Literature source

This work This work Watson et al.d

(a*, b*)c

(a, b)

Iso-octane Toluene

a

vol%

1

±

1

±

1

±

100

0

6.5

0.2 8.3

1.8 6.2

0.6

95

5

8.2

0.3 10.0

1.8 8.8

0.5

90

10

11.8

0.6 13.7

1.9 10.8

0.8

80

20

13.9

0.6 15.8

1.9 15.9

1.0

60

40

19.4

0.9 21.3

2.1 22.3

2.5

TSI derived from the fuel mass flow rate at the SP.

b c

vol%

TSI constants obtained as done in ref 6, using cyclohexane and decalin as reference compounds.

TSI constants obtained as done in ref 8.

d

Data from ref 21.


Page 43 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 6. Experimental compendium of SP heights and TSIs.

Fuel / Fuel blend

Mw

hSP

g/mol

mm

TSI (a*, b*)a ±

%

1

±

%

Diesel

190.00b 16.63 0.71 4.27 29.38 2.37 8.07

Decalin(trans-Decahydronaphthalene)

138.25

21.68 0.20 0.92 16.81 1.80 10.71

2,2,4-Trimethylpentane(iso-Octane)

114.23

38.60 0.46 1.19 8.34

1.80 21.58

Cyclohexene

82.14

27.60 0.68 2.46 5.35

1.76 32.90

Cyclohexane

84.16

47.97 0.69 1.44 8.38

1.79 21.36

Naphthalene 15 / BB 85 vol%

101.38

9.90


99.84

12.00 0.62 5.17 21.68 2.17 10.01


98.30

14.33 0.71 4.95 18.05 2.04 11.30

0.36 3.64 26.40 2.16 8.18

1-Methylnaphthalene 15 / BB 85 vol% 103.20

9.90

0.40 4.04 26.87 2.22 8.26

1-Methylnaphthalene 10 / BB 90 vol% 101.04

11.61 0.23 1.98 22.58 1.95 8.64

1-Methylnaphthalene 5 / BB 95 vol%

98.89

13.57 0.25 1.84 19.07 1.89 9.91

Tetralin 40 / BB 60 vol%

110.50

9.10


103.56

12.40 0.46 3.71 21.73 2.05 9.43


100.14

14.43 0.62 4.30 18.23 2.00 10.97

Benzene 40 / BB 90 vol%

87.57

9.79


91.78

11.92 0.41 3.44 20.11 1.98 9.85


94.16

14.42 0.33 2.29 17.19 1.88 10.94

Cyclopentene 60 / BB 40 vol%

77.04

13.00 0.19 1.46 15.70 1.84 11.72


82.57

14.20 0.22 1.55 15.42 1.84 11.93


89.05

15.50 0.50 3.23 15.22 1.87 12.29

n-Octane 10 / BB 90 vol%

98.19

20.03 0.28 1.40 13.16 1.78 13.53

0.20 2.20 31.10 2.12 6.82

0.20 2.04 23.18 1.96 8.46


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

TSI (a*, b*)a

Mw

hSP

g/mol

mm


99.67

21.13 0.31 1.47 12.70 1.79 14.09


102.71

25.77 0.22 0.85 10.88 1.81 16.64


106.29

32.65 0.40 1.23 9.07

n-Heptane 60/Toluene 40 vol%

96.33

15.05 0.76 5.05 16.87 2.01 11.91

n-Heptane 65/Toluene 35 vol% (BB)

96.76

16.92 0.48 2.84 15.18 1.87 12.32


98.13

27.94 0.4

1.43 9.71

1.78 18.33


99.13

37.79 0.43 1.14 7.51

1.77 23.57

Fuel / Fuel blend

a

Page 44 of 46

±

%

1

±

%

1.81 19.96

TSI constants obtained as done in ref 8.

b

Literature data from ref 30.

Table 7. Extrapolated TSI values with respective PI95. Fuel

Structure Mw g/mol

Naphthalene

C10H8

PI95

Regression results

1

±

Line

R2

128.18 99.03 15.22 y = -34.42x + 39.53 0.99

1-Methylnaphthalene C11H10

a

TSI

142.20 97.08 10.37 y = -33.06x + 38.74 0.99

Tetralin

C10H12

132.20 58.34 5.73

y = -18.04x + 23.12 0.99

Toluenea

C7H8

110.60 33.66 1.20

y = 9.94x + 2.79

0.99

Benzene

C6H6

78.11

31.75 4.31

y = -6.68x + 12.40

0.98

Cyclopentene

C5H8

66.11

15.98 0.04

y = 0.43x + 5.60

0.99

n-Octane

C8H18

114.23 4.96

0.40

y = 3.65 + 1.60

0.99

n-Heptane

C6H16

100.21 3.34

0.98

y = 11.16x + 0.94

0.98

Derived from the toluene/iso-octane calibration blends of the ASTM D1322 norm from ref 5.


ACS Paragon Plus Environment

96.9

C6H10 C5H8 C610H18 C6H10 C6H6 C7H8 C10H12

Cyclohexene

Cyclopentened

Decalin

Diesel

Benzened

Toluened

Tetralind

1-Methylnaphthalened C11H10

Naphthalened

31.7

29.8

27.4

14.1

15.0

6.6

6.5

3.6

15.2

10.4

5.7

1.2

4.3

1.3

0.04

0.4

0.27

0.2

0.16

0.4

1.0

±

99.0

97.1

58.3

33.7

31.8

29.4

16.8

16.0

8.4

8.3

5.4

5.0

3.3

1

15.2

10.4

5.7

1.2

4.3

2.4

1.8

0.04

1.8

1.8

1.8

0.4

1.0

±

5.7

5.6

3.2

3.2

2.7

1

100.0 100.0

91.0 89.0

61.0 56.0

44.0 50.0

29.0 31.0

15.0 13.0

16.0 15.0

5.9

6.4

3.5

3.2

2.6

1

1

100.0 91.0

71.0

40.0

30.0

20.0

6.8

1

2.9

0.6

±

100.0 1.20

35.5

6.2

1

100.0

94.2

62.7

41.4

30.0

16.0

15.5

5.8

6.3

3.4

3.2

2.7

1

4.8

7.6

7.8

1.0

3.6

0.7

0.1

0.5

0.2

0.1

±

constants obtained as done in ref 6, using cyclohexane and decalin as reference compounds. bTSI constants obtained as done in ref 8. cAveraged TSI value from refs 8,10,21,38,39. dExtrapolated value.

aTSI

94.9

C8H18

iso-Octane

C10H8

56.3

C6H10

Cyclohexane

3.2

C8H18

n-Octaned

1.6

C6H16

1

Structure This work (a, b)a This work (a*, b*)b Ref 8 Ref 38 Ref 10 Ref 39 Ref 21

TSI literature source

n-Heptaned

Name

Fuel TSIrefc

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 8. TSI Experimental compendium of neat hydrocarbons compared with literature data.

Page 45 of 46 Energy & Fuels

45

Energy & Fuels

Table of Content Graphic (For Table of Contents Only) Soot image 100 200 300

400 500 600

700 50 100 150

Radial / pixel

1800 1600 1400 1200 1000 800 600 400 200 0

20 15 10 5 0 -5 -10 -15 -20 -25 -30 0

Vertical gradient / (counts/pixel)

Position: 20 pixel right to center Soot intensity / counts

Longitudinal / pixel

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 46 of 46

100 200 300 400 500 600 700

Vertical position / pixel


Advanced Methodology for the Detection of Smoke Point Heights in

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