Derived Cetane Number Research Articles

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.

Rational Design and Testing of Anti-Knock Additives

An innovative and informed methodology for the rational design and testing of anti-knock additives is reported. Interaction of the additives with OH● and HO2● is identified as the key reaction pathway by which non-metallic anti-knock additives are proposed to operate. Based on this mechanism, a set of generic design criteria for anti-knock additives is outlined. It is suggested that these additives should contain a weak X-H bond and form stable radical species after hydrogen atom abstraction. A set of molecular structural, thermodynamic, and kinetic quantities that pertain to the propensity of the additive to inhibit knock by this mechanism are identified and determined for a set of 12 phenolic model compounds. The series of structural analogues was carefully selected such that the physical thermodynamic and kinetic quantities could be systematically varied. The efficacy of these molecules as anti-knock additives was demonstrated through the determination of the research octane number (RON) and the derived cetane number(DCN), measured using an ignition quality tester (IQT), of a RON 95 gasoline treated with 1 mole % of the additive. The use of the IQT allows the anti-knock properties of potential additives to be studied on one tenth of the scale, compared to the analogous RON measurement. Using multiple linear regression, the relationship between DCN/RON and the theoretically determined quantities is studied. The overall methodology reported is proposed as an informed alternative to the non-directed experimental screening approach typically adopted in the development of fuel additives.

Combustion characteristics of crude oils for gas turbine applications by DCN measurements and NMR spectroscopy

Operating combined cycle gas turbines and/or low speed diesel engines on light petroleum crudes rather than distillate or heavy fuels produced from them avoids the carbon emissions associated with refining while continuing to achieve high energy conversion efficiencies. However, crude assays generated for refinery feed stock characterization do not include an ignition propensity property indicator, and the wide distillation range of crudes disfavors the use of the Calculated Carbon Aromaticity Index or Cetane Index used to characterize heavy or distillate fuel ignition quality. Here, the derived cetane number (DCN) of a single (whole) light crude is reported and the liquid volume fractions and DCNs of light end distillation fractions of this and three other light crudes are compared. Using ASTM D86 distillation method, four crudes were distilled into four light fractions as typically reported in crude assays: 1) light naphtha; 2) heavy naphtha; 3) kerosene; 4) light gas oil. DCNs were obtained using an ignition quality tester (IQT) and ASTM D6890 procedures. The DCNs of the fractions 1) – 4) for all crudes increased from 23 to 35 for the lowest boiling point fraction to 50–60 for the highest tested, in the range of the DCN measured for one of the whole crudes (52.6). The large DCN variation with distillation temperature suggests that preferential vaporization is likely relevant to pre-vaporized/premixed gas turbine combustion behaviors near operational limits. 1H and 13C NMR spectra were also acquired for the distilled samples. A QSPR regression developed using a Scheffé simplex-polynomial descriptor indicates that n-paraffinic CH2 groups play the most significant role in determining crude global ignition propensity. Results suggest that the reactivity potential of crude oils can be estimated reasonably well by employing a well-trained QSPR prediction tool for DCN, based upon key chemical functional groups determined from 1H and 13C NMR spectral analyses.

A new jet fuel surrogate formulated by emulating the distribution of pyrolysis products obtained from shock tube experiments

A new jet fuel surrogate is developed by emulating the distribution of pyrolysis products obtained from shock tube experiments. The distribution of pyrolysis products is described by the use of a series of pyrolysis curves, which refers to a graphical depiction of the concentrations of pyrolysis products plotted against temperatures. Besides, the matching on chemical properties of jet fuel, including molecular weight (MW), hydrogen/oxygen ratio (H/C ratio), derived cetane number (DCN), lower heating value (LHV) and threshold sooting index (TSI), is also taken into account during the formulation process. The new surrogate is a mixture of n-decane, iso-cetane and m-xylene, and these three components are selected through the simulation of pyrolytic process based on the consideration that their mixture can provide similar pyrolysis curves to the target fuel. The validity of the new surrogate has been evaluated extensively against available experimental results from homogeneous reaction systems and low dimensional premixed flames. Meanwhile, a definition of “Error function” is introduced to quantitatively analyze the agreement between calculated values by surrogate and measured data of Jet A. As a reference, the predictive capabilities of four surrogates published in the last ten years and one hybrid-chemistry model for jet fuel are also investigated under the same conditions. According to the simulated results, the new surrogate with a detailed chemical mechanism from CRECK Modeling group (Version 1412) is capable of presenting reasonable predictions on the major combustion behaviors of Jet A across a wide range of conditions, such as ignition delay time, laminar burning velocity and oxidative products distribution.

Variation of gas phase combustion properties of complex fuels during vaporization: Comparison for distillation and droplet scenarios

Surrogate mixtures for modeling real fuels are formulated based on gaseous combustion property targets and liquid physical properties. A batch distillation model was developed to evaluate the vaporization characteristics of some existing surrogates for Jet-A. Chinese aviation fuel RP-3 was then used as a target to experimentally obtain distillation curves and variation of chemical functional groups. A 24-component surrogate was formulated mainly to capture the distillation behavior of RP-3. This surrogate was then used in two droplet vaporization models (Finite Thermal Conductivity/Finite Diffusivity (FTC/FD), Infinite Thermal Conductivity/Infinite Diffusivity (ITC/ID)) to investigate the effects of preferential vaporization on gaseous combustion properties of a complex real fuel. The results obtained from FTC/FD and ITC/ID provide regional bounds for droplets in a vaporizing spray. Four combustion property targets (Molecular Weight (MW), Hydrogen to Carbon ratio (H/C), Derived Cetane Number (DCN) and Threshold Sooting Index (TSI)) were employed as indicators of gas combustion properties. It was found that due to a wide distribution of compounds’ volatility, gaseous combustion properties vary significantly during droplet vaporization. The results suggest development of vaporization models that well capture preferential vaporization of a target real fuel for further spray modeling.

Ignition and combustion characteristics of decanoic acid derived alkyl esters in a fuel ignition tester

This work investigated the combustion characteristics of decanoic acid derived alkyl esters in an ASTM standard Fuel Ignition Tester (FIT), with special emphasis on the influence of carbon number variation for the alkyl moiety within the alkoxy group on the autoignition delay times. The compounds of interest include methyl, ethyl, propyl, and butyl decanoate. It was found that higher carbon numbers lead to an increase in reactivity in terms of the decreased ignition delay times for methyl through propyl decanoate. However, there was a small reduction in relative reactivity for butyl decanoate. With increasing air temperature, while the ignition delay times showed a monotonic reduction for all the four fuels, the maximum rate of pressure rise exhibited a non-linear variation. Specifically, the maximum rate of pressure rise was found to increase in the temperature range of 700–758 K and then decrease within 758–825 K. The post-combustion peak pressures also exhibited a similar trend. It is hypothesized that this reduction in reactivity with increasing temperature correlates to the negative temperature coefficient behavior. In addition, all the test fuels show a two-stage ignition response at the lowest oxidizer temperatures investigated. Therefore, the current experiments demonstrate the suitability of the FIT as a research tool that can be used to extract information on fuel reactivity other than the widely studied metric of the derived cetane number.

Effects of branch structure of alkylbenzenes on spray auto-ignition of n-decane and alkylbenzenes blends

Spray auto-ignition characteristics of the blends of n-decane and several alkylbenzenes were carried out on a heated constant-volume spray combustion chamber. The derived cetane numbers of the fuel blends were determined, and the temperature-dependent ignition delay times and combustion durations were measured across a range of temperatures from 808 to 911 K. The results reveal that blending alkylbenzene to n-decane inhibits fuel spray auto-ignition propensity. For mono-alkylbenzenes, the fuel blend containing toluene has a higher derived cetane number than those with ethylbenzene and n-propylbenzene, but has a lower derived cetane number than the fuel blend containing n-butylbenzene. For those binary fuels containing ethylbenzene, n-propylbenzene and n-butylbenzene, their derived cetane numbers increase with the side alkyl chain length. The derived cetane numbers of the fuel blends with C8H10 isomers follow the trend of n-decane/ o-xylene > n-decane/ethylbenzene > n-decane/ m-xylene ∼ n-decane/ p-xylene, given the alkylbenzene blending fraction. For the blends with C9H12 isomers, those containing 1,2,3-trimethylbenzene and 1,3,5-trimethylbenzene have the highest and lowest derived cetane numbers, respectively, while the fuel blends containing 1,2,4-trimethylbenzene, n-propylbenzene and i-propylbenzene have comparatively intermediate derived cetane numbers. The blending effects of alkylbenzenes on ignition delay time are consistent with the observation on fuel derived cetane numbers. Both the number and proximity of substituted methyl groups significantly affect fuel auto-ignition propensity, and the adjacent methyl groups could increase the auto-ignition propensity. The combustion duration for the test fuels, except for n-decane and the n-decane/ n-butylbenzene blend, monotonically decreases with increased temperature. The non-monotonic dependence of combustion duration on temperature, for neat n-decane and the n-decane/ n-butylbenzene blend, may result from the increased diffusive burnt fraction. Finally, the comparison between gas-phase and spray auto-ignition reactivity of the test fuels highlights the contribution of both fuel physics and chemistry in spray auto-ignition.

Potential oxygenated biofuels synthesized from fusel pentanols

Domestically produced biofuels may help to reduce dependence on imported oil for powering transportation and infrastructure in the future. In this report, five oxygenated biofuels were synthesized by simple condensation reactions of fusel pentanols, 3-methyl-1-butanol and 2-methyl-1-butanol, forming ethers, acetals and carbonate ester. Basic fuel property testing (melting point, density, kinematic viscosity, derived cetane number and calorific value) of the fusel biofuels were collected. The difusel carbonate was the least useful of the group with the lowest energy content (30.46 kJ/g) and lowest cetane number (22.8). The ether and acetal derivatives appeared useful as diesel fuels or additives with energy content of 35.3–39.94 kJ/g and cetane numbers of 53.5–94. The two ether derivatives had energy content and cetane numbers which surpassed those of biodiesel.

Fischer-Tropsch coal-to-liquid fuel negative temperature coefficient region (NTC) and low-temperature heat release (LTHR) in a constant volume combustion chamber (CVCC)

The purpose of the study was to investigate the correlation between thermal characteristics of neat Iso-Paraffinic Kerosene (IPK) in relation to Low Temperature Heat Release (LTHR), ignition delay, and combustion delay within the Negative Temperature Coefficient region (NTC), utilizing a Box-Behnken design matrix. There were 15 trials of 3 control input parameters which were strategic manipulations of ASTM standard D7668-14a. The standard parameters are: 1000 bar for injection pressure, a combustion chamber temperature of 595.5 °C, and an injection pulse width of 2.5 ms. It was observed that, at ASTM standard, the Derived Cetane Number of neat Ultra-Low Sulfur Diesel (ULSD) and IPK was 47.38 and 25.9, respectively. Results show that the LTHR duration and energy release were reduced when two parameters were simultaneously increased in ULSD operation. Meanwhile, for both fuels, the duration and energy release in LTHR has increased when two parameters were simultaneously reduced. It was found that the lower set wall temperature resulted in increased NTC region and LTHR increased to over 10% of the total energy release. The maximum combustion pressure for both ULSD and IPK where increased by 17.2% and 16.1% respectively from the standard due to the increase in injection pressure and pulse width.

Superior performance biodiesel from biomass-derived fusel alcohols and low grade oils: Fatty acid fusel esters (FAFE)

We demonstrated production of a superior performance biodiesel referred to here as fatty acid fusel alcohol esters (FAFE) – by reacting fusel alcohols (isobutanol, 3-methyl-1-butanol, and (S)-(-)-2-methyl-1-butanol) with oil (glyceryl trioleate) using lipase from Aspergillus oryzae. Reaction conditions corresponding to a molar ratio of 5:1 (fusel alcohols to oil), enzyme loading of 2% w/w, reaction temperature of 35 °C, shaking speed of 250 rpm, and reaction time of 24 h achieved >97% conversion to FAFE. Further, FAFE obtained from reacting a fusel alcohol mixture with corn oil were evaluated for use as a fuel for diesel engines. FAFE mixtures showed superior combustion and cold-flow properties, with the derived cetane numbers up to 4.8 points higher, cloud points up to −6 °C lower, and the heat of combustion up to 2.1% higher than the corresponding FAME samples, depending on the fusel mixture used. This represents a significant improvement for all three metrics, which are typically anti-correlated. FAFE provides a new opportunity for expanded usage of biodiesel by addressing feedstock limitations, fuel performance, and low temperature tolerance.

On estimating physical and chemical properties of hydrocarbon fuels using mid-infrared FTIR spectra and regularized linear models

The concept of a compact, economical FTIR-based analyzer for estimating the properties of hydrocarbon fuels with small amounts of fuel is proposed. The high correlations between mid-IR FTIR absorption spectra of fuel vapor in the range 3300–3550 nm and 15 physical and chemical properties, such as density, initial boiling point, surface tension, kinematic viscosity, number of carbon and hydrogen per average molecule, and derived cetane number, for 64 hydrocarbon fuels are demonstrated. Lasso-regularized linear models based on linear combination of absorption cross sections at selected wavelengths are built for each of these physical and chemical properties, yielding accurate estimations.

Autoignition Comparison of n-Dodecane/Benzene and n-Dodecane/Toluene Blends in a Constant Volume Combustion Chamber

The derived cetane numbers (DCNs) of the n-dodecane/benzene and n-dodecane/toluene blends were measured using a constant volume combustion chamber facility. The autoignition behaviors of the two sets of fuel blends, including ignition delay (ID) and combustion delay (CD) times, pressure traces, as well as the heat release rates at the DCN determination conditions, that is, 883 K ambient temperature and 20 bar ambient pressure, were also characterized. The results revealed that the n-dodecane/benzene blends have lower DCNs than those of the n-dodecane/toluene blends given the aromatic blending fractions. The two sets of fuel blends exhibit almost the same ID timescales with low aromatic blending fractions, but the ID of the dodecane/toluene blend becomes longer when the aromatic blending fraction rises to 60%. The CDs of the n-dodecane/toluene blends are slightly shorter at low aromatic blending fractions, and this difference becomes more apparent at a higher aromatic blending fraction. The n-dodecane/benz...

Preferential vaporization impacts on lean blow-out of liquid fueled combustors

Recent experimental works have shown that the global equivalence ratio defining lean blow-out (LBO) in model gas turbine combustors correlates with the derived cetane number (DCN) of the tested fuel, which represents the chemical reactivity potential of the fuel, but additional physical and kinetic parameters of the fuel also have influence. The current work explores the significance of preferential vaporization impacts on LBO behaviors; i.e., rather than parameterizing the fuel by overall averaged fuel properties, it looks at DCN correlations based upon distillation properties prior to full vaporization. Preferential vaporization potentials of six fuels are evaluated by measuring the DCN values of five distillation cuts (each of 20% liquid distillation volume recovered). In spite of relatively large disparities in total fuel DCN values (∼9.1), two petroleum-derived jet fuels are found to have nearly the same LBO equivalence ratios, which is attributed to the relatively indiscernible difference of DCN values (∼2) for the initial 20% distillation cut of each fuel. Trade-off impacts between fuel chemical and physical properties are demonstrated by comparing n-dodecane and Gevo-ATJ, which do not have preferential vaporization potential. LBO results suggest that fuel physical properties (particularly fuel boiling characteristics) predominantly control LBO behaviors at low air inlet temperature conditions, whereas fuel chemical properties appear to gain significance with increasing air inlet temperature. Further evidence of preferential vaporization effects on LBO is discussed with two surrogate mixtures formulated to emulate the fully pre-vaporized combustion behaviors of Jet-A, but having drastically different preferential vaporization potentials. Finally, the relationship between DCNs and LBO equivalence ratios is re-examined using the DCN values of initial 20% distillation cuts of all six fuels. The results display a significantly improved correlation, suggesting that the relevance of preferential vaporization on LBO can be significant for fuels that exhibit significant departure of the DCN for high volatile fractions (i.e., the initially vaporized constituents) in comparison to the overall fuel DCN.

Potential Vegetable‐Based Diesel Fuels from Perkin Condensation of Furfuraldehyde and Fatty Acid Anhydrides

AbstractDomestically produced biofuels may help to reduce dependence on imported oil for powering transportation and infrastructure in the future. In this report, we reacted medium‐chain and long‐chain fatty anhydrides (capric, caprylic, lauric, and palmitic) with furfuraldehyde by the Perkin condensation to produce 2‐n‐alkenylfurans. In the second step, the 2‐n‐alkenylfurans were hydrogenated to form 2‐n‐alkyltetrahydrofurans. Basic fuel property testing (melting point, density, kinematic viscosity, derived cetane number, and calorific value) of the 2‐n‐alkyltetrahydrofurans indicates they are potentially useful as fuels for diesel engines. The mixture composed of 2‐octyl‐ and 2‐decyltetrahydrofuran had the best combination of fuel properties including a low melting point (−39 °C), high cetane number (63.1), high flash point (98.2 °C), and low viscosity (2.26 mm2 s−1, 40 °C), which compares favorably with specifications for diesel #2 and biodiesel.

The development and testing of Navy jet fuel (JP-5) surrogates

In this study five naval jet fuel JP-5 surrogates were developed and tested in comparison to a nominal JP-5 fuel. Because the military uses jet fuel in diesel engines under varied circumstances, the JP-5 fuel surrogates were tested in both the Advanced Engine Technologies Ignition Quality Tester (IQT) and a Yanmar L100W Tier 4 engine. The surrogates were prepared from compounds that represent the classes of components found in JP-5: linear and branched alkanes, aromatic compounds, and cycloalkanes. Five different four-component surrogates containing n-dodecane, 2,2,4,4,6,8,8-heptamethylnonane (iso-cetane), n-butylbenzene, and n-butylcyclohexane conformed to JP-5 military specifications for flash point, density, viscosity, hydrogen content, aromatic content, and distillation behavior and span a range of reactivities. The flash point of JP-5 is higher than commercial aviation fuel, therefore the surrogates were formulated with higher flashpoint components. The surrogates had very similar physical properties, which compared favorably to those of a base JP-5 fuel. The similar physical properties were chosen to minimize physical spray preparation differences in the various combustion rigs (IQT and Yanmar engine). This result was analyzed directly in the constant volume combustion chamber IQT, in which the analyzed physical delay times were very similar for all the fuels tested. The principle differences between the five surrogates were n-dodecane (high reactivity) and iso-cetane (low reactivity) concentrations, producing derived cetane numbers (DCN) from 34 to 52. Military jet fuel specifications do not limit the value of DCN, so these surrogates could represent qualified jet fuel. The lower cetane surrogates performed poorly in the Yanmar engine. This shows that a qualified jet fuel could fail to combust if used in an emergency diesel generator. One surrogate mixture (Mix-4, mole fractions of 0.25 n-dodecane, 0.20 iso-cetane, 0.15 n-butylbenzene, and 0.40 n-butylcyclohexane) had a DCN of 47, that matched the base JP-5 fuel (DCN = 46.4). In both the steady-state and cold-start engine testing, the Mix-4 surrogate and JP-5 showed very similar combustion behaviors. Thus, it is believed that Mix-4 will function as a strong surrogate for JP-5 performance in other diesel engines as well.

Experimental investigation on alternative fuel combustion performance using a gas turbine combustor

In order to ensure reliable combustion performance and low emissions profiles for prospective alternative fuels, this study was conducted in order to evaluate the impact of fuel properties and their composition on lean blowout performance and emission characteristics of various fuels. Significant contributions to knowledge have been achieved using visual images of the flames at the occurrence of lean blowout (LBO) that were captured by a high-speed camera and analysed to develop a new model for the evaluation of the LBO of current and future alternative fuels.The results show that high-density and high aromatic content fuel has the potential to produce higher soot formation. In addition, a low lean blowout equivalence ratio and low soot propensity is unlikely to be achieved at the same time by simply altering the value of fuel properties. It was discovered that the Derived Cetane number was observed to have a considerable effect on improving the LBO performance without inducing heavier soot emissions. An analysis of the impact of the fuel aromatic content (type and proportion) presents a hypothesis that not all aromatics species produce the same levels of particulate matter emissions.This work provides a comprehensive data foundation, analytical concepts and potential research techniques for the application of expeditious fuel screening tools to assess the combustion behaviour of current fuels, and also facilitates the potential for further operational fuel development. The visualisation method used in this work could contribute towards developing applications for flame detection in fuel performance assessment.

Liquid Fuel Property Effects on Lean Blowout in an Aircraft Relevant Combustor

This paper describes results from an experimental study on influences of liquid fuel properties on lean blowout (LBO) limits in an aero-type combustor. In particular, this work aimed to elucidate the roles of fuel chemical and physical properties on LBO. Fuel chemical properties stem from the fuel chemical structure, thus governing chemical kinetic behaviors of oxidation characteristics (e.g., ignition or extinction time scales) and others (e.g., fuel thermal stability or sooting tendencies). Fuel physical properties affect the spray characteristics (e.g., atomization and evaporation rates). Eighteen different fuels, with a wide range of physical and chemical fuel properties, were tested. Several of these fuels were custom blends, developed to break intercorrelations between various physical and chemical properties. Fuel physical and chemical property effects were further separated by measuring blowout boundaries at three air inlet temperatures between 300 and 550 K, enabling variation in vaporization rates. The condition at 300 K corresponds to a temperature that is less than the flash point for most of the studied fuels and, therefore, forming a flammable mixture was challenging in this regime. The opposite scenario occurred at 550 K, where fuel droplets evaporate quickly, and the temperature actually exceeds the auto-ignition temperatures of some of the fuels. At 300 K, the data suggest that blowout is controlled by fuel physical properties, as a correlation is found between the blowout boundaries and the fuel vaporization temperature. At 450 and 550 K, the blowout boundaries correlated well with the derived cetane number (DCN), related to the global chemical kinetic reactivity.

A new method of estimating derived cetane number for hydrocarbon fuels

A new spectroscopic predictor for estimating ignition characteristics including derived cetane number is proposed for hydrocarbon fuels. This spectroscopic predictor is the ratio of room temperature absorbance of unreacted fuel vapor at 3.41 and 3.39 μm, termed here as the “3.41/3.39 absorption ratio.” Its wide availability and applicability are demonstrated for a range of pure hydrocarbons, mixtures of pure hydrocarbons, and distillate and synthetic jet fuels. Quasi-linear calculation methods are provided for practical use. Spectroscopic and kinetic interpretations are provided based on the fraction of –CH2– hydrogen relative to all carbon-bonded hydrogen. In addition, the correlations between the proposed predictor and ignition delay time and C2H4 yield are presented and discussed to exhibit the predictor’s potential as a fuel screening tool.

Autoignition and select properties of low sample volume thermochemical mixtures from renewable sources

Catalytic thermochemical processes can convert biomass-derived liquids into hydrocarbon mixtures that are potential liquid transportation blendstocks. However, few measurements of the autoignition behavior of these mixtures are reported in the open literature. Pacific Northwest National Laboratory reports on the autoignition behavior of 36 mixtures of catalytically upgraded liquids—including distillation fractions—from biomass liquefaction technologies. The technologies whose output was subsequently upgraded include direct routes (fast pyrolysis and hydrothermal liquefaction) and indirect routes (syngas to ethanol). The propensity of the biomass-derived hydrocarbons to autoignite was measured using an ignition quality tester (IQT) according to ASTM D6890, which measures the time it takes a fuel-air mixture to autoignite under conditions relevant to cetane number measurements to yield a derived cetane number (DCN). This measurement was converted to a derived research octane number (dRON) using three empirical correlations reported in the literature (Kalghatgi et al., 2005; Naser et al., 2017; McCormick et al., 2017). The simulated distillation curve of each sample was measured using ASTM D2887, and the autoignition behavior in different boiling range fractions was evaluated. Gas chromatography/mass spectrometry and 1H/13C nuclear magnetic resonance spectroscopy were used to determine the chemical composition of the liquids, and the impact on the research octane number of various functional groups present in the mixture was assessed. In general, aromatics and olefins enhanced octane number, in agreement with existing literature. The presence of esters was also found to increase dRON. The dRON method required smaller samples and gave an acceptable approximation of the research octane number measured using a certified fuel rating engine.

Critical fuel property evaluation for potential gasoline and diesel biofuel blendstocks with low sample volume availability

We show that early-stage evaluation of critical fuel properties of new gasoline or diesel blendstock candidates can be accomplished using small volumes of material (<15 mL, compared to the ∼1 L typically required). The approach utilizes dilution and autoignition resistance via measurement of ignition delay to estimate the octane number or cetane number of a new blendstock. The ignition delay can be converted to a derived cetane number and derived octane number, providing a useful estimate of a critical combustion property. The results were validated against known compounds. Measurement of autoignition is important for evaluating blendstocks derived from biomass, where generating large volumes for initial evaluation may be prohibitively expensive. We have used this approach for several materials identified as having potential biological production pathways. Also, synthetic organic chemistry was employed to produce sufficient quantities of samples for autoignition measurement for those materials with no established biological scale-up route. The materials investigated were isomers of 5,5-dimethyl-2-ethyl-1,3-cyclopentadiene; branched alcohols and ketones; and hydrotreated terpenoid mixtures. Several candidates were identified with favorable fuel properties for either gasoline (derived research octane number greater than 90) or diesel (derived cetane number higher than 40).