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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Ignition delay time and speciation of dibutyl ether at high pressures

Dibutyl ether (DBE) is a promising biofuel due to its high cetane number (~ 100) and high volumetric energy density (31.6 MJ/L). It could either be used directly in compression ignition engines or blended with other conventional or renewable fuels. Oxidation and pyrolysis kinetics of DBE are not well known, particularly at high pressures. In this work, we have experimentally investigated the chemical kinetics of DBE in three domains: (a) ignition delay time measurements in a rapid compression machine over T = 550–650 K, P = 10, 20, 40 bar, φ = 0.5, 1; (b) ignition delay time measurements in a shock tube over T = 900–1300 K, P = 20, 40 bar, φ = 0.5, 1; (c) laser-based carbon monoxide speciation measurements in a shock tube during DBE pyrolysis and oxidation over T = 1100–1400 K, P = 20 bar. Pressure time-histories measured in RCM experiments exhibited unique 3-stage and 4-stage ignition behavior predominantly at fuel-lean conditions. Experimental data were compared with the predictions of two recent chemical kinetic models of DBE. Sensitivity analyses were carried out to identify key reactions which may have caused the discrepancy between experiments and simulations. We found that the rate of decomposition of DBE may need to be revisited to improve the oxidative and pyrolytic predictions of DBE kinetic model.

09 BIOMASS FUELS↗
DOE OSTI2023

Effect of the ..beta..-Hydroxy Group on Ester Reactivity: Combustion Kinetics of Methyl Hexanoate and Methyl 3-Hydroxyhexanoate

One of the major biofuels used today is biodiesel, composed of fatty acid methyl esters. The fats and oils feedstocks used to make biodiesel are in relatively short supply. To meet increasing global demand, engineered microorganisms have been developed to catalyze conversion of sugar to fatty acid esters that contain unique ..beta..-hydroxy-esters. This study investigated the effect of a hydroxyl group on the combustion characteristics of methyl esters by comparing the chemical behavior of methyl hexanoate (MHx) and methyl 3-hydroxyhexanoate (M3OHHx) - used as surrogates for diesel-boiling-range esters with longer fatty acid chains. The oxidation of these esters was studied experimentally in a flow reactor at 0.84 and 10 bar, 600 to 1,100 K, and stoichiometric conditions; and in a constant volume combustion chamber at 5 and 10 bar, 600 to 900 K, and equivalence ratios of 0.3 and 0.6. MHx was more reactive in the constant volume chamber at temperatures below 800 K at 10 bar and equivalence ratio of 0.6. MHx also exhibited a higher indicated cetane number (16.4) than M3OHHx (8.1). We investigated this reactivity trend using an updated MHx kinetic model and M3OHHx model developed as part of this work. The kinetic models predicted that radicals formed from MHx were consumed by low-temperature chemistry reactions, whereas the M3OHHx reactivity was significantly governed by the ..beta..-radical (on the same carbon as the OH group) chemistry which mainly terminated via the less reactive chain propagation pathway to methyl-3-oxohexanoate + HO2. This study extends our understanding of structural effects on ester reactivity, which will allow for accurate surrogate formulation and performance simulations.

AFIDA↗
DOE OSTI2015

Ethyl 3-ethoxybutyrate, a new component of the transportation renewable fuel portfolio

The vast majority of energy that powers our global economy is from combustion of fossil fuels with the unintended consequence of increased deposition of carbon dioxide in the atmosphere and oceans. The scientific and technical challenges for the energy sector are to develop renewable energy sources that are sufficient to meet human energy consumption, are economically viable, and are ecologically sustainable. We investigated ethyl 3-ethoxybutyrate (EEB) as a fuel oxygenate in ultra low sulfur diesel (ULSD) with a bench-scale research engine and determined its economic potential as a renewable fuel with technoeconomic modeling using wastewater treatment plant biosolids as the feedstock for poly-3-hydroxyalkanoates (PHB), a bacterial storage polymer from which EEB can be synthesized. EEB blended well with ULSD, and cetane values of 10% and 20% v/v EEB-ULSD blends exceeded 40. A diesel internal combustion engine fueled with 5%, 10%, and 20% EEB-ULSD blends met or exceeded all tested transportation diesel fuel emissions criteria. Inedible organic feedstocks may be used to produce PHB; and thus, EEB might contribute to carbon reductions without compromising performance or air pollutant emissions. However, further research is needed to determine its role in the overall fuel portfolio. (C) 2015 Elsevier Ltd. All rights reserved.

09 BIOMASS FUELS↗
DOE OSTI2023

Diesel fuel properties of renewable polyoxymethylene ethers with structural diversity

Polyoxymethylene ethers (POMEs) are a class of low-soot and high-cetane oxygenate oligomers of structure RO-(CH 2 O-) $n$ -R, with different chain lengths ($n$) and end-groups (R) that determine their diesel-like fuel properties. Commercial POMEs with methyl end-groups (MM-POME 3-6 ) exhibit undesirably low energy density and high-water solubility. A previous computational assessment indicated that the lower heating value (LHV) and water solubility for MM-POME 3-6 both improve upon end-group exchange with larger butyl, $iso$-butyl and $iso$-pentyl end-groups. Here, we expanded upon our initial trans-acetalization reaction that employed 1-butanol to install butyl end-groups to also include branched, higher carbon-number end-groups using $iso$-butanol and fusel oil as reagents. Additionally, these new products are termed $i$B*POME 1-6 , and FOil*POME 1-5 , respectively, and collectively referred to as R*POMEs. They possess the advantaged properties of the parent MM-POME 3-6 while exhibiting higher LHV (31 MJ kg -1 and 28 MJ kg -1 for $i$B*POME 1-6 , and FOil*POME 1-5 , respectively) and much reduced water solubility (2.7 g L -1 and 1 g L -1 for $i$B*POME 1-6 , and FOil*POME 1-5 , respectively). Additional fuel property analyses were performed using 20 vol% blends of the R*POMEs with a base diesel fuel. Overall, the greater energy density and decreased water solubility of the R*POMEs, as well as their synergistic blending with diesel at moderate blend levels, provide the greatest benefits to consumers and position this group of products as an environmentally friendlier blendstock alternative to the commercially available MM-POME 3-6 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

An analysis of alcohol compression ignition strategies on different engine platforms

Strategies that enable ignition of the low cetane alcohol fuels (methanol and ethanol) include intake heating (direct or via hot residual trapping), increased compression ratio (CR), multi-injection strategies, ignition enhancers, and active prechambers. The literature consistently shows alcohol compression ignition (CI) is more efficient than diesel at high loads irrespective of ignition strategy but shows contradictory results at low loads. To understand this, this work combines data from four different engine platforms ranging from a displaced volume of 0.4 to 2.1 L/cyl. using different alcohol CI ignition strategies. Using modeling to support experimental analysis, alcohol-specific efficiency penalties are highlighted to inform alcohol combustion system development. The alcohols’ lower energy density means more fuel must be injected near top dead center to achieve a given load, increasing the relative penalty of sensible/latent heating. Pilot injections help reduce this penalty. Intake heating incurs both a heat transfer penalty and a thermodynamic penalty due to a reduced ratio of specific heats during compression. A strategy that combines elevated CR, large pilot injections, and ignition enhancers can avoid this penalty. Alternatively, a prechamber strategy can achieve this without changing the CR, nor needing ignition enhancers in the fuel. At low loads, diesel burns in a partially premixed mode characterized by high burn rates and low heat losses, reducing alcohol-specific combustion benefits. Alcohol CI on the light-duty platform showed abnormally high heat transfer over diesel compared to other platforms, favoring a more premixed/partially premixed strategy despite a combustion efficiency tradeoff.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2027

Hydrotreating pine-derived catalytic fast pyrolysis oil to jet fuel: Process durability and impact of operating conditions

Hydrotreating woody biomass-derived catalytic fast pyrolysis (CFP) oil to jet fuel has the potential to enhance energy security due to the large abundance of forest and woody resources. CFP oil produced from pine over ZSM-5 was hydrotreated over sulfided NiMo/Al 2 O 3 for 410 h to study the impact of hydrotreating conditions (pressure, temperature, and weight hourly space velocity (WHSV)). The degree of deoxygenation remained high across the tested hydrotreating conditions, and the products contained < 0.01 wt% oxygen. Increasing hydrotreating pressure from 84 to 125 bar enhanced hydrogenation of aromatic rings and the formation of cycloalkanes and increasing the temperature from 385 to 400 degrees C enhanced cracking and the formation of jet-range molecules. Decreasing the weight hourly space velocity from 0.2 to 0.1 g/(g cat h) further enhanced cracking and led to higher gasoline- and lower jet fuel-range fractions. The highest jet fuel fraction (49 wt%) was obtained at 400 degrees C, 125 bar, 0.2 g/(g cat h) WHSV. CFP oils produced from pine over phosphorous-modified ZSM-5 were hydrotreated at this condition for 588 h to investigate the process durability. The hydrogenation performance of the catalyst gradually stabilized in approximately 300 h after which the product composition remained constant. Of the final hydrotreated CFP oil, 53 wt% fell in the jet fuel range with most of the tested fuel properties meeting ASTM D4054 and/or ASTM D7566 specifications. The freeze points were < -50 degrees C vs. guideline of < -40 degrees C and the viscosities at -20 degrees C were 3.8-4.1 mm 2 /s vs guideline of 8 mm 2 /s. Increasing the fraction of cycloalkanes could increase the cetane number and heating value, which did not meet the guidelines.

09 BIOMASS FUELS↗
DOE OSTI2026

A single-zone zero-dimensional study of HCCI combustion of methanol dehydration products to enable ignition of direct-injected methanol

Methanol is an alternative fuel gaining traction in the maritime sector. Its direct adoption, however, is accompanied by a unique set of technical challenges, such as low cetane number and high latent heat of vaporization. An approach to overcome these challenges is being developed at the US Department of Energy’s Oak Ridge National Laboratory, where onboard generation of dimethyl ether (DME) via catalytic dehydration of methanol can be used to assist in the mixing controlled combustion of direct-injected (DI) methanol. The generated mixture from this dehydration process can be premixed with intake air to condition the cylinder via. homogeneous charge compression ignition (HCCI) for subsequent DI methanol. In this preliminary work, various catalyst or reactor conversion efficiencies were simulated (using bottles) at constant DME and water flow at low load on a single-cylinder marine-variant of a CAT® C18 18 L engine with a 145 mm bore. To substantiate the experimental findings, a zero-dimensional engine model was developed in Cantera using a DME mechanism with 79 species and 658 reactions. Results presented include experimental and simulation heat release rate comparisons, species evolution information, and constant volume ignition delay (ID) for DI methanol with and without background species from HCCI of the premixed products from different reactor efficiencies. The results suggest that thermal effects dominate the DI methanol ignition process, and this work provides a chemical kinetic foundation or guideline for developing future control schemes.

Tyrewala, Daanish [ORNL] (ORCID:0000000208599324)↗
DOE OSTI2020

A Perspective on Biomass-Derived Biofuels: From Catalyst Design Principles to Fuel Properties

The hazards to health and the environment associated with the transportation sector include smog, particulate matter, and greenhouse gas emissions. Conversion of lignocellulosic biomass into biofuels has the potential to provide significant amounts of infrastructure-compatible liquid transportation fuels that reduce those hazardous materials. However, the development of these technologies is inefficient, due to: (i) the lack of a priori fuel property consideration, (ii) poor shared vocabulary between process chemists and fuel engineers, and (iii) modern and future engines operating outside the range of traditional autoignition metrics such as octane or cetane numbers. In this perspective, we describe an approach where we follow a “fuel-property first” design methodology with a sequence of (i) identifying the desirable fuel properties for modern engines, (ii) defining molecules capable of delivering those properties, and (iii) designing catalysts and processes that can produce those molecules from a candidate feedstock in a specific conversion process. Computational techniques need to be leveraged to minimize expenses and experimental efforts on low-promise options. This concept is illustrated with current research information available for biomass conversion to fuels via catalytic fast pyrolysis and hydrotreating; outstanding challenges and research tools necessary for a successful outcome are presented.

BIOMASS FUELS↗
DOE OSTI2020

A comparison of computational models for predicting yield sooting index

Sooting propensity, a measurement of how much particulate matter is produced when a fuel is burned, is a property of significant interest among researchers who are striving to discover the next generation of cleaner, more efficient fuels and fuel additives. Many compounds are not viable as fuels and/or fuel additives, and as a result, designing cleaner-burning biofuels using only experimental techniques is inefficient. Predictive models have been instrumental in reducing this inherent difficulty, providing researchers with a tool to preemptively screen compounds before production and testing. The present work compares the accuracies and interpretabilities of existing models used to predict a particular measure of sooting propensity, Yield Sooting Index (YSI). These models include artificial neural networks, graph neural networks, and multivariate equations. A novel equation for predicting YSI based on atom path count and bond order is proposed, which can highlight key structural components that contribute to YSI. It was found that artificial neural networks slightly outperform graph neural networks and greatly outperform multivariate equations in blind (test set) prediction accuracy; however, graph neural networks and multivariate equations provide significantly more interpretability as to how compound structure relates to YSI. Predictions of YSI are compared to experimental measurements for previously un-tested compounds with cetane numbers comparable to diesel fuel (50-60) (butyl decanoate, ethyl decanoate, 1,4-bis(ethenoxymethyl)cyclohexane, and 5-heptyloxolan-2-one), and it was found that these compounds produce significantly less soot compared to diesel fuel.

09 BIOMASS FUELS↗
DOE OSTI2014

Transportation fuel production by combination of LDPE thermal cracking and catalytic hydroreforming

Highlights: • h-Beta samples were impregnated with Ni nitrate to achieve Ni contents of 1.5%, 4%, 7% and 10%. • Larger and more easily reducible metal particles were obtained on Ni 7%/h-Beta and Ni 10%/h-Beta. • Higher Ni contents increased the amount of gases at the expenses of diesel fractions. • Maximum selectivity to automotive fuels (∼81%) was obtained with Ni 7%/h-Beta. • Ni loading also enhanced olefins saturation up to Ni 7%/h-Beta. - Abstract: Fuel production from plastics is a promising way to reduce landfilling rates while obtaining valuable products. The usage of Ni-supported hierarchical Beta zeolite (h-Beta) for the hydroreforming of the oils coming from LDPE thermal cracking has proved to produce high selectivities to gasoline and diesel fuels (>80%). In the present work, the effect of the Ni loading on Ni/h-Beta is investigated in the hydroreforming of the oils form LDPE thermal cracking. h-Beta samples were impregnated with Ni nitrate, calcined and reduced in H{sub 2} up to 550 °C to achieve different Ni contents: 1.5%, 4%, 7% and 10%. Larger and more easily reducible metal particles were obtained on Ni 7%/h-Beta and Ni 10%/h-Beta. Hydroreforming tests were carried out in autoclave reactor at 310 °C, under 20 bar H{sub 2}, for 45 min. Ni content progressively increased the amount of gases at the expenses of diesel fractions, while gasoline remained approximately constant about 52–54%. Maximum selectivity to automotive fuels (∼81%) was obtained with Ni 7%/h-Beta. Ni loading also enhanced olefins saturation up to Ni 7%/h-Beta. High cetane indices (71–86) and octane numbers (89–91) were obtained over all the catalysts. Regarding the different studied Ni contents, Ni 7%/h-Beta constitutes a rather promising catalyst for obtaining high quality fuels from LDPE thermal cracking oils.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Metabolic engineering of β-oxidation to leverage thioesterases for production of 2-heptanone, 2-nonanone and 2-undecanone

Medium-chain length methyl ketones are potential blending fuels due to their cetane numbers and low melting temperatures. Biomanufacturing offers the potential to produce these molecules from renewable resources such as lignocellulosic biomass. Here, we designed and tested metabolic pathways in Escherichia coli to specifically produce 2-heptanone, 2-nonanone and 2-undecanone. We achieved substantial production of each ketone by introducing chain-length specific acyl-ACP thioesterases, blocking the β-oxidation cycle at an advantageous reaction, and introducing active β-ketoacyl-CoA thioesterases. Using a bioprospecting approach, we identified fifteen homologs of E. coli β-ketoacyl-CoA thioesterase (FadM) and evaluated the in vivo activity of each against various chain length substrates. The FadM variant from Providencia sneebia produced the most 2-heptanone, 2-nonanone, and 2-undecanone, suggesting it has the highest activity on the corresponding β-ketoacyl-CoA substrates. We further tested enzyme variants, including acyl-CoA oxidases, thiolases, and bi-functional 3-hydroxyacyl-CoA dehydratases to maximize conversion of fatty acids to β-keto acyl-CoAs for 2-heptanone, 2-nonanone, and 2-undecanone production. In order to address the issue of product loss during fermentation, we applied a 20% (v/v) dodecane layer in the bioreactor and built an external water cooling condenser connecting to the bioreactor heat-transferring condenser coupling to the condenser. Finally, using these modifications, we were able to generate up to 4.4 g/L total medium-chain length methyl ketones.

2-Heptanone↗
DOE OSTI2020

Methodology for the development of empirical models relating 13C NMR spectral features to fuel properties

Effective formulation of new gasoline or diesel fuels for internal combustion engines would benefit from the development of reliable models for predicting key fuel properties based on a set of molecular descriptors obtained from a single measurement. This is particularly relevant in the case of renewable fuels, where the available fuel sample quantity may be limited. In this work, we present a statistically-based methodology for building empirical models to predict multiple properties from one-dimensional 13C nuclear magnetic resonance (NMR) spectra measured on around 200 microliters of a liquid fuel. NMR spectra contain information about the molecular composition of a sample and the carbon types and molecular substructures therein. Our approach uses this information to build sparse, interpretable models, where the predicted properties are linked to specific molecular features. The approach takes into consideration the constrained nature of the features making up the one-dimensional NMR spectrum, which, after standardization, represent a relative fuel composition. We point to the limitations in interpretability that arise when building this type of empirical predictive model and suggest how these limitations may be diminished. Among the many properties important for maximizing engine performance and minimizing emissions, we build models that predict derived cetane number and distillation temperatures as these are of particular interest because of their links to fuel economy, drivability, and engine-out emissions. Results suggest that the properties of interest may be impacted by only a few of the 27 13C NMR regions represented in the data, pointing to new directions for further testing in the development of improved fuels.

predictive models, biofuels., NMR Analysis↗
DOE OSTI2020

Biodiesel Ethers: Fatty Acid-Derived Alkyl Ether Fuels as Improved Bioblendstocks for Mixing-Controlled Compression Ignition Engines

In the last 20 years, biodiesel consumption in the United States has swiftly increased to ~2 billion gallons per year as a renewable supplement to fossil fuel. However, further expansion of biodiesel use is currently limited in part by poor cold weather performance, which prevents year-round blending and necessitates blend walls ≤5% v/v. In order to provide a diesel fuel blendstock with improved cold weather performance (cloud point, pour point, and cold filter plug point), while at the same time maintaining other required fuel performance specifications, several biodiesel redox analogues were synthesized and tested. The best performing candidate fuels from this class showed improvement in the derived cetane number (29.3% shorter ignition delay), lower heating value (+4.7 MJ/kg), relative sooting tendency (–7.4 YSI/MJ), and cloud point (15 °C lower) when compared to a B100 biodiesel composed of an identical fatty acid profile. It was observed as a general trend that the reduced form of biodiesel, fatty alkyl ethers (FAEs), shows performance improvements in all fuel property metrics. The suite of improved properties provided by FAEs gives biodiesel producers the opportunity to diversify their portfolio of products derived from lipid and alcohol feedstocks to include long-chain alkyl ethers, a biodiesel alternative with particular applicability for winter weather conditions across the US.

09 BIOMASS FUELS↗
DOE OSTI2021

SCALEABLE HYDROTREATING OF HTL BIOCRUDE TO PRODUCE FUEL BLENDSTOCKS

Hydrothermal liquefaction (HTL) offers an attractive route to produce fuel blendstocks from wet wastes. Scaleable hydrotreating data for the conversion of HTL biocrude to fuels is critical to the commercialization of HTL. Herein, we demonstrate pore diffusion limitations for the hydrotreating of HTL biocrudes. We demonstrate scale-able hydrotreating of HTL biocrude to produce a high cetane diesel fuel and demonstrate the hydrotreating limitations.

Biofuel, hydrotreating, HTL biocrude, hydrothermal↗
DOE OSTI2024

Scale-Up Studies for the Dehydration of C 4+ Alcohols into Drop-In Diesel Fuel

Herein, we demonstrate the production of liter quantities of drop-in diesel-range ethers from biomass-derived alcohols. We report scale-up resultsfor the dehydration of a mixture of C 4+ alcohols using powder and pellet zeolite Ycatalyst in continuous flow and batch reactors. The activity of zeolite Y decreaseswith the introduction of an alumina binder. Large alcohols, as well as branchedand secondary alcohols, increase the coke content over the pellet Y catalyst. Thepellet formulation had lower carbon balances and selectivity to C 10+ ethers,suggesting that the pellet formulation increases alcohol absorption and cokeproduction. Crushing the pellet Y catalyst to smaller particle sizes does notrecover the activity of zeolite Y in its powder form. Cold flow experiments showthat particle agglomeration contributes to pressure buildup in the continuous flowreactor. C 10+ ether blends can be produced in batch reactors at high alcohol conversion regimes. One liter of a diesel #2 blend wasproduced by scaling up this reaction. The final blend consists of a substantial portion of C 10+ ethers (63.7 wt %), followed by heavyunknown products (27.4 wt %). Furthermore, the final alcohol and butyl ether concentration values were 7.3 and 1.5 wt %, respectively. Theblendstock reported in this paper can satisfy diesel #2 ASTM standards for density, cloud point, flashpoint, and cetane number.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Diesel Fuel Property Effects on In-Cylinder Liquid Penetration Length: Impact on Smoke Emissions and Equivalence Ratio Estimates at the Flame Lift-Off Length

Here in this study, elastic scattering was employed to investigate diesel fuel property effects on the liquid length (i.e., the maximum extent of in-cylinder liquid-phase fuel penetration) using select research fuels: an ultralow-sulfur #2 diesel emissions-certification fuel (CF) and four of the Coordinating Research Council (CRC) Fuels for Advanced Combustion Engines (FACE) diesel fuels (F1, F2, F6, and F8). The experiments were performed in a single-cylinder heavy-duty optical compression-ignition engine under time-varying, noncombusting conditions to minimize the influence of chemical heat release on the liquid-length measurement. The FACE diesel fuel and CF liquid lengths under combusting conditions were also predicted using Siebers’ scaling law and pressure data from previous work using the same fuels at similar in-cylinder conditions. The objective was to observe if the liquid length under noncombusting or combusting conditions provides additional insights into the relationships among the main fuel properties (i.e., cetane number (CN), the 90 vol % distillation recovery temperature (T90), and aromatic content) and smoke emissions. Results suggest that liquid-length values are best correlated to fuel distillation characteristics measured with ASTM D2887 (simulated distillation method). This work also studied the relationship between liquid length and lift-off length, H (i.e., distance from the fuel-injector orifice exit to the position where the standing premixed autoignition zone stabilizes during mixing-controlled combustion). Two possible cases were identified based on the relative magnitudes of liquid length under combusting conditions (Lc) and H. The low-CN fuels are representative of the first case, L c < H, in which the fuel is always fully vaporized at H. The high-CN fuels are mostly representative of the second case, L c ≥ H, in which there is still liquid fuel at H. Lc ≥ H would suggest higher smoke emissions, but there is not enough evidence in this work to support a compounding effect of a longer liquid length on top of the aromatic-content effect on smoke emissions for fuels with similar CN, supporting previous findings in the literature that lift-off length plays a more important role than liquid-length on diesel combustion. At the same time, the experimental results suggest a decrease in the fuel-jet spreading angle, i.e., a decrease in the entrainment rate into the jet at and downstream of H, under combusting conditions, that is not accounted for in the model used to predict the values of $\phi$(H). Lastly, as a result, L c may be of interest for accurate predictions of $\phi$(H), especially for combustion strategies designed to lower in-cylinder soot by operating near or below the nonsooting $\phi$(H)-value (i.e., $\phi$(H) ≈ 2).

02 PETROLEUM↗
DOE OSTI2019

Camphorane as a Renewable Diesel Blendstock Produced by Cyclodimerization of Myrcene

Camphorene was synthesized by the thermal Diels–Alder cyclodimerization of myrcene and subsequently hydrogenated to produce camphorane. On the basis of common fuel metrics (density, lower heating value, cetane, and viscosity) the prepared camphorane fuel exhibits appropriate physicochemical properties for its implementation in compression ignition engines. The high viscosity of camphorane necessitates its blending with petroleum diesel, which offers a final fuel within the ASTM specification for diesel. Soot production measurements of camphorane and its blends with diesel demonstrate a potential to significantly reduce soot emissions. The physicochemical and combustion properties of camphorane are further compared to those of other terpene biofuels along with biodiesel.

09 BIOMASS FUELS↗
DOE OSTI2017

Understanding Trends in Autoignition of Biofuels: Homologous Series of Oxygenated C5 Molecules

Oxygenated biofuels provide a renewable, domestic source of energy that can enable adoption of advanced, high-efficiency internal combustion engines, such as those based on homogeneously charged compression ignition (HCCI). Of key importance to such engines is the cetane number (CN) of the fuel, which is determined by the autoignition of the fuel under compression at relatively low temperatures (550-800 K). For the plethora of oxygenated biofuels possible, it is desirable to know the ignition delay times and the CN of these fuels to help guide conversion strategies so as to focus efforts on the most desirable fuels. For alkanes, the chemical pathways leading to radical chain-branching reactions giving rise to low-temperature autoignition are well-known and are highly coincident with the buildup of reactive radicals such as OH. Key in the mechanisms leading to chain branching are the addition of molecular oxygen to alkyl radicals and the rearrangement and dissociation of the resulting peroxy radials. Prediction of the temperature and pressure dependence of reactions that lead to the buildup of reactive radicals requires a detailed understanding of the potential energy surfaces (PESs) of these reactions. In this study, we used quantum mechanical modeling to systematically compare the effects of oxygen functionalities on these PESs and associated kinetics so as to understand how they affect experimental trends in autoignition and CN. The molecules studied here include pentane, pentanol, pentanal, 2-heptanone, methylpentyl ether, methyl hexanoate, and pentyl acetate. All have a saturated five-carbon alkyl chain with an oxygen functional group attached to the terminal carbon atom. The results of our systematic comparison may be summarized as follows: (1) Oxygen functionalities activate C-H bonds by lowering the bond dissociation energy (BDE) relative to alkanes. (2) The R-OO bonds in peroxy radicals adjacent to carbonyl groups are weaker than corresponding alkyl systems, leading to dissociation of ROO radicals and reducing reactivity and hence CN. (3) Hydrogen atom transfer in peroxy radicals is important in autoignition, and low barriers for ethers and aldehydes lead to high CN. (4) Peroxy radicals formed from alcohols have low barriers to form aldehydes, which reduce the reactivity of the alkyl radical. In conclusion, these findings for the formation and reaction of alkyl radicals with molecular oxygen explain the trend in CN for these common biofuel functional groups.

09 BIOMASS FUELS↗