Conventional Jet Fuels Research Articles

Impact of biofuels on contrail warming

Contrails and contrail-cirrus may be the largest source of radiative forcing (RF) attributable to aviation. Biomass-derived alternative jet fuels are a potentially major way to mitigate the climate impacts of aviation by reducing lifecycle CO2 emissions. Given the up to 90% reduction in soot emissions from paraffinic biofuels, the potential for a significant impact on contrail RF due to the reduction in contrail-forming ice nuclei (IN) remains an open question. We simulate contrail formation and evolution to quantify RF over the United States under different emissions scenarios. Replacing conventional jet fuels with paraffinic biofuels generates two competing effects. First, the higher water emissions index results in an increase in contrail occurrence (~ +8%). On the other hand, these contrails are composed of larger diameter crystals (~ +58%) at lower number concentrations (~ −75%), reducing both contrail optical depth (~ −29%) and albedo (~ −32%). The net changes in contrail RF induced by switching to biofuels range from −4% to +18% among a range of assumed ice crystal habits (shapes). In comparison, cleaner burning engines (with no increase in water emissions index) result in changes to net contrail RF ranging between −13% and +5% depending on habit. Thus, we find that even 67% to 75% reductions in aircraft soot emissions are insufficient to substantially reduce warming from contrails, and that the use of biofuels may either increase or decrease contrail warming—contrary to previous expectations of a significant decrease in warming.

ALTERNATIVE FUELS FOR CIVIL AVIATION

[For the English full text of the article please see the attached PDF-File (English version follows Russian version)].ICAO Member States have agreed on a new 2050 Vision for Sustainable Aviation Fuels which will now help to ensure that conventional jet fuels are substituted with sustainable alternatives to a significant percentage by 2050. Retrieved and compiled from ICAO web-site. Original source: https://www.icao.int/ Newsroom/Pages/ICAO-Conference-on-sustainable-alternative-fuels-agrees-on-new- 2050-Vision-to-guide-future-development-and-deployment.aspx

Soot formation in non-premixed counterflow flames of conventional and alternative jet fuels

With increasing concerns over fuel cost, environmental pollutions, and energy security, the development of alternative fuels from renewable sources has gained considerable attention in the past decade. To evaluate the sooting propensities of representative conventional and alternative jet fuels, the present study has investigated soot formation in non-premixed combustion for three conventional reference jet fuels, i.e., Jet-A, JP-8, and JP-5, and three selected alternative jet fuels, i.e., Fischer-Tropsch Synthetic Paraffinic Kerosene (FT-SPK), Hydroprocessed Esters and Fatty Acids from camelina (HEFA-Camelina), and Alcohol-to-Jet (ATJ). The soot volume fraction profiles of these jet fuels in the atmospheric-pressure counterflow non-premixed flame configuration were measured using Laser-Induced Incandescence technique. In addition, the effects of global strain rate and reactant concentration on soot formation were investigated. At the same stoichiometric mixture fraction, the experimental results show that the sooting level increases with increasing fuel and O2 concentrations, while it decreases with increasing global strain rate, as expected. It is also worth noting that the three alternative jet fuels tested demonstrated greater sensitivity to variations in global strain rate and reactant concentration, as compared to the three conventional jet fuels. Based on the measured soot volume fractions, the sooting propensity of the six jet fuels are ranked as follows: JP-5>Jet-A>JP-8>ATJ>FT-SPK>HEFA-Camelina. The observed ranking is consistent with the aromatics content in each jet fuel except when comparing FT-SPK and ATJ. While ATJ has a lower aromatics content than FT-SPK, it contains much heavier hydrocarbon components, thereby leading to higher sooting propensity. Furthermore, the correlations of soot volume fraction with aromatics content and hydrogen content are examined for all six jet fuels. Although such correlations work well for the three conventional jet fuels, the present results suggest that they cannot be directly transferable to the alternative jet fuels, as these alternative fuels are composed of negligible amounts of aromatics, as well as composed of distinct chemical compositions.

Chemical ignition delay of candidate drop-in replacement jet fuels under fuel-lean conditions: A shock tube study

Ignition delay times were measured behind reflected shock waves under fuel lean, high pressures conditions for conventional (JP-8) and alternative jet fuels — Fischer-Tropsch (F-T), alcohol to jet (ATJ), direct sugar to hydrocarbon (DSHC), and four bio-jet — and a biodiesel-like fuel. The primary goal of this study was to investigate the effect of fuel structure on ignition delay in order to assess differences in fuel ignition delay relative to JP-8. To support this effort, the ignition characteristics of a few hydrocarbons that are proposed as jet fuel surrogate components were also investigated: n-heptane, n-dodecane, m-xylene, n-dodecane/m-xylene blend (77%/23% by volume) and 2,2,4,6,6-pentamethylheptane (iso-dodecane). Two single-pulse shock tubes (heated and non-heated) were used to obtain the current data set. Using argon as the diluent (93% by volume), the experimental conditions covered a pre-ignition temperature range of approximately 980–1800K at a pressure of 16±0.8atm and an equivalence ratio of 0.5. Experimental results show negligible differences between the ignition delay times of JP-8, F-T, DSHC, biodiesel, and the four bio-jet fuels. They are very similar to those of n-heptane, n-dodecane, n-dodecane/m-xylene blend and iso-dodecane under similar conditions. However, the ignition delay times of the ATJ were slightly longer at higher temperatures, and similar to iso-dodecane. m-Xylene reported significantly longer ignition delay times than the other fuels tested under identical conditions. Kinetic modeling results show that light branching and carbon chain length of large n-paraffins do not alter ignition delay because the predominant reactions are oxidation of C1-C4 fuel fragments. They also show for the n-dodecane/m-xylene blend that a discernable slowing of ignition delay by fuel decomposition and oxidation of m-xylene occurs at m-xylene concentrations greater than 50% (by mol.). Further testing is required to understand this behavior at stoichiometric and fuel rich conditions. In addition, an empirical correlation was obtained between the global activation energy of the measured ignition delay times for the single paraffinic species and their derived cetane numbers. This contributes to recent efforts aimed to provide relationships between pre-vaporized, homogeneous combustion properties with existing combustion indicators.

Synthesis of jet fuel rang cycloalkane from isophorone with glycerol as a renewable hydrogen source

For the first time, 1,​1,​3-​trimethyl-cyclohexane (a jet fuel range cycloalkane) was synthesized by coupling the aqueous phase reforming (APR) of glycerol and the hydrodeoxygenation (HDO) of isophorone which can be obtained from lignocellulose. Among the investigated catalysts, Pt/Al2O3 was found to be the most active for the production of 1,​1,​3-​trimethyl-cyclohexane with the hydrogen which was in-situ generated by the APR of glycerol. Over it, high carbon yield (67.0%) of 1,​1,​3-​trimethyl-cyclohexane can be achieved at 533K in the absence of external hydrogen. The excellent performance of Pt/Al2O3 catalyst can be explained because Pt is highly active for both APR and HDO reactions. Besides glycerol, many other lignocellulose derived polylols (such as ethylene glycol, xylitol and sorbitol) and methanol can also be used as renewable hydrogen source for the HDO of isophorone. As a potential application, the 1,​1,​3-​trimethyl-cyclohexane as obtained can be blended into the conventional jet fuels to improve their volumetric heat values.

A six-component surrogate for emulating the physical and chemical characteristics of conventional and alternative jet fuels and their blends

Conventional and alternative jet fuels, such as petroleum-derived Jet-A, coal-derived IPK, and natural-gas-derived S-8, display significant chemical and physical fuel property differences that influence their ignition characteristics. The current work addresses the need for surrogate mixtures capable of emulating the various properties of these fuels and their select blends, which are often used within compression ignited engines for acceptable ignition behavior. A six-component surrogate palette is proposed with species that are readily available within recent kinetic mechanisms, including n-dodecane, n-decane, iso-cetane, iso-octane, decalin, and toluene. The use of these species allows for a seamless compositional transition between the neat target jet fuels and their blends. The surrogate optimizer, which includes various correlations and models to estimate properties of model mixtures, is used to determine the surrogate composition that best matches target fuel properties. For an accurate ignition quality prediction during the optimization, a non-linear Derived Cetane Number regression equation is generated from Ignition Quality Tester experiments of 76 surrogate component mixtures. The newly formulated surrogates and their blends successfully capture the wide range of properties present within the target fuels, including temperature-dependent physical properties such as density, viscosity, specific heat, and volatility, along with experimental ignition delays obtained from a constant volume spray chamber. Kinetic modeling with a detailed mechanism showed that predicted ignition delay times are in good agreement with shock tube and rapid compression machine ignition delay experiments. A sensitivity analysis with variations in the composition of the Jet-A surrogate showed that its calculated ignition delay times are most sensitive to the composition of n-dodecane among the four Jet-A surrogate constituents over the range of temperatures and pressures examined.

Alteration of fatty acid chain length of Chlamydomonas reinhardtii by simultaneous expression of medium‐chain‐specific thioesterase and acyl carrier protein

SUMMARYBiofuel from fatty acids with chain lengths of 8–15 (C8–C15) have properties similar to those of conventional diesel and jet fuels, thus, can save time and reduce costs for the refurbishment of engines and maintenance of oiling facilities. Most oil‐producing algae yield C16–C18 fatty acids; however, the manipulation of algae using genetic engineering is a promising approach to obtain C8–C15 fatty acids. The introduction of a medium‐chain‐specific thioesterase (TE) is expected to effectively alter algae to produce medium‐chain fatty acids (MCFAs). TE is the main determinant of fatty acid chain length as it releases fatty acids from the acyl carrier protein (ACP) in the fatty acid elongation cycle. In a previous study, the introduction of heterologous C8–C12‐specific TEs into Chlamydomonas reinhardtii did not increase the yield of MCFAs. This effect was attributed to a low affinity of the heterologous TEs to C. reinhardtii ACP. Therefore, we introduced both the C10–C14‐specific TE gene and the ACP gene from the land plant Cuphea lanceolata into C. reinhardtii. We measured free fatty acids (FFAs) and triacylglycerols (TAGs) in the transformants using liquid chromatography–mass spectrometry. The production of C12:0 and C14:0, chain length 12 and 14 without unsaturation, FFAs was not significantly increased in any of the tested strains. However, we found a slight but significant increase in TAG‐containing MCFAs in both TE only and TE–ACP transformants. The increased production rate of C14:0‐containing TAGs ranged from 1.25‐ to 1.58‐fold, indicating the ability of medium‐chain‐specific TE to increase MCFAs. These results suggest that the selection of specific TEs is important when modifying eukaryotic algae to produce MCFAs.

Low temperature autoignition of conventional jet fuels and surrogate jet fuels with targeted properties in a rapid compression machine

The autoignition characteristics of conventional jet fuels (category A) and alternative fuels with targeted properties (category C) are investigated using a rapid compression machine and the direct test chamber charge preparation approach. The category C fuels were purposefully built to anticipate special property variations that generally occur in alternative fuels. Ignition delay measurements were made to examine the effects of these unique fuels at low compressed temperatures (625K≤Tc≤735K), a compressed pressure of Pc=20bar and equivalence ratios of ϕ=0.25, 0.5 and 1.0 in synthetic dry air. Chemical makeup of the fuel shows insight into the effect of the amount of branching in isoalkanes and aromatic influences on autoignition. The results show noteworthy variability in the ignition properties at these low temperature and lean conditions. This variability may impact combustion performance when the engine is running outside the normal operational map or for new engine architectures in the future.

Genetic Algorithm optimised Chemical Reactors network: A novel technique for alternative fuels emission prediction

Sustainability of the conventional jet fuels and climate change has attracted the aviation sector to diversity to alternative fuels. However, fuel diversification requires an assessment of the long term impact to engine performance and engine emissions through the combustion process, as alternative fuels are not as well understood as conventional jet fuel. A detailed experimental study on alternative fuels emissions across the entire aircraft fleet is impractical. Therefore a plausible method of computer modelling combined Genetic Algorithm and Chemical Reactors network was developed to predict alternative fuels gaseous emissions, namely, Carbon Monoxide, Nitrogen Oxides and Unburned Hydrocarbons in aircraft engines. To evaluate the feasibility and accuracy of the technique, exhaust emission measurements were performed on a re-commissioned Artouste Mk113 Auxiliary Power Unit, located at the University of Sheffield׳s Low Carbon Combustion Centre. The simulation produced results with good agreements with the experimental data. The optimised model was used to extrapolate emissions data from different blends of alternative fuels that did not operate during the campaign. The proposed technique showed that it can develop a data base of alternative fuels emissions and also act as a guideline for alternative fuels development.

The microphysical pathway to contrail formation

AbstractA conceptual framework to predict microphysical and optical properties of contrail particles within a wingspan behind the source aircraft is developed. Results from two decades of contrail observations and numerical simulations are reviewed forming the basis of theoretical model development. The model utilizes cloud theory applied to the dynamics and thermodynamics of jet aircraft exhaust plumes in upper tropospheric conditions. Droplet nuclei include soot particles emitted from aircraft engines and atmospheric particles entrained into the plume. These precursor particles activate into copious homogeneously freezing water droplets as the plume relative humidity rises beyond liquid water saturation. A unimodal size spectrum of ice particles develops wherein ice particles grow to micrometer mean sizes. Contrail particle formation is analyzed over a wide range of soot emissions relating to conventional jet fuels as well as to alternative aviation fuels producing much less soot and volatile particle emissions. For current aviation fuels and propulsion technology, the number of contrail ice particles scales roughly in proportion to the number of emitted soot particles that act as water condensation nuclei despite their poor hygroscopicity. Close to the contrail formation threshold, only few plume particles can be water activated and freeze. Implications for effects of alternative fuels on contrails, an arena for future scientific exploration, are outlined.

Conventional and Bio-Derived Jet Fuel Surrogate Modeling in Low Temperature and Lean Combustion

Recently published chemical kinetic mechanisms are used to evaluate autoignition characteristics for conventional and alternative hydrotreated renewable jet (HRJ) fuels at low temperature and under...

From lignin to cycloparaffins and aromatics: Directional synthesis of jet and diesel fuel range biofuels using biomass

The continual growth in commercial aviation fuels and more strict environmental legislations have led to immense interest in developing green aviation fuels from biomass. This paper demonstrated a controllable transformation of lignin into jet and diesel fuel range hydrocarbons, involving directional production of C8–C15 aromatics by the catalytic depolymerization of lignin into C6–C8 low carbon aromatic monomers coupled with the alkylation of aromatics, and the directional production of C8–C15 cycloparaffins by the hydrogenation of aromatics. The key step, the production of the desired C8–C15 aromatics with the selectivity up to 94.3%, was achieved by the low temperature alkylation reactions of the lignin-derived monomers using ionic liquid. The synthetic biofuels basically met the main technical requirements of conventional jet fuels. The transformation potentially provides a useful way for the development of cycloparaffinic and aromatic components in jet fuels using renewable lignocellulose biomass.

Green Engines: Possible Damages by Firing Alternative Fuels and Protection

With the rising cost of fossil fuels along with greenhouse gas emission such as NOx and COx, use of alternative fuels such as syngas and biofuels is intense interesting, and in the meantime using ceramic matrix composites that eliminate the need of film cooling in combustors, vanes and other hot section components to improve the efficiency of gas turbine engine and reduce the NOx and COx emission becomes increasingly attractive for green engines. However, the alternative fuels have an increased hydrogen/carbon ratio; in turn during combustion it produces more water vapor than the conventional jet fuels. The increased water vapor level will have an impact on the protective oxide scale developed on the gas turbine hot section components, particularly on those made of SiC/SiC ceramic matrix composites (CMC), leading to an accelerated degradation of the turbine components. In addition, some alternative fuels derived from biomass may contain alkali elements such as potassium, sodium and calcium, as well as chlorine, sulfur and/or phosphorus, which may result in possible corrosion of the hot section components in gas turbines, leading to premature failure during service. This paper will review some of the alternative fuels and their combustion products, the possible damages to gas turbine hot section components, as well as some potential protective coatings that may mitigate such damage

Comparison of Vibrations and Emissions of Conventional Jet Fuel with Stressed 100% SPK and Fully Formulated Synthetic Jet Fuel

The rapid growth of the aviation sector around the globe has witnessed an overwhelming impact on fossil fuel resources. With the implementation of stricter environmental laws over emissions by conventional jet fuels, growing demand for research on alternative fuels has become imperative. One-hundred percent Synthetic Paraffinic Kerosene (SPK) and Fully Formulated Synthetic Jet Fuel have surfaced as viable alternatives for gas turbine engines due to their similar properties as that of Jet Fuel. This paper presents results from an experimental study performed on a small gas turbine engine, comparing emissions performance and vibrations for conventional Jet A-1 Fuel, thermally stressed 100% SPK and Fully Formulated Synthetic Jet Fuel. Different vibration frequencies, power spectra were observed for different fuels. Gaseous emissions observed were nearly the same, whereas, significant changes in particulates emissions were observed.

A diesel engine study of conventional and alternative diesel and jet fuels: Ignition and emissions characteristics

Measurements of ignition delay, CO and NO emissions, and fuel consumption were carried out in a light-duty single-cylinder direct-injection diesel engine for operation with petroleum and alternative hydroprocessed and Fischer–Tropsch diesel and jet fuels. Ignition measurements carried out for a fixed engine speed and injection timing quantify the decrease in in-cylinder ignition delay with increasing derived cetane number (DCN) over a range of DCN relevant to diesel engine operation (DCN=40–80) and show no discernible dependence of ignition delay on other fuel properties. Brake specific fuel consumption (BSFC) was found to decrease with increasing DCN with strong correlation due to a reduction in ignition time for fixed-injection-timed operation. Brake specific CO emissions were also found to decrease with increasing DCN due to increased time provided for CO burn out due to earlier ignition. Brake specific NO emissions were found to decrease with increasing hydrogen-to-carbon (H/C) ratio, due to the lower peak combustion temperatures and thermal NOx occurring for fuels with higher H/C.

Global Reduced Model for Conventional and Alternative Jet and Diesel Fuel Autoignition

A global reduced model for the autoignition of conventional petroleum-derived and alternative, hydroprocessed and Fischer–Tropsch, jet and diesel fuels is presented. The model is based on a seven-step model from the literature (Zheng, J.; Miller, D. L.; Cernansky, N. P. A Global Reaction Model for the HCCI Combustion Process, SAE Paper 2004-01-2950, 2004) and includes steps to predict oxidation and autoignition in the three temperature regimes of interest to engine applications, the high-, low-, and negative-temperature-coefficient (NTC) regimes. Here we have included dependence of reaction rate parameters on the derived cetane number (DCN) to predict the influence of fuel variability on autoignition and optimized the reduced model to best fit target shock tube ignition delay time data for jet and diesel fuels. The standard deviation between model predictions for ignition delay and the target shock tube data set is ±21% and the model captures all experimental trends for ignition delay variation with DCN, temperature, pressure, and fuel–air equivalence ratio in all temperature regimes. Comparisons to experimental ignition delay time data not contained in the target data set show model–experiment deviation similar to the comparisons with the target data, with global standard deviation of ±20–30% and differences of at most a factor of 2. The model comparisons with shock tube data suggest that the model is suitable for autoignition prediction for fuels containing large quantities of aliphatic compounds with DCN = 30–80 for 650–1300 K, 8–80 atm, and fuel–air equivalence ratios of 0.25–1.5.

EFFECT OF FUEL PROPERTIES ON SPRAY CHARACTERISTICS OF ALTERNATIVE JET FUELS USING GLOBAL SIZING VELOCIMETRY

Increasing oil prices and strict emission policies drive the need for cleaner, alternative energy sources. Gas-to-liquid (GTL) jet fuel, a synthetic jet fuel produced from natural gas using Fischer−Tropsch synthesis, has grabbed global attention due to its cleaner combustion aspects when compared to conventional jet fuels. Since the production methodology of GTL and conventional jet fuels are different, their chemical and physical properties are different from each other. Consequently, these differences can affect atomization, mixing, combustion, and pollutant formation in the combustion chamber. Atomization is the precursor to evaporation and mixing processes. Hence, it is important to study atomization in detail in order to gain a better understanding of the other processes that directly affect combustion and emission characteristics. In this work, the microscopic spray characteristics of two GTL fuels and conventional Jet A-1 fuel are investigated and compared with each other. The spray characteristics of these fuels are studied for three injection pressures at different spatial locations downstream of a pressure swirl nozzle exit using a planar-laser diagnostic technique known as global sizing velocimetry. The results demonstrate that the influence of change in the fuel physical properties is insignificant on the spray characteristics at high injection pressures. Furthermore, the spray characteristics of the GTL fuels are found to be similar to those of the conventional Jet A-1 fuel.

Characteristics of Deposits in Gas Turbine Combustion Chambers Using Synthetic and Conventional Jet Fuels

The synthetic fuel industry is poised to experience large-scale growth and profoundly affect current aviation fuel infrastructure. New candidate technologies, such as Camelina oil-derived synthetic fuel have been demonstrated to not only provide satisfactory quasi drop-in characteristics for conventional fuels, but in life cycle analysis studies have also been shown to potentially offer positive improvements relative to conventional feedstocks with respect to economic, environmental, and land use considerations. As part of a multiyear study at the Royal Military College of Canada to evaluate combustion related parameters of fuel additives and alternative fuels for gas turbine applications, a Camelina-derived synthetic fuel blend was assessed to determine potential combustion related benefits as compared to conventional and other synthetic blends. The Combustion Chamber Sector Rig (CCSR) which houses a Rolls Royce T-56-A-15 combustion section was utilized for the evaluation of emissions and deposits. Following combustion testing, several combustion system components, including the combustion chamber, fuel nozzle, and igniter plug were analyzed for relative levels of deposit build-up. As with other Fischer Tropsch derived synthetic fuels, there were positive benefits found with Camelina blends in terms of emissions performance and deposit production tendencies.

Blended aviation biofuel from esterified Jatropha curcas and waste vegetable oils

Conventional petroleum-based jet fuels, including Jet A-1, are not renewable and generate a considerable amount of particulate and gaseous pollutants. Non-edible low cost vegetable oil such as waste vegetable oil (WVO) and Jatropha curcas can be used as feedstock for jet biofuel production with positive influence on the world climate change. In this work, an aviation biofuel was produced through blending of the methyl esters of waste vegetable and jatropha oils with Jet A-1 aviation fuel. A process was designed and fabricated to pretreat the waste vegetable oil obtained from local restaurant by means of dewatering and filtration to remove water and solid contaminants, respectively. Waste oil and J. curcas oil were converted to their methyl esters through a two-step catalytic reaction. Several blends of the produced methyl esters with Jet A-1 were prepared and characterized to determine the most suitable ratio based on the jet fuel specifications. The characterizations confirm that the jet biofuel with 10 and 20% methyl ester contents have comparable properties with the commercial available aviation fuel. Production of jet biofuel from waste vegetable and jatropha oil can be an alternative to reduce the amount of waste oil being disposed, to address the problems of energy and food self-sufficiency and to produce a clean fuel.

Application of a novel charge preparation approach to testing the autoignition characteristics of JP-8 and camelina hydroprocessed renewable jet fuel in a rapid compression machine

A variety of new, alternative jet fuels are being considered as replacements for conventional petroleum-derived jet fuels, and the autoignition chemistry of these fuels are of prime interest. However, traditional batch-based premixture preparation approaches used in chemical kinetics studies are burdened by the low volatility of these fuels. In this work, a new charge preparation approach is described and characterized in which a fuel and air premixture is created directly in the test chamber of a rapid compression machine. The approach relies on a fuel injector to load a small quantity of fuel into the test chamber with high resolution. Preparation of the test charge directly in the device rather than in a mixing vessel reduces the mixture pressure, and hence the fuel partial pressure and mixture temperature requirements to avoid thermal decomposition of the fuel. Gas chromatography/mass spectrometry is used to confirm that an accurately known mass of JP-8 jet fuel is injected into the rapid compression machine, and that all components of the fuel are evaporated and homogeneously mixed within 2min of the fuel injection, for temperatures from 105°C to 145°C. Ignition delays for JP-8 in air are measured at low temperatures (670–750K) and low pressures (7 and 10bar) and the measurements are compared with literature data. The autoignition characteristics of the bio-based camelina hydroprocessed renewable jet fuel are also measured and contrasted with those of JP-8. Under similar compressed conditions, the camelina hydroprocessed renewable jet fuel ignition properties are distinct from JP-8, which provides motivation for pursuing new test strategies to elicit the autoignition chemistry of alternative jet fuels and other non-volatile fuels.