Thermal Stability Measurement Of Alternative Jet Fuels Using Ellipsometry

Thermal stability is an important characteristic of alternative fuels that must be evaluated before they can be used in aviation engines. Thermal stability refers to the degree to which a fuel breaks down when it is heated prior to combustion. This characteristic is of great importance to the effectiveness of the fuel as a coolant and to the engine\u27s combustion performance. The thermal stability of Sasol IPK, a synthetic alternative to Jet-A, with varying levels of naphthalene has been studied on aluminum and stainless steel substrates at 300 to 400 °C. This was conducted using a spectroscopic ellipsometer to measure the thickness of deposits left on the heated substrates. Ellipsometry is an optical technique that measures the changes in a light beam\u27s polarization and intensity after it reflects from a thin film to determine the film\u27s physical and optical properties. It was observed that, as would be expected, increasing the temperature increased the deposit thickness for a constant concentration of naphthalene on both substrates. The repeatability of these measurements was verified using multiple trials at identical test conditions. Lastly, the effect of increasing the naphthalene concentration at a constant temperature was found to also increase the deposit thickness

Measurements Of Propanal Ignition Delay Times And Species Time Histories Using Shock Tube And Laser Absorption

Propanal is an aldehyde intermediate formed during the hydrocarbon combustion process. Potentially, the use of oxygenated biofuels reduces greenhouse gas emissions; however, it also results in increased toxic aldehyde by-products, mainly formaldehyde, acetaldehyde, acrolein, and propanal. These aldehydes are carcinogenic, and therefore it is important to understand their formation and destruction pathways in combustion systems. In this work, ignition delay times were measured behind reflected shock waves for stoichiometric (Φ = 1) mixtures of propanal (CH3CH2CHO) and oxygen (O2) in argon bath gas at temperatures of 1129 K \u3c T \u3c 1696 K and pressures around 1 and 6 atm. Measurements were conducted using the kinetics shock tube facility at the University of Central Florida. Current results were compared to available data in the literature as well as to the predictions of three propanal combustion kinetic models: Politecnico di Milano (POLIMI), National University of Ireland at Galway, and McGill mechanisms. In addition, a continuous wave-distributed feedback interband cascade laser centered at 3403.4 nm was used for measuring methane (CH4) and propanal time histories behind the reflected shock waves during propanal pyrolysis. Concentration time histories were obtained at temperatures between 1192 and 1388 K near 1 atm. Sensitivity analysis was carried for both ignition delay time and pyrolysis measurements to reveal the important reactions that were crucial to predicting the current experimental results. Adjustments to the POLIMI mechanism were adopted to better match the experimental data. Further research was suggested for the H abstraction reaction rates of propanal. In addition to extending the temperature and pressure region of literature ignition delay times, we provide the first high-temperature species concentration time histories during propanal pyrolysis

The Effect Of Diluent Gases On High-Pressure Laminar Burning Velocity Measurements Of An Advanced Biofuel Ketone

The 2,4-dimethyl-3-pentanone (DIPK) is a promising biofuel candidate for automotive applications that is produced by the endophytic fungal conversion process which can be optimized for widespread utilization. There are some studies in the literature on combustion properties of DIPK, such as ignition delay times and laminar burning velocity (LBV) measurements. However, most studies are conducted one atmospheric (atm) pressure which are far away from the high-pressure conditions present inside reciprocating engines. Therefore, we present LBV measurements at high pressures up to 10 atm for this fuel using a spherical flame speed facility. It is known that the flame in a constant volume chamber develops cellular structure (hydrodynamic instability) as the initial pressure increases because of the reduction in flame thickness. In addition, the diffusional-thermal instability prevents experiments for rich mixtures because of the reduction of Lewis number (Le). An earlier study from our lab showed that the flame instability prevented a proper extraction of LBV for stoichiometric and rich mixtures at 5 atm with nitrogen (N2) diluent. Therefore, helium (He) and argon (Ar) were used to suppress flame instability in the present study. Several oxygen-to-diluent ratios were used at 5 atm, 403 K, and a wide range of equivalence ratios (0.8-1.6) to provide the general trend of LBV. It was observed that He provided a smooth spherical flame without cellular structure even at a rich equivalence ratio of 1.6 and delivered a wider range of data points compared to other gases. A similar observation was noticed by increasing the diluent ratio from 3.76 to 5, because of the increase in flame thickness relative to the density jump or density difference between unburned and burned gases. Since the constant volume approach is used for determining LBV, many data points can be extracted out of a single experiment (up to 10 atm and 503 K) which brings several validation targets for DIPK chemical kinetic mechanisms

Thermal Stability Analysis Of Gevo Jet Fuel Using Ellipsometry

Thermal stability is an important characteristic of alternative fuels that must be evaluated before they can be used in aviation engines. This characteristic is of great importance to the effectiveness of the fuel as a coolant and to the engine\u27s combustion performance. In this work, the thermal stability of Gevo fuel, an alcohol to jet fuel made from plant derived feedstock, was studied. This analysis was used to comment on the effectiveness of the current thermal stability test standard. This work was performed using a spectroscopic ellipsometer to measure the thickness of deposits left on aluminum substrates. It was observed that Gevo deposit thickness increased slowly up to 375°C and much more rapidly after that point. Similar behavior was observed in JP-8 fuel. Comparisons were also made between color standard ratings and ellipsometric thickness measurements, and it was found that in some cases, darker colors did not indicate thicker deposits. Reference tubes were used to validate the optical models used in this work, and different optical constants were found to best model the results than what are published in the ASTM D3241 test method for thermal stability

A Kinetic Model For The High-Temperature Oxidation Of N-Butanol Based On Recent Shock Tube/Laser Absorption Experiments

Butanol is a very promising biofuel candidate that has received considerable attention from the combustion community. However, the literature kinetic models are not able to predict shock tube data with reasonable accuracy. Therefore, an improved hightemperature kinetic mechanism is presented here for the oxidation of n-butanol in shock tubes. The mechanism is based on the published Sarathy et al. 2012 [1] mechanism. This study reinforces the strategy of chemical kinetic model development using a comprehensive set of reaction pathways with reaction rate rules based on expert knowledge. We demonstrate that a model for n-butanol oxidation can be modified only slightly to better predict a new set of experimental data while also improving predictive capabilities at other combustion relevant conditions. Discussions are presented on the validity of the proposed mechanism against recent shock tube experiments

Flame Propagation In Premixed Mixtures Of Liquid Biofuels

There is a great potential for biofuels in automotive applications because they show advantages in mitigating greenhouse-gases, improving air quality, and reducing our dependence of fossil fuels. Ketones are new class of biofuels produced from endophytic conversion of cellulose. 2,4-Dimethyl-3-pentanone (DIPK) is a promising ketone for automotive applications. In this study, the laminar burning velocity (LBV) of DIPK was investigated in a spherical combustion chamber at initial T=120°C and various initial pressures using two ignition (laser and spark) techniques. Both constant pressure and constant volume approaches were used to derive the LBV values. The flame stability was assessed based on Markstein length, linear, and nonlinear extrapolation methods. The extended LBV values along one isentrope in constant volume method, helps in obtaining LBV values in a high pressure and temperature environment similar to automotive engines. Current data can be compared to the predictions of recent DIPK chemical kinetic mechanisms

Laminar Burning Velocity Measurements In Dipk-An Advanced Biofuel

The biofuel and engine co-development framework was initiated at Sandia National Labs. Here, the synthetic biologists develop and engineer a new platform for drop-in fuel production from lignocellulosic biomass, using several endophytic fungi. Hence this process has the potential advantage that expensive pretreatment and fuel refining stages can be optimized thereby allowing scalability and cost reduction; two major considerations for widespread biofuel utilization. Large concentrations of ketones along with other volatile organic compounds were produced by fungi grown over switchgrass media. The combustion and emission properties of these new large ketones are poorly known. Therefore, fundamental measurements of representative molecules are needed to provide feedback on their desirability in advanced combustion engines (e.g., HCCI: homogeneous charge compression ignition engines) and their impact on emissions, as well as other combustion devices such as micro-combustors. 2,4-Dimethyl-3-pentanone, also known as diisopropyl ketone (DIPK), is a promising candidate biofuel for automotive applications produced by the fungal conversion process. Laminar burning velocity (LBV) is an important fundamental property of a fuel/air mixture and it depends on the composition, temperature, and pressure. Therefore, the knowledge of the dependence of the laminar burning velocity on above mentioned parameters can be used to design advanced engines as it can affect efficiency and heat release rates. We provide LBV measurements for DIPK, using the University of Central Florida (UCF) spherical flame chamber connected to a modified spark plug. Both pressure and direct flame visualization (shadowgraph) were utilized to ensure that the flame is spherical and stable (no cellular structure was observed within the flame) in order to provide reliable results with the constant volume approach. LBV measurements were also performed in iso-octane (C8H18), a relatively well characterized fuel, in order to validate our facility and measurement technique. The LBV results of C8H18/air and DIPK/air mixtures are compared with several oxygenated fuels in the literature and numerical values predicted by two chemical kinetic mechanisms

Ellipsometric Measurements Of The Thermal Stability Of Alternative Fuels

Thermal stability is an important characteristic of alternative fuels that must be evaluated before they can be used in aviation engines. Thermal stability refers to the degree to which a fuel breaks down when it is heated prior to combustion. This characteristic is of great importance to the effectiveness of the fuel as a coolant and to the engine\u27s combustion performance. The thermal stability of Sasol iso-paraffinic kerosene (IPK), a synthetic alternative to Jet-A, with varying levels of naphthalene has been studied on aluminum and stainless steel substrates at 300-400°C. This was conducted using a spectroscopic ellipsometer to measure the thickness of deposits left on the heated substrates. Ellipsometry is an optical technique that measures the changes in a light beam\u27s polarization and intensity after it reflects from a thin film to determine the film\u27s physical and optical properties. It was observed that, as would be expected, increasing the temperature minimally increased the deposit thickness for a constant concentration of naphthalene on both substrates. The repeatability of these measurements was verified using multiple trials at identical test conditions. Finally, the effect of increasing the naphthalene concentration at a constant temperature was found to also minimally increase the deposit thickness

Laminar Burning Velocity Measurements in DIPK-An Advanced Biofuel

The biofuel and engine co-development framework was initiated at Sandia National Labs. Here, the synthetic biologists develop and engineer a new platform for drop-in fuel production from lignocellulosic biomass, using several endophytic fungi. Hence this process has the potential advantage that expensive pretreatment and fuel refining stages can be optimized thereby allowing scalability and cost reduction; two major considerations for widespread biofuel utilization. Large concentrations of ketones along with other volatile organic compounds were produced by fungi grown over switchgrass media. The combustion and emission properties of these new large ketones are poorly known. Therefore, fundamental measurements of representative molecules are needed to provide feedback on their desirability in advanced combustion engines (e.g., HCCI: homogeneous charge compression ignition engines) and their impact on emissions, as well as other combustion devices such as micro-combustors. 2,4-Dimethyl-3-pentanone, also known as diisopropyl ketone (DIPK), is a promising candidate biofuel for automotive applications produced by the fungal conversion process. Laminar burning velocity (LBV) is an important fundamental property of a fuel/air mixture and it depends on the composition, temperature, and pressure. Therefore, the knowledge of the dependence of the laminar burning velocity on above mentioned parameters can be used to design advanced engines as it can affect efficiency and heat release rates. We provide LBV measurements for DIPK, using the University of Central Florida (UCF) spherical flame chamber connected to a modified spark plug. Both pressure and direct flame visualization (shadowgraph) were utilized to ensure that the flame is spherical and stable (no cellular structure was observed within the flame) in order to provide reliable results with the constant volume approach. LBV measurements were also performed in iso-octane (C8H18), a relatively well characterized fuel, in order to validate our facility and measurement technique. The LBV results of C8H18/air and DIPK/air mixtures are compared with several oxygenated fuels in the literature and numerical values predicted by two chemical kinetic mechanisms