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

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

On The High-Temperature Combustion Of N-Butanol: Shock Tube Data And An Improved Kinetic Model

The combustion of n-butanol has received significant interest in recent years, because of its potential use in transportation applications. Researchers have extensively studied its combustion chemistry, using both experimental and theoretical methods; however, additional work is needed under specific conditions to improve our understanding of n-butanol combustion. In this study, we report new OH time-history data during the high-temperature oxidation of n-butanol behind reflected shock waves over the temperature range of 1300-1550 K and at pressures near 2 atm. These data were obtained at Stanford University, using narrow-line-width ring dye laser absorption of the R1(5) line of OH near 306.7 nm. Measured OH time histories were modeled using comprehensive n-butanol literature mechanisms. It was found that n-butanol unimolecular decomposition rate constants commonly used in chemical kinetic models, as well as those determined from theoretical studies, are unable to predict the data presented herein. Therefore, an improved high-temperature mechanism is presented here, which incorporates recently reported rate constants measured in a single pulse shock tube [C. M. Rosado-Reyes and W. Tsang, J. Phys. Chem. A 2012, 116, 9825-9831]. Discussions are presented on the validity of the proposed mechanism against other literature shock tube experiments. © 2013 American Chemical Society

Jet Fuel Thermal Stability Investigations Using Ellipsometry

Jet fuels are typically used for endothermic cooling in practical engines where their thermal stability is very important. In this work the thermal stability of Sasol IPK (a synthetic jet fuel) with varying levels of naphthalene has been studied on stainless steel substrates using spectroscopic ellipsometry in the temperature range 385-400 K. Ellipsometry is an optical technique that measures the changes in a light beam’s polarization and intensity after it reflects off of a thin film to determine the film’s thickness and optical properties. All of the tubes used were rated as thermally unstable by the color standard portion of the Jet Fuel Thermal Oxidation Test, and this was confirmed by the deposit thicknesses observed using ellipsometry. A new amorphous model on a stainless steel substrate was used to model the data and obtain the results. It was observed that, as would be expected, increasing the temperature of the tube increased the overall deposit amount for a constant concentration of naphthalene. The repeatability of these measurements was assessed using multiple trials of the same fuel at 385 K. Lastly, the effect of increasing the naphthalene concentration in the fuel at a constant temperature was found to increase the deposit thickness

Improved Combustion Kinetic Model And Hcci Engine Simulations Of Di-Isopropyl Ketone Ignition

Di-isopropyl ketone (DIPK) is considered a promising biofuel candidate produced using endophytic fungal conversion. In the current study, homogeneous charge compression ignition (HCCI) simulations of DIPK engine experiments were conducted with single-zone and multi-zone engine models. Both adiabatic and non-adiabatic single-zone HCCI models were explored. The non-adiabatic model employed the Woschni correlation to account for heat transfer observed in the experiments. The HCCI simulations utilized a literature DIPK kinetic model with slight modifications to better reproduce experimental data. The modifications were done by including additional intermediate species and radical reactions, which were not considered in the original reaction mechanism. In addition, zero dimensional simulations were conducted to validate the updated model against limited shock tube and pyrolysis experimental data available in the literature. The single-zone model of HCCI engine with the updated kinetic model provided good agreement for pressure during compression until ignition, however, it over predicted the peak pressure, as expected. The improved kinetic mechanism was able to predict the pressure, heat release rate, and temperature in a 5-zone model of HCCI engine with good agreement to the experiments. Brute force sensitivity analyses revealed that the most sensitive reaction in which DIPK participates is the H-abstraction reaction from the fuel by HO2. Discussions are provided on the validity of the DIPK model in comparison with the parametric engine data over a range of temperature, pressure, equivalence ratio, and engine speed

Jet Fuel Thermal Stability Investigations Using Ellipsometry

Jet fuels are typically used for endothermic cooling in practical engines where their thermal stability is very important. In this work the thermal stability of Sasol IPK (a synthetic jet fuel) with varying levels of naphthalene has been studied on stainless steel substrates using spectroscopic ellipsometry in the temperature range 385-400 K. Ellipsometry is an optical technique that measures the changes in a light beam’s polarization and intensity after it reflects off of a thin film to determine the film’s thickness and optical properties. All of the tubes used were rated as thermally unstable by the color standard portion of the Jet Fuel Thermal Oxidation Test, and this was confirmed by the deposit thicknesses observed using ellipsometry. A new amorphous model on a stainless steel substrate was used to model the data and obtain the results. It was observed that, as would be expected, increasing the temperature of the tube increased the overall deposit amount for a constant concentration of naphthalene. The repeatability of these measurements was assessed using multiple trials of the same fuel at 385 K. Lastly, the effect of increasing the naphthalene concentration in the fuel at a constant temperature was found to increase the deposit thickness

Design And Development Of A Porous Heterogeneous Combustor For Efficient Heat Production By Combustion Of Liquid And Gaseous Fuels

This work focuses on the design and operation of a heterogeneous combustor capable of operating on both gaseous and liquid fuels, featuring a highly porous (up to 90% porosity) silicon carbide ceramic media within the combustion chamber where the combustion reactions take place. Four interlinked devices – a heat exchanger, a vaporization chamber where liquid fuel may be injected, a mixing chamber, and combustion chamber – comprise the flow loop of the combustor. Operation of the combustor is presented using temperatures recorded via thermocouples at various locations in the flow loop as well as along the axis of the combustion chamber. Demonstration of the combustor\u27s ability to operate on gaseous methane and air at a low equivalence ratio of 0.50 is presented across various total flow rates. Additionally, the ability of the combustor to operate on liquid fuel was also verified upon the inclusion of kerosene in the fuel-air mixture

Reacting Unsteady Reynolds-Averaged Navier-Stokes With The Tabulated Premixed Conditional Moment Closure Method

The tabulated premixed conditional moment closure model has shown the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable run times in a Reynolds-averaged Navier-Stokes formulation. The tabulated premixed conditional moment closure model is a table lookup combustion model that tabulates species, reaction rates, and thermodynamic data for use by the computational-fluid-dynamics code during run time. In this work, the tabulated premixed conditional moment closure model is extended to unsteady Reynoldsaveraged Navier-Stokes. The new model is validated against particle image velocimetry and laser Raman measurements of an enclosed turbulent reacting methane jet from the German Aerospace Center. The flame\u27s reaction progress variable, its variance, and the scalar dissipation rate are calculated by the computational fluid dynamics in three dimensions. These three parameters are used to index detailed species information from the table for use by the computational-fluid-dynamics code. The scalar dissipation is used to account for the effects of the smallscale mixing, whereas a presumed shape beta function probability density function is used to account for the effects of large-scale turbulence on the reaction rates. Velocity, temperature, and major species are compared to the experimental data. Accurate predictions of the velocity fields were obtained, but accurate predictions of scalar quantities were limited by the adiabatic assumption of the tabulated premixed conditional moment closure model

Quantum Chemical Study Of Ch3 + O2 Combustion Reaction System: Catalytic Effects Of Additional Co2 Molecule

The supercritical carbon dioxide diluent is used to control the temperature and to increase the efficiency in oxycombustion fossil fuel energy technology. It may affect the rates of combustion by altering mechanisms of chemical reactions, compared to the ones at low CO2 concentrations. Here, we investigate potential energy surfaces of the four elementary reactions in the CH3 + O2 reactive system in the presence of one CO2 molecule. In the case of reaction CH3 + O2 → CH2O + OH (R1 channel), van der Waals (vdW) complex formation stabilizes the transition state and reduces the activation barrier by ∼2.2 kcal/mol. Alternatively, covalently bonded CO2 may form a six-membered ring transition state and reduce the activation barrier by ∼0.6 kcal/mol. In case of reaction CH3 + O2 → CH3O + O (R2 channel), covalent participation of CO2 lowers the barrier for the rate limiting step by 3.9 kcal/mol. This is expected to accelerate the R2 process, important for the branching step of the radical chain reaction mechanism. For the reaction CH3 + O2 → CHO + H2O (R3 channel) with covalent participation of CO2, the activation barrier is lowered by 0.5 kcal/mol. The reaction CH2O + OH → CHO + H2O (R4 channel) involves hydrogen abstraction from formaldehyde by OH radical. Its barrier is reduced from 7.1 to 0.8 kcal/mol by formation of vdW complex with spectator CO2. These new findings are expected to improve the kinetic reaction mechanism describing combustion processes in supercritical CO2 medium. (Figure Presented)