107 research outputs found
Data for: Co-Optima Fuels Combustion: A comprehensive Experimental Investigation of Prenol Isomers
No full textThis is the supporting experimental dat
Measurements of Propanal Ignition Delay Times and Species Time Histories Using Shock Tube and Laser Absorption
No full textPropanal 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
No full textButanol 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
Unsteady Rans Simulation of an Enclosed, Turbulent Reacting Methane Jet with the Premixed CMC Method
No full textThe premixed conditional moment closure (CMC) method has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in a RANS environment [1]. Here the premixed CMC method is extended to Unsteady RANS. The new model is validated with the PIV and Raman turbulent, enclosed reacting methane jet data from DLR [2]. The experimental data has a rectangular test section at atmospheric pressure and 573 K with a single inlet jet. A jet velocity of 90 m/s is used with an adiabatic flame temperature of 2,064 K. Contours of major species, temperature and equivalence ratio along with their rms values are provided. The CMC model falls into the class of table lookup turbulent combustion models where the combustion model is solved offline over a range of conditions and stored in a table that is accessed by the CFD code. The scalar dissipation is used to account for the effects of the small scale mixing on the reaction rates. A presumed shape beta function PDF is used to account for the effects of large scale turbulence on the reactions. The unsteady RANS version of the open source CFD code OpenFOAM is used with the PISO algorithm solved with the finite volume method. Velocity, temperature and major species are compared to the experimental data. Once validated, this tool will be useful for designing lean premixed combustors for gas turbines. The results match the experimental data better than the steady RANS of [1] and are able to pick up the unsteadiness of the flame
Jet Fuel Thermal Stability Investigations using Ellipsometry
No full textEllipsometry is an optical technique used to measure the thickness of thin films. This technique was used to measure the thickness of deposits created by heated jet fuel, specifically Sasol IPK on stainless steel tubes. A new amorphous model was used to iteratively determine the film thickness. This method was found to be repeatable, and the thickness of deposit increased with increasing temperature and increasing concentration of naphthalene
A Kinetic Model For The High-Temperature Oxidation Of N-Butanol Based On Recent Shock Tube/Laser Absorption Experiments
No full textButanol 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
Quantum Chemical Study of CH<sub>3</sub> + O<sub>2</sub> Combustion Reaction System: Catalytic Effects of Additional CO<sub>2</sub> Molecule
No full textThe 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)
First principles based fuel design: investigating fuel properties and combustion chemistry
No full textAdvanced combustion engine concepts require fuels which are meticulously designed to harness full potential of novel engine technologies. To develop such fuels, better understanding of fuel properties and their effect on combustion parameters is needed. The investigations reported in this work establishes relationships between several fuel properties and combustion parameters at engine relevant conditions. Further, these findings along with conclusions from other studies are utilized to synthesize fuels and surrogate fuels with tailored combustion properties.
This approach of designing fuels relies on constrained non-linear optimization of several combustion properties simultaneously to design surrogate fuels for transportation fuels to enable combustion simulations. This scheme of fuel design has been devised and presented as Fuel Design Tool in Ahmed et al. Fuel 2015.
Detailed investigations have been made to understand the effect of fuel properties on the ignition of fuels in Rapid compression machines utilizing a custom built multi-zone model. The study was further extended to explore fuel effects on engine combustion utilizing experiments and modelling to gather understanding of instances of engine knocking and pollutant formation.
Bio-blended fuels allow mitigation of harmful pollutants and also enables engines to operate at higher efficiency. Ignition characteristics of two high octane bio-blended gasolines were studied experimentally in rapid compression machine and shock tube and detailed chemical kinetic analysis was conducted to understand how the presence of biofuels (i.e., ethanol) in gasoline influences the evolution of important radicals controlling ignition.
Another set of biofuels namely methyl acetate and ethyl acetate were studied employing fundamental experimental and computational methods. The investigation involved development and analysis of combustion chemistry models, speciation studies in jet stirred reactors, ignition delay measurements and determination of laminar burning velocities. These fuels are found suited for high performance advanced spark ignition engines and the developed model and analysis will lead to optimization of combustion performance.
The developed fuel design tool along with enhanced understanding of combustion chemistry and fuel properties enables a complete toolkit ready to be utilized to develop fuels with better suited properties for the advanced combustion modes
LES Simulation of an Enclosed Turbulent Reacting Methane Jet With the Tabulated Premixed CMC Method
No full textThe Tabulated Premixed Conditional Moment Closure Method (T-PCMC) has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in a RANS environment [1]. Here the premixed conditional moment closure method is extended to Large Eddy Simulation. The new model is validated with the turbulent, enclosed reacting methane backward facing step data from El Banhawy [2]. The experimental data has a rectangular test section at atmospheric pressure and temperature with an inlet velocity of 10.5 m/s and an equivalence ratio of 0.9 for two different step heights. Contours of major species, velocity and temperature are provided. The T-PCMC model falls into the class of table lookup turbulent combustion models where the combustion model is solved offline over a range of conditions and stored in a table that is accessed by the CFD code using three controlling variables; the reaction progress variable, variance and local scalar dissipation rate. The local scalar dissipation is used to account for the affects of the small scale mixing on the reaction rates. A presumed shape beta function PDF is used to account for the effects of large scale turbulence on the reactions. Sub-grid scale models are incorporated for the scalar dissipation and variance. The open source CFD code OpenFOAM is used with the compressible Smagorinsky LES model. Velocity, temperature and major species are compared to the experimental data. Once validated, this low runtime CFD turbulent combustion model will have great utility for designing the next generation of lean premixed gas turbine combustors
Optimization of Supercritical CO2 Brayton Cycle for Simple Cycle Gas Turbines Exhaust Heat Recovery Using Genetic Algorithm
No full textFor the application of waste heat recovery (WHR), supercritical CO2 (S-CO2) Brayton power cycles offer significant suitable advantages such as compactness, low capital cost and applicable to a broad range of heat source temperatures. The current study is focused on thermodynamic modelling and optimization of Recuperated (RC) and Recuperated Recompression (RRC) S-CO2 Brayton cycles for exhaust heat recovery from a next generation heavy duty simple cycle gas turbine using a genetic algorithm. The Genetic Algorithm (GA) is mainly based on bio-inspired operators such as crossover, mutation and selection. This non-gradient based algorithm yields a simultaneous optimization of key S-CO2 Brayton cycle decision variables such as turbine inlet temperature, pinch point temperature difference, compressor pressure ratio. It also outputs optimized mass flow rate of CO2 for the fixed mass flow rate and temperature of the exhaust gas. The main goal of the optimization is to maximize power out of the exhaust stream which makes it single objective optimization. The optimization is based on thermodynamic analysis with suitable practical assumptions which can be varied according to the need of user. Further the optimal cycle design points are presented for both RC and RRC configurations and comparison of net power output is established for waste heat recovery.</jats:p
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