John C. Leylegian

Experiments and numerical simulation on the laminar flame speeds of dichloromethane and trichloromethane

The laminar flame speeds of blends of dichloromethane and trichloromethane with methane in air at room temperature and atmospheric pressure were experimentally determined using the counterflow twin-flame technique, varying both the amount of chlorinated compound in the fuel and the equivalence ratio of the unburned mixture. A detailed kinetic model previously employed for simulation of chloromethane combustion was expanded to include the oxidation kinetics of dichloromethane and trichloromethane. Numerical simulation shows that the expanded kinetic model predicted the flame speeds to within 3 cm/s of the measured values. Carbon flux and sensitivity analyses indicate that the reaction kinetics of the methane flame doped with chlorinated methanes are qualitatively similar, despite the variation in the chlorinated methane fuel structure.

Laminar flame speeds and oxidation kinetics of tetrachloromethane

The laminar flame speeds of blends of tetrachloromethane (CCl 4 ) with methane in air at room temperature and atmospheric pressure were experimentally determined using the counterflow twin-flame technique, varying both the amount of CCl 4 in the fuel and the equivalence ratio of the unburned mixture. Flame speeds were measured for stoichiometric mixtures with CCl 4 -to-CH 4 ratios between 0 and 0.429 by volume and for equivalence ratio ranges of 0.7–1.3 and 0.7–1.2 for CCl 4 -to-CH 4 ratios of 0.053 and 0.200, respectively. Comparison between the present experimental results and the previous data of CH 3 Cl-, CH 2 Cl 2 -, and CHCl 3 -CH 4 -air flames demonstrates the dominant influence of the atomic Cl-to-H ratio on the propagation rate of laminar flames with chlorinated methane addition. A detailed kinetic model previously employed for CH 3 Cl, CH 2 Cl 2 , and CHCl 3 combustion was expanded to include additional pathways pertinent to tetrachloromethane combustion. Numerical simulation shows that this model predicts the laminar flame speeds reasonably well. Carbon flux and sensitivity analyses indicate that the oxidation kinetics of CH 4 flames doped with CCl 4 are essentially the same as those doped with other chloromethanes.

Investigation of Short Contact Time Reactors for Regeneratively Cooled Hypersonic Vehicles

To counter the extreme heat loads experienced by hypersonic engine structures, it is imperative that fuels double as coolants. However, the use of logistical fuels (e.g., JP-7 and JP-10) in hypersonic applications is becoming more accepted in near-term flight engine test applications. In order for hydrocarbon based fuels to be viable as scramjet fuels they must be able to absorb heat in the form of sensible, latent, and chemical enthalpies, while attempting to minimize coke formation. In this study, we attempt to achieve these ends using a short contact time (SCT) catalytic reactor. This type of reactor has the advantages of short residence times, enhanced wake mixing, and heat conduction into the core flow of the process stream, while minimizing pressure losses. In this investigation, we have performed experiments using a series of different catalysts (Pt- αAl2O3, Pd-αAl2O3, and zeolite) on a set of logistical fuels (JP-7, JP-8, JP-10 and S-8, a synthetic hydrocarbon fuel currently being investigated by the USAF). Experiments were performed at low (1-3 atmospheres) and elevated (40-50 atmospheres) pressures, at temperatures expected in a hypersonic engine heat exchanger. Experiments measured the production of various gas-phase and liquidphase species in the reactors as a function of pressure, temperature, residence time, and catalyst formulation. Results show the production of small (H2, C1 – C3) species in the gas phase, with a shift from hydrogen and ethylene formation at low pressures towards methane and ethane formation at elevated pressures. In addition, experiments have shown significant coke formation at elevated pressures for all of the fuels investigated. Detailed kinetic modeling has identified shortcomings in models used for describing the pyrolysis of these fuels.

Incorporation of Path Flux and Steepest Descent Methods in Kinetic Model Reduction for CFD Applications

This paper outlines updates made to a method for chemical kinetic model reduction. The original method used the directed relation graph with error propagation to generate a skeletal model, and the solution mapping method to tune the remaining rate constants to match reduced model responses to those of the original detailed model. In the current work, skeletal model generation is performed using a path flux analysis, and changes have been made to the optimization process, by including an intermediate steepest-descent method in order to make the optimization process more efficient. The new method is then applied to the reduction of a methane-air model for two different sets of initial conditions. Results show rapid optimization of the model is possible as compared to previous work. Results for the optimized models also are able to predict the perfectly-stirred reactor response better than the optimized models generated using the older method.

Method of Kinetic Model Reduction for Computational Fluid Dynamics Applications

A new method for kinetic model reduction is proposed. This method consists of two steps: skeletal model reduction using the directed relation graph method, followed by tuning of the remaining rate constants using the solution mapping method. The method can generate reduced models without the need for nonelementary reactions or non-Arrhenius rate constants. The method is demonstrated on a hydrogen–oxygen model and a methane–air model. The results for models at different levels of reduction are compared with the original full models. Results show that the reduced models that underwent optimization are capable of replicating the temperature profile produced by the full model for constant-pressure stream tube reactions, over a limited range of initial conditions, and can now replicate laminar flame speeds at the condition specified by the current optimization. However, perfectly stirred reactor temperatures cannot be accurately predicted. Recommendations are made for further refinement of the technique.

A New Method of Chemical Kinetic Model Reduction for CFD Applications

A new method for kinetic model reduction is proposed. This method consists of two steps: skeletal model reduction using the Directed Relation Graph method, followed by tuning of the remaining rate constants using the Solution Mapping Method. The method can generate reduced models quickly, without the need for non-elementary reactions or non-Arrhenius rate constants. The method is demonstrated on a hydrogen-oxygen model, and the results for models at different levels of reduction are compared to the original full model, as well as another reduced model generated using a different method. Results show that the reduced models which underwent optimization are capable of replicating the temperature profile produced by the full model for constant-pressure time-evolving reactions over a range of initial conditions, but cannot adequately replicate laminar flame speeds or perfectly-stirred reactor ignition or extinction times. Recommendations are made for further refinement of the technique.

Design of Experiments: An Integral Part of a Thermal/Fluids Laboratory Course

Laboratory courses can be, and are often used to provide practical demonstrations of physical phenomena studied in various lecture courses. At Manhattan College, a senior-level Thermal-Fluids Laboratory incorporates a Design of Experiments (DoE) component into the syllabus, in which students learn about development of a text matrix, construction of an experiment to fulfill that matrix, and statistical analyses to confirm hypotheses. This paper describes the entire course syllabus, the portions of the course relevant to DoE, and some of the experiments conducted in recent years.Copyright

Development of a Chemical Kinetic Model to Describe the Endothermic Reforming of Logistical Fuels

In recent years, interest in scramjet engines has increased due to its possible use in the propulsion system for two-stage-to-orbit (TSTO) vehicles. Part of the design process is to determine the best possible fuel. Thus far, scramjet design has shown that the fuel must act as a heat sink in order to actively cool the leading edges and combustion chamber of the craft. Logistical hydrocarbon fuels such as JP-7, JP-8, JP-10, and S-8 have become the focus of research. In this study, a chemical kinetic model has been assembled in an attempt to predict the products of endothermic reforming in an oxygen free environment. This study used experimentally determined mole fractions from a previous study to optimize the chemical kinetic model, using the Solution Mapping Method. The optimization process produced a model which could predict the gaseous reformate for S-8. The results for JP-8, JP-7, and JP-10 identified shortcomings in the model due to both the models and the optimization process.

Development of a Kinetic Model to Describe the Reforming of Logistical Fuels

In this study, a chemical kinetic model has been assembled in an attempt to predict the products of endothermic reforming of JP-7, JP-8, JP-10, and S-8 fuel in a pyrolytic environment. Experimentally determined mole fractions from a previous study were used to optimize the chemical kinetic model, using the solution mapping method. The optimization process produced a model that could predict the gaseous reformate for S-8 fuel. The results for JP-7, JP-8, and JP-10 identified shortcomings in the model due to both the models and the optimization process.

Further Progress on a Kinetic Model Reduction Method for CFD Applications

Further progress on a method for kinetic model reduction is reported. This method consists of two steps: skeletal model reduction using the Directed Relation Graph method, followed by tuning of the remaining rate constants using the Solution Mapping Method. Updates to the method include the redefinition of the ignition time, the generation of the Directed Relation Graph based on temperature-averaged reaction rates, the addition of extra targets for the Solution Mapping Method, a change in the form of the response functions from second- to third-order polynomials, and the introduction of a steepestdescent method to determine the rate constants for the optimized model. The updated method is demonstrated on a hydrogen-oxygen model and a methane-air model. Results show that the reduced models which underwent optimization are capable of replicating the temperature profile produced by the full model for constant-pressure streamtube reactions over a range of initial conditions as before, and can now adequately replicate laminar flame speeds. However, perfectly-stirred reactor temperatures cannot be accurately predicted. Recommendations are made for further refinement of the technique.