The current capabilities of kinetic modeling of hydrocarbon oxidation in shock waves are discussed. The influence of molecular size and structure on ignition delay times are stressed. The n-paraffin fuels from CH4 to n-C5H12 are examined under shock tube conditions, as well as the branched chain fuel isobutane, and the computed results are compared with available experimental data. The modeling results show that it is important in the reaction mechanism to distinguish between abstraction of primary, secondary and tertiary H atom sites from the fuel molecule. This is due to the fact that both the rates and the product distributions of the subsequent alkyl radical decomposition reactions depend on which H atoms were abstracted. Applications of the reaction mechanisms to shock tube problems and to other practical problems such as engine knock are discussed.

An axi-symmetric shock-tube model has been developed to simulate the shock-wave propagation and reflection in both non-reactive and reactive flows. Simulations were performed for the full shock-tube geometry of the high-pressure shock tube facility at Texas A & M University. Computations were carried out in the CFD solver FLUENT based on the finite volume approach and the AUSM+ flux differencing scheme. Adaptive mesh refinement (AMR) algorithm was applied to the time-dependent flow fields to accurately capture and resolve the shock and contact discontinuities as well as the very fine scales associated with the viscous and reactive effects. A conjugate heat transfer model has been incorporated which enhanced the credibility of the simulations. The multi-dimensional, time-dependent numerical simulations resolved all of the relevant scales, ranging from the size of the system to the reaction zone scale. The robustness of the numerical model and the accuracy of the simulations were assessed through validation with the analytical ideal shock-tube theory and experimental data. The numerical method is first applied to the problem of axi-symmetric inviscid flow then viscous effects are incorporated through viscous modeling. The non-idealities in the shock tube have been investigated and quantified, notably the non-ideal transient behavior in the shock tube nozzle section, heat transfer effects from the hot gas to the shock tube side walls, the reflected shock/boundary layer interactions or what is known as bifurcation, and the contact surface/bifurcation interaction resulting into driver gas contamination. The non-reactive model is shown to be capable of accurately simulating the shock and expansion wave propagations and reflections as well as the flow non-uniformities behind the reflected shock wave. Both the inviscid and the viscous non-reactive models provided a baseline for the combustion model iii which involves elementary chemical reactions and requires the coupling of the chemistry with the flow fields adding to the complexity of the problem and thereby requiring tremendous computational resources. Combustion modeling focuses on the ignition process behind the reflected shock wave in undiluted and diluted Hydrogen test gas mixtures. Accurate representation of the Shock-tube reactive flow fields is more likely to be achieved by the means of the LES model in conjunction with the EDC model. The shock-tube CFD model developed herein provides valuable information to the interpretation of the shock-tube experimental data and to the understanding of the impact the facility-dependent non-idealities can have on the ignition delay time measurements.

A shock tube technique has been developed to allow the separation of heatup from ignition delay time for a metal particle. An analytical model was formulated to predict the position, velocity and temperature of a boron particle in the shock tube as a function of time. The model was used to determine ignition delay time and particle temperature at ignition. Ignition delay times were measured for boron particles of nominally one micron diameter. Particle size and shape diagnostics were conducted by means of scanning electron microscope and floatation tests. Shock tube experiments were conducted using mixtures of ten, twenty, and fifty percent oxygen in argon. Particle ignition occurred over a range of 2200K to 3600K and 100 to 400 psia. Ignition delay was shown to vary directly with particle diameter and inversely with gas temperature and oxidizer pressure. The data were used to calculate an activation energy for the boron ignition reaction. Particle temperature at ignition was calculated. (Modified author abstract).

Supercritical carbon dioxide has brought about new questions on the chemical kinetics of several small hydrocarbon fuels and the effects of carbon dioxide as the primary diluent on the different fuels. This report presents work on the ignition delay times and several species time-histories of methane, ethylene and syngas over a range of conditions. All experiments were conducted behind reflected shock waves using two different shock tubes. The ignition delay times were measured using a GaP photodetector to measure the emission of light. The species time-histories were measured using single laser spectroscopy. The effect of CO2 as a diluent on the fluid dynamics of the system were also examined using high-speed camera images. It was determined that the ignition delay times and fuel time-histories were able to be accurately predicted by mechanisms in the literature for pressures up to 30 atm but the literature mechanisms were unable to predict the carbon monoxide time-histories beyond qualitative trends for the various fuels. It was also determined that the carbon monoxide had a string effect on the fluid dynamics of the experiments resulting in a significantly smaller chemical reaction zone. Experiments were also performed to examine the effects of water as a diluent with a ratio up to 66% of the total diluent on the ignition delay times. Using the experimental data, a global kinetic mechanism was created for methane and syngas to predict the ignition delay times and the carbon monoxide time-histories for pressures up to 300 atm.