| Control of ignition is crucial for the satisfactory performance of combustors and for the prevention of fires and explosions. The low- to intermediate-temperature chemistry relevant for ignition is rather complex. The level of complexity is further elevated when ignition takes place in a non-uniform medium and as such is also affected by convective-diffusive transport. This thesis research is to investigate the chemistry and physics behind the ignition of hydrogen and hydrocarbons in a non-uniform environment.; The intricacies of inhomogeneous ignition were illustrated by first considering the ignition of a lean premixed hydrogen/air stream. Experimental results backed by computational simulation show that, compared to the three explosion limits for homogeneous mixtures, ignition now takes place at higher temperatures and exhibits five limits over the pressure range investigated. Furthermore, such a behavior can be largely attributed to the reduced residence time and the self enrichment of the original fuel-lean mixture through the preferential diffusion of the highly mobile hydrogen---a sufficient though not necessary condition.; We then examined the non-premixed ignition of a series of hydrocarbons, including ethylene, propylene, 1,3-butadiene, dimethyl ether and the four butene isomers, focusing on the effects of aerodynamic strain rate and pressure. Sensitivity analysis was performed to identify the controlling features for ignition. The key sensitive reactions were found to belong to two groups, namely H2/CO chain reactions and reaction pathways involving the fuel and its intermediates. Ignition was also found to be sensitive to the binary diffusion between fuel and nitrogen.; The third component of the thesis is a study through ab initio calculations on the thermochemistry analysis of three important pathways for ignition of the butene isomers, and the isobutenyl radical oxidation. For the butene isomers, the calculated reaction rates of these three reaction paths were used to help understand the experimentally determined ignition trend for the butene isomers, and through it to study the effect of molecular structure on ignition. Moreover, for the isobutenyl radical oxidation pathway, the potential energy diagrams for O2 addition were constructed, and the high-pressure limit rate constants for each reaction channel were determined for further kinetic model development. |
