UC San Diego

The urgent need to address the shortage of fossil fuels and mitigate environmental impacts from carbon emissions and greenhouse gases necessitates the exploration of renewable biofuels. This dissertation investigates the interactions during autoignition between biofuels and alkanes, focusing on the effects of additives on auto-ignition conditions and the catalytic methanation of biomass producer gas, augmented with hydrogen derived from power-to-gas technology, to optimize biomethane production. The first part of the study focuses on the impact of iso-butanol on the auto-ignition of n-decane and n-heptane. Counterflow flame experiments and simulations show that small additions of iso-butanol significantly elevate the ignition temperature at low strain rates, effectively inhibiting the low-temperature chemistry of n-decane and n-heptane. Further investigations on the addition of ethanol to n-heptane using the same experimental setup and advanced computa- tional models revealed that ethanol suppresses the low-temperature chemistry of n-heptane by competing for oxygen, particularly impacting the reaction O2 + CH3CHOH → HO2 + CH3CHO. To further investigate auto-ignition in n-heptane/ethanol counterflow diffusion flames, it is introduced a novel analytical method inspired by Zurada’s sensitivity approach for neural networks. This method identifies critical species influencing the heat release rate and examines their interactions across various temperature regions. When applied to mixtures of n-heptane and ethanol under low strain rates, this method quantifies the influence of chemical kinetics and species diffusion, offering detailed insights into the interactions among species in reactive flow field. In the second part, this study delves into biogas production, focusing on the catalytic methanation of biomass producer gas with additional hydrogen from power-to-gas. Evaluations of a Ni-Ru-MgO catalyst in both fixed and fluidized bed reactors under various conditions have identified the optimal operational parameters. The optimal operational temperature for this catalyst in a fixed bed reactor is determined to be around 400 °C, considering both the catalyst’s activation temperature and the influence of temperature on chemical equilibrium. A higher hydrogen/carbon ratio is also shown to enhance the methanation process. In fluidized bed reactors, the addition of C2H4 in a hydrogen-rich environment notably improves methanation, demonstrating the catalyst’s adaptability across different reactor configurations.