Increasing global concern over energy security and the continued ecological impact of using fossil fuels has pushed the development of sustainable energy alternatives – making research into renewable fuels essential. Identifying and implementing environmentally viable fuel sources requires understanding the combustion process and hence the chemistry of these biofuels. Low residence time flow reactors (≤100 µs), when combined with photoionization mass spectrometry (PIMS) and Matrix Fourier Transform Infrared FTIR spectroscopy, have the capability to probe the elementary pyrolytic reaction mechanism for various fuels directly. When combined with advanced computational methods, these results produce reliable and scalable models that can predict combustion behavior. 

First, an explanation of this hybrid experimental and theoretical approach is presented, followed by its application to evaluating the pyrolysis chemistry of three isomers of methylcyclohexene. The nuanced capabilities of this approach are highlighted in the ability of this technique to explain subtle differences in the combustion behavior of these isomers through the results obtained from these evaluations. A similar study is carried out to elucidate the reduced sooting observed when oxygen-containing polyoxymethylene ethers (POM-E) are blended with diesel. The combined approach is used to identify trends in the decomposition of these molecules as a function of increasing the number of oxymethylene units (-O-CH2-)_n and altering the terminal alkyl group. The radicals formed because of these secondary decompositions are critical to suppressing soot formation and are among these molecules' first high-level quantum calculations.

Second, an analysis of the micro-reactor, a key component in previously described experimental techniques, is presented. A qualitative examination of flow inside these reactors (straight tubes approximately 1mm inner diameter and 3cm in length made of SiC) suggests pressure and velocity significantly change along the length of the reactor. This presents a challenge in determining actual flow conditions within the reactor, making it complicated to establish conditions at which pyrolytic chemistry occurs. Computational and experimental testing has been used to optimize a new reactor geometry to control the flow profiles by adding a constriction at one end of the reactor. The nozzle has been shown computationally to stabilize fluid flow within the reactor. A novel digital manufacturing method to fabricate these geometries is detailed, which harnesses the rapid iterability of 3D printing and combines it with the knowledge base for fabricating ceramics conventionally. The capability of this processing technique is extended to other high aspect ratio structures and ceramic types, showcasing its broad applicability. Material characterization studies are presented to compare features of the sintered SiC geometries constructed using this process to typical fabrication methods. The novel reactor geometry is validated through experiments in the PIMS setup, with results showcasing the impact of stabilized pressure, velocity, and increased residence times. The novel design of these micro-reactors will provide researchers with a fundamentally new technique to probe the short residence time pyrolytic reactions of fuels. Combining theory, experiment, model development, and simulation will enable qualitative or even quantitative predictions for many combustion situations of practical relevance. Understanding key elements of this chemistry is an essential step toward the intelligent selection of next-generation alternative fuels.