Investigation of the chemical kinetics of incomplete oxidation processes in shock tubes

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The development of polygeneration processes requires detailed knowledge about chemical processes in reaction systems with a large fuel excess. On one hand, information about the limiting conditions between gas-phase processes and soot formation is necessary, on the other hand, validated reaction mechanisms are required to enable a simulation-based development and optimization of polygeneration processes. In the first funding period, partial oxidation of methane was studied at phi = 2. Additives were used to accelerate the autoignition of methane so that engines can be operated in a self-igniting mode at polygeneration conditions. Under the conditions investigated so far, besides CO2 and H2O, mostly synthesis gas (CO & H2) was formed. In the second funding period, the studies were expanded towards mixtures with even higher fuel excess that enable the formation of carbon-carbon bonds and the generation of unsaturated hydrocarbons. Here, natural gas and new additives (DME and DEE) were used. Measured ignition delay times and product compositions served as basis for further development of the FOR1993-based mechanism (PolyMech) in project GM1.Since the additives account for a significant part of the fuel consumption at fuel-rich conditions, the next funding period will focus on ozone as an additive using the previously established experimental approaches. Ozone has the advantage that it increases the reactivity of the fuel even in very low concentrations. An additional advantage is that it can be generated online at low cost with an ozone generator. Its reaction kinetics in fuel-rich conditions, however are not sufficiently studied so far. As validation data within the FOR1993, ignition delay times, end product concentrations, and time-resolved methane, ozone, carbon monoxide concentrations, and temperatures will be measured in the shock tube using methane and natural gas as fuels.Increasing the amount of air in very fuel-rich conditions increases the fuel consumption, but also leads to higher end temperatures that promote the formation of soot. By using oxygenated additives, soot formation can be suppressed because they shift the low- temperature onset of soot formation towards higher temperatures. In this context, the suitability of various additives such as alcohols or ethers will be investigated in the shock tube by measuring soot inception times and soot volume fractions. In addition, time-resolved detection of soot precursors such as benzene and PAH (polycyclic aromatics) via spectrally- and temporally-resolved absorption measurements will help to determine the limiting conditions for soot formation with and without additives. From these results, conditions will be determined, in which the soot formation in polygeneration processes can be avoided in the engine.