Butyl Acetate Pyrolysis and Combustion Chemistry: Mechanism Generation and Shock Tube Experiments.

The combustion and pyrolysis behaviors of light esters and fatty acid methyl esters have been widely studied due to their relevance as biofuel and fuel additives. However, a knowledge gap exists for midsize alkyl acetates, especially ones with long alkoxyl groups. Butyl acetate, in particular, is a promising biofuel with its economic and robust production possibilities and ability to enhance blendstock performance and reduce soot formation. However, it is little studied from both experimental and modeling aspects. This work created detailed oxidation mechanisms for the four butyl acetate isomers (normal-, sec-, tert-, and iso-butyl acetate) at temperatures varying from 650 to 2000 K and pressures up to 100 atm using the Reaction Mechanism Generator. About 60% of species in each model have thermochemical parameters from published data or in-house quantum calculations, including fuel molecules and intermediate combustion products. Kinetics of essential primary reactions, retro-ene and hydrogen atom abstraction by OH or HO2, governing the fuel oxidation pathways, were also calculated quantum-mechanically. Simulation of the developed mechanisms indicates that the majority of the fuel will decompose into acetic acid and relevant butenes at elevated temperatures, making their ignition behaviors similar to butenes. The adaptability of the developed models to high-temperature pyrolysis systems was tested against newly collected high-pressure shock experiments; the simulated CO mole fraction time histories have a reasonable agreement with the laser measurement in the shock tube. This work reveals the high-temperature oxidation chemistry of butyl acetates and demonstrates the validity of predictive models for biofuel chemistry established on accurate thermochemical and kinetic parameters.

A detailed kinetic model for the thermal decomposition of hydroxylamine.

Hydroxylamine may decompose explosively if processed and stored in certain conditions, posing critical safety issues that need to be carefully addressed. A key aspect is related to the characterization of chemical aspects involved in the explosive decomposition of hydroxylamine (HA), requiring accurate and detailed kinetic mechanisms. This work was devoted to the experimental and numerical characterization of the thermal decomposition of aqueous solutions of HA included in the range of 10%w to 50%w. The onset temperatures of thermal decomposition were determined in the range of 143-198 °C under heating rates of 2 and 5 °C min-1, respectively. A reduced mechanism listing 13 species and 11 reactions involving nitrogen-containing species was produced and validated against experimental measurements. Reaction pathways ruling the decomposition of HA were identified. The hydrogen abstraction toward HNOH and H2NO dominates the primary steps of NH2OH decomposition. The generated mechanism was adopted for the definition of a dimensionless stability diagram for the safe use of HA. Finally, results show a self-accelerating behaviour for any temperature larger than 186 °C, defining a monitoring criterion for safe storage of hydroxylamine-solutions.

The effect of ultra-low temperature on the flammability limits of a methane/air/diluent mixtures.

Natural gas represents an attractive fuel for industrialized and developing countries seeking an alternative to petroleum. Due to economic and safety considerations, liquefied natural gas (LNG) at cryogenic conditions is preferred for storage and transportation. The main drawback is the poor understanding of the physical and chemical phenomena that occur at the storage conditions of liquid methane, i.e. at ultra-low temperatures around 110 K and, if released, at temperatures below ambient. In this work, a procedure to evaluate the laminar burning velocity, the flammability limit (FL) and the limiting oxygen concentration (LOC) of methane-air-diluent mixtures based on detailed kinetic mechanism at ultra-low temperatures is proposed. The estimation of the FL was obtained with the limiting burning velocity theory. The effects of inert content (extinguishing) and agent (N2, H2O and CO2) on FL were evaluated and compared with data retrieved from the literature. The agreement between experimental observation and model results from 200 K-300 K incentivizes the adoption of the new procedure for further studies of fuel reactivity and safety parameters. Moreover, the proposed procedure may be suitable for the estimation of the safety parameters of complex fuel mixtures whose composition is closer to the actual values of LNG.