Pyrolysis and combustion chemistry of pyrrole, a reference component for bio-oil surrogates: Jet-stirred reactor experiments and kinetic modeling

Fast-pyrolysis bio-oils (FPBOs) obtained from lignocellulosic biomass are gaining attention as sustainable fuels for various applications, including the transport sector and power production. A significant fraction of bio-oils is constituted by nitrogen-containing compounds (N fuels) that should be considered when developing surrogate models for FPBOs. Moreover, the content of N fuels in FPBOs is expected to strongly contribute to the production of nitrogen oxides (NOx) directly from fuel-bound nitrogen (fuel NOx), in addition to the thermal NOx formation pathways typical of high-temperature combustion conditions. This work investigates the pyrolysis and combustion chemistry of pyrrole (C4H5N), a candidate reference fuel component for FPBO surrogate models. Speciation measurements in an atmospheric pressure jet-stirred reactor have been performed for both pyrolysis and oxidation conditions. Pyrolysis experiments have been performed for 1% pyrrole/helium mixtures over the temperature range T = 925.1200 K. Oxidation experiments were carried out for 1% pyrrole/oxygen/helium mixtures at three equivalence ratios (φ = 0.5, 1.0, and 2.0) over the temperature range T = 700. 1200 K. These new data significantly extend the number of experimental targets for kinetic model validation available at present for pyrrole combustion. After a thorough revision of previous theoretical and kinetic modeling studies, a preliminary kinetic model is developed and validated by means of comparison to new experimental data and those previously reported in the literature. The rate of production and sensitivity analyses highlight important pathways deserving further investigations for a better understanding of pyrrole and, more in general, N fuel combustion chemistry. A critical discussion on experimental challenges to be faced when dealing with pyrrole is also reported, encouraging further experimental investigation with advanced diagnostics.