THE REDUCTION OF PARTICULATE MATTER EMISSION RELEASED DURING PYROLYSIS AND IGNITION OF THERMALLY THICK WOOD

Abstract

Solid fuels in the indoor home environment are used in day-to-day life by nearly a third of the entire global population. Consequently, exposure to household air pollution from wood burning results in millions of years of lost life, annually. Emission of organic particulate matter with a diameter less than 2.5 µm (PM2.5) is released in the process of burning, especially prior to ignition. Efforts to reduce PM2.5 through improved cook stoves have made some progress, however exposure limits still well exceed the threshold set by the World Health Organization. While improving cook stove technology can be beneficial to achieving lower emission rates, a less common approach to the reduction of PM2.5 is the use of wood burning fundamentals. Developing new methods of burning is an under-utilized approach to reduce organic PM2.5 from wood combustion. Emission reductions derived from quick ignition and formation of a flame may aid in reducing PM2.5 exposure rates. This dissertation reports findings from the application of ignition theory developed by the field of fire safety engineering to the ignition of wood as a method of reducing PM2.5. Four objectives are addressed including (1) identify necessary language and frameworks to communicate needs from the cook stoves research field to fire science engineers for reducing PM pollution, (2) experimentally isolate limiting factors for controlling ignition that aims to reduce energy demand and PM release, (3) experimentally characterize pre-ignition PM release associated with ignition limitation factors, and (4) identify guidelines for ideal burning using ignition and PM release factors identified from experimentation to provide recommendations for exposure reduction. This work couples heat and mass transfer principles with aerosol sampling methodologies to identify burning mechanisms required for deliberate ignition of wood. Experiments were performed that leverage the anisotropic heat and mass transfer properties of wood in a series of pyrolysis and ignition trials. Results were used to identify a previously unidentified ignition factor called pyrolytic acceleration. A metric called Ignition Energy Ratio was defined to quantify energy demands associated with wood grain direction, heat flux, and wood type. Particle measurements were used to identify a new burning mechanism involving reactions which produce particulate matter before pyrolytic acceleration occurs. Lastly, results were compiled to provide guidance for stove designers and developers of wood burning protocol based on findings. In conclusion, this dissertation reports on the use of fire science principles for the reduction of PM2.5 and establishes a link between previously unaffiliated fields of research.