Numerical modeling of multi-component viscous fuels combustion

The worldwide concern regarding global warming has increased the interest of using biomass as a renewable and CO2 neutral source of energy. Pyrolysis oil (PO), as one of the most important product of biomass conversion, has the potential to be used as a fuel oil substitute in many applications for heat and electricity generation. However, pyrolysis oil properties and its behavior during combustion are considerably different from conventional fossil fuels. From a chemical point of view, PO contains large number of oxygenated compounds derived from the decomposition of biomass during thermal treatment. It has also considerable amount of water originated from both moisture content and the decomposition reactions. Water is homogeneously dissolved in the oil and cannot be eliminated with drying processes without losing volatile hydrocarbon compounds [1]. From the physical point of view, bio-oils are characterized by high viscosity and surface tension, low heating value and, due to multicomponent composition, a very wide boiling range [2]. Moreover, they are thermally unstable and when heated, undergo polymerization processes, leading to the formation of carbonaceous solid material (char) in the fuel supply line, at the nozzle tip and in the combustion chamber [1]. Van Rossum et al. [3] found that pyrolysis oil evaporation is always coupled with the formation of char. Literature survey indicates that combustion behavior of pyrolysis oil is still unknown process. More investigations is required to understand PO spray formation, evaporation and combustion. Especially, the impact of char formation on the combustion characteristics, which has been not yet explored, needs detailed assessment. Knowledge and data about the specifics of the processes and phenomena which interact during combustion of PO will support efficiency increase and design of new generation of burners operating on this bio-fuel. The objective of this work is to investigate pyrolysis oil combustion, taking into account mutual interactions between gaseous, liquid and solid fields. A numerical model that takes into account liquid fuel evaporation and gaseous and char combustion has been developed in OpenFOAM. The char is considered to be present in the fuel droplets and its oxidation is modeled after complete evaporation of liquid.