D3.7 Fundamental spray combustion characteristics of FPBO and blends

Fast pyrolysis is an efficient process to convert solid biomass to liquid bio-oils. The EU funded SmartCHP project is aiming to develop a smart and flexible small-scale combined heat and power (CHP) system running on fast-pyrolysis bio-oil (FPBO). In SmartCHP system, FPBO is used in the stationary diesel engines for power generation. However, the special physical and chemical properties of FPBO, such as high viscosity and low chemical reactivity, limit its direct application in diesel engines.

To broaden our knowledge on FPBO combustion under engine-like conditions, the fundamental spray combustion characteristics of wood-based FPBO (reference), FPBO/alcohol blends, FPBO blended with ignition improver, and FPBO from different biomass origins are experimentally investigated in this deliverable. A combustion research unit (CRU) equipped with the heavy-fuel oil injection system and high-temperature chamber is employed to provide the well-defined initial ambient conditions for fuel spray combustion. It also has a borescope port which accommodates to the high-speed diagnostics on fuel spray flames. The pressure-based heat release analysis is used to determine fuel ignition and combustion characteristics, while the high-speed imaging technique is adopted to visualize flame natural luminosity during the fuel spray combustion.

Results show that the flame natural luminosity of FPBO is much lower than diesel. At the injection pressure of 300 bar, the atomization quality of FPBO is quite poor, leading to lots of discrete soot parcels, and some of nozzle orifices are quickly blocked within several injections. The increase of FPBO injection pressure could obviously improve the atomization quality and nozzle durability. The fuel dribble phenomenon for FPBO is alleviated compared with diesel. For FPBO/alcohol blends, 30% ethanol addition could significantly reduce the flame natural luminosity, while 30% n-butanol addition could improve the ignitability. Adding ignition improver, Beraid, into FPBO/ethanol blends could improve the ignitability, extending the lower limit of required ambient temperature for complete combustion. For FPBO samples made from different biomass origins, the sample from sunflower husks has both the lowest ignitability and sooting tendency, while FPBO made from miscanthus has the highest sooting tendency.