Performance and emission characteristics of a diesel engine operated with wood pyrolysis oil

The vast storage of biomass available worldwide has the potential to displace the significant amounts of fuel that are currently derived from petroleum sources. Fast pyrolysis of biomass is one of the possible paths by which we can convert biomass to higher-value products. Wood pyrolysis oil has been regarded as an alternative fuel to petroleum fuels for use in diesel engines. However, the use of wood pyrolysis oil in diesel engines requires modifications to those engines owing to the low energy density, the high water content, the high acidity and the high viscosity of wood pyrolysis oil. The easiest ways to adopt wood pyrolysis in a diesel engine without engine modifications are blending or emulsification of the wood pyrolysis oil with diesel or biodiesel. Wood pyrolysis oil is immiscible with diesel and biodiesel; hence appropriate surfactants or co-solvents are needed for emulsification or blending. In this study, a diesel engine operated with diesel, biodiesel, wood pyrolysis oil-diesel emulsion and wood pyrolysis oil-biodiesel emulsion was investigated experimentally. The combustion performance and the gaseous and particle emission characteristics of a diesel engine fuelled by diesel, biodiesel and wood pyrolysis oil emulsions were examined. The results showed that stable engine operation was possible with the emulsions and that the engine output power was comparable with those of diesel and biodiesel operation. However, in the case of wood pyrolysis oil-diesel emulsion operation, the total hydrocarbon and carbon monoxide emissions were increased owing to the increased ignition delay and poor spray atomization, and the nitogen oxide and the soot emissions were decreased owing to the high water content and the high oxygen content in the fuel. Long-term validation of adopting wood pyrolysis oil in diesel engines is still needed because the oil is acidic, with the consequent problems of corrosion and clogging, especially in the injection system.