The vast stores of biomass available worldwide have the potential to replace significant amounts of petroleum fuels. Fast pyrolysis of biomass is one of several paths by which biomass can be converted to higher value products. Wood pyrolysis oil (WPO) has been regarded as an alternative to petroleum fuel for use in diesel engines. However, the application of WPO in diesel engines is constrained by the poor fuel properties of WPO, such as low energy density, high acidity, high viscosity, and low cetane number. One possible method by which these shortcomings may be circumvented is to co-fire WPO with other petroleum fuels. WPO has poor miscibility with petroleum fuel oils; the most suitable candidate fuel for direct fuel mixing is ethanol. Early mixing with ethanol has the added benefit of significantly improving the storage and handling properties of WPO. For separate injection co-firing, a WPO-ethanol blended fuel can be fired through diesel pilot injection in a dual-injection diesel engine. In this study, we examined the performance and emission characteristics of a dual-injection diesel engine fueled with diesel (pilot injection) and WPO-ethanol blended fuel (main injection) experimentally. Results showed that although stable engine operation was possible with dual injection, the indicated fuel conversion efficiency was slightly lower than that of diesel combustion. Regarding exhaust emissions, HC and CO emissions were slightly increased, while NOx and PM emissions were significantly decreased due to the high water content and oxygen content in the WPO-ethanol blended fuel. (C) 2015 Elsevier Ltd. All rights reserved.