The impact of mixed fuels containing pyrolysis oil, diesel, n-butanol and 2-EHN on emissions and performance of diesel engine

The environmental impactof fossil fuels and their limited availability increase the need for research into alternative energy sources. In this research, pyrolysis oil (PO) was obtained from waste sour cherry kernels. PO cannot be used directly as fuel in diesel engines because of its negative fuel properties, such as low energy density, high viscosity, high water content, and low cetane number. Therefore, PO was blended with diesel at various weight proportions (wt%) using n-butanol (NB) as cosolvent, and 2-ethylhexyl nitrate (2-EHN) as cetane improver. Blended fuels containing 40 wt% diesel i.e., D2 (Diesel 40% / PO 0% / NB 55% / 2-EHN %5), D3 (Diesel 40 / PO 5% / NB 50% / 2-EHN 5%) and D4 (Diesel 40% / PO 15% / NB 40% / 2-EHN 5%) were identified as optimal blend compositions regarding the physicochemical characteristics of fuel. These fuels were tested for engine performance and emission characteristics at engine speeds of 1500, 1800, 2400, 3000 and 3600 rpm under full engine load (10 Nm) in a single-cylinder diesel engine. All data (i.e. cylinder pressure, engine torque and performance changes, heat release rate, and emission characteristics) were recorded using a Kistler KiBox data acquisition system. The engine tests showed a decrease in NOx, HC and soot emissions when blended fuels (D2, D3 and D4) were compared to D1 (Diesel 100% / PO 0% / NB 0% / 2-EHN 0%). The lower NOx emissions in the blended fuels are explained by the PO's water content. Water raises the specific heat capacity of the fuel-air mixture while reducing the internal cylinder temperature. Additionally, the high latent heat of evaporation of n-butanol may contribute to reduce NOx emissions. In addition, the decrease in HC emissions may be caused by the increase in the oxygen ratio of blended fuels, while the decrease in soot emissions may be caused by the low C/H ratio and high oxygen content of blended fuels. To conclude, blends of PO, diesel n-butanol, and 2-EHN can be used as biofuels in diesel engine applications.