Combustion performance and emission characteristics of a diesel engine under low-temperature combustion of pine oil-diesel blends

Pine oil is a biofuel derived from pine trees; its cetane number, kinematic viscosity, and boiling point are lower than those of diesel. Because of its inherent oxygen content, high calorific value, and good solubility, pine oil is considered as a potential alternative of diesel. In this work, we investigated the combustion and emission characteristics of pine oil-diesel blends in a high-speed four-cylinder turbocharged diesel engine under different loads and exhaust gas recirculation (EGR) rates. Four fuels, diesel blended with pine oil in proportions of 0%, 20%, 40%, and 50% (named as P0, P20, P40, and P50, respectively), were tested. The results show that when the load ranged from 40% to 100%, the equivalent brake specific fuel consumption (BSFC) of P50 was only 2.08-3.5% higher than that of P0, whereas that of P20 was <1% than pure diesel. The addition of pine oil to diesel decreased the soot emission, but NOx emission increased. For pine oil-diesel blends, with the increase in the EGR rate from 0 to 24.6%, the variations in the soot, CO, and THC emissions were not obvious, whereas the NOx emissions significantly decreased. Under the same EGR rate, with the increase in the proportion of pine oil, the NOx emissions increased; the effects of an increase in the EGR rate on the NOx emissions were higher than an increase in the pine oil fraction in the blend. When the EGR rate exceeded 24.6%, the soot, CO and, THC emissions sharply increased. However, it is possible to significantly reduce the soot emissions at a high EGR rate by increasing the blend proportion of pine oil.