Effects of pine oil additive and pilot injection strategies on energy distribution, combustion and emissions in a diesel engine at low-load condition

Pine oil is mainly produced from the pine tree, which has some prominent fuel-related properties, such as lower boiling point and viscosity than those of the pure diesel. Particularly, its low heating value is similar to that of diesel. In addition, pine oil and diesel can be mixed in any ratio, and the engine can directly burn the pine oil/diesel mixtures without any further modification. Therefore, pine oil is considered to be a promising additive to diesel fuel. However, when pine oil is fueled in a diesel engine via single injection the engine NOx emissions deteriorate. In this present study, the effects of pilot injection (PI) strategies, including pilot injection rate (PIR) and pilot-main interval (PMI) on energy distribution, emissions and combustion were explored in a diesel engine fueling with diesel/pine oil mixtures at low-load condition. Three test fuels were pure diesel (denoted as P0), a mixture of 80% diesel and 20% pine oil (denoted as P20), and 60% diesel and 40% pine oil (denoted as P40), respectively. The results showed that, after utilizing the PI strategies, the peaks of in-cylinder pressure of the three fuels increased compared to single injection, while the maximum pressure rise rates decreased along with an increase in the break thermal efficiency (BTE). After blending pine oil in pure diesel, both the soot and CO emissions were reduced, although the NOx and THC emissions slightly increased. The small PMI strategies could reduce the energy loss of THC, CO emissions and friction, and improve STE. However, the soot emission increased. At low-load condition, when fueling with P20 blended fuel and using small PMI strategies, the system could achieve higher thermal efficiency and lower soot-NOx emissions than the strategy employing pure diesel.