An investigation into the impact of burning diesel/lubricant oil mixtures on the nature of particulate emissions: Implications for DPF ash-loading acceleration method

Ever-tightening particulate emissions regulation and the need of extending diesel particulate filter (DPF) manual cleaning period require an in-depth investigation into exhaust-borne ash components that may potentially deposit in DPF using a variety of methods to accelerate loading. Currently, the most common method used is blending a certain volume of lubricant oil into diesel. Predictably, the addition of lubricant oil will alter the nature of particles emitted from engines, creating an artifact between “accelerated” and real ash and therefore biasing the functionality of this method. However, such impacts haven't been carefully evaluated. In this paper, the mass, number, size-resolved distribution, morphology, and elemental analysis of the particles from a Euro-5 compliant, 2.5 L diesel engine consuming conventional diesel, diesel+2v% lubricant oil, and diesel+4v%lubricant oil were measured and compared 24. The results indicate that with the addition of lubricant oil into diesel, both the particulate mass and number emission increased dramatically, a proportional increase in particle numbers of all size stages was seen with 2% lubricant oil blending, while 4% blending only increased the number concentrations of nuclei-mode and relatively large particles. Adding lubricant oil into diesel tended to complicate the microstructure of particles. Particle-bound phosphorus and zinc were only identified when lubricant oil was dosed. An increased oxygen mass fraction with the presence of lubricant oil also suggests heavier volatile materials emissions. Lastly, although burning diesel/lubricant oil mixtures enables an accelerated ash loading process in a DPF, excessive blending ratio could alter the nature of engine-out particles and increase uncertainty. It is recommended to achieve fast ash accumulation at a high engine load with diesel+2v%lubricant oil.