Measuring diesel ash emissions and estimating lube oil consumption using a high temperature oxidation method

Diesel engine ash emissions are composed of the non-combustible portions of diesel particulate matter derived mainly from lube oil, and over time can degrade diesel particulate filter performance. This paper presents results from a high temperature oxidation method (HTOM) used to estimate ash emissions, and engine oil consumption in real-time. Atomized lubrication oil and diesel engine exhaust were used to evaluate the HTOM performance. Atomized fresh and used lube oil experiments showed that the HTOM reached stable particle size distributions and concentrations at temperatures above 700°C. The HTOM produced very similar number and volume weighted particle size distributions for both types of lube oils. The particle number size distribution was unimodal, with a geometric mean diameter of about 23 nm. The volume size distribution had a geometric volume mean diameter of about 65 nm. Inductively coupled mass spectrometry (ICP-MS) was used to determine the ash content of different lube oils, revealing the differences in elemental compositions of ash for a fresh lube oil and an used lube oil; the most notable changes were a 166% increase in Mg and a 194% increase in Fe concentrations. The mass penetration fraction of lube oil using the HTOM was compared to the oil ash concentrations found from the ICP-MS analysis and the results are discussed. The HTOM was also used to measure exhaust ash concentrations from a passenger car Diesel engine during steady-state and transient engine conditions. Using known oil ash compositions the HTOM was used to estimate engine oil consumption rates from exhaust ash measurements.