Ash, mostly from essential lubricant additives, affects diesel particulate filter (DPF) pressure-drop sensitivity and limits filter service life. It raises concern in the lubricant industry to properly specify new oils, and engine and aftertreatment system manufacturers have attempted to find ways to mitigate the problem. To address these issues, results of detailed measurements of ash characteristics in the DPF and their effects on filter performance are presented.
In this study, a heavy-duty diesel engine was outfitted with a specially designed rapid lubricant degradation and aftertreatment ash loading system. Unlike previous studies, this system allows for the control of specific exhaust characteristics including ash emission rate, ash-to-particle ratio, ash composition, and exhaust temperature and flow rates independent of the engine operating condition. Cordierite DPFs with two different catalyst formulations were subjected to an accelerated ash loading cycle which approximates slightly more than 180,000 miles of ash accumulation in the field.
A post-mortem analysis of all diesel particulate filters aged and loaded with ash in the laboratory was conducted and the results compared to a number of field-aged DPFs. Differences in ash distribution and ash properties such as packing density, porosity, and composition enhance understanding of the underlying fundamental mechanisms influencing the observed effects of ash accumulation on DPF performance.
These results, among few fundamental data of this kind, correlate changes in diesel particulate filter performance with lubricant chemistries and exhaust conditions affecting ash compositional and morphological characteristics. Results will be useful in optimizing the design of the combined engine-aftertreatment-lubricant system for future diesel engines, balancing the requirements of additives for adequate engine protection with the requirements for robust aftertreatment systems.