Overview of Projects

Stringent emission control requirements by the US EPA (Environmental Protection Agency) for vehicles sold beyond 2007 have required diesel engine manufacturers to employ advanced aftertreatment technologies to curtail pollutants (such as NOx, Particulate Matter, CO, and unburnt hydrocarbons) within prescribed limits.
Aftertreatment systems currently used with heavy-duty diesel engines mainly comprise of DOC (Diesel Oxidation Catalyst), DPF (Diesel Particulate Filter), SCR (Selective Catalytic Reduction) and the ASC (Ammonia Slip Catalyst)

Over the past few years we’ve investigated the role of mid-channel ash deposits (MCD) in the DPF on long-term after-treatment durability, effects on vechicle fuel economy and developing advanced characterization tools for investigation of micrometer scale morphology of ash deposits.
These deposits can vary anywhere from 3-10cm in length and effectively block as much as 50%-80% of the volume of a single inlet channel. The percentage of inlet channels having mid-channel deposits in the collection of field samples is in range of 10% to 75%.
Diesel engine exhaust aftertreatment components, especially the diesel particulate filter (DPF), are subject to various modes of degradation over their lifetimes.
One particular adverse effect on the DPF is the significant rise in pressure drop due to the accumulation of engine lubricant-derived ash which coats the inlet channel walls effectively decreasing the permeability of the filter.
The mid-channel ash deposit reduces the effective filtration length and decreases the channel open width in the middle of the channel resulting in augmented pressure drop and fuel penalty. Additionally, mid-channel ash deposits lead to challenges in DPF cleaning process, since it is rather difficult, or in many cases impossible, to remove them via reverse pulse flow or oven regeneration.
The decreased permeability due to ash in the DPF can result in increased filter pressure drop and decreased fuel economy.
A unique two-step approach, consisting of experimental measurements and direct numerical simulations using ultra-high resolution 3D imaging data, has been utilized in these study to better understand the effects of ash accumulation on engine aftertreatment component functionality.
X-Ray computed tomography (CT) is a non-destructive imaging technique where a sample is rotationally scanned in order to generate a 3D dataset. X-ray photons are fired at a sample, some of which absorb into the sample, where the absorption is a function of sample density, thickness and chemical composition. 2D radiographs are recorded at fractions of a degree over 360° (2000-3000 images are recorded for most scans in this study) and then reconstructed with the Nikon CT 3D Pro software, where alignment, beam hardening and noise reduction algorithms can be applied.
Bright regions in the CT scans indicate the presence of high-density ash plugs that can exist closer to the inlet face of the DPF, ash end-plugs closer to the outlet, or form patterns in the middle (axial center) of the DPF.

Collaboration with Dr. Carl Justin Kamp from MIT and Kymanetics, Inc has resulted in the following publications and ongoing projects.

Relevant Publications for further Reading:

Evolution of DPF ash morphology upon soot oxidation at 600C

Monitoring the phase changes in DPF ash and influence of DPF additive species on ash morphology

Patterns in DPF ash deposits originating from variation in lubricant additive composition and engine/aftertreatment operation

X-ray CT images of field-aged DPF channels showing mid-channel ash deposits and loss of soot storage capacity

For a given ash loading, a filter with MCDs (mid-channel deposits) has less open inlet channel volume than a filter without MCDs.
Generally, ash is deposited on the wall of the inlet channel and in a plug at the inlet channel outlet. MCDs are an exception to the rule where abnormal ash accumulation dominates and gives rise to severe pressure drop issues, often to the point of filter failure.
The phenomenon of MCDs is of crucial interest to the automotive and catalysis industry in particular; however, it has been rarely discussed in literature as the underlying mechanisms for MCD are poorly understood.

Characterizing the Ash to Gap (A:G) ratios in field-returned DPFs to identify prolematic DPFs

A:G ratio is defined by the average total length of ash-plugs or MCD segments per channel, divided by the average total length to the point in the channel (measured from end-plug) where ash deposits blocks the remaining channel volume.
We found that many failed DPFs (due to excessive pressure drop or frequent regeneration), have A:G values of approximately 80% or less.