Characteristics of particles downstream of a partially failed diesel particulate filter.

Abstract

A diesel particulate filter (DPF) can be used to reduce the particulate matter (PM) emissions from a vehicle. However, when these devices fail the tailpipe emissions can change. The main goal of this project was to determine if a soot sensor provided by Honeywell could detect a failed filter, defined as an exhaust aerosol concentration downstream of the DPF greater than the current US heavy duty PM standard of 13 mg/kWh (10 mg/bhp-hr). In this study a DPF failure was first simulated on an engine dynamometer test stand using an exhaust bypass valve. Then the valve was removed and the filter was actually failed in a series of steps by drilling out individual channel end caps. Exhaust was cooled and diluted using a partial flow air ejector dilution tunnel, and dilution ratios were determined using raw and dilute nitric oxide (NO) measurements. Dilute diesel exhaust aerosol was characterized upstream and downstream of a DPF. Filter samples and an AVL photo-acoustic soot sensor were used to estimate PM mass emissions, and TSI aerosol instruments were used to measure aerosol size distributions and total number concentrations. An electrostatic precipitator, DMA, electrometer and CPC were used to evaluate the aerosol charge distribution. Downstream measurements were repeated as the filter was progressively failed in a series of steps. These measurements were then used to evaluate the response of the Honeywell exhaust soot sensor. Under certain steady state conditions the sensor output showed a statistically significant increase as the filter was failed but the output was susceptible to interference from mechanical vibration and was dependent on engine operating conditions, and the exhaust system used. Exhaust aerosol charge measurements showed the concept is viable but further work is required to refine the sensor.